Trimethylsilyl ether derivatives

Synthesis of 31 by Method I (107,108) and its conversion to the related anti and syn diol epoxide derivatives (32,33) has been reported (108). The isomeric trans-1,lOb-dihydrodiot 37) and the corresponding anti and syn diol epoxide isomers (38,39) have also been prepared (108) (Figure 19). Synthesis of 37 from 2,3-dihydro-fluoranthene (109) could not be accomplished by Prevost oxidation. An alternative route involving conversion of 2,3-dihydrofluoranthene to the i8-tetrahydrodiol (3-J) with OsO followed by dehydration, silylation, and oxidation with peracid gave the Ot-hydroxyketone 35. The trimethylsilyl ether derivative of the latter underwent stereoselective phenylselenylation to yield 36. Reduction of 3 with LiAlH, followed by oxidative elimination of the selenide function afforded 3J. Epoxidation of 37 with t-BuOOH/VO(acac) and de-silylation gave 38, while epoxidation of the acetate of JJ and deacetylation furnished 39. 

On studying the KDO content of LPS from Xanthomonas sinensis, Volk and coworkers64 found that only one KDO residue per LPS chain is present in this organism. Moreover, the authors observed the formation of 4,7- and 4,8-anhydro derivatives (39 and 40) of KDO (see Scheme 14) under the conditions used for mild hydrolysis of the LPS with acetic acid. Free KDO was also shown to yield the anhydro derivatives under analogous conditions. The structures of these unusual side-products were identified by mass spectrometry, as follows. Reduction of 39 and 40 with sodium borohydride gave the two epimeric mixtu.es, 41 and 42. These were subjected to periodate treatment followed by borohydride reduction, the products separated by paper electrophoresis, and their trimethylsilyl ether derivatives analyzed by... 

Svendsen, J.S. Sydnes, L.K. Whist, J.E. Mass Spectrometric Study of Dimethyl Esters of Trimethylsilyl Ether Derivatives of Some 3-Hydroxy Dicarboxylic Acids. Org. Mass Spectrom. 1987,22,421-429. 

Batta AK, Salen G, Rapole KR, Batta M, Earnest D, Alberts D (1998) Capillary gas chromatographic analysis of serum bile acids as the n-butyl ester-trimethylsilyl ether derivatives. J Chromatogr Biomed Sci Appl 706 337-341... 

Cooper et al. (10) and Cox (11) were the first to report the gas chromatographic analysis of urinary pregnanediol. These methods normally involved hydrolysis, extraction, and the chromatographic analysis of the free pregnanediol, the acetate derivative, the trimethylsilyl ether derivative, or the bis-heptafluor-obutyrate derivative. 

Derivative formation prior to chromatographic analysis has been used successfully. An unidentified component of urine was found which had a retention time very close to that of pregnanediol and which could not be separated from it by thin layer chromatography. The trimethylsilyl ether derivatives and the tri-fluoroacetate derivatives of the two compounds would not provide resolution only the acetate derivatives could be separated. 

There are a number of gas chromatographic procedures for the determination of the catecholamines. Methods generally accepted are making the trimethylsilyl ether derivative of the alcoholic group after using diazomethane to prepare the methyl ester and the heptafluorobutyryl derivative. The ethyl esters have been used for the separation of HVA and isoHVA and mass spectrometry applied to study their characterization. 

Several methods promoted by a stoichiometric amount of chiral Lewis acid 38 [51] or chiral Lewis bases 39 [52, 53] and 40 [53] have been developed for enantioselective indium-mediated allylation of aldehydes and ketones by the Loh group. A combination of a chiral trimethylsilyl ether derived from norpseu-doephedrine and allyltrimethylsilane is also convenient for synthesis of enan-tiopure homoallylic alcohols from ketones [54,55]. Asymmetric carbonyl addition by chirally modified allylic metal reagents, to which chiral auxiliaries are covalently bonded, is also an efficient method to obtain enantiomerically enriched homoallylic alcohols and various excellent chiral allylating agents have been developed for example, (lS,2S)-pseudoephedrine- and (lF,2F)-cyclohex-ane-1,2-diamine-derived allylsilanes [56], polymer-supported chiral allylboron reagents [57], and a bisoxazoline-modified chiral allylzinc reagent [58]. An al-lyl transfer reaction from a chiral crotyl donor opened a way to highly enantioselective and a-selective crotylation of aldehydes [59-62]. Enzymatic routes to enantioselective allylation of carbonyl compounds have still not appeared. 

Influence of Solvents. Etherification is also considerably affected by the solvent system used (211-217]. The preparation of cellulose trimethylsilyl ether derivative was considerably enhanced by conducting it in a DMSO-PF solution [212]. In a heterogeneous dihydroxypropylation of cellulose with glycidol, the DS cannot exceed the 1.5 level [215]. 

Figure SAQ 5.6 Electron-impact mass spectra of (a) 6-0-monoacetylmorphine, and (b) its trimethylsilyl ether derivative (after reaction with N,0-BSA), following gas chromatographic separation.

Limitations of the reaction due to the substitution pattern of the allylic alcohols were overcome by the use of tetrapropylammonium perruthenate (TRAP) as a catalyst and monosubstituted, disubstituted and trisubstituted allyl alcohols were converted into the corresponding saturated aldehydes and ketones [5]. Intermediacy of the ruthenium alkoxide in this reaction was evidenced from the complete lack of reactivity of the trimethylsilyl ether derived from the allylic alcohol. 

All of the calystegines isolated to date have been obtained as amorphous white solids and melting points have therefore not been reported. Structures have been determined by spectroscopic methods, in particular H and 1SC NMR spectroscopy and high-resolution mass spectrometry. Additional confirmatory evidence has been obtained from analysis of the alkaloids as trimethylsilyl ether derivatives by gas chromatography - mass spectrometry (Section 4.4). In certain cases the structures and absolute configurations have been confirmed by synthesis (Section 6). 

RETENTION INDICES OF DIASTEREOMERIC EPHEDRINES5 as N-acetyl-O-trimethylsilyl ether derivatives... 

V9. Vecchi, M., and Kaiser, K., The gas chromatographic determination of ascorbic acid in the form of its trimethylsilyl ether derivative. J. Chromatog. 26, 22-29 (1967). 

In the Croteau and Fogerson study, the triperpenic alcohols and sterols were derivatized into their trimethylsilyl ether derivatives using bis-trimethylsilylacetamide. The isopropanol-chloroform extract contained higher amounts of sterols and triteipenic alcohols such as p-sitosterol and amyrin compared to the SF extract. This could be due to the high polarity of the extracting liquid solvent as opposed to the supercritical fluid, and the increased volatility of the silylated sterols and triteipenic compounds relative to our fatty acid methyl esters, in addition to these compounds, the isopropanol-chloroform extract reported earlier also contained ursolic acid, a polar triteipenic acid, which was not extracted with pure CO2. 

Total extracts and/or liquid chromatographic subfractions are then analyzed by capillary colnmn gas chromatography nsing a flame ionization detector. Except for hydrocarbon fractions, derivatization is commonly applied to render polar lipids more volatile in order to reduce gas chromatographic retention times and to improve peak shape at the detector. Carboxylic acids are usually transformed into their methyl esters, and hydroxyl or amine gronps into their trimethylsilyl ether derivatives. Alternatively, both acid and hydroxyl groups can be silylated. Acetate formation is another common derivatization method. A variety of derivatization reagents are conunercially available for this purpose. 

The hydroxy- and oxo-compounds derived from di- and tri-saccharides after the sequence of periodate oxidation, sodium borohydride reduction, and acid hydrolysis have been identified by g.l.c. of their 0-trimethylsilyl ether derivatives, thus giving useful information for linkage analysis. ... 

Those with (1 - 6)-links eluted quickly while those comprised of pentose units (e.g. xylotriose) were strongly retarded, the opposite of their behaviour as trimethylsilyl ether derivatives. 

Figure 1. Electron ionization mass spectra (a) n-heptanol (b) n-heptanol trimethylsilyl ether derivative.

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