Title of Invention	"NOVEL ETHER DERIVATIVES OF DIHYDROARTEMISNIN AS ANTIMALARIALS AND THE PROCESS THEREOF"
Abstract	Novel ether derivatives of dihydroartemisinin and the process thereof. A process for the preparation of w-succinoyloxy ethers of dihydroartemisinin. Dihydroartemisinin is an antimalarial, easily available by NaBH4 reduction of naturally occurring antimalarial artemisinin. Both artemisinin and dihydroartemisinin are insoluble in water and cannot be administered as aqueous solutions. Artesunic acid and artelinic acid are known water-soluble derivatives of dihydroartemisinin and both have antimalarial activity.

Title of Invention

"NOVEL ETHER DERIVATIVES OF DIHYDROARTEMISNIN AS ANTIMALARIALS AND THE PROCESS THEREOF"

Abstract

Novel ether derivatives of dihydroartemisinin and the process thereof. A process for the preparation of w-succinoyloxy ethers of dihydroartemisinin. Dihydroartemisinin is an antimalarial, easily available by NaBH4 reduction of naturally occurring antimalarial artemisinin. Both artemisinin and dihydroartemisinin are insoluble in water and cannot be administered as aqueous solutions. Artesunic acid and artelinic acid are known water-soluble derivatives of dihydroartemisinin and both have antimalarial activity.

Full Text	This invention relates to a novel ether derivatives of dihydroartemisinin and the process thereof. This invention relates to a novel ether derivatives of dihydroartemisinin useful as antimalarials. This invention also relates to a process for the preparation of novel ether derivatives of dihydroartemisinin. This invention particularly relates to a process for the preparation of w-succinoyloxyalkyl ethers of dihydroartemisinin of formula 7 as a new series of water-soluble antimalarial agents. The present invention provides a process for the preparation of w-succinoyloxy ethers of dihydroartemisinin of formula 7. Dihydroartemisinin (2) is an antimalarial, easily available by NaBH4 reduction of naturally occurring antimalarial artemisinin (1). Both artemisinin and dihydroartemisinin are insoluble in water and cannot be administered as aqueous solutions. Artesunic acid (3) and artelinic acid (4) are known water-soluble derivatives of dihydroartemisinin and both have antimalarial activity. While artesunic acid has poor stability in aqueous solutions, synthesis of artelinic acid requires methyl p-hydroxymethyl benzoate, a costly chemical [For recent reviews on artmisinin and its derivatives, including water soluble derivatives see : (a) Meshnick S.R.; Tayler, T.E.; Kamchonwonpaisan, S. Microbial Rev, 1996, 60, 301. (b) Gumming, J.N.; Ploypradith, P.; Posner, G.H. Adv. Pharmacol, 1997, 37,2253. (c) Haynes, R.K.; Vonwiller, S.C. Ace. Chem. Res. 1997, 30, 73. (d) Ziffer, H., Highet, R.J.; Klayman, D.L. Prog. Chem. Org. Nat. Prod. 1997, 72, 123 ]. The main objective of this invention is to provide novel water-soluble ether derivatives of dihydroartemisinin. The objective of this invention is also to provide novel ether derivatives of dihydroartemisinin. Another object of the invention is to provide a process for the preparation of novel ether derivatives of dihydroartemisinin which are water soluble and are useful as antimalarials. Accordingly, the present invention provides novel ether derivatives of dihydroartemisinin of formula 7 given below wherein n is 2 to 12 useful as antimalarials prepared by the process described herein: (Formula Removed) The process of preparation of novel ether derivatives of dihydroartemisinin has been disclosed and claimed in our copending application no.:211 Del 2000 Compounds of formula 7 are hemisuccinate derivatives, and are soluble in aqueous bicarbonate solutions. These compounds have been tested against multi-drug resistant P. yoelii in mice and have shown promising antimalarial activity. Thus the invention relates to pharmaceutical industry. Accordingly the present invention provides a process for the preparation of novel ether derivatives of dihydroartemisinin of formula 7 where in n is 2 to 12 which comprises reacting dihydroartemisinin of formula 2 with alkane diols of formula 5, wherein n = 2 to 12, under acidic conditions in an organic solvent under known reaction conditions to furnish ω-hydroxyalkyl ethers of formula 6, wherein n has the same meaning as above, reacting co-hydroxyalkyl ethers of formula 6 with succinic anyhdride in presence of organic base in an organic solvent in the temperature range of 0°C to room temperature neutralizing the above reaction mixture with mineral acids isolating and purifying the ether derivatives of formula 7 wherein n has the same meaning as above by conventional methods. In an embodiment of the present invention the reaction of dihydroartemisinin with alkane diols may be effected under acidic conditions using acidic catalysts such as BF3.OEt2, p-toluenesulfonic acid, HCI, cation exchanger such as Amberlyst-15. In another embodiment of the invention the organic solvent used may be such as CH2Cl2, benzene, CH3CN, toluene. In yet another embodiment of the invention, the organic base used may be such as pyridine, triethylamine, 4-dimethylaminopyridine (DMAP). In an embodiment of the invention mineral acid used for neutralization may be such as HCI, H2SO4, H3PO4- Purification of compounds of formula 7 may be carried out by column chromatography using hexane - ethylacetate, CH2CI2 - ethylacetate, CHCI3 -MeOH, benzene - ether. All these combinations have been used for purification of compound 7h. If fact any combination consisting of a non-polar solvent such as hexane, CH2CI2, CHCI3, benzene with a polar solvent such as ethylacetate, ether, methanol can be used for chromatography. In the process, dihydroartemisinin of formula 2 is reacted with alkane diols of formula 5 in presence of an acid catalyst such as BF3.OEt2, p-toluene sulfonic acid, HCI, cation exchanger such as Amberlyst-15, in an aprotic solvent such as CH2CI2, benzene, to furnish co-hydroxyalkyl ethers of formulae. Compounds of formula 6 are mixture of a and ß-isomers, they can be separated into pure a and p-isomers by known methods such as column chromatography or can be used as mixture in the next step. Compounds 6d, 6f, 6g, 6i [formula 6 ; n = 5, 8, 9, 12] are new compounds while compounds 6a, 6b, 6c, 6e, 6h [formula 6, n = 2, 3, 4, 6, 10] have been prepared earlier [Chandan Singh and Rani Kanchan, Indian Patent Application no. 5600, Date 5.9.1997]. In the process w-hydroxyalkyl ethers of formula 6 are reacted with succinic anhydride in presence of a base such as Et3N, pyridine, 4-dimethylaminopyridine (DMAP), in an organic solvent such as CH2CI2, CH3CN, toluene, to give ω-succinoyloxyalkyl ethers of formula 7. Compounds of formula 7 are hemisuccinate derivatives of compounds of formula 6. These hemisucinate derivatives of formula 7 are new compounds and have not been prepared earlier. Compounds of formula 7 have a free carboxyl group and are soluble in aqueous bicarbonate solutions. These compounds of formula 7 can be used as antimalarials either as pure isomers or as mixture of a and p-isomers. Compounds of formula 7 can be isolated and purified using standard laboratory conditions such as column chromatography on silica gel using a hydrocarbon solvent in conjuction with a polar organic solvent as eluant. This invention is further illustrated by the following examples which should not, however, be construed to limit the scope of the present invention. Example 1 2-Hydroxylethyl ether of dihydroartemisinin (Compound 6a, formula 6, n = 2) To a solution of dihydroartemisinin (1.0 g, 3.52 mmole) and ethylene glycol (2 ml) in CHCI3 (10 ml) was added Amberlyst-15 (H+ form, 100 mg) and the reaction mixture was refluxed for 4.5 h. The resin was filtered off, the filtrate was concentrated and the crude product was chromatographed on silica gel using hexane-ethylacetate (85 : 15) as eluant to furnish 680 mg of pure ß-isomer of 6a, 110 mg of a-isomer of 6a and 220 mg of a mixture of a and p-isomers ; combined yield 86%. 2-Succinoyloxyethyl ether of dihydroartemisinin (Compound 7a, formula 7, n = 2) To a solution of p-isomer of compound 6a (200 mg) in pyridine (4 ml) was added succinic anhydride (300 mg) and the reaction mixture was kept at room temperature for 15 h. The reaction mixture was cooled in ice-bath, acidified with 10% aqueous HCI and extracted with ether. The ether extract was washed with water, dried (Na2SO4), concentrated and the crude product was chromatographed on silica gel to furnish 160 mg (62% yield) of ß-isomer of compound 7a as an oil. Compound 7a was obtained in 87% yield when the reaction was carried out in CH2CI2 using Et3N as a base. A mixture of a and p-isomers of compound 7a was obtained in 70% yield when the mixture of a and p-isomers of compound 6a was reacted with succinic anhydride under the above conditions. Example 2 3-Hydroxypropyl ether of dihydroartemisinin (Compound 6b, formula 6, n = 3) To a solution of dihydroartemisinin (1.0 g, 3.52 mmol) and 1,3-propanediol (2.0 g) in benzene (20 ml) was added cation exchanger IR-120 (100 mg) and the reaction mixture was refluxed for 6 h. The resin was filtered off and the filtrate was concentrated. The crude product was purified by column chromatography on silica gel (50 g, elution with 10% ethylacetate in hexane) to give 310 mg of p-isomer of 6b and 500 mg of a mixture of a and p-isomers of 6b (combined yield 67%). 3-Succinoyloxypropyl ether of dihydroartemisinin (compound 7b, formula 7, n = 3) To an ice-cooled solution of 3-hydroxypropyl ether 6b (p-isomer, 160 mg) and succinic anhydride (300 mg) in CH2CI2 (5 ml) were aded Et3N (1 ml) and DMAP (15 mg) and the reaction mixture was stirred at 0°C for 1.5 h. It was acidified with 10% aqueous HCI, extracted with ether, the ether extract was washed with water, dried, concentrated and chromatographed on silica gel using 40% ethyl acetate in hexane as eluant to furnish 160 mg (78% yield) of p-isomers of 7b as an oil. Reaction of a mixture of a and p-isomers of compound 6b with succinic anhydride under similar conditions furnished a mixture of a and p-isomers of compound 7b in 79% yield. Example 3 4-Hydroxybutyl ether of dihydroartemisinin (compound 6c, formula 6, n = 4) To a solution of dihydroartemisinin (1.0 g) and 1,4-butanediol (2.0 g) in benzene (20 ml) was added IR-120 (100 mg) and the reaction mixture was refluxed for 7 h. The resin was filtered off and, the filtrate was concentrated and chromatographed on silica gel as above to furnish 360 mg of p-isomers of 6c and 240 mg of a mixture of a and p-isomers of 6c (combined yield 48%). 4-Succinoyloxybutyl ether of dihydroartemisinin (compound 7c, formula 7, n = 4) To an ice-cooled solution of 4-hydroxybutyl ether 6c (p-isomers, 230 mg) and succinic anhydride (300 mg) in CH2CI2 (6 ml) were added Et3N (1 ml) and DMAP (10 mg) and the reaction mixture was stirred at 0°C for 1 h. The reaction mixture was worked up and crude product was purified using the procedure as given in example 2 to furnish 200 mg (68% yield) of hemisuccinate 7c as an oil. Example 4 5-Hydroxypentyl ether of dihydroartemisinin (compound 6d, formula 6, n = 5) To a solution of dihydroartemisinin (2.0 g) and 1,5-pentanediol (3.0 g) in CH2CI2 (80 ml) was added BF3.OEt2 (7 drops) and the mixture was stirred at room temperature for 15 h. It was diluted with saturated aquoeus sodium acetate solution. Organic extract was washed with water, dried (Na2SO4), concentrated and chromatographed on silica gel (60 g) using 20% ethyl acetate in hexane as eluant to furnish 1.38 g of p-isomer, 210 mg α-isomer and and 110 mg of mixutre of a and p-isomers of 6d (combined yield 65%). 5-Succinoyloxypentyl ether of dihydroartemisinin (compound 7d, formula 7, n = 5) A mixture of compound 6d (p-isomer, 300 mg) and succinic anhydride (600 mg) was reacted in CH2CI2 (10 ml) in presence of Et3N (1 ml) and DMAP (25 mg) at room temperature for 2 h. The reaction mixture was worked up and the crude product was purified by chromatography using the procedure given in the above examples to furnish 320 mg (78% yield) of p-isomer of 7d as an oil. a-lsomer of 7d was obtained as an oil in 71% yield when α-isomer of 6d was reacted under similar conditions. Example 6 6-Hydroxyhexyl ether of dihydroartemisinin (compound 6e, formula 6, n = 6) To a solution of dihydroartemisinin (1.5 g) in 1,6-hexanediol (3.0 g) in CH2CI2 (40 ml) was added BF3.OEt2 (7 drops) and the reaction mixture was stirred at room temperature for 15 h. The reaction mixture was worked up and product was purified by chromatography following the procedure as given in above examples to furnish 650 mg of p-isomer and 300 mg of a mixture of a and p-isomers of 6e (combined yield 47%). Compound 6e was obtained in 46% yield when the reaction was carried out in benzene at refluxing temperature using IR-120 as catalyst. 6-Succinoyloxyhexyl ether of dihydroartemisinin (compound 7e, formula 7, n = 6) To an ice-cooled solution of compound 6e (p-isomer, 200 mg) and succinic anhydride (200 mg) in CH2CI2 (16 ml) were added Et3N (0.8 ml) and DMAP (10 mg) and the reaction mixture was stirred at 0°C for 1 h. Work up and purification done following the procedure as given in above examples to furnish 180 mg (71% yield) of p-isomer of 7e as an oil. Example 6 8-Hydroxyoctyl ether of dihydroartemisinin (compound 6f, formula 6, n = 8) To a solution of dihydroartemisinin (2.0 g) and 1,8-octanediol (2.0 g) in CH2CI2 (60 ml) was added BF3.OEt2 (8 drops) and the reaction mixture was stirred at room temperature for 5 h. Usual aqueous work up followed by chromatography on silica gel (60 g, 25% ethyl acetate in hexane as eluant) furnished 1.02 g p-isomer and 620 mg of a mixture of a and p-isomers of 6f (combined yield 57%). 8-Succinoyloxyoctyl ether of dihydroartemisinin (compound 7f, formula 7, n = 8) To an ice-cooled solution of compound 6f (p-isomer, 80 mg) and succinic anhydride (80 mg) in CH2CI2 (80 ml) was added Et3N (0.5 ml) and the reaction mixture was kept at room temperature for 35 minutes. It was acidified with 10% aqueous HCI and extracted with ether. Organic layer was washed with water, dried (Na2SO4), concentrated and chromatographed on silica gel to furnish 90 mg (87% yield) of p-isomer of compound 7f, as an oil. Example 7 9-Hydroxynonyl ether of dihydroartemisinin (compound 6g, formula 6, n = 9) To a stirred solution of dihydroartemisinin (2.0 g) in 1,9-nonanediol (3.6 g) in CH2CI2 (50 ml) was added BF3.OEt2 (1 ml) and the reaction mixture was stirred at room temperature for 6 h. Usual aqueous work up followed by chromatography on silica gel furnished 940 mg (31% yield) of a mixture of a and p-isomers of 6g, as an oil. 9-Succinoyloxynonyl ether of dihydroartemisinin (compound 7g, formula 7, n = 9) A mixture of compound 6g (mixture of a and p-isomers, 370 mg), succinic anhydride (12 ml) was stirred at room temperature for 1 h. Usual work up followed by chromatography on silica gel furnished 380 mg (83% yield) of a mixture of a and p-isomers of compound 7g, as an oil. Example 8 10-Hydroxydecyl ether of dihydroartemisinin (compound 6 h, formula 6, n = 10) To a solution of dihydroartemisinin (1.15 g) and 1,10-decanediol (2.0 g) in CH2CI2 (45 ml) was added BF3.OEt2 (7 drops) and the reaction mixture was stirred at room temperature for 5 h. Usual aqueous work up followed by chromatography on silica gel furnished 630 mg of p-isomer and 390 mg of a mixture of a and p-isomers of compound 6h (combined yield 58%). Compound 6h was obtained as a mixture of a and p-isomers in 27% yield when dihydroartemisinin was reacted with 1,10-decanediol in refluxing benzene in presence of IR-120 as catalyst. 10-Succinoyloxydecyl ether of dihydroartemisinin (compound 7h, formula 7, n = 10) To an ice-cooled solution 10-hydroxydecyl ether 6 h (ß-isomer, 100 mg) and succinic anhydride (100 mg) in CH2CI2 (5 ml) were added Et3N (1 ml) and DMAP (10 mg) and the reaction mixture was stirred at 0°C for 1 h. It was acidified with 10% aqueous HCI, extracted with ether, ether extract was washed with water, dried and chromatographed on silica gel using 40% ethyl acetate in CH2CI2 as efuant to furnish 100 mg (83% yield) of p-isomer of compound 7h as an oil. Reaction of a mixture of a and p-isomers of compound 6h with succinic anhydride under similar conditions furnished a mixture of a and p-isomers of compound 7h in 90% yield. Compound 7h (p-isomer) was also prepared using different reaction conditions. Results are summerised in table 1. Table 1(Table Removed) Example 9 12-Hydroxydodecyl ether of dihydroartemisinin (compound 6i, formula 6, n = 12) To a solution of dihydroartemisinin (2.0 g) and 1,12-dodecanediol (3.0 g) in CH2CI2 (80 ml) was added BF3.OEt2 (7 drops) and the reaction mixture was stirred at room temperature for 6 h. Aqueous work up followed by chromatography on silica gel (elution with 20% ethyl acetate in hexane) furnished 900 mg of p-isomer and 260 mg of a mixture of a and ß-isomers of compound 6i (combined yield 39%). 12-Succinoyloxydodecyl ether of dihydroartemisinin (compound 7i, formula 7, n = 12) To an ice-cooled solution of compound 6i (p-isomer, 80 mg) and succinic anhydride (80 mg) in CH2CI2 (10 ml) was added Et3N (0.6 ml) and the reaction mixture was kept at room temperature for 1 h. The reaction mixture was stripped off solvents and then acidified with 10% aqueous HCI and extracted with ether (2 x 25 ml). Ether extract was washed with water, dried (Na2SO4), concentrated and chromatogrphed on silica gel to furnish 80 mg (82% yield) of p-isomer of compound 7i as an oil. Reaction of a mixture of a and p-isomers of compound 6i with succinic anhydride under similar conditions furnished a mixture of a and p-isomers of compound 7i in 83% yield. Antimalarial activity The blood schizontocidal activity of the test compounds was evaluated in rodent model using multidrug resistant strain of Plasmodium yoelii Nigeriensis in swiss mice. General Procedure : Random bred swiss mice of either sex (20 ± 2 gm) were inoculated intraperitoneally with 1 x 105 P. yoelii (MDR) parasites in day O. The treatment with test compounds were administered to groups of 6 mice each at different dose levels ranging between 12-96 mg/kg/day. The compounds were administered as solutions in 5% aqueous NaHCO3 solution via intramuscular route for 4 consecutive days (day 0-3). Artesunic acid was used as positive control. Blood smears from experimental mice were observed on day 4 and 7, day 10 and thereafter at regular interval till day 28 or death of the animal. The parasitaemia level on day 4 was compared with the vehicle control group and the percent suppression of parasitaemia in treated groups was calculated. The compounds which showed more than 90% suppression were identified for further screening. For determing the curative dose of a compound the treated mice were observed till day 28. The dose at which no parasitaemia develops during the observation period has been recorded as the curative dose. The results are shown in table 2. Table 2 : Blood schizontocidal activity of compounds 7a-i against P. yoelii in mice Compound Dose mg/kg x Suppression of Cured/Treated 4 days Parasitaemia (%) (Table Removed) We claim : 1. Novel ether derivatives of dihydroartemisinin of formula 7 given below wherein n is 2 to 12 useful as antimalarials prepared by the process described herein (Formula Removed) 2. Novel ether derivatives as claimed in claim 1 wherein the said compounds having the structural formulae 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h, 7i as shown below(Formula Removed) 7a n=2 7b n=3 7c n=4 7d n=5 7e n=6 7f n=8 7g n=9 7h n=10 7i n=12 3. Novel ether derivatives of dihydroartemisinin as claimed in claims 1-2 substantially as herein described with reference to the examples and the drawing accompanying the specification.

Full Text

This invention relates to a novel ether derivatives of dihydroartemisinin and the process thereof.
This invention relates to a novel ether derivatives of dihydroartemisinin useful as antimalarials.
This invention also relates to a process for the preparation of novel ether derivatives of dihydroartemisinin.
This invention particularly relates to a process for the preparation of w-succinoyloxyalkyl ethers of dihydroartemisinin of formula 7 as a new series of water-soluble antimalarial agents.
The present invention provides a process for the preparation of w-succinoyloxy ethers of dihydroartemisinin of formula 7. Dihydroartemisinin (2) is an antimalarial, easily available by NaBH4 reduction of naturally occurring antimalarial artemisinin (1). Both artemisinin and dihydroartemisinin are insoluble in water and cannot be administered as aqueous solutions. Artesunic acid (3) and artelinic acid (4) are known water-soluble derivatives of dihydroartemisinin and both have antimalarial activity. While artesunic acid has poor stability in aqueous solutions, synthesis of artelinic acid requires methyl p-hydroxymethyl benzoate, a costly chemical [For recent reviews on artmisinin and its derivatives, including water soluble derivatives see : (a) Meshnick S.R.; Tayler, T.E.; Kamchonwonpaisan, S. Microbial Rev, 1996, 60, 301. (b) Gumming, J.N.; Ploypradith, P.; Posner, G.H. Adv. Pharmacol, 1997, 37,2253. (c) Haynes, R.K.; Vonwiller, S.C. Ace. Chem. Res. 1997, 30, 73. (d) Ziffer, H., Highet, R.J.; Klayman, D.L. Prog. Chem. Org. Nat. Prod. 1997, 72, 123 ].
The main objective of this invention is to provide novel water-soluble ether derivatives of dihydroartemisinin. The objective of this invention is also to provide novel ether derivatives of dihydroartemisinin.
Another object of the invention is to provide a process for the preparation of novel ether derivatives of dihydroartemisinin which are water soluble and are useful as antimalarials.
Accordingly, the present invention provides novel ether derivatives of dihydroartemisinin of formula 7 given below wherein n is 2 to 12 useful as antimalarials prepared by the process described herein:
(Formula Removed)
The process of preparation of novel ether derivatives of dihydroartemisinin has been disclosed and claimed in our copending application no.:211 Del 2000
Compounds of formula 7 are hemisuccinate derivatives, and are soluble in aqueous bicarbonate solutions. These compounds have been tested against multi-drug resistant P. yoelii in mice and have shown promising antimalarial activity. Thus the invention relates to pharmaceutical industry.
Accordingly the present invention provides a process for the preparation of novel ether derivatives of dihydroartemisinin of formula 7 where in n is 2 to 12 which comprises reacting dihydroartemisinin of formula 2 with alkane diols of formula 5, wherein n = 2 to 12, under acidic conditions in an organic solvent under known reaction conditions to furnish ω-hydroxyalkyl ethers of formula 6, wherein n has the same meaning as above, reacting co-hydroxyalkyl ethers of formula 6 with succinic anyhdride in presence of organic base in an organic solvent in the temperature range of 0°C to room temperature neutralizing the above reaction mixture with mineral acids isolating and purifying the ether derivatives of formula 7 wherein n has the same meaning as above by conventional methods.
In an embodiment of the present invention the reaction of dihydroartemisinin with alkane diols may be effected under acidic conditions using acidic catalysts such as BF3.OEt2, p-toluenesulfonic acid, HCI, cation exchanger such as Amberlyst-15.
In another embodiment of the invention the organic solvent used may be such as CH2Cl2, benzene, CH3CN, toluene.
In yet another embodiment of the invention, the organic base used may be such as pyridine, triethylamine, 4-dimethylaminopyridine (DMAP).
In an embodiment of the invention mineral acid used for neutralization may be such as HCI, H2SO4, H3PO4-
Purification of compounds of formula 7 may be carried out by column chromatography using hexane - ethylacetate, CH2CI2 - ethylacetate, CHCI3 -MeOH, benzene - ether. All these combinations have been used for purification of compound 7h. If fact any combination consisting of a non-polar solvent such as hexane, CH2CI2, CHCI3, benzene with a polar solvent such as ethylacetate, ether, methanol can be used for chromatography.
In the process, dihydroartemisinin of formula 2 is reacted with alkane diols of formula 5 in presence of an acid catalyst such as BF3.OEt2, p-toluene sulfonic acid, HCI, cation exchanger such as Amberlyst-15, in an aprotic solvent such as CH2CI2, benzene, to furnish co-hydroxyalkyl ethers of formulae. Compounds of formula 6 are mixture of a and ß-isomers, they
can be separated into pure a and p-isomers by known methods such as column chromatography or can be used as mixture in the next step.
Compounds 6d, 6f, 6g, 6i [formula 6 ; n = 5, 8, 9, 12] are new compounds while compounds 6a, 6b, 6c, 6e, 6h [formula 6, n = 2, 3, 4, 6, 10] have been prepared earlier [Chandan Singh and Rani Kanchan, Indian Patent Application no. 5600, Date 5.9.1997].
In the process w-hydroxyalkyl ethers of formula 6 are reacted with succinic anhydride in presence of a base such as Et3N, pyridine, 4-dimethylaminopyridine (DMAP), in an organic solvent such as CH2CI2, CH3CN, toluene, to give ω-succinoyloxyalkyl ethers of formula 7. Compounds of formula 7 are hemisuccinate derivatives of compounds of formula 6. These hemisucinate derivatives of formula 7 are new compounds and have not been prepared earlier. Compounds of formula 7 have a free carboxyl group and are soluble in aqueous bicarbonate solutions.
These compounds of formula 7 can be used as antimalarials either as pure isomers or as mixture of a and p-isomers. Compounds of formula 7 can be isolated and purified using standard laboratory conditions such as column chromatography on silica gel using a hydrocarbon solvent in conjuction with a polar organic solvent as eluant.
This invention is further illustrated by the following examples which should not, however, be construed to limit the scope of the present invention. Example 1
2-Hydroxylethyl ether of dihydroartemisinin (Compound 6a, formula 6, n = 2)
To a solution of dihydroartemisinin (1.0 g, 3.52 mmole) and ethylene glycol (2 ml) in CHCI3 (10 ml) was added Amberlyst-15 (H+ form, 100 mg)
and the reaction mixture was refluxed for 4.5 h. The resin was filtered off, the filtrate was concentrated and the crude product was chromatographed on silica gel using hexane-ethylacetate (85 : 15) as eluant to furnish 680 mg of pure ß-isomer of 6a, 110 mg of a-isomer of 6a and 220 mg of a mixture of a and p-isomers ; combined yield 86%.
2-Succinoyloxyethyl ether of dihydroartemisinin (Compound 7a, formula 7, n = 2)
To a solution of p-isomer of compound 6a (200 mg) in pyridine (4 ml) was added succinic anhydride (300 mg) and the reaction mixture was kept at room temperature for 15 h. The reaction mixture was cooled in ice-bath, acidified with 10% aqueous HCI and extracted with ether. The ether extract was washed with water, dried (Na2SO4), concentrated and the
crude product was chromatographed on silica gel to furnish 160 mg (62% yield) of ß-isomer of compound 7a as an oil.
Compound 7a was obtained in 87% yield when the reaction was carried out in CH2CI2 using Et3N as a base.
A mixture of a and p-isomers of compound 7a was obtained in 70% yield when the mixture of a and p-isomers of compound 6a was reacted with succinic anhydride under the above conditions. Example 2
3-Hydroxypropyl ether of dihydroartemisinin (Compound 6b, formula 6, n = 3)
To a solution of dihydroartemisinin (1.0 g, 3.52 mmol) and 1,3-propanediol (2.0 g) in benzene (20 ml) was added cation exchanger IR-120 (100 mg) and the reaction mixture was refluxed for 6 h. The resin was filtered off and the filtrate was concentrated. The crude product was purified by column chromatography on silica gel (50 g, elution with 10% ethylacetate in hexane) to give 310 mg of p-isomer of 6b and 500 mg of a mixture of a and p-isomers of 6b (combined yield 67%). 3-Succinoyloxypropyl ether of dihydroartemisinin (compound 7b, formula 7, n = 3)
To an ice-cooled solution of 3-hydroxypropyl ether 6b (p-isomer, 160 mg) and succinic anhydride (300 mg) in CH2CI2 (5 ml) were aded Et3N (1 ml)
and DMAP (15 mg) and the reaction mixture was stirred at 0°C for 1.5 h. It was acidified with 10% aqueous HCI, extracted with ether, the ether extract was washed with water, dried, concentrated and chromatographed on silica gel using 40% ethyl acetate in hexane as eluant to furnish 160 mg (78% yield) of p-isomers of 7b as an oil.
Reaction of a mixture of a and p-isomers of compound 6b with succinic anhydride under similar conditions furnished a mixture of a and p-isomers of compound 7b in 79% yield. Example 3
4-Hydroxybutyl ether of dihydroartemisinin (compound 6c, formula 6, n = 4)
To a solution of dihydroartemisinin (1.0 g) and 1,4-butanediol (2.0 g) in benzene (20 ml) was added IR-120 (100 mg) and the reaction mixture was refluxed for 7 h. The resin was filtered off and, the filtrate was concentrated and chromatographed on silica gel as above to furnish 360 mg of p-isomers of 6c and 240 mg of a mixture of a and p-isomers of 6c (combined yield 48%).
4-Succinoyloxybutyl ether of dihydroartemisinin (compound 7c, formula 7, n = 4)
To an ice-cooled solution of 4-hydroxybutyl ether 6c (p-isomers, 230 mg) and succinic anhydride (300 mg) in CH2CI2 (6 ml) were added Et3N (1 ml)
and DMAP (10 mg) and the reaction mixture was stirred at 0°C for 1 h. The
reaction mixture was worked up and crude product was purified using the
procedure as given in example 2 to furnish 200 mg (68% yield) of
hemisuccinate 7c as an oil.
Example 4
5-Hydroxypentyl ether of dihydroartemisinin (compound 6d, formula 6, n
= 5)
To a solution of dihydroartemisinin (2.0 g) and 1,5-pentanediol (3.0 g) in CH2CI2 (80 ml) was added BF3.OEt2 (7 drops) and the mixture was
stirred at room temperature for 15 h. It was diluted with saturated aquoeus
sodium acetate solution. Organic extract was washed with water, dried (Na2SO4), concentrated and chromatographed on silica gel (60 g) using 20%
ethyl acetate in hexane as eluant to furnish 1.38 g of p-isomer, 210 mg α-isomer and and 110 mg of mixutre of a and p-isomers of 6d (combined yield 65%).
5-Succinoyloxypentyl ether of dihydroartemisinin (compound 7d, formula 7, n = 5)
A mixture of compound 6d (p-isomer, 300 mg) and succinic anhydride (600 mg) was reacted in CH2CI2 (10 ml) in presence of Et3N (1 ml) and
DMAP (25 mg) at room temperature for 2 h. The reaction mixture was worked up and the crude product was purified by chromatography using the procedure given in the above examples to furnish 320 mg (78% yield) of p-isomer of 7d as an oil.
a-lsomer of 7d was obtained as an oil in 71% yield when α-isomer of 6d was reacted under similar conditions. Example 6
6-Hydroxyhexyl ether of dihydroartemisinin (compound 6e, formula 6, n = 6)
To a solution of dihydroartemisinin (1.5 g) in 1,6-hexanediol (3.0 g) in CH2CI2 (40 ml) was added BF3.OEt2 (7 drops) and the reaction mixture
was stirred at room temperature for 15 h. The reaction mixture was worked up and product was purified by chromatography following the procedure as given in above examples to furnish 650 mg of p-isomer and 300 mg of a mixture of a and p-isomers of 6e (combined yield 47%).
Compound 6e was obtained in 46% yield when the reaction was carried out in benzene at refluxing temperature using IR-120 as catalyst. 6-Succinoyloxyhexyl ether of dihydroartemisinin (compound 7e, formula 7, n = 6)
To an ice-cooled solution of compound 6e (p-isomer, 200 mg) and succinic anhydride (200 mg) in CH2CI2 (16 ml) were added Et3N (0.8 ml) and
DMAP (10 mg) and the reaction mixture was stirred at 0°C for 1 h. Work up
and purification done following the procedure as given in above examples
to furnish 180 mg (71% yield) of p-isomer of 7e as an oil.
Example 6
8-Hydroxyoctyl ether of dihydroartemisinin (compound 6f, formula 6, n =
8)
To a solution of dihydroartemisinin (2.0 g) and 1,8-octanediol (2.0 g) in CH2CI2 (60 ml) was added BF3.OEt2 (8 drops) and the reaction mixture
was stirred at room temperature for 5 h. Usual aqueous work up followed by chromatography on silica gel (60 g, 25% ethyl acetate in hexane as eluant) furnished 1.02 g p-isomer and 620 mg of a mixture of a and p-isomers of 6f (combined yield 57%).
8-Succinoyloxyoctyl ether of dihydroartemisinin (compound 7f, formula 7, n = 8)
To an ice-cooled solution of compound 6f (p-isomer, 80 mg) and succinic anhydride (80 mg) in CH2CI2 (80 ml) was added Et3N (0.5 ml) and
the reaction mixture was kept at room temperature for 35 minutes. It was acidified with 10% aqueous HCI and extracted with ether. Organic layer was washed with water, dried (Na2SO4), concentrated and chromatographed on
silica gel to furnish 90 mg (87% yield) of p-isomer of compound 7f, as an oil. Example 7
9-Hydroxynonyl ether of dihydroartemisinin (compound 6g, formula 6, n = 9)
To a stirred solution of dihydroartemisinin (2.0 g) in 1,9-nonanediol (3.6 g) in CH2CI2 (50 ml) was added BF3.OEt2 (1 ml) and the reaction mixture was
stirred at room temperature for 6 h. Usual aqueous work up followed by chromatography on silica gel furnished 940 mg (31% yield) of a mixture of a and p-isomers of 6g, as an oil.
9-Succinoyloxynonyl ether of dihydroartemisinin (compound 7g, formula 7, n = 9)
A mixture of compound 6g (mixture of a and p-isomers, 370 mg), succinic anhydride (12 ml) was stirred at room temperature for 1 h. Usual
work up followed by chromatography on silica gel furnished 380 mg (83% yield) of a mixture of a and p-isomers of compound 7g, as an oil. Example 8
10-Hydroxydecyl ether of dihydroartemisinin (compound 6 h, formula 6, n = 10)
To a solution of dihydroartemisinin (1.15 g) and 1,10-decanediol (2.0 g) in CH2CI2 (45 ml) was added BF3.OEt2 (7 drops) and the reaction
mixture was stirred at room temperature for 5 h. Usual aqueous work up followed by chromatography on silica gel furnished 630 mg of p-isomer and 390 mg of a mixture of a and p-isomers of compound 6h (combined yield 58%).
Compound 6h was obtained as a mixture of a and p-isomers in 27% yield when dihydroartemisinin was reacted with 1,10-decanediol in refluxing benzene in presence of IR-120 as catalyst. 10-Succinoyloxydecyl ether of dihydroartemisinin (compound 7h, formula 7, n = 10)
To an ice-cooled solution 10-hydroxydecyl ether 6 h (ß-isomer, 100 mg) and succinic anhydride (100 mg) in CH2CI2 (5 ml) were added Et3N (1 ml)
and DMAP (10 mg) and the reaction mixture was stirred at 0°C for 1 h. It was acidified with 10% aqueous HCI, extracted with ether, ether extract was
washed with water, dried and chromatographed on silica gel using 40% ethyl acetate in CH2CI2 as efuant to furnish 100 mg (83% yield) of p-isomer of
compound 7h as an oil.
Reaction of a mixture of a and p-isomers of compound 6h with succinic anhydride under similar conditions furnished a mixture of a and p-isomers of compound 7h in 90% yield.
Compound 7h (p-isomer) was also prepared using different reaction conditions. Results are summerised in table 1.
Table 1(Table Removed)
Example 9
12-Hydroxydodecyl ether of dihydroartemisinin (compound 6i,
formula 6, n = 12)
To a solution of dihydroartemisinin (2.0 g) and 1,12-dodecanediol (3.0 g) in CH2CI2 (80 ml) was added BF3.OEt2 (7 drops) and the reaction
mixture was stirred at room temperature for 6 h. Aqueous work up followed by chromatography on silica gel (elution with 20% ethyl acetate in hexane) furnished 900 mg of p-isomer and 260 mg of a mixture of a and ß-isomers of compound 6i (combined yield 39%).
12-Succinoyloxydodecyl ether of dihydroartemisinin (compound 7i, formula 7, n = 12)
To an ice-cooled solution of compound 6i (p-isomer, 80 mg) and succinic anhydride (80 mg) in CH2CI2 (10 ml) was added Et3N (0.6 ml) and
the reaction mixture was kept at room temperature for 1 h. The reaction mixture was stripped off solvents and then acidified with 10% aqueous HCI
and extracted with ether (2 x 25 ml). Ether extract was washed with water, dried (Na2SO4), concentrated and chromatogrphed on silica gel to
furnish 80 mg (82% yield) of p-isomer of compound 7i as an oil.
Reaction of a mixture of a and p-isomers of compound 6i with succinic anhydride under similar conditions furnished a mixture of a and p-isomers of compound 7i in 83% yield.
Antimalarial activity
The blood schizontocidal activity of the test compounds was evaluated in rodent model using multidrug resistant strain of Plasmodium yoelii Nigeriensis in swiss mice.
General Procedure : Random bred swiss mice of either sex (20 ± 2 gm) were inoculated intraperitoneally with 1 x 105 P. yoelii (MDR) parasites in day O. The treatment with test compounds were administered to groups of 6
mice each at different dose levels ranging between 12-96 mg/kg/day. The compounds were administered as solutions in 5% aqueous NaHCO3 solution
via intramuscular route for 4 consecutive days (day 0-3). Artesunic acid was used as positive control.
Blood smears from experimental mice were observed on day 4 and 7, day 10 and thereafter at regular interval till day 28 or death of the animal. The
parasitaemia level on day 4 was compared with the vehicle control group and the percent suppression of parasitaemia in treated groups was calculated. The compounds which showed more than 90% suppression were identified for further screening.
For determing the curative dose of a compound the treated mice were observed till day 28. The dose at which no parasitaemia develops during the observation period has been recorded as the curative dose. The results are shown in table 2.
Table 2 : Blood schizontocidal activity of compounds 7a-i against P. yoelii in mice
Compound Dose mg/kg x Suppression of Cured/Treated
4 days Parasitaemia (%)
(Table Removed)

We claim :
1. Novel ether derivatives of dihydroartemisinin of formula 7 given below wherein n is 2 to 12 useful as antimalarials prepared by the process described herein (Formula Removed)
2. Novel ether derivatives as claimed in claim 1 wherein the said compounds having the structural formulae 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h, 7i as shown below(Formula Removed)
7a n=2
7b n=3
7c n=4
7d n=5
7e n=6 7f n=8 7g n=9 7h n=10 7i n=12 3. Novel ether derivatives of dihydroartemisinin as claimed in claims 1-2
substantially as herein described with reference to the examples and the drawing accompanying the specification.

Documents:

212-del-2000-abstract.pdf

212-del-2000-claims.pdf

212-del-2000-correspondence-others.pdf

212-del-2000-correspondence-po.pdf

212-del-2000-description (complete).pdf

212-del-2000-form-1.pdf

212-del-2000-form-19.pdf

212-del-2000-form-2.pdf

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Patent Number

211244

Indian Patent Application Number

212/DEL/2000

PG Journal Number

45/2007

Publication Date

09-Nov-2007

Grant Date

23-Oct-2007

Date of Filing

09-Mar-2000

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	CHANDAN SINGH	CENTRAL DRUG RESEARCH INSTITUTE, CHATTAR MANZIL PALACE, LUCKNOW-226 001 (U.P), INDIA.
2	SUNIL KUMAR PURI	CENTRAL DRUG RESEARCH INSTITUTE, CHATTAR MANZIL PALACE, LUCKNOW-226 001 (U.P), INDIA.
3	RANI KANCHAN	CENTRAL DRUG RESEARCH INSTITUTE, CHATTAR MANZIL PALACE, LUCKNOW-226 001 (U.P), INDIA.

PCT International Classification Number

A61K 31/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA