Synthesis of Four-Disulfide Insulin Analogs via Sequential Disulfide Bond Formation.

Naturally occurring, multiple cysteine-containing peptides are a structurally unique class of compounds with a wide range of therapeutic and diagnostic applications. The development of reliable, precise chemical methods for their preparation is of paramount importance to facilitate exploration of their utility. We report here a straightforward and effective approach based on stepwise, sequentially directed disulfide bond formation, exemplified by the synthesis of four-disulfide bond-containing insulin analogs. Cysteine protection consisted of tert-butylthiol (StBu), thiol-trimethoxyphenyl (STmp), trityl (Trt), 4-methoxytrityl (Mmt), S-acetamidomethyl (Acm), and tert-butyl (tBu). This report describes chemistry that is broadly applicable to cysteine-rich peptides and the influence of a fourth disulfide bond on insulin bioactivity.