Patent ID: 7385076

Claim:
A process for the preparation of (S)-isomer of compound of formula I, wherein R 1 is hydrogen, linear, branched or cyclic lower alkyl, cyclohexyl, allyl, propargyl or benzyl; R 2 is hydrogen, methyl, ethyl or propyl; or R 1 and R 2 together with the nitrogen to which they are attached form a cyclic moiety of three to eight-membered ring, with or without a hetero atom like nitrogen or oxygen; R 3 is hydrogen or lower alkyl; R 4 and R 5 are the same or different and each is a lower alkyl; comprising reacting compound of formula II, wherein R 3 , R 4 and R 5 are as defined above, with compound of formula III, wherein R 1 and R 2 are as defined above, in the presence of a base, and further resolving the compound of formula I to obtain (S)-isomer of compound of formula I, substantially free of R-isomer.