Anhydro-oligosaccharides

Direct and non destructive analysis (HPLC, and HPLC coupled with MS) shows that ILC contains anhydro-oligosaccharides with degrees of polymerization ranging from 7 to 2 and levoglucosan. These species result from the depolymerization of the cellulose molecules, It is important to note that the chemical composition of ILC does not depend on the operating conditions (heat flux densities and flash times). 

Radlein, A.G. Grinshpun, A. Piskorz, J. Scott, D.S. On the presence of anhydro-oligosaccharides in the syrups from the fast pyrolysis of cellulose. J. Anal. Appl. Pyrolysis 1987, 12, 39-49. 

Figure 14 In-source pyrolysis ammonia chemical ionization mass spectrum of cellulose, showing pseudomolecular ions [MNHJ of a series of 1,6-anhydro-oligosaccharides, ranging from the monomer (miz 180) to the dodecamer (miz 1962). The spectrum was obtained using a Pt-Rh filament probe and an E-B-type sector instrument. Reproduced by permission of Elsevier Science from Boon JJ (1992) Analytical pyrolysis mass spectrometry new vistas opened by temperature-resolved in-source PYMS. International Journal of Mass Spectrometry and Ion Processes 118/119 755-787.

Fourteen DFAs and some oligomers were identified in caramel obtained by thermal treatment of inufin. - Monosaccharides (glucose, fructose), dehydration products (1,6-anhydro-p-D-glucopyranose, 1,6-anhydro-p-D-glucofuranose), disaccharides (gentiobiose and isomaltose), and oligosaccharides were also found in glucose and sucrose caramel. ... 

The identification of L-iduronic acid as the major glycuronic acid constituent of heparin proved to be a much slower process than the identification of the amino sugar residue. Although this compound was detected in acid hydrolyzates of heparin116117 and heparin oligosaccharides,118 its yield was usually poor, because of the drastic conditions used for the acid hydrolysis (which are known to lead to extensive destruction of uronic acid).119120 Also, L-iduronic acid escaped detection as L-idose in the hydrolyzates of carboxyl-reduced heparin, probably because L-idose is readily converted into 1,6-anhydro-L-idose under the usual hydrolytic conditions. 

As a further illustration of the scope for use of 1,6-anhydro sugars in the preparation of uncommon sugars, the rare L-idose derivative 210 has been prepared recently and used in the preparation of oligosaccharides containing iduronic acid... 

Figure 5. 22.63-MHz C-13-NMR spectra of (a) agarose (4a.) (b) neoagaro-oligo-saccharides ("lb, n = 3.9) produced by enzymic hydrolysis of 4a with p-agarase and (c) agaro-oligosaccharides ( 4c, n = 2.5) produced by enzymic hydrolysis of 4a with u-agarase. Spectra recorded in DgO solution at 33°C (3b,5c) or 93°C (5a). G = D-galactose, A = 3,6-anhydro-h-galactose.

Anhydro derivatives of mono- and disaccharides have been particularly useful as glycosyl donors and acceptors for the production of dextran-type oligosaccharides [5]. 

The last method is by intramolecular delivery (Scheme 43, d) 422-425 although elegant, this method has not yet found practical application in the synthesis of complex oligosaccharides. It remains to be seen if the method will work with the rather unreactive 4 -hydroxy group of chitobiose derivatives. This reactivity has been increased both by application of phthaloyl protection of the 2-amino groups and by application of the inverted conformation of l,6-anhydro-2-azido-2-deoxyglucopyranose. 8 ... 

Trimethylsilylation is adversely affected by moisture, and therefore, hydrolyzates should be evaporated to dryness as completely as possible. If trimethylsilylation is catalyzed by trifluoroacetic acid, instead of chlorotrimethylsilane, moderate proportions of water may be tolerated,117,127-129 but, even under these conditions, extra peaks may be obtained from partly trimethylsilylated derivatives.130 Catalysis with trifluoroacetic acid is useful when aqueous aliquots from a reaction are to be trimethylsilylated.131 A further advantage of this method, which has been used in the determination of 1,6-anhydro-jS-D-glucopyranose in corn syrup,132 for cycloamyloses,133 and for a series of malto-oligosaccharides,134 is that ammonium trifluoroacetate is soluble in pyridine. 

The reaction of carbohydrates in alkaline or acidic aqueous solutions results in a myriad of products, many of which have been recognized for well over a century. The number of identified products has greatly increased in recent years, owing to the development of sophisticated techniques for separation and identification. With the exception of anhydro sugars and oligosaccharides, found as concentration-dependent, equilibrium constituents (reversion products) in acidic solutions, all of the products result from reactions of intermediates present in the Lobry de Bruyn-Alberda van Ekenstein transformation. 

For glycoproteins, the formation of anhydro rings from hexosamine residues is important in chromogen formation, especially in relation to the Ehrlich reaction and its modifications (3). / -Elimination is involved in the removal of oligosaccharide or polysaccharide chains from the protein core of glycoproteins when they are attached by O-glycosidic linkages to serine or threonine residues. A subsequent -elimination may also... 

A number of 1 ->4-linked anomerically modified oligosaccharides can be obtained by NIS glycosylations. By treatment of the 2,3-anhydro-a//o derivative 195 with lithium iodide the trans-opening predominantly gives the 2-deoxy-2-iodo-altro glycoside 196, which in turn can be reductively eliminated to furnish the D-digitoxal. After acetylation to 197 and glycosylation with a second molecule of a//o-epoxide 195, the disaccharide 198 is obtained in 72 % yield. 

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