Sitagliptin is the first new anti-diabetic drug in DPP-IV inhibitor class. The general synthesis of sitagliptin is by coupling of the b-amino acid fragment with the heterocycle fragment. Though the specific b-amino acid can be easily made from the corresponding R-amino acid by Arndt-Eistert homologation, the optically pure precursor R-amino acid is difficult to prepare.We herein reported a practical protocol to make the trifluorophenyl substituted R-amino acid 4 in>99.9% ee and 40.3% yield by the enzymatic resolution employing enantioselective hydrolysis and a general separation procedure. This protocol requires only cheap starting materials and friendly reaction condition. The procedure not only allows people to prepare the drug substance, but also provides an alternative method for prepareing the rare a-amino acid and the subsequent b-amino acid.