Andrée Gadelle

Chitin oligosaccharides as elicitors of chitinase activity in melon plants

Chitin oligosaccharides elicited chitinase activity in melon plants. Hexamer to nonamer were the most efficient elicitors: hexamer for maximal stimulation of colorimetrically assessed chitinase activity, heptamer for maximal stimulation of radiochemically assessed chitinase activity. Chitinase elicitation was a rapid response to these elicitors: it occurred within 6 hours after treatment and was maximal at 12-24 hours. In addition, chitinase induction in melon plants by these oligosaccharides was both local and systemic.

The behaviour of d-fructose and inulin towards anhydrous hydrogen fluoride☆

Abstract Inulin and d -fructose are quantitatively converted into a mixture of d -fructose dianhydrides on treatment with anhydrous hydrogen fluoride. Of the six dianhydrides isolated, five are known compounds, whereas one, β- d -fructofuranose β- d -fructopyranose 2,1′:3,2′-dianhydride, has not been described hitherto. The structures of two of the known dianhydrides have been revised. The relative amounts of dianhydrides obtained depend on the reaction conditions. The reaction of d -fructose with hydrogen fluoride is shown, using 13 C-n.m.r. spectroscopy, to involve d -fructofuranosyl fluoride as a probable intermediate. Dianhydrides are also formed when d -fructose is treated with methanol and sulfuric acid under Fischer glycosidation conditions or with trifluoroacetic acid.

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.

The behavior of cellulose, amylose, and β-d-xylan towards anhydrous hydrogen fluoride☆

Abstract Cellulose, amylose, and d -glucose are converted into α- d -glucopyranosyl fluoride ( 3 ) when dissolved in anhydrous hydrogen fluoride. The fluoride subsequently undergoes condensation to afford a mixture of ligosaccharides, probably via an oxocarbonium ion. The fluoride 3 and the oligosaccharides are in an equilibrium, which was studied by 13 C-n.m.r. spectroscopy; in dilute solution in hydrogen fluoride, the d -glucosyl fluoride is the main product present, but when the hydrogen fluoride is evaporated, the equilibrium is shifted towards the oligosaccharides. These constitute a complex mixture which was studied by methylation and subsequent analysis of the methylated alditols derived therefrom. (1→4)-β- d -Xylan and d -xylose behave similarly to the d -glucose derivatives towards hydrogen fluoride.

Inclusion and solubilization properties of 6-S-glycosyl-6-thio derivatives of β-cyclodextrin

The synthesis and physico-chemical properties of branched β-cyclodextrins substituted by one or seven thioglycoside units at the primary hydroxy side are described. The solubilities in water of these compounds are strongly increased compared with the parent β-cyclodextrin although large differences are found between α- and β-anomers, the former exhibiting the larger solubility. The inclusion capacity of these derivatives has been investigated using NMR spectroscopy as the major analytical technique for various host–guest pairs. The apparent discrepancies between the intrinsic solubilities of these host molecules and their ability to solubilize hydrophobic hosts can be explained from geometrical considerations derived from detailed NMR studies. The respective roles of the side of inclusion, of steric effects and of stabilizing interactions are evidenced and allow an a priori selection of the optimal host derivative for a given guest molecule.

Hydrogen fluoride-catalyzed formation of glycosides. Preparation of methyl 2-acetamido-2-deoxy-β-d-gluco- and -β-d-galacto-pyranosides, and of β-(1→6)-linked 2-acetamido-2-deoxy-d-gluco- and -d-galacto-pyranosyl oligosaccharides☆

Dissolution of 2-acetamido-2-deoxy-d-glucose (1) or -d-galactose (2) in anhydrous hydrogen fluoride, followed by addition of methanol, gave stereospecifically the corresponding methyl β-d-glycopyranosides 7 and 8. When solutions of 1 or 2 in hydrogen fluoride were slowly evaporated, mixtures of exclusively β-d-(1→6)-linked di- to hexa-saccharides containing 2-acetamido-2-deoxy-glucosyl (9) and -galactosyl (10) residues were obtained; these were separated by gel permeation chromatography to give pure products. Compounds 7 and 9 were also obtained when solutions of chitin were treated under appropriate conditions.

Hydrogen fluoride-mediated synthesis of 1-thiotrehaloses involving reaction of D-glucose with hydrogen sulfide.

Hydrogen sulfide reacted with D-glucose in hydrogen fluoride solution to yield preponderantly alpha,alpha-1-thiotrehalose, beta,beta-1-thiotrehalose, and the alpha,beta anomer. Conditions were found under which the thiotrehaloses were obtained in the respective proportions of 8:5:5.

The behavior of l-sorbose towards anhydrous hydrogen fluoride☆

Abstract l -Sorbose was converted into a mixture of l -sorbose dianhydrides by treatment with anhydrous hydrogen fluoride. Of the six dianhydrides isolated, two were known compounds. The structures have been established by n.m.r. spectroscopy. The relative amounts of dianhydrides obtained depended on the reaction conditions. By use of 13C-n.m.r. spectroscopy, the reaction of l -sorbose with hydrogen fluoride was shown to involve l -sorbofuranosyl fluoride as an intermediate. Dianhydrides were also formed when l -sorbose was treated with methanol and sulfuric acid under Fischer glycosidation condition, or with trifluoroacetic acid.

Branched thiocyclomalto-oligosaccharides: Synthesis and properties of 6-S-α- and 6-S-β-d-glucopyranosyl-6- thiocyclomaltoheptaose☆☆☆★

Abstract 6- S -α- ( 2 ) and 6- S -β- d -glucopyranosyl-6-thiocyclomaltoheptaose ( 3 ) have been prepared by treatment of 6- O - p -tolylsulphonylcyclomaltoheptaose ( 1 ) with the sodium salts of 1-thio-α- and -β- d -glucopyranose, respectively, in 1,3-dimethyl- 2-oxohexahydropyrimidine. Compounds 2 and 3 , which were characterised by f.a.b.-m.s. and 1 H- and 13 C-n.m.r. spectroscopy, are more soluble in water than cyclomaltoheptaose, and enhance the solubility of hydrophobic compounds by inclusion.

Acetal and ester protecting-groups in the hydrogen fluoride-catalysed synthesis of d-fructose and l-sorbose difuranose dianhydrides

Abstract Treatment of acetylated inulin with anhydrous hydrogen fluoride under mild conditions gave a good yield of tri- O -acetyl-α- d -fructofuranose tri- O -acetyl-β- d -fructofuranose 1,2′:2,1′-dianhydride together with smaller amounts of the corresponding β,β-anomer. When 2,3:4,6-di- O -isopropylidene-α- l -sorbofuranose was treated with hydrogen fluoride under similar conditions, with a short reaction time, α- l -sorbofuranose β- l -sorbofuranose 1,2′:2,1′-dianhydride was obtained. A longer reaction time led to a rearranged product, di-α- l -sorbofuranose 2,1′:3,2′-dianhydride.