Title of Invention

A PROCESS FOR PREPARING AN ASPARTYL DIPEPTIDE ESTER DERIVATIVES

Abstract

The present invention is directed to a process for preparing a novel aspartyl dipeptide ester derivatives (including salts thereof) represented by fornlula (1) having an excellent sweetening effect and usable as sweeteners such as N- [N- [3- (3-methyl-4- hydroxyphenyl) propyl] -L-α-aspartyl] -L-phenylalanine I-methyl ester and N- [N- [3- (3-hydroxy-4- methoxyphenyl) propyl] -L-α-aspartyl] -L-phenylalanine 1- methyl ester, and excellent sweeteners, etc. containing these novel derivatives are provided.A low-calory sweetener having especially an excellent sweetening potency can be provided in comparison with conventional ones.

Full Text

10-97701 [name of document] Specification [title of invention] ASPARTYL DIPEPTIDE ESTER DERIVATIVES AND SWEETENERS [claims] [claim l] Aspartic directive ester derivatives (including salts thereof) represented by formula (1): [chemical formula l] wherein Rib and Rare independently from each other, represent a substituent selected from a hydrogen atom, a hydroxyl group, a ethoxy group and an ethoxy group, or R and Rn together form a methylenedioxy group, R, represents a hydrogen atom or a hydroxyl group, and R4 represents a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group, provided the derivatives in which and Rn are all hydrogen atoms, and the derivatives in which is a hydroxyl group. and Rj is a methoxy group, are excluded, [claim 2] The derivatives of claim 1, wherein R is a methoxy group, Rn is a hydroxyl group, R3 is a hydrogen atom, and R4 is a methyl group. [claim 3] The derivatives of claim 1, wherein R’ and R’ are methoxy groups, R3 is a hydrogen atom, and R’ is a methyl group, [claim 4] The derivatives of claim 1, wherein R’ and Rj together form a methylenedioxy group, R3 is a hydrogen atom, and R4 is a methyl group, [claim 5] The derivatives of claim 1, wherein Ri is a hydroxyl group, Rj and R3 are hydrogen atoms, and R4 is a methyl group, [claim 6] The derivatives of claim 1, wherein R’ is a methoxy group, R2 and R3 are hydrogen atoms, and R4 is a methyl group, [claim 7] The derivatives of claim 1, wherein Rj is an ethoxy group, R2 and R3 are hydrogen atoms, and R4 is a methyl group, [claim 8] The derivatives of claim 1, wherein R’ and R3 are hydrogen atoms, Rj is a hydroxyl group, and R4 is a methyl group, [claim 9] The derivatives of claim 1, wherein R’ and R3 are hydrogen atoms, R2 is a methoxy group, and R’ is a methyl group, [claim 10] The derivatives of claim 1, wherein R’ is a methoxy group, Rj and R3 are hydroxyl groups, and R’ is a methyl group, [claim 11] A sweetener or products such as foods having a sweetness , comprising at least one derivative selected from the derivatives of claim 1 as an active ingredient. [detailed explanation of invention] [0001] [field of invention] The present invention relates to novel aspartyl dipeptide ester derivatives, and a sweetener and products such as foods having a sweetness, which contain the same as an active ingredient. [0002] [prior art] In recent years, as eating habits have been improved to a high level, fatness caused by excessive intake of sugar and diseases accompanied by fatness have been at issue. Accordingly, the development of a low-calory sweetener that replaces sugar has been in demand. As a sweetener that has been widely used at present, there is aspartame which is excellent in a safety and organoleptic properties. However, this is somewhat problematic in the stability. In WO 94/11391, it is stated that derivatives in which an alkyl group is introduced in an amino group of aspartic acid constituting aspartame markedly improves sweetening potency and the stability is slightly improved. It is reported that the best compound described in this document is N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester having a 3,3-dimethylbutyl group as an alkyl group and the sweetening potency thereof is 10,000 times. Aspartame derivatives having introduced therein 20 types of substituents other than the 3,3-dimethylbutyl group are indicated therein, and the sweetening potency thereof is reported to be less than 2,500 times. Derivatives having a 3-(substituted phenyl)propyl group as an alkyl group are also shown. However, it is reported that the sweetening potency of N-[N-(3-phenylpropyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester is 1,500 times and that of N-[N-[3-(3-methoxy-4-hydroxypheny1)propyl]-L-a-asparty1]-L-phenylalanine 1-methyl ester is 2,500 times. Thus, these are far less than that (10,000 times) of N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester. [0003] [problems invention is to solve] It is an object of the invention to provide novel aspartyl dipeptide ester derivatives which are excellent in the safety and which have sweetening potency equal to or higher than that of the N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine 1-mehtyl ester, and a low-calory sweetener containing the same as an active ingredient. [0004] [means to solve problems] In order to solve the problems, the present inventors have synthesized several aspartame derivatives in which various 3-(substituted phenyl)propyl groups are introduced in an amino group of aspartic acid constituting the aspartame derivatives by use of cinnam aldehyde having various substituents on 3-phenylpropianaldehyde having various substituents that can easily derived therefrom an precursor aldehydes, and have examined the sweetening potency of them. They have consequently found that with respect to the sweetening potency, the novel compounds that they have found are by far higher than not only N-[N-(3-phenylpropyl)-L-a- aspartylJ-L-phenylalanine 1-methyl ester which is reported to have the sweetening potency of 1,500 times in WO 94/11391 but also N- [M-(3,3-dimethylbutyl)-L-a-aspartyl]-L- phenylalanine 1-methyl ester which is reported therein to have the sweetening potency of 10,000 times, and that especially the compounds represented by the following formula (1) are excellent as a sweetener. These findings have led to the completion of the invention. The present invention ( Claim 1 ) is directed to novel aspartyl dipeptide ester derivatives ( including the salt forms thereof ) represented by the general formula (1): [0005] [chemical formula 2] CH2 , CO2H COOR4 CO—NH i’-f’H CH2-CH2-CH2—NH»4-IH CH2 [0006] wherein Ri and R’, independently from each other, represent a substituent selected from a hydrogen atom (H), a hydroxyl group (OH), a methoxy group (OMe) and an ethoxy group (OEt) , or Ri and R, together form a methylenedioxy group (OCHjO) , provided the case where R’ and R’ are all hydrogen atoms and the case where R’ is a hydroxyl group and R2 is a methoxy group, are excluded, Rj represents a hydrogen atom or a hydroxyl group, and R4 represents a substituent selected from a methyl group (CH3), an ethyl group (CH2CH3), an isopropyl group (CH(CH3)j), a normal (n-) propyl group (CH2CH2CH3) and a t-butyl group (C(CH3)3) . [0007] [embodiments for carrying the invention] The novel aspartyl dipeptide ester derivatives of the invention include the compounds represented by formula (1) and salts thereof. Amino acids constituting the derivatives are preferably L-isomers in that these are present in nature. [0008] With respect to the compounds of the present invention, the following inventions are preferably included. [1] Compounds of formula (1) wherein R’ is a substituent selected from a methoxy group and an ethoxy group, R2 is a substituent selected from a hydrogen atom, a hydroxyl group, a methoxy group and an ethoxy group, or R’ and Rj together form a methylenedioxy group (OCHjO), R3 is a hydrogen atom or a hydroxyl group, and R’ is a substituent selected from a methyl group, an ethyl group, an isopropyl group, a normal (n-) propyl group and a t-butyl group. [2] Compounds of formula (1) wherein R’ is a hydrogen atom, Rj is a substituent selected from a hydroxyl group, a methoxy group and an ethoxy, or R’ and Rj together form a methylenedioxy group (OCH’O), R3 is a hydrogen atom or a hydroxyl group, and R’ is a substituent selected from a methyl group, an ethyl group, an isopropyl group, a normal (n-) propyl group and a t-butyl group. [0009] [3] Compounds of formula (1) wherein R’ is a hydroxy1 group, Rj is a substituent selected from a hydrogen atom, a hydroxy 1 group and an ethoxy group, or R’ and R’ together form a methylenedioxy group (OCHjO), R3 is a hydrogen atom or a hydroxyl group, and R’ is a substituent selected from a methyl group, an ethyl group, an isopropyl group, a normal (n-) propyl group and a t-butyl group. [4] Compounds of formula (1) wherein R’ is a methoxy group, R2 is a hydroxyl group, R3 is a hydrogen atom, and R4 is a methyl group. [5] Compounds of formula (1) wherein R’ and Rj are each a methoxy group, R3 is a hydrogen atom, and R4 is a methyl group. [0010] [6] Compounds of formula (1) wherein R’ stnd R’ together form a methylenedioxy group, R, is a hydrogen atom, and R, is a methyl group. [7] Compounds of formula (1) wherein R’ is a hydroxyl group, Rj and R3 are each a hydrogen atom, and R4 is a methyl group. [8] Compounds of formula (1) wherein Rj is a methoxy group, Rj and R3 are each a hydrogen atom, and R4 is a methyl group. [0011] [9] Compounds of formula (1) wherein R’ is an ethoxy group, Rj and R3 are each a hydrogen atom, and R’ is a methyl group. [10] Compounds of formula (1) wherein R’ and R3 are each a hydrogen atom, Rj is a hydroxyl group, and R’ is a methyl group. [11] Compounds of formula (1) wherein R’ and R3 are each a hydrogen atom, R’ is a methoxyl group, and R, is a methyl group. [12] Compounds of formula (1) wherein R’ is a methoxy group, Rj and R3 are each a hydroxyl group, and R4 is a methyl group. [0012] Examples of the salts of the compounds in the present invention include salts with alkali metals such as sodium and potassium; salts with alkaline earth metals such as calcium and magnesium; salts with amines such as monoethanol amine; salts with inorganic acids such as hydrochloric acid and sulfuric acid; and salts with organic acids such as citric acid and acetic acid. These are included in the derivatives of the invention as described above. [0013] The aspartyl dipeptide ester derivatives of the present invention can easily be formed by reductively alkylating aspartame derivatives with cinnamaldehydes having various substituents and a reducing agent (for example, hydrogen/palladium carbon catalyst). Alternatively, the derivatives can be formed by subjecting aspartame derivatives (for example, P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester) having a protective group in a carboxylic acid in the P-position which derivatives can be obtained by the usual peptide synthesis method (Izumiya et al.. Basis of Peptide Synthesis and Experiments Thereof, Maruzen, published January 20, 1985) to reductive alkylation with cinnamaldehydes having various substituents and a reducing agent (for example, NaB(0Ac)3H) (A. F. Abdel-Magid et al.. Tetrahedron Letters, 31, 5595 (1990)), and then removing the protective group. However, the method of forming the compounds of the invention is not limited thereto. 3-Phenylpropionai.dehydes having various substituents or acetal derivatives thereof can of course be used as precursor aldehydes in the reductive alkylation instead of cinnamaldehydes having various substituents. [0014] As a result of an organoleptic test, the compounds and the salts thereof in the invention were found to have a strong sweetening potency and have organoleptic properties similar to that of sugar. For example, the sweetening potency of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 20,000 times, that of N-[N-[3-(3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 8,000 times (relative to sugar), that of N~[N-[3-(4- methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 6,500 times (relative to sugar) , and that of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a -aspartyl]-L-tyrosine 1-methyl ester was approximately 16,000 times (relative to sugar). With respect to the aspartyl dipeptide derivatives (represented by formula (2)) formed, the structures and tlie results of the organoleptic test are shown in Table 1. [0015] [chemical formula 3] "--P- R; CH2 ‘ (2) COOCH3 CO~NH»*4-«H CH2-CH2--CH2—NH*4—H CH2 [0016] [Table 1] Structures and sweetening potency of aspartyl dipeptide ester derivatives Compound No. Ri R2 R3 sweetening potency 1 . OCH. OH H 20000 2 OCH. OCH:, H 2500 3 OCH .0 H 5000 4 OH H H 5000 5 OCH:, H H 6500 6 OCH.CH:, H H 1500 7 H OH H 8000 8 H OCH.-, H 3500 9 OCH. OH OH 16000 *) Relative to sweetening potency of a 4% sucrose aqueous solution [0017] When the compounds (including salts thereof) of the present invention are used as a sweetener, these may of course be used in combination with other sweeteners unless inviting any special troubles. When the derivatives of the present invention are used as a sweetener, an appropriate carrier and/or an appropriate bulking agent may be used as required. For example, a carrier which has been so far used is available. The derivatives of the present invention can be used as a sweetener or an ingredient therefor, and further as a sweetener for products such as foods and the like to which a sweetness has to be imparted, for example, confectionary, chewing gum, hygiene products, toiletries, cosmetics, pharmaceutical products and veterinary products for animals. Still further, they can be used in a method of imparting a sweetness to the products. This method can be, for example, a conventional method for using a sweetening ingredient for a sweetener in the sweeteners or the method of imparting a sweetness. [0018] EXAMPLKg The invention is illustrated specifically by referring to the following Examples. EXAMPLE 1 Synthesis of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Five milliliters of a solution of 4N-HCL and dioxane were added to 485 mg (1.0 mmol) of N-t-butoxycarbonyl-P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester, and the mixture was stirred at room temperature for 1 hour. The reaction solution was concentrated under reduced pressure. Thirty milliliters of a 5% sodium hydrogencarbonate aqueous solution were added to the residue, and the mixture was extracted twice with 30 ml of ethyl acetate. The organic layer was washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate. Then, magnesium sulfate was removed by filtration, and the filtrate was concentrated under reduced pressure to obtain 385 mg of p-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester as a viscous oil. [0019] The P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester (385 mg, 1.0 mmol) was dissolved in 15 ml of THF, and the solution was maintained at 0°C. To this were added 268 mg (1.0 mmol) of 3-benzyloxy-4-methoxycinnamaldehyde, 0.060 ml (1.0 mmol) of acetic acid and 318 mg (1.5 mmol) of NaB(0Ac)3H. The mixture was stirred at 0°C for 1 hour and further overnight at room temperature. To the reaction solution were added 50 ml of a saturated aqueous solution of sodium hydrogen carbonate, and the mixture was extracted twice with 30 ml of ethyl acetate. The organic layer was washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate. Then, magnesium sulfate was removed by filtration, and the filtrate was concentrated under reduced pressure. The residue was purified with PTLC ( Preparative Thin Layer Chromatography ) to obtain 523 mg (0.82 mmol) of N-[N-[3-(3-benzyloxy-4-methoxyphenyl)propenyl]-P-0-benzyl-L-a-aspartyl]-L-phenylalanine 1-methyl ester as a viscous oil. [0020] The N-[N-[3-(3-benzyloxy-4-methoxyphenyl)propenyl]-P-0-benzyl-L-a-aspartyl]-L-phenylalanine 1-methyl ester (523 mg, 0.82 mmol) was dissolved in a mixed solvent of 30 ml of methanol and 1 ml of water, and 200 mg of 10% palladium carbon (water content 50%) were added thereto. The mixture was reduced in a hydrogen stream at room temperature for 3 hours. The catalyst was removed by filtration, and the filtrate was concentrated under reduced pressure. In order to remove an odor adsorbed, the residue was purified with PTLC to obtain 228 mg (0.48 mmol) of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester as a solid. [0021] "HNMR (DMSO-da) 6 : 1. 50-1. 60 (m, 2"H), 2. 15-2. 40 (m, 6H), 2. 87-2. 97 (dd, IH), 3. 0 5-3. 13 (dd, IH), 3, 37-3, 43 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 3H), 4. 50-4. 60 (m, IH), 6. 52 (d, IH), 6. 60 (s, IH), 6. 79 (d, IH), 7. 18-7. 30 (m, 5H), 8. 52 (d, IH), 8. 80 (brs, IH). E S I -M S 4 5 9 . 2 (MH 0 [0022] Sweetening potency (relative to sugar): 20,000 times [0023] EXAMPLE 2 Synthesis of N-[N-[3-(3,4-dimethoxyphenyl)propyl]-L-a- aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,4-dimethoxycinnamaldehyde was used Instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3,4-dimethoxyphenyl )propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 48.7% as a solid. [0024] "HNMR (DMSO-d«) 6 : 1. 52-1. 62 (m, 2H), 2. 18-2. 50 (m, 6H), 2, 86-2. 76 (dd, IH), 3. 0 4-3. 12 (dd, IH), 3. 37-3. 44 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 3H), 3. 73 (s, 3H), 4. 52-4. 62 (m, IH), 6. 66 (d, IH), 6. 76 (s, IH), 6. 83 (d, IH), 7. 18-7. 30 (m, 5H), 8. 50 (d, IH). ESI-MS 473.2 (MH •) [0025] Sweetening potency (relative to sugar): 2,500 tim?i, [0026] EXAMPLE 3 Synthesis of N-[N-[3-(3,4-methylenedioxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,4-methylenedioxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3,4-methylenedioxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 42.1% as a solid. [0027] "HNMR (DMSO-d.) 6 : 1. 48-1. 60 (m, 2H), 2. 14-2. 48 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 3-3. 12 (dd, IH), 3. 37-3. 43 (m, IH), 3. 62 (s, 3H), 4. 54-4. 59 (m, IH), 5. 94 (s, IH), 5. 95 (s, IH), 6. 61 (d, IH), 6. 74 (s, IH), 6. 78 (d, IH), 7, 15-7. 30 (m, 5H), 8. 47 (d, IH). ESI-MS 457. 2 (MH") [0028] Sweetening potency (relative to sugar): 5,000 times [0029] EXAMPLE 4 Synthesis of N-[N-[3-(4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 4-benzyloxycinnamaldehyde was used instead of 3-benzyJtoxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-hydroxyphenyl)propyl]-L-a-aspartyl]-L~phenylalanine 1-methyl ester in a total yield of 40.6% as a solid. [0030] "HNMR (DMSO-dO 6 : 1. 48-1. 60 (m, 2H), 2. 14-2. 43 (ni, 6H), 2. 86-2. 96 (dd, IH), 3. 0 4-3. 14 (dd, IH), 3. 37-3. 42 (m, IH), 3. 62 (s, 3H), 4. 52-4. 62 (m, IH), 6. 65 (d, 2H), 6. 93 (d, 2H), 7. 16-7. 29 (m, 5H), 8. 49 (d, IH), 9. 12 (b r s , 1 H). ESI-MS 429. 2 (MH") [0031] Sweetening potency (relative to sugar): 5,000 times [0032] EXAMPLE 5 Synthesis of N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine l-methyl ester (1) Example 1 was repeated except that 4-methoxycinnamaldehyde was used instead of 3-ben2yloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 50.0% as a solid. [0033] "HNMR (DMSO-d«) 6:1. 50-1. 62 (m, 2"H), 2. 16-2. 48 (m, 6H), 2. 84-2. 94 (dd, IH), 3 . 0 4-3. 12 (dd, IH), 3. 38-3. 44 (m, IH), 3. 62 Ks, 3H), 3. 71 (s, 3H), 4. 52-4. 62 (m, IH), 6. 83 (d, 2H), 7. 08 (d, 2H), 7. 17-7. 29 (m, 5H), 8. 50 (d, 1 H). ESI-MS 443. 3 (MH") [0034] Sweetening potency (relative to sugar): 6,500 times [0035] EXAMPLE 6 Synthesis of N-[N-[3-(4-ethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 4-ethoxyclnnamaldehyde was used Instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-ethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 57.1% as a solid. [0036] "HNMR (DMSO-d.) 6:1. 30 (t, 3H), 1. 50-1. 62 (m, 2H), 2. 16-2. 48 (m, 6H), 2. 85-2. 95 (dd, IH), 3. 02-3. 12 (dd, IH), 3. 39-3. 44 (m, IH), 3. 62 (s, 3H), 3. 96 (q, 2H),4. 52-4. 59 (m, IH), 6. 81 (d, 2H), 7. 05 (d, 2H), 7. 17-7. 28 (m, 5H), 8. 50 (d, IH). E S I -M S 4 5 7 . 2 (MH ") [0037] Sweetening potency (relative to sugar): 1,500 times [0038] EXAMPLE 7 Synthesis of N-[N-[3-(3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-benzyloxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 46.6% as a solid, [0039] "HNMR (DMSO-d„) 6:1. 50-1. 62 (m, IH), 2. 10-2. 48 (m, 6H), 2. 87-2. 96 (dd, IH), 3. 4 0-3. 12 (dd, IH), 3. 33-3. 38 (m, IH), 3. 62 (s, 3H), 4. 52-4. 60 (m, IH), 6. 53-6. 60 (m, 3H), 7. 04 (t, IH), 7, 17-7. 30 (m, 5H), 8. 50 (d, IH), 9. 4 0 ( b r s , 1 H ). ESI-MS 429. 2 (MHO [0040] Sweetening potency (relative to sugar): 8,000 times [0041] EXAMPLE 8 Synthesis of N-[N-[3-(3-methoxyphenyl)propyll-L-a- aspartyl]-L-phenylalanine 1-methyl ester ‘» Example 1 was repeated except that 3-methoxycinnamaldehyde was used instead of 3-benzyloxy~4-methoxycinnamaldehyde to obtain N-[N-[3-(3-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 55.6% as a solid. [0042] "HNMR (DMSO-dO 6 : 1. 54-1. 66 (m, 2H), 2. 18-2. 50 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 2-3. 12 (dd, IH), 3. 40-3. 46 (m, IH), 3. 62 (s, 3H), 3. 73 (s, 3H), 4. 53-4. 61 (m, IH), 6. 70-6. 78 (m, 3H), 7. 13-7. 30 (m, 5H), 8. 50 (d, IH). ESI-MS 443.1(iyiH") [0043] Sweetening potency (relative to sugar): 3,500 times [0044] EXAMPLE 9 Synthesis of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]~L-tyrosine 1-methyl ester Example 1 was repeated except that N-t-butoxycarbonyl-P-0-benzyl-a-L-aspartyl-L-tyrosine methyl ester was used instead of M-t-butoxycarbonyl-P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester to obtain N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-tyrosine 1-methyl ester in a total yield of 45.4% as a solid. [0045] "HNMR (DMSO-dc) 6 : 1. 52-1. 64 (m, 2H), 2. 24-2. 48 (m, 6H), 2. 74-2. 84 (dd, IH), 2, 9 1-2. 99 (dd, IH), 3. 47-3. 54 (m, IH), 3. 61 (s, 3H), 3. 72 (s, 3H), 4. 45-4. 53 (m, IH), 6. 54 (d, IH), 6. 60 (s, IH), 6, 65 (d, 2H), 6. 79 (d, IH), 6. 98 (d, 2H), 8. 54 (d, IH), 8. 78 (brs, IH), 9. 25 ( b r s , 1 H). ESI-MS 475. 2 (MH") [0046] Sweetening potency (relative to sugar): 16,000 times [0047] [effects of invention] The novel aspartyl dipeptide ester derivatives of the present invention have especially an excellent sweetening potency in comparison with conventional sweeteners. The invention can provide novel chemical substances having excellent organoleptic properties as a sweetener. Accordingly, such novel derivatives in the present invention can be used as a sweetener, and also can impart a sweetness to products such as beverages and foods requiring a sweetness. [name of document] Paper for ABSTRACT [abstract] [problems] It is required that a low-calory substance having especially an excellent sweetening potency is provided in comparison with conventional products. [means to solve them] Novel aspartyl dipeptide ester derivatives (including salts thereof) such as N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester can be used as an excellent sweetener, which can solve the above problems. Accordingly, a sweetener containing the same can be provided. [selected drawing] non VER TFTfJATTON I, Yasumasa Ishida, Dr. Eng., registered patent attorney of Bohsei Bldg., 3-20-12 Shin-Yokohama, Kohoku-ku, Yokohama, Kanagawa-ken, Japan hereby certify that to the best of my knowledge and belief the following is a true translation made by me of which I accept responsibility, of the documents attached. ‘(Yasumasa Ishida, Dr. Eng. Signed this 11 -’ day o f Octi4’’ 2000 CERTIFICATE (translation) PATENT OFFICE JAPANESE GOVERNMENT This is to certify that the annexed is a true copy of the following application as filed with this Office, Date of Application: 17 February 1999 Application Number : Patent Application No.11-38190 Applicant : AJINOMOTO CO.,INC. Commissioner Patent Office (signature) (seal) (Proof of filing documents 1999/02/17) [Name of Document] Application for Patent [Ref. No.] 99-027 [Date of Submission] Year Month Day Heisei 11 2 12 [sic 17] [Addressed to] Commissioner, Patent Office [IPC] C07K 5/075 [Title of the Invention] ASPARTYL DIPEPTIDE ESTER DERIVATIVES AND SWEETENERS [Number of claims] 23 [Inventor] [Address]c/o Amino Science Laboratories, AJINOMOTO CO., INC. No.1-1, Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa-ken, Japan [Name] Yusuke AMINO [Inventor] [Address]c/o Amino Science Laboratories, AJINOMOTO CO., INC. No.1-1, Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa-ken, Japan [Name] Kazuko YUZAWA [Inventor] [Address]c/o Amino Science Laboratories, AJINOMOTO CO., INC. No.1-1, Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa-ken, Japan [Name] Tadashi TAKEMOTO [Inventor] [Address]c/o Amino Science Laboratories, AJINOMOTO CO., INC. No.1-1, Suzuki-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa-ken, Japan [Name] Ryoichiro NAKAMURA [Applicant] [Identification No.] 000000066 [Name] AJINOMOTO CO., INC. [Representative] Kunio EGASHIRA [phone number] 03-5250-8178 [Claiming priority based on prior application] [Application Number] 10-97701 [Date of Application] 09 April 1998 [Fee] [Amount] Yen21,000. [List of Documents] [Name of document] Specification 1 [Name of document] Abstract 1 [Proof] Necessary 11-38190 [name of document] Specification [title of invention] ASPARTYL DIPEPTIDE ESTER DERIVATIVES AND SWEETENERS [claims] [claim l] Novel aspartyl dipeptide ester derivatives (including salts thereof) represented by formula (1): [chemical formula l] COOR7 ‘2 p’ CO-NH»"C- R4 R5 I ‘ r II ‘‘‘ CO2H R3-/_V-CH2-CH2-CH2--NH»-C--H CH2 wherein Rj, R2, R3, R4 and Rj, independently from each other, represent a substituent selected from a hydrogen atom, a hydroxy 1 group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or Rj and Rj, or Rj and R, together form a methylenedioxy group wherein R4, R5, and R’ or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, each represents any substituents as mentioned above designated for the R’, R3, R’ and R5,respectively, R’ represents a hydrogen atom or a hydroxy1 group, and R, represents a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group, provided the derivatives in which R’ to R5 are all hydrogen atoms, or the derivatives in which R, is a methoxy group and R3 is a hydroxyl group are excluded, [claim 2] The derivatives of claim 1, wherein Rj is a hydroxyl group, R3 is a methoxy group, R’, R’, R5 and Rg are hydrogen atoms, and R’ is a methyl group, [claim 3] The derivatives of claim 1, wherein R’ and R3 are methoxy groups, Rj, R4, R5 and Rg are hydrogen atoms, and R, is a methyl group. [claim 4] The derivatives of claim 1, wherein Rj and R3 together form a methylenedioxy group, Rj, R4, R5 and Rg are hydrogen atoms, and R7 is a methyl group, [claim 5] The derivatives of claim 1, wherein R3 is a hydroxyl group, Rj, Rj, R4, Rj and Rg are hydrogen atoms, and R, is a methyl group. [claim 6] The derivatives of claim 1, wherein R3 is a methoxy group, Ri, Rj, R4, Rs and Rg are hydrogen atoms, and R, is a methyl group, [claim 7] The derivatives of claim 1, wherein R3 is an ethoxy group, Rj, R2, R4, R5 and Rg are hydrogen atoms, and R, is a methyl group, [claim 8] The derivatives of claim 1, wherein Rj is a hydroxyl group, Ri, R3, R4, Rg and Rg are hydrogen atoms, and R’ is a methyl group. [claim 9] The derivatives of claim 1, wherein Rj is a methoxy group, Rx, R3, R4, Rs and Rg are hydrogen atoms, and R’ is a methyl group, [claim 10] The derivatives of claim 1, wherein R3 is a methoxy group, R2 and Rg are hydroxyl groups, R’, R4 and Rj are hydrogen atoms, and R’ is a methyl group, [claim 11] The derivatives of claim 1, wherein R’ is a hydroxyl group, R3 is a methoxy group, Rj, R4, Rg and Rg are hydrogen atoms, and R, is a methyl group, [claim 12] The derivatives of claim 1, wherein Rj is a hydroxyl group, Rj is a methoxy group, R3, R4, Rj and Rg are hydrogen atoms, and R, is a methyl group. [claim 13] The derivatives of claim 1, wherein R’ is a hydroxyl group, Rj is a methoxy group, Rj, R3, R5 and R’are hydrogen atoms, and Ry is a methyl group, [claim 14] The derivatives of claim 1, wherein R’ is a hydroxyl group, R3 and R’ are methyl groups, and Rj, R,, R5 and Rg are hydrogen atoms. [claim 15] The derivatives of claim 1, wherein R’ and R3 are methoxy groups, R2, R4, R5 and Rg are hydrogen atoms, and R’ is a methyl group. [claim 16] The derivatives of claim 1, wherein Ri is an ethoxy group, R3 is a methoxy group, R’, R4, R5 and Rj are hydrogen atoms, and R-, is a methyl group, [claim 17] The derivatives of claim 1, wherein Rj and R, are methyl groups, R3 is a hydroxyl group, and R’, R,, Rg and R’ are hydrogen atoms. [claim 18] The derivatives of claim 1, wherein Rj is a hydroxyl group, R3 and R, are methyl groups, and R’, R4, R5 and Rg are hydrogen atoms. [claim 19] The derivatives of claim 1, wherein Rj and R’ are methyl groups, R3 is a raethoxy group, and R’, R4, R5 and Rg are hydrogen atoms. [claim 20] The derivatives of claim 1, wherein Rj and R’ are methoxy groups, Ri, R3, R5 and Rg are hydrogen atoms, and R, is a methyl group. [claim 21] The derivatives of claim 1, wherein R3 is a 2-hydroxyethoxy group, Rj, Rj, R’, R5 and Rg are hydrogen atoms, and R’ is a methyl group, [claim 22] The derivatives of claim 1, wherein R3 and R, are methyl groups, and R’, R,, R’, R5 and Rg are hydrogen atoms. [claim 23] A sweetener or products such as foods having a sweetness, comprising at least one derivative selected from the derivatives of claim 1 as an active ingredient. [detailed explanation of invention] [0001] [field of invention] The present invention relates to novel aspartyl dipeptide ester derivatives, and a sweetener and products such as foods having a sweetness, which contain the same as an active ingredient. [OOO2J [prior art] In recent years, as eating habits have been improved to a high level, fatness caused by excessive intake of sugar and diseases accompanied by fatness have been at issue. Accordingly, the development of a low-calory sweetener that replaces sugar has been in demand. As a sweetener that has been widely used at present, there is aspartame which is excellent in a safety and organoleptic properties. However, this is somewhat problematic in the stability. In WO 94/11391, it is stated that derivatives in which an alkyl group is introduced in an amino group of aspartic acid constituting aspartame markedly improves sweetening potency and the stability is slightly improved. It is reported that the best compound described in this document is N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine l-methyl ester having a 3,3-dimethylbutyl group as an alkyl group and the sweetening potency thereof is 10,000 times. Aspartame derivatives having introduced therein 20 types of substituents other than the 3,3-dimethylbutyl group are indicated therein, and the sweetening potency thereof is reported to be less than 2,500 times. Derivatives having a 3-(substituted phenyl)propyl group as an alkyl group are also shown. However, it is reported that the sweetening potency of N-[N-(3- phenylpropyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester is 1,500 times and that of N-[N-[3-(3-methoxy-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester is 2,500 times. Thus, these are far less than that (10,000 times) of N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester. [0003] [problems invention is to solve] It is an object of the invention to provide novel aspartyl dipeptide ester derivatives which are excellent in the safety and which have sweetening potency equal to or higher than that of the N-[N-(3,3-diraethylbutyl)-L-a-aspartyl]-L-phenylalanine 1-mehtyl ester, and a low-calory sweetener containing the same as an active ingredient. [0004] [means to solve problems] In order to solve the problems, the present inventors have synthesized several aspartame derivatives in which various 3-(substituted phenyl)propyl groups are introduced in an amino group of aspartic acid constituting the aspartame derivatives by use of cinnam aldehyde having various substituents on 3-phenylpropianaldehyde having various substituents that can easily derived therefrom an precursor aldehydes, and have examined the sweetening potency of them. They have consequently found that with respect to the sweetening potency, the novel compounds that they have found are by far higher than not only N-[N-(3-phenylpropyl)-L-a- aspartyl]-L-phenylalanine 1-methyl ester which is reported to have the sweetening potency of 1,500 times in WO 94/11391 but also N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L- phenylalanine 1-methyl ester which is reported therein to have the sweetening potency of 10,000 times, and that especially the compounds represented by the following formula (1) are excellent as a sweetener. These findings have led to the completion of the invention. The present invention ( Claim 1 ) is directed to novel aspartyl dipeptide ester derivatives ( including the salt forms thereof ) represented by the general formula (1): [0005] [chemical formula 2] COOR7 R4 R5 ,’2 1’, ‘ ‘‘‘ CO2H [0006] wherein Rir ‘ir R3/ R4 2ind R5, independently from each other, represent a substituent selected from a hydrogen atom (H), a hydroxy! group (OH), an alkoxy group (OR; methoxy group, ethoxy group, propoxy groups, or the like ) having from 1 to 3 carbon atoms, an alkyl group (R; methyl group, ethyl group, propyl groups, or the like) having from 1 to 3 carbon atoms and a hydroxyalkyloxy group (for examples, 0(CH2)jOH or OCH2CH(OH)CH3) having 2 or 3 carbon atoms, or R’ and Rj, or R, and R3 together form a methylenedioxy group (OCHjO) wherein R’, R5 and, R’ or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, represent any substituents as mentioned above designated for the R’, R3, R’ and R5, respectively, provided the case where R’ to R5 are all hydrogen atoms and the case where R, is a methoxy group and R3 is a hydroxy 1 group are excluded, Rg represents a hydrogen atom or a hydroxyl group, and R7 represents a substituent selected from a methyl group (CH3), an ethyl group (CH2CH3), an isopropyl group (CH(CH3)2, an n-propyl group (CHjCHjCHj) and a t-butyl group (€(0113)3). [0007] [embodiments for carrying the invention] The novel aspartyl dipeptide ester derivatives of the invention include the compounds represented by formula (1) and salts thereof. Amino acids constituting the derivatives are preferably L-isomers in that these are present in nature. [0008] With respect to the compounds of the invention, the following inventions are preferably included. [1] Compounds of formula (1) wherein R3 is a substituent selected from a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms,. Ri, Rj, R4 and R5 are each a substituent selected from a hydrogen atom, a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or R’ and Rj, or Rj and R3 together form a methylenedioxy group (OCHjO) wherein R’, R5 and, R’ or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, represent any substituents as mentioned above for the Ri, R3, R4 and Rj, Rg is a hydrogen atom or a hydroxyl group, and R, is a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group. [2] Compounds of formula (1) wherein R3 is a hydrogen atom, Ri, Rj, R4 and Rj are each a substituent selected from a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or R’ and R2, or Rj and R3 together form a methylenedioxy group (OCHjO) wherein R’, R5 and, Rj or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, represent any substituents as mentioned above designated for the Rj, R3, R4 and R5,respectively, Rg is a hydrogen atom or a hydroxyl group, and R7 is a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group. [0009] [3] Compounds of formula (1) wherein R3 is a hydroxyl group, Ri, R3, R4 and R5 are each a substituent selected from a hydrogen atom, a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or R’ and R,, or R, and R, together form a methylenedioxy group (OCHjO) wherein R4, R5, and Ri or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, represent any substituents as mentioned above designated for the Rj, R3, R4 and Rj, respectively, Rg is a hydrogen atom or a hydroxyl group, and R, is a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group. [4] Compounds of formula (1) wherein Rj is a hydroxyl group, R3 is a methoxy group, Ri, R4, Rj and Rg are each a hydrogen atom, and R’ is a methyl group. [5] Compounds of formula (1) wherein Rj and R3 are each a methoxy group, Rj, R4, Rj and Rg are each a hydrogen atom, and R, is a methyl group. [OOIO] [6] Compounds of formula (1) wherein Rj and R3 together form a methylenedioxy group, R’, R’, Rj and Rg are each a hydrogen atom, and R’ is a methyl group. [7] Compounds of formula (1) wherein R3 is a hydroxyl group, R’, Rj, R4, R5 and Rg are each a hydrogen atom, and R’ is a methyl group. [8] Compounds of formula (1) wherein R3 is a methoxy group, Ri, Rj, R4, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [0011] [9] Compounds of formula (1) wherein R3 is an ethoxy group, Ri, Rj, R4, Rs and Rg are each a hydrogen atom, and R, is a methyl group. [10] Compounds of formula (1) wherein R’ is a hydroxyl group, Ri, R3, R4, Rg and Rg are each a hydrogen atom, and R, is a methyl group. [11] Compounds of formula (1) wherein Rj is a methoxy group, Ri, R3, R4, RJ and Rg are each a hydrogen atom, and R’ is a methyl group. [12] Compounds of formula (1) wherein R3 is a methoxy group, R2 and Rg are each a hydroxyl group, R’, R’ and R5 are each a hydrogen atom, and R’ is a methyl group. [13] Compounds of formula (1) wherein R’ is a hydroxyl group, R3 is a methoxy group, Rj, R’, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [14] Compounds of formula (1) wherein Rj is a hydroxy 1 group, Rj is a methoxy group, R3, R’, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [15] Compounds of formula (1) wherein R’ is a hydroxyl group, R4 is a methoxy group, R’, R3, R’ and Rg are each a hydrogen atom, and R’ is a methyl group. [16] Compounds of formula (1) wherein R’ is a hydroxyl group, R3 and R, are each a methyl group, and R2, R4, R5 and Rg are each a hydrogen atom. [17] Compounds of formula (1) wherein R’ and R3 are each a methoxy group, Rj, R4, R5 and Rg are each a hydrogen atom, and R7 is a methyl group. [18] Compounds of formula (1) wherein R’ is an ethoxy group, R3 is a methoxy group, Rj, R4, R5 and Rg are each a hydrogen atom, and R’ is a methyl group. [19] Compounds of formula (1) wherein Rj and R, are each a methyl group, R3 is a hydroxyl group, and Rj’, R4, R5 and Rg are each a hydrogen atom. [20] Compounds of formula (1) wherein Rj is a hydroxyl group, R3 and R7 are each a methyl group, and R’, R4, R5 and Rg are each a hydrogen atom. [21] Compounds of formula (1) wherein Rj and R, are each a methyl group, R3 is a methoxy group, and R’, R4, R5 and Rg are each a hydrogen atom. [22] Compounds of formula (1) wherein Rj and R’ are each a methoxy group, Rj, R3, R5 and R’ are each a hydrogen atom’ and R7 is a methyl group. [23] Compounds of formula (1) wherein R3 is a 2-hydroxyethoxy group, Rj, Rj, R4, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [24] Compounds of formula (1) wherein R, and R’ are each a methyl group, and R’, R,, R’, R5 and Rg are each a hydrogen atom. [0012] Examples of the salts of the compounds in the present invention include salts with alkali metals such as sodium and potassium; salts with alkaline earth metals such as calcium and magnesium; ammonium salts with ammonia; salts with amino acids such as lysine and arginine; salts with inorganic acids such as hydrochloric acid and sulfuric acid; and salts with organic acids such as citric acid and acetic acid. These are included in the derivatives of the invention as described above. [0013] The aspartyl dipeptide ester derivatives of the present invention can easily be formed by reductively alkylating aspartame derivatives with cinnamaldehydes having various substituents and a reducing agent (for example. hydrogen/palladium carbon catalyst). Alternatively, the derivatives can be formed by subjecting aspartame derivatives (for example, P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester) having a protective group in a carboxylic acid in the P-position which derivatives can be obtained by the usual peptide synthesis method (Izumiya et al.. Basis of Peptide Synthesis and Experiments Thereof, Maruzen, published January 20, 1985) to reductive alkylation with cinnamaldehydes having various substituents and a reducing agent (for example, NaB(0Ac)3H) (A. F. Abdel-Magid et al.. Tetrahedron Letters, 31, 5595 (1990)), and then removing the protective group. However, the method of forming the compounds of the invention is not limited thereto. 3-Phenylpropionaldehydes having various substituents or acetal derivatives thereof can of course be used as precursor aldehydes in the reductive alkylation instead of cinnamaldehydes having various substituents. [0014] As a result of an organoleptic test, the compounds and the salts thereof in the invention were found to have a strong sweetening potency and have organoleptic properties similar to that of sugar. For example, the sweetening potency of N-[N-[3-(3-methyl-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 35,000 times (relative to sugar), that of N-[N-[3-(2-hydroxy-4- methylpheny1)propyl]-L-a-aspartyl]-L-a-phenylalanine 1-methyl ester was approximately 30,000 times (relative to sugar), that of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl] -L-phenylalanine l-methyl ester was approximately 20,000 times, that of N-[N-[3-(2-hydroxy-4-methoxypheny1)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 20,000 times (relative to sugar), that of N-[N-[3-(3-hydroxy-4-methylphenyl)propyl]-L-a-aspartyl] -L-phenylalanine l-methyl ester was approximately 15,000 times (relative to sugar), that of N-[N-[3-(3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 8,000 times (relative to sugar), that of N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine l-methyl ester was approximately 6,500 times (relative to sugar), and that of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-tyrosine l-methyl ester was approximately 16,000 times (relative to sugar). With respect to the aspartyl dipeptide derivatives (represented by formula (2)) formed, the structures and the results of the organoleptic test are shown in Table 1. [0015] [chemical formula 3] COOCH3 CO-NH»-C-*H R3- R4 R5 ‘‘2 CO2H (2) [Table l] Structures and sweetening potency of aspartyl dipeptide ester derivatives Ccmpound fl. R, R3 No. 1 H OH OCH;, 2 H OCH OCH;, 3 H OCH2O 4 H H OH 5 H H OCH;. 6 H H OCH.CH. 7 H OH H 8 H OCH:. H 9 H OH OCH;. 1 0 OH H OCHa 1 1 OH OCH;. H 1 2 OH H H 1 3 OH H CH;. 1 4 OCH;, H OCH. 1 5 OCH»CH. H OCH:. 1 6 H CH:. OH 1 7 H OH CH:, 1 8 H CH. OCH. 1 9 H OCH;, H 2 0 H H OCH.CH.OH 2 1 H H CH;. R. Rg sweetening potency H H H 20000 H H H 2500 H H H 5000 H H H 5000 H H H 6500 H H H 1500 H H H 8000 H H H 3500 H H OH 16000 H H H 20000 H H H 10000 OCH;. H H 1500 H H H 30000 H H H 4000 H H H 2500 H H H 35000 H H H 15000 H H H 8000 OCH;. H H 800 H H H 1000 H H H 4000 *) Relative to sweetening potency of a 4% sucrose aqueous solution [0017] When the compounds (including salts thereof) of the present invention are used as a sweetener, these may of course be used in combination with other sweeteners unless inviting any special troubles. When the derivatives of the present invention are used as a sweetener, an appropriate carrier and/or an appropriate bulking agent may be used as required. For example, a carrier which has been so far used is available. The derivatives of the present invention can be used as a sweetener or an ingredient therefor, and further as a sweetener for products such as foods and the like to which a sweetness has to be imparted, for example, confectionary, chewing gum, hygiene products, toiletries, cosmetics, pharmaceutical products and veterinary products for animals. Still further, they can be used in a method of imparting a sweetness to the products. This method can be, for example, a conventional method for using a sweetening ingredient for a sweetener in the sweeteners or the method of imparting a sweetness. [0018] EXAMPLES The invention is illustrated specifically by referring to the following Examples. EXAMPLE 1 Synthesis of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Five milliliters of a solution of 4N-HCL and dioxane were added to 485 mg (1.0 mmol) of N-t-butoxycarbonyl-P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester, and the mixture was stirred at room temperature for 1 hour. The reaction solution was concentrated under reduced pressure. Thirty milliliters of a 5% sodium hydrogencarbonate aqueous solution were added to the residue, and the mixture was extracted twice with 30 ml of ethyl acetate. The organic layer was washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate. Then, magnesium sulfate was removed by filtration, and the filtrate was concentrated under reduced pressure to obtain 385 mg of p- " 0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester as a . viscous oil. [0019] The p-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester (385 mg, 1.0 mmol) was dissolved in 15 ml of THF, and the solution was maintained at 0°C. To this were added 268 mg (1.0 mmol) of 3-benzyloxy-4-methoxycinnamaldehyde, 0.060 ml (1.0 mmol) of acetic acid and 318 mg (1.5 mmol) of NaB(0Ac)3H. The mixture was stirred at 0°C for 1 hour and further overnight at room temperature. To the reaction solution were added 50 ml of a saturated aqueous solution of sodium hydrogen carbonate, and the mixture was extracted twice with 30 ml of ethyl acetate. The organic layer was washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate. Then, magnesium sulfate was removed by filtration, and the filtrate was concentrated under reduced pressure. The residue was purified with PTLC ( Preparative Thin Layer Chromatography ) to obtain 523 mg (0.82 mmol) of N-[N-(3-(3-benzyloxy-4-methoxyphenyl)propenyl]-P-0-benzyl-L-a-aspartyl]-L-phenylalanine 1-methyl ester as a viscous oil. [0020] The N-[N-[3-(3-benzyloxy-4-methoxyphenyl)propenyl]-P-0-benzyl-L-a-aspartyl]-L-phenylalanine 1-methyl ester (523 mg, 0.82 mmol) was dissolved in a mixed solvent of 30 ml of methanol and 1 ml of water, and 200 mg of 10% palladium ckrbon (water content 50%) were added thereto. The mixture was reduced in a hydrogen stream at room temperature for 3 hours. The catalyst was removed by filtration, and the filtrate was concentrated under reduced pressure. In order to remove an odor adsorbed, the residue was purified with PTLC to obtain 228 mg (0.48 mmol) of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester as a solid. [0021] "HNMR (DMSO-d«) 6 : 1. 50-1. 60 (m, 2H), 2. 15-2. 40 (m, 6H), 2. 87-2, 97 (dd, IH), 3. 0 5-3. 13 (dd, IH), 3. 37-3. 43 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 3H), 4. 50-4. 60 (m, IH), 6. 52 (d, IH), 6. 60 (s, IH), 6. 7 9 (d, IH), 7. 18-7. 30 (m, 5H), 8. 52 (d, IH), 8. 80 (brs, IH). ESI-MS 459. 2 (MHO [0022] Sweetening potency (relative to sugar): 20,000 times [0023] EXAMPLE 2 Synthesis of N-[N-[3-(3,4-dimethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,4-dimethoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3,4-|j5 dimethoxyphenyl)propyl] -L-a-aspartyl] -L-phenylalanine 1-r’ methyl ester in a total yield of 48.7% as a solid. [0024] "HNMR (DMSO-d.) 6 : 1. 52-1. 62 (m, 2H), 2. 18-2. 50 (m, 6H), 2. 86-2. 76 (dd, IH), 3. 0 4-3. 12 (dd, IH), 3. 37-3. 44 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 3H), 3. 73 (s, 3H), 4. 52-4. 62 (m, IH), 6. 66 (d, IH), 6. 76 (s, IH), 6. 83 (d, IH), 7. 18-7. 30 (m, 5H), 8. 50 (d, IH). ESI-MS 473. 2 (MH") [0025] Sweetening potency (relative to sugar): 2,500 time [0026] EXAMPLE 3 Synthesis of N-[N-[3-(3,4-methylenedioxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,4-methylenedioxycinnamaldehyde was used Instead of 3-benzyloxy-4-methoxyclnnainaldehyde to obtain N-[N-[3-(3,4-methylenedloxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanlne 1-methyl ester In a total yield of 42.1% as a solid. [0027] "HNMR (DMSO-dO 6 : 1 . 48-1. 60 (m, 2H), 2. 14-2. 48 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 3-3. 12 (dd, IH), 3. 37-3. 43 (m, IH), 3. 62 (s, 3H), 4. 54-4. 59 (m, IH), 5. 94 (s, IH), 5. 95t?(s, IH), 6. 61 (d, IH), 6. 74 (s, IH), 6. 78 (d, IH?), 7. 15-7. 30 (m, 5H), 8. 47 (d, IH). ESI-MS 457.2 (MH ") [0028] Sweetening potency (relative to sugar): 5,000 times [0029] EXAMPLE 4 Synthesis of N-[N-[3-(4-hydroxyphenyl)propyl]-L-a-aspartyl] -L-phenylalanlne 1-methyl ester Example 1 was repeated except that 4-benzyloxycinnamaldehyde was used Instead of 3-benzyloxy-4- methoxyclnnamaldehyde to obtain N-[N-[3-(4- hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanlne 1- methyl ester In a total yield of 40.6% as a solid. [0030] "HNMR (DMSO-d«) 6 : 1. 48-1. 60 (m, 2H), 2. 14-2. 43 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 4-3. 14 (dd, IH), 3. 37-3. 42 (m, IH), 3. 62 (s, 3H), 4. 52-4. 62 (m, IH), 6. 65 (d, 2H), 6. 93 (d, 2H), 7. 16-7. 29 (m, 5H), 8. 49 (d, IH), 9. 12 (b r s , 1 H). ESI-MS 429. 2 (MH’) [0031] Sweetening potency (relative to sugar): 5,000 times [0032] EXAMPLE 5 Synthesis of N-[N-[3-(4-methoxyphenyl)propyl]-L-a-■ aspartyl]-L-phenylalanlne 1-methyl ester (1) Example 1 was repeated except that 4-methoxyclnnamaldehyde was used Instead of 3-benzyloxy-4-methoxyclnnamaldehyde to obtain N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester In a total yield of 50.0% as a solid. [0033] "HNMR (DMSO-d») 6 : 1. 50-1. 62 (m, 2H), 2. 16-2. 48 (m, 6H), 2. 84-2. 94 (dd, IH), 3. 0 4-3. 12 (dd, IH), 3. 38-3. 44 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 3H), 4. 52-4. 62 (m, IH), 6. 83 (d, 2H), 7. 08 (d, 2H), 7. 17-7. 29 (m, 5H), 8. 50 (d, 1 H). ESI-MS 443.3(MH") [0034] Sweetening potency (relative to sugar): 6,500 times [0035] EXAMPLE 6 Synthesis of N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester (2) 4-Methoxycinnamaldehyde (405 mg, 2.5mmol), 735 mg (2.5 mmols) of aspartame and 350 mg of 10% palladium carbon (water content 50%) were added to a mixed solvent of 15 ml of methanol and 5 ml of water, and the mixture was stirred in a hydroge)’ stream overnight at room temperature. The catalyst wa’ removed by filtration, and the filtrate was concentrated under reduced pressure. To the residue were added 30 ml of ethyl acetate, and the mixture was stirred for a while. Then, the insoluble material was collected by filtration. The insoluble material collected was washed with a small amount of ethyl acetate. To this were added 50 ml of a mixed solvent of ethyl acetate and methanol (5:2), and the mixture was stirred for a while. The insoluble material was removed by filtration, and the filtrate was concentrated. Then, the overall residue was solidified. This was dried under reduced pressure, and then recrystallized from a mixed solvent of methanol and water to obtain N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 43.4% as a solid. [0036] EXAMPLE 7 Synthesis of N-[N-[3-(4-ethoxyphenyl)propyl]-L-a-aspartyl] -L-phenylalanine 1-methyl ester Example 1 was repeated except that 4-ethoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-ethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 57.1% as a solid. [0037] "HNMR (DMSO-d«) 6 : 1. 30 (t, 3H), 1. 50-1. 62 (m, 2H), 2. 16-2. 48 (m, 6H), 2. 85-2. 95 (dd, IH), 3. 02-3. 12 (dd, IH), 3. 39-3. 44 (m, IH), 3, 62 (s, 3H), 3. 96 (q, 2H), 4. 52-4. 59 (m, IH), 6. 81 (d, 2H), 7. 05 (d, 2H), 7. 17-7, 28 (m, 5H), 8. 50 (d, IH). ESI-MS 457. 2 (MHO [0038] Sweetening potency (relative to sugar): 1,500 times [0039] EXAMPLE 8 Synthesis of N-[N-[3-(3-hydroxyphenyl)propyl]-L-a- aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3- benzyloxyclnnamaldehyde was used instead of 3-benzyloxy-4- methoxycinnamaldehyde to obtain N-[N-[3-(3- hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 46.6% as a solid. [0040] "HNMR (DMSO-d.) 6:1. 50-1. 62 (m, IH), 2. 10-2. 48 (m, 6H), 2. 87-2. 96 (dd, IH), 3. 4 0-3. 12 (dd, IH), 3. 33-3, 38 (m, IH), 3. 62 (s, 3H), 4, 52-4. 60 (m, IH), 6. 53-6. 60 (m, 3H), 7. 04 (t, IH), 7. 17-7. 30 (m, 5H), 8. 50 (d, IH), 9. 4 0 ( b r s , 1 H). E S I - M S 4 2 9 . 2 (M H 0 [0041] Sweetening potency (relative to sugar): 8,000 times [0042] EXAMPLE 9 Synthesis of N-[N-[3-(3-methoxyphenyl)propyl]-L-a-aspartyl] -L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 55.6% as a solid. [0043] "HNMR (DMSO-d«) 6 : 1. 54-1. 66 (m, 2H), 2. 18-2. 50 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 2-3. 12 (dd, IH), 3. 40-3. 46 (m, IH), 3. 62 (s, 3H), 3. 73 (s, 3H), 4. 53-4. 61 (m, IH), 6. 70-6. 78 (m, 3H), 7. 13-7. 30 (m, 5H), 8. 50 (d, IH). ESI-MS 443.1 (MHO [0044] Sweetening potency (relative to sugar): 3,500 times [0045] EXAMPLE 10 Synthesis of N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L- a~aspartyl]-L-tyrosine 1-methyl ester l’. Example 1 was repeated except that N-t-butoxycaji*i>onyl-P-0-benzyl-a-L-aspartyl-L-tyrosine methyl ester was used instead of N-t-butoxycarbonyl-P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester to obtain N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-tyrosine 1-methyl ester in a total yield of 45.4% as a solid. [0046] "HNMR (DMSO-d.) 6 : 1. 52-1. 64 (m, 2H), 2. 24-2. 48 (m, 6H), 2. 74-2. 84 (dd, IH), 2. 9 1-2. 99 (dd, IH), 3. 47-3. 54 (m, IH), 3. 61 (s, 3H), 3. 72 (s, 3H), 4. 45-4. 53 (m, IH), 6. 54 (d, IH), 6. 60 (s, IH), 6. 65 (d, 2H), 6. 79 (d, IH), 6. 98 (d, 2H), 8. 54 (d, IH), 8. 78 (brs, IH), 9. 25 ( b r s , 1 H). ESI-MS 475. 2 (MH") [0047] Sweetening potency (relative to sugar): 16’000 times [0048] EXAMPLE 11 Synthesis of N-[N-[3-(2-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-benzyloxy-4-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(2-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 54.4% as a solid. -."‘ [0049] •HNMR (DMSO-d.) 8 : 1 . 52-1. 57 (m, 2H), 2. 20-2. 31 (m, 2H), 2. 26-2. 41 (m, 4H), 2. 88 -3. 11 (m, 2H), 3. 41-3. 44 (m, IH), 3. 62 (s, 3H), 3. 65 (s, 3H), 4. 53-4. 59 (m, IH), 6. 28-6. 36 (m, 2H), 6. 88-6. 90 (d, IH), 7. 19-7. 29 (m, 5H), 8. 5 5 ( d , 1 H). ESI-MS 459. 3 (MH") [0050] Sweetening potency (relative to sugar): 20,000 times [0051] EXAMPLE 12 Synthesis of N-[N-[3-(2-hydroxy-3-methoxyphenyl)propyl]-L- a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-benzyloxy-3-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(2-hydroxy-3-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 33.4% as a solid. [0052] "HNMR (DMSO-d.) 6 : 1. 53-1, 58 (m, 2H), 2. 04-2. 25 (m, 2H), 2. 26-2. 32 (m, 4K), 2. 90 -3. 12 (m, 2H), 3. 51-3. 53 (m, IH), 3, 61 (s, 3H), 3. 76 (s, 3H), 4. 52-4. 58 (m, IH), 6. 64-6. 78 (m, 3H), 7. 18-7. 29 (m, 5H), 8. 52 (d, IH). i, E S I - M S 4 5 9 . 4 (MH 0 "■ [0053] Sweetening potency (relative to sugar): 10,000 times [0054] EXAMPLE 13 Synthesis of N-[N-[3-(2-hydroxy-5-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-benzyloxy-5-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(2-hydroxy-5-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 57.6% as a solid. [0055] "HNMR (DMSO-dO 6 : 1. 52-1. 63 (m, 2H), 2. 19-2. 35 (in, 2H), 2. 27-2. 47 (m, 4H), 2. 89 -3. 14 (m, 2H), 3. 47-3. 50 (m, IH), 3. 62 (s, 3H), 3. 65 (s, 3H), 4. 50-4. 58 (m, IH), 6. 57-6. 71 (m, 3H), 7. 19-7. 30 (m, 5H), 8. 62 (d, IH). 8. 84 (b r s , 1 H). ESI-MS 459. 3 (MHO [0056] Sweetening potency (relative to sugar): 1,500 times [0057] EXAMPLE 14 Synthesis of N-[N-[3-(2-hydroxy-4-methylphenyl)propyl]-L;-a -aspartyl]-L-phenylalanine 1-methyl ester ,’ Example 1 was repeated except that 2-benzyloxy-,4i-methylcinnamaldehyde was used instead of 3-benzyloxy-4~ methoxycinnamaldehyde to obtain N-[N-[3-(2-hydroxy-4-methylphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 35.7% as a solid. [0058] "HNMR (DMSO-d«) 6 : 1. 52-1. 58 (m, 2H), 2. 17 (s, 3H), 2. 19-2. 32 (m, 2H), 2. 37-2. 44 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 39-3. 42 (m, IH), 3. 62 (s, 3H), 4. 53-4. 58 (m, IH), 6. 50 (d, 2H), 6. 58 (s, IH), 6. 80 (d, IH), 7. 15-7. 29 (m, 5H), 8 . 5 4 ( d , 1 H). ESI-MS 443. 3 (MH") [0059] Sweetening potency (relative to sugar): 30,000 times [0060] EXAMPLE 15 Synthesis of N-[N-[3-(2,4-dimethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanlne 1-methyl ester Example 1 was repeated except that 2,4-dimethoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(2,4-dime’lhoxyphenyl)propyl] -L-a-aspartyl] -L-phenylalanine 1-methyl ester in a total yield of 32.4% as a solid. [0061] "HNMR (DMSO-d«) 6 : 1. 50-1. 54 (m, ‘‘H), 2. 20-2. 31 (m, 2H), 2. 25-2. 43 (m, 4H), 2. 88 -3. 12 (m, 2H), 3. 44-3. 82 (m, IH), 3. 62 (s, 3H), 3. 72 (s, 3H), 3, 75 (s, 3H), 4. 54~4, 59 (m, IH), 6. 40-6. 50 (m, 2H), 6. 96-6. 98 (m, IH), 7. 19- 7 . 2 9 (m, 5 H), 8 . 5 1 ( d , 1 H). ESI-MS 473.3(MH") [0062] Sweetening potency (relative to sugar): 4,000 times [0063] EXAMPLE 16 Synthesis of N-[N-[3-(2-ethoxy-4-methoxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-ethoxy-4-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(2-ethoxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 35.6% as a solid. [0064] "HNMR (DMSO-d«) 6 : 1. 30-1. 34 (t, 3H), 1. 50-1. 57 (m, 2H), 2. 19-2. 41 (m, 2H), 2. 24 -2. 43 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 38-3. 42 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 3H), 3. 70-4, 0 3 (q, 2H), 4. 53-4. 60 (m, IH), 6. 40-6. 48 (m, 2 H), 6. 96-6. 98 (m, IH), 7. 19-7. 29 (m, 5H), 8. 5 1 ( d , 1 H ). ESI -MS 487. 4 (MHO [0065] Sweetening potency (relative to sugar): 2,500 times [0066] EXAMPLE 17 Synthesis of N-[N-[3-(3-methyl-4-hydroxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-methyl-4-benzyloxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3-methyl-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 32.2% as a solid. [0067] "HNMR (DMSO~d») 6:1. 50-1. 58 (m, 2H), 2. 08 (s, 3H), 2. 09-2. 30 (m, 2H), 2. 26-2. 38 (m, 4H), 2. 89-3, 09 (m, 2H), 3. 35-3. 42 (m, IH), 3. 62 (s, 3H), 4. 54-4. 59 (m, IH), 6. 65-6. 83 (m, 3H), 7. 19-7. 28 (m, 5H), 8. 52 (d, IH). 9. 04 (b r s , 1 H). ESI-MS 443. 4 (MHO [0068] Sweetening potency (relative to sugar): 35,000 times [0069] EXAMPLE 18 Synthesis of N-[N-[3-(3-hydroxy-4-methylphenyl)propyl|-L-a -aspartyl]-L-phenylalanine 1-methyl ester .’ Example 1 was repeated except that 3-benzyloxy-4-methylcinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3-hydroxy~4-methyIpheny1)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 46.9% as a solid. [0070] "HNMR (DMSO-d«) 6 : 1. 51-1. 58 (m, 2H), 2. 06 (s, 3H), 2. 18-2. 32 (m, 2H), 2. 24-2. 39 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 39-3. 43 (m, IH), 3. 62 (s, 3H), 4. 54-4. 60 (m, IH), 6. 47-6. 58 (m, 2H), 6. 90-6. 93 (m, IH), 7. 12-7. 29 (m, 5H), 8. 52 (d, IH). 9. 12 (brs, IH). ESI~MS 443. 4 (MH") [0071] Sweetening potency (relative to sugar): 15,000 times [0072] EXAMPLE 19 Synthesis of N-[N-[3-(3-methyl-4-methoxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-methyl-4-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(3-methyl-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 34.0% as a solid. [0073] "HNMR (DMSO-d«) 6:1. 52-1. 59 (m, 2’), 2. 11 (s, 3H), 2. 20-2. 38 (m, 2H), 2. 26-2.43 (m, 4H), 2. 89-3. 10 (m, 2H), 3. 39-3. 43 (m, IH), 3. 62 (s, 3H), 3. 73 (s, 3H), 4. 52-4. 59 (m, IH), 6. 79-6. 82 (m, IH), 6. 92-6. 94 (m, 2H), 7. 19- 7. 28 (m, 5H), 8. 53 (d, IH). ESI-MS 457. 4 (MH") [0074] Sweetening potency (relative to sugar): 8,000 times [0075] EXAMPLE 20 Synthesis of N-[N-[3-(3,5-dimethoxyphenyl)propyl]-L-a- aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,5-dimethoxycinnamaldehyde was used Instead of 3-benzyloxy-4-methoxyclnnamaldehyde to obtain N-[N-l3-(3,5-dimethoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 41.0% as a solid. [0076] "HNMR (DMSO-d«) 6:1. 56-1. 62 (m, 2H), 2. 18-2. 38 (m, 2H), 2. 25-2. 47 (m, 4H), 2. 88 -3. 11 (m, 2H), 3. 38-3. 44 (m, IH), 3. 62 (s, 3H), 3. 71 (s, 6H), 4. 53-4. 59 (m, IH), 6. 30-6. 35 (m, 3H), 7. 19-7. 28 (m, 5H), 8. 55 (d, IH). ESI-MS 473. 3 (MHO [0077] Sweetening potency (relative to sugar): 800 timesj« [0078] EXAMPLE 21 Synthesis of N-[N-[3-(4-(2-hydroxyethoxy)phenyl)propylJ-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 4-(2-hydroxyethoxy)cinnamaldehyde was used instead of 3-ben2yloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-(2-hydroxyethoxy)phenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 33.8% as a solid. [0079] "HNMR (DMSO-d«) 6 : 1. 52-1. 60 (m, 2H), 2. 18-2. 35 (m, 2H), 2. 24-2. 47 (m, 4H), 3. 38 -3. 43 (m, IH), 3. 62 (s, 3H), 3. 67-3. 71 (m, 2H), 3. 92-3. 95 (m, 2H), 4. 53-4, 59 (m, IH), 6. 82- 6. 85 (d, 2H), 7. 05-7. 07 (d, 2H), 7. 19-7. 29 (m, 5 H), 8 . 5 1 (d , 1 H). ESI-MS 473. 3 (MHO [0080J Sweetening potency (relative to sugar): 1,000 times [0081] EXAMPLE 22 Synthesis of N-[N-[3-(4-methylphenyl)propyl]-L~a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except thatp. 4-methylcinnamaldehyde was used instead of 3-ben2yl "HNMR (DMSO-dO 6 : 1. 50-1. 63 (m, 2H), 2. 18-2. 39 (m, 2H), 2. 25 (s, 3H), 2. 29-2. 46 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 41-3. 47 (m, IH), 3. 61 (s, 3H), 4. 53-4. 61 (m, IH), 7. 03-7. 09 (m, 4H), 7. 17-7. 29 (m, 5H), 8. 58 (d, IH). ESI-MS 427.4 (MH ") [0083] Sweetening potency (relative to sugar): 4,000 times [0084] [effects of invention] The novel aspartyl dipeptide ester derivatives of the present invention have especially an excellent sweetening potency in comparison with conventional sweeteners. The invention can provide novel chemical substances having excellent organoleptic properties as a sweetener. Accordingly, such novel derivatives in the present invention can be used as a sweetener, and also can impart a sweetness to products such as beverages and foods requiring a sweetness. [name of document] Paper for ABSTRACT [abstract] [problems] It is required that a low-calory sweetener having especially an excellent sweetening potency is provided in comparison with conventional products. [means to solve them] Novel aspartyl dipeptide ester derivatives (including salts thereof) such as N-[N-[3-(3-methyl-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester and N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester can be used as an excellent sweetener, which can solve the above problems. Accordingly, a sweetener containing the same can be provided. [selected drawing] non C3 CD FORM 2 o li THE PATENTS ACT, 1970 (39 of 1970) COMPLETE cV Q "C""" J f_ z ."ii IBBM -’ CD pmmtm a: £= O T VA (See Section 10) ‘ TITLE AM ASPARTYL DIPEPTIDE ESTER DERIVATIVES " APPLICANTS Da C_3 AJINOMOTOCO.,INC of No. 15-1, Kyobashi 1-chome, Chuo-ku, Tdcyo, 104-8315, Japan (a Japanese Corporation) cr-3 The following specification particularly describes the nature of this invention and the manner in vAuch it is to be pofoimed P—* The present invention relates to a process for preparing a novel aspartyl dipeptide ester derivatives (including salts thereof) represented by formula (1), and a sweetener and products such as foods having a sweetness, which contain the same as an active ingredient. BACKGROUND ART In recent years, as eating habits have been improved to a high level, fatness caused by excessive intake of sugar and diseases accompanied by fatness have been at issue. Accordingly, the development of a low-calory sweetener that replaces sugar has been in demand. As a sweetener that has been widely used at present, there is aspartame which is excellent in a safety and taste properties. However, this is somewhat problematic in the stability. In WO 94/11391, it is stated that derivatives in which an alkyl group is introduced in an amino group of aspartic acid constituting aspartame markedly improves sweetening potency and the stability is slightly improved. It is reported that the best compound described in this document is N- [N-(3,3-dimethylbutyl) -L-a-aspartyl] -L-phenylalanine 1-methyl ester having a 3,3-dimethylbutyl group as an alkyl group and the sweetening potency thereof is 10,000 times. Aspartame derivatives having introduced therein 20 types of substituents other than the 3,3-dimethylbutyl group are indicated therein, and the sweetening potency thereof is reported to be less than 2,500 times. Derivatives having a 3 -(substituted phenyl)propyl group as an alkyl group are also shown. However, it is reported that the sweetening potency of N-[N-(3-phenylpropyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester is 1,500 times and that of N- [N-[3 -(3-methoxy-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester is 2,500 times. Thus, these are far less than that (10,000 times) of N- [N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine 1-methyl ester. PROBLEMS INVENTION IS TO SOLVE. OBJECT THEREOF It is an object of the invention to provide novel aspartyl dipeptide ester derivatives which are excellent in the safety and which have sweetening potency equal to or higher than that of the N-[N-(3,3-dimethylbutyl)-L-a-aspartyl]-L-phenylalanine l-"methyl ester, and a low-calory sweetener containing the same as an active ingredient. DISCLOSURE OF INVENTION In order to solve the problems, the present inventors have synthesized several aspartame derivatives in which various 3- (substituted phenyl) propyl groups are introduced in an amino group of aspartic acid constituting the aspartame derivatives by use of cinnamaldehyde having various substituents on 3-phenylpropianaldehyde having various substituents that can easily derived therefrom an precursor aldehydes, and have examined the sweetening potency of them. They have consequently found that with respect to the sweetening potency, the novel compounds that they have found are by far higher than not only N-[N- (3-phenylpropyl) -L-a- aspartyl] -L-phenylalanine 1-methyl ester which is reported to have the sweetening potency of 1,500 times in WO 94/11391 but also N-[N- (3,3-dimethylbutyl) -L-a-aspartyl] -L- phenylalanine 1-methyl ester which is reported therein to have the sweetening potency of 10,000 times, and that especially the compounds represented by the following formula (1) are excellent as a sweetener. These findings have led to the completion of the invention. The present invention is directed to a process for preparing a novel aspartyl dipeptide ester derivatives (including salts thereof) represented by formula (1) B3’ COOR, R " R ? I / ‘ CO—NH*-C-*H CHa-CHa-CHs-NH’C-H CH R4 Re CH2 CO2H (1) wherein Ri, R2, R3, R4, and R5, independently from each other, represent a substituent selected from a hydrogen atom, a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or Ri and R2, or R2 and R3 together form a methylenedioxy group wherein R4, R5 and Ri or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, each represents any substituents as mentioned above designated for the Ri, R3, R4 and R5, respectively, R’ represents a hydrogen atom or a hydroxyl group, and R7 represents a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group, provided the derivatives in which Ri to R5 are all hydrogen atoms, and the derivatives in which R2 or R4 is a methoxy group and R3 is a hydroxyl group are excluded, which comprises subjecting aspartame itself or aspartame derivatives to reductive alkylation with cinnamaldehydes or 3-phenylpropionaldehydes having various substituents and a reducing agent. EMBODIMENTS OF INVENTION The novel aspartyl dipeptide ester derivatives of the invention include the compounds represented by formula (1) and salts thereof. Amino acids constituting the derivatives are preferably L-isomers in that these are present in nature. With respect to the compounds of the invention, the following inventions are preferably included. [1] Compounds of formula (1) wherein R3 is a substituent selected from a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, Rj’, Rj, R4 and R5 are, independently from each other, each a substituent selected from a hydrogen atom, a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or Rj and R’, or R’ and R3 together form a methylenedioxy group (OCHjO) wherein R4, R5 and, R’ or R3 which does not form the methylenedioxy group as a part thereof , independently from each other, represent any substituents as mentioned above for the R’’, R3, R’ and R5, Rg is a hydrogen atom or a hydroxyl group, and R, is a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group. [2] Compounds of formula (1) wherein R3 is a hydrogen atom, R’, R2, R4 and Rj are, independently from each other, each a substituent selected from a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or R’ and R2, or Rj and R3 together form a methylenedioxy group (OCHjO) wherein R’, Rj and, R’ or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, represent any substituents as mentioned above designated for the Rj, R3, R’ and R5, respectively, Rg is a hydrogen atom or a hydroxyl group, and R, is a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group. [3] Compounds of formula (1) wherein R3 is a hydroxyl group, Ri, Rj, R’ and R5 are each a substituent selected from a hydrogen atom, a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or Ri and Rj, or Rj and R3 together form a methylenedioxy group (OCHjO) wherein R’, R5, and R’ or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, represent any substituents as mentioned above designated for the R’, R3, R’ and R5, respectively, Rg is a hydrogen atom or a hydroxyl group, and R, is a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group. [4] Compounds of formula (1) wherein R’ is a hydroxyl group, R3 is a methoxy group, Rj, R’, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [5] Compounds of formula (1) wherein R, and R3 are each a methoxy group, Ri, R4, R5 and Rg are each a hydrogen atom, and R7 is a methyl group. [6] Compounds of formula (1) wherein Rj and R3 together form a methylenedioxy group, R’, R4, R5 and Rg are each a hydrogen atom, and R’ is a methyl group. [7] Compounds of formula (1) wherein R3 is a hydroxyl group, Ri, Rj, R’, Rs and Rg are each a hydrogen atom, and R, is a methyl group. [8] Compounds of formula (1) wherein R3 is a methoxy group, Rj, Rj, R4, Rj and Rg are each a hydrogen atom, and R, is a methyl group. [9] Compounds of formula (1) wherein R3 is an ethoxy group, R’, Rj, R4, R5 and Rg are each a hydrogen atom, and R’ is a methyl group. [103 Compounds of formula (1) wherein Rj is a hydroxyl group, Rj, R3, R4, R5 and Rg are each a hydrogen atom, and R’ is a methyl group. [11] Compounds of formula (1) wherein Rj is a methoxy group, Ri, R3, R’, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [12] Compounds of formula (1) wherein R3 is a methoxy group, Rj and Rg are each a hydroxyl group, R’, R’ and R5 are each a hydrogen atom, and R, is a methyl group. [13] Compounds of formula (1) wherein R’ is a hydroxyl group, R3 is a methoxy group, Rj, R’, Rj and Rg are each a hydrogen atom, and R, is a methyl group. [14] Compounds of formula (1) wherein R’ is a hydroxyl group, R2 is a methoxy group, R3, R’, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [15] Compounds of formula (1) wherein R’ is a hydroxyl group, R4 is a methoxy group, R,, R3, R5 and Rg are each a hydrogen atom, and R’ is a methyl group. [16] Compounds of formula (1) wherein R’ is a hydroxyl group, Rj and R, are each a methyl group, and R’, R’, R5 and Rg are each a hydrogen atom. [17] Compounds of formula (1) wherein R’ and R3 are each a methoxy group, R2, R4, Rs and Rg are each a hydrogen atom, and R7 is a methyl group. [18] Compounds of formula (1) wherein R’ is an ethoxy group, R3 is a methoxy group, Rj, R4, R5 and Rg are each a hydrogen atom, and R, is a methyl group. [19] Compounds of formula (1) wherein R, and R, are each a methyl group, R3 is a hydroxyl group, and R’, R4, R5 and Rg are each a hydrogen atom. [20] Compounds of formula (1) wherein Rj is a hydroxyl group, R3 and R, are each a methyl group, and R’, R4, R5 and Rg are each a hydrogen atom. [21] Compounds of formula (1) wherein Rj and R, are each a methyl group, R3 is a methoxy group, and R’, R4, R5 and Rg are each a hydrogen atom. [22] Compounds of formula (1) wherein Rj and R4 are each a methoxy group, R’, R3, R5 and Rg are each a hydrogen atom, and R7 is a methyl group. [23] Compounds of formula (1) wherein R3 is a 2-hydroxyethoxy group, R’, Rj, R’, R5 and Rj are each a hydrogen atom, and R’ is a methyl group. [24] Compounds of formula (1) wherein R3 and R7 are each a methyl group, and Rj, Rj, R4, Rs and Rg are each a hydrogen atom. Examples of the salts of the compounds in the invention include salts with alkali metals such as sodium and potassium; salts with alkaline earth metals such as calcium and magnesium; ammonium salts with ammonia; salts with amino acids such as lysine and arginine; salts with inorganic acids such as hydrochloric acid and sulfuric acid; and salts with organic acids such as citric acid and acetic acid. These are included in the derivatives of the invention as described above. The aspartyl dipeptide ester derivatives of the invention can easily be formed by reductively alkylating aspartame derivatives with cinnamaldehydes having various substituents and a reducing agent (for example, hydrogen/palladium carbon catalyst). Alternatively, the derivatives can be formed by subjecting aspartame derivatives (for example, P-0-benzyl -a-L-aspartyl -L-phenylalanine methyl ester) having a protective group in a carboxylic acid in the P-position which derivatives can be obtained by the usual peptide synthesis method (Izumiya et al., Basis of Peptide Synthesis and Experiments Thereof, Maruzen, published January 20, 1985) to reductive alkylation with cinnamaldehydes having various substituents and a reducing agent (for example, NaB(0Ac)3H) (A. F. Abdel-Magid et al., Tetrahedron Letters, il, 5595 (1990)), and then removing the protective group. However, the method of forming the compounds of the invention is not limited thereto. 3-Phenylpropionaldehydes having various substituents or acetal derivatives thereof can of course be used as precursor aldehydes in the reductive alkylation instead of cinnamaldehydes having various substituents. As a result of a sensory evaluation, the compounds and the salts thereof in the invention were found to have a strong sweetening potency and have taste properties similar to that of sugar. For example, the sweetening potency of N-[N-[3-(3-methyl-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 35,000 times (relative to sugar), that of N-[N-[3 -(2-hydroxy-4-methylphenyl)propyl]-L-a-aspartyl]-L-a-phenylalanine 1-methyl ester was approximately 30, 000 times (relative to sugar) , that of N- [N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 20,000 times, that of N-[N-[3 -(2-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 20, 000 times (relative to sugar) , that of N-[N-[3 - (3-hydroxy-4-methylphenyDpropyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 15,000 times (relative to sugar), that of N-[N-[3-(3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 8, 000 times (relative to sugar) , that of N-[N- [3 - (4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester was approximately 6,500 times (relative to sugar), and that of N- [N-[3 -(3-hydroxy-4-me thoxyphenyl)propyl]-L-a-aspartyl] -L-tyrosine 1-methyl ester was approximately 16,000 times (relative to sugar). With respect to the aspartyl dipeptide derivatives (represented by formula (2)) formed, the structures and the results of the sensory evaluation are shown in Table 1. COOCH3 ‘2 pi go—NH’(5-*H R3—’’)—CH2-CH2-CH2—NH*’C-«H CH2 R4 R5 I ‘ CO2H (2) Table 1 Structures and sweetening potency of aspartyl dipeptide ester derivatives Compouid R’ R, R3 R4 Rs Re sweetening No. potency*’ 1 H OH OCH3 H H H 20000 2 H OCH: OCH3 H H H 2500 3 H OCHJO H H H 5000 4 H H OH H H H 5000 5 H H OCHa H H H 6500 6 H H OCH2CH3 H H H 1500 7 H OH H H H H 8000 8 H OCH3 H H H H 3500 9 H OH OCH3 H H OH 16000 1 0 OH H OCH3 H H H 20000 1 1 OH OCH3 H H H H 10000 1 2 OH H H OCH3 H H 1500 1 3 OH H CH3 H H H 30000 1 4 OCH3 H OCH3 H H H 4000 1 5 OCH.CH3 H OCH3 H H H 2500 1 6 H CH3 OH H H H 35000 1 7 H OH CH3 H H H 15000 1 8 H CH3 OCH3 H H H 8000 1 9 H OCH 3 H OCH3 H H 800 2 0 H H OCH2CH2OH H H H 1000 2 1 H H CH3 H H H 4000 *) Relative to sweetening potency of a 4% sucrose aqueous solution As understood from the results of Table 1, the novel derivatives in the present invention are excellent in sweetening potency. When the compounds (including those in the form of a salt) of the invention are used as a sweetener, these may of course be used in combination with other sweeteners unless inviting any special troubles. When the derivatives of the invention are used as a sweetener, an appropriate carrier and/or an appropriate bulking agent may be used as required. For example, a carrier which has been so far used is available. The derivatives of the invention can be used as a sweetener or an ingredient therefor, and further as a sweetener for products such as foods and the like to which a sweetness has to be imparted, for example, confectionary, chewing gum, hygiene products, toiletries, cosmetics, pharmaceutical products and veterinary products for animals. Still further, they can be used in a method of imparting a sweetness to the products. This method can be, for example, a conventional method for using a sweetening ingredient for a sweetener in the sweeteners or the method of imparting a sweetness. PREFERRED EMBODIMENTS OF INVENTION The invention is illustrated specifically by referring to the following Examples. EXAMPLE 1 Synthesis of N-[N-[3 -(3-hydroxy-4-methoxyphenyl)propyl]-L- a-aspartyl]-L-phenylalanine 1-methyl ester Five milliliters of a solution of 4N-HC1 and dioxane were added to 485 mg (1.0 mmol) of N-t-butoxycarbonyl-P-O-benzyl -a-L-aspartyl -L-phenylalanine methyl ester, and the mixture was stirred at room temperature for 1 hour. The reaction solution was concentrated under reduced pressure. Thirty milliliters of a 5% sodium hydrogencarbonate aqueous solution were added to the residue, and the mixture was extracted twice with 30 ml of ethyl acetate. The organic layer was washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate. Then, magnesium sulfate was removed by filtration, and the filtrate was concentrated under reduced pressure to obtain 385 mg of P* 0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester as a viscous oil. The P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester (385 mg, 1.0 mmol) was dissolved in 15 ml of THF, and the solution was maintained at O"C. To this were added 268 mg (1.0 mmol) of 3-benzyloxy-4-methoxycinnaroaldehyde, 0.060 ml (1.0 mmol) of acetic acid and 318 mg (1.5 mmol) of NaB(0Ac)3H. The mixture was stirred at 0°C for 1 hour and further overnight at room temperature. To the reaction solution were added 50 ml of a saturated aqueous solution of sodium hydrogen carbonate, and the mixture was extracted twice with 30 ml of ethyl acetate. The organic layer was washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesixim sulfate. Then, magnesiiim sulfate was removed by filtration, and the filtrate was concentrated under reduced pressure. The residue was purified with PTLC ( Preparative Thin Layer Chromatography ) to obtain 523 mg (0.82 mmol) of N-[N-[3* (3-ben2yloxy-4-methoxyphenyl)propenyl]-P-0-benzyl-L-a-aspartyl]-L-phenylalanine 1-methyl ester as a viscous oil. The N-[N-[3-(3-benzyloxy-4-methoxyphenyl)propenyl]-P-O-benzyl-L-a-aspartyl] -L-phenylalanine 1-methyl ester (523 mg, 0.82 mmol) was dissolved in a mixed solvent of 30 ml of methanol and 1 ml of water, and 200 mg of 10% palladium carbon (water content 50%) were added thereto. The mixture was reduced under a hydrogen atmosphere at room temperature for 3 hours. The catalyst was removed by filtration, and the filtrate was concentrated under reduced pressure. In order to remove an odor adsorbed, the residue was purified with PTLC to obtain 228 mg (0.48 mmol) of N-[N-[3 -(3-hydroxy-4-methoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine 1- methyl ester as a solid. "HNMR (DMSO-d.) (5:1. 50-1. 60 (m, 2H), 2. 15-2. 40 (m. 6H), 2. 87-2. 97 (dd. IH). 3. 0 5-3. 13 (dd, IH), 3. 37-3. 43 (ra, IH), 3. 62 (s, 3H), 3. 71 (s, 3H). 4. 50-4. 60 (m. IH), 6. 52 (d. 1 H), 6. 60 (s, IH), 6. 79 ( d , IH), 7. 18-7. 30 (m, 5H), 8. 52 (d, 1 H), 8. 80 (brs, IH). E S I -M S 4 5 9 . 2 (MHO Sweetening potency (relative to sugar): 20,000 times EXAMPLE 2 Synthesis of N- [N- [3■(3,4-dimethoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,4-dimethoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N- [N- [3 - (3,4-dimethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 48.7% as a solid. "HNMRCDMSO-de) 5:1. 52-1. 62 (m. 2H), 2. 18-2. 50 (m, 6H). 2. 86-2. 76 (dd. IH). 3. 0 4-3. 12 (dd, IH), 3. 37-3. 44 (m, IH). 3. 62 (s. 3H). 3. 71 (s. 3H). 3. 73 (s. 3H), 4. 52-4. 62 (m, IH), 6. 66 (d, 1 H), 6. 76 (s, IH). 6. 83 (d, IH), 7. 18-7. 30 (m. 5H), 8. 50 (d, IH). ESI-MS 473.2 (MHO Sweetening potency (relative to sugar): 2,500 times EXAMPLE 3 Synthesis of N-[N-[3 -(3,4-methylenedioxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,4-methylenedioxycinnamaldehyde was used instead of 3- benzyloxy-4-methoxycinnainaldehyde to obtain N-[N-[3 - (3 , 4-methylenedioxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 42.1% as a solid. "HNMR (DMSO-d.O (5:1. 48-1. 60 (m, 2H). 2. 14-2. 48 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 3-3. 12 (dd, IH), 3. 37-3. 43 (m, IH), 3. 62 (s, 3H). 4. 54-4. 59 (m, IH). 5. 94 (s, IH). 5. 95 (s, IH), 6. 61 (d. IH), 6. 74 (s. IH), 6. 78 (d, IH), 7. 15-7. 30 (m, 5H), 8. 47 (d, IH). ESI-MS 457. 2 (MH*) Sweetening potency (relative to sugar): 5,000 times EXAMPLE 4 Synthesis of N- [N- [3 - (4-hydroxyphenyl)propyl]-L-a-aspartyl] - L-phenylalanine 1-methyl ester Example 1 was repeated except that 4-benzyloxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 40.6% as a solid. "HNMR (DMSO-de) 6 : 1. 48-1. 60 (m, 2H), 2. 14-2. 43 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 4-3. 14 (dd, IH), 3. 37-3. 42 (m, IH), 3. 62 (s, 3H), 4. 52-4. 62 (m, IH). 6. 65 (d, 2H), 6. 93 (d, 2H), 7. 16-7. 29 (m, 5H), 8. 49 (d, IH), 9. 12 (b r s , 1 H). ESI-MS 429.2 (MH*) Sweetening potency (relative to sugar): 5,000 times EXAMPLE 5 Synthesis of N-[N- [3 - (4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester (1) Example 1 was repeated except that 4-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 50.0% as a solid. •HNMRCDMSO-ds) 6:1. 50-1. 62 (m, 2H), 2. 16-2. 48 (m, 6H), 2. 84-2. 94 (dd, IH), 3. 0 4-3. 12 (dd, IH), 3. 38-3. 44 (m, IH), 3. 62 (s. 3H), 3. 71 (s, 3H), 4. 52-4. 62 (m. IH), 6. 83 Cd, 2H), 7. 08 (d, 2H), 7. 17-7. 29 (m, 5H), 8. 50 (d, 1 H). ESI-MS 443. 3 (MHO Sweetening potency (relative to sugar): 6,500 times EXAMPLE 6 Synthesis of N- [N- [3 - (4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester (2) 4-Methoxycinnamaldehyde (405 mg, 2.5mmol), 735 mg (2.5 mmols) of aspartame and 350 mg of 10% palladium carbon (water content 50%) were added to a mixed solvent of 15 ml of methanol and 5 ml of water, and the mixture was stirred under a hydrogen atmosphere overnight at room temperature. The catalyst was removed by filtration, and the filtrate was concentrated under reduced pressure. To the residue were added 3 0 ml of ethyl acetate, and the mixture was stirred for a while. Then, the insoluble material was collected by filtration. The insoluble material collected was washed with a small amount of ethyl acetate. To this were added 50 ml of a mixed solvent of ethyl acetate and methanol (5:2), and the mixture was stirred for a while. The insoluble material was removed by filtration, and the filtrate was concentrated. Then, the overall residue was solidified. This was dried under reduced pressure, and then recrystallized from a mixed solvent of methanol and water to obtain N- [N- [3 - (4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 43.4% as a solid. EXAMPLE 7 Synthesis of N- [N-[3 -(4-ethoxyphenyl)propyl] -L-a-aspartyl] -L-phenylalanine 1-methyl ester Example 1 was repeated except that 4-ethoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3-(4-ethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 57.1% as a solid. ‘HNMR(DMSO-d6) (5:1. 3 0 (t, 3H), 1. 50-1. 62 (m, 2H), 2. 16-2. 48 (m, 6H), 2. 85-2. 95 (dd, IH), 3. 02-3. 12 (dd. IH), 3. 39-3. 44 (m, IH), 3. 62 (s, 3H). 3. 96 (q. 2H), 4. 52-4. 59 (m. IH), 6. 81 (d, 2H), 7. 05 (d, 2H), 7. 17-7. 28 (m, 5 H), 8 . 5 0 (d , 1 H). ESI-MS 457. 2 (MHO Sweetening potency (relative to sugar): 1,500 times EXAMPLE 8 Synthesis of N- [N- [3 - (3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine l-methyl ester Example 1 was repeated except that 3-benzyloxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-t3-{3-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 46.6% as a solid. "HNMR(DMSO-dJ 5:1. 50-1. 62 (m, IH), 2. 10-2. 48 (m. 6H). 2. 87-2. 96 (dd, IH), 3. 4 0-3. 12 (dd, IH), 3. 33-3. 38 (m, IH), 3. 62 (s. 3H), 4. 52-4. 60 (m, IH). 6. 53-6. 60 (m, 3H), 7. 04 (t. IH), 7. 17-7. 30 (m, 5H), 8. 50 (d, IH). 9. 4 0 ( b r s , 1 H). ESI-MS 4 2 9 . 2 (MHO Sweetening potency (relative to sugar): 8,000 times EXAMPLE 9 Synthesis of N- [N- [3 - (3-methoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine l-methyl ester Example 1 was repeated except that 3-methoxycinnamaldehyde was used instead of 3-benzyloxy-4- methoxycinnamaldehyde to obtain N-[N-[3-(3-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 55.6% as a solid. "HNMR (DMSO-d„) 6 : 1. 54-1. 66 (m, 2H), 2. 18-2. 50 (m, 6H), 2. 86-2. 96 (dd, IH), 3. 0 2-3. 12 (dd, IH), 3. 40-3. 46 (m, IH), 3. 62 (s, 3H), 3. 73 (s, 3H), 4. 53-4. 61 (m, IH), 6. 70-6. 78 (m, 3H), 7. 13-7. 30 (m, 5H), 8. 50 (d, IH). ESI-MS 443. 1 (MHO Sweetening potency (relative to sugar): 3,500 times EXAMPLE 10 Synthesis of N-[N- [3 -(3-hydroxy-4-methoxyphenyl)propyl] -L-a-aspartyl]-L-tyrosine 1-methyl ester Example 1 was repeated except that N-t-butoxycarbonyl p.0-benzyl-a-L-aspartyl-L-tyrosine methyl ester was used instead of N-t-butoxycarbonyl-P-0-benzyl-a-L-aspartyl-L-phenylalanine methyl ester to obtain N- [N-[3 -(3-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-tyrosine 1-methyl ester in a total yield of 45.4% as a solid. "HNMR (DMSO-d.) 6 : 1. 52-1. 64 (m. 2H), 2. 24-2. 48 (m, 6H), 2. 74-2. 84 (dd, IH), 2. 9 1-2. 99 (dd, IH). 3. 47-3. 54 (m, IH), 3. 61 (s, 3H), 3. 72 (s, 3H), 4. 45-4. 53 (m. IH), 6. 54 (d, 1 H), 6. 60 (s, IH), 6. 65 (d, 2H), 6. 79 (d, IH), 6. 98 (d, 2H), 8. 54 (d, IH), 8. 78 (brs, IH), 9. 25 (b r s , 1 H). ESI-MS 475.2 (MHO Sweetening potency (relative to sugar): 16,000 times EXAMPLE 11 Synthesis of N-[N-[3 - (2-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-benzyloxy-4■ methoxycinnamaldehyde was used instead of 3-benzyloxy- 4-methoxycinnamaldehyde to obtain N- [N- [3 -(2-hydroxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 54.4% as a solid. "HNMR(DMSO-d6) 6:1. 52-1. 57 (m, 2H), 2. 20-2. 31 (m, 2H), 2. 26-2. 41 (m, 4H), 2. 88 -3. 11 (m, 2H), 3. 41-3. 44 (m. IH), 3. 62 (s, 3H). 3. 65 (s, 3H), 4. 53-4. 59 (m, IH), 6. 28-6. 36 (m, 2H), 6. 88-6. 90 (d, IH). 7. 19-7. 29 (m, 5H), 8. 5 5 (d , 1 H). ESI-MS 459. 3 (MHO Sweetening potency (relative to sugar): 20,000 times EXAMPLE 12 Synthesis of N-[N-[3 - (2-hydroxy-3-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-benzyloxy-3-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3 -(2-hydroxy-3-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 33.4% as a solid. "HNMR(DMSO-d6) 5:1. 53-1. 58 (m, 2H), 2. 04-2. 25 (m, 2H). 2. 26-2. 32 (m, 4H). 2. 90 -3. 12 (m. 2H), 3. 51-3. 53 (m, IH), 3. 61 (s, 3H), 3. 76 (s, 3H), 4. 52-4. 58 (m, IH), 6. 64-6. 78 (m, 3H), 7. 18-7. 29 (m. 5H), 8. 52 (d. IH). ESI-MS 459. 4 (MH*) Sweetening potency (relative to sugar): 10,000 times EXAMPLE 13 Synthesis of N- [N- [3 -(2-hydroxy-5-methoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-benzyloxy-5-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N- [N- [3 - (2-hydroxy-5-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 57.6% as a solid. "HNMR(DMSO-d6) 6:1. 52-1. 63 (m. 2H). 2. 19-2. 35 (m, 2H), 2. 27-2. 47 (m. 4H), 2. 89 -3. 14 (m, 2H), 3. 47-3. 50 (m, IH), 3. 62 (s, 3H). 3. 65 (s, 3H), 4. 50-4. 58 (m. IH). 6. 57-6. 71 (m, 3H), 7. 19-7. 30 (m, 5H), 8. 62 (d, IH). 8. 84 (b r s . 1 H). ESI-MS 459. 3 (MHO Sweetening potency (relative to sugar): 1,500 times EXAMPLE 14 Synthesis of N-[N-[3 - (2-hydroxy-4-methylphenyDpropyl]-L-a -aspartyl]-L-phenylalanine l-methyl ester Example 1 was repeated except that 2-benzyloxy-4-methylcinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N- [N- [3 - (2-hydroxy-4-methylphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 35.7% as a solid. ■HNMRCDMSO-de) 6:1. 52-1. 58 (m. 2H), 2. 17 (s, 3H), 2. 19-2. 32 (m, 2H), 2. 37-2. 44 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 39-3. 42 (m. IH). 3. 62 (s, 3 H), 4. 53-4. 58 (m. IH), 6. 50 (d, 2H). 6. 58 (s, 1 H), 6. 80 (d. IH), 7. 15-7. 29 (m, 5H), 8 . 5 4 ( d , 1 H). ESI-MS 443. 3 (MHO Sweetening potency (relative to sugar): 30,000 times EXAMPLE 15 Synthesis of N-[N- [3 -(2,4-dimethoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine l-methyl ester Example 1 was repeated except that 2,4-dimethoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3 -(2,4-dimethoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 32.4% as a solid. "HNMR (DMSO-d„) 2. 20-2. 31 (m, 2H), 2. 25-2. 43 (m, 4H), 2. 88 -3. 12 (m. 2H), 3. 44-3. 82 (m, IH). 3. 62 (s, 3H), 3. 72 (s, 3H), 3. 75 (s, 3H), 4. 54-4. 59 (m, IH), 6. 40-6. 50 (m, 2H). 6. 96-6. 98 (m, IH), 7. 19-7.29 (m, 5 H), 8 . 51 (d , 1 H). ESI-MS 473. 3 (MHO Sweetening potency (relative to sugar): 4,000 times EXAMPLE 16 Synthesis of N-[N-[3 -(2-ethoxy-4-methoxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 2-ethoxy-4-methoxycinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N- [3 - (2-ethoxy-4-methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 35.6% as a solid. "HNMR (DMSO-df) 6 : 1. 30-1. 34 (t, 3H), 1. 50-1. 57 (m, 2H), 2. 19-2. 41 (m, 2H). 2. 24 -2. 43 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 38-3. 42 (m, 1 H), 3. 62 (s, 3H), 3. 71 (s. 3H), 3. 70-4. 0 3 (q, 2H), 4. 53-4. 60 (m, IH), 6. 40-6. 48 (m, 2 H), 6. 96-6. 98 (m. IH), 7. 19-7. 29 (m, 5H), 8. 5 1 ( d , 1 H). ESI-MS 487. 4 (MHO Sweetening potency (relative to sugar): 2,500 times EXAMPLE 17 Synthesis of N-[N-[3 -(3-methyl-4-hydroxyphenyl)propyl]-L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-methyl-4-benzyloxycinnamaldehyde was used instead of 3-benzyloxy-4 - methoxycinnamaldehyde to obtain N-[N-[3 -(3-methyl-4-hydroxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 32.2% as a solid. ‘HNMR (DMSO-dr.) <1.> 2. 08 (s, 3H), 2. 09-2. 30 (m, 2H), 2. 26-2. 38 (m, 4H). 2. 89-3. 09 (m, 2H), 3. 35-3. 42 (m, IH), 3. 62 (s, 3H), 4. 54-4. 59 (m, IH), 6. 65-6. 83 (m. 3H), 7. 19-7. 28 (m, 5H), 8. 52 (d, IH). 9. 04 (b r s , 1 H). ESI-MS 443. 4 (MHO Sweetening potency (relative to sugar): 35,000 times EXAMPLE 18 Synthesis of N-[N-[3 -(3-hydroxy-4-methylphenyl)propyl] -L-a -aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-benzyloxy-4-methylcinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N-[N-[3 -(3-hydroxy-4-methylphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 46.9% as a solid. "HNMR (DMSO-de) 5:1. 51-1. 58 (m, 2H). 2. 06 (s, 3H), 2. 18-2. 32 (m, 2H), 2. 24-2. 39 (m, 4H), 2. 87-3. 11 (m, 2H), 3. 39-3. 43 (m. IH), 3. 62 (s, 3H), 4. 54-4. 60 (m, IH), 6. 47-6. 58 (m, 2H), 6. 90-6. 93 (m, IH), 7. 12-7. 29 (m, 5H), 8. 5 2 ( d , 1 H). 9. 12 (brs, IH). ESI-MS 443.4 (MHO Sweetening potency (relative to sugar): 15,000 times EXAMPLE 19 Synthesis of N-[N-[3 -(3-methyl-4-methoxyphenyl)propyl]-L-a •aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3-methyl-4- methoxycinnamaldehyde was used instead of 3-ben2yloxy-4- methoxycinnamaldehyde to obtain N-[N-[3 - (3-methyl-4- methoxyphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 34.0% as a solid. "HNMR (DMSO-de) 2. 11 (s, 3H), 2. 20-2. 38 (m, 2H), 2. 26-2. 43 (m. 4H). 2. 89-3. 10 (m. 2H). 3. 39-3. 43 (m, IH), 3. 62 (s, 3H), 3. 73 (s. 3H). 4. 52-4. 59 (m, IH), 6. 79-6. 82 (m, IH), 6. 92-6. 94 (m. 2H), 7. 19- 7.28 (m, 5 H), 8 . 53 (d . 1 H). ESI-MS 457. 4 (MHO Sweetening potency (relative to sugar): 8,000 times EXAMPLE 2 0 Synthesis of N-[N-[3 - (3,5-dimethoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine 1-methyl ester Example 1 was repeated except that 3,5-dimethoxycinnamaldehyde was used instead of 3-ben2yloxy-4-methoxycinnamaldehyde to obtain N-[N-[3 -(3,5-dimethoxyphenyl)propyl] -L-a-aspartyl]-L-phenylalanine 1-methyl ester in a total yield of 41.0% as a solid. "HNMR(DMSO-d6) 5:1. 56-1. 62 (m. 2H), 2. 18-2. 38 (m, 2H), 2. 25-2. 47 (m, 4H), 2. 88 -3. 11 (m, 2H), 3. 38-3. 44 (m, IH), 3. 62 (s. 3H), 3. 71 (s, 6H), 4. 53-4. 59 (m, IH), 6. 30-6. 35 (m, 3H), 7. 19-7. 28 (m, 5H), 8. 55 (d, IH). ESl-MS 473. 3 (MHO Sweetening potency (relative to sugar): 800 times EXAMPLE 21 Synthesis of N- [N-[3 -(4 -(2-hydroxyethoxy)phenyl)propyl] -L-a-aspartyl]-L-phenylalanine l-methyl ester Example 1 was repeated except that 4-(2-hydroxyethoxy)cinnamaldehyde was used instead of 3-benzyloxy-4-methoxycinnamaldehyde to obtain N- [N- [3 - (4 - (2-hydroxyethoxy)phenyl)propyl]-L-a-aspartyl]-L-phenylalanine l-methyl ester in a total yield of 33.8% as a solid. ‘HNMR(DMSO-dO (5:1. 52-1. 60 (m. 2H), 2. 18-2. 35 (m. 2H), 2. 24-2. 47 (m, 4H), 3. 38 -3. 43 (m, IH), 3. 62 (s, 3H), 3. 67-3. 71 (m, 2H), 3. 92-3. 95 (m, 2H), 4. 53-4. 59 (m, IH). 6. 82- 6. 85 (d, 2H), 7. 05-7. 07 (d, 2H), 7. 19-7. 29 (m, 5 H). 8 . 5 1 (d , 1 H). ESI-MS 473. 3 (MHO Sweetening potency (relative to sugar): 1,000 times EXAMPLE 22 Synthesis of N-[N- [3 - (4-methylphenyl)propyl] -L-a-aspartyl]-L-phenylalanine l-methyl ester Example 1 was repeated except that 4- methylcinnamaldehyde was used instead of 3-benzyloxy-4- methoxycinnamaldehyde to obtain N-[N-[3-(4- methylphenyl)propyl]-L-a-aspartyl]-L-phenylalanine 1- methyl ester in a total yield of 54.1% as a solid. ■HNMR (DMSO-de) 3:1. 50-1. 63 (m, 2H), 2. 18-2. 39 (m. 2H). 2. 25 (s. 3H), 2. 29-2. 46 (m. 4H). 2. 87-3. 11 (m, 2H), 3. 41-3. 47 (m, IH), 3. 61 (s, 3H), 4. 53-4. 61 (m, IH), 7. 03-7. 09 (m, 4H), 7. 17-7. 29 (m, 5H), 8. 58 (d. IH). ESI-MS 427. 4 (MHO Sweetening potency (relative to sugar): 4,000 times EFFECTS OF INVENTION The novel aspartyl dipeptide ester derivatives of the invention have especially an excellent sweetening potency in comparison with conventional sweeteners. The invention can provide novel chemical substances having excellent taste properties as a sweetener. Accordingly, such novel derivatives in the present invention can be used as a sweetener, and also can impart a sweetness to products such as beverages and foods requiring a sweetness. WE CLAIM; 1. A process for preparing a novel aspartyl dipeptide ester derivatives (including salts thereof) represented by formula (1) wherein R1, R2, R3, R4, and R5, independently from each other, represent a substituent selected from a hydrogen atom, a hydroxyl group, an alkoxy group having from 1 to 3 carbon atoms, an alkyl group having from 1 to 3 carbon atoms and a hydroxyalkyloxy group having 2 or 3 carbon atoms, or R1 and R2, or R2 and R3 together form a methylenedioxy group wherein R4, R5 and R1 or R3 which does not form the methylenedioxy group as a part thereof, independently from each other, each represents any substituents as mentioned above designated for the Ri, R3, R4 and R5, respectively, R6 represents a hydrogen atom or a hydroxyl group, and R7 represents a substituent selected from a methyl group, an ethyl group, an isopropyl group, an n-propyl group and a t-butyl group, provided the derivatives in which R1 to R5 are all hydrogen atoms, and the derivatives in which R2 or R4 is a methoxy group and R3 is a hydroxyl group are excluded, which comprises subjecting aspartame itself or aspartame derivatives to reductive alkylation with cinnamaldehydes or 3-phenylpropionaldehydes having various substituents and a reducing agent. 2. The process as claimed in claim 1, wherein in formula (1) R2 is a hydroxyl group, R3 is a methoxy group, R1, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 3. The process as claimed in claim 1, wherein in formula (1) R2 and R3 are methoxy groups, R1, R4, R5, and R6 are hydrogen atoms, and R7 is a methyl group. 4. The process as claimed in claim 1, wherein in formula (1) R2 and R3 together form a methylenedioxy group, Ri, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 5. The process as claimed in claim 1, wherein in formula (1) R3 is a hydroxyl group, R1, R2, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 6. The process as claimed in claim 1, wherein in formula (1) R3 is a methoxy group, R1, R2, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 7. The process as claimed in claim 1, wherein in formula (1) R3 is an ethoxy group, R1, R2, R4, R5 and R6 are hydrogen atoms, and R3 is a methyl group. 8. The process as claimed in claim 1, wherein in formula (1) R2 is a hydroxyl group, Ri, R3, R4, R5 and Rg are hydrogen atoms, and R7 is a methyl group. 9. The process as claimed in claim 1, wherein in formula (1) R2 is a methoxy group, R1, R3, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 10. The process as claimed in claim 1 wherein in formula (1) R3 is a methoxy group, R2 and R6 are hydroxyl groups, R1, R4 and R5 are hydrogen atoms, and R7 is a methyl group. 11. The process as claimed in claim 1, wherein in formula (1) Ri is a hydroxyl group, R3 is a methoxy group, R2, R4, R5 and Rg are hydrogen atoms, and R7 is a methyl group. 12. The process as claimed in claim 1, wherein in formula (1) R1 is a hydroxyl group, R2 is a methoxy group, R3, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 13. The process as claimed in claim 1, wherein in formula (1) R1 is a hydroxyl group, R4 is a methoxy group, R2, R3, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 14. The process as claimed in claim 1, wherein in formula (1) R1 is a hydroxyl group, R3 and R7 are methyl groups, and R2, R4, R5 and R6 are hydrogen atoms. 15. The process as claimed in claim 1, wherein in formula (1) Ri and R3 are methoxy groups, R2, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 16. The process as claimed in claim 1, wherein in formula (1) R1 is an ethoxy group, R3 is a methoxy group, R2, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 17. The process as claimed in claim 1, wherein in formula (1) R2 and R7 are methyl groups, R3 is a hydroxyl group, and R1, R4, R5 and R6 are hydrogen atoms. 18. The process as claimed in claim 1, wherein in formula (1) R2 is a hydroxyl group, R3 and R7 are methyl groups, and R1, R4, R5 and R6 are hydrogen atoms. 19. The process as claimed in claim 1, wherein in formula (1) R2 and R7 are methyl groups, R3 is a methoxy group, and R1, R,, R5 and R6 are hydrogen atoms. 20. The process as claimed in claim 1, wherein in formula (1) R2 and R4 are methoxy groups, R1, R3, R5 and R^ are hydrogen atoms, and R7 is a methyl group. 21. The process as claimed in claim 1, wherein in formula (1) R3 is a 2-hydroxyethoxy group, R1, R2, R4, R5 and R6 are hydrogen atoms, and R7 is a methyl group. 22. The process as claimed in claim 1, wherein in formula (1) R3 and R7 are methyl groups, and R1, R2, R4, R5 and R6 are hydrogen atoms. 23. A process for preparing a sweetener, which comprises adding the novel aspartyl dipeptide ester derivatives (including salts thereof) of formula (1) prepared by the process as claimed in claims 1 to 24 to a known carrier and/or bulking agent. 24. A method of imparting sweetness to products such as foods having a sweetness, which comprises using the novel aspartyl dipeptide ester derivatives (including salts thereof) of formula (1) prepared by the process as claimed in claims 1 to 22. 25. A process for preparing a novel aspartyl dipeptide ester derivatives (including salts thereof) represented by formula (1) substantially as herein described and exemplified.

Documents:

in-pct-2000-0480-che abstract.pdf

in-pct-2000-0480-che claims-duplicate.pdf

in-pct-2000-0480-che claims.pdf

in-pct-2000-0480-che description (complete)-duplicate.pdf

in-pct-2000-0480-che description (complete).pdf

in-pct-2000-0480-che form-1.pdf

in-pct-2000-0480-che form-19.pdf

in-pct-2000-0480-che form-26.pdf

in-pct-2000-0480-che form-3.pdf

in-pct-2000-0480-che form-5.pdf

in-pct-2000-0480-che others document.pdf

in-pct-2000-0480-che others.pdf

in-pct-2000-0480-che pct.pdf

in-pct-2000-0480-checorrespondences-others.pdf

in-pct-2000-0480-checorrespondences-po.pdf