Isolation and characterization of the sesquiterpene lactones costunolide, parthenolide, costunolide diepoxide, santamarine, and reynosin from Magnolia grandiflora L.

The germacranolide sesquiterpene lactones costunolide, parthenolide, and costunolide diepoxide were isolated from the leaves of Magnolia grandiflora L. Costunolide diepoxide might be, at least in part, an artifact derived from air oxidation of parthenolide. The root bark yielded only costunolide together with the two eudesmanolides, santamarine and reynosin. In an attempt to synthesize costunolide diepoxide, the action of m-chloroperbenzoic acid on parthenolide and on costunolide was studied. The products were costunolide diepoxide from parthenolide and the two cyclized derivatives, santamarine and reynosin, from costunolide. The elusive 1,10-epoxide was obtained by epoxidizing costunolide using a biphasic system containing sodium bicarbonate. Under these conditions, epoxidation of costunolide took place without cyclization.