Efficient syntheses of [¹¹C]zidovudine and its analogs by convenient one-pot palladium(0)-copper(I) co-mediated rapid C-[¹¹C]methylation

Abstract

The nucleosides zidovudine (AZT), stavudine (d4T), and telbivudine (LdT) are approved for use in the treatment of human immunodeficiency virus (HIV) and hepatitis B virus (HBV) infections. To promote positron emission tomography (PET) imaging studies on their pharmacokinetics, pharmacodynamics, and applications in cancer diagnosis, a convenient one-pot method for Pd(0)-Cu(I) co-mediated rapid C-C coupling of [(11)C]methyl iodide with stannyl precursor was successfully established and applied to synthesize the PET tracers [(11)C]zidovudine, [(11)C]stavudine, and [(11)C]telbivudine. After HPLC purification and radiopharmaceutical formulation, the desired PET tracers were obtained with high radioactivity (6.4-7.0 GBq) and specific radioactivity (74-147 GBq/µmol) and with high chemical (>99%) and radiochemical (>99.5%) purities. This one-pot Pd(0)-Cu(I) co-mediated rapid C-[(11)C]methylation also worked well for syntheses of [methyl-(11)C]thymidine and [methyl-(11)C]4'-thiothymidine, resulting twice the radioactivity of those prepared by a previous two-pot method. The mechanism of one-pot Pd(0)-Cu(I) co-mediated rapid C-[(11)C]methylation was also discussed.

Keywords: Rapid C-[11C]methylation; [11C]Stavudine ([11C]d4T); [11C]Telbivudine ([11C]LdT); [11C]Zidovudine ([11C]AZT); [Methyl-11C]4′-thiothymidine ([11C]4DST); [Methyl-11C]thymidine.