Cytochrome P450 as Dimerization Catalyst in Diketopiperazine Alkaloid Biosynthesis

Since dimeric natural products frequently exhibit useful biological activities, identifying and understanding the mechanism of dimerization is of great interest. One such compound is (–)-ditryptophenaline isolated from Aspergillus flavus that inhibits substance P receptor for potential analgesic and anti-inflammatory activity. Through targeted gene knockout in A. flavus and yeast heterologous gene expression, we determined for the first time the gene cluster and pathway for the biosynthesis of a dimeric diketopiperazine alkaloid. We also identified that a single cytochrome P450 DtpC is responsible for not only pyrroloindole ring formation but also concurrent dimerization of the N-methylphenylalanyltryptophanyl diketopiperazine monomers into a homodimeric product. Furthermore, DtpC exhibits relaxed substrate specificity, allowing the formation of two new dimeric compounds from a non-native monomeric precursor, brevianamide F. A radical-mediated mechanism of dimerization is proposed.