Combined NMR, grid search/MM3 and Metropolis lonte Carlo/GEGOP studies of two L-fucose containing disaccharides: α-L-Fuc-(1,4)-β-D-GlcN Ac-Ome and α-L-Fuc-(1,6)-β-D-Glcn Ac-OMe

摘要

Complete proton NMR data provided a firm experimental basis to infer the conformational properties of the Lewis type Jsacchnride a-L-Fuc-(l,4)-3-D-GlcNAc-OMe 1 and the N-glycoprotein type disaccharide a-L-Fuc-(l,6)-E-D-GIcNAc-0Me 2 aqueous solution.. Relaxed potential energy maps from systematic grid searches (GS) using the MM3 force field and Metropolis Monte Carlo (MMC) simulations employing the GEGOP force field were used to calculate corresponding ensemble mage NMR data such as 1D transient NOE curves and vicinal coupling constants J(H,H). For the disaccharide with a flexible ,6) linkage (2), the relaxed potential energy surface based on the MM3 force field was calculated with three variable dihedral hgles,φ,ψ and w. R-factors derived from a comparison of experimental and theoretical NOE data allowed an evaluation of the Jialily of the conformational models derived from the calculations. Seven inter glycosidic ID transient NOE curves were Basured for each of both disaccharides, 1 and 2, Overall K-factors of approximately 17% for the 1-4 linked disaccharide and for the 1 -6 linked disaccharide indicate a very satisfying agreement between theoretical calculations, both GS/MM3 and C/GEGOP, and experimental NOR data, indicating that the gross conformational picture developed is realistic. On the r hand, a close inspection of individual NOE curves arid vicinal coupling constants 3/(H5,H6-pro-R) and V(H5,H6-pro-S) Hth corresponding theoretical values revealed shortcomings of the computational methods applied. Firstly, the qonformational librium around the C5-C6 bond of the GlcNAc unit in disaccharide 1 is not correctly described by the GS/MM3 method. his can lead to a; false interpretation of NOE data involving protons attached to C6 of GlcNAc. Secondly, relaxation of ring ;eomcliy (GS/MM3) was found to have a measurable improvement of intra glycosidic NOEs in both disaccharides, 1 and 2. In &mmary, the conFormational models derived for disaccharides 1 and2 represent a starting point for further analysis of potential informational changes that may occur upon binding of these compounds to specific receptor proteins such as lectins or libodies.