Evolution of a Manufacturing Route to Omarigliptin, A Long-Acting DPP-4 Inhibitor for the Treatment of Type 2 Diabetes

Development of a convergent synthesis of omarigliptin (MK-3102) suitable for commercial manufacture is described. The target molecule is assembled through a diastereoselective reductive amination of a highly functionalized pyranone with a mesylated pyrazole followed by deprotection of a Boc group. The synthesis of the pyranone relies on three Ru-catalyzed reactions: (1) a DKR reduction of a rac-α-aminoketone to set the two contiguous stereogenic centers, (2) a cycloisomerization of a bis-homopropargylic alcohol to a dihydropyran, and, finally, (3) a Ru-catalyzed oxidation of a pyranol to the desired pyranone. The regioselective synthesis of a N-Boc-1-mesyl pyrazole fragment was achieved via base-promoted mesyl group isomerization to afford 30:1 selectivity. A highlight of the endgame process development is telescoping a Boc deprotection and reductive amination followed by direct crystallization of the penultimate from the reaction mixture. This avoids handling of an unstable, mutagenic 1-mesylpyrazole BSA salt used in the earlier multikilogram deliveries and improves the overall diastereoselectivity and efficiency of the route.