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At least 1,531 records · Page 85Linked to original sources
PubMed2000

Flavonol glycosides from Asplenium foreziense and its five related taxa and A. incisum.

The flavonoids of Asplenium foreziense, A. fontanum subsp. fontanum and subsp. pseudofontanum, A. obovatum subsp. obovatum var. obovatum and var. protobillotii, A. obovatum subsp. lanceolatum, and A. incisum were isolated and identified for chemotaxonomic survey. A major constituent of all taxa was kaempferol 3-O-gentiobioside. As minor compounds, kaempferol 3,7-O-glycoside and/or kaempferol 3-O-glycoside were found in A. fontanum, A. obovatum and A. foreziense, and kaempferol 3-O-gentiobioside-4'-O-glucoside, kaempferol 3-O-glucoside and quercetin 3-O-diglucoside in A. incisum. It was suggested that A. foreziense, A. fontanum including subsp. pseudofontanum and A. obovatum including subsp. lanceolatum are not only morphologically but also chemotaxonomically related. The East Asian A. incisum was chemically and geographically different from these taxa.

Journal Article↗
PubMed1986

Pulse radiolysis study of daunorubicin redox reactions: redox cycles or glycosidic cleavage?

Two aspects of daunorubicin reactivity were investigated by pulse radiolysis. The reactions of O2 and O2- with the semiquinone and the hydroquinone transients of daunorubicin were determined and their rate constants measured. Although O2- can reduce the drug and its semiquinone form, it is a more powerful oxidant towards the two reduced transients. The hydroquinone daunorubicin glycosidic cleavage in aqueous solution was studied. Three intermediates were seen and characterized by their absorption spectra, their formation and decay kinetics. The competition between these two main processes was evaluated in the conditions of pulse radiolysis. Even under low O2 partial pressures the redox cycles are much more rapid than the glycosidic cleavage and a relatively high O2- steady state is settled. Biological implications are discussed.

Daunorubicin↗
PubMed2002

Linckosides A and B, two new neuritogenic steroid glycosides from the Okinawan starfish Linckia laevigata.

Two new steroid glycosides, named linckosides A and B, were isolated from the Okinawan starfish Linckia laevigata, and their stereostructures were elucidated by spectroscopic methods and chemical derivatization. Each of them possesses two monosaccharide units at C-3 and C-29 of a polyhydroxylated steroid aglycon. These steroid glycosides showed not only notable neuritogenic activity against PC12 cells but also significant synergistic effects on the NGF-induced neuronal differentiation of PC12 cells. Linckoside B showed higher activities than those of linckoside A, though the structural difference is only the kind of a sugar.

Animals↗
PubMed1981

Oxygen-18 leaving group kinetic isotope effects on the hydrolysis of nitrophenyl glycosides. 2. Lysozyme and beta-glucosidase: acid and alkaline hydrolysis.

Oxygen-18 leaving group kinetic isotope effects (KIEs) have been measured for a set of glycosyl transfer reactions with p-nitrophenyl beta-D-glycosides as substrates. Acid-catalyzed hydrolysis and alkaline hydrolysis exhibit KIEs of K16/k18 = 1.0355 +/- 0.0015 and 1.0386 +/- 0.0032, respectively. Lysozyme and beta-glucosidase A show KIEs on Vmax/Km (V/K) of (V/KI)16/(V/K)18 = 1.0467 +/- 0.0015 and 1.0377 +/0 0.0061, respectively. The large magnitude of these KIEs requires that carbon-oxygen bond scission be far advanced in the transition states for these reactions; therefore in the transition states for the first irreversible steps in these reaction sequences, scission of the glycosidic bond must be essentially complete for the reactions catalyzed by lysozyme and beta-glucosidase A, which are thought to proceed via SN1 and SN2 mechanisms, respectively. Acid-catalyzed hydrolysis is shown to proceed through a transition state involving at least 80% C-O bond cleavage and only partially proton transfer to the leaving p-nitrophenyl oxygen atom.

Glucosidases↗
PubMed2003

Detailed kinetic analysis of a family 52 glycoside hydrolase: a beta-xylosidase from Geobacillus stearothermophilus.

Geobacillus stearothermophilus T-6 encodes for a beta-xylosidase (XynB2) from family 52 of glycoside hydrolases that was previously shown to hydrolyze its substrate with net retention of the anomeric configuration. XynB2 significantly prefers substrates with xylose as the glycone moiety and exhibits a typical bell-shaped pH dependence curve. Binding properties of xylobiose and xylotriose to the active site were measured using isothermal titration calorimetry (ITC). Binding reactions were enthalpy driven with xylobiose binding more tightly than xylotriose to the active site. The kinetic constants of XynB2 were measured for the hydrolysis of a variety of aryl beta-D-xylopyranoside substrates bearing different leaving groups. The Brønsted plot of log k(cat) versus the pK(a) value of the aglycon leaving group reveals a biphasic relationship, consistent with a double-displacement mechanism as expected for retaining glycoside hydrolases. Hydrolysis rates for substrates with poor leaving groups (pK(a) > 8) vary widely with the aglycon reactivity, indicating that, for these substrates, the bond cleavage is rate limiting. However, no such dependence is observed for more reactive substrates (pK(a) < 8), indicating that in this case hydrolysis of the xylosyl-enzyme intermediate is rate limiting. Secondary kinetic isotope effects suggest that the intermediate breakdown proceeds with modest oxocarbenium ion character at the transition state, and bond cleavage proceeds with even lower oxocarbenium ion character. Inhibition studies with several gluco analogue inhibitors could be measured since XynB2 has low, yet sufficient, activity toward 4-nitrophenyl beta-D-glucopyranose. As expected, inhibitors mimicking the proposed transition state structure, such as 1-deoxynojirimycin, bind with much higher affinity to XynB2 than ground state inhibitors.

Bacillaceae↗
PubMed2001

Rapid HPLC screening of jasmonate-induced increases in tobacco alkaloids, phenolics, and diterpene glycosides in Nicotiana attenuata.

A rapid, HPLC-based screening procedure for the main classes of secondary metabolites in Nicotiana attenuata leaves (alkaloids, phenolics, and diterpene glycosides) is reported. In a single step, leaves are extracted in aqueous acidified (0.5% acetic acid) methanol, and the extracted compounds are separated by reversed-phase HPLC with an acidic water/acetonitrile gradient in <30 min. The utility of the method in quantifying changes in the secondary metabolites after methyl jasmonate treatment of the plants, a treatment known to elicit resistance to herbivores in nature, is illustrated. Methyl jasmonate treatment elicited dramatic increases in some secondary metabolites (caffeoylputrescine, nicotine, and diterpene glycosides increased 12.5-, 1.4-, and 1.9-fold, respectively) but left others, such as rutin, unchanged. Such broad-based analytical screens will help characterize environmental and genetic changes in secondary metabolite profiles.

Alkaloids↗
PubMed2002

Quercetin, but not its glycosides, is absorbed from the rat stomach.

Absorption and metabolism of quercetin, isoquercitrin (quercetin 3-O-glucose), and rutin (quercetin 3-O-glucose-rhamnose) were investigated in rats after in situ gastric administration (15 micromol/L) for 30 min. At the end of the experiment, 38% of the initial dose of quercetin had disappeared. Quercetin was rapidly absorbed by the stomach, and was recovered in the bile 20 min after infusion (4.07 +/- 0.10 micromol/L). The administration of rutin and isoquercitrin indicated that these glycosides were not hydrolyzed nor absorbed by this tissue. In conclusion, when flavonols are present in the diet as aglycons, they could be partly absorbed in the stomach, in contrast to their glycosidic forms which are not absorbed.

Absorption↗
PubMed2000

Mass spectrometric identification and high-performance liquid chromatographic determination of a flavonoid glycoside naringin in human urine.

The aim of this study was to evaluate the absorption of a citrus flavonoid, naringin, as its glycosylated form. Six healthy volunteers (three males and three females) were studied. After a single oral administeration of 500 mg of naringin, intact naringin was isolated from 2-4 h urine. Isolated naringin was identified by the LC/electrospray ionization mass spectrometry (ESI-MS), MS/MS, and MS/MS/MS techniques. The cumulative urinary excretion of naringin and its metabolites (naringenin and naringenin glucuronides) was determined by HPLC for 0-24 h. Approximately 0.02% of the administered dose was recovered in urine as unchanged naringin, whereas urinary recoveries of naringenin and naringenin glucuronides were approximately 0.4 and 3.6% of the administered dose, respectively. It was concluded that trace amounts of orally administered naringin can be absorbed as the glycoside. However, it is not clear whether the glycoside is cleaved before or after absorption to generate naringenin.

Antioxidants↗
PubMed1989

Cardiac glycoside-like structure and function of 5 beta,14 beta-pregnanes.

5 beta-Reduction and 14 beta-substitution convert the planar progesterone molecule to the cardiac glycoside configuration--A and D rings of the steroid moiety are bent toward the alpha-face relative to the B and C rings. Potency of the 5 beta,14 beta-derivative in a [3H]ouabain binding assay or its ability to inhibit the sodium pump in red blood cells is enhanced by 3 beta-hydroxylation, 20 beta-hydroxylation, and 3 beta-glycosidation. Synthesis of 14,20 beta-dihydroxy-3 beta-(beta-D-glucopyranosyloxy)- 5 beta,14 beta-pregnane from digitoxin is described. The glucoside is 1/20 as potent as ouabain and elicits prominent, sustained, positive inotropy in isolated cardiac muscle.

Animals↗
PubMed2002

Stereoselective synthesis of the beta-anomer of 4'-thionucleosides based on electrophilic glycosidation to 4-thiofuranoid glycals.

Three types of 4-thiofuranoid glycal with different 3,5-O-silyl protecting groups were prepared and their electrophilic glycosidation was investigated. The 3,5-bis-O-(tert-butyldimethylsilyl)-4-thiofuranoid glycal (5) was obtained through mesylation of 2-deoxy-4-thio-D-erythro-pentofuranose (4) and subsequent base-promoted elimination, while thermal elimination of sulfoxide derivatives was suitable for the preparation of 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) (9) and 3,5-O-(di-tert-butylsilylene) (11) 4-thioglycals. The glycosidation reactions of these 4-thioglycals were carried out, in the presence of either PhSeCl or NIS, by using silylated derivatives of uracil, thymine, cytosine, and N(6)-benzoyladenine. Among the three 4-thioglycals, 11 was found to be an excellent glycosyl donor, forming the desired beta-anomer exclusively irrespective of the nucleobase employed.

Catalysis↗
PubMed2006

Synthesis of L-daunosamine and L-ristosamine glycosides via photoinduced aziridination. Conversion to thioglycosides for use in glycosylation reactions.

Application of photoinduced acylnitrene aziridination to the syntheses of L-daunosamine and L-ristosamine glycosides is reported. Photoreaction of methyl 4-O-azidocarbonyl-2,3,6-trideoxy-L-hex-2-enopyranosides, followed by aziridine opening, leads to 3-amino-3-N-,4-O-carbonyl-2,3,6-trideoxy precursors to the aminosugar methyl glycosides. Conversion of these precursors to their thioglycoside analogues followed by N-acetylation of the carbamate moiety permits high yielding and, in some cases, stereoselective glycosylations using the 1-benzenesulfinylpiperidine-triflic anhydride activation method developed by Crich and co-workers. Glycosylations involving activation with N-iodosuccinimide and silver triflate were also successful, but the stereoselectivities of these reactions in general were lower.

Hexosamines↗
PubMed1997

Synthesis of alpha- and beta-D-(1-->6)-C-Disaccharides by Wittig Olefination of Formyl C-Glycosides with Glycopyranose 6-Phosphoranes.

The synthesis of (1-->6)-C-disaccharides by Wittig condensation of formyl C-glycofuranosides and pyranosides with galacto- and glucopyranose 6-phosphoranes is described herein. The method involves the coupling of the sugar aldehydes with the ylides and the reduction of the double bond of the resulting sugar alkenes, in most of the cases by catalytic hydrogenation. The reduction with nickel boride or diimide is employed in some special cases. O-Benzyl protective groups are removed by catalytic hydrogenation either in the course of the reduction of the double bond or in a subsequent step, while O-isopropylidene groups are cleaved by treatment with Amberlite IR-120. In this way, eight free beta-D-(1-->6)-C-disaccharides have been prepared in 26-61% overall yield starting from beta-linked formyl C-glycosides. These include C-linked analogues of the biologically active disaccharides allolactose (Galbeta1,6Glc), gentiobiose (Glcbeta1,6Glc), and N-acetylamino disaccharides (GalNHAcbeta1,6Gal and GalNHAcbeta1,6Glc). Moreover, the synthesis of two alpha-D-(1-->6)-C-disaccharides is described from formyl C-furanosides. The limiting condition of the synthesis of these stereoisomers is the configurational instability of the alpha-linked formyl C-glycosides under the basic conditions of the Wittig olefination.

Journal Article↗
PubMed2003

Secoiridoid glycoside and alkaloid constituents of Hydrangea chinensis.

A new secoiridoid glycoside, hydrachoside A (1), along with 14 known compounds, was isolated from the leaves of Hydrangea chinensis. The absolute stereochemistry of the side chain attached to C-15 on the secoiridoid glycoside hydrangenoside E (2) was determined by NMR spectral analysis. The structures of compounds 1 and 2 were elucidated on the basis of spectral data. The previously reported structure, hydrachine A (3), was revised as its epimer, (-)-neodichroine (4), a new compound.

Alkaloids↗
PubMed2004

A new anti-HIV alkaloid, drymaritin, and a new C-glycoside flavonoid, diandraflavone, from Drymaria diandra.

A novel anti-HIV alkaloid, drymaritin (1), and a new C-glycoside flavonoid, diandraflavone (2), along with eight known compounds, torosaflavone A, isovitexin, spinasterol beta-d-glycoside, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, cis-p-coumarate, methyl 5-hydroxy-4-oxopentanoate, and glycerol-alpha-lignocerate, were isolated from Drymaria diandra. Drymaritin (1) exhibited anti-HIV effects in H9 lymphocytes with an EC(50) value of 0.699 microg/mL and a TI of 20.6. Compound 2 showed significantly selective inhibition on superoxide anion generation from human neutrophils stimulated by fMLP/CB with an IC(50) value of 10.0 microg/mL.

Alkaloids↗
PubMed1997

Spinonin, a novel glycoside from Ononis spinosa subsp. leiosperma.

The roots of Ononis spinosa subsp. leiosperma (Leguminosae) afforded a new glycoside, spinonin (1), possessing a novel skeleton, in addition to the known isoflavonoid glycoside, ononin [7beta-(glucosyloxy)formononetin] (2) and the known pterocarpan, 7-demethoxy-7-D-(glucosyloxy)homopterocarpin (3). The structure of the new isolate was elucidated by spectral methods including 1H and 13C NMR, COSY, APT, HETCOR, HMBC, NOESY, CD, FABMS, HRMS, EIMS, CIMS, and some chemical reactions. Spinonin was inactive against a number of human cancer cell lines and HIV-1 reverse transcriptase. The compounds 1 and 3 showed weak activity against Pseudomonas aeruginosa, whereas 2 was active against beta-hemolytic Streptococcus.

Acetylation↗
PubMed1998

A new flavonol glycoside gallate ester from Acer okamotoanum and its inhibitory activity against human immunodeficiency virus-1 (HIV-1) integrase.

Bioassay-directed chromatographic fractionation of an ethyl acetate extract of the leaves of Acer okamotoanum using HIV-1 integrase afforded a new acylated flavonol glycoside, quercetin 3-O-(2",6"-O-digalloyl)-beta-D-galactopyranoside (1), together with six known flavonol glycosides and three known phenolic compounds. The structure of the new compound was determined by spectroscopic methods. The most active compounds were quercetin 3-O-(2"-galloyl)-alpha-L-arabinopyranoside (6) and 1, which exhibited IC50 values of 18.1 +/- 1.3 and 24.2 +/- 6.6 micrograms/mL, respectively, against HIV-1 integrase.

Anti-HIV Agents↗
PubMed1998

Antiviral phenylpropanoid glycosides from the medicinal plant Markhamia lutea.

Three new phenylpropanoid glycosides, named luteoside A (3), luteoside B (4), and luteoside C (5), were isolated together with the known compounds verbascoside (1) and isoverbascoside (2) from the roots of the medicinal plant Markhamia lutea. The structures of the new compounds were determined to be 1-O-(3, 4-dihydroxyphenyl)ethyl beta-D-apiofuranosyl(1-->2)-alpha-l-rhamnopyranosyl(1-->3)-4-O- caffeo yl-6-acetyl-beta-d-glucopyranoside, 1-O-(3,4-dihydroxyphenyl)ethyl beta-d-apiofuranosyl(1-->2)-alpha-l-rhamnopyranosyl(1-->3)-6-O- caffeo yl-beta-d-glucopyranoside, and 1-O-(3,4-dihydroxyphenyl)ethyl beta-D-apiofuranosyl(1-->2)-alpha-l-rhamnopyranosyl(1-->3)-6-O- ferulo yl-beta-d-glucopyranoside, respectively, on the basis of chemical and spectroscopic data. All five phenylpropanoid glycosides exhibited potent in vitro activity against respiratory syncytial virus.

Antiviral Agents↗
PubMed1999

Flavonol glycosides from cassia hirsuta

A new flavonol glycoside, kaempferol 3-O-alpha-L-rhamnopyranosyl (1-->2)-alpha-L-rhamnopyranoside (1), was isolated from the flowers of Cassia hirsuta along with two known flavonol glycosides, kaempferol 3-O-rutinoside and rutin. The structure of compound 1 has been established on the basis of spectral data and by acid hydrolysis.

Journal Article↗