Process for preparation of glucocorticoid steroids

1. A process for the preparation of 16,17-acetals of pregnane derivatives having formula (I)

wherein:

R 1 is H or CH 3 ;

R 2 is C 1 -C 6 linear or branched alkyl, alkynyl group or cycloalkyl group, aryl or heteroaryl group; or

R 1 and R 2 combine to form a saturated or unsaturated C 3 -C 6 cyclic or heterocyclic ring;

R 3 and R 4 are the same or different and each independently represents H or halogen; and

R 5 is —OH or —OCOR wherein R represents H or C 1 -C 6 linear, branched or cyclic alkyl group that is optionally substituted; comprising the steps of:

(i) dihydroxylation of the compound of formula II to obtain the compound of formula III;

(ii) bromination of the compound of formula III to obtain the hydroxylated brominated compound of formula IV;

(iii) debromination of the compound of formula IV to obtain the compound of formula V;

(iv) deacetylation of the compound of formula V to obtain the compound of formula VI;

and

(v) alkylation of the compound of formula VI to obtain the compound of formula I.

2. The process as claimed in claim 1 , wherein in step (i) dihydroxylation of compound of formula (II) is carried out with an oxidizing agent selected from potassium permanganate, potassium dichromate, chromic acid, peroxyacids, formic acid, and sodium metabisulphite, or mixtures thereof, to form a compound of formula (III).

3. The process as claimed in claim 1 , wherein in step (ii) the compound of formula (III) is brominated with a brominating agent selected from dibromantin and N-bromosuccinamide, in presence of organic solvent selected from tetrahydrofuran, acetone, N,N-dimethyl formamide, DMSO, methanol, methylene dichloride, acetonitrile, ethyl acetate, diethyl ether, 1-butanol, methylethyl ketone, 1-propanol, and formamide, to form a compound of formula (IV).

4. The process as claimed in claim 1 , wherein in step (iii) the compound of formula (IV) is debrominated to form a compound of formula (V) in the presence of a catalyst, a thiol compound of formula (VIII), and an aprotic solvent, wherein formula (VIII) is:

R t —SH   Formula VIII

wherein R t is —CH 2 COOH or —CH 2 CH 2 COOH.

5. The process as claimed in claim 4 , wherein the catalyst is selected from chromous or chromium sulfate and chromous or chromium chloride or its hydrate.

6. The process as claimed in claim 4 , wherein the aprotic solvent is selected from DMF, DMAC, acetone, methylene chloride, THF, acetonitrile, DMSO and mixtures thereof.

7. The process as claimed in claim 1 , wherein the compound of formula (VI) is 16α-Hydroxy Prednisolone (16-HPN), wherein C-16 and C-17 is OH.

8. The process as claimed in claim 1 , wherein the compound of formula (VI) is converted to a compound of formula (I) reagents selected from N-butyraldehyde, cyclohexane carboxaldehyde, sodium metabisulphite complex, isobutyryl chloride, acetone, hydrofluoric acid, isopropenyl acetate, dibromantin, select fluor, perchloric acid, 3,3-dimethyl butyryl chloride and triethylamine, or a combination thereof.

9. The process as claimed in claim 1 , wherein the compound of formula (VI) is converted to a compound of formula (I) by treating with N-butyraldehyde and hydrochloric acid such that in the compound of formula (I) thus obtained, R 1 is —H, R 2 is —CH 2 CH 2 CH 3 , and R 5 is —OH.

10. The process as claimed in claim 1 , wherein the compound of formula (I) is obtained as a mixture of epimer A and epimer B, wherein the amount of epimer A is in the range of 54 to 44% w/w.

11. The process as claimed in claim 1 , wherein the compound of formula (VI) is converted to a compound of formula (I) by treating with cyclohexane carboxaldehyde, sodium metabisulphite and isobutyryl chloride, such that in the compound of formula (I) thus obtained R 1 is —H, R 2 is —C 6 H 11 , and R 5 is —OCOCH(CH 3 ) 2 .

12. The process as claimed in claim 1 , wherein the compound of formula (VI) having R 3 and R 4 as H is converted to a compound of formula (I) by treating with acetone and perchloric acid, such that in the compound of formula (I) thus obtained R 1 is —CH 3 , R 2 is —CH 3 , and R 5 is —OH.

13. The process as claimed in claim 1 , wherein the compound of formula (VI) having R 4 as H is converted to a compound of formula (I) by treating with acetone, dibromantin, hydrofluoric acid, such that in the compound of formula (I) thus obtained, R 1 is —CH 3 , R 2 is —CH 3 , R 5 is —OH, R 3 is —F, and R 4 is —H.

14. The process as claimed in claim 1 , wherein the compound of formula (VI) having R 3 and R 4 as H is converted to a compound of formula (I) by treating with acetone, isopropenyl acetate and select fluor, such that in the compound of formula (I) R 1 is —CH 3 , R 2 is —CH 3 , R 5 is —OH, R 3 is —H, and R 4 is —F.

15. The process as claimed in claim 1 , wherein the compound of formula (VI) having R 4 as H is converted to a compound of formula (I) by treating with perchloric acid, dibromantin, hydrofluoric acid and 3,3-dimethyl butyryl chloride such that in the compound of formula (I) thus obtained, R 1 and R 2 are —CH 3 , R 5 is —OH, R 3 is —F, and R 4 is —H.

16. The process as claimed in claim 1 , wherein in step (i) dihydroxylation of the compound of formula (II) is carried out with an oxidizing agent selected from potassium permanganate, formic acid, and sodium metabisulphite, to form the compound of formula (III).

17. The process as claimed in claim 1 , wherein in step (ii) the compound of formula (III) is brominated with dibromatin in presence of tetrahydrofuran to obtain a compound of formula (IV).

18. The process as claimed in claim 4 , wherein the thiol compound is Rt-SH wherein Rt is —CH 2 COOH.

19. The process as claimed in claim 5 , wherein the catalyst is chromium chloride hexahydrate.

20. The process as claimed in claim 4 , wherein the aprotic solvent is selected from DMF, DMSO, and mixtures thereof.