Studies on steroids. XLV. Synthesis of the four stereoisomers of 20,22-dihydroxycholesterol.
作者:MASUO MORISAKI、SUSUMU SATO、NOBUO IKEKAWA
DOI:10.1248/cpb.25.2576
日期:——
The four stereoisomers of 20, 22-dihydroxycholesterol 9, 10, 17 and 19 were synthesized from pregnenolone. Vinylation of the 3, 5-cyclo derivative 1 of pregnenolone gave the [20S]-carbinol 2, which was then oxidized with m-chloroperbenzoic acid to afford the [22S]-22, 23-epoxide 3 and its [22R]-isomer 4 (7 : 2). Reaction of 3 and 4 with i-Bu2CuLi followed by acid treatment yielded 20R, 22S-dihydroxycholesterol 9 and its 20R, 22R-isomer 10, respectively. The latter triol 10 was more effectively prepared by a Grignard reaction on the [20S]-20-formyl-carbinol 14, which was derived from pregnenolone THP ether 12, through the 1, 3-dithiane derivative 13. Oxidation of 20-dehydrocholesterol acetate 16 with OsO4 gave stereoselectively the 20S, 22S-glycol 17 (R=Ac). Treatment 17 (R=Ac) with N-chlorosuccinimide-dimethylsulfide followed by reduction with LiAlH4 afforded 20S, 22R-dihydroxycholesterol 19 together with the 20S, 22S-isomer 17 (R=H) (3 : 2). Acid-catalyzed epoxide opening reactions of 20, 22-epoxycholesterols were also discussed.
从孕激素合成了四种立体异构体的20, 22-二羟基胆固醇9、10、17和19。孕激素的3, 5-环烯衍生物1经过乙烯化反应得到[20S]-卡宾醇2,随后用对氯过苯甲酸氧化得到[22S]-22, 23-环氧化物3及其[22R]-异构体4(比例7:2)。3和4与i-Bu2CuLi反应后,经酸处理分别得到20R, 22S-二羟基胆固醇9及其20R, 22R-异构体10。后者三醇10更有效的合成方式是通过对[20S]-20-甲酰基卡宾醇14进行Grignard反应,14源自孕激素THP醚12,通过1, 3-二硫烷衍生物13合成。用四氧化锇对20-脱氢胆固醇醋酸酯16氧化,选择性地得到20S, 22S-醇17(R=Ac)。用N-氯丁二酰亚胺-二甲基硫化物处理醇17(R=Ac),再用LiAlH4还原,得到20S, 22R-二羟基胆固醇19及20S, 22S-异构体17(R=H)(比例3:2)。还讨论了20, 22-环氧胆固醇的酸催化开环反应。