A ¹H‐NMR Spectroscopic Investigation of the Conformation of the Acetamido Group in Some Derivatives of N‐Acetyl‐D‐allosamine and ‐D‐glucosamine

Abstract

The population of the conformations obtained by rotation around the C (2) Introduction. -We have described an unprecedented neighboring-group participation of the acetamido group in the glycosidation of alcohols by the diazirines 16 and 17 derived from 2-acetamido-2-deoxyhexoses, leading preferentially to CI -D-glycosides [ 11. We rationalized this selectivity on the basis of a bonufide H-bond from the appropriately oriented acetamido group of the reactive intermediates to the glycosyl acceptor. This raises the question about the conformation of the NHAc-C(2) group, which is of evident importance considering the prominent biological role of N-acetylglucosamine and its glycosides. There is evidence that the conformational behavior of the NHAc-C(2) group depends upon the constitution and configuration of the saccharide. The extent of the dependence of the chemical shift of the H-N group on the temperature is a criterium for inter-vs. intramolecular H-bonds. It is linear and in agreement with an intramolecular H-bond for solutions in CD,C12 of the N-acetylallosamine-derived diazirine 16, but nonlinear for the N-acetylglucosamine analogue 17 [l]; it is also linear and in agreement with an intramolecular H-bond for the hexafluoroisopropyl N-acetyl-allosamine CI -D-6 and for the hexafluoroisopropyl N-acetylglucosamine CI -D-9, but again curved for the

Positive electrospray ion trap multistage mass spectrometric fragmentation of synthetic analogs of saccharide part of lipopolysaccharides of Vibrio cholerae O:1

“…Five torsional angles describe the conformation of the NHDGT-C(4) group (Table 1), namely 1 ϭ [C(3)-C(4)- , respectively. The calculated preference of the (Z)-anti conformer is in conformity with the experimental data on ␣-d-glucopyranosides [17]. Therefore, the optimized structures of the (Z)-anti conformer was selected to generate the initial structures of Na ϩ complexes positioning the sodium cation at seven different locations depicted in Figure 2.…”

Intra- and Intermolecular H-Bonds of Alcohols in DMSO, 1H-NMR Analysis of Inter-Residue H-Bonds in Selected Oligosaccharides: Cellobiose, Lactose, N,N′-Diacetylchitobiose, Maltose, Sucrose, Agarose, and Hyaluronates

“…Several conformers obtained by rotation around the C(2)ÀN bond have been observed for N-acetyl-a-d-and -b-d-glucosamine derivatives [26], but they have only a weak influence upon the chemical shift of HOÀC (3) …”

“…1308 for the H-bonded species, avoiding a too close contact between the carbonyl group and OÀC(3) (see[26] for preferred conformations of GlcNAc derivatives). According to the equation of Bystrov[53], this angle corresponds to a J(H,NH) value of 5.0 Hz.…”

Glycosylidene Carbenes. Part 23. Regioselective glycosidation of deoxy‐ and fluorodeoxy‐myo‐inositol derivatives

“…4: 1. The (E)-configuration ( = trunu-arrangement of NR and OR) is assumed for the main rotamer (CJ [40]). Aryl N-methylcarbarnates prefer this configuration in solution [41].…”