A new triterpenoid glycoside from the leaves and stems of Duranta repens

A new triterpenoid glycoside (1) was isolated from the methanol extract of the leaves and stems of Duranta repens L. (Verbenaceae) along with 14 known compounds consisting of eight triterpenoids, four iridoids, one phenylethanoid glycoside and one flavonoid. The chemical structure of 1 was determined to be bayogenin 3-O-[β-D-glucopyranoside]-28-O-[α-L-rhamnopyranosyl-(1→5)-O-β-D-apiofuranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosyl] ester, based on spectroscopic data. In addition, the inhibitory effects of the isolates on lipoxygenase activity were examined. Among them, acteoside and apigenin resulted in 94 ± 3.6% and 82 ± 4.7% inhibition, respectively, at 0.5 mM.     

New flavonol glycosides from the leaves of Caragana brachyantha

Two new flavonol glycosides, brachysides C and D, together with three known flavonol glycosides, were isolated from the leaves of Caragana brachyantha. The structures of brachysides C and D were elucidated on the basis of detailed spectroscopic analysis as quercetin 5-O-[α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside]-7-O-[α-l-rhamnopyranoside] and quercetin 5-O-[α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside]-7-O-[α-l-rhamnopyranoside]-4′-O-[α-l-rhamnopyranoside], respectively. The presence of flavonol tetra- and triglycosides bearing a sugar moiety at position 5 was the first report from this genus Caragana.     

Two new quercetin glycoside derivatives from the fruits of Gardenia jasminoides var. radicans

Two new quercetin glycoside derivatives named quercetin-3-O-[2-O-trans-caffeoyl-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside] (1) and quercetin-3-O-[2-O-trans-caffeoyl-β-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside] (2) along with three known flavonoids, 5-hydroxy-6,7,3′,4′,5′-pentamethoxyflavone (3), 5,7-dihydroxy-8-methoxyflavone (4) and kaempferol 3-O-β-d-glucopyranoside (5), were isolated from the fruits of Gardenia jasminoides var. radicans. The structures of the new compounds were determined by means of extensive spectroscopic analysis (1D, 2D NMR and HR-ESI-MS), glycoside hydrolysis and sugar HPLC analysis after derivatisation. This is the first report on the isolation of a pair of compounds with α or β-l-rhamnopyranosyl configuration from plant and the first detail assignment of their NMR data.     

A new acylated flavonoid tetraglycoside with anti-inflammatory activity from Tipuana tipu leaves

A new acylated kaempferol glycoside, kaempferol 3-O-α-l-rhamnopyranosyl-(1 → 6)-O-[β-d-glucopyranosyl-(1 → 2)-4-O-acetyl-α-l-rhamnopyranosyl-(1 → 2)]-β-d-galactopyranoside, has been isolated from the leaves of Tipuana tipu (Benth.) Lillo growing in Egypt, along with three known flavonol glycosides, kaempferol 3-O-rutinoside, quercetin 3-O-rutinoside (rutin) and kaempferol 3-O-[α-l-rhamnopyranosyl-(1 → 6)]-[α-l-rhamnopyranosyl-(1 → 2]-β-d-glucopyranoside. Structure elucidation was achieved through different spectroscopic methods. Structure relationship with anti-inflammatory activity using carrageenin-induced rat paw oedema model is discussed.     

SYNTHESIS OF NEW OXAMIDE DERIVATIVES OF D-GLUCOSAMINE AND ALIPHATIC OR AROMATIC AMINES

New oxamides, derivatives of D-glucosamine and aliphatic or aromatic amines were prepared by acylation of methyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-α- or -β-D-glucopyranoside (1c or 1d) with oxalyl chloride, followed by reaction with amine. The reaction was assumed to proceed by the intermediate of N-carbomethoxy N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-α or β-D-glucopyranosid-2-yl) oxamic acid chloride which reacted with amines, and afforded N-acetyl, N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-α- or -β-D-glucopyranosid-2-yl), N′-alkyl or aryloxamide (5–7), and N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-α- or -β-D-glucopyranosid-2-yl), N′-alkyl or aryloxamide (8–13).     

Characterization of flavonoid glycosides from rapeseed bee pollen using a combination of chromatography,spectrometry and nuclear magnetic resonance with a step-wise separation strategy

To identify the structures of flavonoid glycosides in bee pollen collected from rapeseed plants (Brassica napus L.), we utilised an approach that combined liquid chromatography–diode array detector–electrospray ionization–mass spectrometry (LC–DAD–ESI–MS) and nuclear magnetic resonance (NMR) technology with a step-wise separation strategy. We identified four constituents of high purity in rape bee pollen samples: (1) quercetin-3-O-β-D-glucosyl-(2→l)-β-glucoside, (2) kaempferol-3, 4′-di-O-β-D-glucoside, (3) 5, 7, 4′-trihydroxy-3′-methoxyflavone-3-O-β-D-sophoroside and (4) kaempferol-3-O-β-D-glucosyl-(2→l)-β-D-glucoside. This study will also provide useful reference standards for qualification and quantification of four flavonoid glycosides in natural products.     

Flavonoids of Alcea rosea L. and their immune stimulant,antioxidant and cytotoxic activities on hepatocellular carcinoma HepG-2 cell line

Alcea rosea L. is widely cultivated in gardens of Egypt as an ornamental plant and it has a great history of folkloric medicinal uses. In the present work, phytochemical investigation of the alcoholic extract of the flowers of A. rosea L. led to the isolation of six flavonoids (1–6). Dihydrokaempferol-4′-O-β-d-glucopyranoside (1), dihydrokaempferol (2), kaempferol-3-O-[6″-(E-coumaroyl)]-β-d-glucopyranoside (3), kaempferol-3-O-β-d-glucopyranoside (4), Apigenin (5) and kaempferol-3-O-α-l-rhamnopyranosyl-(1′″→6″)-β-d-glucopyranoside (6). Four of the isolated compounds were evaluated for their antioxidant, immunostimulant and cytotoxic activities against HepG-2 cell line. Compound (3) showed potent cytotoxic activity against HepG-2 cell line with high selectivity towards hepatocellular carcinoma in vitro (with IC₅₀ = 3.8 μg/mL). Compounds 1 and 2 exhibited significant antioxidant activity and compound 4 showed a significant immune stimulant activity. Compound 1 is isolated for the first time from genus Alcea and this is the first report for its biological investigation.     

Synthesis of 6-S-(5-Acetamido-3,5-Dideoxy-D-Glycero-α-D-Galacto-2-Nonulopyranosylonic Acid)-6-Thio-Hexopyranosides

The reaction of the sodium salt of methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-α-D-galacto-2-nonulo-pyranosonate with a variety of 6-bromo-6-deoxy-D-hexopyranosides, such as methyl 2,3,4-tri-O-acetyl-6-bromo-6-deoxy-α-D-glucopyranos-ide, -galactopyranoside, allyl 2,3,4-tri-O-acetyl-6-bromo-6-deoxy-β-D-glucopyranoside, and allyl 2-acetamido-3,4-di-O-acetyl-6-bromo-2,6-dideoxy-β-D-glucopyranoside, gave the corresponding (2→6)-linked disaccharides, α-glycosides of 2-thio-N-acetylneuraminic acid derivative in good yields. These disaccharides were converted, via O-deacetylation, followed by hydrolytic removal of the ester group, into the title compounds.     

SYNTHESIS AND CONFORMATIONAL INVESTIGATIONS OF SULFATED CARBOHYDRATES[1]

Starting from the finding that methyl 2,3,4,6-tetra-O-sulfonato-β-D-glucopyranoside (3) existed in a conformational equilibrium of the two chair conformers, the effect of sulfation on conformational equilibria was further investigated using a number of sulfated saccharides. Three sulfate groups on positions 3,4, and 6 or two on positions 2 and 3 were not sufficient to induce the conformational change as shown with methyl 2-amino-2-deoxy-3,4,6-tri-O-sulfonato-β-D-glucopyranoside. N-Sulfation of the amino group of the latter compound furnished an equilibrium of chair conformers with less ¹ C ₄ conformer content than for 3. The presence of persulfated methyl β-D-galactopyranoside in the usual ⁴ C ₁ conformation suggested the involvement of the 4-O-sulfate in the effect. Methyl 2,3,4-tri-O-sulfonato-β-D-xylopyranoside was found to prefer the “all-axial” ¹ C ₄ conformation demonstrating that O-sulfates facilitate 1,3-O/O-diaxial interactions better than ester groups and in particular benzoates. Also, sulfated 1,5-anhydro-D-glucitol occurred as a conformational mixture, the influence of the anomeric effect may thus have been overestimated in the previous discussion of this conformational effect.     

SYNTHESIS OF SIALYL-α-(2→3)-NEOLACTOTETRAOSE DERIVATIVES MODIFIED AT C-2 OF THE N-ACETYLGLUCOSAMINE RESIDUE: PROBES FOR INVESTIGATION OF ACCEPTOR SPECIFICITY OF HUMAN α-1,3-FUCOSYLTRANSFERASES,FUC-TVII,AND FUC-TVI *

A variety of sialyl-α-(2→3)-neolactotetraose (IV³NeuAcnLcOse₄ or IV³NeuGcnLcOse₄) derivatives (23, 31–37, 58–60) modified at C-2 of the GlcNAc residue have been synthesized. The phthalimido group at C-2 of GlcNAc in 2-(trimethylsilyl)ethyl (3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (5) was systematically converted to a series of acylamino groups, to give the per-O-benzylated trisaccharide acceptors (6–11). On the other hand, modification of the hydroxyl group at C-2 of the terminal Glc residue in 2-(trimethylsilyl)ethyl (4,6-O-benzylidene-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (42) gave three different kinds of trisaccharide acceptors containing D-glucose (49), N-acetyl-d-mannosamine (50), and D-mannose (51) instead of the GlcNAc residue. Totally ten trisaccharide acceptors (5–11 and 49–51) were each coupled with sialyl-α-(2→3)-galactose donor 12 to afford the corresponding pentasaccharides (14–21 and 52–54) in good yields, respectively, which were then transformed into the target compounds. Acceptor specificity of the synthetic sialyl-α-(2→3)-neolactotetraose probes for the human α-(1→3)-fucosyltransferases, Fuc-TVII and Fuc-TVI, was examined.     

Synthesis of the Upstream Terminal Disaccharide of the O-Antigenic Polysaccharide of Vibrio cholerae O37

The terminal disaccharide of the O-antigenic polysaccharide of Vibrio cholerae O37, 4-O-methyl-α-D-QuiNAc-(1→4)-α-d-QuiNAc, was synthesized as methyl glycoside involving glycosylation between glycosyl donor ethyl 2-azido-3-O-benzyl-2,6-dideoxy-4-O-methyl-6-iodo-1-thio-α-d-glucopyranoside and glycosyl acceptor methyl 2-azido-3-O-benzyl-2,6-dideoxy-6-iodo-α-d-glucopyranoside. Dehalogenation, global deprotection, and reduction of the azide to amine were effected in one step by catalytic hydrogenation. It was followed by selective N-acetylation to give the desired deprotected disaccharide.     

New pregnane glycoside derivative from Caralluma retrospiciens (Ehrenb)

Retrospinoside (1) is a new polyoxy pregnane glycoside which was isolated and characterised from the aerial parts of Caralluma retrospiciens (Ehrenb.) N. E. Br., family Apocynaceae. The structure was established as 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-(3-O-methyl-6-desoxygalactopyranosy)]-14,15,20-trihydroxy-4β-pregnane. Its structural elucidation was performed through extensive spectroscopic measurements including 1D- and 2D-NMR, and HRMS, in addition to chemical methods.     

SYNTHESIS OF O-METHYLATED DISACCHARIDES RELATED TO EXCRETORY/ SECRETORY ANTIGENS OF TOXOCARA LARVAE[1]

The disaccharides 2-O-Me-α-L-Fucp-(1→2)-β-D-Galp-(1→OAllyl) 12, α-L-Fucp-(1→2)-4-O-Me-β-D-Galp-(1→OAllyl) 15, and 2-O-Me-α-L-Fucp-(1→2)-4-O-Me-β-D-Galp-(1→OAllyl) 18 have been synthesized. Glycosylation reactions were performed using ethyl 1-thiofucopyranosides as glycosyl donors and N-iodosuccinimide-triflic acid as the activating agent. The O-methylated disaccharides correspond to highly immunogenic O-glycan antigens occurring at the surface of Toxocara canis and Toxocara cati larvae.     

A FACILE SYNTHESIS OF MANNOSE TRI- AND TETRASACCHARIDE REPEATING UNITS OF FUNGAL CELL-WALL POLYSACCHARIDE FROM MICROSPORUM AND TRYCHOPHYTON SPECIES

ABSTRACT

A facile synthesis of the trisaccharide α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→6)-α-D-mannopyranose and the tetrasaccharide α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→6)-α-D-mannopyranosyl-(1→6)-D-mannopyranose, the repeating units of fungal cell-wall polysaccharide from Microsporum gypseum and Trychophyton, was achieved using α-(1→2)-linked disaccharide imidate as the donor. The disaccharide imidate was prepared from the self-condensation of 3,4,6-tri-O-benzoyl-1,2-O-allyloxyethylidene-β-D-mannopyranose.     

Two new triterpenoids from Nauclea officinalis

Two new triterpenoids and three 27-nor-triterpenoids were isolated from the stems (with bark) of Nauclea officinalis. Their structures were identified to be 2β,3β,19α,23-tetrahydroxy-urs-12-en-28-oic acid (1), 2β,3β,19α,23-tetrahydroxy-urs-12-en-28-O-[β-d-glucopyranosyl (1-2)-β-d-glucopyranosyl] ester (2), pyrocincholic acid 3β-O-α-l-rhamnopyranoside (3), pyrocincholic acid 3β-O-α-l-rhamnopyranosy1-28-O-β-d-glucopyranosyl ester (4), pyrocincholic acid 3β-O-α-l-rhamnopyranosy1-28-O-β-d-glucopyranosyl-(1-6)-β-d-glucopyranosyl ester (5) by spectroscopic methods including 1D, 2D NMR and HR-MS analyses. The cytotoxic activity of 1–5 against lung cancer A-549 cells was also investigated.     

Mimics of the Structural Elements of Type III Group B Streptococcus Capsular Polysaccharide. Part I: Synthesis of a Carboxylate-Containing Pentasaccharide

Abstract

A carboxylate-containing pentasaccharide, methyl O-(β-d-galactopyranosyl)-(1→4)-O-(β-d-glucopyranosyl)-(1→6)-O-{3-O-[(S)-1-carboxyethyl]-β-d-galactopyranosyl-(1→4)-O}-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-β-d-galactopyranoside (27) was synthesized by block condensation of suitably protected donors and acceptors. Phenyl 3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (17) was condensed with methyl 2,4,6-tri-O-benzyl-β-d-galactopyranoside (4) to afford a disaccharide, methyl O-(3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (18). Removal of chloroacetyl groups gave 4,6-diol, methyl 0-(3-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (19), in which the primary hydroxy group (6-OH) was then selectively chloroacetylated to give methyl O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (20). This acceptor was then coupled with 2,4,6-tri-O-acetyl-3-O-[(S)-1-(methoxycarbonyl)ethyl]-α-d-galactopyranosyl trichloroacetimidate (14) to afford a trisaccharide, methyl O-{2,4,6-tri-O-acetyl-3-O-[(S)-l-(methoxycarbonyl)ethyl]-β-d-galactopyranosyl}-(1→4)-O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (21). Removal of the 6-O-chloroacetyl group in 21 gave 22, which was coupled with 4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (23) to yield protected pentasaccharide 24. Standard procedures were used to remove acetyl groups and the phthalimido group, followed by N-acetylation, and debenzylation to yield pentasaccharide 27 and a hydrazide by-product (28) in a 5:1 ratio, respectively. Compound 27 contains a complete repeating unit of the capsular polysaccharide of type III group B Streptococcus in which terminal sialic acid is replaced by an (S)-1-carboxyethyl group.     

LARGE SCALE SYNTHESIS OF 2-AZIDODEOXY GLUCOSYL DONORS

Starting from readily available phenyl 1-thio-β-D-mannopyranoside, phenyl 2-azido-2-deoxy-1-thio-β-D-glucopyranoside (9) was synthesized on multigram scale using inexpensive reagents.     

SYNTHESIS OF 3-O-ARABINOSYLATED (1→6)-β-D-GALACTAN EPITOPES

Two tetrameric arabinogalactans, β-D-galactopyranosyl-(1→6)-β-D-galactopyranosyl-(1→6)-[α-L-arabinofuranosyl-(1→3)]-D-galactopyranose (14) and α-L-arabinofuranosyl-(1→3)-β-D-galactopyranosyl-(1→6)-β-D-galactopyranosyl-(1→6)-D-galactopyranose (25), which are good candidates for CCRC-M7 epitope characterization, were synthesized efficiently using a convergent strategy. Migration of an acceptor acetyl group proved to be an obstacle to synthesis, but regioselective glycosylation or 4-O-benzyl protection of the acceptor circumvented this problem allowing efficient synthesis of the 1→6 linked target compounds.     

Cytotoxic flavonoids and other constituents from the stem bark of Ochna schweinfurthiana

Seven flavonoids, hemerocallone (1), 6,7-dimethoxy-3′,4′-dimethoxyisoflavone (2), amentoflavone (4), agathisflavone (6), cupressuflavone (8), robustaflavone (9) and epicatechin (10), together with three other compounds, lithospermoside (3), β-D-fructofuranosyl-α-D-glucopyranoside (5) and 3β-O-D-glucopyranosyl-β-stigmasterol (7), were isolated from the ethyl acetate extract of the stem bark of Ochna schweinfurthiana F. Hoffm. All the compounds were characterised by spectroscopic and mass spectrometric methods, and by comparison with literature data. Cytotoxicity of the extracts and compounds against cervical adenocarcinoma (HeLa) cells was evaluated by MTT assay. Compounds 4 and 6 exhibited good cytotoxic activity, with IC₅₀ values of 20.7 and 10.0 μM, respectively.