Silylation of sugars

A recent study extensively investigated the pyrolysis of polysaccharide binders, with and without a silylating agent [56]. Some of the main results relative to the pyrolysis silylation of sugars and polysaccharide binders can be summarised as follows [56 59] ... 

Lablanc and Ball [414] modified this method and applied it to the silylation of sugars... 

Silylation of sugar phosphates requires more drastic conditions [434,435], as follows. 

Chung M-K, Orlova G, Goddard JD, Schlaf M, Harris R, Beveridge TJ, White G, Hallett FR (2002) Regioselective silylation of sugars through palladium nanoparticle-catalyzed silane alcoholysis. J Am Chem Soc 124 10508... 

DJ Leblanc, AJS Ball. A fast one-step method for the silylation of sugars and sugar phosphates. Anal Biochem 84 574—578, 1978. 

The purpose of the experiment is to illustrate the application of derivatisation in the analysis of sugar and related substances by gas-liquid chromatography. The silylation method described is an almost universal derivatisation procedure for carbohydrate analysis by GC.79... 

Gas lasers, 14 681-696 carbon dioxide, 14 693-696 excimer lasers, 14 691-693 helium-neon, 14 681-683 ion lasers, 14 683-688 molecular nitrogen, 14 688-691 Gas lift electrolyte circulation, 9 621 Gas-liquid base stocks, 15 217 Gas-liquid chromatography (glc), 6 374 analysis of sugars via, 23 476 silylation for, 22 692, 697 Gas-liquid contactor, reciprocating jet,... 

Although many analyses are performed on alditol acetates (see Section VII, p. 56), in order to avoid the formation of multiple peaks, such a reduction is not practical when the mixture contains ketoses, notably fructose. Such analyses are mainly encountered with medical samples and in the examination of sugars occurring free in Nature. Furthermore, the peak-area ratios may be used as a means of identification, to check on the completeness of trimethylsilylation,67,89 and, despite the complex chromatograms obtained from trimethyl-silyl derivatives, they have the merit of being rapidly formed.89 For all of these reasons, improvements in the separation of monosaccharides as their trimethylsilyl derivatives continue to be of considerable importance. 

The use of a silyl ether temporary linkage introduced by Nishiyama [82J and Stork [77,83] allows the facile cleavage of the five-membered ring formed in the cyclization by oxidation of the carbon-silicon bond. This procedure has been successfully used for the hydroxymethylation of sugars at position 3, 4, and 6 [84-86] (Scheme 24). 

M. M. Andrade and M. T. Barros, Facile conversion of O-silyl protected sugars into their corresponding formates using POCl3/DMF complex, Tetrahedron, 60 (2004) 9235-9243. 

An entirely different approach to the introduction of isolated double bonds is illustrated by the selective silylation of the 3-hydroxy group of 155 and Swern oxidation at C-2 to give 156 following spontaneous elimination. Final conversion of the enone to the free sugar 157 is accomplished by carbonyl reduction that induces an ester migration (Scheme 17).176... 

If a uniform product cannot be obtained, efforts must be aimed to control the derivatization reaction, maintaining the ratio of different reaction products constant. In addition to silylation procedures, the preparation of ethers, especially methyl ethers, and acyl derivatives offer has been widely applied. Wells et al. [395] and Sloneker [396] described the derivatization problems and GC analysis of sugars in detail. 

The determination of sugars in fruits and other materials involves extraction of the sample with 80% ethanol, transfer of sugars into an aqueous phase with the aid of a chloroform—methanol—water system (64 32 24) and drying. The analysis is carried out on SE-54 or SE-52 stationary phase after silylation [424,425]. The concentrations of monosaccharides can similarly be determined in the course of a fermentation process [426] and, after hydrolysis, also in polysaccharides from cellular walls and apple tissues [427,428]. SE-30 served as a stationary phase for these analyses. 

VORBRUGGEN Nucleoside synthesis Synthesis of nucleosides by condensation of sugars with silyl heteiocycies and Lewis acids such as SnCU or trimethylsilyf Inflate 3. 

The intramolecular aldol reaction in the presence of a titanium Lewis acid is a viable means of preparation of cyclic compounds. The cyclization is most conveniently performed between an enol silyl ether and an acetal, because the former is a reactive enol derivative and is readily prepared by silylation of the corresponding ketone in the presence of the acetal moiety in the same molecule. Equation (12) exemplifies a substrate undergoing intramolecular ring closure mediated by TiCU [74]. The conversion of sugar derivatives to carbocycles (called the Perrier reaction [75,76]) has been reported to occur in the presence of a Lewis acid. This process involves the aldol reaction between the enol ether and acetal moieties in the same molecule promoted by a titanium salt, as illustrated in Eq. (13) [77]. The similar reaction of a different type of substrate was also reported [78]. 

Anionic nucleophiles provide valuable and versatile routes for the preparation of C-glycosides. However, the most extensively used technologies lie within the chemistry of Lewis acid-mediated reactions of carbohydrates with unsaturated hydrocarbons and derivatives thereof. In the next series of examples, reactions of sugars and sugar derivatives with olefins and their silyl-, stannyl-, and aluminum derivatives are discussed. 

Early reviews on the mass spectra of nucleotides, more particularly of mononucleotides, " covered trimethylsilyl and methyl derivatives of nucleotides. The silylation of nucleotides, for instance, takes place on the base, on the sugar hydroxyls, and on the free phosphate hydroxyls under mild (room temperature) and basic (pyridine) silylation conditions (BSTFA/TMCS). The fragmentation of derivatives obtained from both procedures has been well studied. Several typical fragments ([M — CHj]", [base -I- 2H], silylated and desilylated sugar, S-TMSOH, etc.), as well as a weak M+ ion have been recorded. The FD spectrum of an underivatized... 

Field desorption spectra clearly show the cleavage of the phosphate - sugar and the base-sugar bonds. This technique, along with the silylation of the... 

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