FLUOROACYLATION AGENTS BASED ON SMALL NCA [F-18] FLUOROCARBOXYLIC ACIDS

Three methods for fluoroacylation of amines are compared using 2-[F-18]fluoroaliphatic acyl moieties as small prosthetic groups. [F-18]fluoroacetic and -propionic acid alkylesters are common intermediates for all three methods and obtained with >90% radiochemical yields. They can directly be used- for fluoroacylation of primary amines. In the second method the free [F-18]fluoroaliphatic acid is condensed with amines using dicyclohexyl carbodiimide (DCC). However, formation of byproducts limits the radiochemical yield to about 60%. Alternatively imidazolides or p-nitrophenyl and succinimidyl esters were prepared. Fluoroacylation yields with these highly activated esters exceed 90% in organic solvents. Fluoroacylation of dipeptides in aqueous solution proceeds with a yield of 70-80%. N-succinimidyl 4-[F-18]fluorobenzoate was also prepared with a 3-fold higher radiochemical yield (75%) than reported earlier.