Sitagliptin synthesis

The disclosure relates to processes for the preparation of enantiomerically enriched -amino acid derivatives such as (-amino esters useful for the synthesis of enantiomerically enriched biologically active molecules such as synthesis of enantiomerically pure sitagliptin and salts thereof, wherein the key step involves the resolution of the racemate with mandelic acid. The preferred embodiment discloses the process comprising the steps of: (a) treating racemic methyl (3RS)-3-amino-4-(2,4,5-trifluorophenyl)butanoate or a derivative thereof with (R)-(-)-mandelic acid or a derivative thereof to obtain enantiomerically enriched methyl (3R)-3-amino-4-(2,4,5-trifluorophenyl)butanoate (R)-(-)mandelate or a derivative thereof; (b) optionally crystallising the enantiomerically enriched methyl (3R)-3-amino-4-(2,4,5-trifluorophenyl)butanoate (R)-(-)-mandelate or the derivative thereof; and (c) dissolving or suspending the enantiomerically enriched methyl (3R)-3-amino-4-(2,4,5-trifluorophenyl)butanoate (R)-(-)-mandelate or the derivative thereof obtained in step (a) or (b) in an organic solvent or water or a mixture thereof, and adjusting the pH of the solution or suspension with a base to obtain enantiomerically enriched methyl (3R)-3-amino-4-(2,4,5-trifluorophenyl)butanoate.