Oxetane Graft Selectively Insertable into Natural Disulfide

3,3-Bis(bromomethyl)oxetane (1) is chemoselectively inserted into the disulfide bond of peptides under mild conditions and can form stable sulfide bonds. Under mild conditions following reduction of the disulfide bridge with tris(2-carboxyethyl)phosphine, 1 reacts with the free sulfides to afford an oxetane grafted peptide. The obtained peptide shows conformational behavior and biological activity similar to the natural peptide. This reaction can be applied not only to the synthesis of stapled peptides but also to the optimization of pharmacokinetics.