TOTAL SYNTHESIS OF HUMAN INSULIN BY REGIOSELECTIVE DISULFIDE FORMATION USING THE SILYL CHLORIDE SULFOXIDE METHOD

Total synthesis of human insulin, a two-chain peptide containing three disulfide bonds, was achieved unambiguously by sequential and selective formation of disulfide bonds in the protein for the first time. The key reaction in the synthesis is separate regioselective formation of three disulfide bonds using a silyl chloride method developed by us. Prior to the insulin synthesis, it was confirmed by the syntheses of double-disulfide peptides, conotoxin M1, beta-hANP, and an unnatural parallel dimer of alpha-hANP, that no disulfide exchange occurred during the silyl chloride treatment. Using three orthogonal thiol-protecting groups, Trt, Acm, and t-Bu, the three disulfide bonds of human insulin were efficiently constructed by successive reactions using thiolysis, iodine oxidation, and the silyl chloride method. Each reaction for the stepwise disulfide formation proceeded within 15-60 min with no polymeric product and no solubility problem. The synthetic human insulin had the correct structure and was indistinguishable from natural human insulin.