A Concise Synthesis of (S)-ESBA, the First Selective KATII Inhibitor and Their Analogs

A straightforward preparation of enantiomerically highly enriched N-substituted (S)-4-(ethylsulfanyl)benzoylalanine will be presented. This process involves the tandem of crystallization-induced asymmetric transformation (CIAT) with conjugate addition of N-nucleophiles to the corresponding aroylacrylic acids and their oxidized analogs. Further transformations to (S)-4-(ethylsulfanyl)benzoylalanine, (S)-4-(ethylsulfoxide)benzoylalanine and (S)-4-(ethylsulfonyl)benzoylalanine via periodate oxidation are also described. The targeted amino acid (S)-4-(ethylsulfonyl)benzoylalanine (S)-ESBA is the first selective kynurenine aminotransferase (KAT II) inhibitor.