Sesquiterpene Lactones of Hymenoxys insignis. X-ray Analyses of Hymenograndin and Hymenosignin

Article abstract of DOI:10.1021/jo01291a024

Hymenoxys insignis yielded the new guaianolide hymenosignin (2) and the new helenanolide acetylhymenograndin (3b).The structures were established by physical methods.These included X-ray analyses of 2 and hymenograndin (3a), whose previously postulated stereochemistry at C-2 and C-3 was found to require revision.Conformations of the various compounds and their bearings on the CD curves of substances related to 3a,b are discussed, and a suggestion is made to account for the co-occurrence of hymenosignin and acetylhymenograndin.