A guaianolide and four melampolides from Melampodium leucanthum

The aerial parts of Melampodium leucanthum from central Texas afforded a new guaianolide dilactone, which was named austinolide. Its structure was determined by spectral methods and the molecular structure was established by single crystal X-ray diffraction. In addition, two new 4 beta H-dihydrogermacranolides, 4-epimelnerins A and B, and two new melampolides, 3 alpha-hydroxyenhydrin and 9-desacetoxyleucanthinin, were isolated. The aerial parts of a mountain population of M. leucanthum from Colorado afforded the known melampolides melampodin A acetate, leucanthin B and leucanthinin as well as 3 alpha-hydroxyenhydrin. Peracid oxidation of leucanthinin provided the 4,5-monoepoxide derivative, the physical data of which were identical with 3 alpha-hydroxyenhydrin. (C) 1997 Published by Elsevier Science Ltd.