Cholesteryl acetate labelled

Bortolomeazzi et al. (1994) used GC/EI/MS with an ion trap to identify the thermal oxidation products of cholesteryl acetate as the 7P-hydroperoxy and 7a-hydroperoxy cholesteryl acetate, 7keto-cholesteryl acetate, the a and P isomers of 7-hydroxycholesteryl acetate, the a- and P-5,6-epoxy isomers and several derivatives arising from the loss of acetate and water. Dzeletovic et al. (1995b) have observed that saponification during sample preparation did not hydrolyse all of the oxysterol esters completely and that separation of oxysterols from cholesterol by HPLC was tedious and incomplete. They developed a stable isotope dilution GC/EI/MS SIM method for the determination of cholesterol oxidation products in human plasma. Nine oxysterols were determined by using deuterium-labelled internal standards. 

Temperatuie dependence of apparent viscosity of cholesteryl acetate. Capillary shear rate. Curves labeled with different symbols correspond to shear rates 5000 (a), 1000 (b), 100 (c) and 10 (d) in s. (After Porter et al. )... 

Havinga and Bots (1954) were the first to describe a method for the preparation of C -labeled cholecalciferol. Cholecalciferol-3-C was obtained by irradiation of 7-dehydrocholesterol synthesized from labeled cholesteryl acetate. The photochemical conversion from 7-dehydrocholesterol to cholecalciferol is accompanied by the formation of several other products such as lumisterols, tachysterols, and prechole-calciferol. A solution of NaNOs in water (0.4 ) effectively absorbs ultraviolet rays of wavelengths shorter than 250 mji which are supposed to promote die formation of side products. In order to minimize the formation of overirradiation products the ethereal solution of 7-dehy-drocholesterol-3-C is irradiated till 44.5% has been converted. The Havinga-Bots irradiation vessel, unique in itself, consists of three annular chambers made of quartz enclosing the irradiating lamp. 7-Dehydrocholesterol-3-C has been prepared recently from diolesterol-3-C (Kulkami et al., 1963) by the appKcation of an isocaproate adaptation (Nes et al., 1956) of the allylic bromination of cholesterol with 2V-bromosuccinimide followed by dehydrobromination. 

Mahadevan and Lundberg (1962) presented a method preparing cholesteryl esters of labeled long-chain fatty acids and gave details for the microsynthesis of C -labeled cholesteryl oleate from cholesteryl acetate and from randomly labeled C -meAyl oleate. They also proposed the synthesis of cholesteryl esters of other long-chain fatty acids (C12 to C22) and of the Cis unsaturated fatty acids, oleic, linoleic, and linolenic. 

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