Correlations between the Structure of the Silylether Derivatives of Pregnane-17, 20, 21-triols and their Mass Spectral Fragmentations. I. Synthesis of (20α)- and (20β)-4-Pregnene-17α, 20, 21-triol-3-one Isomers

摘要

A reaction of N,O-bis(diethylhydrogensilyl)trifluoroacetamide with 5β-pregnene-3α,17α, 20α, 21-tetraol and its 20β-isomer afforded different diethylhydrogensilyl(DEHS) cyclic diethylsilylene(DES) derivatives. From the mass spectral fragmentations, the 20β-isomer was suggested to yield the 3α,21-bisDEHS-17α, 2Oβ-DES compound, whereas the 20α-isomer seemed to afford the 3α,17α-bisDEHS-20α, 21-DES derivative as a major product with trace amounts of the 3α, 20α-bisDEHS-17α, 21-DES derivative. To confirm their structures chemically, (20α)- and (20β)-4-pregnene-17α, 20, 21-triol-3-ones, model compounds, were synthesized from cortexolone. Partial reduction of cortexolone with NaBH_4 afforded the 20β-model mainly, whereas reduction of cortexolone 17, 21-acetonide 3-methyl enolether yielded the 20α-model as a major product after hydrolysis. The 20α- and 20β-models were able to be separated and purified by TLC in the form of their 20, 21-diacetates, each of which afforded the pure compound after deacetylation.