Ipolearoside: A new glycoside from Ipomoea leari with anti-cancer activity

Ipolearoside, a new glycoside with anticancer activity, has been isolated from Ipomoea leari Paxt. On acid hydrolysis in methanol, it gave the aglycone methyl ester, characterised as methyl 3,11-dihydroxyhexadecanoate. Ipolearoside is a complex glycoside of 3,11-dihydroxyhexadecanoic acid and glucose, rhamnose and fucose.     

Iridoid allosides from Viburnum opulus

Arbutin and four novel iridoid glycoside esters, named opulus iridoids I–IV, have been isolated from foliage of Viburnum opulus (Caprifoliaceae). Each opulus iridoid constitutes an inseparable mixture of two compounds, differing by containing either 2-methyl- or 3-methylbutyric acid in ester linkage at the 1-OH-group in an iridoid glycoside. In all glycosides 2′,3′-di-O-acetyl-β-D-allopyranose is linked through a glycosidic bond to C-11 in the iridoid aglycone. The opulus iridoids differ by the degree of acetylation of the aglycone and by the attachment, in III and IV, of a β-D-xylopyranosyl group at C-4 of the allose moiety. The structures have been elucidated by ¹H and ¹³C-NMR spectroscopy and by cleavage of the glycosidic linkage with boron trifluoride etherate in acetic anhydride, yielding the acetates of the cyclized aglycone and of the appropriate mono- or disaccharide. This is the second report of an iridoid attached to a sugar other than glucose and the second time allose has been encountered in higher plants. The systematic position of Viburnum is briefly discussed.     

绿盖粉孢牛肝菌中一个新的甾体糖苷

从绿盖粉孢牛肝菌（Tylopilus virens）中分离得到一个新的麦角甾烷型甾体糖苷,其化学结构通过波谱学方法鉴定为：（22E,24R）-麦角甾-7,22-二烯-5α,6β-二醇-3β-O-[3-（3-苯基丙酰氧基）]-β-D-葡萄吡喃糖苷,命名为tylopiloside（1）,同时,其苷元cerevisterol（2）也从该菌中分离得到。值得注意的是,这种糖片段上有芳环取代的烷酰氧基基团的麦角甾烷型甾体糖苷为真菌中首次报道。     

New neuritogenic steroidal saponin from Ophiopogon japonicus (Thunb.) Ker-Gawl

A new steroidal saponin was isolated from Ophiopogon japonicus. This saponin possesses a modification by 2-hydroxy-3-methylvalerylation of the hydroxyl group at C-4' of the sugar, linked to C-1 of the aglycone. It exhibited significant neuritogenic activity for PC12 cells. The structure-activity relationship revealed the aglycone, rather than the sugar moieties and acylation, to be important for the neuritogenic activity.     

The O-linked fucose glycosylation pathway: identification and characterization of a uridine diphosphoglucose: fucose-beta1,3-glucosyltransferase activity from Chinese hamster ovary cells.

O-Linked fucose is an unusual carbohydrate modification in which fucose is linked directly to the hydroxyl groups of serines or threonines. It has been found on the epidermal growth factor-like modules of several secreted proteins involved in blood coagulation and fibrinolysis. We have recently reported the existence of an elongated form of O-linked fucose in Chinese hamster ovary cells consisting of a glucose linked to the 3'-hydroxyl of fucose (Glcbeta1,3Fuc- O-Ser/Thr). This structure is highly unusual for two reasons. First, in mammalian systems fucose is usually a terminal modification of N - and O-linked oligosaccharides. Here the fucose is internal. Secondly, terminal beta-linked glucose is extremely rare on mammalian glycoconjugates. Thus, the Glcbeta1,3Fuc structure is a very unique mammalian carbohydrate structure. Here we report the identification and initial characterization of a novel enzyme activity capable of forming this unique linkage: UDP-glucose: O-linked fucose beta1,3 glucosyltransferase. The enzyme utilizes UDP-glucose as the high energy donor and transfers glucose to alpha-linked fucose residues. The activity is linearly dependent on time, enzyme, and substrate concentrations and is enhanced in the presence of manganese ions. Activity is present in extracts of cultured cells from a variety of species (hamster, human, mouse, rat, chicken) and is enriched in brain and spleen of a normal adult rat. Thus, while this glycosyltransferase appears to be widespread in biology, it forms a very unique linkage, and it represents the first mammalian enzyme identified capable of elongating fucose.     

A protein-glucan intermediate during paramylon synthesis.

A sodium deoxycholate extract containing glucosyltransferase activity was obtained from a particulate preparation from Euglena gracilis. It transferred glucose from UDP-[14C]glucose into material that was precipitated by trichloroacetic acid. This material released beta-(1 leads to 3)-glucan oligosaccharides into solution on incubation with weak acid, weak alkali and beta-(1 leads to 3)-glucosidase. The products of the incubation of the deoxycholate extract with UDP-[14C]glucose were analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Radioactive bands were obtained that had the properties of beta-(1 leads to 3)-glucan covalently linked to protein by a bond labile to weak acid. High-molecular-weight material containing a beta-(1 leads to 3)-glucan was also shown to be present by gel filtration. The bond linking glucan to aglycone is possibly a pyrophosphate linkage. It is proposed that in Euglena gracilis beta-(1 leads to 3)-glucan (paramylon) is synthesized on a protein primer.     

A trinorsesterterpene glycoside from the North American fern Woodwardia virginica (L.) Smith

A new trinorsesterterpene glycoside was isolated from the ethanol extract of the American fern Woodwardia virginica having a 3-[6-(4,8-dimethyl-nona-1,3,7-trienyl)-4-hydroxy-2,6-dimethyl-cyclohex-1-enyl]-3-hydroxypropionic acid, as the aglycone and a saccharide moiety linked at C-4 to glucoses, xylose or arabinofuranose. The structure was elucidated using extensive spectroscopic analysis (1D and 2D NMR, MS, IR and UV) including determination of absolute stereochemistry by means of the MTPA and PGME derivatives and also by chemical methods.     

Isolation and chemical study of the glycosaminoglycans from squid cornea

1. Oversulphated chondroitin sulphate (ca 93% of tissue glycosaminoglycans) with average molecular weight 72,500, chondroitin sulphate (5%) and small amounts of lowsulphated chondroitin sulphate were isolated from squid cornea. 2. The sulphation pattern of oversulphated chondroitin sulphate was delta di-4S (52%), delta di-diSD (28%), delta di-6S (9%) and delta di-OSCS (11%) and that of chondroitin sulphate 49, 1, 20 and 30% respectively. 3. All glycosaminoglycans contained neutral monosaccharides, glucose being the predominant neutral monosaccharide in oversulphated chondroitin sulphate and chondroitin sulphate and fucose in low-sulphated chondroitin sulphate. 4. Although L-iduronic acid was not detected, the digestion of oversulphated chondroitin sulphate with chondroitinases ABC and AC gave unexpected results.     

Novel acetylated triterpenoid saponins in a chromatographic fraction from Quillaja saponaria Molina

Six novel fucose 3-O-acetylated saponins, with a quillaic acid aglycone, were isolated from a bark extract from the Quillaja saponaria Molina tree. In addition, a saponin with a novel aglycone (phytolaccagenic acid) and a novel fatty acyl group [(S)-2-methylbutanoyl] for Quillaja saponins was found. The compounds were characterised using NMR spectroscopy, mass spectrometry and chemical methods.     

Structural basis for langerin recognition of diverse pathogen and mammalian glycans through a single binding site

Langerin mediates the carbohydrate-dependent uptake of pathogens by Langerhans cells in the first step of antigen presentation to the adaptive immune system. Langerin binds to an unusually diverse number of endogenous and pathogenic cell surface carbohydrates, including mannose-containing O-specific polysaccharides derived from bacterial lipopolysaccharides identified here by probing a microarray of bacterial polysaccharides. Crystal structures of the carbohydrate-recognition domain from human langerin bound to a series of oligomannose compounds, the blood group B antigen, and a fragment of β-glucan reveal binding to mannose, fucose, and glucose residues by Ca²⁺ coordination of vicinal hydroxyl groups with similar stereochemistry. Oligomannose compounds bind through a single mannose residue, with no other mannose residues contacting the protein directly. There is no evidence for a second Ca²⁺-independent binding site. Likewise, a β-glucan fragment, Glcβ1-3Glcβ1-3Glc, binds to langerin through the interaction of a single glucose residue with the Ca²⁺ site. The fucose moiety of the blood group B trisaccharide Galα1-3(Fucα1-2)Gal also binds to the Ca²⁺ site, and selective binding to this glycan compared to other fucose-containing oligosaccharides results from additional favorable interactions of the nonreducing terminal galactose, as well as of the fucose residue. Surprisingly, the equatorial 3-OH group and the axial 4-OH group of the galactose residue in 6SO₄-Galβ1-4GlcNAc also coordinate Ca²⁺, a heretofore unobserved mode of galactose binding in a C-type carbohydrate-recognition domain bearing the Glu-Pro-Asn signature motif characteristic of mannose binding sites. Salt bridges between the sulfate group and two lysine residues appear to compensate for the nonoptimal binding of galactose at this site.     

Structure of a safflower steroid cellobioside

Structural identification of a steroid diglucoside from Carthamus tinctorius whose aglycone is 15α-20β-dihydroxy-Δ⁴-pregnen-3-one has been completed. We have analyzed the sugar moiety of the glycoside and found it to be cellobiose, β-linked to C-20 of the aglycone.     

Human liver N-acetylglucosamine-6-sulphate sulphatase. Catalytic properties.

Kinetic parameters (Km and kcat.) of the two major forms (A and B) and a minor form (C) of human liver N-acetylglucosamine-6-sulphate sulphatase [Freeman, Clements & Hopwood (1987) Biochem. J. 246, 347-354] were determined with a variety of substrates matching structural aspects of the physiological substrates in vivo, namely heparin, heparan sulphate and keratan sulphate. Enzyme activity is highly specific towards glucosamine 6-sulphate or glucose 6-sulphate residues. More structurally complex substrates, in which several aspects of the aglycone structure of the natural substrate were maintained, are hydrolysed with catalytic efficiencies up to 3900 times above that observed for the monosaccharide substrate N-acetylglucosamine 6-sulphate. Forms A and B both desulphate substrates derived from keratan sulphate and heparin. Aglycone structures that influence substrate binding and/or enzyme activity were penultimate-residue 6-carboxy and 2-sulphate ester groups for heparin-derived substrates and penultimate-residue 6-sulphate ester groups for keratan sulphate-derived substrates. The 4-hydroxy group of the N-acetylglucosamine 6-sulphate or the 2-sulphaminoglucosamine 6-sulphate under enzymic attack is involved in the catalytic mechanism. The presence of a 2-amino group in place of a 2-acetamido or a 2-sulphoamino group considerably decreases the catalytic efficiency of the sulphatase, particularly in the absence of a penultimate-aglycone-residue 6-carboxy group. Both forms A and B are exo-enzymes, since activity towards internal sulphate ester bonds was not observed. The effect of incubation pH on enzyme activity towards the variety of substrates evaluated was complex and dependent on substrate aglycone structure. The presence of aglycone 2-sulphate ester, 6-carboxy group and 6-sulphate ester groups on the glucosamine 6-sulphate residue under attack considerably affects the pH response. Sulphate and phosphate ions are potent inhibitors of enzyme activity.     

Starfish saponins—XI. Isolation and partial characterization of the saponins from the starfish Marthasterias glacialis

• 1.1. The saponin mixture isolated from Marthasterias glacialis was resolved through a series of chromatographic steps into four principal individual components, named marthasteroside A₁, A₂, B and C.
• 2.2. The isolated sulphate steroidal glycosides were characterized by ¹H-NMR, ¹³C-NMR, Fast Atom Bombardment mass spectrometry and GLC analysis of the sugars after acid hydrolysis.
• 3.3. Marthasteroside A₁ and A₂ contained the aglycone thornastrol A and six sugar units. The second group of compounds, marthasteroside B and C, contained five sugar units; the aglycone of marthasteroside B was identified as marthasterone, while that of marthasteroside C was identified as dihydromarthasterone. In all compounds the sulphate group is attached at C-3 of the steroid.

     

Excretion of miserotoxin and detoxification of the aglycone by grasshoppers (Orthoptera: Acrididae).

Two species of grasshoppers (Melanoplus bivittatus and M. sanguinipes) tolerated high levels of miserotoxin (3-nitro-1-propyl-beta-D-glucopyranoside) in their diet. Miserotoxin is a causative agent in cattle poisoning when timber milkvetch (Astragalus miser) is consumed. Toxic effects were averted by grasshoppers in part by excretion of the intact glycoside. When the aglycone was administered, detoxification was achieved by two routes: by oxidation of the aglycone to 3-nitropropionic acid which was then conjugated with glycine, and by glucosylation of the aglycone to miserotoxin, in each case followed by excretion.     

Carbohydrates of the antarctic brown seaweed Ascoseira mirabilis

Mannitol, sucrose and four monosaccharides were obtained from an ethanolic extract of Ascoseira mirabilis. Sequential extraction with aqueous calcium chloride, dilute acid and dilute alkali gave mixtures of laminaran, ‘fucan’ and alginic acid. Laminarans fractionated from the extracts contained different proportions of uniformly (1 → 3) and (1 → 6) linked chains of β-D-glucose residues. The ‘fucan’ contained varying proportions of fucose, galactose and glucuronic acid, small amounts of xylose, mannose, glucose, half ester sulphate and protein. Extraction of the weed under mild alkaline conditions gave a yield of 13.4% of low molecular weight calcium alginate with a mannuronate to guluronate ratio of 30:70 and only a small proportion of sequences of alternating residues. Selective extraction and fractionation gave alginate fractions rich (> 80%) in mannuronate or guluronate.     

Measurement of endo-α-mannosidase activity using a fluorescently labeled oligosaccharide derivative

Endo-α-mannosidase, a GH99-family glycoside hydrolase, cleaves α-mannoside linkages with glucose residues. This enzyme is proposed to play a critical role in N-glycan processing for deglucosylation. To measure endo-α-mannosidase activity, we synthesized a fluorescently labeled tetrasaccharide derivative (Glcα1-3Manα1-2Manα1-2Manα1-O–C₃H₆–NH-Dansyl) in a stereocontrolled manner. The tetrasaccharide skeleton was prepared by step-wise coupling using mannose donors 4 and 7. The 1,2-cis α-glycosidic linkage on the non-reducing end of the glucose residue was constructed by inversion of the stereochemistry of the C-2 hydroxyl group in the α-mannose residue. Finally, the dansyl group was introduced at the reducing end via an aminopropyl linker. This probe successfully measured endo-α-mannosidase activity.     

Metabolism of [14C]glucose by regenerating spheroplasts of Candida albicans

Spheroplasts of Candida albicans were regenerated in [14C]glucose and buffered magnesium sulphate (0.1 M-Tris/HCl; 0.5 M-MgSO4, pH 7.2) at 35 degrees C. Uptake of glucose by spheroplasts was faster than that by intact yeast cells. After 6 h, 65% of the glucose taken up by the yeast appeared as CO2 and 30% was incorporated into the cellular material. With spheroplasts, 55% of the glucose taken up was expired as CO2, 25% was excreted into the medium as other metabolites and 20% was incorporated into the cells. The regenerating spheroplasts excreted 14C-labelled carbohydrates into the medium which were fractionated on a Sephadex G-15 column. Acid hydrolysis of the low molecular-weight fraction yielded the following sugars: mannose (75.7%), fucose (3.8%), arabinose (3%), galactose (2.1%) and an unidentified monosaccharide (14%). Spheroplasts did not incorporate mannoprotein into the regenerated wall. The wall carbohydrate from regenerated spheroplasts was fractionated on the basis of solubility in sodium hydroxide. The alkali-insoluble fraction was analysed by sequential enzyme hydrolysis; 40% of the incorporated counts were associated with beta (1----3)-linked glucan and 50% with a mixed glucan comprising beta (1----3)- and beta (1----6)-linkages and chitin.     

Effect of O-glycosilation on the antioxidant activity and free radical reactions of a plant flavonoid,chrysoeriol

Chrysoeriol and its glycoside (chrysoeriol-6-O-acetyl-4'-beta-D-glucoside) are two natural flavonoids extracted from the tropical plant Coronopus didymus. The aqueous solutions of both the flavonoids were tested for their ability to inhibit lipid peroxidation induced by gamma-radiation, Fe (III) and Fe (II). In all these assays chrysoeriol showed better protecting effect than the glycoside. The compounds were also found to inhibit enzymatically produced superoxide anion by xanthine/xanthine oxidase system; here the glycoside is more effective than the aglycone. The rate constants for the reaction of the compounds with superoxide anion determined by using stopped-flow spectrometer were found to be nearly same. Chrysoeriol glycoside reacts with DPPH radicals at millimolar concentration, but the aglycone showed no reaction. Using nanosecond pulse radiolysis technique, reactions of these compounds with hydroxyl, azide, haloperoxyl radicals and hydrated electron were studied. The bimolecular rate constants for these reactions and the transient spectra of the one-electron oxidized species indicated that the site of oxidation for the two compounds is different. Reaction of hydrated electron with the two compounds was carried out at pH 7, where similar reactivity was observed with both the compounds. Based on all these studies it is concluded that chrysoeriol exhibits potent antioxidant activity. O-glycosylation of chrysoeriol decreases its ability to inhibit lipid peroxidation and reaction with peroxyl radicals. However the glycoside is a more efficient scavenger of DPPH radicals and a better inhibitor of xanthine/xanthine oxidase than the aglycone.     

Enzymic synthesis of steroid sulphates. XIV. Properties of human adrenal steroid alcohol sulphotransferase

Pure steroid alcohol sulphotransferase (EC 2.8.2.-) has the property of sulphurylating hydroxyl groups on different positions of the steroid ring. It has now been established that although only monosulphates are formed from substrates such as 3,17-diols, the position of the sulphate group depends on the relative configuration of the hydroxyl groups. Androst-5-ene-3 beta,17 beta-diol, for example, is sulphurylated mainly at the 17-position. In addition, compounds such as epitestosterone and 17 alpha-estradiol are sulphurylated at much higher rates than their respective 17 beta-epimers. It is believed that the steroid can approach the sulphurylation site via (i) ring A with the beta-side upwards, and in this mode a 3 beta-hydroxyl is sulphurylated at a higher rate than a 3 alpha-hydroxyl, or (ii) ring D with the beta-side downwards, and in this mode a 17 alpha-hydroxyl group is oriented in an analogous fashion to the 3 beta-hydroxyl in (i). The enzyme exhibits non-Michaelis-Menten kinetics within physiological concentrations (0-2 micro M) of the substrate dehydroepiandrosterone and evidence was obtained for the presence of multiple interacting steroid-binding sites. A regulatory role for the enzyme in the secretion of dehydroepiandrosterone from the human adrenal gland is proposed.     

The carbohydrate components of hydrolysates of gastric secretion and extracts from mucous glands of the gastric body mucosa and antrum

1. The sugars and amino sugars of hydrolysates of gastric secretion were determined by gas-liquid chromatography. 2. All the gastric aspirations examined showed on hydrolysis the presence of fucose, galactose, mannose, glucose, galactosamine, glucosamine, N-acetylneuraminic acid and sulphate. 3. Galactose and glucosamine were always found in equimolar amounts, but the galactose/galactosamine ratio in different aspirations was 2:1, 3:1, 4:1 or 5:1. Repeated gastric aspirations of each subject examined showed constant ratios of these carbohydrate components. 4. Fucose and sialic acid appear to be related to glucosamine and galactosamine respectively. 5. The carbohydrate components of extracts from the mucous glands of the body mucosa and antrum did not differ from those of gastric secretion.