Abstract Four different no carrier added (nca) 4-[18 F] fluorophenylurea derivatives are synthesized as model compounds via two alternative routes. In both cases carbamate-4- nitrophenylesters are used as intermediates. Either nca 4-[18 F] fluoroaniline reacts with carbamates of several amines, or the carbamate of nca 4-[18 F] fluoroaniline is formed at first and an amine is added subsequently to yield the urea derivative. The choice of the ...