Cholesterol → Glycidyl cholesterol

Beteiligte Stoffe

Reaktionsbedingungen

Reaktionsschritte

Cholesterol (5.80 g; 15 mmol; Sigma, St. Louis, Mo.) was dissolved in 76 ml dry N,N-dimethylacetamide (DMAc) under a flow of dry argon. The solution was cooled to 10° C. and 15 ml (15 mmol) of a 1.0M solution of lithium tert-butoxide in hexanes (Sigma) was added. After further cooling to 5° C., 10 ml (117 mmol) of freshly distilled epibromohydrin was added and the mixture was stirred at 3-5° C. for 2 hours. The temperature was allowed to slowly rise to 21-23° C. and the reaction was allowed to continue for another hour. The reaction mixture was then diluted with 500 ml of 0.5% aqueous KHCO3 and extracted with 350 ml n-heptane and then twice more with 100 ml n-heptane. The combined organic layers were dried over Na2SO4. After filtration from the desiccant, the solvent was removed in vacuo. The syrupy residue (7.3 g) was purified by flash-chromatography on silica gel employing elution with hexane, hexane/toluene (1:1 mixture), and toluene. The fractions containing pure glycidyl-cholesterol (thin layer chromatography (TLC)-monitoring) were pooled and dried in vacuo until crystallization occurred. The procedure yielded 4.25 g glycidyl-cholesterol (64%). The product displayed an Rf of 0.38 by TLC (silica gel, n-heptane/ethyl acetate, 85:15 by volume). The signals (only those produced by the glycidyl group not present in the starting cholesterol) obtained by 1H NMR analysis of the product are as follows: 2.62 and 2.87 (both m, 1H and 1H, two non-equivalent H of oxirane CH2), 3.15 (m, 1H, CH), and 3.47 and 3.72 (both m, 1H and 1H, diastereotopic H of CH2O).

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