One-step iodination of the diazocyclopentadien-2-ylcarbonyl group - a new and convenient preparation of effective radiolabelled photoaffinity probes

A detailed study devoted to direct iodination of the photoactivatable diazo cyclopentadien-2-ylcarbonyl (Dcp) group is presented. The iodination does n ot influence the high carbene reactivity of the Dcp-generated carbene. It w as shown that the Dcp substituent forms 4-mono-, 5-mono- and 4,5-diiododeri vatives upon iodination under oxidative conditions (76, 20 and 4%, respecti vely, when DcpOMe 2 is iodinated). Photolysis of the individual products of iodination in cyclohexane resulted in rather high insertion into non-activ ated CH bonds, without noticeable loss of iodine. Syntheses of new phosphol ipid and ganglioside membrane probes are also described which incorporate t he Dcp function via a labile ester bond. A [I-125]-Dcp-phosphatidylcholine probe exhibiting high specific radioactivity (similar to 500 Ci mmol(-1)) w as easily prepared at yields of 90% (on the starting Na I-125), by using pe racetic acid as an oxidant. Furthermore, it was successfully used for photo labelling of the integral protein hemagglutinin in a well-characterised inf luenza virus model. In summary, the Dcp group is efficient for labelling a wide variety of molecules, and as such, it provides a new tool for explorin g a diverse range of biological systems.