Showing papers by "Serge Pérez published in 1990"

Data bank of three-dimensional structures of disaccharides, a tool to build 3-D structures of oligosaccharides

Abstract: This work presents the first part of a database of conformations for all the disaccharide fragments that are found inN-glycans. The conformational study of the five disaccharides found in the oligo-mannose type are presented here. For each disaccharide, several possible conformations are described. A method is presented to obtain realistic models of oligosaccharides using molecular mechanic methods. Analysis of some possible conformations of the oligo-mannose type glycan Man6-GlcNAc2 is given as an illustration of the possibilities.

Relaxed potential energy surfaces of N‐linked oligosaccharides: The mannose‐α(1 → 3)‐mannose case

Abstract: We report calculations of potential energy surfaces where all the internal coordinates of the disaccharide Man-α(1 → 3)-Man-α-O-Me were relaxed and minimized through an extensive molecular mechanics scheme. Flexibility within the mannopyranose rings plays a crucial role. Introduction of the relaxed principle into the conformational description of the disaccharide does not greatly alter the overall shape of the low-energy domains but it reveals new local minima. However, its principle effect is the lowering of energy barriers in the potential energy surface. New conformational transitions about the glycosidic bonds appear, permiting pathways among the low energy sections. This occurs with only little variation of the classical 4C1 conformation of the mannopyranose residues. All the conformations observed in the solid state, along with those already predicted through the joint use of NMR and modeling techniques, fall into the populations of stable conformers calculated in the present work. Moreover, a satisfactory agreement is reached between previously observed NOE values, and the theoretical one, calculated from the averaging of more than 500 microstates. The present results reconciliate most of the apparently conflicting data previously reported; they provide strong support for the application of the concept of conformational averaging to solution behavior. Some limitations of the proposed methodology are also discussed.

Solvent effect on the stability of isomaltose conformers

Abstract: The conformational equilibria of the low-energy conformers of isomaltose have been studied in different solvents. The structure of each individual conformer was refined from the 18 distinct low-energy regions determined from potential energy function. Molecular geometry optimization was carried out using the quantum chemical method of perturbative configuration interaction with localized orbitals or PCILO and yielded to 15 distinct minima. Carbon-proton vicinal coupling constants 3JC-H have been calculated based on the finite perturbation theory formulation with the intermediate neglect of differential overlap for these minima. For evaluation of the influence of the environment on the conformational structure of isomaltose, the population of the low-energy conformers was estimated in four solvents by a method in which the total energy is divided into the energy of the isolated molecule and the solvation energy. The calculated abundances of conformers depend strongly on the solvents. Based on the determined abundance of conformers, thermodynamically averaged torsion angles and coupling constants 3JC-H describing the “average” conformation about glycosidic linkage have been calculated. Results obtained are compared with available experimental data from solution and solid state.