Synthesis of new carbon-11 labeled benzoxazole derivatives for PET imaging of 5-HT(3) receptor.

5-HT(3) receptor is an attractive target for the development of therapeutic agents for use in brain, heart and cancer diseases, and imaging agents for use in biomedical imaging technique PET. Benzoxazole derivatives are a novel class of 5-HT(3) receptor partial agonists with high binding affinity. Carbon-11 labeled benzoxazole derivatives have been synthesized as new potential PET radioligands for imaging 5-HT(3) receptor. The target tracers were prepared by N-[(11)C]methylation of their corresponding precursors using [(11)C]CH(3)OTf and isolated by HPLC purification procedure in 40-50% radiochemical yields, which were decay corrected to the end of bombardment (EOB), based on [(11)C]CO(2). The overall synthesis time was 20-25min from EOB. The radiochemical purity was >99%, and specific activity was in a range of 74-111 GBq/micromol at the end of synthesis (EOS).