On the relative stereochemistry of atomaric acid and related compounds

The stereochemistry at C-3 of the known compounds atomaric acid 2a, 5'a-desmethyl-5'-acetylatomaric acid 4a, and stypoquinonic acid 5a is revised to 2, 4, and 5 on the basis of a careful study of 2D NOESY experiments and also from comparison of their H-1 and C-13 chemical shifts with those of the related metabolites 6 and 7 isolated from Stypopodium zonale. Compound 7 is a novel unusually functionalized 1-keto-5'a-desmethyl atomaric acid derivative whose structure and stereochemistry were determined by spectroscopic means. (C) 2003 Elsevier Science Ltd. All rights reserved.