5â²-Deoxy-5â²-fluoroadenosine is the first step in the biosynthesis of organic fluorides. It is synthesized by the fluorinase catalyzed addition of a fluoride ion to S-adenosyl-<small>L</small>-methionine, releasing <small>L</small>-methionine as a by product. Purine nucleoside phosphorylase mediates a phosphorolytic cleavage of the adenine base to generate 5-fluoro-5-deoxy-<small>D</small>-ribose-1-phosphate.