5′-Fluoro-5′-deoxyinosine (5′-FDI) is identified as an adventitious side product that accumulates in cell free incubations of SAM and fluoride ion in Streptomyces cattleya. 5′-FDI was identified by a combination of isotopic labelling studies and co-synthesis studies as well as enzymatic degradation. Although it is an efficiently generated end product of the cell free incubations, 5′-FDI is not a biosynthetic intermediate and it does not accumulate as a fluorometabolite with fluoroacetate and 4-fluorothreonine in whole cell incubations of S. cattleya. Clearly the purine deaminase which converts 5′-fluoro-5′-deoxyadenosine (5′-FDA) to 5′-FDI in the cell free extract does not come into contact with 5′-FDA in whole cells, suggesting some level of compartmentalisation in cells of S. cattleya. The biotransformation of 5′-FDI from fluoride ion extends the range of organofluorine products, beyond biosynthetic intermediates, that can be generated by this system, for applications such as enzymatic labelling with fluorine-18 for positron emission tomography applications. (c) 2005 Elsevier Inc. All rights reserved.