Use of positively charged,leaving groups in the synthesis of α-D-linked galactosides. Attempted synthesis of 3-O-α-(D-(galactopyranosyl)-D-galactose

Quaternary ammonium and phosphonium salts were readily obtained by treating 2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl bromide with tertiary amines and phosphines in various solvents under anhydrous conditions. Optical rotations and n.m.r. spectra of the hygroscopic syrups indicated that they exist mainly in the β-D configuration. Several dialkyl sulfides reacted very slowly with the galactosyl bromide and no conclusive evidence for sulfonium salt formation was obtained. 2,3,4,6-Tetra-O-benzyl-α-D-galactopyranosyl chloride failed to react with any of the nucleophiles.Methanolysis reactions of the phosphonium salts were too slow to be practical and were not studied extensively. Methanolyses of several quaternary ammonium salts in various solvents were not completely stereospecific, but gave good yields of methyl 2,3,4,6-tetra-O-benzyl-α-D-galactopyranoside. Attempted reactions of benzyl 2-O-benzoyl-4,6-O-benzylidene-β-D-galactopyranoside with quaternary ammonium salts derived from 2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl bromide failed to produce the corresponding derivative of 3-O-(α-D-galactopyranosyl)-D-galactose.     

Derivatives of β-D-fructofuranosyl α-D-galactopyranoside

De-etherification of 6,6′-di-O-tritylsucrose hexa-acetate (2) with boiling, aqueous acetic acid caused 4→6 acetyl migration and gave a syrupy hexa-acetate 14, characterised as the 4,6′-dimethanesulphonate 15. Reaction of 2,3,3′4′,6-penta-O-acetylsucrose (5) with trityl chloride in pyridine gave a mixture containing the 1′,6′-diether 6 the 6′-ether 9, confirming the lower reactivity of HO-1′ to tritylation. Subsequent mesylation, detritylation, acetylation afforded the corresponding 4-methanesulphonate 8 1′,4-dimethanesulphonate 11. Reaction of these sulphonates with benzoate, azide, bromide, and chloride anions afforded derivatives of β-D-fructofuranosyl α-D-galactopyranoside (29) by inversion of configuration at C-4. Treatment of the 4,6′-diol 14 the 1,′4,6′-triol 5, the 4-hydroxy 1′,6′-diether 6 with sulphuryl chloride effected replacement of the free hydroxyl groups and gave the corresponding, crystalline chlorodeoxy derivatives. The same 4-chloro-4-deoxy derivative was isolated when the 4-hydroxy-1′,6′-diether 6 was treated with mesyl chloride in N,N-dimethylformamide.     

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.     

Synthesis of 5-O-β-D-galactofuranosyl-D-galactofuranose

Conversion of benzyl αβ-D-galactofuranoside into the 5,6-O-[α-(dimethyl-amino)benzylidene] derivative, followed by acetylation of HO-2 and HO-3, and selective ring opening or the acetal, gave benzyl 2,3-di-O-acetyl-6-O-benzoyl-αβ-D-galactofuranoside(4). The title disaccharide was synthesised from4 by reaction with 3,4,6-tri-O-acetyl-α-D-galactofuranose 1,2-(methyl orthoacetate) followed by removal of protecting groups     

α-D-Mannosidase-catalyzed hydrolysis of substituted phenyl α-D-mannopyranosides

The influence substituents on the hydrolysis of substituted phenyl α-D-mannopyranosides by α-D-mannosidase from Medicago sativa L. has been investigated. As indicated by structure-activity relations, the electronic effect of the substituent has an influence on the rate of formation of the intermediate mannosyl-enzyme complex. This effect depends not only on the nature of the substituent, but also on its position (meta or para) and on the temperature of the experiment. Hammett-type linear free energy relationships show that the reaction constant p changes its sign at ～27°. Substrates with strong electron-withdrawing groups show values of log V that are linearly related to 1/T, whereas the Arrhenius plots for other substrates are severely curved. This complex behaviour is tentatively explained by assuming that some meta-substituents have an unusual, temperature- and substituent-dependent influence on the formation of the Michaelis—Menten complex.     

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).     

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.     

Aminoglycosides of D-pinitol. The 3-amino-3-deoxy-α-D-glucopyranoside,THE 3-acetamidino analog,and the 3,6-dideoxy-3,6-epimino-α-D-glucopyranoside

3-Azido-2,4,6-tri-O-benzyl-3-deoxy-α-D-glucopyranosyl chloride (7), prepared conventionally from the azido precursor 2, was coupled with “diisopropylidene-D-pinitol” (8) to give the α-D-glucoside 9 in good yield, together with some β anomer. Removal of the O-benzyl groups from 9 and reduction of the azido group to ?NH₂ were accomplished simultaneously. Further deprotection yielded 11, a 3-amino-3-deoxy-α-D-glucoside of D-pinitol (1a). Compound 11 was converted into the (impure) 3-acetamidino hydrochloride 12. The synthesis of 3,6-epimino-D-glucosides was accomplished by ring closure of the 3-N-tosyl-6-O-tosyl intermediates 17 and 13. The products, after deprotection, were methyl 3,6-dideoxy-3,6-epimino-β-D-glucopyranaside (20) and the novel 3,6-epimino analog 15 of the pinitol D-glucoside 11.     

A sensitive determination of α-keto acids by gas-liquid chromatography and its application to the assay of l-glutamate dehydrogenase and aminotransferases

A sensitive and selective determination of α-keto acids was established by the use of a gas chromatograph equipped with an electron capture detector. α-Keto acids (pyruvic, oxaloacetic, α-ketobutyric, and α-ketoglutaric acids) were reacted with pentafluorophenylhydrazine, and the derivatives were extracted with ethyl ether, reacted with diazomethane, and were subjected to gas-liquid chromatography with an electron capture detector. In the course of the reaction, oxaloacetic acid was decarboxylated, and yielded pyruvic acid. In the case of pyruvic (oxaloacetic) and α-ketobutyric acids two peaks corresponding to the syn and anti forms of the hydrazone appeared, and in the case of α-ketoglutaric acid, two peaks corresponding to the hydrazone and the cyclization compound produced from the hydrazone. The sum of the two peaks was taken for the determination. The present method was applicable to the assay of l-glutamate dehydrogenase, aspartate: 2-oxoglutarate, and l-alanine: 2-oxoglutarate aminotransferases.     

Synthesis of 4-O-β-D-mannopyranosyl-L-rhamnopyranose

The title disaccharide (16) has been synthesized in 50% overall yield by way of condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-α-D-mannopyranosyl bromide 5 with methyl 2,3-O-isopropylidene-α-L-rhamnopyranoside (1) in chloroform solution, in the presence of silver oxide. The disaccharide was characterized as the crystalline isopropyl alcoholate of methyl 4-O-β-D-mannopyranosyl-α-L-rhamnopyranoside (11) and as 1,2,3-tri-O acetyl-4-O- (2,3,4,6-tetra-O-acetyl-β-D-mannopyranosyl)-α-L-rhamnopyranose (15). Methyl β-D-mannopyranoside isopropyl alcoholate 7 was readily obtained in 85% yield via the reaction of bromide 5 with methanol.Reduction of 2,3-di-O-methyl-L-rhamnose with sodium borohydride, followed by acetylation, may result in the formation of an appreciable proportion of a boric ester, namely 1,5-di-O-acetyl-4-deoxy-2,3-di-O-methyl-L-rhamnitol-4-yl dimethyl borate, depending on the procedure used.     

The use of positively charged leaving-groups in the synthesis of α-D-linked glucosides. Synthesis of methyl 2,3,4-tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-α-D-glucopyranoside

Quaternary ammonium and triphenylphosphonium salts of 2,3,4-tri-O-benzyl-6-O-(N-phenylcarbamoyl)-D-glucopyranosyl bromide were readily prepared by reaction with tertiary amines and triphenylphosphine under anhydrous conditions. Methanolysis of these salts was studied to determine the conditions of solvent and temperature that would produce the highest yields of α-D-glucosides. The quaternary ammonium salts gave the highest yields with solvents of low dielectric constant and room temperature. The phosphonium salts gave moderate yields with diethyl ether at 50°. The synthesis of methyl 2,3,4-tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-α-D-glucopyranoside by treatment of the quaternary ammonium salt of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide with methyl 2,3,4-tri-O-benzyl-α-D-glucopyranoside was studied as a model for the synthesis of oligosaccharides. The anomeric composition of the disaccharide product could be easily determined from the optical rotation since the specific rotations of both the final product and of the gentiobioside analog are known. Under the best conditions, the yield of disaccharide was low (50%) and the reactions were not completely stereoselective.     

The oxidation of methyl α-D-glucopyranoside with methyl sulproxide and acetic anhydride

The relative proportions of carbonyl, O-acetyl, and O-(methylthio)methylsugars resulting from the partial oxidation of methyl α-D-glucopyranoside with methyl sulphoxide and acetic anhydride have been investigated@ the preparation of the 2- and 6-(methylthio)methyl ethers of methyl α-D-glucopyranoside is described.     

Conformational studies of per-O-trimethylsilyl derivatives of D-fructoses and oligosaccharides containing β-D-fructofuranose residues by 220- and 300-MHz P.M.R. spectroscopy

The interpretation of 220- and 300-MHz P.M.R. spectra and the accurate chemical shifts and coupling constants of a number of per-O-trimethylsilyl-(TMS-) D-fructose derivatives and TMS-oligosaccharides containing β-D-fructofuranose residues are presented. On the basis of calculations with an adapted Karplus equation it is concluded that TMS-α- and -β-D-fructopyranose occur in the ²C₅(D) chair conformation whereas the D-glucopyranose rings in the oligosaccharides adopt the usual ⁴C₁(D) chair conformation. The structure of the latter units is very similar to that of TMS-α-_D-glucopyranose. The ⁴E(D) envelope and ⁴T₅(D) twist are the principal conformations of the D-fructofuranose rings. The conformation of the furanose ring depends on the number and kind of monosaccharide units attached thereto. The calculated, preferred conformation of the C-5-CH₂OTMS group of the D-fructofuranose moieties correlates with the time-averaged displacement of C-4 above the plane of C-2, C-3, and O-5.     

The strucrure of trans-O-β-D-glucopyranosyl methyl acetoacetate,and the interpretation of its optical rotations

Crystal-structure determination of trans-O-β-D-glucopyranosyl methyl acetoacetate, C₁₁H₁₈O₈, m.p. 186°, confirmed the trans orientation deduced previously from physical properties. The conformation of the D-glucopyranosyl group is ⁴C₁, although the most symmetrical chair-conformer is actually ³C_o. The glycosidic link is sc, with a CO anomeric bond of 1.428 Å (142.8 pm), i.e. longer than is normal in methyl β-glycopyranosides. All of the hydrogen bonding is intermolecular. The unusual optical rotations in solution can be interpreted in terms of rotameric populations that are derived from the solid-state conformers and are stabilized by intramolecular or solvent hydrogen-bonding.     

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.     

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.     

Transport of 3-O-methyl d-glucose and β-methyl d-glucoside by rabbit ileum

The intestinal transport of three actively transported sugars has been studied in order to determine mechanistic features that, (a) can be attributed to stereospecific affinity and (b) are common.The apparent affinity constants at the brush-border indicate that sugars are selected in the order, $\text{β-methyl glucose >}\text{d}\text{-galactose}\text{> 3-O-}\text{methyl}$ glucose, (the K_m values are 1.23, 5.0 and 18.1 mM, respectively.) At low substrate concentrations the K_t values for Na⁺ activation of sugar entry across the brush-border are: 27.25, and 140 mequiv. for β-methyl glucose, galactose and 3-O-methyl glucose, respectively. These kinetic parameters suggest that Na⁺, water, sugar and membrane-binding groups are all factors which determine selective affinity.In spite of these differences in operational affinity, all three sugars show a reciprocal change in brush-border entry and exit permeability as Ringer [Na] or [sugar] is increased. Estimates of the changes in convective velocity and in the diffusive velocity when the sugar concentration in the Ringer is raised reveal that with all three sugars, the fractional reduction in convective velocity is approximately equal to the (reduction of diffusive velocity)². This is consistent with the view that the sugars move via pores in the brush-border by convective diffusion.Theophylline reduces the serosal border permeability to β-methyl glucose and to 3-O-methyl glucose relatively by the same extent and consequently, increases the intracellular accumulation of these sugars.The permeability of the serosal border to β-methyl glucose entry is lower than permeability of the serosal border to β-methyl glucose exit, which suggests that β-methyl glucose may be convected out of the cell across the lateral serosal border.     

6-thio and -seleno-β-D-glucose esters of dimethylarsinous acid

Syntheses of 2-Se-(1,2,3,4-tetra-O-acetyl-β-D-glucopyranosyl)-3-N,N-dimethyl-selenopseudourea hydroiodide (3), 1,2,3,4-tetra-O-acetyl-6-S-dimethylarsino-6-thio-β-D-glucopyranose (4), 1,2,3,4-tetra-O-acetyl-6-Se-dimethylarsino-6-seleno-β-D-glucopyranose (7), 6-S-dimethylarsino-6-thio-β-D-glucopyranose (5), and 6-Se-dimethylarsino-6-seleno-β-D-glucopyranose (9) are described. Various spectral properties of the compounds are given. The relative rates of alkaline hydrolysis of 5 and 9 are compared.     

The synthesis and decomposition of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-(N-nitroso)acetamido-α- and β-D-glucopyranose

The synthesis of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-(N-nitroso)acetamido-α- and β-D-glucopyranose is described. Decomposition of the α-nitrosoamide in chloroform containing 2% of ethanol at room temperature afforded β-D-glucopyranose pentaacetate and ethyl β-D-glucopyranoside tetraacetate as major products, the former predominating. Reaction in 1:5 (v/v) acetic acid—acetic anhydride containing sodium acetate also gave β-D-glucose pentaacetate as major product, together with 1,1,3,4,6-penta-O-acetyl-2,5-anhydro-D-mannose aldehydrol. Decompositions of both α and β-nitrosoamides in 1:1 (v/v) acetone—water gave mainly 3,4,6-tri-O-acetyl-2,5-anhydro-D-mannose and its aldehydrol form. The synthesis, from 2,5-anhydro-D-mannose, of four new derivatives is also reported.     

Obtention de I-D-ribofuranosylade´nines

The I-D-ribosyladenines have been obtained by treatment of 5-amino-4-cyanoimidazole (N-substituted or not) with ethyl N-(2,3-O-isopropylidene-D-ribofuranosyl)formimidate. The anomeric mixtures of the corresponding O-isoprophylidene nucleoside have been separated and the anomer fully characterized. In neutral aqueous medium, these compounds are transformed into an anomeric mixture of the corresponding 6-D-ribofuranosyladenine. In basic medium, however, anomerisation of the starting compounds to give an α,β equilibrium, in which the α anomer preponderates, takes place.