An Unusual Oxidative Rearrangement Catalyzed by a Divergent Member of the 2‐Oxoglutarate‐Dependent Dioxygenase Superfamily during Biosynthesis of Dehydrofosmidomycin

Abstract

The biosynthesis of the natural product dehydrofosmidomycin involves an unusual transformation in which 2‐(trimethylamino)ethylphosphonate is rearranged, desaturated and demethylated by the enzyme DfmD, a divergent member of the 2‐oxoglutarate‐dependent dioxygenase superfamily. Although other members of this enzyme family catalyze superficially similar transformations, the combination of all three reactions in a single enzyme has not previously been observed. By characterizing the products of in vitro reactions with labeled and unlabeled substrates, we show that DfmD performs this transformation in two steps, with the first involving desaturation of the substrate to form 2‐(trimethylamino)vinylphosphonate, and the second involving rearrangement and demethylation to form methyldehydrofosmidomycin. These data reveal significant differences from the desaturation and rearrangement reactions catalyzed by other family members.

Substrate-Dependent Mechanism Switch in the Desaturation Reactions of the Mononuclear Nonheme Iron Enzyme PtlD

“…29 In the context of desaturation reactions between nonactivated carbons, NHFe/α-KG enzymes play a crucial role in breaking two inert C−H bonds. According to the consensus mechanistic models in NHFe/α-KG enzyme desaturation reactions, 6,27,30 three potential pathways have been outlined to depict the removal of the second hydrogen (Scheme 1C). Pathway (a) involves an Fe III −OH intermediate abstracting the second hydrogen, resulting in radical recombination and olefin formation.…”

“…In addition, recent findings have expanded our understanding as an increasing number of reactions without a lone-pair-bearing α-heteroatom assistance have been reported. These cases include the desaturation reactions catalyzed by PenD in the pentalenolactone biosynthesis (Scheme B), CAS (also known as CS2) in clavaminate biosynthesis, , BcmF in the bicyclomycin biosynthesis, SptF and AndF in meroterpenoids biosynthesis, , DfmD in dehydrofosmidomycin biosythesis, PhrA in berkeleydione biosynthesis, , and AusE in preaustinoid A3 biosynthesis , and the VioC reaction with the non-natural substrate l -homoarginine . Computational studies on VioC, CAS, flavonol synthase, and carbapenem synthase (CarC) , have suggested that the radical recombination proposal [Scheme C, pathway (a)] could also be employed to overcome the barriers.…”