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

Galactan synthesis in a single step via oligomerization of monosaccharides

Galactans ranging in length from one to five residues were prepared in a single step by treatment of the glycosyl donor 2,3,4-tri-O-benzoyl-β-D-galactopyranosyl fluoride with lanthanum perchlorate in the presence of an initiator alcohol. The product oligosaccharides were readily chromatographically separable. This oligomerization was used to synthesize a pentagalactan in a single step from monosaccharide building blocks in reasonable overall yields.

Protonic reactivity of sucrose in anhydrous hydrogen fluoride

Sucrose reacts quantitatively, when dissolved at high concentration in anhydrous hydrogen fluoride, to afford a complex mixture of difructose dianhydrides and their glucosylated derivatives. Oligo- and small poly-saccharides up to dp 14 were detected by FABMS. Oligosaccharides up to dp 4, representing approximately 50% of the total mixture, have been isolated and characterized by mass spectrometry, 13C NMR spectroscopy, and comparison with reference oligosaccharides previously obtained by unambiguous synthesis. alpha-D-Fructofuranose beta-D-fructopyranose 1,2':2,1'-dianhydride is the main spirodioxanyl pseudodisaccharide entity found in the mixture, either free or glucosylated at C-6 and to a lesser extent at C-3, C-4, C-4', C-6, and C-5' C-6. Minor spirodioxanyl pseudodisaccharide components are di-beta-D-fructopyranose 1,2':2,1'-dianhydride, which has also been found glucosylated at C-5, alpha-D-fructopyranose beta-D-fructopyranose 1,2':2,1'-dianhydride, beta-D-fructofuranose beta-D-fructopyranose 1,2':2,3'-dianhydride, and the 6,6'-diglucosylated alpha-D-fructofuranose beta-D-fructofuranose 1,2':2,1'-dianhydride. A 13C NMR examination of the higher mass oligomeric fraction suggests that it may involve 6-O-isomaltooligoglycosyl alpha-D-fructofuranose beta-D-fructopyranose 1,2':2,1'-dianhydrides as the main structural components. The reaction of sucrose in anhydrous HF is believed to proceed through initial selective protonic activation of the tertiary anomeric carbon atom of the fructose moiety, resulting in the quantitative formation of difructose dianhydrides, which subsequently suffer electrophilic substitution by glucopyranosyl oxocarbenium ions generated in a second step by action of the HF.

Carbohydrate composition analysis of bacterial polysaccharides: optimized acid hydrolysis conditions for HPAEC-PAD analysis

The capsular polysaccharide from Haemophilus influenzae type b (polyribosyl ribitol-phosphate; PRP) and the capsular polysaccharides from Streptococcus pneumoniae types 6B, 14, 18C, and 23F (Pn6B, Pn14, Pn18C, and Pn23F) were subjected to acid hydrolysis using hydrofluoric (HF) and/or trifluoroacetic acid (TFA) and high-pH anion-exchange chromatography with pulsed amperometric detection in an effort to identify optimum hydrolysis conditions for composition analysis of their carbohydrate components. With the exception of PRP, composition analyses of polysaccharides containing a phosphate moiety in the repeating unit structure (Pn6B, Pn18C, and Pn23F) are significantly improved by subjecting the sample to HF hydrolysis (65 degrees C, 1 h) followed by TFA hydrolysis (98 degrees C, 16 h). This results in essentially quantitative hydrolysis of the phosphodiester bond to the carbohydrate components, which otherwise remained predominantly phosphorylated and poorly accounted for in the analysis. Optimum analysis of PRP was achieved following a 2-h hydrolysis with TFA at 80 degrees C, whereas Pn14 showed optimum results after a 16-h hydrolysis with TFA at 98 degrees C. These analyses also provide information about the relative susceptibility to acid hydrolysis of the various glycosidic and phosphodiester bonds in these polysaccharides, with evidence to suggest that the acid lability of a given bond can be dramatically different from one polysaccharide to another.

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.

Structural studies of the O-antigenic polysaccharide of Escherichia coli O86, which possesses blood-group B activity

The O-specific side-chains of the lipopolysaccharide from Escherichia coli O86:K2:H2 have been investigated using n.m.r. spectroscopy, methylation analysis, and specific degradations, and shown to be composed of the pentasaccharide repeating-unit (formula; see text) which represents the biological repeating-unit. The blood-group B activity was confirmed by an enzyme-linked immunosorbent assay.