Derivatisation of Steroid Hormones with t-Butyldimethylsilyl Imidazole

An efficient procedure for the derivatisation of hydroxyl and α, β-unsaturated ketonic steroids using t-butyldimethylsilyl imidazole is described. The conditions which employ potassium acetate as a basic catalyst result in quantitative formation of BDMS ethers and >96% yield of BDMS-enol ethers. Various mechanisms involving the catalysed and uncatalysed reactions of t-butyldimethylsilyl imidazole with alcohols and enols are also discussed. The mass spectra of the BDMS-enol ethers, in contrast to the BDMS ethers, are dominated by an intense molecular ion, which facilitates the quantitation of these derivatives in biological samples. An example of the method is shown by the determination of 4-androstene-3,17-dione in urine using a stable-isotope internal standard.