TOWARD THE DEVELOPMENT OF RADIOLABELED FLUOROPHENYL AZIDE-BASED PHOTOLABELING REAGENTS - SYNTHESIS AND PHOTOLYSIS OF IODINATED 4-AZIDOPERFLUOROBENZOATES AND 4-AZIDO-3,5,6-TRIFLUOROBENZOATES

Two approaches for the incorporation of iodine into functionalized perfluorophenyl azides (PFPAs) were demonstrated by the synthesis of 3, 5, and 8, with the azido and iodo groups in the same aryl ring, and 14 and 15, with the azido and iodo groups in different aryl rings. These compounds opened the way for the incorporation of radioactive iodine into PFPAs and for their attachment to other molecules as photolabels. The syntheses of trifluorophenyl azides (TFPAs) 21-23 and iodide 20 provide two possible approaches for the incorporation of a tritium atom into fluorinated photolabels. Photolysis of azide 3 in cyclohexane gave 20% of CH insertion product and in Et2NH/cyclohexane gave 24% of NH insertion product. The relatively low yield of CH and NH insertion from 3 compared with the corresponding noniodinated PFPA 24 was probably due to the heavy atom effect. Photolysis of azide 15 in Et2NH/cyclohexane gave 41% of NH insertion product. Some photodeiodination was observed both with 3 and 15. Our results demonstrate that the iodinated PFPAs studied are much better at undergoing CH and NH insertion than their nonfluorinated analogues, thus constituting an improved series of iodinated photolabeling reagents. Photolysis of TFPA 22 in cyclohexane gave 37% of CH insertion product and in Et2NH/cyclohexane gave 63% of NH insertion product, results comparable to those of PFPA 24. Thus, the desirable photochemical characteristics of the PFPAs are largely preserved in the TFPAs.