Simple synthesis of new carbon-11-labeled 1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives for PET imaging of A3 adenosine receptor

• New 1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives were synthesized.
• New 11C-labeled 1,2,4-triazolo[4,3-a]quinoxalin-1-one derivatives were synthesized.
• A simplified SPE technique was employed in radiosynthesis.

The reference standards 4a-b, 6a-b, 7a-c, and desmethylated precursors 9a-b, 10a-b, 8a-c were synthesized from 4-methoxyaniline, ethyl 2-chloro-acetoacetate and substituted benzene-1,2-diamines with 3, 5, 6 steps in 61–67%, 34–41%, 23–31%, and with 4, 6, 7 steps in 49–57%, 28–35%, 20–27% overall chemical yield, respectively. The target tracers [11C]4a-b, [11C]6a-b, [11C]7a-c were synthesized from their corresponding precursors with [11C]CH3OTf through O-[11C]methylation and isolated by simplified SPE in 40–60% decay corrected radiochemical yields at EOB, with 185–370 GBq/μmol specific activity at EOS.