Supplemental Observations on Atropisomerism of Fungal Bis(naphtho-y-pyrone)s

Abstract

Epimerization reactions of bis(naphtho-y-pyrone) derivatives, ustilaginoidin A (2) and dihydroisoustilaginoidin A (6), were examined by refluxing the compounds in acetic acid and in p-xylene. The epimerization occurred in acetic acid but not in p-xylene. From the reaction mixture in the case of dihydroisoustilaginoidin A, the starting material and the epimer at the biaryl linkage, dihydroustilaginoidin A (7), were isolated and characterized. The circular dichroism Cotton effects due to chiral exciton coupling of biaryl compounds is discussed. © 1990, The Pharmaceutical Society of Japan. All rights reserved.