Synthesis of sitagliptin phosphate 1, a novel DPP-IV inhibitor for the treatment of type 2 diabetes mellitus has been accomplished starting from chiral synthon (1,4-bis[(R)-1-phenylethyl]piperazine-2,5-dione) 2, involving high stereocontrolled (>98%) alkylation as a key step, in a good overall yield of 50% over six steps.
