Fragmentation disaccharide

S. Cros, C. Herve du Penhoat, N. Bouchemal, H. Ohassan, A. Imberty, and S. Perez, Int. ]. Biot. Macromol., 14,313 (1992). Solution Conformation of a Pectin Fragment Disaccharide Using Molecular Modelling and Nuclear Magnetic Resonance. 

Fragments (disaccharides to pentasaccharides) of complex structures are often sufficient for full biological activity, of which some examples are listed in Table I (6). These structures have been produced mainly by chemical synthesis or by isolation from natural sources. Although these methods are well-developed for the preparation of mg- to g-quantites, they are not suitable for synthesis of g- to kg-quantities. 

In 1967, Heidelberger, Stacey et al. reported the purification, some structural features, and the chemical modification of the capsular polysaccharide from Pneumococcus Type I. Difficulties of direct hydrolysis of the polysaccharide were overcome and it was possible to identify some of the fragments in the hy-drolyzate. At least six products resulted from nitrous acid deamination. Two were disaccharides, which were identified, and sequences of linked sugar units were proposed. As modification of the polysaccharide decreased the amounts of antibody precipitated by anti-pneumococcal Type I sera, the importance of the unmodified structural features in contributing to the specificity of the polysaccharide was indicated. 

In Fig. 3 all conformers are plotted within 3 kcal/mol above, the global minimum found by CICADA for each of the glycosidic torsions, superimposed on the corresponding disaccharide relaxed map. Fig. 4 clearly indicates that most of the local minima present in the corresponding disaccharide fragments are also explored along the PES of the pentasaccharide by CICADA... 

Scheme 5.—Typical Cleavage of Heparin (Arbitrary Sequence) with Heparinase (HEPase) and Heparanase (HSase). [Fragments longer than a tetrasaccharide may be obtained by separate use of each enzyme. The combined use of the two enzymes produces only disaccharides.]...

Saliva begins the process of chemical digestion with salivary amylase. This enzyme splits starch molecules into fragments. Specifically, polysaccharides, or starches, are broken down into maltose, a disaccharide consisting of two glucose molecules. Salivary amylase may account for up to 75% of starch digestion before it is denatured by gastric acid in the stomach. 

Polysaccharide (starch) Amylase Fragment polysaccharides into disaccharides (maltose) Salivary glands pancreas Mouth stomach small intestine... 

In fact, other studies have shown that TMSOTf catalyzes the glycosylation of a silylated acceptor with a silylated hemiacetal donor [49]. Nudel man s procedure was applied to the synthesis [1-glucuronide 30, isolated in 57% yield. Kiyoi and Kondo have applied the TMSOTf activation protocol to protected L-fucose hemiacetal donors for glycopeptide synthesis and obtained glycopeptide fragment 31 in 74% yield (a p, 20 1) [50], Posner and Bull have developed a procedure that uses excess TMSOTf in the presence of molecular sieves (SYLOSIV A4) to synthesize various l.l -linked disaccharides such as the galactopyranose dimer 32 [51,52]. 

Preliminary treatment of the disaccharide IX with methyl alcoholic hydrogen chloride at room temperature, followed by methylation and subsequent methanolysis, enabled the series of reactions XIII — XIV — XV + XVI to be effected. Identification of the two fragments XV and XVI was then carried out in the usual way. ... 

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