A new and efficient synthesis of unnatural amino acids and peptides by selective 3,3-dimethyldioxirane side-chain oxidation

N-Boc derivatives of Leu, Met, Thr, Trp, and Pro, the properties of which r esemble those of the respective alpha-amino acid residues present in protei ns, rapidly oxidize in the presence of 3,3-dimethyldioxirane to give differ ent products depending on the structure of the oxidizable group in the side chain. A high regioselectivity for the oxygen atom insertion into the gamm a-CH bond of Leu residues with respect to the weaker alpha-CH bond was obse rved. A position selectivity in the oxidation of peptides containing more t han one Leu residue was also found.