Overlapping anomeric effects in a sucrose analogue

✍ Scribed by Alfred D. French; Lothar Shaäfer; Susan Q. Newton

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 669 KB
• Volume: 239
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(93)84202-h

✦ Synopsis

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, ub 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-furanylIoxy]-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.