Development of a Practical Large-Scale Synthesis of Denagliptin Tosylate

A large-scale synthesis of denagliptin tosylate has been developed. The efficiency of the synthesis has been improved from the initially scaled route by changing the order of steps (performing a dehydration at a late stage). The key step of the synthesis is a single-step peptide coupling/dehydration, mediated by n-propanephosphonic acid cyclic anhydride. The challenges of developing this synthesis into a robust and practical manufacturing route are described.