CD and 1H NMR Study of the Rotational Population Dependence of the Hydroxymethyl Group in .beta. Glucopyranosides on the Aglycon and Its Absolute Configuration

Conformation, dynamics, solvation and relative stabilities of selected β-hexopyranoses in water: a molecular dynamics study with the gromos 45A4 force field

“…The formation of intramolecular hydrogen-bonds in aqueous environment appears to be an 'opportunistic' consequence of the close proximity of hydrogen-bonding groups, rather than a major conformational driving force promoting this proximity. In particular, hydrogen-bonding seems to have a very limited influence on the conformational properties of the hydroxymethyl group in water 92,96,101,102,104,131,144,152,157,180,189,190,305,351,[354][355][356][357] Experimental evidence 121,122,125,126,148,149,155 suggests that this principle also applies to the high-occurrence 1,3-syn-diaxial hydrogen-bond between the 2-OH and 4-OH groups in Tal (i.e., this hydrogen-bond occurs because the two groups are 'locked' in l,3-syn-diaxial orientation in the most stable 4 C 1 ring conformer, but does not in itself contribute to the stability of this conformer). In fact, in water, the cumulative effect of steric repulsion and hydrogen-bonding between two 1,3-syn-diaxial hydroxyl groups probably represents an overall destabilizing factor for a given molecular conformation.…”

“…104,241,251,[293][294][295]333,353 On the other hand, the limited impact of intramolecular hydrogen-bonding between the 4-OH and 6-OH groups in water on this conformational distribution has been clearly evidenced experimentally by (i) examining the influence of the solvent polarity on this distribution; 101,102,131,152,157,180,189,190,305,351 (ii) analyzing the correlation between the rotamer populations of the x and v 6 dihedral angles 96 (see above); and (ii) investigating hexopyranose analogs and model compounds lacking specific potential hydrogen-bonding groups. 92,101,102,104,131,144,152,189,190,305,351,[354][355][356][357] Many of these studies also hint toward a negligible effect of H 6 !O 5 hydrogen-bonding.…”

Assignment of absolute configuration using chiral reagents and NMR spectroscopy

“…(R)- (2) and (S)-(1)-Phenylglycine methyl ester (PGME) (38) are especially effective reagents for the assignment of absolute configuration of carboxylic acids. The amide derivatives adopt a preferred conformation and the sign of the Dd RS values are used in making the assignment.…”

Interplay of Protecting Groups and Side Chain Conformation in Glycopyranosides. Modulation of the Influence of Remote Substituents on Glycosylation?

“…23−25 The interplay between the conformation of the side chain and the glycosidic bond is further apparent from the work of Vázquez and co-workers in which it is demonstrated by CD and NMR methods that both the anomeric configuration and the nature of the aglycone influence the population of the different side chain conformers. 26−30 …”