Synthesis and rapid purification of ³²P-labeled photoactive analogs of farnesyl pyrophosphate

To study the binding sites of protein prenyltransferases, we have synthesized photoaffinity labeling analogs that contain photoactive benzophenone units. Here we describe the syntheses and a method for the rapid purification of two ³²P-labeled analogs; phosphorylation was accomplished by reacting the corresponding alcohols with CCl₃CN and [³²P]-H₃PO₄ in CH₃CN and the purification was performed using C₁₈ reversed-phase cartridges. Analog [³²P]-3a was prepared from 2.4 mg of starting alcohol 4a and was obtained in 3.3% yield, 50% radiochemical purity and 480 Ci/mol specific activity. Further purification by preparative thin layer chromatography yielded material with a radiochemical purity of 90%. A second analog, [³²P]-3b, was prepared from 1.2 mg of alcohol 4b and was obtained in 1.0% yield, 54% radiochemical purity and 700 Ci/mol specific activity. Further purification by preparative thin layer chromatography yielded material with a radiochemical purity of 91%.