title: Structure revision of xanthalongin and further sesquiterpene lactones from flowers of Arnica longifolia.
abstract: In addition to the helenanolide and xanthanolide type sesquiterpene lactones previously isolated from A. longifolia D.C. Eaton, we report on 13 further sesquiterpene lactones (7 helenanolides, 1 xanthanolide, 3 1,5-trans-guaianolides, 1 1,5-cis-guaianolide and 1 eudesmanolide) occurring in the flowerheads of this species. The structure of xanthalongin is revised to a 10beta-methyl configurated xanthanolide on the basis of new NMR spectral evidence. Furthermore, the 1,5-cis-guaianolide 2- O-acetylarnimollin, in contrast with our previous assignment, possesses a 2alpha-O-acyl configuration. A sesquiterpene lactone pattern as diverse as that of A. longifolia consisting of 1,5-trans-guaianolides and pseudoguaianolides (helenanolides), 1,5-cis-guaianolides and xanthanolides as well as eudesmanolides, which are postulated to be derived from three different biogenetic pathways, is particularly remarkable.
authors.affiliation: Institut für Pharmazeutische Biologie der Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany. willuhn@uni-duesseldorf.de
authors.forename: G
authors.initials: G
authors.lastname: Willuhn
authors.forename: A
authors.initials: A
authors.lastname: Skibinski
authors.forename: T J
authors.initials: TJ
authors.lastname: Schmidt