Mm3 Modeling of Aldopentose Pyranose Rings

Abstract

MM3 (version 1992, ϵ=3.0) was used to study the ring conformations of d-xylopyranose, d-lyxopyranose and d-arabinopyranose. The energy surfaces exhibit low-energy regions corresponding to chair and skew forms with high-energy barriers between these regions corresponding to envelope and half-chair forms. The lowest energy conformer is 4 C 1 for α-and β-xylopyranose and α-and β-lyxopyranose, and the lowest energy conformer is 1 C 4 for α-and β-arabinopyranose. Only α-lyxopyranose exhibits a secondary low-energy region ( 1 C 4 ) within 1 kcal/mol of its global minimum. Overall, the results are in good agreement with NMR and crystallographic results. For many of these molecules, skew conformations are found with relatively low energies (2.5 to 4 kcal/mol above lowest energy chair form). The 2 S O and 1 C 4 conformers of crystalline benzoyl derivatives of xylopyranose are in secondary low-energy regions on the β-xylopyranose surface, within 3.8 kcal/mol of the global 4 C 1 minimum. Disciplines Biochemical and Biomolecular Engineering | Biological Engineering | Chemical Engineering

Synthesis of Fusion‐Isomeric Imidazopyridines and Their Evaluation as Inhibitors of syn‐ and anti‐Protonating Glycosidases

“…J(1,2) 2.4, J(2,3) 3.0 Hz are in agreement with a preferred 4 C 1 conformation. The data are consistent with coupling constants calculated for the 4 C 1 conformer of a-d-lyxose (J(1,2) 2.1, J(2,3) 3.1, J(3,4) 8.8, J(4, 5 eq ) 5.8, J(4,5 ax ) 10.5 Hz) [40], which is more stable than the 1 C 4 conformer by ca. 0.9 kcal/ mol.…”

“…0.9 kcal/ mol. These interpretations are supported by MM3 calculations [40]. Crystalline methyl a-d-lyxopyranoside also adopts the 4 C 1 conformation [41].…”

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

“…Ring conformation: Pyranose systems may present at least eight relevant conformers in solution 1,2,18,20,[41][42][43][44] (which are most easily distinguished geometrically by means of appropriate pseudorotation variables 20,[45][46][47][48][49][50][51][52][53], namely two chair forms (originally labelled C1 and 1C or, more recently, 4 C 1 and 1 C 4 ) and six boat forms (labelled 1,4 B, 2,5 B, 3,0 B, B 1,4 , B 2,5 and B 3,0 ). Skewboat forms may also be of relevance for some systems.…”

Conformational fluctuation in palladium(II)–methyl aldopentopyranoside complexes

“…25,26 The coupling constants thus indicate a 1:1 mixture of the 4 C 1 and the 1 C 4 conformers of methyl b-D-ribopyranoside. The Unlike the arabinopyranoside and the lyxopyranoside, the ribopyranoside provides a special bonding mode to the palladium(II) central metal.…”

“…25,26 The formation of five-membered chelate rings by the attack of a vicinal diol function is the predominant mode of palladium(II)-pyranose binding. Both cis-or trans-diolate binding is common, the latter requiring a diequatorial conformation.…”