On the relative stereochemistry of atomaric acid and related compounds

The stereochemistry at C-3 of the known compounds atomaric acid , 5′a-desmethyl-5′-acetylatomaric acid , and stypoquinonic acid is revised to , , and on the basis of a careful study of 2D NOESY experiments and also from comparison of their 1H and 13C chemical shifts with those of the related metabolites and isolated from Stypopodium zonale. Compound is a novel unusually functionalized 1-keto-5′a-desmethyl atomaric acid derivative whose structure and stereochemistry were determined by spectroscopic means.