|Title of Invention||
"AN IMPROVED PROCESS FOR THE PREPARATION OF GUGGULSTERONES-A PHARMACOLOGICALLY ACTIVE CONSTITUENT OF GUGULIPID"
|Abstract||The present invention relates to An improved process for the preparation of Guggulsterones a pharmacologically active constituent of gugulipid. The present invention particularly relates to an improved process for the preparation of a mixture of trans- and cis- 4.17 (20) - pregnadiene - 3.16 dione or Guggulsterone -E and -Z useful as hypolipidemic agent of the formula Iα and Ib as shown in accompanied drawings.The process uses on oxidant-hydrogen peroxide on solid support which provide the reagent at the reaction rite in high concentration.|
|Full Text||The present invention relates to an improved process for the preparation of Guggulsterones. The present invention particularly relates to an improved process for the preparation of.a mixture of trans- and cis- 4.17(20) - pregnadiene - 3,16-dione or Guggulsterone -E and -Z useful as hypolipidemic agent of the formula Ia and Ib as shown in accompanied drawings. BACKGROUND OF THE INVENTION
The compound of the present invention is known in the literature prior in seventies in connection with their utility in synthesis of steroidal alkaloids and saponines [S.V. Kessar and A.L. Rampal, Chem.Ind., 1957 (1963); Tetrahedron Letters, 4319 (1966). These compounds were later isolated from the resin (gum guggul) obtained from Commiphora mukul which is an important drug in the Ayurvedic system for arthritis and inflammation. There is also reference regarding its anti-obesity activity in Charak Sanghita [G.V. Satyavati, in Economic and Medicinal Plant Research, Vol. 5, Plants and Traditional Medicine pp 47 (1991), Academic Press]. After extensive research work on gum-guggul through extractive fractionation followed by bio-evaluation at Central Drug Research Institute, Lucknow jointly with Malti-Chem Research Centre, Baroda, a lexicologically safe extract was standardized for hypolipidemic activity. The product is being marketed as 'Guglip' by CIPLA Ltd., Bombay. It was simultaneously established in the study that the hypolipidemic activity was due to the presence of Ia and Ib to the extent of 4-5% in the product and hence the name guggulsterone was coined to the product I.
The results of this pioneering work provoked considerable efforts among industries and academia world-over in Guglip and as a result several additional activities
were established in the preparation such as prevention of sebum secretion [US Pat. No. 5, 6980, 948], anti-inflammatory by Bombardelli et. al. [US Pat. No. 5, 273, 747] and use in benign prostate hypertrophy and acne. Bessett et.al. [US Pat. No. 4, 847, 071 and 4, 847, 069] and Piazza et.al. [US Pat No. 5, 521, 223] disclosed photo-protective and anti-wrinkle actions.
Guggulsterone content in gugulipid is highest to the extent of 4-5% and therefore many of the activities of gugulipid have been implicated because of guggulsterone. The hypolipidemic activity has already been established. In pursuance of our efforts further in guggulipid and its constituents, we improved upon the process of guggulsterone synthesis, which is one of the major subject matter of our claims in present invention.
In yet another aspect of the invention, there is provided with two methods of guggulsterone synthesis. The first method is as follows:
5,17(20)-pregnadiene-3, 16-diol (Fig 1 , V) is the key intermediate in the synthesis [WR Benn and RM Dodson, J. Org. Chem. 29, 1142 (1964)]. The reduction of a p-unsaturated carbonyl function of 16-DPA with lithiumaluminumhydride (LAH) yields 5,16-pregnadiene 3, 20-diol (III) which on acid catalyzed allylic rearrangement produces the key intermediate IV. The oxidation of IV yields guggulsterone.
However, the process has many drawbacks. During the process of reduction, a by-product through 1,4-hydride addition is always inevitable (to the extent of 40%) and hence a chromatographic separation is required. The slight impurity of this product will contaminate the final product with progesterone after oxidation on the other hand, use of pyrrophoric and inflammable reagents like LAH and solvent ether at industrial scale is also a cause of reluctance for industrial production [W.R. Benn, J. Org. Chem. 28, 3557
The alternate process is as follows:
The unsaturated carbonyl function of 16-DPA is converted to 16,17-epoxy carbonyl followed by Kishner reduction-elimination under Huang-Minion condition yields the key intermediate (Fig 2). However, this procedure is also not suitable for large-scale preparation because of simultaneous formation of pyrazole, a by-product in appreciably high yields.
The epoxidaiton with hydrogen peroxide is not reproducible instead a Michael addition product is obtained as a by-product in reported conditions. Also because of the supply of hydrogen perioxide of variable strength, it is difficult to fix the reaction parameters.
The main object of the invention is to provide an improved process for the preparation of Guggulsterones.
Another object of the invention is to provide a process using an oxidant hydrogen periode on solid supports which provide the reagent at the reaction site in high concentrations.
Yet another object of the invention is to provide the process in which no side product is product.
Accordingly the present invention provides an improved process for the preparation of Guggulsterones a pharmacologically active constituent of gugulipid which
comprises epoxidation of 16-dihydropegnenolone acetate (16 DP A) characterized in
that by reacting the 16-dihydropregenolone acetate with hydrogen peroxide-reagent
adduct in the presence of a co-base in a polar solvent to obtain 3 P hydroxyl-16 a, 17-
oxido-5- pregnen-20 -one , converting 3 P hydroxyl-16 a, 17-oxido-5-pregnen-20 -
one by reacting with hydrazine in the presence of a strong base at a refluxing
temperature ranging between 100-130°C to obtain 5, 17-(20)-cis and trans
pregnadinene-3p hydroxyl-16-diol, followed by oxidation with known reagents to
obtain the desired guggulsterones, a mixture of trans-and cis-4,17(20), pregnadiene-
3,16 dione of the formula la and Ib of the accompanying drawing.
In an embodiment of the invention the hydrogen peroxide-regent adduct used may be
selected from hydrogen perioxde-urea adduct and hydrogen peroxide-sodium carbonate
In another embodiment of the invention the co-base used may be selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide and phase transfer catalyst.
In yet another embodiment of the invention wherein the polar solvent used may be selected from methanol, ethanol and the mixture thereof.
In further embodiment of the invention the strong base used may be selected from the group consisting of trialkylamines, substituted amidines, guanidine potassium tertiarybutaoxide, alkalimetal-hexadimethylisilazane and lithiumdiisopropylamide.
The present inventors therefore have made extensive research related to these problems. As a result, we analyzed the reactions very carefully to sort out the problems. The cause of sluggish epoxidation is the low percentage of oxidizing entity. We therefore
used hydrogen peroxide on solid support in order to provide the reagent at the reaction site in high concentrations.
The analysis of the mechanism of rearrangement reaction is depicted in Fig. 3, which suggests the intermediacy of hydrazone. There are two possible courses of reactions for hydrazone to undergo in subsequent step. In the first mode of reaction, the nucleophilic ring opening by nitrogen will provide pyrazole after aromatization. In the second mode, abstraction of a proton under the basic influence of hydrazine will generate N-anion, which may either stabilize itself through resonance to another intermediate diazo or proceed for cyclization. However, it will not go for cyclization mode because in cyclization mode electron pair will rest on oxygen atom whereas in diazo intermediacy mode it will rest on carbon. Since carbon anion is more basic than oxygen anion and hence proton will prefer to stay at carbon anion. The cyclization therefore should not prefer. The reaction from B to D is also not possible according to Baldwin's rule of cyclization. Hence, once the proton is abstracted fast, the by-product should not appear. (Figure Removed)
Figure - 3
However, the abstraction of the first proton by hydrazine base (where N atom has sp3 hybridization) from the nitrogen atom of some hybridization (sp3) is not a favourable proposition. As a result both the possible mode of reaction will be operating to yield mixture of products.
The present invention therefore relates with the use of base of higher pka value than hydrazine (A pka) for rearrangement of epoxy hydrazone (generated in situ).
According to the present invention, a process for producing gugulsterone was improved to a large extent and with good efficiency as compared with the process disclosed by Benn, W.R. et al. in their publication [The synthesis and stereochemistry of isomeric 16-hydroxy-17 (20)-pregnenes, J. Org. Chem. 29: 1142-48 (1963)].
The compound obtained according to the process of the present invention is very useful as hypolipidemic and antioxidant agent. It can also be admixed with guglip and other hypolipidemic agents.
The following example is given by way of explaination and should not construed the scope of the invention.
Example Step. 1: Preparation of 16 a, 17-oxido-5-pregnen-20-one of the formula (VI)
16-Dehydropregnenolone acetate (35 g) is suspended in methanol (500 ml). The solution is treated, after cooling to 5° C with 4N NaOH (8.9gm in 50 ml F^O) followed by immediately with hydrogen peroxide urea adduct (UHP, 18g,). The mixture is then stored in the refrigerator at 5°C for 72. hr. The reaction mixture is shaken intermittently. The reaction mixture is poured into 500 ml. of ice water. The product is isolated by centrifugation after wash up with water till neutrality to pH paper. The product is dried (63.Og, 97%) M.P. 187-90 (lit 187-90°).
'H-NMR (CDC13): 8 5.3 (m, IH, olefmic proton), 3.67 (s, 'H, CI6-H), 3.5 (m, 'H, C3-H), 2.0 (s, 3H, CH3CO); 1.2 and 1.0 (2s, 3H each, C,8Me, Ci9Me).
Step 2: Preparation of 5.17(20)-cis and trans pregnadiene -3B. -16 -diol. of the formula (V)
A suspension of 3ß-hydroxy-16a, 17-oxido-5-pregnen-20-one (10 gm) in hydrazine (anhydrous, 100 ml), lithiumhexamethyldisilazane (10 ml, IMol Sol) was brought slowly to reflux temperature (100-120°C) under stirring and protection of outlet with calcium chloride tube. The reaction was run till evolution of nitrogen (3-4 hrs) and then allowed to
cooling to room temperature . The reaction mixture was poured into ice water and product filtered and dried. Yield (9.0g, 90 %).
'H-NMR (CDC13):'65.4 (m, 'H, olefmic H), 4.8 (m, 'H, olefinic H) 3.5 (m, 'H, C-3 H) Step 3: Preparation of guggulsterone of the formula (Ia,b)
Diol V on oxidation with known reagents can be converted to the required product guggulstrone. The details are given below:
A three neck 2 It R.B. flask immersed in oil bath, is equipped with nitrogen inlet, mechanical stirrer and condenser with a device to remove some solvent during the course of reaction. The assembly is protected from moisture with calcium chloride guard tube. The flask is then charged with toluene (1200 ml) and started distillation of a portion of toluene in order to dry the system by azeotropic distillation. Then diol (30g) and cyclohexanone (120 ml) are added to the flask. After an additional 50ml of toluene has been distilled, aluminium isopropoxide (15g) is added and toluene is kept on distilling dropwise till the reaction is complete so that about 600ml of tolune has distilled. An additional 300 ml of tolune is distilled and then reaction is brought to room temperature. 400 ml of a saturated solution of NaK tartarate is added to the mixture and the organic layer becomes clear and orange. The nitrogen inlet is then removed and reaction was steam distilled to remove cyclohexanone. The reaction mixture is then cooled to room temperature and separated oil is extracted with ethyl acetate. Organic solution is then dried (Naa 864) and solvent removed. The residual Oil is chromatographed over flash silica gel column using hexane, toluene and ethyl acetate. The yield is 61% white amorphous powder having melting point 150-54° C.
1. An improved process for the preparation of Guggulsterones a pharmacologically
active constituent of gugulipid which comprises epoxidation of 16-
dihydropegnenolone acetate (16 DPA) characterized in that by reacting the 16-
dihydropregenolone acetate with hydrogen peroxide-reagent adduct in the
presence of a co-base in a polar solvent to obtain 3 p hydroxyl-16 a, 17-oxido-5-
pregnen-20 -one , converting 3 p hydroxyl-16 a, 17-oxido-5-pregnen-20 -one by
reacting with hydrazine in the presence of a strong base at a refluxing temperature
ranging between 100-130°C to obtain 5, 17-(20)-cis and trans pregnadinene-3p
hydroxyl-16-diol,followed by oxidation with known reagents to obtain the desired
guggulsterones, a mixture of trans-and cis-4,17(20), pregnadiene-3,16 dione of
the formula la and Ib of the accompanying drawing.
2. A process as claimed in claim 1, wherein the hydrogen peroxide-reagent adduct
used is selected from hydrogen peroxide-urea adduct and hydrogen peroxide-
sodium carbonate adduct.
3. A process as claimed in claims 1,2 wherein the co-base used is selected from the
group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide
and phase transfer catalyst.
4. A process as claimed in claims 1,3, wherein the polar solvent used is selected
from methanol, ethanol and the mixture thereof.
5. A process as claimed in claims 1-4, wherein the strong base used is selected from
the group consisting of trialkylamines, substituted amidines, guanidine potassium
tertiarybutaoxide, alkalimetal-hexadimethylsilazane and lithiumdiisopropylamide.
6. An improved process for the preparation of Guggulsterones a pharmacologically
active constituent of gugulipid substantially as herein described with reference to
|Indian Patent Application Number||780/DEL/2001|
|PG Journal Number||01/2009|
|Date of Filing||20-Jul-2001|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG NEW DELHI- 110 001|
|PCT International Classification Number||C07J13/00|
|PCT International Application Number||N/A|
|PCT International Filing date|