Selenium derivatives of L-arabinose, D-ribose,and D-xylose

Attempted cyclization of 2,3,4-tri-O-methyl-5-seleno-L-arabinose dimethyl acetal in acidic solution gave the corresponding diselenide. Intramolecular attack by the selenobenzyl group at C-5 of 5-O-p-tolylsulfonyl-L-arabinose dibenzyl diseleno-acetal resulted in the formation of benzyl 1,5-diseleno-L-arabinopyranoside. Similarly, 2,3,5-tri-O-methyl-4-O-p-tolylsulfonyl-D-xylose dibenzyl diselenoacetal gave benzyl 2,3,5-tri-O-methyl-1,4-diseleno-L-arabinofuranoside, and 2,3,4-tri-O-acetyl-5-O-p-tolylsulfonyl-D-xylose (or ribose) dibenzyl diselenoacetal gave benzyl 2,3,4-tri-O-acetyl-1,5-diseleno-D-xylo- (or ribo-)pyranoside. The glycosylic benzylseleno group was removed from the pyranoside with mercuric acetate, but attempted deacetylation of the product led to decomposition and not to the expected 5-seleno-D-xylopyranose.     

Proton magnetic resonance spectra of D-gluco-oligosaccharides and D-glucans

The p.m.r. spectra of some D-gluco-oligosaccharides and D-glucans in deuterium oxide were studied with respect to the anomeric proton. In (1→2)-linked glucobioses, the effect of change in configuration of the hydroxyl group at C-1 on the chemical shifts of the glycosidic proton is noted. Equilibrium mixtures of (1→2)-linked glucobioses contained more α-anomer than did the other examples, despite the cis configuration of substituents at C-1 and C-2. Some D-glucans were investigated with regard to the degree of branching, although solubility was a limitation.     

α-D-mannosidase and α-D-galactosidase from protein bodies of Lupinus angustifolius cotyledons

Two forms of p-nitrophenyl α-D-mannosidase and p-nitrophenyl α-D-galactosidase were purified from the protein bodies of mature Lupinus angustifolius seeds. A MW of 300 000 was calculated for both α-mannosidase A and B with K_m = 1.92 and 2.70 mM and activation energies of 10.9 and 10.8 kcal/mol, respectively. α-Galactosidase I and II had MWs of 70800 and 17000 with K_m = 0.282 and 0.556 mM and activation energies 17.7 and 11.5 kcal/mol, respectively. The enzymes had acid pH optima and were inhibited by various metal ions, carbohydrates and glycoproteins. They were able to release free sugar from several putative natural substrate oligosaccharides and the Lupinus storage glycoprotein, α-conglutin.     

Preparation of some acylated D-arabino-hexopyranosuloses and 4-deoxy-D-glycero-hex-3-enopyranosuloses

Oxidation of 1,3,4,6-tetra-O-benzoyl-α- and β-D-glucopyranose gave the tetra-O-benzoyl-α- and -β-D-arabino-hexopyranosuloses (3α and β), from which benzoic acid was readily eliminated to give the anomeric tri-O-benzoyl-4-deoxy-D-glycero-hex-3-enopyranosuloses (4α and β). The anomeric 1-O-acetyl-tri-O-benzoyl-D-arabino-hexopyranosuloses (7α and β) were obtained as very unstable syrups which readily lost benzoic acid. Treatment of tetra-O-benzoyl-2-O-benzyl-D-glucopyranose (1) with hydrogen bromide gave 3,4,6-tri-O-benzoyl-α-D-glucopyranosyl bromide (5) in one step.     

Spontaneous reactions of the irreversible β-D-galactosidase inhibitor 2,6-anhydro-1-deoxy-1-diazo-D-glycero-L-manno-heptitol

2,6-Anhydro-1-deoxy-1-diazo-D-glycero-L-manno-heptitol (2) decomposes in 0.01M methanolic sodium methoxide with a half-life of approx. 18 min. Decomposition in aqueous solution is too rapid for spectrophotometric measurement. Seven products could be identified in methanolic and aqueous reaction mixtures. 2,6-Anhydro-1-deoxy-D-galacto-hept-1-enitol (6), 2,7-anhydro-1-deoxy-β-D-galacto-heptulopyranose (10), and 4-O-vinyl-D-lyxose (12) are products of rapid intramolecular reactions. The major portion consists of the direct solvolysis products 2,6-anhydro-1-O-methyl-D-glycero-L-manno-heptitol (3) and 2,6-anhydro-D-glycero-L-manno-heptitol (5).     

Untersuchungen zur modifikation der cellobiose und synthese von methyl-2,6-didesoxy-4-O-(6-desoxy-β-D-glucopyranosyl)-α-D-arabino-hexopyranosid (methyl-4-O-β-D-chinovosyl-α-D-olivosid)

Starting with cellobiosides, several different procedures were employed to prepare 6,6′-dichloro-6,6′-dideoxy, 6,6′-dibromo-6,6′-dideoxy, and 6,6′-dideoxy-6,6′-diiodo derivatives. Reduction with lithium aluminum hydride or nickel boride afforded peracetyl derivatives of methyl, phenyl, and benzyl 6-deoxy-4-O-(6-deoxy-β-D-glucopyranosyl)-β-D-glucopyranoside. Following acetolysis or hydrogenolysis, the glycosyl halide and the corresponding-glycal 40 were prepared. Iodomethoxylation of 40 and subsequent reduction gave the title compound. Alternatively, the halomethoxylation products of cellobial hexaacetate gave, by various procedures, the 2,6,6′-trideoxy-2,6,6′-trihalo derivatives, which, in turn, could be reduced to the title compound. The structures of the derivatives prepared were unequivocally assigned by n.m.r. spectroscopy. The various reaction sequences were compared with respect to the number of steps and the yields obtained.     

Metabolism of 14C-labelled D-glucose, D-fructose and allitol by Itea plants

The metabolism of D-[1-¹⁴C]glucose, D-[6-¹⁴C]glucose, D-[1-¹⁴C]fructose and D-[6-¹⁴C]fructose by leafy spurs of Itea plants results in rapid incorporation of label into allitol and D-allulose. The patterns of labelling found in the allitol and D-allulose are discussed, a direct interconversion from D-glucose and D-fructose being indicated. Allitol has been found to be an active metabolite in Itea plants.     

D-Galactose 6-phosphate: anomeric distribution and analysis of its synthesis from D-galactose and polyphosphoric acid

D-Galactose 6-phosphate as synthesized by direct phosphorylation of D-galactose with polyphosphoric acid is contaminated with two of its positional isomers. These were separated from D-galactose 6-phosphate and from each other, and identified as D-galactose 3- and 5-phosphate by enzymic, chromatographic, and mass-spectral analysis. The previous misidentification of these isomers as furanose forms of D-galactose 6-phosphate has led to erroneous reports concerning the anomeric distribution of D-galactose 6-phosphate. The anomeric distribution of D-galactose 6-phosphate in a purified preparation was determined by gas-liquid chromatography and ¹³C-n.m.r. spectroscopy to be 32% α-pyranose, 64% β-pyranose, and no more than 4% furanose anomers.     

A non-hydrogen-bonding role for the 4-hydroxyl group of D-Galactose in its reaction with D-Galactose oxidase

Several 4-deoxy analogs of methyl β-D-galactopyranoside are oxidized by D-galactose oxidase. The rates associated with their various, axially attached 4-substituents follow the sequence OH>NH₂>F?>Cl> H; these differences are attributed mainly to variations in K_m. Other 4-deoxy analogs, namely, the 4-azido-4-deoxy, 4-bromo-4-deoxy-, 4-deoxy-4-iodo, and 4-thio derivatives were found to be inactive. These observations indicate that the axial 4-hydroxyl group of D-galactopyranose does not play a hydrogen-bonding role primarily, but constitutes a substituent of a size optimal for interaction with the enzyme.     

Synthesis of D-ristosamine and its derivatives

A convenient preparative route involving eleven steps starting from D-glucose is described for the synthesis of D-ristosamine (15) hydrochloride. Methyl 2-deoxy-β-D-arabino-hexopyranoside, prepared from 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-arabino-hex- 1-enitol, was benzylidenated, and the product mesylated to give methyl 4,6-O-benzylidene-2-deoxy-3-O-methylsulfonyl-β-D-arabino-hexopyranoside. Azidolysis of this compound and subsequent opening of the 1,3-dioxane ring with N-bromosuccinimide gave methyl 3-azido-4-O-benzoyl-6-bromo-2,3,6-trideoxy-βD-ribo-hexopyranoside. Simultaneous reduction of the azido and bromo groups gave a mixture that was benzoylated to give methyl N,O-dibenzoyl-β-D-ristosaminide and then hydrolyzed to 15 hydrochloride (3-amino-2,3,6-trideoxy-D-ribo-hexopyranose hydrochloride).     

Synthesis of methyl 4,6-O-methylene-D-glycopyranosides

Methyl 4,6-O-methylene-D-glycopyranosides having the α-D-altro, α- and β-D-gluco, α-D-manno, and α-D-galacto configurations were prepared in 3.4 to 27.4% yields by condensing formaldehyde from 1,3,5-trioxane with the methyl glucosides in anhydrous 1,4-dioxane at 95° with boron trifluoride as the catalyst. A crystalline methyl 2,3:4,6-di-O-methylene-α-D-mannopyranoside was also isolated. Crystalline methyl 4,6-O-methylene 2,3-di-O-p-tolylsulfonyl-α-D-galacto- and α-D-glucopyranosides were prepared in 78 and 54.4% yields. N.m.r. coupling constants of the 2,3-di-O-acetyl derivatives of the 4,6-O-methylene glycosides were used to establish the Cl(D) conformation for each derivative.     

Synthesis of 2,4-diacetamido-2,4,6-trideoxy-D-Galactose

Treatment of benzyl 2-acetamido-3-O-benzyl-2,6-dideoxy-4-O-(methylsulfonyl)-α-D-glucopyranoside (1) with sodium azide in hexamethylphosphoric triamide gave the 4-azido-α-D-galacto derivative (2), which was converted into benzyl 2,4-di-acetamido-3-O-benzyl-2,3,6-trideoxy-α-D-galactopyranoside (3) by hydrogenation and subsequent acetylation. Hydrogenolysis of 3 at atmospheric pressure afforded benzyl 2,4-diacetamido-2,4,6-tridcoxy-α-D-galactopyranoside (4), which was acetylated to give the 3-O-acetyl derivative (5). The n.m.r. spectrum of 5 was in agreement with the assigned structure and different from that of benzyl 2,4-di-acetamido-3-O-acetyl-α-D-glucopyranoside (9), which was prepared from the known benzyl 2,4-diacetamido-3-O-benzyl-2,4,6-trideoxy-α-D-glucopyranoside. Catalytic hydrogenolysis of 4 gave 2,4-diacetamido-2,4,6-trideoxy-D-galactose (6).     

Synthesis of 3-O Substituted D-Mannoses

1,2,4,6-Tetra-O-acetyl-3-O-benzyl-α-D-mannopyranose (7) was obtained in good yield from 3,4,6-tri-O-benzyl-1,2-O-(1-methoxyethylidene)-β-D-mannopyranose (1) by acetolysis. Hydrogenolysis of 7 afforded 1,2,4,6-tetra-O-acetyl-α-D-mannopyranose which is a versatile intermediate for the preparation of other 3-O-substituted D-mannoses, such as 3-O-methyl-D-mannose and 3-O-α-D-mannopyranosyl-D-mannose. 3,4-Di-O-methyl-D-mannose was readily prepared from 1,2,6-tri-O-acetyl-3,4-di-O-benzyl-α-D-mannopyranose, which was also obtained from 1 by controlled acetolysis.     

Methanolysis of D-galacturonic acid: dimethyl acetals

Dimethyl acetals of D-galacturono-6,3-lactone and methyl D-galacturonate have been detected during methanolysis of D-galacturonic acid. The products of methanolysis were studied by ion-exchange chromatography and by g.l.c. of the trimethylsilyl (TMS) derivatives. Structural determinations were made from the mass spectra of the TMS derivatives. The course of methanolysis was monitored by g.l.c.     

Reaction of some D-glucobioses with 2,2-dimethoxypropane

Laminarabiose, cellobiose, and gentiobiose were acetonated with 2,2-dimethoxy-propane under various conditions. Two isopropylidene acetals in which the reducing D-glucose residue had the furanoid form were obtained from laminarabiose, and two, in which the reducing D-glucose residue formed the acyclic dimethyl acetal, from cellobiose. Gentiobiose gave both types of isopropylidene compound.     

Characterization of structurally similar neutral and acidic tetrasaccharides obtained from the enzymic hydrolyzate of a 4-O-methyl-D-glucurono-D-xylan

Two similar tetrasaccharides, one neutral and one acidic, were isolated from the products released by the attack of a xylanase on the in situ reduced 4-O-methyl-D-glucurono-D-xylan from aspen (Populus tremuloides). Paper chromatography, gel filtration behavior, methylation followed by reduction, and mass spectrometry showed that the oligosaccharides were O-(4-O-methyl-α-D-glucopyranosyluronic acid)-(1→2)-D-xylotriose and-O-(4-O-methyl-α-D-glucopyranosyluronic acid)-(1→2)-D-xylotriose. Independent of the acidic or neutral substituent on the present xylan chain, the enzymic cleavage led preferentially to oligosaccharides substituted at the nonreducing end. The existence, in wood, of a few uronic acid substituents of the D-xylan in the esterified form was confirmed, and their linkage to lignin postulated.     

Changes in enzymic activities of UDP-D-glucuronate decarboxylase and UDP-D-xylose 4-epimerase during cell division and xylem differentiation in

The time course of the specific activities of UDP-D-glucuronate decarboxylase (E.C. 4.1.1.35) and UDP-D-xylose 4-epimerase (E.C. 5.1.3.5) have     

Alkali and oxygen-alkali treatment of D-arabino-hexosulose and O-β-D-glucopyranosyl-(1 → 4)-d-arabino-hexosulose.

Benzilic acid rearrangement of D-arabino-hexosulose (1) and O-β-D-glucopyranosyl-(1→4)-D-arabino-hexosulose (2) favours formation of mannonic acid and mannonic acid moieties, respectively. The results show that formation of aldonic acid end-groups via terminal aldosulose moieties is of little importance during oxygen-hydrogencarbonate treatment of (1→4)-linked polysaccharides. The major reaction of 1 in the absence of oxygen involves loss of C-1 as formic acid. The enediol intermediate gives rise to pentoses and pentuloses (degraded completely at high alkalinity), and 3-deoxypentonic acids. The yield of 3-deoxypentonic acids is decreased in the presence of oxygen, whereas that of arabinonic, erythronic, and glycolic acids is increased. The main reaction of 2 giving rise to aliphatic hydroxy acids is β-elimination of the glucose moiety, yielding a tricarbonyl intermediate (3) which, in sodium hydrogencarbonate, is decomposed mainly to 3,4-dihydroxybutanoic and glycolic acids. In sodium hydroxide, 3-deoxypentonic acids are among the major reaction products. In addition, a complex mixture of u.v.-absorbing solutes is formed, some of which are held irreversibly by anion exchangers.