Overlapping anomeric effects in a sucrose analogue.
Previous calculations with the molecular mechanics program MM3 gave unusually high energies (as much as 5.5 kcal/mol) for sucrosyl geometries found in single-crystal diffraction studies of oligosaccharides. Comparable MM3 energies for observed interresidue linkage conformations of disaccharides such as maltose and cellobiose are all within 2.8 kcal/mol. These results suggest that some energies calculated by MM3 for the linkage between anomeric centers of a pyranose ring and a furanose ring are too high. In the present paper, ab initio calculations at the 4-21G level and MM3 were used to study the conformational energies and geometry of a sucrose analogue, tetrahydro-2-[(tetrahydro-2-furanyl)oxy]-2H-pyran. The range of energies of the observed structures was substantially reduced (to 2.4 kcal/mol) with the 4-21G calculations for the analogue despite an increase for the analogue (to 7.5 kcal/mol) based on new MM3 calculations. Besides the improved energy values, the 4-21G calculations also reproduced the observed variations in the endocyclic C-O bond lengths better than did MM3.
French
A D
AD
Southern Regional Research Center, U.S. Department of Agriculture, New Orleans, Louisiana 70179.
Schäfer
L
L
Newton
S Q
SQ
D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D008432:Mathematical Computing; D008956:Models, Chemical; D008969:Molecular Sequence Data; D013237:Stereoisomerism; D013395:Sucrose / Q000031:analogs & derivatives* / Q000737:chemistry
C080412:tetrahydro-2-((tetrahydro-2-furanyl)oxy)-2H-pyran; D013395:Sucrose