Stereospecific approach to the synthesis of [18F]2-deoxy-2-fluoro-D-mannose

The reaction of methyl 4,6-O-benzylidene-3-O-benzyl-2-O-trifluoromethanesulfonyl-beta-D- glucopyranoside in acetonitrile at 75 degrees C for 30 min with [18F]tetra-n-butylammonium fluoride, followed by silica gel column chromatographic purification, gave the corresponding [18F]methyl 4,6-O-benzylidene-3-O-benzyl-2-fluoro-beta-D-mannopyranoside with complete regio- and stereoselectivity (42% radiochemical yield). Hydrolysis of the radiolabeled fluoromannopyranoside intermediate with either 6 N HCl or 50% methanesulfonic acid for 30 min at 120 degrees C, followed by purification by column chromatography (ion retardation resin and neutral alumina), gave pure [18F]2-deoxy-2-fluoro-D-mannose ([18F]2-FDM) with an overall radiochemical yield (from [18F]fluoride ion) of 34%. Extension of this methodology to the no carrier added (nca) synthesis under phase transfer conditions (Kryptofix 222/K 18F/acetonitrile) gave nca [18F]2-FDM in a radiochemical yield of 75%. Purity and identity of the fluorinated products were confirmed by 1H and 19F NMR spectroscopy. The synthetic procedure described here permits for the first time the routine preparation of large amounts of [18F]2-FDM for tomographic studies.