Indole Diketopiperazine Dimerization Catalyzed by Dye-Decolorizing Peroxidases via Hydroxyl-to-Carbon Radical Relay

This is the authors' abstract. We don't add key points for this paper.

Indole diketopiperazine (DKP) alkaloids constitute an important class of fungal natural products with diverse biological activities. Although dimeric indole DKPs have been isolated from natural sources and often exhibit enhanced bioactivities compared with their monomeric counterparts, enzymatic dimerization of indole DKPs remains rare and mechanistically poorly understood. Here, we investigate the enzymatic dimerization of 6-hydroxy-deoxybrevianamide E (6-OH-DoE), an indole DKP intermediate selected based on reports of naturally occurring dimeric derivatives. In vitro assays revealed that dye-decolorizing peroxidases (DyPs) catalyze the regioselective dimerization of 6-OH-DoE, affording di-6-OH-DoE through exclusive C7–C7′ coupling on the indole moiety. Combined experimental and computational analyses indicate that the reaction proceeds through a hydroxyl-to-carbon radical relay pathway, initiated by oxidation of the indole hydroxyl group, followed by intramolecular radical transfer to the C7 position, rather than direct C–H hydrogen-atom abstraction. This mechanistic proposal was further validated by substrate analogue studies and radical-probing experiments. Furthermore, a homologous DyP enzyme from the native producer was shown to catalyze the same transformation. Collectively, this study elucidates the enzymatic mechanism of indole DKP dimerization and expands the catalytic repertoire of DyP peroxidases, highlighting their potential as biocatalysts for regioselective radical-mediated C–C bond formation in indole DKP scaffolds.