Nonproteinogenic amino acids: an efficient asymmetric synthesis of (S)-(−)-acromelobic acid and (S)-(−)-acromelobinic acid

An efficient synthesis of (S)-(−)-acromelobic acid () and (S)-(−)-acromelobinic acid () is described via asymmetric hydrogenation protocol. Asymmetric hydrogenation of dehydroamino acid derivative using (R,R)-[Rh(DIPAMP)(COD)]BF4 catalyst followed by removal of the protective groups afforded (S)-(−)-acromelobic acid () in >98% ee. The key intermediate was prepared from citrazinic acid (). The dehydroamino acid derivative required for the synthesis of was prepared from 2,5-lutidine (), which upon hydrogenation using (S,S)-[Rh(Et-DuPHOS)(COD)]BF4 catalyst afforded in 93% yield and >96% ee. Removal of protective groups in afforded (S)-(−)-acromelobinic acid () in good overall yield.