Synthesis of [11C] platelet-activating factor (PAF) analogs for in vivo imaging of PAF receptors

1-O-Hexadecyl-2-O-N, N-dimethylcarbamoyl-sn-glycero-3-phosphocholine[choline methyl-11C] ([11C]dimethylcarbamoyl-PAF) and 1-O-Hexadecyl-2-O-acetyl-sn-glycero-3-phosphocholine[choline methyl-11C] ([11C]C16-PAF) were synthesized as follows; Each of non-labeled dimethylcarbamoyl-PAF and C16-PAF was treated with sodium benzene thiolate to derive their desmethyl-precursors containing a dimethylphosphoethanolamine at sn-3. 11C-Labeled dimethylcarbamoyl-PAF and C16-PAF were synthesized by methylation of the respective desmethyl-precursors using [11C]CH3I. The radiochemical yield of methylation in [11C]dimethylcarbamoyl-PAF and [11C]C16-PAF was about 15 and 10% (decay corrected), respectively. The lower yield of [11C]C16-PAF compared with that of [11C]dimethylcarbamoyl-PAF was attributed to hydrolysis of the 2-acetyl group of [11C]C16-PAF during methylation. To study the stability to enzymatic hydrolysis, [11C]dimethylcarbamoyl-PAF or [11C]C16-PAF was incubated with mouse plasma at 37 °C.