Structures of the O-antigens of Escherichia coli O13, O129, and O135 related to the O-antigens of Shigella flexneri

O-Polysaccharides (O-antigens) were isolated from Escherichia coli O13, O129, and O135 and studied by chemical analyses along with 2D ¹H and ¹³C NMR spectroscopy. They were found to possess a common →2)-l-Rha-(α1→2)-l-Rha-(α1→3)-l-Rha-(α1→3)-d-GlcNAc-(β1→ backbone, which is a characteristic structural motif of the O-polysaccharides of Shigella flexneri types 1-5. In both the bacterial species, the backbone is decorated with lateral glucose residues or/and O-acetyl groups. In E. coli O13, a new site of glycosylation on 3-substituted Rha was revealed and the following O-polysaccharide structure was established:The structure of the E. coli O129 antigen was found to be identical to the O-antigen structure of S. flexneri type 5a specified in this work and that of E. coli O135 to S. flexneri type 4b reported earlier.     

Isolation and structural characterization of a polysaccharide FCAP1 from the fruit of Cornus officinalis

A water-soluble polysaccharide, FCAP1, was isolated from an alkaline extract from the fruits of Cornus officinalis. Its molecular weight was 34.5 kDa. Monosaccharide composition analysis revealed that it was composed of fucose, arabinose, xylose, mannose, glucose, and galactose in a molar ratio of 0.29:0.19:1.74:1:3.30:1.10. On the basis of partial acid hydrolysis and methylation analysis, FCAP1 was shown to be a highly branched polysaccharide with a backbone of β-(1→4)-linked-glucose partially substituted at the O-6 position with xylopyranose residues. The branches were composed of (1→3)-linked-Ara, (1→4)-linked-Man, (1→4,6)-linked-Man, (1→4)-linked-Glc, and (1→2)-linked-Gal. Arabinose, fucose, and galactose were located at the terminal of the branches. The structure was further elucidated by a specific enzymatic degradation with an endo-β-(1→4)-glucanase and MALDI-TOF-MS analysis. Oligosaccharides generated from FCAP1 indicated that FCAP1 contained XXXG-type and XXG-type xyloglucan fragments.     

The structural characterization of the O-polysaccharide antigen of the lipopolysaccharide of Escherichiacoli serotype O118 and its relation to the O-antigens of Escherichiacoli O151 and Salmonellaenterica O47

Mild acid hydrolysis of the lipopolysaccharide produced by Escherichiacoli O118:H16 standard strain (NRCC 6613) afforded an O-polysaccharide (O-PS) composed of d-galactose, 2-acetamidoylamino-2,6-dideoxy-l-galactose , 2-acetamido-2-deoxy-d-glucose, ribitol, and phosphate (1:1:1:1:1). From DOC-PAGE, sugar and methylation analyses, one- and two-dimensional NMR spectroscopy, capillary electrophoresis-mass spectrometry, hydrolysis, and sequential Smith-type periodate oxidation studies, the O-PS was determined to be an unbranched linear polymer having the structure:[6)-α-d-Galp-(1→3)-α-l-FucpNAm-(1→3)-β-d-GlcpNAc-(1→3)-Rib-ol-5-P-(O→]_nThe structure of the O-PS is consistent with the reported DNA data on the O-antigen gene-cluster of E. coli O118 and interestingly, the O-PS is similar to the structures of the O-antigens of Salmonellaenterica O47 and E. coli O151:H10 reference strain 880-67, as predicted from the results of DNA sequencing of their respective O-antigen gene-clusters.     

Enzymatic liberation of lycotetraose from the Solanum glycoalkaloid alpha-tomatine

The branched tetrasaccharide, O-β-d-glucopyranosyl-(1 → 2)-O-[β-d-xylopyranosyl-(1 → 3)]-O-β-d-glucopyranosyl-(1 → 4)-d-galactose (lycotetraose) is a key constituent of many biologically interesting natural products. Described herein is a convenient enzymatic preparation of lycotetraose from the readily available Solanum glycoalkaloid α-tomatine. The preparation makes use of the recombinant endo-glycosidase, tomatinase, from the plant pathogen Fusarium oxysporum f. sp. lycopersici.     

Structural and genetic characterization of the O-antigen of Escherichia coli O161 containing a derivative of a higher acidic diamino sugar, legionaminic acid

The O-antigen is an essential component of lipopolysaccharide on the surface of Gram-negative bacteria and plays an important role in its pathogenicity. Composition and structure of the O-antigens of Escherichia coli are highly diverse mainly due to genetic variations in the O-antigen gene cluster. In this work, the chemical structure and the gene cluster of the O-antigen of E. coli O161 were studied. Chemical degradations, sugar analyses, and NMR spectroscopy showed that the O161 antigen possesses a trisaccharide O-repeating unit containing a 5-N-acetyl-7-N-(d-alanyl) derivative of 5,7-diamino-3,5,7,9-tetradeoxy-d-glycero-d-galacto-non-2-ulosonic (legionaminic) acid (Leg5Ac7Ala) and having the following structure:

→8)-α-Legp5Ac7Ala-(2→4)-β-d-GlcpA-(1→3)-β-d-GlcpNAc-(1→     

Characterization of substrate and product specificity of the purified recombinant glycogen branching enzyme of Rhodothermus obamensis

Background

Glycogen and starch branching enzymes catalyze the formation of α(1 → 6) linkages in storage polysaccharides by rearrangement of preexisting α-glucans. This reaction occurs through the cleavage of α(1 → 4) linkage and transfer in α(1 → 6) of the fragment in non-reducing position. These enzymes define major elements that control the structure of both glycogen and starch.

Methods

The kinetic parameters of the branching enzyme of Rhodothermus obamensis (RoBE) were established after in vitro incubation with different branched or unbranched α-glucans of controlled structure.

Results

A minimal chain length of ten glucosyl units was required for the donor substrate to be recognized by RoBE that essentially produces branches of DP 3–8. We show that RoBE preferentially creates new branches by intermolecular mechanism. Branched glucans define better substrates for the enzyme leading to the formation of hyper-branched particles of 30–70 nm in diameter (dextrins). Interestingly, RoBE catalyzes an additional α-4-glucanotransferase activity not described so far for a member of the GH13 family.

Conclusions

RoBE is able to transfer α(1 → 4)-linked-glucan in C4 position (instead of C6 position for the branching activity) of a glucan to create new α(1 → 4) linkages yielding to the elongation of linear chains subsequently used for further branching. This result is a novel case for the thin border that exists between enzymes of the GH13 family.

General significance

This work reveals the original catalytic properties of the thermostable branching enzyme of R. obamensis. It defines new approach to produce highly branched α-glucan particles in vitro.     

A lichenase-like family 12 endo-(1-->4)-beta-glucanase from Aspergillus japonicus: study of the substrate specificity and mode of action on beta-glucans in comparison with other glycoside hydrolases

Using anion-exchange chromatography on Source 15Q followed by hydrophobic interaction chromatography on Source 15 Isopropyl, a lichenase-like endo-(1→4)-β-glucanase (BG, 28 kDa, pI 4.1) was isolated from a culture filtrate of Aspergillus japonicus. The enzyme was highly active against barley β-glucan and lichenan (263 and 267 U/mg protein) and had much lower activity toward carboxymethylcellulose (3.9 U/mg). The mode of action of the BG on barley β-glucan and lichenan was studied in comparison with that of Bacillus subtilis lichenase and endo-(1→4)-β-glucanases (EG I, II, and III) of Trichoderma reesei. The BG behaved very similar to the bacterial lichenase, except the tri- and tetrasaccharides formed as the end products of β-glucan hydrolysis with the BG contained the β-(1→3)-glucoside linkage at the non-reducing end, while the lichenase-derived oligosaccharides had the β-(1→3)-linkage at the reducing end. The BG was characterized by a high amino acid sequence identity to the EG of Aspergillus kawachii (UniProt entry Q12679) from a family 12 of glycoside hydrolases (96% in 162 identified aa residues out of total 223 residues) and also showed lower sequence similarity to the EglA of Aspergillus niger (O74705).     

Antimutagenic specificities of two plant glycosylases, oxoguanine glycosylase and formamidopyrimidine glycosylase, assayed in vivo

The base-excision repair process protects genomes by removing and replacing altered bases in DNA. Two analogous glycosylases, oxoguanine glycosylase (OGG) and formamidopyrimidine glycosylase (FPG), can start the process by removing oxidized guanine, the most common modification that leads to misreading of DNA. Plants possess genes for both types of glycosylases. We have tested the hypothesis that the two enzymes in plants have diverged in their specificities by inserting the genes for each enzyme from Arabidopsis thaliana L. into Escherichia coli strains designed to indicate the frequencies of the six possible single-base changes. Both enzymes retain the ability to reduce the rate of GC → TA transversion mutations. Both enzymes also reduce the frequency of two other base-change mutations, GC → AT and AT → TA. We do not find a divergence in the repair capabilities of the two enzymes, as measured in E. coli, although surprisingly FPG appears to increase the rate of mutations in one particular strain.     

Improved procedures for the selective chemical fragmentation of rhamnogalacturonans

The structural characterization of branched rhamnogalacturonans (RGs) requires the availability of methods that selectively cleave the Rhap-(1→4)-α-GalAp linkage and thereby generate oligosaccharide fragments that are suitable for mass spectrometric and NMR spectroscopic analyses. Enzymic cleavage of this linkage is often ineffective, especially in highly branched RGs. Therefore, we have developed an improved chemical fragmentation method based on β-elimination of esterified 4-linked GalpA residues. At least 85% of the carboxyl groups of the GalA residues in Arabidopsis thaliana seed mucilage RG is esterified using methyl iodide or 3-iodopropanol in Me₂SO containing 8% water and 1% tetrabutylammonium fluoride. However, β-elimination fragmentation at pH 7.3 and 120 °C is far more extensive with hydroxypropyl-esterified RG than with methyl-esterified RG. The non-reducing 4-deoxy-β-l-threo-hex-4-enepyranosyluronic acid residue formed by the β-elimination reaction is completely removed by treatment with aqueous N-bromosuccinimide, thereby simplifying the structural characterization of the chemically generated oligoglycosyl fragments. This newly developed procedure was used to selectively fragment the branched RG from peppergrass seed mucilage. The products were characterized using MALDI-TOF mass spectrometry, glycosyl residue composition analysis, and 1 and 2D NMR spectroscopy. Our data show that the most abundant low-molecular weight fragments contained a backbone rhamnose residue substituted at O-4 with a single sidechain, and suggest that peppergrass seed mucilage RG is composed mainly of the repeating unit 4-O-methyl-α-d-GlcpA-(1→4)-β-d-Galp-(1→4)-[→4)-α-d-GalpA-(1→2)-]-α-l-Rhap-(1→.     

The O-antigen of Salmonella enterica O13 and its relation to the O-antigen of Escherichia coli O127

The following structure of the O-polysaccharide (O-antigen) of Salmonella enterica O13 was established by chemical analyses along with 2D ¹H and ¹³C NMR spectroscopy:→2)-α-l-Fucp-(1→2)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→3)-α-d-GlcpNAc-(1→The O-antigen of S. enterica O13 was found to be closely related to that of Escherichia coli O127, which differs only in the presence of a GalNAc residue in place of the GlcNAc residue and O-acetylation. The location of the O-acetyl groups in the E. coli O127 polysaccharide was determined. The structures of the O-polysaccharides studied are in agreement with the DNA sequence of the O-antigen gene clusters of S. enterica O13 and E. coli O127 reported earlier.     

Structural analysis of the O-specific polysaccharide isolated from Plesiomonas shigelloides O51 lipopolysaccharide

Plesiomonasshigelloides strain CNCTC 110/92 (O51) was identified as a new example of plesiomonads synthesising lipopolysaccharides (LPSs) that show preference for a non-aqueous surrounding during phenol/water extraction. Chemical analyses combined with ¹H and ¹³C NMR spectroscopy, MALDI-TOF and ESI mass spectrometry showed that the repeating units of the O-specific polysaccharides isolated from phenol and water phase LPSs of P. shigelloides O51 have the same structure: →4)-β-d-GlcpNAc3NRA-(1→4)-α-l-FucpAm3OAc-(1→3)-α-d-QuipNAc-(1→, containing the rare sugar constituent 2,3-diamino-2,3-dideoxyglucuronic acid (GlcpNAc3NRA), and substituents such as d-3-hydroxybutyric acid (R) and acetamidino group (Am). The HR-MAS NMR spectra obtained for the isolated LPSs and directly on bacteria indicated that the O-acetylation pattern was consistent throughout the entire preparation. The ¹H chemical shift values of the structure reporter groups identified in the isolated O-antigens matched those present in bacteria. We have found that the O-antigens recovered from the phenol phase showed a higher degree of polymerisation than those isolated from the water phase.     

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.     

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.     

Acylated triterpene saponins from the roots of Securidaca longepedunculata

Four triterpene saponins, 3-O-β-d-glucopyranosylpresenegenin 28-O-β-d-apiofuranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-{4-O-[(E)-3,4,5-trimethoxycinnamoyl]}-β-d-fucopyranosyl ester, 3-O-β-d-glucopyranosylpresenegenin 28-O-β-d-apiofuranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-[(6-O-acetyl)-β-d-glucopyranosyl-(1 → 3)]-{4-O-[(E)-3,4,5-trimethoxycinnamoyl]}-β-d-fucopyranosyl ester, 3-O-β-d-glucopyranosylpresenegenin 28-O-β-d-apiofuranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-[β-d-galactopyranosyl-(1 → 3)]-{4-O-[(E)-3,4,5-trimethoxycinnamoyl]}-β-d-fucopyranosyl ester, and 3-O-β-d-glucopyranosylpresenegenin 28-O-β-d-apiofuranosyl-(1 → 3)-[α-l-arabinopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-{4-O-[(E)-3,4,5-trimethoxycinnamoyl]}-β-d-fucopyranosyl ester, were isolated from the roots of Securidaca longepedunculata, together with three known compounds. Their structures were established mainly by 2D NMR techniques and mass spectrometry.     

Triterpenoid saponins from a cytotoxic root extract of Sideroxylonfoetidissimum subsp. gaumeri

Evaluation of the cytotoxicity of an ethanolic root extract of Sideroxylonfoetidissimum subsp. gaumeri (Sapotaceae) revealed activity against the murine macrophage-like cell line RAW 264.7. Systematic bioassay-guided fractionation of this extract gave an active saponin-containing fraction from which four saponins were isolated. Use of 1D (¹H, ¹³C, DEPT135) and 2D (COSY, TOCSY, HSQC, and HMBC) NMR, mass spectrometry and sugar analysis gave their structures as 3-O-(β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, 3-O-β-d-glucopyranosyl-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, 3-O-(β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, and the known compound, 3-O-β-d-glucopyranosyl-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-protobassic acid. Two further saponins were obtained from the same fraction, but as a 5:4 mixture comprising 3-O-(β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)[β-d-apiofuranosyl-(1 → 3)]-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid and 3-O-(β-d-apiofuranosyl-(1 → 3)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)[β-d-xylopyranosyl-(1 → 4)]-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, respectively. This showed greater cytotoxicity (IC₅₀ = 11.9 ± 1.5 μg/ml) towards RAW 264.7 cells than the original extract (IC₅₀ = 39.5 ± 4.1 μg/ml), and the saponin-containing fraction derived from it (IC₅₀ = 33.7 ± 6.2 μg/ml).     

Isolation, structural characterization and antioxidant activity of a new water-soluble polysaccharide from Acanthophyllum bracteatum roots

ABPS-1, a new water-soluble polysaccharide with molecular weight of 26 kDa and a specific optical rotation of +170° (c 1.0, H₂O), was extracted from the roots of Acanthophyllum bracteatum by warm water and further successively purified through DEAE-cellulose A52 and Sephadex G-100 columns. Monosaccharide analysis revealed that the ABPS-1 was composed of Glc, Gal and Ara with a relative molar ratio of 1.4:5.2:1.0. Its structural features were elucidated by a combination of FT-IR, methylation and GC-MS analysis, periodate oxidation and Smith degradation, partial acid hydrolysis and ¹³C and ¹H NMR spectroscopy. The data obtained indicate that ABPS-1 possessed a backbone of α-(1 → 6)-linked Gal with branches attached to O-2 by α-1 → linked Glc and at O-3 by α-1 → linked Gal and by α-(1 → 3)-linked Ara. The in vitro antioxidant activity showed that ABPS-1 possesses DPPH radical-scavenging activity in a concentration-dependent manner with an EC₅₀ value of 2.6 mg/ml.     

Studies on the chemical structure and antitumor activity of an exopolysaccharide from Rhizobium sp. N613

The molecular structure of the rhizobium exopolysaccharide (REPS) was analyzed by enzymolysis, periodate oxidation, and Smith degradation, and by IR and NMR spectroscopy. The results indicated that REPS was a β-glucan with a backbone of β-d-(1→4)-linked glucose residues and branches of β-d-(1→6)-linked glucose residues. The branch was attached to the main chain at the 6-O-position. The molar ratio of 1→4 and 1→6 was 2:1. The terminal C3 of the (1→6)-Glc branch had an O-acetyl group. The molecular weight was estimated to be 35 kDa by Sephadex G-100 column chromatography. The antitumor activity of REPS was evaluated in mice bearing sarcoma 180, hepatoma 22, and Ehrlich ascites carcinoma tumor, respectively. At doses of 10-60 mg/kg, it was observed that tumor formation decreased significantly (P <0.01), but the relative spleen and thymus weight, the phagocytic function of monocytes, lymphocyte proliferation, and serum hemolysis antibody increased significantly (P <0.05). Results of these studies demonstrated that the REPS polysaccharide possessed antitumor activity.     

Flavonol tetraglycosides from fruits of Styphnolobium japonicum (Leguminosae) and the authentication of Fructus Sophorae and Flos Sophorae

The dried fruits and seeds of Styphnolobium japonicum (L.) Schott (syn. Sophora japonica L.) are used in traditional Chinese medicine and known as Fructus Sophorae or Huai Jiao. The major flavonoids in these fruits and seeds were studied by LC-MS and other spectroscopic techniques to aid the chemical authentication of Fructus Sophorae. Among the flavonoids were two previously unreported kaempferol glycosides: kaempferol 3-O-β-glucopyranosyl(1 → 2)-β-galactopyranoside-7-O-α-rhamnopyranoside and kaempferol 3-O-β-xylopyranosyl(1 → 3)-α-rhamnopyranosyl(1 → 6)[β-glucopyranosyl(1 → 2)]-β-glucopyranoside, the structures of which were determined by NMR. Two further tetraglycosides were identified for the first time in S. japonicum as kaempferol 3-O-β-glucopyranosyl(1 → 2)[α-rhamnopyranosyl(1 → 6)]-β-glucopyranoside-7-O-α-rhamnopyranoside and kaempferol 3-O-β-glucopyranosyl(1 → 2)[α-rhamnopyranosyl(1 → 6)]-β-galactopyranoside-7-O-α-rhamnopyranoside; the latter was the main flavonoid in mature seeds. The chromatographic profiles of 27 recorded flavonoids were relatively consistent among fruits of similar ages collected from five trees of S. japonicum, and those of maturing unripe and ripe fruits were similar to a market sample of Fructus Sophorae, and thus provide useful markers for authentication of this herbal ingredient. The flower buds (Huai Mi) and flowers (Huai Hua) of S. japonicum (collectively Flos Sophorae) contained rutin as the main flavonoid and lacked the flavone glycosides that were present in flower buds and flowers of Sophora flavescens Ait., reported to be occasional substitutes for Flos Sophorae. The single major flavonoid in fruits of S. flavescens was determined as 3′-hydroxydaidzein.     

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.     

Structural characterization of a highly branched polysaccharide from the seeds of Plantago asiatica L.

In this paper, polysaccharides were extracted from the seeds of Plantago asiatica L. with hot water and separated into three fractions PLP-1 (18.9%), PLP-2 (52.6%) and PLP-3 (28.5%) by Sephacryl™ S-400 HR column chomatography. The main fraction PLP-2's structure was elucidated using oxalic acid hydrolysis, partial acid hydrolysis, methylation, GC, GC-MS, 1D and 2D NMR. PLP-2 was composed of Rha, Ara, Xyl, Man, Glc and Gal, in a molar ratio of 0.05:1.00:1.90:0.05:0.06:0.10. Its uronic acid was GlcA. PLP-2 was highly branched heteroxylan which consisted of a β-1,4-linked Xylp backbone with side chains attached to O-2 or O-3. The side chains consisted of β-T-linked Xylp, α-T-linked Araf, α-T-linked GlcAp, β-Xylp-(1 → 3)-α-Araf and α-Araf-(1 → 3)-β-Xylp, etc. Based on these results, the structure of PLP-2 was proposed.