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A simple procedure for the esterification of steroid carboxylic acid groups using an acetyl chloride/alcohol reagent has been carefully evaluated. The ease with which these esters can be formed using this reagent depends on the acid and the ester required. C24 bile acids form methyl esters using acetyl chloride/methanol (1:20, v/v) almost instantaneously at 50°C, whereas the C20 aetienic acid studied requires 2 h at 50°C. The formation of isopropyl esters of 5β-cholanic acid takes longer (4 h at 50°C) than the formation of n-propyi esters (1 h at 50°C). The identity of various esters of cholanic acids formed using this reagent have been checked by gas chromatography-mass spectrometry and various other procedures used for the methylation of fatty acids have been examined to establish whether they can be used for the quantitative esterification of bile acids.