Capillary gas chromatographic behaviour of tert.-hydroxylated steroids by trialkylsilylation

Capillary gas chromatographic behaviour was studied for a variety of struct urally different bile acids and sterols having one to two tert.-hydroxy gro ups, together with several sec.-hydroxy groups, at positions C-3, -5, -7, - 12, -14, -17, -20, -24, and/or -25. The tert.-hydroxylated steroids were su bjected to trimethylsilylation with hexamethyldisilazane/trimethylchlorosil ane/pyridine and N,O-bis(trimethylsilyl)acetamide/N-trimethylsilylimidazole /trimethylchlorosilane, and dimethylethylsilylation with N,N,-dimethylethyl silylimidazole. The methylene unit values of the resulting trialkylsilylati on products were used for determining their structures of partially and/or fully derivatised ethers. The reactivity of the trialkylsilylation of tert. -hydroxy groups was found to be significantly dependent not only on the der ivatisation reagents and conditions used, but also on the position and ster ic factor of the tert.-hydroxy groups. The following general order of the d ecreasing reactivity of tert-hydroxy groups in steroids by trialkylsilyl et herification was observed: 25 > 20, 24 >5 beta > 17 alpha > > 14 alpha. (C) 2001 Elsevier Science B.V. All rights reserved.