Domino Process Achieves Site-Selective Peptide Modification with High Optical Purity. Applications to Chain Diversification and Peptide Ligation

The development of peptide libraries by site-selective modification of a few parent peptides would save valuable time and materials in discovery processes but still is a difficult synthetic challenge. Herein, we introduce natural hydroxyproline as a convertible unit for the production of a variety of optically pure amino acids, including expensive N-alkyl amino acids, homoserine lactones, and Agl lactams, and to achieve the mild, efficient, and site-selective modification of peptides. A domino process is used to cleave the customizable Hyp unit under mild, metal-free conditions. Both terminal and internal positions can be modified, and similar customizable units can be differentiated. The resulting products possess two reactive chains which can be manipulated independently. The versatility and scope of this process is highlighted by its application to the ligation of two peptide chains, and the generation of peptides with several chains and peptides with conformational restrictions.