One-step syntheses of cyclic trimer 2 and tetramer 3 of lithocholate were achieved from the cycloesterification of lithocholic acid (1) by using 2-chlorobenzoyl chloride and 4-dimethylaminopyridine (DMAP). The tetramer 5 of 7,12-diacetyl-24-norcholid acid (4) was synthesized by a similar method. These results suggest that the cyclotrimer is the preferred cycle size for the cholic acid system and that the cyclotetramer is the preferred cycle size for the 24-norcholic acid system. Cyclotetramerization of lithocholic acid is preferred over cyclodimerization. The structure of tetramer 3 was verified by a multistep synthesis. The structures and stereochemistry of all dimers, oligomers, and intermediate products were determined by means of spectroscopic analyses.
利用 2-
氯苯甲酰氯和 4-二甲
氨基吡啶(
DMAP)将
石胆酸(1)环酯化,一步合成了
石胆酸的环状三聚体 2 和四聚体 3。用类似的方法合成了 7,12-
二乙酰基-24-
去甲胆酸的四聚体 5(4)。这些结果表明,环三聚体是
胆酸体系的首选循环尺寸,而环四聚体是 24-
去甲胆酸体系的首选循环尺寸。
石胆酸的环四聚体化比环二聚体化更可取。四聚体 3 的结构通过多步合成得到了验证。通过光谱分析确定了所有二聚体、低聚物和中间产物的结构和立体
化学性质。