Scheme 14.

Synthetic route to [³H]HS665. (a) DIPA, NBS, CH₂Cl₂, r.t.; (b) Triethylamine (TEA), PdO/BaSO₄ catalyst, tritium gas, r.t. HS665 (13) was first brominated using NBA and DIPA in CH₂Cl₂ to afford the dibrominated analogue 79. A mixture of 79, DMF, TEA, and PdO/BaSO₄ catalyst was reacted with tritium gas at r.t. The crude product was obtained with 216 mCi in ethanol. This product was purified by RP-HPLC to afford [³H]HS665 with a radioactive purity of ≥95% and with a specific activity of 30.65 Ci/mmol.