Cholesterol acetate

Figure 3 Comparison of the densities (in g/cm ) of model compounds for membrane lipids computed from constant-pressure MD simulations with the coiTespondmg experimental values. The model compounds include solid octane and tricosane, liquid butane, octane, tetradecane, and eico-sane, and the glycerylphosphorylcholme, cyclopentylphosphorylcholme monohydrate, dilauroly-glycerol, anhydrous cholesterol, cholesterol monohydrate, and cholesterol acetate crystals. (Models from Refs. 18, 42, and 43).

Addition of fluorine to 3-chloro- and 3-acetoxycholest-5-ene likewise furnishes crystalline difluorides. The product derived from cholesterol acetate in 10-20% yield is identical with the 5a,6a-difluoride (3) prepared by Barnes and Djerassi by the PbF procedure (see below). Fluorination of cholest-5-en-3-one does not proceed satisfactorily. 

In contrast to the wide application that nitrosyi chloride has found in terpene chemistry, nitrosyi fluoride has only recently been discovered. Its first use in steroid chemistry was reported by Boswell who treated cholesterol acetate with nitrosyi fluoride at 0° in methylene dichloride and obtained the 5a-fluoro-6-nitrimine (31) already mentioned in section VI (page 461) in connection with the synthesis of 6,6-difluoro steroids. This... 

Sorm" " found that when cholesterol acetate (67) is oxidized by chromic acid in acetic acid-water at 55°, crystalline keto seco-acid (69) is obtained in 25-30 % yield from the mother liquors after removal of successive crops of 7-ketocholesterol acetate (68). Reaction of keto acid (69) with benzoyl chloride in pyridine gives a dehydration product, shown" to be the )5-lactone... 

Acid (69)." To a well-stirred mixture of 108 g (0.232 mole) of cholesterol acetate and 1.2 liters of glacial acetic acid is added over a period of 2 hr, a solution of 70 g of chromium trioxide in 200 ml of 50 % glacial acetic acid. The reaction mixture is maintained at a temperature of 55°. Upon completion of the addition, the mixture is stirred for an additional 2 hr at 55°. Excess chromic acid is destroyed by addition of 60 ml of methanol, and then 800 ml of acetic acid is removed by distillation under reduced pressure at a bath temperature of 40°. The remaining liquid is diluted with 50 ml of water and allowed to stand for 12 hr. The crystalline 7-ketocholesterol acetate which separates is removed by filtration and washed with 80 % acetic acid to yield 33.3 g (35%) of (68) mp 149-152°. 

Ozonization of A -steroids usually gives complex mixtures (however, see ref. 48). Ozonolysis became a practical step in the general synthesis of B-norsteroids with the discovery that added methanol" (or formaldehyde ) improves yields significantly. Thus, Tanabe and Morisawa prepared 5/ -hydroxy-6/ -formyl-B-norsteroids (74) from cholesterol acetate, dehydroepiandrosterone acetate and pregnenolone acetate in overall yields of 64-74% by the reaction sequence represented below. 

P-Formyl-B-nor-5 -cholestane-3, 5P-diol 3-Acetate (74). To an ozonized solution of 5 g of cholesterol acetate prepared as above is added 10 g of zinc dust followed by dropwise addition of 40 ml of acetic acid with stirring and... 

Calculate the thermodynamics of acetylation of cholesterol (to cholesterol acetate) using both acetic anhydride and ethyl acetate. Data for acetic acid and ethanol are available. Which reaction is more favorable ... 

Cholesterol Acetic-anhydride (Liebermann-Burchard Reagent) 625... 

BF3 - OEt2 (1.0 mL, 8.1 mmol) was added to a solution of cholesterol acetate a-epoxide (1.0 g, 2.24 mmol) in anhyd Et20/benzene (1 1, 100 mL). After keeping at rt for 3 h, the solution was washed with 5% NaHC03 and H20, and then dried (Na2S04) and evaporated. A solution of the product in benzene/ hexane (1 1, 50 mL) was adsorbed onto neutral alumina (50 g). Elution with benzene (400 mL) gave 6/1-fluorocholestane-3/ ,5a-diol 3-monoacetate yield 470 mg (45%) mp 202-207cC, raised by three crystallizations from acetone/hexane to 214-216 C [a]D —20. 

STANDARDS. A standard solution of 5-a-cholestane, 20 pg/cm, is made up in absolute ethyl alcohol. This serves as the internal standard, which is placed in the sample tubes as described above. The chromatographic standard is a mixture of 5a-cholestane and cholesterol acetate (0.5 pg/pl of each, in CS2). 

Peak height cholesterol acetate in GLC standard IS = pig 5-a-cholestane added to unknown TV = total urine volume in liters... 

Figure 8.1.2 13 C NMR (100 MHz) spectra of cholesterol acetate under static- and continu-...

The sterols provide a method of distinguishing between animal and vegetable fats by means of their acetates. Cholesterol acetate has a melting point of 114°C, whereas phytosterol acetates melt in the range of 126 to 137°C. This provides a way to detect adulteration of animal fats with vegetable fats. 

The accuracy and reproducibility of this method is such that, for example, the solid-solid phase transition of cholesterol acetate at 40 C has been detected by means of the temperature dependence of the contact angle of water 26], The discontinuity in the contact angle curve was about 0.3 of arc. For water on siliconized glass plates, the deviations of individual points in the plot of contact angle versus temperature were found to be about 0.1 128). in good agreement with the error limits estimated above. 

Vapor deposition has been found to yield very smooth surfaces for low-molecular-weight nonpolar and polar materials such as hexatriacontane and cholesterol acetate 5.7. organic pigments 98. and silicon compounds 128.183]. In all cases, the deposited material must not decompose under the elevated temperatures required to cause evaporation. 

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