2-(TRIBUTYLSTANNYL)-4-[3-(TRIFLUOROMETHYL)-3H-DIAZIRIN-3-YL]BENZYL ALCOHOL - A BUILDING-BLOCK FOR PHOTOLABELING AND CROSS-LINKING REAGENTS OF VERY HIGH SPECIFIC RADIOACTIVITY

A general approach for the synthesis of novel, radioiodinated photolabeling and cross-linking reagents at no-carrier-added (nea) specific radioactivity (> 2000 Ci/mmol) is described. In this approach, 2-(tributylstannyl)-4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzyl alcohol 12 serves as a module which, through acylation of its alcohol function, is connected to other structural/functional elements to make the tin-containing precursor forms of the reagents. The final, radioactive compounds are then conveniently prepared in yields varying from 15-50% by electrophilic aromatic substitution of the tributylstannyl group by I-125(+) generated in situ from I-125(-) by peracetic acid. Using this approach, we have synthesized two analogues of phosphatidylcholine (PC) (20 and 21), an analogue of ceramide (36), as well as two heterobifunctional label-transfer cross-linkers (29 and 33). PC 21, examined more closely, is a substrate of the PC-specific phospholipid exchange protein from beef liver and of phospholipase D from cabbage. The latter was utilized to enzymatically convert PC 21 into two additional phospholipids, phosphatidylserine (PS) 25 and phosphatidic acid (PA) 26. Reagents that contain this iodinated photophor also combine desirable photochemical properties. Thus, evidence is presented that they undergo efficient photolysis to generate a (singlet) carbene intermediate which inserts efficiently into hydrocarbon CH bonds. In addition, we demonstrate that the diazirine can be photolyzed in a selective manner, that is, without photodeiodination to occur to a significant extent.