Synthesis of α‑Amino Acid Derivatives and Peptides via Enantioselective Addition of Masked Acyl Cyanides to Imines

ABSTRACT: A general, asymmetric synthesis of amino acid derivatives is reported. Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective additions to N-Boc-aldimines. The re-actions are catalyzed by a modified cinchona alkaloid, which can function as a bifunctional, hydrogen bonding catalyst, and afford adducts in excellent yields (90−98%) and high enantioselectivities (up to 97.5:2.5 er). Unmasking the addition products gives acyl cyanide intermediates that are intercepted by a variety of nucleophiles to afford α-amino acid derivatives. Notably, the methodology provides an alternative method for peptide bond formation. Constituting the structural basis of peptides and proteins,α-amino acids continue to be at the forefront of chemical synthesis research.1 The prevalence of natural and unnatura