1α-Hydroxyvitamin D3 (20) was prepared from cholesterol (1) in ca. 1% overall yield. Hydroboration of the tetrahydropyranyl ether 2 followed by chromic acid oxidation and NaBH4 reduction gave the 6β-ol 5. Brief treatment of its acetate 6 with acid followed by Jones oxidation gave the 6β-acetoxy-3-one (7) in 55% yield from 1. Introduction of C-1 double bond (64%) was effected by bromination of 7, followed by dehydrobromination with CaCO3, yielding the 3-oxo-1-ene 9. Oxidation of 9 with alkaline H2O2 afforded the 1α, 2α-epoxide 10 (80%) and this was converted by successive 6 steps sequences to 1α-hydroxycholesterol 15 in 43% yield. The 5, 7-diene 19 was obtained from the acetate 16 in 40% yield by allylic bromination with N-bromosuccinimide, dehydrobromination with trimethyl phosphite and saponification. Ultraviolet irradiation of 19 in benzene solution followed by thermal isomerization, produced 1α-hydroxyvitamin D3 (20) (20%).
1α-Hydroxyvitamin D3(20)由
胆固醇(1)制备而成,总收率约为 1%。将
四氢吡喃基醚 2 加氢
硼化,然后进行
铬酸氧化和 NaBH4 还原,得到 6β-ol 5。通过对 7 进行
溴化,然后用 CaCO3 进行脱氢
溴化,得到 3-氧代-1-烯 9,从而引入 C-1 双键(64%)。用碱性
H2O2 氧化 9 得到 1α,2α-
环氧化物 10(80%),然后通过连续的 6 个步骤将其转化为 1α-羟基
胆固醇 15,收率为 43%。通过 N-
溴代丁二
酰亚胺的烯丙基
溴化反应、亚
磷酸三甲酯的脱氢
溴化反应和皂化反应,从
醋酸酯 16 中得到 5,7-二烯 19,收率为 40%。在苯溶液中对 19 进行紫外线照射,然后进行热异构化反应,可生成 1α- 羟基
维生素 D3 (20)(20%)。