Esterification of tertiary alcohols in steroids under different conditions

Steroids can be made more lipid-soluble or more water-soluble simply by making suitable ester derivatives of hydroxyl groups. In this study, esterification of tertiary alcohols of cyproterone (CYP) and medroxyprogesterone (MPG) was comparatively conducted under different conditions. Several catalysts including basic and acidic ones such as dimethylaminopyridine (DMAP), N-methylimidazole, pyridine, 3-(1-methyl-2-pyrolidinyl) pyridine, and N-bromosuccinimide (NBS) were examined in the presence of appropriate acid anhydride or acyl chlorides. The results showed that NBS could be used as an effective catalyst for synthesis of propionate, butyrate, pentanoate, and hexanoate esters of CYP and MPG under mild conditions. The yield and the rate of the reactions were dependent on the chain length of substituted acyl groups. The yield ranged from 85% to 95% and the reaction time was between 10 and 12 h. Benzoate ester of CYP was also directly produced using CYP acetate and benzoic acid in the presence of sulfuric acid as catalyst.

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