Syntheses of 3-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-galactopyranose (“lacto-N-biose II”) and 3,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-galactopyranose

3- O-(2-Acetamido-2-deoxy-β-d-glucopyranosyl)-α-d-galactopyranose (10, “Lacto-N-biose II”) was synthesized by treatment of benzyl 6-O-allyl-2,4-di-O-benzyl-β-d-galactopyranoside with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)[2,1-d]-2-oxazoline (5), followed by selective O-deallylation, O-deacetylation, and catalytic hydrogenolysis. Condensation of 5 with benzyl 6-O-allyl-2-O-benzyl-α-d-galactopyranoside, followed by removal of the protecting groups, gave 10 and a new, branched trisaccharide, 3,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-galactopyranose (27).     

Synthesis of phenyl O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-α-d-galactopyranoside

phenyl 2-acetamido-2-deoxy-4,6-O-(p-methoxybenzylidene)-3-O-[4,6-O-(p-methoxybenzylidene)-β-d-alactopyranosyl]-α-d-galactopyranoside (3) was prepared from phenyl 2-acetamido-2-deoxy-4,6-O-(p-methoxybenzylidene)-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-galactopyranoside by zemplén deacetylation, followed by reaction with p-methoxybenzaldehyde in the presence of anhydrous zinc chloride. The selective benzoylation of 3 gave the 3′-benzoate which, on condensation with 2,3,4-tri-O-benzyl-α- l-fucopyranosyl bromide under catalysis by halide ion, afforded a crystalline trisaccharide from which the title trisaccharide was obtained by debenzoylation followed by catalytic hydrogenolysis.     

β-elimination in aldonolactones. Synthesis of 2-deoxy-D-lyxo-hexose and 2-deoxy-D-arabino-hexose

Benzoylation of D-glycero-L-manno-heptono-1,4-lactone (1) with benzoyl chloride and pyridine for 2 h afforded crystalline penta-O-benzoyl-D-glycero-L-manno-heptono-1,4-lactone (2), but a large excess of reagent during 8 h also led to 2,5,6,7-tetra-O- benzoyl-3-deoxy-D-lyxo-hept-2-enono-1,4-lactone (3). Catalytic hydrogenation of 3 was stereoselective and gave 2,5,6,7-tetra-O-benzoyl-3-deoxy-D-galacto-heptono-1,4-lactone (4). Debenzoylation of 4 followed by oxidative decarboxylation with ceric sulfate in aqueous sulfuric acid gave 2-deoxy-D-lyxo-hexose (5). Application of the same reaction to 3-deoxy-D-gluco-heptono-1,4-lactone afforded 2-deoxy-D-arabino-hexose (6).     

Acid-catalyzed and almond β-d-glucosidase-catalyzed hydrolysis of purin-6-yl 2-deoxy-1-thio-β-d-arabino-hexopyranoside

Hydrolysis of purin-6-yl 2-deoxy-1-thio-β-d-arabino-hexopyranoside (2) to 6-mercaptopurine and 2-deoxy-d-glucose is catalyzed by hydronium ion and almond β-d-glucosidase. The dependence of rate on acidity in water and deuterium oxide indicates that 2 and its conjugate acid undergo hydrolysis via a mechanism that involves a partially rate-limiting proton transfer. Although 2 is ≈103 more reactive than 6-purinyl β-d-glucothiopyranoside (1) in dilute aqueous acid, 1 is a better substrate for almond β-d-glucosidase.     

β-d-glucosidase-catalysed transfer of the glycosyl group from aryl β-d-gluco- and β-d-xylo-pyranosides to phenols

The effect of phenols on the hydrolysis of substituted phenyl β-d-gluco- and β-d-xylo-pyranosides by β-d-glucosidase from Stachybotrys atra has been investigated. Depending on the glycon part of the substrate and on the phenol substituent, the hydrolysis is either inhibited or activated. With aryl β-d-xylopyranosides, transfer of the xylosyl residue to the phenol, with the formation of new phenyl β-d-xylopyranosides, is observed. With aryl β-d-glucopyranosides, such transfer does not occur when phenols are used as acceptors, but it does occur with anilines. A two-step mechanism, in which the first step is partially reversible, is proposed to explain these observations. A qualitative analysis of the various factors determining the overall effect of the phenol is given.     

Synthesis of 5-O-α-and-β-d-glucopyranosyl-d-glucofuranose and 5-O-α-d-glucopyranosyl-d-fructopyranose (leucrose)

Reaction of 1,2-O-cyclopentylidene-α-d-glucofuranurono-6,3-lactone (2) with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide (1) gave 1,2-O-cyclopentylidene- 5-O-(2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl)-α-d-glucofuranurono-6,3-lactone (3, 45%) and 1,2-O-cyclopentylidene-5-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-α-d-glucofuranurono-6,3-lactone (4, 38%). Reduction of 3 and 4 with lithium aluminium hydride, followed by removal of the cyclopentylidene group, afforded 5-O-α-(9) and -β-d-glucopyranosyl-d-glucofuranose (12), respectively. Base-catalysed isomerization of 9 yielded crystalline 5-O-α-d-glucopyranosyl-d-fructopyranose (leucrose, 53%).     

X-ray crystal structure of maltitol (4-O-α-d-glucopyranosyl-d-glucitol

Maltitol, crystallised from aqueous solution, has m.p. 146.5–147°, [α]_d + 106.5° (water), and is orthorhombic with the space group P2₁2₁2₁ and Z = 4, and with cell dimensions a = 8.166(5), b = 12.721(9), and c = 13.629(6) Å. The molecule shows a fully extended conformation with no intramolecular hydrogen-bonds. All nine hydroxyl groups are involved in intermolecular hydrogen-bond networks and in bifurcated, finite chains. The d-glucopyranosyl moiety has the ⁴C₁ conformation, and the conformation about the C-5–C-6 bond is gauche-gauche. The d-glucitol residue has the bent [ap, Psc, Psc (APP)] conformation. The empirical formula for the solubility in water is C = 119.1 + 1.204 T + 4.137 × 10^?2 T² ? 7.137 × 10^?4 T³ + 7.978 × 10^?6 T⁴. The thermal properties are as follows: ΔH_f = 13.5 kcal.mol^?1, and Q = ?5.57 kcal.mol^?1.     

The synthesis of 3-amino-3-deoxy-α-d-glucopyranosyl α-d-glucopyranoside (3-amino-3-deoxy-α,α-trehalose

The preparation of 2,3-di-O-benzoyl-4,6-O-benzylidene-α-d-glucopyranosyl-2-O-benzoyl-4,6-O-benzylidene-α-d-ribo-hexopyranosid-3-ulose (3) from 4,6:4′,6′-di-O-benzylidene-α,α-trehalose (1) via the 2,3,2′-tribenzoate 2 has been improved. Reduction of 3 with sodium borohydride gave 2-O-benzoyl-4,6-O-benzylidene-α-d-allopyranosyl 2,3-di-O-benzoyl-4,6-O-benzylidene-α-d-glucopyranoside (4), which was converted into the methanesulfonate 5 and trifluoromethanesulfonate 6. Displacement of the sulfonic ester group in 6 with lithium azide was very facile and afforded a high yield of 3-azido-2-O-benzoyl-4,6-O-benzylidene-3-deoxy-α-d-glucopyranosyl 2,3-di-O-benzoyl-4,6-O-benzylidene-α-d-glycopyranoside (7), whereas similar displacement in 5 proceeded sluggishly, giving a lower yield of 7 together with an unsaturated disaccharide (8). The azido sugar 7 was converted by conventional reactions into the analogous 2,3,2′-triacetate 9, the corresponding 2,3,2′-triol 10, and deprotected 3-azido-3-deoxy-α-d-glucopyranosyl α-d-glucopyranoside (11). Hydrogenation of 11 over Adams' catalyst furnished crystalline 3-amino-3-deoxy-α,α-trehalose hydrochloride (12), the overall yield from 3 being 35%.     

Practical synthesis of O-β-d-mannopyranosyl-, O-α-d-mannopyranosyl-, and O-β-d-glucopyranosyl-(1→4)-O-α-l-rhamnopyranosyl-(1→3)-d-galactoses

The koenigs-Knorr glycosylation of 4,6-O-ethylidene-1,2-O-isopropylidene-3-O-(2,3-O-isopropylidene-α-l-rhamnopyranosyl)-α-d-galactopyranose (3) by 4,6-di-O-acetyl-2,3-O-carbonyl-α-d-mannopyranosyl bromide (10), as well as Helferich glycosylations of 3 by tetra-O-acetyl-α-d-mannopyranosyl and -α-d-glucopyranosyl bromides, proceeded smoothly to give high yields of trisaccharide derivatives (12, 16, and 17). An efficient procedure for the transformation of 12, 16, and 17 into the α-deca-acetates of the respective trisaccharides has been developed. Zemplén de-acetylation then afforded the title trisaccharides in yields of 53, 52, and 62 %, respectively, from 3. A new route to 1,4,6-tri-O-acetyl-2,3-O-carbonyl-α-d-mannopyranose is suggested.     

X-ray structure of 1,3,4-tri-O-acetyl-2-deoxy-β-d-erythro-pentopyranose

Peracetylated 2-deoxy-d-erythro-pentose (2-deoxy-d-ribose) was synthesized through the acetylation of 2-deoxy-d-ribose with acetic anhydride in pyridine, and the products (including all four ring forms) exist in form of either a white solid or a syrup. A single crystal of 1,3,4-tri-O-acetyl-2-deoxy-β-d-erythro-pentopyranose was obtained from the syrup and its structure was determined by X-ray diffraction. The crystal adopts the ¹C₄ conformation, presenting an orthorhombic system, space group P2₁2₁2₁ with Z = 4, unit cell dimensions a = 7.2274 (3) Å, b = 8.0938 (5) Å, and c = 22.0517 (11) Å.     

Identification of neoschaftoside as 6-C-β-d-glucopyranosyl-8-C-β-l-arabinopyranosylapigenin

The structure of neoschaftoside is shown for the first time to be 6-C-β-d-glucopyranosyl-8-C-β-l-arabinopyranosylapigenin. A variety of chemical and spectroscopic techniques are involved.     

The synthesis of 5-O-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-β-D-glucofuranose

Condensation of dimeric 3,4,6-tri-O-acetyl-2-deoxy-2-nitroso-α-D-glucopyranosyl chloride (1) with 1,2-O-isopropylidene-α-D-glucofuranurono-6,3-lactone (2) gave 1,2-O-isopropylidene-5-O-(3,4,6-tri-O-acetyl-2-deoxy-2-hydroxyimino-α-D-arabino-hexopyranosyl)-α-D-glucofuranurono-6,3-lactone (3). Benzoylation of the hydroxyimino group with benzoyl cyanide in acetonitrile gave 1,2-O-isopropylidene-5-O-(3,4,6-tri-O-acetyl-2-benzoyloxyimino-2-deoxy-α-D-arabino-hexopyranosyl)-α-D-glucofuranurono-6,3-lactone (4). Compound 4 was reduced with borane in tetrahydrofuran, yielding 5-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1,2-O-isopropylidene-α-D-glucofuranose (5), which was isolated as the crystalline N-acetyl derivative (6). After removal of the isopropylidene acetal, the pure, crystalline title compound (10) was obtained.     

Monomolar acetalations of methyl α-d-mannosides—synthesis of methyl α-d-talopyranoside

Methyl α-d-mannopyranoside (1 mole) reacts with 2,2-dimethoxypropane (1 mole), to give the 4,6-O-isopropylidene derivative (2) which rearranges to the 2,3-O-isopropylidene derivative (4). Compound4 can also be prepared by graded hydrolysis of methyl 2,3:4,6-di-O-isopropylidene-α-d-mannopyranoside. Successive benzoylation, oxidation, and reduction of4 provides a useful route to a number ofd-talopyranoside compounds. Methyl α-d-mannofuranoside (1 mole) reacts with 1–2 moles of 2,2-dimethoxypropane to give the 5,6-O-isopropylidene derivative (16) in 90% yield.     

Synthesis of 2-(6-aminohexanamido)ethyl 1-thio-β-d-galactopyranoside and 1-thio-β-d-glucopyranoside,and related compounds

2-(6-Aminohexanamido)ethyl 1-thio-β-d-galactopyranoside (5) and 1-thio-β-d-glucopyranoside (9) were prepared by the following scheme: 2,3,4,6-tetra-O-acetyl-1-thio-β-d-aldopyranoses, generated from 2-S-(2,3,4,6-tetra-O-acetyl-β-d-aldopyranosyl)-2-thiopseudourea hydrobromides, were aminoethylated with ethylenimine, followed by N-acylation of the products with 6-(trifluoroacetamido)hexanoic acid (1), and O-deacylation. These reactions could be carried out consecutively without isolation of intermediates, and the products obtained after gel chromatography were de(trifluoroacetyl)ated to obtain the final products. The chain lengths of the aglycons were further extended by repeating the acylation and the de(trifluoroacetyl)ation. An analog containing glycerol in lieu of a sugar was prepared by a similar reaction-scheme.     

2′-Azido-2′-deoxy- and 2′-amino-2′-deoxy-β-d-arabino-furanosyl purine nucleosides

A general method for the preparation of 2′-azido-2′-deoxy- and 2′-amino-2′-deoxyarabinofuranosyl-adenine and -guanine nucleosides is described. Selective benzoylation of 3-azido-3-deoxy-1,2-O-isopropylidene-α-d-glucofuranose afforded 3-azido-6-O-benzoyl-3-deoxy-1,2-O-isopropylidene-α-d-glucofuranose (1). Acid hydrolysis of 1, followed by oxidation with sodium metaperiodate and hydrolysis by sodium hydrogencarbonate gave 2-azido-2-deoxy-5-O-benzoyl-d-arabinofuranose (3), which was acetylated to give 1,3-di-O-acetyl-2-azido-5-O-benzoyl-2-deoxy-d-arabinofuranose (4). Compound 4 was converted into the 1-chlorides 5 and 6, which were condensed with silylated derivatives of 6-chloropurine and 2-acetamido-hypoxanthine. The condensation reaction gave α and β anomers of both 7- and 9-substituted purine nucleosides. The structures of the nucleosides were determined by n.m.r. and u.v. spectroscopy, and by correlation of the c.d. spectra of the newly prepared nucleosides with those published for known purine nucleosides.     

A synthesis of 3-O-(α-d-mannopyranosyl)-d-mannose and its protein conjugate

Methods for the synthesis of 3-O-(α-d-mannopyranosyl)-d-mannose and 2-(4-aminophenyl)ethyl 3-O-(α-d-mannopyranosyl)-α-d-mannopyranoside have been investigated by a number of sequences. Glycosidations with 2,3-di-O-acetyl-4,6-di-O-benzyl-d-mannopyranosyl and 2-O-benzoyl-3,4,6-tri-O-benzyl-d-mannopyranosyl p-toluenesulfonates were found to give better yields than the Helferich modification, the use of a peracylated d-mannopyranosyl halide, or the use of triflyl leaving group. Only the α anomer was obtained. Factors influencing glycosidation reactions are discussed. A mercury(II) complex was used for selective 2-O-acylation of 4,6-di-O-benzyl-α-d-mannopyranosides. A disaccharide—protein conjugate was prepared by the isothiocyanate method.     

Synthesis of 2,5-dideoxy-2-C-methyl-d-arabinose derivatives from methyl 2,3-anhydro-5-deoxy-α-d-ribofuranoside

Treatment of methyl 2,3-anhydro-5-deoxy-α-d-ribofuranoside with lithium dimethyl cuprate gave methyl 2,5-dideoxy-2-C-methyl-α-d-arabinofuranoside (54% yield) and methyl 3,5-dideoxy-3-C-methyl-α-d-xylofuranoside (10%). The former was converted into its 3-O-acetyl and 3-O-benzyl derivatives, which, upon acid hydrolysis, afforded 3-O-acetyl- and 3-O-benzyl-2,5-dideoxy-2-C-methyl-d-arabinofuranose in 60–75% overall yield. Treatment of the 3-O-benzyl compound with ethanethiol in the presence of trifluoromethanesulfonic acid afforded 3-O-benzyl-2,5-dideoxy-2-C-methyl-d-arabinose diethyl dithioacetal (20%) and ethyl 3-O-benzyl-2,5-dideoxy-2-C-methyl-1-thio-α-d-arabinoside (73%). The former, which was also available from the latter by equilibration in acidic ethanethiol, was acetylated at O-4 and the product converted into the corresponding dimethyl acetal (85% overall yield). This compound was, after debenzylation, hydrolyzed with acid, to provide 4-O-acetyl-2,5-dideoxy-2-C-methyl-d-arabinose in 70% overall yield.     

Chemical Syntheses of 4-O-α and -β-D-galactopyranosyl-D-galactose and 3-O-α- and -β-D-galactopyranosyl-D-galactose

Reaction of 2,3-di-O-acetyl-1,6-anhydro-β-D-galactopyranose (2) with 2,3,4,6-tetra- O-acetyl-α-D-galactopyranosyl bromide in the presence of mercuric cyanide and subsequent acetolysis gave 1,2,3,6-tetra-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl)-α-D-galactopyranose (4, 40%) and 1,2,3,6-tetra-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-α-D-galactopyranose (5, 30%). Similarly, reaction of 2,4-di-O-acetyl-1,6-anhydro-β-D-galactopyranose (3) gave 1,2,4,6-tetra-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl)-α-D-galactopyranose (6, 46%) and 1,2,4,6-tetra-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-α-D-galactopyranose (7, 14%). The anomeric configurations of 4-7 were assigned by n.m.r. spectroscopy. Deacetylation of 4-7 afforded 4-O-α-D-galactopyranosyl-D-galactose (8), 4-O-β-D-galactopyranosyl-D-galactose (9), 3-O-α-D-galactopyranosyl-D-galactose (10), and 3-O-β-D-galactopyranosyl-D-galactose (11), respectively.     

The crystal structure of methyl 3,4-O-isopropylidene-2,6-di-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-galactopyranoside at 97 K

The crystal structure of methyl 3,4-O-isopropylidene-2,6-di-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-galactopyranoside (1), C₃₈H₅₄O₂₄ · (C₄H₈O₂)_0.32 was determined by X-ray diffraction;1 crystallises in space group P2₁ with a = 12.480(3), b = 8.821(3), c = 21.182(4)Å, β = 98.46(3)°, and Z = 2. The structure was solved by Patterson-search and Fourier-recycling procedures and refined to R_w(R) = 0.048(0.063), using 4348 [3112 with I> 2σ(I)] independent reflections. The β-d-galactosyl rings are slightly distorted and, due to the isopropylidene group, the α-d-galactoside ring is severely distorted. The conformation near the β-(1→6) and β-(1→2) linkages between the pyranoid rings is not significantly affected by the acetyl groups, but the anomeric C-O-C bridge angles have unusual values. The C-6O-6 bond in the β-d-galactosyl group (1→2)-linked to the α-d-galactoside residue has an unusual gauche—trans conformation with respect to C-4 and O-5. The CH₃-(C = O)-O-C moieties are planar within 0.01Å, and 32.6% of all unit cells contain a molecule of ethyl acetate.