Biosynthesis of Guatrypmethine C Implies Two Different Oxidases for exo Double Bond Installation at the Diketopiperazine Ring

Heterologous expression of a silent gene cluster from Streptomyces cinnamoneus led to identification of guatrypmethine C, a guaninylated cyclo-L-Trp-L-Met derivative with two exo double bonds at the diketopiperazine ring. Structural elucidation was achieved using MS, H-1, C-13, and N-15 NMR analyses including H-1-C-13 and H-1-N-15 HMBC. Gene combination and biochemical investigation proved that the formation of the two C=C bonds are catalyzed by two distinct enzyme families (i.e., cyclodipeptide oxidase and Fe-II/2OG-dependent oxygenase).