EXPERIMENTAL AND THEORETICAL-STUDY OF STEREOELECTRONIC AND H-BOND CONTROL OF REACTIVITY IN ALPHA-METHYL AND BETA-METHYL D-GLUCOPYRANOSIDE OZONOLYSIS

The topography of the molecular electrostatic potential (MEP) of alpha and beta anomers of methyl D-glucopyranosides has been used to analyz e the reactivity of these species towards electrophilic attack and to complete the results we obtained during the ozonation reaction. Molecu lar mechanics (MM) and molecular dynamics (MD) simulations have been p erformed to screen the conformational space of alpha- and beta-methyl D-glucopyranosides in order to determine the chair conformations which correspond to a global minimum energy conformation. Density Functiona l Theory (DFT) (Faststructure) and PM3 (semiempirical) calculations ha ve been carried out to refine the geometries of the C-4(1) and C-1(4) chair conformations of both anomers. The MEPs of the alpha and beta an omers in their C-4(1) chair conformations have been determined by DFT calculations and have been used to predict their respective reactiviti es. The good agreement between predicted and experimental results obse rved in organic solutions compared with those performed in aqueous sol utions indicates that the water molecules play an ''active'' role in m odifying the intramolecular H-bonds which control the MEP topography a nd consequently the chemical reactivity of both anomers in solutions. (C) 1998 Elsevier Science B.V. All rights reserved.