Biomimetic Synthesis of Equisetin and (+)-Fusarisetin A

(+)-FusarisetinA belongs to a group of acyl tetramic acid natural products that show potential anticancer activity. Equisetin, a biogenetically related acyl tetramic acid, contains the basic skeleton of (+)-fusarisetinA. We proposed that equisetin and (+)-fusarisetinA share a biosynthetic pathway that starts with naturally occurring (S)-serine and an unsaturated fatty acid. In support of this hypothesis, we have demonstrated that a cyclization sequence involving an intramolecular Diels-Alder reaction followed by a Dieckmann cyclization of polyenoylamino acid yielded equisetin. The aerobic oxidation of equisetin, promoted by either Mn-III/O-2 or a reactive oxygen species (ROS) produced by visible-light chemistry, gave peroxyfusarisetin, which could be easily reduced to (+)-fusarisetinA. We report herein detailed information on the biogenetic synthesis of equisetin and (+)-fusarisetinA.