Synthesis of (R)-3-(tert-Butoxycarbonylamino)-4-(2,4,5-trifluorophenyl)butanoic Acid, a Key Intermediate, and the Formal Synthesis of Sitagliptin Phosphate.

An alternate formal synthesis of Sitagliptin phosphate is disclosed from 2,4,5-trifluorobenzadehyde in 8 linear steps with an overall yield of 31%. The chiral β-amino acid moiety present in sitaglitpin is installed via an asymmetric hydrogenation followed by a stereoselective Hofmann rearrangement as the key steps. The key chiral intermediate Boc-amino acid 1 prepared by this novel route was further converted to Sitagliptin phosphate following the known literature protocol.