Molybdenum-Catalyzed Asymmetric Amination of α-Hydroxy Esters: Synthesis of α-Amino Acids

Unnatural α-amino acids are found in a wide variety of bioactive compounds ranging from proteins to pharmaceutical agents to materials science. As a result, the investigation of efficient and simple methods for their synthesis is a major purpose in reaction development. In this study, it is found that a catalyst based on molybdenum, an earth-abundant transition metal, can facilitate the amination of readily accessible α-hydroxy esters to afford N-protected unnatural α-amino acid esters in high yield. This simple process also enables enantioselective amination, which proceeds through cooperative catalysis of chiral molybdenum complex with chiral phosphoric acid (CPA), and complements earlier procedures to the catalytic synthesis of this important class of compounds. The obtained protected α-amino acid ester products are directly useful or further utilized for the synthesis of commercially available drugs and analogs.