An Enantioselective Hydrogenation of an Alkenoic Acid as a Key Step in the Synthesis of AZD2716

A classical resolution of a racemic carboxylic acid through salt formation and an asymmetric hydrogenation of an α,β-unsaturated carboxylic acid were investigated in parallel to prepare an enantiomerically pure alkanoic acid used as a key intermediate in the synthesis of an antiplaque candidate drug. After an extensive screening of rhodium- and ruthenium-based catalysts, we developed a rhodium-catalyzed hydrogenation that gave the alkanoic acid with 90% ee, and after a subsequent crystallization with (R)-1-phenylethanamine, the ee was enriched to 97%. The chiral acid was then used in sequential Negishi and Suzuki couplings followed by basic hydrolysis of a nitrile to an amide to give the active pharmaceutical ingredient in 22% overall yield.