Naupliolide, a sesquiterpene lactone with a novel tetracyclic skeleton from Nauplius graveolens subsp odorus

The aerial parts of Nauplius graveolens subsp. odorus (Schousb) Wikl. afforded a novel sesquiterpene lactone (1) named nauptiolide together with the known 6,7,9,10-tetradehydroasteriscanolide 2 and asteriscunolides A-D 3a-d. The structure of compound I corresponds to a novel skeleton of 14,15-dimethyl-7,13-dioxotricyclic[6.4.0.0(9,11)]dodeca-12,13-olide, and was established on the basis of spectroscopic methods including 2D-NMR. The coexistence of nauptiolide 1 together with the structurally related sesquiterpene lactones asterisculolides A-D (3a-d) and 6,7,9,10-tetradehydroasteriscanolide 2, seems to indicate their biosynthetic relationship. (c) 2006 Elsevier Ltd. All rights reserved.