Synthesis and intramolecular reactions of Tyr-Gly and Tyr-Gly-Gly related 6-O-glucopyranose esters

6-O-(L-Tyrosylglycyl)- and 6-O-(L-tyrosylglycylglycyl)-D-glucopyranose were synthesized by condensation of the pentachlorophenyl esters of the respective di- and tripeptide with fully unprotected D-glucose. The intramolecular reactivity of the sugar conjugates was studied in pyridine-acetic acid and in dry methanol, at various temperatures and for various incubation times. The composition of the incubation mixtures was monitored by a reversed-phase HPLC method that permits simultaneous analysis of the disappearance of the starting material and the appearance of rearrangement and degradation products. To determine the influence of esterification of the peptide carboxy group on its amino group reactivity, parallel experiments were done in which free peptides were, under identical reaction conditions, incubated with D-glucose (molar ratios 1:1 and 1:5). Depending on the starting compound, different types of Amadori products (cyclic and bicyclic form), methyl ester of peptides, and Tyr-Gly-diketopiperazine were obtained.     

Oxidation of methyl α-d-galactopyranoside by galactose oxidase: products formed and optimization of reaction conditions for production of aldehyde

The reaction conditions of galactose oxidase-catalyzed, targeted C-6 oxidation of galactose derivatives were optimized for aldehyde production and to minimize the formation of secondary products. Galactose oxidase, produced in transgenic Pichia pastoris carrying the galactose oxidase gene from Fusarium spp., was used as catalyst, methyl α-d-galactopyranoside as substrate, and reaction medium, temperature, concentration, and combinations of galactose oxidase, catalase, and horseradish peroxidase were used as variables. The reactions were followed by ¹H NMR spectroscopy and the main products isolated, characterized, and identified. An optimal combination of all the three enzymes gave aldehyde (methyl α-d-galacto-hexodialdo-1,5-pyranoside) in approximately 90% yield with a substrate concentration of 70 mM in water at 4 °C using air as oxygen source. Oxygen flushing of the reaction mixture was not necessary. The aldehyde existed as a hydrate in water. The main secondary products, a uronic acid (methyl α-d-galactopyranosiduronic acid) and an α,β-unsaturated aldehyde (methyl 4-deoxy-α-d-threo-hex-4-enodialdo-1,5-pyranoside), were observed for the first time to form in parallel. Formation of uronic acid seemed to be the result of impurities in the galactose oxidase preparation. ¹H and ¹³C NMR data of the products are reported for the α,β-unsaturated aldehyde for the first time, and chemical shifts in DMSO-d₆ for all the products for the first time. Oxidation of d-raffinose (α-d-galactopyranosyl-(1-6)-α-d-glucopyranosyl-(1-2)-β-d-fructofuranoside) in the same optimum conditions also proceeded well, resulting in approximately 90% yield of the corresponding aldehyde.     

Synthesis of polyhydroxy amino acids based on D- and L-alanine from D-glycero-D-gulo-heptono-1,4-lactone

2-Amino-2,3-dideoxy-D-manno-heptonic acid (7) has been synthesized from 2,5,6,7-tetra-O-acetyl-3-deoxy-D-gluco-heptono-1,4-lactone (1), which was readily prepared from D-glycero-D-gulo-heptono-1,4-lactone. O-Deacetylation of 1 followed by treatment with 13:1 (v/v) 2,2-dimethoxypropane/acetone in the presence of p-toluenesulfonic acid gave methyl 3-deoxy-4,5:6,7-di-O-isopropylidene-D-gluco-heptonate (3) as a crystalline product (80% yield). The free hydroxyl group (OH-2) of 3 was mesylated and substituted by azide to give the corresponding azide derivative 5. Hydrogenolysis and further hydrolysis of the ester function of 5 afforded alpha-amino acid 7 (43% overall yield from 1). Compound 7 is an analog of L-alanine having a polyhydroxy chain attached to C-3. The diastereoisomer of 7 at C-2, 2-amino-2,3-dideoxy-D-gluco-heptonic acid (12) was also prepared from 3, by a route that involved 2,3-dideoxy-2-iodo derivative 8 as a key intermediate.     

Evaluation of carbohydrate molecular mechanical force fields by quantum mechanical calculations

A quantitative evaluation of 20 second-generation carbohydrate force fields was carried out using ab initio and density functional methods. Geometry-optimized structures (B3LYP/6-31G(d)) and relative energies using augmented correlation consistent basis sets were calculated in gas phase for monosaccharide carbohydrate benchmark systems. Selected results are: (i). The interaction energy of the alpha-d-glucopyranose.H(2)O heterodimer is estimated to be 4.9 kcal/mol, using a composite method including terms at highly correlated (CCSD(T)) level. Most molecular mechanics force fields are in error in this respect; (ii). The (3)E envelope (south) pseudorotational conformer of methyl 5-deoxy-beta-d-xylofuranoside is 0.66 kcal/mol more stable than the (3)E envelope (north) conformer and the alpha-anomer of methyl d-glucopyranoside is 0.82 kcal/mol more stable than the beta-anomer; (iii). The relative energies of the (gg, gt and tg) rotamers of methyl alpha-d-glucopyranoside and methyl alpha-d-galactopyranoside are (0.13, 0.00, 0.15) and (0.64, 0.00, 0.77) kcal/mol, respectively. The results of the quantum mechanical calculations are compared with the results of calculations using the 20 second-generation carbohydrate force fields. No single force field is consistently better than the others for all the test cases. A statistical assessment of the performance of the force fields indicates that CHEAT(95), CFF, certain versions of Amber and of MM3 have the best overall performance, for these gas phase monosaccharide systems.     

Synthesis of D- and L-myo-inositol 2,4,5-trisphosphate and trisphosphorothioate: structural analogues of D-myo-inositol 1,4,5-trisphosphate

The preparation of D- and L-myo-inositol 2,4,5-trisphosphate is described, together with the phosphorothioate counterparts. The known chiral diols D- and L-1,4-di-O-benzyl-5,6-bis-O-p-methoxybenzyl-myo-inositol were regioselectively protected at the 3-position using a benzyl group via a 2,3-O-stannylene acetal. Removal of the p-methoxybenzyl groups of each enantiomer gave D- and L-1,3,6-tri-O-benzyl-myo-inositol. Phosphitylation with bis(benzyloxy)diisoproplyaminophosphine and 1H-tetrazole gave the trisphosphite intermediate for each enantiomer. Oxidation with 3-chloroperoxybenzoic acid gave the fully protected D- and L-myo-inositol 2,4,5-trisphosphates. Sulphoxidation of the D- and L-2,4,5-trisphosphite intermediates gave the fully protected D- and L-myo-inositol 2,4,5-trisphosphorothioate compounds. The fully protected trisphosphates were deblocked using hydrogenolysis and the phosphorothioates were deprotected using sodium in liquid ammonia. The individual compounds were then purified using ion exchange chromatography to afford pure D- and L-myo-inositol 2,4,5-trisphosphates together with the corresponding phosphorothioates.     

Synthesis of a library of allyl alpha-L-arabinofuranosyl-alpha- or beta-D-xylopyranosides; route to higher oligomers

Six isomeric disaccharides allyl 2,3,5-tri-O-benzoyl-alpha-l-arabinofuranosyl-alpha-d-xylopyranosides and beta-d-xylopyranosides were synthetized by the stereoselective glycosylation of pure allyl alpha- or beta-d-xylopyranosides with 1-O-acetyl-2,3,5-tri-O-benzoyl-l-arabinofuranose as donor, catalyzed with BF(3).Et(2)O in DCM. Regio- and stereoselective glycosylation with excess of donor furnished almost exclusively the trisaccharides allyl 2,3-di-O-(2,3,5-tri-O-benzoyl-alpha-l-arabinofuranosyl)-alpha- or beta-d-xylopyranosides. Extension of the reaction to the triol beta-d-xylopyranosyl-(1-->4)-1,2,3-tri-O-acetyl-alpha-d-xylopyranose, obtained from the 4-hydroxyl penta-O-acetyl-alpha-xylobiose, gave in the same manner the tetrasaccharide [2,3-di-O-(2,3,5-tri-O-benzoyl-alpha-l-arabinofuranosyl)-beta-d-xylopyranosyl]-(1-->4)-1,2,3-tri-O-acetyl-alpha-d-xylopyranose. The protocol described herein should offer the possibility to produce branched oligosaccharides with a 2,3-di-O-(alpha-l-Ara(f))-beta-d-Xyl(p) block unit at the terminal non-reducing end.     

1-O-Acetyl-beta-D-galactopyranose: a novel substrate for the transglycosylation reaction catalyzed by the beta-galactosidase from Penicillium sp

1-O-Acetyl-beta-D-galactopyranose (AcGal), a new substrate for beta-galactosidase, was synthesized in a stereoselective manner by the trichloroacetimidate procedure. Kinetic parameters (K(M) and k(cat)) for the hydrolysis of 1-O-acetyl-beta-D-galactopyranose catalyzed by the beta-D-galactosidase from Penicillium sp. were compared with similar characteristics for a number of natural and synthetic substrates. The value for k(cat) in the hydrolysis of AcGal was three orders of magnitude greater than for other known substrates. The beta-galactosidase hydrolyzes AcGal with retention of anomeric configuration. The transglycosylation activity of the beta-D-galactosidase in the reaction of AcGal and methyl beta-D-galactopyranoside (1) as substrates was investigated by 1H NMR spectroscopy and HPLC techniques. The transglycosylation product using AcGal as a substrate was beta-D-galactopyranosyl-(1-->6)-1-O-acetyl-beta-D-galactopyranose (with a yield of approximately 70%). In the case of 1 as a substrate, the main transglycosylation product was methyl beta-D-galactopyranosyl-(1-->6)-beta-D-galactopyranoside. Methyl beta-D-galactopyranosyl-(1-->3)-beta-D-galactopyranoside was found to be minor product in the latter reaction.     

Efficient synthesis of 2-deoxy-L-erythro-pentose (2-deoxy-L-ribose) from L-arabinose

An efficient and practical route for the large-scale synthesis of 2-deoxy-L-erythro-pentose (2-deoxy-L-ribose) starting from L-arabinose was developed using Barton-type free-radical deoxygenation reaction as a key step. The radical precursor, a phenoxythiocarbonyl ester, was prepared in situ, and the most efficient deoxygenation was achieved by slow addition of tributyltin hydride to the reaction mixture.     

Optimized synthesis of specific sizes of maltodextrin glycosides by the coupling reactions of Bacillus macerans cyclomaltodextrin glucanyltransferase

Bacillus macerans cyclomaltodextrin glucanyltransferase (CGTase, EC 2.4.1.19), in reaction with cyclomaltohexaose and methyl alpha-D-glucopyranoside, methyl beta-D-glucopyranoside, phenyl alpha-D-glucopyranoside, and phenyl beta-D-glucopyranoside gave four kinds of maltodextrin glycosides. The reactions were optimized by using different ratios of the individual d-glucopyranosides to cyclomaltohexaose, from 0.5 to 5.0, to obtain the maximum molar percent yields of products, which were from 68.3% to 78.6%, depending on the particular D-glucopyranoside, and also to obtain different maltodextrin chain lengths. The lower ratios of 0.5-1.0 gave a wide range of sizes from d.p. 2-17 and higher. As the molar ratio was increased from 1.0 to 3.0, the larger sizes, d.p. 9-17, decreased, and the small and intermediate sizes, d.p. 2-8, increased; as the molar ratios were increased further from 3.0 to 5.0, the large sizes completely disappeared, the intermediate sizes, d.p. 4-8, decreased, and the small sizes, d.p. 2 and 3 became predominant. A comparison is made with the synthesis of maltodextrins by the reaction of CGTase with different molar ratios of d-glucose to cyclomaltohexaose.     

An efficient synthesis of methyl 1,3-O-isopropylidene-alpha-D-fructofuranoside and 2,3:5,6-di-O-isopropylidene-D-glucose dimethyl acetal derivatives from sucrose

Acetalation of sucrose with 2,2-dimethoxypropane in 1,4-dioxane in the presence of p-toluenesulfonic acid, followed by acetylation, afforded methyl 4,6-di-O-acetyl-1,3-O-isopropylidene-alpha-D-fructofuranoside and 4-O-acetyl-2,3:5,6-di-O-isopropylidene-D-glucose dimethyl acetal as major products, while tosylation of the intermediate acetals provided methyl 6-O-tosyl-1,3-O-isopropylidene-alpha-D-fructofuranose.     

Base catalysed isomerisation of aldoses of the arabino and lyxo series in the presence of aluminate

Base-catalysed isomerisation of aldoses of the arabino and lyxo series in aluminate solution has been investigated. L-Arabinose and D-galactose give L-erythro-2-pentulose (L-ribulose) and D-lyxo-2-hexulose (D-tagatose), respectively, in good yields, whereas lower reactivity is observed for 6-deoxy-D-galactose (D-fucose). From D-lyxose, D-mannose and 6-deoxy-L-mannose (L-rhamnose) are obtained mixtures of ketoses and C-2 epimeric aldoses. Small amounts of the 3-epimers of the ketoses were also formed. 6-Deoxy-L-arabino-2-hexulose (6-deoxy-L-fructose) and 6-deoxy-L-glucose (L-quinovose) were formed in low yields from 6-deoxy-L-mannose and isolated as their O-isopropylidene derivatives. Explanations of the differences in reactivity and course of the reaction have been suggested on the basis of steric effects.     

Synthesis and intramolecular transesterifications of pivaloylated methyl alpha-D-galactopyranosides

Selective pivaloylations of methyl alpha-D-galactopyranoside have been studied under various reaction conditions. Partially pivaloylated products were submitted to additional acetylations. The structures were established by 1H and 13C NMR spectroscopies. Both, 2,6- and 3,6-dipivalates underwent intramolecular cyclization in neutral conditions (phosphate buffered saline, pH 7.2) to give a stable 2,3-orthoacid with a parallel 6-->4 migration of the pivaloyl group.     

Regioselective synthesis of 6-S-alkyl and 6-S-glycosyl-6-thio-D-mannofuranose derivatives from 5,6-O-cyclic sulfate precursors

C-6 opening of 5,6-cyclic sulfate derivatives of mannofuranose with a thiolate anion followed by acidic hydrolysis of the acyclic sulfate gave 6-S-alkyl derivatives in good yields (70-95%) and short reaction times (10-15min). This methodology was applied to the synthesis of methyl 2,3-O-isopropylidene-6-S-(2,3,4,6-tetra-O-acetyl-beta-d-glucopyranosyl)-6-thio-alpha-d-mannofuranoside (70%), 2,3-O-isopropylidene-6-S-(2,3,4,6-tetra-O-acetyl-beta-d-glucopyranosyl)-6-thio-alpha-d-mannofuranose (87%) and 2,3-O-isopropylidene-6-S-(1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranos-6-yl)-6-thio-alpha-d-mannofuranose (87%).     

Phenolic and other constituents of fresh water fern Salvinia molesta

Two glycosides, 6'-O-(3,4-dihydroxy benzoyl)-beta-D-glucopyranosyl ester (1), and 4-O-beta-d-glucopyranoside-3-hydroxy methyl benzoate (2), along with five known compounds methyl benzoate (3), hypogallic acid (4), caffeic acid (5), paeoniflorin (6) and pikuroside (7) were isolated for the first time from a fresh water fern Salvinia molesta D.S. Mitch. These compounds showed a potent antioxidant radical scavenging activity in a non-physiological assay. Their structures were determined by NMR spectroscopic and CID mass spectrometry techniques.     

Synergism between hydrogen sulfide (H(2)S) and nitric oxide (NO) in vasorelaxation induced by stonustoxin (SNTX), a lethal and hypotensive protein factor isolated from stonefish Synanceja horrida venom

Stonustoxin (SNTX) is a 148 kDa, dimeric, hypotensive and lethal protein factor isolated from the venom of the stonefish Synanceja horrida. SNTX (10-320 ng/ml) progressively causes relaxation of endothelium-intact, phenylephrine (PE)-precontracted rat thoracic aortic rings. The SNTX-induced vasorelaxation was inhibited by L-N(G)-nitro arginine methyl ester (L-NAME), suggesting that nitric oxide (NO) contributes to the SNTX-induced response. Interestingly, D, L-proparglyglycine (PAG) and beta-cyano-L-alanine (BCA), irreversible and competitive inhibitors of cystathionine-gamma-lyase (CSE) respectively, also inhibited SNTX-induced vasorelaxation, indicating that H(2)S may also play a part in the effect of SNTX. The combined use of L-NAME with PAG or BCA showed that H(2)S and NO act synergistically in effecting SNTX-induced vasorelaxation.     

Stereoselective entry into the d-GalNAc series starting from the d-Gal one: a new access to N-acetyl-d-galactosamine and derivatives thereof

A new stereoselective preparation of N-aceyl-d-galactosamine (1b) starting from the known p-methoxyphenyl 3,4-O-isopropylidene-6-O-(1-methoxy-1-methylethyl)-β-d-galactopyranoside (10) is described using a simple strategy based on (a) epimerization at C-2 of 10 via oxidation-reduction to give the talo derivative 11, (b) amination with configurational inversion at C-2 of 11 via a S_N2-type reaction on its 2-imidazylate, (c) anomeric deprotection of the p-methoxyphenyl β-d-galactosamine glycoside 14, (d) complete deprotection. Applying the same protocol to 2,3:5,6:3′,4′-tri-O-isopropylidene-6′-O-(1-methoxy-1-methylethyl)-lactose dimethyl acetal (4), directly obtained through acetonation of lactose, the disaccharide β-d-GalNAcp-(1→4)-d-Glcp (1a) was obtained with complete stereoselectivity in good (40%) overall yield from lactose.     

Structural analysis of a novel saccharide isolated from fermented beverage of plant extract

Fermented beverage of plant extract was prepared from about 50 kinds of vegetables and fruits. Natural fermentation was carried out mainly by lactic acid bacteria (Leuconostoc spp.) and yeast (Zygosaccharomyces spp. and Pichia spp.). Three kinds of saccharides have been found in this beverage and produced by fermentation. The saccharides isolated from the beverage using carbon-Celite column chromatography and preparative HPLC, were identified as a new saccharide, beta-d-fructopyranosyl-(2-->6)-d-glucopyranose, laminaribiose and maltose by examination of constituted sugars, GLC and GC-MS analyses of methyl derivatives and MALDI-TOF-MS and NMR measurements of the saccharides.     

Synthesis of 2,5-anhydro-(beta-d-glucopyranosyluronate)- and (alpha-l-idopyranosyluronate)-d-mannitol hexa-O-sulfonate hepta sodium salt

Glycosidation of 2,5-anhydro-1,6-di-O-benzoyl-D-mannitol with methyl(2,3,4-tri-O-acetyl-alpha-d-glucopyranosyl-1-O-trichloroacetimidate)uronate in the presence of trimethylsilyl triflate afforded the corresponding 3-O-beta-glycoside, which after deprotection was converted into its hexa-O-sulfate with DMF x SO3 to give after treatment with sodium acetate and subsequent saponification of the methyl ester with sodium hydroxide the hepta sodium salt of 2,5-anhydro-3-O-(beta-d-glucopyranosyl uronate)-D-mannitol hexa-O-sulfate. Glycosidation of the same acceptor with the alpha-thiophenylglycoside of methyl 2,4-di-O-acetyl-3-O-benzyl-L-idopyranosyl uronate in the presence of NIS/TfOH afforded the corresponding 3-O-alpha-glycoside in very low yield, therefore the alpha-thiophenylglycoside of 2-O-acetyl-2,4-O-benzylidene-3-O-benzyl-L-idopyranose was used as donor. The terminal hydroxymethyl group of the obtained disaccharide was subsequently oxidised with NaOCl/TEMPO and the obtained iduronic acid derivative was converted into the hepta sodium salt of 2,5-anhydro-3-O-(-alpha-L-idopyranosyluronate)-D-mannitol hexa-O-sulfonate with DMF x SO3 and subsequent treatment with sodium acetate.     

Iridoid glycosides from Gardeniae Fructus for treatment of ankle sprain

The iridoid glycosides, genipin 1-O-β-d-isomaltoside (1) and genipin 1,10-di-O-β-d-glucopyranoside (2), together with six known iridoid glycosides, genipin 1-O-β-d-gentiobioside (3), geniposide (4), scandoside methyl ester (5), deacetylasperulosidic acid methyl ester (6), 6-O-methyldeacetylasperulosidic acid methyl ester (7), and gardenoside (8) were isolated from an EtOH extract of Gardeniae Fructus. The structures and relative stereochemistries of the metabolites were elucidated on the basis of 1D- and 2D-NMR spectroscopic techniques, high-resolution mass spectrometry, and chemical evidence. Geniposide (4), one of the main compounds of Gardeniae Fructus, was tested for treatment of ankle sprain using an ankle sprain model in rats. From the second to fifth day, the geniposide (4) (100 mg/ml) treated group exhibited significant differences (p < 0.01) with ∼21-34% reduction in swelling ratio compared with those of the vehicle treated control group. This indicated the potential effect of geniposide (4) for the treatment of disorders such as ankle sprain.     

A selective Sc(OTf)3-catalyzed trialkylsilyl ether to acetyl ester exchange reaction with beta-l-idopyranoside and 3,4-O-isopropylidene-beta-D-galactopyranoside derivatives

The selective silylation of monosaccharide building blocks is useful for preparing complex oligosaccharides. We now report that the diol, methyl (dimethylthexylsilyl 3-O-pivaloyl-beta-L-idopyranosyl)uronate, can be selectively silylated at the O-2 position by trialkylsilyl triflates. After protection of O-4, the O-2 silyl group can be selectively replaced by acetate by taking advantage of a trialkylsilyl-acetate exchange reaction catalyzed by Sc(OTf)3 in the presence of acetic anhydride. The high O-2 selectivity is shown for triethylsilyl (TES), tert-butyldimethylsilyl (TBS), and triisopropylsilyl (TIPS). The selective cleavage reaction only worked well for TES and TBS derivatives. A selection of silyl triflates and silyl chlorides were used as silylating reagents with ethyl 3,4-O-isopropylidene-1-thio-beta-D-galactopyranoside. In most cases, silylation afforded 2,6-di-O-silylated products in high yields. Studies on the cleavage reaction showed that only the primary silylated protecting groups were replaced by acetyl groups. This reaction worked with a variety of silyl protecting groups but not the tert-butyldiphenylsilyl (TBDPS) protecting group. Unfortunately, the 1-thioethyl group was also sensitive to the Sc(OTf)3, leading in these conditions to alpha/beta mixtures of the 1-acetates, which compromised the synthetic utility of this reaction for these compounds. The sequence presented here is a useful synthetic route to differentially protected L-iduronic acid building blocks.