The NMR Coupling Constants, and Conformational and Structural Properties of Flexible Aldopyranosyl Rings: α- and β-D-Idopyranose
The flexible ring structures of α- and β-D-idopyranose have been investigated by conformational analysis using structures generated by MacroModel and GMMX search protocols. The lowest energy structures found during the conformer search for the 4 C 1 , 1 C 4 , O S 2 and the 3 S 1 structures were then...
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Published in | Journal of carbohydrate chemistry Vol. 19; no. 7; pp. 959 - 974 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Taylor & Francis Group
01.01.2000
|
Online Access | Get full text |
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Summary: | The flexible ring structures of α- and β-D-idopyranose have been investigated by conformational analysis using structures generated by MacroModel and GMMX search protocols. The lowest energy structures found during the conformer search for the
4
C
1
,
1
C
4
,
O
S
2
and the
3
S
1
structures were then examined by AM1 and Gaussian ab initio methods at the HF/6-311G** and HF/6-31+G* levels. The B
2,5
conformer found for β-D-idopyranose at 14 kJ/mol by GMMX and 29.5 kJ/mol for α-D-idopyranose by MacroModel would not contribute to Boltzmann-averaged
1
H NMR coupling constants. The Merck MMFF force field tends to overweight the
1
C
4
structures, making these the lowest energy conformers for both anomers. Boltzmann-averaged coupling constants are heavily weighted by this structure in the MMFF search conformer ensemble. Averaged proton coupling constants determined using MMFF fit very well for α-D-idopyranose compared to the observed values, but fit poorly for the β-anomer. Ab initio results place the
1
C
4
conformer at lowest energy for the α-anomer and place the
4
C
1
conformer at lowest energy for the β-anomer. The GMMX and MM3* force fields find the
4
C
1
conformer to have the lowest energies for both anomers. |
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ISSN: | 0732-8303 1532-2327 |
DOI: | 10.1080/07328300008544128 |