Recovery and purification of no-carrier-added [18F]fluoride with bistrimethylsilylsulfate (BTMSS)

Abstract

No-carrier-added trimethylsilyl[18F]fluoride (TMS[18F]F) was rapidly liberated from a variety of dry supports containing unreactive [18F]fluoride by simply heating with neat bistrimethylsilylsulfate. The supports included calcium phosphate, anion exchange resins, alumina, borosilicate and porous carbon beads, to which [18F]fluoride was applied by absorption or evaporation of aqueous solution. TMS[18F]F was evolved essentially free of entrained moisture or excess silylating agent and was efficiently absorbed and rapidly cleaved to free [18F]fluoride ion by 0.1% benzyltrimethylammonium methoxide in anhydrous methanol. Passage of this solution through a strong cation exchange column provided purified hydrogen[18F]fluoride, which was subsequently trapped on a quaternary 4-aminopyridinium resin and used for heterogeneous nucleophilic radiofluorination of 1,3,4,6-tetraacetyl-beta-mannopyranose-2-triflate in 70% yield. The purified [18F]fluoride was also used for solution phase nucleophilic labeling of ethyl [18F]4-fluorobenzoate following addition of K2CO3/Kryptofix and DMSO. This approach provides a simplified way to ensure high reactivity in [18F]fluoride ion from cyclotron targets. It also may be used to salvage active [18F]fluoride ion from insoluble complexes and radiofluorination reaction residues.