Natural Pseudoguaianolides Prepared from Damsin

Damsin (1) is a pseudoguaianolide sesquiterpene possessing potent biological activities, reported as a metabolite of several medicinal plants belonging to the genus Ambrosia together with related compounds. Starting from 1, which can be isolated in good amounts from Ambrosia arborescens, the five natural pseudoguaianolides ambrosin (2), isodamsin (3), 3 alpha-hydroxydamsin (4), 3 alpha-acetoxydamsin (5), and 11 beta,13-dihydrodamsin (8) were prepared by regio- and stereo-selective synthetic modifications.