Photolabile derivatives of bile salts. Synthesis and suitability for photoaffinity labeling

In an approach to the identification of bile salt-binding carriers, the photoactivable bile acid derivatives A) 3 beta-azido, 7 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oic acid, B) 7,7-azo-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oic acid, and C) 11 xi-azido-12-oxo-3 alpha,7 alpha-dihydroxy-5 beta-cholan-24-oic acid were synthesized in unconjugated and taurine-conjugated form. Photolysis of the 3 beta-azido derivatives was studied using a light source with a maximum emission at 300 nm and established a half-life time of 18.5 min. The photochemistry of the 7,7-azo derivatives was investigated using light with a maximum at 350 nm and had a half-life time of 2.2 min. The 11 xi-azido-12-oxo derivatives were photolyzed with light having a maximum at 300 nm resulting in a half-life time of 8.5 min. The suitability of the 7,7-azo derivatives for photoaffinity labeling was demonstrated by photolyses in 14C-labeled methanol and acetonitrile. The generated carbene reacted with the solvents under covalent bond formation of 6 to 12%. The efficiency of all synthesized photolabile derivatives for photoaffinity labeling of bile salt binding proteins was demonstrated.