This paper reports a novel catalyst-free method for synthesizing unnatural α-amino acids and peptide macrocycles using visible light. The method exploits the homolytic cleavage of the pyridinium C-N bond in Katritzky salts, promoted by ionic compounds and visible light, to generate alkyl radicals. These radicals then participate in deaminative hydroalkylation reactions with various alkenes, including dehydroalanine, to yield β-alkyl-substituted unnatural amino acids. The method is also successfully applied to the deaminative cyclization of peptide N-terminals, forming peptide macrocycles. The use of Et3N or PPh3 as reductants and H2O as a hydrogen source offers practical advantages.
