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/O₂ 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. Make the change to bio! Biomimetic synthesis of equisetin and (+)-fusarisetinA was achieved based on a biosynthetic hypothesis. An intramolecular Diels-Alder reaction followed by a Dieckmann cyclization of polyenoylamino ester furnished equisetin. The aerobic oxidation of equisetin to give (+)-fusarisetinA was mediated by a Mn^III/O₂ system or reactive oxygen species (ROS) (see scheme).