Disaccharides conformational analysis

The conformational analysis was developped recently by different authors first on the disaccharide units to investigate the role of the charge on C-6 position on the conformation [29-32]. From this study, the 2i or right-handed 3i helices were described as most problable conformations [30,31]. These conformations were also demonstrated from x-ray diffraction [33] or on the basis of circular dichroTsm [34], From these data, the repeat unit in the axial-axial conformation has a 4.3 A° length which will be used to characterize the electrostatic properties. 

Our procedure depends on a new computer program, RAMM (RAndom Molecular Mechanics), which is applicable to any kind of biomolecule. It is described in detail elsewhere (KoS r, T./ Petrak, F. Galova, Z. TvaroSka, I. Carbohvdr. Res.. in Press). Only the basic characteristics of RAMM and its application to conformational analysis of disaccharides are discussed here, concentrating on the effect of the orientations of pendant groups on the energy values at the various < ) and f torsion angles. 

We briefly present here a conformational analysis of the disaccharide, methyl (4-0-P-D-xylopyranosyl-p-D-xylopyranoside)... 

This review presents a brief account on the conformation of biologically active oligosaccharides. Emphasis will be put on the conformational analysis of heterooligomers. The conformational preferences of some disaccharides will be included for reference purposes. Conformational aspects of homo-oligomers and homopolymers will not be discussed. 

This article is the third in the current series on the bibliography of crystal structures of polysaccharides.1,2 In the past decade, many advances in the methods for building theoretical models were witnessed, not only for the conformational analysis of isolated chains, but also for the subsequent or simultaneous packing of the chains in the crystallographic lattice. Many complex polysaccharides, having disaccharide to hexasaccharide repeating units, are now being studied. 

N. Bouchemal-Chibani, I. Braccini, C. Derouet, C. Herve du Penhoat and V. Michon. Conformational Analysis of disaccharides using molecular dynamics and NMR methods. Int. J. Biol. Macromol. 17 (1995) 177. 

The conformational analysis of monosaccharides, disaccharides, and ohgosaccharides is reviewed. Conformational terms are introduced through examination of the conformations of cyclohexane and cyclopentane then applied to the pyranose, furanose, and septanose rings. Concepts such as the anomeric effect are discussed. Topics of current interest, such as hydroxymethyl group and hydroxyl group rotation and disaccharide conformations are summarized. Physical methods for studying conformation are outlined. 

NMR and UV-vis spectroscopic studies as well as molecular mechanics calculations have been performed for the trans and cis isomers of a series of chlorine substituted stilbenes. In a continuing study on the use of hydroxy protons in conformational analysis of saccharides in aqueous solution by NMR, a number of disaccharides with 1,3-, 1,4- and 1,6-hnkages were investigated. ... 

In disaccharides one can also observe a slower secondary P-relaxation. Recently, it was shown that twisting rotation of the monosugar units around glycosidic bond is responsible for occurrence of this relaxation. This supposition was confirmed by theoretical conformational analysis. Additionally, it was proven that the activation energy provides direct information about structural rigidity of the examined disaccharides. 

Figures 1.2.2 (Yuan Wang, Peter G. Goekjian, David M. Ryckman, William H. Miller, Stefan A. Babirad, Yoshito Kishi "Preferred Conformations of C-Glycosides. 9. Conformational Analysis of 1,4-Linked Carbon Disaccharides" The Journal of Organic Chemistry 1992,...

Several problems associated with the interpretation of NOE data in carbohydrate conformational analysis have been elegantly illustrated by Widmalm et al., who were able to reproduce only two of three NOE buildup curves for the disaccharide a-L-Rha(l-2)a-L-Rha... 

Several physical studies have been carried out on cyclodextrin derivatives. Thus the X-ray structure of per-(6-bromo-6-deoxy-2,3-di-0-methyl)P-cyclodextrin has been examined by single crystal X-ray diffraction analysis. The conformation deviates significantly from C symmetry. Likewise the X-ray structure of heptakis-2,3,6-tri-C>-methyl-P-cyclodextrin shows that one of the seven rings is inverted. Conformational analysis of an extensive set of per-O-substituted p-cyclodextrins reveals that several show conformational isomerism. The relevance of this to the use of cyclodextrins in molecular device design is examined. Related work undertook n.m.r. and molecular modeling studies on a-cyclodextrin in vriiich one of the units is in the 3,6-anhydro from. The work included the examination of two model disaccharide imits. ... 

A conformational analysis of furanoid - pyranoid non-reducing disaccharides, based on crystallographic data, has been published, and the conformation of trehalose incorporated in a micelle has been studied by H-n.m.r, spectroscopy. Conformational analysis by use of various and C-n.m.r. techniques in combination with theoretical calculations has been achieved for the two galactobiosides (18) and (19), for the eight-membered 3,2 -O-isopropylidene acetals (20) and (21) of methyl / -cellobioside and benzyl -D-lactoside, respectively. 

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