Base-mediated decomposition of a Mannose triflate during the synthesis of 2-deoxy-2-18F-fluoro-d-glucose

The effect of potassium carbonate, potassium bicarbonate and potassium fluoride on the base-mediated decomposition of 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulphonyl-β-d-mannopyranose (I) during the synthesis of 2-deoxy-2-18F-fluoro-d-glucose (2-18FDG) was investigated using 19F-NMR. It has been shown that the addition of KF, K2CO3 or KHCO3 to solutions of I in acetonitrile containing 2,2,2-crypt resulted in the elimination of trifluoromethane-sulphonate anion from I presumably by an E2 mechanism. It has also been shown that the substitution of triflate by [18F]fluoride is 90% complete in less than a minute when preparation of the dry [18F]fluoride and the subsequent nucleophilic fluorination is done using a domestic microwave oven. Using the modified method the average yield of 2-18FDG after 30 production runs was found to be very reproducible (47 ± 4% at the end of synthesis).