Synthesis and NMR and conformational studies of the four anomeric methyl glycosides of the trisaccharideD-Glcp-(1→2)-D-Glcp-(1→3)-α-D-Glcp

Abstract

The four anomeric methyl glycosides of the trisaccharide D -G l c p -( l ~2 ) -D -G l c p -( l ~3 ) -a -D -G l c p have been synthesized and used for l H and 13C N M R studies. All "H and 13C N M R resonances were assigned and comparison was made between the observed glycosylation shifts, i.e. the differences between chemical shifts for signals from the trisaccharides and those of the respective monomers, and those derived by addition of the glycosylation shifts for each disaccharide element. With a few exceptions, only minor deviations were found and the differences were mostly confined to signals from linkage carbons and the attached protons. Conformational analysis was performed using the HSEA and GESA approaches and measurements of the nuclear Overhauser enhancements. The results indicate that minimum energy conformations are similar to those of the disaccharides but that rotational freedom around some of the glycosidic bonds is restricted.NMR and conformational studies have previously been performed on a number of 2,3-' and 3,4-branched2*, trisaccharides with the purpose of studying models for vicinally disubstituted branchpoint regions in oligo-and poly-saccharides. The glycosylation shifts in the trisaccharides were shown to deviate from the sum of the glycosylation shifts of the constituent disaccharides, and for many of the signals from atoms at or near a linkage large deviations were observed. This was assumed to be due to atomic interactions between sugar residues, causing displaced energy minima with changed values for torsional angles, and restricted rotational freedom around the glycosidic bonds. As deviations from additivity of glycosylation shifts were observed for one type of vicinally disubstituted residues, and an understanding of the phenomenon was desired, studies on other related trisaccharides were implied. We now report synthesis of, and NMR and conformational studies on, the four anomers of the trisaccharide D-GIcP-(1-+2)-~-Glcp-( 1-3)-a-~-Glcp-OMe. The aim of the study is to investigate whether additivity of NMR glycosylation shifts holds at a 1,2-linked residue, which is not a branched residue but nevertheless vicinally disubstituted. This would help in the prediction of NMR spectra of 1,2-linked residues, and of neighbouring residues, as performed by the computer program CASPER4*' used for structural studies of oligo-and polysaccharides. The glycosylation shifts are needed in the computer analysis. ExperimentalMaterials.-The structure of trisaccharides 1-4 are given in Table 1. The syntheses of the intermediates 5,6 7,' 11,8 13 and 14,9 18," 22 and 2412 have been reported. General Methods.-Concentrations were performed under reduced pressure at temperatures < 40 "C (bath). Optical rotations were measured at 22 "C for solutions in chloroform or water (c = 1.0-1.7 mg cm3) with a Perkin-Elmer 241 polarimeter. Silver trifluoromethanesulphonate-mediated couplings were performed essentially as described.' 3-'6 Data on coupling reactions and deprotection procedures, together with physical con...

Oligosaccharides Display Both Rigidity and High Flexibility in Water as Determined by13C NMR Relaxation and1H,1H NOE Spectroscopy: Evidence ofanti-φ andanti-ψ Torsions in the Same Glycosidic Linkage

“…General: The synthesis of the trisaccharide b-d-Glcp-(1 3 2)-b-d-Glcp-(1 3 3)-a-d-Glcp-OMe (1) has been described previously, [70] together with 1 H and 13 C NMR assignments of most resonances in D 2 O. Atoms in the terminal glucosyl residue are denoted by a double prime, in the middle residue they are labeled by a prime, and in the O-methyl residue the atoms are unprimed.…”

Application of NMR, molecular simulation, and hydrodynamics to conformational analysis of trisaccharides

“…26 The 1 H and 13 C chemical shifts obtained agree with published values. 16,17 Adaptation of this experiment to include a 13 C inversionrecovery 27 component immediately preceding the constanttime evolution period ( Figure 2) was used to measure 13 C spin-lattice (T 1 ) relaxation times. Ten relaxation delays (denoted t in Figure 2) ranging from 10 ms to 5 s were used for both I and II.…”

“…16,17 All samples were prepared in 100% deuterium oxide (D 2 O) obtained from Sigma (St. Louis, MO). NMR samples of I and II contained 33 and 29 mM trisaccharide, respectively.…”

Development of a 1H NMR structural-reporter-group concept for the primary structural characterisation of α-d-glucans

“…[8][9][10][11][12][13] It should be noted that for the development of the CASPER CASPER computer program the 1 H NMR data were recorded at 340 K, [14][15][16] yielding some differences, especially where inter-residual hydrogen bonds are involved. In principle, the CASPER CASPER computer program was developed to predict repeating-unit structures and oligosaccharides when all chemical shifts are available, in combination with substitution pattern information from methylation analysis.…”