Potamopholide, a New Sesquiterpene Lactone From Vernonia potamophila

A new sesquiterpene lactone, named potamopholide, was isolated along with the known triterpene lupeol from the leaves of Vernonia potamophila. The stereochemical structure of the new compound, (3R*,4S*,5E,8S*,10S*)-3,8-epoxy-3,4,13-trihydroxy-1-oxogermacra-5,7(11)-dien-6,12-olide, was elucidated by mass spectrometric (CIMS, EIMS, HREIMS) and NMR spectroscopic (HMQC, HMBC, NOESY) analyses and by comparison with closely related compounds. The analysis was confirmed by MM+ geometry optimisation of the conformational structure. This 3,8-O-bridged 10-membered ring hemiacetal seems to be related structurally to known 1,4-O-bridged compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)