Steroids TBDMS deriv

The mass spectra of the ADMS derivatives of steroids and prostanoids exhibit an abundant ion produced by the elimination of the allyl moiety, [M —41]. The ion currents carried by this latter ion were slightly less than those for the corresponding [M — 57] ion for TBDMS derivatives. However, the spectra contain more abundant ions characteristic of compound structure. ADMS derivatives possess shorter GC retention times and lower... 

Further alkyidimethylsilyl derivatives have been evaluated in mixed derivatives for the GC—MS analysis of steroids [107-109] and prostaglandins and thromboxane Bj [110]. Although they have favourable properties, they generally provide no significant advantages over the TBDMS derivatives. 

The allyldimethylsilyl derivatives were originally made in an attempt to obtain mass spectral characteristics similar to diose of TBDMS derivatives, but with leady formation from hindered hydroxy groups. Never really satisfactory, owing to the formation of multiple reaction products and reduced sensitivity in certain cases [961 they have, however, been applied to steroids [111, 1121... 

Gaskell and co-workers [208a,b] developed a technique for assaying endogenous steroids in blood plasma samples after first creating the TBDMS ether derivative. 

As discussed earlier (see also Chapter 6), oxime derivatives are often prepared for polyfunctional compounds containing ketone groups in order to prevent the formation of mixed enol-silyl ethers. An alternative approach is to use a catalyst to enhance the yield of enol-silyl ethers (see also above. Section 4.2.3, for TMS ethers). The use of potassium acetate in toluene as catalyst is reported to produce a quantitative yield of TBDMS ethers and >96% yield of TBDMS-enol ethers of a, -unsaturated keto steroids [326]. An alternative to this approach, set out below, uses sodium formate to catalyse enol-silyl ether formation with fewer by-products being produced [12, 13]. 

A problem can arise with unprotected keto groups owing to the formation of the hydrolytically and thermally unstable enol-TMS ethers, which are difficult to prepare quantitatively (see Chapter 4). However, examples are given below of the application of TMS enol—TMS ether derivatives in the steroid field (see also Section 3.2, TBDMS). In many cases multiple products are formed, he analysis. 

Ketosteroids may be converted to enol—TBDMS ether derivatives with t-butyidimethyliodosilane as a catalyst [103]. Steroid enol-TBDMS and mixed TBDMS-TMS derivatives have been appiied to the analysis of steroids in rat testes [104]. The enol-TBDMS mass spectra are characterized by the presence of intense M ions. 

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