Enzymatic Fluorination in Streptomyces cattleya Takes Place with an Inversion of Configuration Consistent with an S N 2 Reaction Mechanism

The stereochemical course of the recently isolated fluorination enzyme from Streptomyces cattleya has been evaluated. The enzyme mediates a reaction between the fluoride ion and S ‐ adenosyl‐ L ‐methionine (SAM) to generate 5′‐fluoro‐5′‐deoxyadenosine (5′‐FDA). Preparation of (5′ R )‐[5‐ 2 H 1 ]‐ATP generated (5′ R )‐[5‐ 2 H 1 ]‐5′‐FDA in a coupled enzyme assay involving SAM synthase and the fluorinase. The stereochemical analysis of the product relied on 2 H NMR analysis in a chiral liquid‐crystalline medium. It is concluded that the enzyme catalyses the fluorination with an inversion of configuration consistent with an S N 2 reaction mechanism.