Steroid Trimethylsilyl Ethers. Derivative Formation for Compounds with Highly Hindered Hydroxyl Groups

Highly hindered hydroxyl groups in steroids (17α-ol groups in steroids with a 17α, 20α, 21- or 17α,20β,21-triol structure) maybe converted to TMSi ether groups by reaction with N-trimethylsilylimidazole, alone or in combination with bis-trimethylsilylacetamide and with or without trimethylchlorosilane as a catalyst. At or above 150°C, the rates of catalyzed and non-catalyzed silylation reactions with these reagents are s imilar. This method may be used to prepare fully silylated MO-TMSi and TMSi derivatives of human steroid metabolites; the derivatives are stable, have good GC properties and show no adsorption (trailing) on column packings.