STRUCTURE REVISION OF XANTHALONGIN AND FURTHER SESQUITERPENE LACTONESFROM FLOWERS OF ARNICA-LONGIFOLIA

In addition to the helenanolide and xanthanolide type sesquiterpene la ctones previously isolated from A. longifolia D.C. Eaten, we report on 13 further sesquiterpene lactones (7 helenanolides, 1 xanthanolide, 3 1,5-trans-guaianolides, 1 1,5-cis-guaianolide and 1 eudesmanolide) oc curring in the flowerheads of this species. The structure of xanthalon gin is revised to a 10 beta-methyl configurated xanthanolide on the ba sis of new NMR spectral evidence. Furthermore, the 1,5-cis-guaianolide 2-O-acetylarnimollin, in contrast with our previous assignment, posse sses a 2 alpha-O-acyl configuration. A sesquiterpene lactone pattern a s diverse as that of A, longifolia consisting of 1,5-transguaianolides and pseudoguaianolides (helenanolides), 1,5-cis-guaianolides and xant hanolides as well as eudesmanolides, which are postulated to be derive d from three different biogenetic pathways, is particularly remarkable .