On the Synthesis of Stereocalpin A: Partial Retraction/Correction of Previous Results and Rationalization of the Hidden Difficulties

Abstract

In continuation/checking of a previous synthesis directed toward the literature structure of stereocalpin A it was found that the data for a substantial part of the intermediates reported before were incorrect. Some of the transformations were not successfully reproduced and the failures were shown to be consequences of the presence of the N-Me and the particular location of the ester linkage. The origins of the "extra/minor" signals in the NMR for most of the intermediates, which tend to be mistaken as signs for the presence of impurity/isomers, are also discussed.

Total Synthesis and Stereochemical Revision of Stereocalpin A: Mirror-Image Approach for Stereochemical Assignments of the Peptide–Polyketide Macrocycle

“…There have been several synthetic studies on stereocalpin A and the stereoisomers . The first total synthesis of the proposed structure 1a of stereocalpin A was achieved by Ghosh et al In their initial investigation, macrocyclization was attempted at site B, which resulted in complete epimerization at the precursor C-terminal Phe to give 11- epi -stereocalpin A 1x with d -Phe (Figure , eq 1) .…”