| 1. |
- Olsson, Ulrika, et al.
(författare)
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Conformational analysis of β-linked glucobiosides based on hetero- and homonuclear couplings across the glycosidic linkage
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:14, s. 4447-4453
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Tidskriftsartikel (refereegranskat)abstract
- Four β-linked glucobioses selectively 13C labeled at C1‘ or C2‘ have been prepared. The inter-residue coupling constants, JCH, and JCC, have been determined and related to the solution conformations of the disaccharides using Karplus-type relationships. Relying only on the experimental coupling constants, glycosidic linkage conformation in methyl α-sophoroside (methyl 2-O-β-d-glucopyranosyl-α-d-glucopyranoside), methyl α-laminarabioside (methyl 3-O-β-d-glucopyranosyl-α-d-glucopyranoside), and methyl α-cellobioside (methyl 4-O-β-d-glucopyranosyl-α-d-glucopyranoside) were found to be close to those observed in the solid state (39° < H < 41°, −24° < ψH < −36°). The laminarabioside and cellobioside were found to have conformations that accommodate an intramolecular hydrogen bond to O5‘ that is observed in the solid state. In all compounds, the exocyclic hydroxymethyl groups retain a conformation close to that observed in unsubstituted glucose (gt/gg 1:1). Methyl α-gentiobioside (methyl 6-O-β-d-glucopyranosyl-α-d-glucopyranoside) shows greater flexibility at the ψ-torsion than the other disaccharides, but the population distribution around the C5−C6 bond is essentially unaffected by substitution. None of the O2‘ hydroxyl groups of the β-d-glucopyranosyl residues in any of the disaccharides appear to be involved in inter-residue hydrogen bonding since 1JCH, 1JCC, and 2JCH values sensitive to C2‘−O2‘ rotamer distribution remain close to those observed in methyl β-d-glucopyranoside.
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| 2. |
- Olsson, Ulrika, et al.
(författare)
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Conformational flexibility and dynamics of two (1→6)-linked disaccharides related to an oligosaccharide epitope expressed on malignant tumour cells
- 2009
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 15:35, s. 8886-8894
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Tidskriftsartikel (refereegranskat)abstract
- The conformational flexibility and dynamics of two (1→6)-linked disaccharides that are related to the action of the glycosyl transferase GnT-V have been investigated. NMR NOE and T-ROE spectroscopy experiments, conformation-dependent coupling constants and molecular dynamics (MD) simulations were used in the analyses. To facilitate these studies, the compounds were synthesised as α-d-[6-13C]-Manp-OMe derivatives, which reduced the 1H NMR spectral overlap and facilitated the determination of two- and three-bond 1H,1H, 1H,13C and 13C,13C-coupling constants. The population distribution for the glycosidic ω torsion angle in α-d-Manp-(1→6)-α-d-Manp-OMe for gt/gg/tg was equal to 45:50:5, whereas in α-d-Manp-OMe it was determined to be 56:36:8. The dynamic model that was generated for β-d-GlcpNAc-(1→6)-α-d-Manp-OMe by MD simulations employing the PARM22/SU01 CHARMM-based force field was in very good agreement with experimental observations. β-d-GlcpNAc-(1→6)-α-d-Manp-OMe is described by an equilibrium of populated states in which the ϕ torsion angle has the exo-anomeric conformation, the ψ torsion angle an extended antiperiplanar conformation and the ω torsion angle a distribution of populations predominantly between the gauche–trans and the gauche–gauche conformational states (i.e., gt/gg/tg) is equal to 60:35:5, respectively. The use of site-specific 13C labelling in these disaccharides leads to increased spectral dispersion, thereby making NMR spectroscopy based conformational analysis possible that otherwise might be difficult to attain.
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