Assay for the Enantiomeric Analysis of [²H₁]-Fluoroacetic Acid: Insight into the Stereochemical Course of Fluorination during Fluorometabolite Biosynthesis in Streptomyces cattleya

A sensitive method for the configurational analysis of (R)- and (S)-[H-2(1)]-fluoroacetate has been developed using H-2{H-1}-NMR in a chiral liquid crystalline solvent. This has enabled biosynthetic experiments to be conducted which reveal stereochemical details on biological fluorination occurring during the biosynthesis of fluoroacetate and 4-fluorothreonine in the bacterium Streptomyces cattleya. In particular, feeding experiments to S. cattleya with isotopically labeled (1R, 2R)- and (1S, 2R)-[1-H-2(1)]-glycerol 3d and 3e and [2,3-H-2(4)]-Succinate 4a gave rise to samples of enantiomerically enriched [2-H-2(1)]-fluoroacetates 1a. The predominant enantiomer resulting from each experiment suggests that the stereochemical course of biological fluorination takes place with an overall retention of configuration between a glycolytic intermediate and fluoroacetate 1. Consequently, this outcome suggests that the stereochemical course of the recently identified fluorinase enzyme which mediates a reaction between fluoride ion and S-adenosyl-L-methionine (SAM), occurs with an inversion of configuration.