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.     

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.     

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%).     

Synthesis of two purple-membrane glycolipids and the glycolipid sulfate O-(β-d-glucopyranosyl 3-sulfate)-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2, 3-di-O-phytanyl-sn-glycerol

The two purple-membrane glycolipids O-β-d-glucopyranosyl- and O-β-d-galactopyranosyl-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2, 3-di-O-phytanyl-sn-glycerol were prepared by coupling O-(2,3,4-tri-O-acetyl-α-d-mannopyranosyl)-(1→2)-O-(3,4,6-tri-O-acetyl-α-d-glucopyranosyl)-(1→1)-2, 3-di-O-phytanyl-sn-glycerol (9) with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide, respectively, followed by deacetylation. The glycolipid sulfate O-(β-d-glucopyranosyl 3-sulfate)-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2,3-di-O-phytanyl-sn-glycerol was prepared by coupling of 9 with 2,4,6-tri-O-acetyl-3-O-trichloroethyloxycarbonyl-α-d-glucopyranosyl bromide in the presence of Hg(CN)₂/HgBr₂ followed by selective removal of the 3?-trichloroethyloxycarbonyl group, sulfation of HO-3?, and deacetylation. The suitably protected key-intermediate 9 could be prepared by two distinct approaches.     

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.     

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).     

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.     

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 p-isothiocyanatophenyl 3-O-(3,5-dideoxy-α-d-ribo-hexopyranosyl)-α-d-mannopyranoside

The synthesis of the title disaccharide derivative (1C), corresponding to the Salmonella O-factor 2¹, is described. Treatment of 2-O-benzyl-4-O-p-nitrobenzoyl-α-paratosyl bromide (5) with p-nitrophenyl 2-O-benzyl-4,6-O-benzylidene-α-d-mannoside in dichloromethane, in the presence of mercuric cyanide, gave the α- and β-linked disaccharide derivatives (6a and 6b) in yields of 34 and 5%, respectively. The disaccharide derivative 10 can react with free amino groups in proteins to produce artificial antigens useful in studies on Salmonella immunology.     

The synthesis of methyl 4-O-(4-O-α-d-galactopyranosyl-β-d-galactopyranosyl)-β-d-glucopyranoside: The methyl β-glycoside of the trisaccharide related to Fabry's disease

As part of a program to synthesize the ceramide trisaccharide (1) related to Fabry's disease, methyl 4-O-(4-O-α-$\text{d}$-galactopyranosyl-β-$\text{d}$-galactopyranosyl)-β-$\text{d}$-glucopyranoside (12) was prepared. Methyl β-lactoside (2) was converted into methyl 4-O-(4,6-O-benzylidene-β-$\text{d}$-galactopyranosyl)-β-$\text{d}$-glucopyranoside (4). Methyl 2,3,6-tri-O-benzoyl-4-O-(2,3,6-tri-O-benzoyl-β-$\text{d}$-galactopyranosyl)-β-$\text{d}$-glucopyranoside (7) was synthesized from 4 through the intermediates methyl 2,3,6-tri-O-benzoyl-4-O-(4,6-O-benzylidene-2,3-di-O-benzoyl-β-$\text{d}$-galactopyranosyl)-β-$\text{d}$-glucopyranoside (5) and methyl 2,3,6-tri-O-benzoyl-4-O-(2,3-di-O-benzoyl-β-$\text{d}$-galactopyranosyl)-β-$\text{d}$-glucopyranoside (6). The halide-catalyzed condensation of 7 with 2,3,4,6-tetra-O-benzyl-$\text{d}$-galactopyranosyl bromide (8) gave methyl 2,3,6-tri-O-benzoyl-4-O-[2,3,6-tri-O-benzoyl-4-O-(2,3,4,6-tetra-O-benzyl-α-$\text{d}$-galactopyranosyl)- β-$\text{d}$-galactopyranosyl]-β-$\text{d}$-glucopyranoside (10). Stepwise deprotection of 10 led to 12, the methyl β-glycoside of the trisaccharide related to Fabry's disease.     

Crystal structure of 2-deoxy-β-d-lyxo-hexose (2-deoxy-β-d-galactose)

2-Deoxy-β-d-lyxo-hexose (2-deoxy-β-d-galactose, C₆H₁₂O₅), M_r = 164.16, is monoclinic, P2₁ with a = 9.811(1), b = 6.953(1), c = 5.315(1) Å, β = 91.58(2)°, V = 362.5(1) ų, Z = 2, and D_x = 1.504 g.cm^?3. The structure was solved by direct methods (MULTAN 79) and refined to R = 0.032 for 800 observed reflections. Each hydroxyl oxygen, acting both as donor and acceptor, is involved in a hydrogen-bonding system, which consists of infinite helical chains around the crystallographic screw axes. Moreover, weak interactions allow the incorporation of the ring-oxygen atoms into an interconnected network.     

The crystal and molecular structure of O-α-D-mannopyranosyl-(1→3)-O-β-D-mannopyranosyl-(1→4)-2-acetamido-2-deoxy-α-D-glucopyranose

The crystal structure of α-D-Manp-(1→3)-β-D-Manp-(1→4)-α-D-GlcNAcp has been determined by the direct method using the multi-solution, tangent formula, and “magic integer” procedures. The space group is P2₂, and 2 molecules are in the unit cell with a  9.894 (5), b  10.372 (6), c  11.816 (6) Å, and β  95.03° (6). The structure was refined to R 0.059 for 2099 reflections measured with Mo Kα radiation. Difference synthesis showed all the hydrogen atoms, and indicated a partial (～30%) substitution of the α-anomer molecules by the β-anomer molecules. The D-mannopyranose and the D-glucopyranose have the normal ⁴C₁ conformation; an intramolecular hydrogen-bond O-3″-H.....O-5′ (2.703 Å) stabilises the GlcNAc in relation to β-D-mannopyranose.     

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.     

Vacuum ultraviolet circular dichroism of (1 → 6)-β-d-glucan

V.u.c.d. spectra recorded for freshly prepared aqueous solutions of (1 → 6)-β)-D-glucan(pustulan) contained a single positive band near 177 nm. This band was similar in position and magnitude to the single positive band observed in the spectrum of (1 → 6)-α-D-glucan (dextran). Pustulan solutions (20 mg/ml) were observed to gel with time at 10 C. Concurrently, a negative band at 190 nm developed in the pustulan v.u.c.d. spectrum followed by a blue shift of both bands with continued aging. Crystalline films of pustulan yield spectra which resembled the blue shifted spectra of aged gels. The time dependent development of the negative band was attributed to pustulan attaining a helical conformation in solution, and the blue shift to aggregation of helices, Na⁺ and Ca²⁺ were found to accelerate gelation presumably by decreasing the activity of the aqueous solvent.     

Synthesis of 4-O-α-d-galactopyranosyl-l-rhamnose and 4-O-α-d-galactopyranosyl-2-O-β-glucopyranosyl-l-rhamnose using dioxolane-type benzylidene acetals as temporary protecting-groups

The Halide ion-catalysed reaction of benzyl exo-2,3-O-benzylidene-α-l-rhamnopyranoside with tetra-O-benzyl-α-d-galactopyranosyl bromide and hydrogenolysis of the exo-benzylidene group of the product 2 gave benzyl 3-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-α-d-galactopyranosyl)-α-l-rhamnopyranoside (6). Compound 2 was converted into 4-O-α-d-galactopyranosyl-l-rhamnose. The reaction of 6 with tetra-O-acetyl-α-d-glucopyranosyl bromide and removal of the protecting groups from the product gave 4-O-α-d-galactopyranosyl-2-O-β-d-glucopyranosyl-l-rhamnose.     

β-Elimination of 2-O-(4-O-methyl-α-d-glucopyranosyluronic acid)-d-xylose with methylsulphinyl carbanion and hydrolysis of the hex-4-enopyranosiduronic linkage

On treatment with m sodium methylsulphinylmethanide at 25°, 2-O-(4-O-methyl-α-d-glucopyranosyluronic acid)-d-xylose (1) was rapidly degraded by β-elimination, to form 2-O-(4-deoxy-β-l-threo-hex-4-enopyranosyluronic acid)-d-xylose (2). The kinetics of hydrolysis of 1 and 2 in 0.5m sulphuric acid have been studied. Compound 2 was hydrolysed 70 times faster than 1. Compared with the rate coefficients of other related compounds, 2 was hydrolysed at approximately the same rate as 2-O-(4-O-methyl-α-d-glucopyranosyl)-d-xylose, 3.5 times more slowly than xylobiose, and twice as fast as the xylosidic bond in O-(4-O-methyl-α-d-glucopyranosyluronic acid)-(1→2)-O-β-d-xylopyranosyl-(1→4)-d-xylose.     

The use of 1-O-tosyl-d-glucopyranose derivatives in α-d-glucoside synthesis

1-O-Tosyl-d-glucopyranose derivatives having a nonparticipating benzyl group at O-2 have been shown to react rapidly in various solvents with low concentrations of alcohols, either methanol or methyl 2,3,4-tri-O-benzyl-α-d-glucopyranoside. The stereospecificity of the glucoside-forming reaction could be varied from 80% of β to 100% of α anomer by changing the solvent or modifying the substituents on the 1-O-tosyl-d-glucopyranose derivative. 2,3,4-Tri-O-benzyl-6-O-(N-phenylcarbamoyl)-1-O-tosyl-α-d-glucopyranose in diethyl ether gave a high yield of α-d-glucoside. Kinetic measurements of reaction with various alcohols (methanol, 2-propanol, and cyclohexanol) show a high rate even at low concentrations of alcohol, and give some insight into the reaction mechanism. The high rate and stereoselectivity of their reaction suggest that the 1-O-tosyl-d-glucopyranose derivatives may be used as reagents for oligosaccharide synthesis.     

The acid-catalyzed hydrolysis of β-d-xylofuranosides

The rate constants for the hydrolysis of six alkyl and four aryl β-d-xylofuranosides in aqueous perchloric acid at various temperatures have been measured. The effects of varying the aglycon structure on the hydrolysis rate are interpreted in terms of two concurrent reactions. Either, the substrate, protonated on the glycosidic oxygen atom, undergoes a rate-limiting heterolysis to form a cyclic oxocarbonium ion, or, an initial rapid protonation of the ring oxygen is followed by a unimolecular cleavage of the five-membered ring, all subsequent reactions being fast. It is suggested that xylofuranosides having strongly electron-attracting aglycon groups react mainly by the former pathway, whereas the latter is more favourable for substrates having electron-repelling aglycon groups. The negative entropies of activation obtained with the latter compounds are attributed to the rate-limiting opening of the five-membered ring. The rate variations of the hydrolyses of alkyl β-d-xylofuranosides in aqueous perchloric acid-methyl sulfoxide mixtures are interpreted as lending further support for the suggested chance in mechanism.     

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.