Total synthesis of apios isoflavones and investigation of their tyrosinase inhibitory activity

Abstract Apios isoflavone glucosides 1 and 2 were synthesized for the first time via Friedel–Crafts reaction, Bischler–Napieralski-type cyclization, and phase-transfer catalyzed glycosylation as the key steps. In addition, aglycones 4 and 5 and related natural isoflavone cajanin (6) were synthesized in short steps. Evaluation of the inhibitory activity of these compounds toward tyrosinase indicated that all the compounds were active. In particular, the half-maximal inhibitory concentration of compound 1 toward tyrosinase was measured to be 729 μM.