Scheme 1

Synthesis of reference standard (5) and radiochemistry precursor (9). Reaction conditions: i) TsCl, TEA, DCM, rt.; ii) TBAF, THF, 100 °C; iii) 4′-aminoacetophenone, NaOH (4 M), EtOH, 50 °C; iv) acryloyl chloride, TEA, CH₃CN, rt.; v) (Boc)₂O, TEA, DCM, rt.; vi) tert-butyl (4-acetylphenyl) carbamate, NaOH, EtOH, 50 °C; vii) TsCl, pyridine, 4 h at 0 °C and then rt