Synthesis of 3~-hydro~y-5-[1,2-~H]Chenodeoxycholic Acid followed establishedprocedures and was given in detail in our previous paper (8).The tritiated compound used in this study is from the same synthesisas thatusedpreviously (0.9 mCi/pmol); but when supplies wereexhausted, it was decided to prepare the isotopic compound labeledat C-24 with I4C because of the theoretical possibility that loss oftritium could occur from C-2 during the formation of the 4-ene-3-oneintermediate that occurs in the synthesis of lithocholic and chenodeoxycholic
acids. Also, unlike the previous synthesis in which isomersoccur during sodium borohydride reduction, no alteration of the A ring is necessary, thus simplifying the purification procedure.
Synthesis of 3~-hydro~y-5-[24-~~C] Chenodeoxycholic Acid began with thepreparation of norcholenyl iodide by photochemical decarboxylation(13) of the 3-acetate of the free acid. Using prepurified argon to
maintain an oxygen-free atmosphere, a solution of iodine (0.533 g,2.1 mmol) in benzene (15 ml) was added dropwise to potassium tbutoxide
(0.157 g, 1.4 mmol) suspended in benzene (11 ml) in a foilwrappedflask. The mixture was stirred at room temperature in thedark for 30 min and then filtered rapidly under argon through asintered glass funnel into a solution of the 3-acetate of Chenodeoxycholic Acid(0.208 g, 5 mmol) in 25 ml of benzene. The solution was irradiatedwith a 1000-watt tungsten lamp with stirring under argon for 45 min.
Sodium thiosulfate (0.1 N) was then added dropwise to discharge thepurple iodine color, and the resultant yellow mixture was then extractedinto benzene Chenodeoxycholic Acidwas washed with water and then pouredover anhydrous MgSOl and concentrated by flash evaporation. Thecrude product was purified by flash chromatography on silica gel
(hexane:ether (lO:l, v/v)) to yield norcholenyl iodide as a white solid(165 mg, 66%, m.p. 135-140 “C with decomposition). For ’H NMRanalysis (250 mHz, CDC13): 6 5.51 (d, J = 5 Hz, lH, Hs), 4.60 (m, lH,H3), 3.31 (m, IH, HZ&), 3.10 (m, IH, Hd, 2.03 (s, 3H, OAc), 1.02 (5,