Substitutional and solvation effects on conformational equilibria. Effects on the interaction between opposing axial oxygen atoms

Abstract

Evidence based both on nuclear magnetic resonance and rotation data primarily obtained from methyl 3-deoxy-13-L-erythro-pentopyranoside and a number of its derivatives is interpreted to show that the electrostatic repulsion between the oxygen atoms at the 2 and 4 positions is substantially less when these oxygens are linked to acyl groups than when in the form of either methyl ethers or as hydroxyl groups hydrogen bonded to solvent. Also, experimental evidence is presented which requires the hydrogen bridge between two axially disposed hydroxyl groups to be s~~bstantially strengthened by hydrogen bonding of the free hydroxyl by solvent.Canadian Journal of Chemistry, 47, 4441 (1969) The DurDose of this communication is to L L report on substitutional and solvation effects on chair-chair conformational equilibria which involve in one conformation an interaction between two oxygen atoms in opposing axial orientation. Profound effects are noted which have an important bearing on the notion that so-called non-bonded interaction free energies can be assigned to such interactions without reference to the kind of compound or to the conditions of the experiment.As seen in Table I, the coupling constants estimated for the di-0-acyl derivatives (16, lc, and ICE) of methyl 3-deoxy-P-L-erythro-pentopyranoside (la) require these compounds to exist largely in the C-1 conformation which has both the acyloxy groups in axial and opposing orien-e R = R' = CH, f R = Ac; R' = CH, g R = H ; R ' = CH3 'Presented by R. U. L. at the Karl Pfister Lecture,

Molecular recognition XII. The binding of the H human blood group determinants and congeners by a lectin of Galactiatenuiflora

“…for C,,H6,NOIs: C 70.05,H 6.44,N 1.29;found: C 69.64,H 6.49,N 1.47. 94.3 (c 0.9, water) and 'H and "C nmr data identical to those reported previously (14) (Table 3).…”

“…Derivatives of H-type I-OMe (5) 5b-H-type 1-OMe N-Deacetyl 4a-Deoxy 6a-Deoxy Dehydroxyrnethylene (5) (6) (14) the 2b-0-acetyl group of 30 by the much bulkier 2,3,4-tri-0-benzyl-a-L-fucopyranosyl group of 32 has little effect on the conformational equilibrium in CDCl, is in accord with expectation based on an important contribution to conformational preference by the e>xo-anomeric effect (1 6). Since this stereoelectronic effect stabilizes the anti-periplanar relationship for the C-4a and C-2b atoms, it will favor projection of the substituted P-D-GlcNAc unit away from the 0-benzylated a-L-FUC residue.…”

1H-NMR Analysis of Intra- and Intermolecular H-Bonds of Alcohols in DMSO: Chemical Shift of Hydroxy Groups and Aspects of Conformational Analysis of Selected Monosaccharides, Inositols, and Ginkgolides

“…9) decreases when the H-accepting OH group is alkylated. This strongly evidences cooperativity between an intramolecular H-bond and an intermolecular H-bond to (D 6 )DMSO [66] 17 ). The larger J(2,OH) value for a-d-glucopyranose (17; 6.8 Hz) than for methyl a-d-glucopyranoside (19; 6.45 Hz [35]) similarly indicates that cooperativity with intermolecular H-bonds to (D 6 )DMSO strengthens a rather weak intramolecular H-bond.…”

The synthesis and conformational properties of the diastereoisomeric βDGal(1→4)βDGlcNAc(1→6)6-C-CH3-D-Gal trisaccharides

“…In the case of 6b, note that H5 and H6 are in anti-periplanar orientation and that the C7-methyl groupis in syn-axial like orientation with H4. depending on its substituents (16). Moreover, the calculations do not include either electrostatic terms or a consideration of the effect on the apparent volume of hydroxyl groups when these are hydrogen bonded to the solvent water.…”