The acyltetramic acid (+)-fusarisetin A, produced by the soil fungus Fusarium sp.FN080326.Biological tests suggest that fusarisetin A holds promise as a valuable anticancer agent.We proposed that equisetin and (+)-fusarisetin A share a biosynthetic pathway starting with naturally occurring (S)-serine and unsaturated fatty acid.In support to this hypothesis, we demonstrated that a cyclization sequence involving an intramolecular Diels-Alder reaction followed by a Dieckmann cyclization of polyenoylamino acid yield equisetin.The aerobic oxidation of equisetin, promoted by either Mn(Ⅲ)/O2 or reactive oxygen species (ROS: superoxide radical anion and singlet oxygen) produced by the visible light chemistry, give peroxyfusarisetin which could be reduced to (+)-fusarisetin A easily.