Methyl ester-trimethylsilyl

Mass Units of Characteristic Fragment-ions A-G Used for the Identification of Natural, N,O-Acylated Sialic Acids, and of the C7 and C8 Analogs of Neu5Ac and Neu5Gc as their Methyl Esters, Trimethylsilyl Ethers, by Mass Spectrometry"... 

Fig. 5.4.4a Methyl ester-trimethylsilyl (TMS) ethers of BAs from a plasma sample, b n-Butyl ester-TMS ethers of BAs from a plasma sample (adapted from [15]). 1 Nor-cholic acid, 2 litho-cholic acid, 3 deoxycholic acid, 4 chenodeoxycholic acid, 5 cholic acid, 6 ursodeoxycholic acid, a cholesterol, b sitosterol)...

PREPARATION OF THE METHYL ESTER—TRIMETHYLSILYL ETHER. The standard acid (0.5 mg) or the residue obtained from the urine extraction was dissolved in 0.5 cm3 of methanol. Ethereal diazomethane (1 cm3) was then added and allowed to stand for 1 min. Ethereal diazomethane was prepared by the reaction of p-tolylsulphonyl-methyl nitrosamide with an alcoholic solution of KOH. 

Cotibined gas chronatography-mass spectronetry. The fragmentation patterns of the methyl ester-trimethylsilyl ether derivatives of the native HETEs and of the saturated cotpounds obtained by catalytic hydrogenation are characteristic. The major fragment ions are listed in Table I. 

In a short note Hanaineh and Brooks describe separation of methyl ester trimethylsilyl ethers of glycine-conjugated bile acids (55). This could perhaps serve as a basis for direct analysis of bile and a similar method has been employed by M. and E. Horning (56). It is not yet possible to separate taurine-conjugated bile acids by gas chromatography. 

Fig. 4.2 Chromatogram of standard phenolic acids separated as their methyl ester-trimethylsilyl ether derivatives on a 6 ft column (0.004 m i.d.) packed with 10 per cent F-60 on silanized Gas Chrom P (80-100 mesh) using temperature programming from 100°C to 240°C at 2°C min" Peak identifications are 1, 2-hydroxyphenylacetate 2, 3-hydroxyphenylacetate 3, 4-hydroxyphenylacetate 4, indoleacetate 5, homovanil-late 6, homogentisate 7, vanillylmandelate 8, 5-hydroxyindoleacetate 9, nonadecanoate (standard). (Redrawn with modifications from Horning etal, 1966)...

A comprehensive collection of spectra from a number of sources of trimethylsilyl derivatives of organic acids of biological interest was compiled by Markey et al (1972) and subsequently included in a larger reference collection (Markey et al., 1974b) and in other library files (e.g. Mass Spectrometry Data Centre Collection, The University, Nottingham, England). In addition to spectra of trimethylsilyl (TMS) derivatives are spectra of free acids, methyl esters, methyl ester-trimethylsilyl ethers (hydroxy acids), and trimethylsilyl esters-trimethylsilyl ethers-methoximes (oxo acids or oxo hydroxy acids). 

Fig. 5.14 Mass spectra of the methyl esters of (a) benzoic acid, (b) 4-hydroxyphenylacetic acid and (c) mandelic acid and (d) of the methyl ester-trimethylsilyl ether of 3-hydroxybutyric acid.

Eglington, G., Hunneman, D.H. and McCormick, A. (1%8), Gas chromatographic-mass spectrometric studies of long chain hydroxy acids. III. The mass spectra of the methyl esters trimethylsilyl ethers of aliphatic hydroxy acids. A facile method of double bond location. Org. Mass Spectrom., 1,593. 

The neutral and acidic metabolites in cerebrospinal fluid were examined using gas-liquid chromatography, by Waterbury and Pearce (1972). These authors, using ethyl acetate and diethyl ether extraction and methyl ester, trimethylsilyl ether derivatives, observed citric, homovanillic, 3,4-dihydroxyphenylacetic, palmitic, stearic and 5-hydroxyindoleacetic acids, with palmitic acid predominating. No quantitative levels were recorded. 

Addition of the alcohol 42 to a solution of BF3 Et20/TMSCN in DCM provided the nitrile 43 in 83% yield. Hydrolysis of nitrile 43 then furnished amide 44 in 85% yield. Demethylation of the methoxyindole 44 with BBra in DCM provided the hydroxyindole 45 in 80% yield. This was followed by alkylation of 45 with the bromide 46 under phase transfer conditions to provide the phosphonate ester 47 and subsequent cleavage of the methyl ester by TMS-I furnished trimethylsilyl phosphonic acid 48, which upon alcoholic workup afforded LY311727. 

In an effort to make productive use of the undesired C-13 epimer, 100-/ , a process was developed to convert it into the desired isomer 100. To this end, reaction of the lactone enolate derived from 100-) with phenylselenenyl bromide produces an a-selenated lactone which can subsequently be converted to a,) -unsaturated lactone 148 through oxidative syn elimination (91 % overall yield). Interestingly, when 148 is treated sequentially with lithium bis(trimethylsilyl)amide and methanol, the double bond of the unsaturated lactone is shifted, the lactone ring is cleaved, and ) ,y-unsaturated methyl ester alcohol 149 is formed in 94% yield. In light of the constitution of compound 149, we were hopeful that a hydroxyl-directed hydrogenation52 of the trisubstituted double bond might proceed diastereoselectively in the desired direction In the event, however, hydrogenation of 149 in the presence of [Ir(COD)(py)P(Cy)3](PF6)53 produces an equimolar mixture of C-13 epimers in 80 % yield. Sequential methyl ester saponification and lactonization reactions then furnish a separable 1 1 mixture of lactones 100 and 100-) (72% overall yield from 149). 

In the presence of catalytic amounts of TMSOTf 20 methyl pyruvate reacts with N,N-bis(trimethylsilyl)formamide 22c in CCI4 to give the silylated 0,N-acetal 433 in 83% yield ]44] this, with allyltrimethylsilane 82 and excess TMSOTf 20, after 30 h at 78 °C in CH2CI2, affords 72% of the methyl ester of 2-allyl-N-formylala-... 

Methyl 2,2-dimethyl-3-(trimethyl iloxy)-1-cyclopropanecarboxylate Cyclopropanecarboxylic acid, 2,2-dimethyl-3-[(trimethylsilyl)oxy]-, methyl ester (10) (77903-45-8)... 

A guinea pig ileum bioassay was used to detect and aid in the isolation of a smooth-muscle-contracting substance from the Japanese gorgonian coral Euplexaura erecta [108]. This process led to the isolation of prostaglandin F2a (17) from the MeOH extract of the coral. Its identification was based on comparison with authentic PGF2a and its methyl ester by TLC, and comparison with authentic methyl PGF2a trimethylsilyl ether by mass spectrometry. Because of the nature of the techniques employed, some aspects of the stereochemistry in this isolate of PGF2a remain uncertain. 

Figure 10.10 Total ion current chromatogram obtained for sample 1998 after acid methano lysis and trimethylsilylation. Dx, methyl ester of diacid with x carbon atoms. Ex y, methyl ester of acid with x carbon atoms and y double bonds...

Sulfides having two silyl groups are also oxidized electrochemically in methanol to give the corresponding methyl esters (Scheme 11 [36, 37]. The alkylation of (phenylthio)bis(trimethylsilyl)methane with alkyl halides followed by the anodic oxidation provides a convenient access to esters with one-carbon... 

Different nucleophiles such as methanol, allylsilanes, silyl enol ethers, trimethylsilyl-cyanide, and arenes can be used in this process [62]. When the sulfide itself contains an unsaturated or aromatic fragment and the process is carried out in the absence of a nucleophile, an intramolecular anodic sub-stitution/cyclization might occur [61-63]. Methyl esters of 2-benzothiazolyl-2-alkyl or aryl-acetic acid, oxidized in MeOH/Et4 NCIO4 or H2SO4 in the presence of CUCI2, form 2,2-dimethoxy products (Eq. 7) [64]. 

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