Structure elucidation of arteannuin O, a novel cadinane diol from Artemisia annua, and the synthesis of arteannuins K, L, M and O

The novel cadinane diol, arteannuin O (1), has been obtained from Artemisia annua and its structure has been established by 2D NMR and X-ray crystallography. A reconstructive synthesis of arteannuin O from artemisinin is described, which also yields the natural products arteannuin K and arteannuin L. Mechanistic considerations have led to the conclusion that the stereochemistry of the 5-hydroxyl group was wrongly assigned when arteannuins K, L and M were first reported as natural products. This was confirmed by derivatization of synthetic arteannuins K, L and M as their Mosher esters.