Synthesis of Cyclogossine B Using a Traceless Pseudoproline Turn-Inducer

Abstract

The first synthesis of the cyclic octapeptide, cyclogossine B, has been achieved, confirming the reported structure of this natural product. Cyclization of a linear precursor containing a cysteine-derived thiazolidine as a traceless turn-inducer occurred in significantly higher yields than cyclization of the analogous alanine-containing precursor under identical conditions. Deprotection of the thiazolidine followed by desulfurization provided cyclogossine B in good overall yield, indicating that cysteine-derived pseudoprolines can be effectively used as traceless turn-inducers to facilitate the cyclization of small peptides.