3-Diazirine-derivatives of bile salts for photoaffinity labeling

New carbene-generating photolabile bile salt derivatives, 3,3-azo-7 alpha,12 alpha-dihydroxy-5 beta 7 beta-3H]cholan-24-oic acid and (3,3-azo-7 alpha,12 alpha-dihydroxy-5 beta 7 beta-3H]cholan-24-oyl)-2- aminoethanesulfonic acid were synthesized with high specific radioactivity. These 3-diazirine-derivatives could be activated to the corresponding carbenes by irradiation with ultraviolet light at 350 nm with a half-life time of 2 min. The 3-diazirine derivatives behaved in enterohepatic circulation like the natural bile salts. The uptake of 3H]taurocholate into isolated hepatocytes was competitively inhibited by (3,3-azo-7 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oyl)-2- aminoethanesulfonic acid indicating that the 3,3-azo-derivative of taurocholate shares the hepatic transport systems for natural bile salts. It was demonstrated that the radioactively labeled 3-diazirine bile salt derivatives are useful probes for photoaffinity labeling of bile salt binding proteins especially in intact cells and tissues.