First synthesis of the immunodominant beta-galactofuranose-containing tetrasaccharide present in the cell wall of Aspergillus fumigatus

β-Galf-(1→5)-β-Galf-(1→6)-α-Manp-(1→6)-α-Manp, the immunodominant epitope in the cell-wall galactomannan of Aspergillus fumigatus, was synthesized for the first time as its allyl glycoside. The key disaccharide glycosyl donor, 2,3,5,6-tetra-O-benzoyl-β-d-galactofuranosyl-(1→5)-2-O-acetyl-3,6-di-O-benzoyl-β-d-galactofuranosyl trichloroacetimidate (10), was constructed by 5-O-glycosylation of 1,2-O-isopropylidene-3,6-di-O-benzoyl-α-d-galactofuranose (4) with 2,3,5,6-tetra-O-benzoyl-β-d-galactofuranosyl trichloroacetimidate (5), followed by 1,2-O-deacetonation, acetylation, selective 1-O-deacetylation, and trichloroacetimidation. The target tetrasaccharide 16 was obtained by the condensation of allyl 2,3,4-tri-O-benzoyl-α-d-mannopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-α-d-mannopyranoside (14) as glycosyl acceptor with the disaccharide glycosyl donor 10, followed by deprotection.     

Synthesis of a tetrasaccharide donor corresponding to the O-specific polysaccharide of Shigella dysenteriae type 1

O-(2,4-Di-O-chloroacetyl-α-l-rhamnopyranosyl)-(1 → 2)-O-(3,4,6-tri-O-benzoyl-α-d-galactopyranosyl)-(1 → 3)-O-(2-acetamido-4,6-di-O-acetyl-2-deoxy-α-d-glycopyranosyl)-(1 → 3)-2,4-di-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (1) was synthesized in a stepwise manner, using the following monosaccharide units: 2-(trimethylsilyl)ethyl 2,4-di-O-benzoyl-α-l-rhamnopyranoside, 2-azido-4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-β-d-glycopyranosyl chloride, methyl 3,4,6-tri-O-benzoyl-2-O-(4-methoxybenzyl)-1-thio-β-d-galactopyranoside, and 2,4-di-O-benzoyl-3-O-chloroacetyl-α-l-rhamnopyranosyl chloride. Compound 1 corresponds to a complete tetrasaccharide repeating unit of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1.     

Synthetic studies on the trisaccharide intermediate of resin glycoside merremoside H2

A protected trisaccharide imidate, 2,3-di-O-acetyl-4,6-O-benzylidene-β-d-glucopyranosyl-(1→3)-2-O-chloroacetyl-3-O-benzyl-4-isobutyryl-α-l-rhamnopyranosyl-(1→4)-2-O-isobutyryl-α-l-rhamnopyranosyl trichloroacetimidate (1), has been synthesized by a block synthesis approach. Compound 1 can serve as a key intermediate in the total synthesis of resin glycoside merremoside H₂.     

Efficient synthesis of a 6-deoxytalose tetrasaccharide related to the antigenic O-polysaccharide produced by Aggregatibacter actinomycetemcomitans serotype c

Concise synthesis of a 6-deoxy-α-l-talose tetrasaccharide, 6-deoxy-α-l-Talp-(1→3)-6-deoxy-α-l-Talp-(1→2)-6-deoxy-α-l-Talp-(1→3)-6-deoxy-α-l-Talp, the dimer of the disaccharide repeating unit of the OPS from Aggregatibacter actinomycetemcomitans serotype c, has been accomplished through suitable protecting group manipulations and stereoselective glycosylation starting from commercially available l-rhamnose. The target oligosaccharide in the form of its p-methoxyphenyl glycoside is suitable for further glycoconjugate formation via selective cleavage of this group.     

Synthesis of oleanolic acid saponins mimicking components of Chinese folk medicine Di Wu

3,28-Di-O-rhamnosylated oleanolic acid saponins, mimicking components of Chinese folk medicine Di Wu, have been designed and synthesized. One-pot glycosylation and ‘inverse procedure’ technologies have been applied thus significantly simplifying the preparation of desired saponins. The cytotoxic activity of compounds 3-O-[α-l-rhamnopyranosyl-(1→2)-β-d-xylopyranosyl]oleanolic acid 28-O-[α-l-rhamnopyranosyl-(1→4)-β-d-glucopyranosyl-(1→6)-β-d-glucopyranosyl] ester (3), 3-O-[α-l-rhamnopyranosyl]oleanolic acid 28-O-[α-l-rhamnopyranosyl- (1→4)-β-d-glucopyranosyl-(1→6)-β-d-glucopyranosyl] ester (4), 3-O-[α-l-rhamnopyranosyl]oleanolic acid 28-O-[α-l-rhamnopyranosyl] ester (5), and 3-O-[α-l-rhamnopyranosyl]oleanolic acid 28-O-[6-O-(α-l-rhamnopyranosyl)hexyl] ester (6) was preliminarily evaluated against HL-60 human promyelocytic leukemia cells. The natural saponin 3 and designed saponin 4 exhibited comparable moderate cytotoxic activity under our testing conditions.     

Acylated flavonol tetraglycosides from Delphinium gracile

An ethanol extract of the aerial parts of Delphinium gracile DC. yielded five flavonol glycosides quercetin-3-O-{[β-d-xylopyranosyl (1 → 3)-4-O-(E-p-caffeoyl)-α-l-rhamnopyranosyl (1 → 6)][β-d-glucopyranosyl (1 → 2)]}-β-d-glucopyranoside (1), quercetin-3-O-{[β-d-xylopyranosyl (1 → 3)-4-O-(E-p-coumaroyl)-α-l-rhamnopyranosyl (1 → 6)][β-d-glucopyranosyl (1 → 2)]}-β-d-glucopyranoside (2), quercetin-3-O-{[β-d-xylopyranosyl (1 → 3)-4-O-(Z-p-coumaroyl)-α-l-rhamnopyranosyl (1 → 6)][β-d-glucopyranosyl (1 → 2)]}-β-d-glucopyranoside (3), kaempferol-3-O-{[β-d-glucopyranosyl (1 → 3)-4-O-(E-p-coumaroyl)-α-l-rhamnopyranosyl (1 → 6)][β-d-glucopyranoside-7-O-(4-O-acetyl)-α-l-rhamnopyranoside (4) kaempferol-3-O-{[β-d-glucopyranosyl (1 → 3)-4-O-(E-p-coumaroyl)-α-l-rhamnopyranosyl (1 → 6)][β-d-glucopyranoside-7-O-(4-O-acetyl)-α-l-rhamnopyranoside (5) in addition to 4-(β-d-glucopyranosyloxy)-6-methyl-2H-pyran-2-one (6) and rutin. Structures were elucidated by spectroscopic methods.     

Synthetic studies on the carbohydrate moiety of the antigen from the parasite Echinococcusmultilocularis

Stereocontrolled syntheses of branched tri-, tetra-, and pentasaccharides displaying a Galβ1→3GalNAc core in the glycan portion of the glycoprotein antigen from the parasite Echinococcusmultilocularis have been accomplished. Trisaccharide Galβ1→3(GlcNAcβ1→6)GalNAcα1-OR (A), tetrasaccharide Galβ1→3(Galβ1→4GlcNAcβ1→6)GalNAcα1-OR (D), and pentasaccharides Galβ1→3(Galβ1→4Galβ1→4GlcNAcβ1→6)GalNAcα1-OR (E) and Gal β1→3(Galα1→4Galβ1→4GlcNAcβ1→6)GalNAcα1-OR (F) (R = 2-(trimethylsilyl)ethyl) were synthesized by block synthesis. The disaccharide 2-(trimethylsilyl)ethyl 2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl-(1→3)-2-azido-4-O-benzyl-2-deoxy-α-d-galactopyranoside served as a common glycosyl acceptor in the synthesis of the branched oligosaccharides. Moreover, linear trisaccharide Galβ1→4Galβ1→3GalNAcα1-OR (B) and branched tetrasaccharide Galβ1→4Galβ1→3(GlcNAcβ1→6)GalNAcα1-OR (C) were synthesized by stepwise condensation.     

Nucleophilic displacement reactions in carbohydrates : Part XX. Displacements on alkyl α-l-talopyranoside 4-sulphonate derivatives

The azide displacement reaction on methyl 6-deoxy-4-O-methanesulphonyl-2,3-di-O-methyl-α-l-talopyranoside (6) in N,N-dimethylformamide yielded methyl 4,6-dideoxy-2,3-di-O-methyl-α-l-threo-hex-3-enopyranoside (7, ca. 50%), methyl 4,6-dideoxy-2,3-di-O-methyl-β-d-erythro-hex-4-enopyranoside (8, ca. 10%), and methyl 4-azido-4,6-dideoxy-2,3-di-O-methyl-α-l-mannopyranoside (9, ca. 40%). The corresponding azide 14 (20%) and the unsaturated sugars 12 (68%) and 13 (12%) were obtained from a comparable reaction on benzyl 6-deoxy-4-O-methanesulphonyl-2,3-di-O-methyl-α-l-talopyranoside (11).     

Unusual oleanane-type saponins from Arenaria montana

Three oleanane-type saponins, 3-O-β-d-glucopyranosylechinocystic acid 28-O-β-d-xylopyranosyl-(1→4)-[α-l-rhamnopyranosyl-(1→2)]-α-l-rhamnopyranosyl ester (1), 3-O-β-d-glucopyranosylechinocystic acid 28-O-α-l-arabinopyranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-[α-l-rhamnopyranosyl-(1→2)]-α-l-rhamnopyranosyl ester (2), 3-O-β-d-glucopyranosylcaulophyllogenin 28-O-β-d-apiofuranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-[β-d-apiofuranosyl-(1→3)]-α-l-rhamnopyranosyl-(1→2)-α-l-rhamnopyranosyl ester (3) were isolated from the whole plant of Arenaria montana. Their unusual structures for the Caryophyllaceae family were established mainly by 2D NMR techniques and mass spectrometry.     

Regioselective synthesis of a glycomimetic trisaccharide of Sialyl Lewis (sLe)

Sialyl Lewis (sLe^x) is the smallest naturally occurring carbohydrate ligand that binds to E-Selectin on the activated endothelium. We report here the total synthesis of acetic acid-sLe^x analog (12), for testing as a therapeutic agent. Methoxyethyl 4-O-(3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (3) was prepared starting from the methoxyethyl-β-d-lactoside (2), which was selectively benzoylated to give the methoxyethyl 2,6-di-O-benzoyl-4-O-(2,6-di-O-benzoyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (4). Glycosylation of acceptor 4 with methyl 2,3,4-tri-O-benzyl-1-thio-β-l-fucopyranoside (5) in the presence of cupric bromide and tetrabutylammonium bromide afforded the corresponding methoxyethyl 2,6-di-O-benzyl-3-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-4-O-(2,6-di-O-benzyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (6). Selective removal of the 4″,6″-O-isopropylidene group from 6 gave the deprotected trisaccharide 7. The regioselective esterification of O-3″ of trisaccharide 8 (obtained from the dibutylstannylene derivative of 7) with benzyl-2-bromoacetate and tetrabutylammonium bromide afforded the 3″-O-carbobenzyloxymethyl trisaccharide derivative 9, which on saponification and hydrogenolysis with palladium-charcoal afforded the target trisaccharide 12 glycomimetic of Sialyl Lewis (sLe^x) trisaccharide omitting the sialic acid moiety.     

Phenolic compounds and rare polyhydroxylated triterpenoid saponins from Eryngium yuccifolium

Phytochemical investigation on the whole plant of Eryngium yuccifolium resulted in the isolation and identification of three phenolic compounds (1-3) and 12 polyhydroxylated triterpenoid saponins, named eryngiosides A-L (4-15), together with four known compounds kaempferol-3-O-(2,6-di-O-trans-p-coumaroyl)-β-d-glucopyranoside (16), caffeic acid (17), 21β-angeloyloxy-3β-[β-d-glucopyranosyl-(1→2)]-[β-d-xylopyranosyl-(1→3)]-β-d-glucuronopyranosyloxyolean-12-ene-15α,16α,22α,28-tetrol (18), and saniculasaponin III (19). This study reports the isolation of these compounds and their structural elucidation by extensive spectroscopic analyses and chemical degradation.     

Sulphated polysaccharides of the grateloupiaceae family : Part VII. Investigation of the acetolysis products of a partially desulphated sample of the polysaccharide of pachymenia carnosa

Investigation of the acetolysis products of a partially desulphated sample of the polysaccharide isolated from Pachymenia carnosa led to the isolation and characterization of the following oligosaccharides: 3-O-α-D-galactopyranosyl-D-galactose (1), 4-O-β-D-galactopyranosyl-D-galactose (2), 3-O-(2-O-methyl-α-D-galactopyranosyl)-D-galactose (3), a 4-O-galactopyranosyl-2-O-methylgalactose (4), 3-O-α-D-galactopyranosyl-6-O-methyl-D-galactose (5), 4-O-β-D-galactopyranosyl-2-O-methyl-D-galactose (6), 2-O-methyl-4-O-(6-O-methyl-β-D-galactopyranosyl)-D-galactose (14), O-β-D-galactopyranosyl-(1→4)-O-α-D-galactopyranosyl-(1→3)-D-galactose (8), O-α-D-galactopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-galactose (9), O-β-D-galactopyranosyl-(1→4)-O-α-(2-O-methyl-D-galactopyranosyl)-(1→3)-D-galactose (11), O-α-(2-O-methyl-D-galactopyranosyl)-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-galactose (12), O-α-D-galactopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-2-O-methyl-D-galactose (13), O-α-(2-O-methyl-D-galactopyranosyl)-(1→3)-O-β-D-galactopyranosyl-(1→4)-2-O-methyl-D-galactose (16), and O-β-D-galactopyranosyl-(1→4)-O-α-D-galactopyranosyl-(1→3)-O-β-D-galactopyranosyl-(1→4)-D-galactose (10). In addition, evidence was obtained for the presence of 4-O-(6-O-methyl-β-D-galactopyranosyl)-D-galactose (7) and O-β-D-galactopyranosyl-(1→4)-O-α-D-galactopyranosyl-(1→3)-6-O-methyl-D-galactose (15).     

Synthesis of the pentasaccharide repeating unit of Escherichia coli O128 antigen

A pentasaccharide, 4-methoxyphenyl 2-acetamido-2-deoxy-β-d-galactopyranosyl-(1→4)-α-d-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-β-d-galactopyranosyl-(1→6)-[α-l-fucopyranosyl-(1→2)]-β-d-galactopyranoside (1), representing the repeating unit of Escherichia coli O128 antigen, was successfully prepared in 23% overall yield via a convergent ‘2+3’ glycosylation strategy.     

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.     

Synthesis of 5(6)-dihydro-OSW-1 analogs bearing three kinds of disaccharides linking at 15-hydroxy and their antitumor activities

In order to study the SAR of 5(6)-dihydro-OSW-1, eight 15(α)β-O-glycosyl analogs (26-33) carrying three kinds of disaccharides including [β-d-Xylp-(1-3)-α-l-Arap], [β-d-Xylp-(1-4)-α-l-Arap] and [α-l-Rhap-(1-2)-(α)β-d-Glcp] were designed and synthesized. Their in vitro antitumor activities were tested by the standard MTT assay which disclosed that compound 33 (IC₅₀ = 0.28-0.52 μM) showed potential antitumor activities.     

Synthesis of trisaccharides containing internal galactofuranose O-linked in Trypanosoma cruzi mucins

The trisaccharides β-d-Galf-(1→2)-β-d-Galf-(1→4)-d-GlcNAc (5) and β-d-Galp-(1→2)-β-d-Galf-(1→4)-d-GlcNAc (6) constitute novel structures isolated as alditols when released by reductive β-elimination from mucins of Trypanosoma cruzi (Tulahuen strain). Trisaccharides 5 and 6 were synthesized employing the aldonolactone approach. Thus, a convenient d-galactono-1,4-lactone derivative was used for the introduction of the internal galactofuranose and the trichloroacetimidate method was employed for glycosylation reactions. Due to the lack of anchimeric assistance on O-2 of the galactofuranosyl precursor, glycosylation studies were performed under different conditions. The nature of the solvent strongly determined the stereochemical course of the glycosylation reactions when the galactofuranosyl donor was substituted either by 2-O-Galp or 2-O-Galf.     

A similarity in the O-acetylation pattern of the O-antigens of Shigellaflexneri types 1a, 1b, and 2a

Shigella flexneri type 2a is the first, and type 1b is the second, most prevalent isolates from patients with shigellosis in Russia. The O-specific polysaccharides (OPSs, O-antigens) of S. flexneri types 1-5 possess a common →2)-α-l-RhapIII-(1→2)-α-l-RhapII-(1→3)-α-l-RhapI-(1→3)-β-d-GlcpNAc-(1→ backbone and differ from each other in its glucosylation or/and O-acetylation at various positions, the modifications being responsible for various O-factors. It was suggested that O-factor 6 expressed by type 1b is associated with O-acetylation of RhaI at position 2 but more than one O-acetyl group has been detected in the type 1b OPS [Kenne, L. et al. Eur. J. Biochem.1978, 91, 279-284]. In this work, O-acetylation of RhapI in the type 1b OPS was confirmed by NMR spectroscopy and location of an additional O-acetyl group at position either 3 (major) or 4 (minor) of RhapIII was determined. Type 1a differs from type 1b in the lack of O-acetylation of RhapI only. In type 2a, in addition to two reported major O-acetyl groups at position 6 of GlcNAc and position 3 of RhapIII [Kubler-Kielb, J. et al. Carbohydr. Res.2007, 342, 643-647], a minor O-acetyl group was found at position 4 of RhaIII. Therefore, RhapIII is O-acetylated in the same manner in all three S. flexneri serotypes studied.     

Fluorinated carbohydrates : Part XIII. 2-deoxy-2-fluoro-D-galactose

Reaction of trifluoro(fluoroxy)methane at ca. −80° with 3,4,6-tri-O-acetyl-D-galactal affords trifluoromethyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-galactopyranoside (2, 39%), 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-galactopyranosyl fluoride (3, 37%), trifluoromethyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-talopyranoside (4, 3%), and 3,4,6-tri-O-acetyl-2-deoxy-2-fluor-α-D-talopyranosyl fluoride (5, 2%). The structures of compounds 2–5 have been established by n.m.r. spectroscopy. Acid hydrolysis of 2 or 3 allords 2-deoxy-2-fluoro-D-galactose.     

Bioactive saponins from Microsechium helleri and Sicyos bulbosus

Eleven oleanane-type saponins (1-11) have been isolated from Microsechium helleri and Sicyos bulbosus roots and were evaluated for their antifeedant, nematicidal and phytotoxic activities. Saponins {3-O-β-d-glucopyranosyl (1 → 3)-β-d-glucopyranosyl-2β,3β,16α,23-tetrahydroxyolean-12-en-28-oic acid 28-O-α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-[β-d-xylopyranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranoside} (1), and {3-O-β-d-glucopyranosyl-2β,3β,16α,23-tetrahydroxyolean-12-en-28-oic acid 28-O-α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-[β-d-xylopyranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranoside} (2) were also isolated from M. helleri roots together with the two known compounds 3 and 4. Seven known structurally related saponins (5-11) were isolated from S. bulbosus roots. The structures of these compounds were established as bayogenin and polygalacic glycosides using one- and two-dimensional NMR spectroscopy and mass spectrometry. Compounds 7, 10, bayogenin (12) and polygalacic acid (13) showed significant (p < 0.05) postingestive effects on Spodoptera littoralis larvae, compounds 5-11 and 12 showed variable nematicidal effects on Meloydogyne javanica and all tested saponins had variable phytotoxic effects on several plant species (Lycopersicum esculentum, Lolium perenne and Lactuca sativa). These are promising results in the search for natural pesticides from the Cucurbitaceae family.     

Perfluoroalkylated derivatives of 6-deoxy-6-ethylamino-d-galactose, 1-deoxy-1-methylamino-d-glucitol, and 1-amino-1-deoxy-d-glucitol: syntheses, hemocompatibility, and effect on perfluorocarbon emulsion

N-Polyfluoroalkyl derivatives of 6-deoxy-6-ethylamino-1,2;3,4-di-O-isopropylidene-α-d-galactopyranose (8-10), 1-deoxy-1-methylamino-d-glucitol (13-15), and 1-amino-1-deoxy-d-glucitol (16-18), all possessing perfluoroalkyl segment, were prepared using nucleophilic epoxide ring opening of 2-[(perfluoroalkyl)methyl]oxiranes 1-3. Co-emulsifying properties and hemolytic activity of the new perfluoroalkylated amphiphiles were tested. Both types of the polyol derivatives 8-10 and 13-18 generally displayed good to excellent co-emulsifying properties on testing on perfluorodecalin/Pluronic F-68 microemulsions. Mono-perfluoroalkylated compounds 8-10 and 13-15 displayed high hemolysis, whereas acyclic bis-perfluoroalkylated compounds 16-18 were non-hemolytic even for short perfluorobutyl segment (16). The properties were generally improving with increasing perfluoroalkyl chain length.