Trimethylsilyl deriv esters

As an alternative, Harpp and coworkers reacted benzenesulfinyl chloride with the trimethylsilyl derivative of menthol to form the diastereomeric esters in 91% yield the epimer of configuration R could be isolated by crystallization in unspecified yield. Grossert and coworkers prepared ester 19 in 51% yield as a mixture of diastereomers by treating p-toluenesulfonyl chloride with sodium p-toluenesulfinate in DMF containing menthol. It was postulated that initial nucleophilic attack by the sulfinate oxygen on the sulfonyl sulfur atom gave the mixed sulfonate-sulfinate anhydride 21, which then reacted... 

By selection of an appropriate derivative the hydroxyl group can become activated towards displacement (via an 8 2 exchange process) with a suitably chosen nucleophile. Conversion to the sulfonate ester (SO2R) [115] promotes displacement by either an acetate ( OAc) (sequence Dl) or phthalimide nucleophile (Sequence D2), whilst the trimethylsilyl derivative facilitates introduction of fluorine (Sequence E) [116]. 

A wide variety of acidic compounds has been trimethylsilylated, and the preferred procedure is to treat the sodium, calcium, or barium salt, as a suspension in pyridine, with bis(trimethylsilyl)acetamide and chlorotrimethylsilane 100,163,164 this gives the trimethylsilyl ester of the O-trimethylsilyl derivative. Lead salts may be used,165 or the potassium salt may be used in methyl sulfoxide, the O-trimethylsilyl derivative becoming concentrated in the upper phase.166... 

The rate of decomposition of O-trimethylsilyl derivatives of a series of oligogalacturonic acids has been studied 170 it was found that the rate increases with the degree of polymerization, but that the methyl esters decay about 55 times as slowly. 

The occurrence of 3-deoxy-D-manno-octulosonic acid in lipopoly-saccharides has prompted its synthesis,537 together with the D-gal-octo158 and the D-gluco analogs.157 Although gas-liquid chromatography was successfully used to analyze the products of these syntheses, it has been reported that methanolysis of a bacterial endotoxin lipopolysaccharide failed to yield 3-deoxy-D-manno-octulosonic acid, presumably because of the lability of the latter to acid.381 However, Kasai and Nowotny have reported four peaks for the O-trimethylsilyl derivatives of 3-deoxy-D-manno-octulosonic acid obtained by methanolysis of the glycolipid from a Salmonella minnesota mutant.538 Reduced 3-deoxy-D-manno-octulosonic acid and its methyl ester have also been analyzed successfully as their acetates.339,539... 

Four more compounds are to be found in Table VI. b Determined by g.l.c. of the trimethylsilyl derivatives. Also, 2% of the keto form. d Also, 2-3% of the keto form. Data are also given for 20, 40, and 50 °. Similar values were found for the sodium salt and for the methyl ester. Also, 15% of the keto form. 

For volatile materials vapor phase chromatography (gas chromatography) permits equilibration between the gas phase and immobilized liquids at relatively high temperatures. Tire formation of volatile derivatives, e.g., methyl esters or trimethylsilyl derivatives of sugars, extends the usefulness of the method.103104 A method which makes use of neither a gas nor a liquid as the mobile phase is supercritical fluid chromatography.105 A gas above but close to its critical pressure and temperature serves as the solvent. The technique has advantages of high resolution, low temperatures, and ease of recovery of products. Carbon dioxide, N20, and xenon are suitable solvents. 

TFA esters have the particular advantage that an electron capture detector may be used, and with the large number of fluorine atoms per molecule of sugar high sensitivity may be achieved. It has been reported that the TFA derivatives are not stable and may not be stored prior to chromatography (88). These ester derivatives also result in multiple peaks related to anomerization and generally are more difficult to prepare than the corresponding trimethylsilyl derivatives. For these reasons there is little reason to choose them as derivatives when other materials can be used. 

Gas chromatography is used to analyze volatile derivatives of amino acids. Phenylthiohydantoins (products of Edman degradation) may be analyzed directly by GC but are better resolved if converted to their trimethylsilyl derivatives with N, O-bis(trimethylsilyl) acetamide. Free amino acids are generally converted to their 7V-trifluoroacetyl- -butyl esters or trimethylsilyl derivatives before GC analysis. For best results, all gas chromatography of amino acid derivatives should be done with a glass column and injection port, as contact with metals causes extensive decomposition of the derivatives. 

Procedures A and B illustrate the two current methods for preparation of N-9-phenylfluoren-9-yl derivatives of amino acids and amino acid esters. Free carboxylate (as in alanine in Step A) or free hydroxyl (e.g., serine7) functions can be blocked for the duration of the reaction as trimethylsilyl (TMS) esters or ethers, respectively, by treatment with chlorotrimethylsilane and triethylamine. The TMS group(s) are then removed by methanolysls from carboxylic acids (as in Step A) and mild acidic hydrolysis from hydroxyl groups, both being accomplished during product isolation. In addition to 2, the N-9-phenylfluoren-9-yl derivatives of serine,7 glutamic add y-methyl ester,8 and aspartic acid 3-methyl ester3 9 have been prepared in this manner. 

Murray [91] has described a gas chromatographic method for the determination in water of triarylphosphate esters (lmol S-140, tricresyl phosphate, cresol phosphate). These substances are used commercially as lubricant oil and plastic additives, hydraulic fluids and plasticisers. The method involves extraction from the samples, hydrolysis and measurement of the individual phenols by gas chromatography as the trimethylsilyl derivatives. The lower detection limit was about 3ppm. 

It converts acids into trimethylsilyl (IMS) esters and polar alcohols into IMS ethers. However, the IMS derivatives are easily hydrolyzed by traces of water, and measurements should proceed directly after derivatization. 

At about the same time, a synthesis of leukotriene-A, also termed SRS-A ( slow reacting substance of anaphylaxis ), which made use of the Wittig olefmation was described77). The ylide of 100 is reacted with ethyl 5-formyl-2,4-pentadienoate 101 to give the ( , , Z, Z)- tetraenoic ester 102. Reduction and mesylation of 102, subsequent conversion into the sulfonium salt, and treatment of the latter with a base yields a sulfonium ylide which is reacted with methyl 4-formylbutanoate 69 to the epoxy-tetraenoic ester 103. After separation of the cis-epoxide by HPLC, 103 was treated with the S-trimethylsilyl derivative of glutathione dimethyl ester N-trifluoroacet-amide. The diastereomeric products thus obtained were separated by means of HPLC and hydrolyzed to 104 77) (Scheme 18). 

Since its introduction in 1986315, the 2-(trimethylsilyl)ethylsuifonyl group has been widely adopted in alkaloid, carbohydrate and amino acid chemistry, it is every bit as stable as the arylsulfonyl groups discussed above it is impervious to the ravages of trifluoroacetic add, hot 6 M HC1, trifluoroborane etherate, or 40% HF in ethanol. Nevertheless, under very specific non-reductive conditions, it can be cleaved. The link with 2-(trimethylsilyl)ethyl esters, 2-(trimethylsilyl)ethoxycarbon-y t derivatives, and 2-(thmethylsilyl)ethoxymethyl ethers hardly needs comment. 

Gas-liquid chromatography Capillary GLC analysis of bile sterols and bile acid methyl esters (as their trimethylsilyl derivatives) was performed on Hewlett-Packard model No. 4890 (equipped with a flame ionization detector) and a split column injector using a CP sil 5 (CB) WCOT capillary colunm (25 m x 0.22 mm with 0.13-mm Him thickness). Helium was used as a carrier gas at a flow rate of 20.2 mL/min (135 kPa). 

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