Claude Bosso

The behavior of chitin towards anhydrous hydrogen fluoride. Preparation of β-(1→4)-linked 2-acetamido-2-deoxy-d-glucopyranosyl oligosaccharides☆

Abstract Fluorohydrolysis of chitin in anhydrous hydrogen fluoride led to β-(1→4)-linked 2-acetamido-2-deoxy- d -glucopyranosyl oligosaccharides in almost quantitative yield. The average d.p. depended on both reaction time and temperature, and was conveniently monitored by 13 C-n.m.r. spectroscopy and gel-exclusion chromatography. Preparative fractionation of oligosaccharides of chitin (d.p. 2–10) was conveniently achieved by gel-exclusion chromatography in Bio-Gel P-4.

Production of lewis x tetrasaccharides by metabolically engineered Escherichia coli

Two tetrasaccharides carrying the trisaccharidic Lewis x motif on a GlcNAc or a Gal residue were produced on the gram‐scale by high‐cell‐density cultures of metabolically engineered Escherichia coli strains that overexpressed the Helicobacter pylori futA gene for α‐3 fucosyltransferase and the Neisseria meningitidis lgtB gene for β‐4 galactosyltransferase. The first compound Galβ‐4(Fucα‐3)GlcNAcβ‐4GlcNAc was produced by glycosylation of chitinbiose, which was endogenously generated in the bacterial cytoplasm by the successive action of the rhizobial chitin‐synthase NodC and the Bacillus circulans chitinase A1, whose genes were additionally expressed in the E. coli strain. The second compound, Galβ‐4(Fucα‐3)GlcNAcβ‐3Gal, was produced from exogenously added Gal by a strain that was deficient in galactokinase activity and overexpressed the additional N. meningitidis lgtA gene for β‐3 N‐acetylglucosaminyltransferase.

Gas-liquid chromatography and mass spectrometry of oligosaccharides obtained by partial acetolysis of glycans of glycoproteins

Abstract A method is described for the analysis and identification of oligosaccharides obtained by acetolysis of glycoproteins. Oligosaccharides were analyzed by gas-liquid chromatography mass spectrometry under their permethylated oligosaccharide alditol form. The suitability of the spectral data to establish the position of the glycosidic bond and the monosaccharide sequence is discussed for each oligosaccharide. This method can give structural information on small glycoprotein samples.

Phæniceroside, the first natural bis-furanone propane derivative from juniperus phænicea L.

Abstract Phaeniceroside 1 or 2,2-bis-(5-methyl-4-( O -β-D-glucopyranosyl)-3(2H)-furanone)-propane have been isolated from Juniperus phaenicea L. (Cupressaceae). The structural elucidation of this new natural product was achieved by UV, MS, 1 H, 13 C NMR spectroscopy. The structure was confirmed by chemical way.

Determination of the stability constants of macrocyclic ligand-alkali cation complexes by fast atom bombardment mass spectrometry

Quantitative studies of the complexation of the macrocylic ligands, 18 crown 6 (18C6,1) and cyclogentiotetraose peracetate (CGD4Ac,2), with alkali cations, have been investigated by fast atom bombardment mass spectrometry (f.a.b.m.s.). Complexation curves of 18C6 with Na+, K+, Rb+ and Cs+ in glycerol, and of CGD4Ac with Cs+ in PEG 200, were obtained by plotting the complex peak intensity against the alkali cation concentration. From these curves we describe a method to calculate the stability constant for an alkali cation-macroyclic ligand complex. There is a good agreement between stability constants obtained either by f.a.b.m.s. or calorimetric techniques for 18C6-alkali cation complexes. These results suggest that the f.a.b. technique can be used to study complex formation and determine the stability constant.

Homopolysaccharides interaction with the dimethyl sulphoxide–paraformaldehyde cellulose solvent system. Selective oxidation of amylose and cellulose at secondary alcohol groups

A 13C n.m.r. study of the interaction properties of the cellulose solvent dimethyl sulphoxide–paraformaldehyde with amylose suggests the reversible formation of hemiacetals between formaldehyde or its oligomers and hydroxy-groups at C-6 and C-2 of the polysaccharide. Such selectivity is, however, not found for the model compound methyl 4-O-methyl-α-D-glucopyranoside, which shows O-3 substitution as well. In agreement with this result, oxidation of amylose in this solvent system by adding acetic anhydride to the homogeneous solution leads to selective formation of carbonyl groups at C-3 in excellent yield. A similar result is obtained when acetic anhydride is added to a cellulose solution in dimethyl sulphoxide–paraformaldehyde. This suggests that the interaction mechanisms of cellulose and amylose with this solvent system must be similar. As a matter of fact, oxidation of a 6-substituted cellulose, such as 6-O-acetylcellulose, mainly takes place at C-2. The 6-O-acetylcellulose was prepared by the action of acetic acid–acetic anhydride in pyridine–tetrachloromethane on a pertrimethylsilyl-cellulose followed by hydrolysis of the remaining 2,3-bis(trimethylsilyl) ether. Previous results on the oxidation of 6-O-triphenylmethyl-cellulose or -amylose have been confirmed and corroborated. Determination of the site and degree of oxidation with the partly oxidized homopolysaccharides was achieved through their reduction with sodium borodeuteride, hydrolysis, and study by g.l.c.–mass spectrometry of the resulting hexoses in the form of their trimethylsilyl O-methyl oximes, or alditol acetate derivatives.

Specific reactivity of the O-(β-d-glucopyranosyl-(1→6)-d-glucopyranose) linkage with acetic anhydride in the presence of trimethylsilyl trifluoromethanesulfonate

On obtient un compose O-[acetoxy-«1» penta-O acetyl-2,3,4,5,6 glucityl]-6 tetra-O-acetyl-1,2,3,4 glucopyranose qui reagit ensuite avec le methanolate de sodium et donne le D-glucose penta-O-acetyle

Mass Spectrometry of Some Benzylidene Imidazolidinediones and Thiazolidinediones. III- Positive and Negative Electron Impact Mass Spectra of Chlorobenzyl Imidazolidinedione or Thiazolidinedione Compounds

Abstract In the present investigation, a study of the electron-impact mass spectrometry in positive- and negative-ion modes is reported for a series of 3-chlorobenzyl-5-benzylidene-imidazolidine-2,4-dione and -thiazolidine-2,4-dione derivatives previously synthetized.

Nitrous acid deamination of acyclic, polyfunctional systems. Part 3. Vicinal participation in the nitrous acid deamination of chiral 1-thio-2-aminoalkanepolyols: the deamination of 2-amino-2-deoxy-D-glucose ethylene and propan-1,3-diyl dithioacetals, and the crystal and molecular structure of 1,2-SS′-ethylene-5,6-O-isopropylidene-1,2-dithio-α-D-mannofuranoside

Deamination of 2-amino-2-deoxy-D-glucose ethylene dithioacetal (1) at pH 5.6, followed by acetylation of the product, gave an 8 : 40 : 3 mixture of 3,5,6-tri-O-acetyl-1,2-SS′-ethylene-1,2-dithio-α-D-mannofuranoside (5b), 3,4,6-tri-O-acetyl-1,2-SS′-ethylene-l,2-dithio-α-D-mannopyranoside (4b), and 3,5,6-tri-O-acetyl-2-deoxy-D-arabino-hexono-1,4-lactone (2b). Deamination of (1) at pH <1 by use of dinitrogen trioxide followed by acetylation gave the lactone (2b) essentially exclusively. Similar treatment of the propan-1,3-diyl analogue (3) of (1) at pH <1 also gave the lactone (2b) : at pH 5.6 the main product was 3,5,6-tri-O-acetyl-1,2-SS′-(propan-1,3-diyl)-1,2-dithio-α-D-mannofuranoside (7b). Structural assignments were based on formation of the 5,6-isopropylidene acetals [(8) and (10)] from the non-acetylated precursors of (5b) and (7b), by 1H n.m.r. spectroscopy at 250 MHz for compounds (2b), (4b), (5b), (7b), (8), and (10), and by electron-impact mass spectrometry. An X-ray crystal structure-determination conducted on 1,2-SS′-ethylene-5,6-O-isopropylidene-1,2-dithio-α-D-mannofuranoside (8) permitted unambiguous assignment of the ring size, relative stereochemistry, and favoured conformation of this strained molecule. The reaction course and product distribution in the deamination were monitored and quantitated by g.l.c.–mass spectrometry of the corresponding per-trimethylsilylated derivatives and are discussed from preparative and mechanistic standpoints.

Complexation of alkali metal and tetramethylammonium ions with polyacids. pH-Metry consequences

Mass Spectrometry (MS) enables the study of alkali metal and tetramethylammonium (TMA) complexes which are formed during potentiometric titrations. Their formation and their evolution as a function of pH are confirmed by means of 23Na NMR spectroscopy. This is a common phenomenon which calls the principle of pH-metric titration of polyacids into question.