Isolation and Identification of Dihydroartemisinic Acid Hydroperoxide fromArtemisia annua:  A Novel Biosynthetic Precursor of Artemisinin

Dihydroartemisinic acid hydroperoxide (2) was isolated for the first time as a natural product from the plant Artemisia annua in a 29% yield. Its structure was identified by (1)H and (13)C NMR spectroscopy. Compound 2 is known as an intermediate of the photochemical oxidation of dihydroartemisinic acid (1) leading to artemisinin (3). The presence of 1 and 2 in the plant and the conditions under which 1 can be converted into 2, which can very easily oxidize to 3, provide evidence for a nonenzymatic, photochemical conversion of 1 into 3, in vivo, in the plant.