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.