THE SYNTHESIS OF TAURINE-CONJUGATED BILE-ACIDS AND BILE-ACID SULFATESWITH C-14 OR H-3 IN THE TAURINE MOIETY

Studies of bile acid transport systems require radio-labeled taurine-c onjugated bile acids with high specific activity. An established synth etic procedure was optimized to provide mild, fast, and effective conj ugation of radio-labeled taurine with different types of bile acids, i ncluding those with labile 7 alpha-hydroxy-3-oxo-Delta 4 or 3 beta,7 a lpha-dihydroxy-Delta 5 structures. Taurine labeled with C-14 or H-3 wa s reacted with excess bile acid anhydride formed from the tributylamin e salt and ethylchloroformate (2/1 M/M) in aqueous dioxane for 25 min at room temperature. The yields were higher than 95% and less than 2% side products were formed. Bile acid sulfates were conjugated with C-1 4- or H-3- labeled taurine by using N-ethoxycarbonyl-2-ethoxy-1,2-dihy droquinoline as the coupling reagent. The products were effectively pu rified by chromatography of the sodium salts on Sephadex LH-20. The yi elds of taurine-conjugated bile acid sulfates were 65-70%.