C-C Bond Cleavage in the Late-Stage Biosynthesis of Huperzine Alkaloids Occurs via Enzymatic Retro-Aza-Prins Reaction.

The demand for novel enzyme-catalyzed reactions in chemical synthesis has spurred the development of many new-to-nature reactions. Additionally, detailed analysis of biosynthetic pathways can uncover unprecedented chemical/enzymatic mechanisms. In this study, we revisited the catalytic mechanism of the 2-oxoglutarate-dependent dioxygenase Pt2OGD-1, involved in the biosynthesis of huperzine alkaloids. Our experimental and computational investigations uncovered a previously unknown enzymatic C-C bond cleavage in the piperidine ring of the alkaloid scaffold, resembling an oxidative retro-aza-Prins reaction. Here, this transformation is initiated by hydrogen abstraction, followed by electron transfer at the 4-position of the heterocycle, triggering ring opening and finally resulting in the loss of a carbon atom as formaldehyde. This discovery expands the toolbox of reactions, enhances our understanding of these enzymes, and may facilitate their application in the biotechnological production of pharmaceutically relevant alkaloid scaffolds as well as the development of biocatalysts with similar activities.