Conformation trisaccharides

The unusual properties of xanthan undoubtedly result from its stmctural rigidity, which in turn is a consequence of its Linear, ceUulosic backbone that is stiffened and shielded by the trisaccharide side chains. The conformation of xanthan in solution is a matter of debate. It does appear that the conformation changes with conditions. 

The trichloroacetimidate method has also been used to prepare bivalent Lex oligosaccharides to study the conformational details of carbohydrate clusters by NMR spectroscopy [437] TWo Le trisaccharides were covalently linked through... 

The 3H chemical shifts, coupling constants, temperature coefficients, exchange rates and inter-residual ROEs of the hydroxyl protons of various synthetic type II trisaccharides, analogues of (3-D-Galp-(l - 4)-p-D-GlcpNAc-(l - 2)-a-D-Man-(l - 0)(CH2)7CH3, were reported and interpreted,8 assisted with molecular dynamic simulations, to deduce key information on the conformational behavior of these important molecules in aqueous solution. 

Smythe (72) observed that the trisaccharide 1-kestose (7a), which bears an additional fructose moiety bound to Cl, binds at the —b pole of the crystal of sucrose. This result implies an extended antiplanar conformation (7b) of the group Cl -C-O-C(fiructose) such that the O-C(fructose) bond (filled circles in 7b) of the additive would point toward - b, away from the crystal interior. Note that, as in the sucrose-raffinose system, the Cl -C-O-H group of sucrose 5b (filled circles) adopts a gauche conformation with the C-OH bond pointing in the +b direction. It is gratifying that the necessary extended conformation of Cl -C-O-C was later demonstrated in an X-ray crystallographic study of 1-kestose 7b (74). 

The branched trisaccharide 1 was defined as the minimal carbohydrate epitope for effective binding to anti-GAS Abs [79]. The bound conformation of 1 in complex with the IgG mAb Strep 9 was investigated by transferred NOE experiments and found to correspond to a local minimum conformation, which differed from the predominant conformation in the free state by a rotation around the xj/ angle of the o -(l-2) linkage [123]. STD-NMR ex-... 

In addition to x-ray elucidation of the structure of the crystalline enzyme, the structure of a crystalline complex of lysozyme and tri(N-acetylglucosamine) was determined (Phillips, 1966). The trisaccharide occupied sites A, B, and C. Assuming that binding of a hexamer (adding hexose residues D, E, and F) would not change the conformation of the enzyme, the conformations of the substrate at... 

Four independent conformations were found in the asymmetric unit cell (see Fig. 3), but their superposition showed that all shared the same global shape (see Fig. 4), albeit with slightly different conformations for the externally placed L-rhamnopyranosyl-(1 3)-(9-a-L-rhamnopyranoside moiety. The internal trisaccharide subunit, L-rhamnopyranosyl-(l 2)-(9-)S-D-glucopyranosyl-(1 2)-0-/l-D-... 

Fig. 4. Superposition of the four independent molecules of tricolorin A (106) showing that the internal trisaccharide subunit has limited conformational freedom due to its macrolactone structure...

Figure 18. Contour diagram for the conformational energy of the terminal residue of a trisaccharide segment of the a-(1 2)-L-fucan constrained to satisfy the helical condition - see text for details. Contours are drawn at absolute energies 2,4, 5, 10, 25, and 50 kcal/mol.

N. V. Ganesh, S. Raghothama, R. Sonti,andN. Jayaraman, Ring expansion of oxyglycals. Synthesis and conformational analysis of septanoside-containing trisaccharides, J. Org. Chem., 75 (2010) 215-218. 

A half-chair conformation of a crystalline monosaccharide has not been observed. A half-chair conformation for the fourth 2-acetamido-2-deoxy-/3-D-glucopyranosyl residue (residue D) in the lysozyme substrate has not been detected, although, on the basis of model fitting, its presence has been suggested (see p. 96). 2-Acetamido-2-deoxy-/3-D-glucosyl groups were added to a molecular model constructed by use of data obtained from the nature of the enzyme-trisaccharide complex it was implicit that the lifetime of the half-chair conformation would be quite short. 

Limited, X-ray diffraction evidence suggested that the chain is a 2(1.52) helix, with an uncoordinated variation about this average conformation. As the projected height of the trisaccharide repeat-unit is 1.52 nm, the average advance per saccharide is 0.507 nm, similar to that in cellulose and D-mannan. 

Figure 2. Conformations of the furanose rings in sucrose and the sucrose-containing trisaccharides, raffinose, planteose, and...

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