Bruce Coxon

A newly discovered cholesteryl galactoside from Borrelia burgdorferi

Two major glycolipids, which comprise ≈36% of the total lipid mass from Borrelia burgdorferi, the etiological agent of Lyme disease, were investigated. We determined the fatty acid type, sugar identity, anomeric configuration, and substituent type and position. The structures were identified as cholesteryl 6-O-acyl-β-d-galactopyranoside (B. burgdorferi glycolipid 1, BbGL-I), and 1,2-di-O-acyl-3-O-α-d-galactopyranosyl-sn-glycerol (BbGL-II). The major fatty acids were palmitate and oleate. The structures were corroborated by gas–liquid chromatography MS, matrix-assisted laser desorption/ionization time-of-flight spectroscopy, fast atom bombardment MS, detailed NMR spectrometry, and metabolic labeling. This is a previously undescribed demonstration of a cholesteryl galactoside in bacteria. Lipopolysaccharide was not detected in B. burgdorferi. The two glycolipids have several properties suggesting they may function as lipopolysaccharide: both are main components of the bacterial membrane, surface exposed, and have a three-domain structure. BbGL-I elicited specific antibodies in mice and rabbits, and BbGL-II elicited antibodies that reacted with both glycolipids.

P.M.R. evidence for the conformations of 1,2-O-benzylidene-α-d-glucofuranose derivatives

Abstract Proton coupling constants and chemical shifts of two 1,2- O -benzylidene- and four 1,2:3,5-di- O -benzylidene-α- d -glucofuranose derivatives have been measured by p.m.r. spectroscopy at 100 MHz. From these parameters, it is deduced that the furanoid rings of the mono- and di-benzylidene acetals exist mainly in symmetric and non-symmetric twist conformations, respectively. The m -dioxane ring of the dibenzylidene acetals adopts that chair conformation in which C-6 of the sugar is axially attached.

Synthesis and two-dimensional nuclear magnetic resonance analysis of a tetra- and a hexa-saccharide fragment of the O-specific polysaccharide of Shigella dysenteriae type 1☆

The synthesis of the tetra- and hexa-saccharide methyl glycosides alpha-D-Galp-(1-->3)-alpha-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->3)- alpha-L-Rhap- OMe (1), and alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->2)-alpha-D-Galp-(1--> 3)-alpha-D-GlcpNAc- (1-->3)-alpha-L-Rhap-(1-->3)-alpha-L-Rhap-OMe (3) is described, which represent various epitopes of the O-specific polysaccharide of Shigella dysenteriae type 1. The following monosaccharide intermediates were used: 1,3-di-O-acetyl-2-O-benzoyl-4-O-benzyl-alpha-L-rhamnopyranose (6 alpha), methyl 2,4-di-O-benzyl-alpha-L-rhamnopyranoside (7), methyl 2,4-di-O-benzoyl-1-thio-alpha-L-rhamnopyranoside (8), 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl bromide (9), methyl 3,4,6-tri-O-benzyl-2-O-(4-methoxybenzyl)-1-thio-beta-D- galactopyranoside (13), methyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D- galactopyranoside (16), and 2-azido-4,6-O-benzylidene-3-O-bromoacetyl-2-deoxy-beta-D- glucopyranosyl chloride (19). A detailed analysis of the 1H and 13C NMR spectra of oligosaccharides 1 and 3 confirmed that the hexasaccharide 3 better approaches the conformation of the native polysaccharide, than either 1 or the homologous pentasaccharide 41.

Proton Magnetic Resonance Spectroscopy: Part I

Publisher Summary Proton magnetic resonance (p.m.r.) spectroscopy is regarded as the most widely used technique for the structural, configurational, and conformational analysis of carbohydrates and their derivatives. In context to instrumentation, sensitivity is often a limiting factor in p.m.r. spectroscopy; however this problem has been tackled by the use of Fourier techniques. It is noted that considerable improvements in the design of probes for research spectrometers have been made, with emphasis on rapid changeover for operation with one nucleus to that for another by means of plug-in sample-inserts, solid-state preamplifiers, circuit boxes for different modes of field-frequency stabilization, and matching networks for tuning the probe to any measuring or decoupling frequency required. The use of field-effect transistors having low noise and high gain in the first stage of the preamplifier has resulted in significant improvement in sensitivity. The full impact of the advances in electronic technology has resulted in all-solid-state spectrometer consoles, with an emphasis on rapid conversion for observation of different nuclei, by switching of radiofrequencies (r.f.), instead of by exchange of bulky r.f. units.

Model parameters for the analysis of skew conformations of carbohydrates by p.m.r. spectroscopy

Abstract The p.m.r. spectrum of 3- O -benzoyl-1,2,4- O -benzylidyne-α- d -ribopyranose 1 ( 1 ) at 100 MHz has been analyzed by an iterative, least-squares method. The resulting geminal, vicinal, and long-range coupling-constants have been correlated with the stereochemistry of the locked, skew conformation of 1 , and used to test applicability of equations that relate coupling constant to dihedral angle. The mean deviation of the approximate proton-proton dihedral angles as calculated from a Karplus equation from those measured from a molecular model was 11°.

Characterization of prenylated xanthones and flavanones by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

Reversed-phase liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) in the positive-ion mode was utilized to analyze crude ether extracts from the root bark of Maclura pomifera, a tree known to have a high content of prenylated xanthones and flavanones. Identification of three xanthones and two flavanones was based on their unique mass spectra. Under optimum conditions peaks corresponding to the [MH](+) ion and characteristic fragments for each compound were observed. (1)H NMR data were used to confirm the identities of two xanthones that had the same molecular mass and similar fragmentation patterns. Fragmentation of the analytes was achieved by application of an electrostatic potential at the entrance of the single quadrupole mass spectrometer. The optimum voltage for fragmentation was found to be related to the class of compounds analyzed and, within each class, to be dependent on the structure of the prenyl moiety. Collision-induced pathways consistent with precedent literature describing the MS characterization of similar compounds and with the observed fragmentation patterns are tentatively proposed.

15N NMR investigation of azo-hydrazone acid-base equilibria of FD and C yellow no. 5 (tartrazine) and two analogs

FD & C Yellow No. 5 and two analogs have been characterized by 15N NMR at several pH values. 15N chemical shift data indicate the existence of azo-hydrazone, acid-base equilibria and suggest that these compounds are present in the hydrazone form at pH 7 and the azo form at pH 12. Approximately equal concentrations of these two species are observed at pH 10.3.

Synthesis of di- to penta-saccharides related to the O-specific polysaccharide of Shigella dysenteriae type 1, and their nuclear magnetic resonance study

The syntheses of oligosaccharide fragments of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1 are described, including disaccharides methyl O-alpha-D-mannopyranosyl-(1-->2)-alpha-D-galactopyranoside (1), and methyl O-(2-deoxy-2-propionamido-alpha-D-glucopyranosyl)-(1-->3)-alpha-L- rhamnopyranoside (2), trisaccharide methyl O-alpha-D-galactopyranosyl-(1-->3)-O-(2-acetamido-2-deoxy-alpha-D- glucopyranosyl)-(1-->3)-alpha-L-rhamnopyranoside (3), tetrasaccharide methyl O-alpha-L-rhamnopyranosyl-(1-->2)-O-alpha-D-galactopyranosyl-(1-->3)- O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-(1-->3)-alpha-L-rhamno -pyranoside (4), and pentasaccharide methyl O-alpha-L-rhamnopyranosyl-(1-->3)-O-alpha-L- rhamnopyranosyl-(1-->2)-O-alpha-D-galactopyranosyl- (1-->3)-O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-(1-->3)-alpha-L- rhamnopyranoside (5). The following monosaccharide building blocks were used as starting compounds: methyl 6-O-tert-butyldiphenylsilyl-3,4-O-isopropylidene-alpha-D-galact opy ranoside (8), methyl 3,4,6-tri-O-benzyl-2-O-(4-methoxybenzyl)-1-thio-beta-D- galactopyranoside (11), methyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-1-thio-alpha- D-glucopyranoside (16), methyl 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-alpha-D- glucopyranoside (18), methyl 2,4-di-O-benzyl-alpha-L-rhamnopyranoside (21), methyl 2,3,4-tri-O-benzoyl-1-thio-alpha-L-rhamnopyranoside (22), 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl bromide (23), and methyl 4-O-benzyl-alpha-L-rhamnopyranoside (24). Nuclear magnetic resonance data indicate that oligosaccharides 4 and 5 partially mimic the conformation of the O-specific polysaccharide of S. dys. type 1.

Conformational analysis of peracetylated hexononitriles

Abstract The conformations of six peracetylated hexononitriles in solution have been investigated by Fourier-transform, proton n.m.r. spectroscopy at 90 MHz, with iterative analysis and simulation of many of the spectra. The conformation of tetra- O -acetyl- L -arabinononitrile has been re-examined by the same methods. A shift reagent [Eu(fod) 3 - d 30 ] and spectra at 220 MHz were used to improve spectral dispersion, where necessary. For practically all of the derivatives studied, the vicinal, proton-proton coupling-constants are consistent with a zigzag conformation in which the cyano group lies in the plane of the other carbon atoms of the chain, unless this conformation contains a parallel 1,3-interaction of substituents. Other conformers that are also consistent with the coupling constants observed are discussed, including rotamers about chain-terminal, carbon-carbon bonds.

The conformations of 1,2:4,6-di-O-benzylidene-α-D-glucopyranose derivatives

Abstract The conformations of a series of 1,2:4,6-di- O -benzylidene-α- D -glucopyranose derivatives in solution have been studied by p.m.r. spectroscopy and double-resonance techniques at 100 MHz. The coupling constants obtained by first-order analysis of the spectra were compared with those computed by iterative analysis. It was concluded that these compounds adopt conformations in which the m -dioxane and pyranoid rings have chair and flattened-chair forms, respectively.