Bombyxin-II and its disulfide bond isomers: synthesis and activity

Bombyxin-II, an insulin superfamily peptide of the silkmoth Bombyx mori, and its disulfide bond isomers have been synthesized by two ways of stepwise, semi-regioselective disulfide bond formation. The disulfide bond CysA20-CysB22 or CysA7-CysB10 was formed first, and then the two other disulfide bonds were formed by iodine oxidation. The conditions for the iodine oxidation were improved to suppress oxidative degradation of unprotected Trp residues. With these conditions, bombyxin-II was synthesized in high yields (26% and 32%). Its disulfide bond isomers were also obtained. Specific activity of the products indicates that the disulfide bond CysA20-CysB22 is important to the bombyxin activity.