Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GLYCOSIDES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63Linked to original sources
PubMed1999

Effects of oleanolic acid glycosides on gastrointestinal transit and ileus in mice.

The effects of various oleanolic acid glycosides obtained from medicinal herbs on gastrointestinal transit (GIT) and ileus were investigated in fasted mice. Ileus was induced by the peritoneal-irritation or by the laparotomy with manipulation. One hour after the oral administration, three oleanolic acid 3-O-monodesmosides (oleanolic acid 3-O-glucuronide (3, 50 mg/kg), momordin Ic (4, 25 and 50 mg/kg), and momordin I (6, 25 mg/kg)) significantly accelerated GIT, but two oleanolic acid 3-O-monodesmosides (28-deglucosyl-chikusetsusaponins IV (8) and V (10)), oleanolic acid 3,28-O-bisdesmosides (momordin IIc (5), chikusetsusaponins IV (7) and V (9)), and their common aglycon (oleanolic acid (1)) (50 mg/kg) showed no significant effect. On the other hand, oleanolic acid 28-O-monodesmoside (compound O (2, 50 mg/kg)) significantly inhibited GIT. 4 (5-25 mg/kg) and 6 (12.5 and 25 mg/kg) also significantly prevented the inhibition of GIT induced by the peritoneal injection of acetic acid. 2 and 9 (50 mg/kg) significantly potentiated the inhibition of GIT, whereas 1, 3, 5, 7, 8, and 10 (50 mg/kg) showed no significant effect. 3, 4, 6, and 10 (50 mg/kg) significantly prevented the inhibition of GIT induced by laparotomy with manipulation, while 1, 2, 5, 7, 8, and 9 (50 mg/kg) showed no significant effect. These results indicate that the 3-O-glycoside moiety seems to be essential to show the GIT accelerating activity, and the 28-O-glucoside moiety reduce the activity. The accelerations of GIT by 3, 4, and 6 were completely abolished by the pretreatment with streptozotocin (100 mg/kg, i.v.), but not by the pretreatment with capsaicin (75 mg/kg in total, s.c.). These results suggest that sympathetic nervous system, but not capsaicin-sensitive sensory nerves, be involved in the enhancements of GIT by 3, 4, and 6. It is worthy to study their therapeutical effect in the prevention of the inhibition of GIT, including ileus, in clinic.

Animals↗
PubMed2001

The kappa-carrageenase of P. carrageenovora features a tunnel-shaped active site: a novel insight in the evolution of Clan-B glycoside hydrolases.

BACKGROUND: kappa-carrageenans are gel-forming, sulfated 1,3-alpha-1,4-beta-galactans from the cell walls of marine red algae. The kappa-carrageenase from the marine, gram-negative bacterium Pseudoalteromonas carrageenovora degrades kappa-carrageenan both in solution and in solid state by an endoprocessive mechanism. This beta-galactanase belongs to the clan-B of glycoside hydrolases. RESULTS: The structure of P. carrageenovora kappa-carrageenase has been solved to 1.54 A resolution by the multiwavelength anomalous diffraction (MAD) method, using a seleno-methionine-substituted form of the enzyme. The enzyme folds into a curved beta sandwich, with a tunnel-like active site cavity. Another remarkable characteristic is the presence of an arginine residue at subsite -1. CONCLUSIONS: The crystal structure of P. carrageenovora kappa-carrageenase is the first three-dimensional structure of a carrageenase. Its tunnel-shaped active site, the first to be reported for enzymes other than cellulases, suggests that such tunnels are associated with the degradation of solid polysaccharides. Clan-B glycoside hydrolases fall into two subgroups, one with catalytic machinery held by an ancestral beta bulge, and the other in which it is held by a regular beta strand. At subsite -1, all of these hydrolases exhibit an aromatic amino acid that interacts with the hexopyranose ring of the monosaccharide undergoing catalysis. In addition, in kappa-carrageenases, an arginine residue recognizes the sulfate-ester substituents of the beta-linked kappa-carrageenan monomers. It also appears that, in addition to the nucleophile and acid/base catalysts, two other amino acids are involved with the catalytic cycle, accelerating the deglycosylation step.

Alteromonas↗
PubMed2003

Incremented alkyl derivatives enhance collision induced glycosidic bond cleavage in mass spectrometry of disaccharides.

Electrospray ionization and collision induced dissociation on a triple quadrupole mass spectrometer were used to determine the effect of spatial crowding of incremented alkyl groups of two anomeric pairs of peralkylated (methyl to pentyl) disaccharides (maltose/cellobiose and isomaltose/gentiobiose). Protonated molecules were generated which underwent extensive fragmentation under low energy conditions. For both the 1 --> 4 and 1 --> 6 alpha and beta isomers, at comparable collision energies the methyl derivative exhibited the least fragmentation followed by ethyl, propyl, butyl, and pentyl. Collision energy is converted to rotational-vibrational modes in competition with bond cleavage, as represented by the slope of product/parent ion (D/P) ratio versus offset energy. Variable rotational freedom at the glycosidic linkage with incremented alkyl groups is hypothesized to be responsible for this effect. Discrimination of anomeric configuration was also assessed for these stereoiosmeric disaccharides. A systematic study showed that an increasing discrimination was attained for the 1 --> 4 isomeric pair as the size of the derivative increased from methyl to pentyl. No anomeric discrimination was attained for the 1 --> 6 isomeric pair. Parent and product ion scans confirmed the consistency of fragmentation pathways among derivatives. Chem-X and MM3 molecular modeling programs were used to obtain minimum energy structures and freedom of motion volumes for the permethylated disaccharides. The modeling results correlated with the fragmentation ratios obtained in the mass spectrometer giving strong indication that the collision induced spectra are dependent on the freedom of rotational motion around the glycosidic bond.

Algorithms↗
PubMed2001

The distribution of free sterols, polyhydroxysteroids and steroid glycosides in various body components of the starfish Patiria (=Asterina) pectinifera.

The distribution of free sterols, polyhydroxysteroids and steroid glycosides in different body components of the Far-eastern starfish Patiria (=Asterina) pectinifera has been studied. It was shown that free sterol fractions from aboral and oral body walls, gonads, stomach and pyloric ceca contained Delta(7) sterols with a preponderance of 5alpha-cholest-7-en-3beta-ol. All these body components had also toxic steroid oligoglycosides. However, polyhydroxysteroids and related low molecular weight steroid glycosides were found in stomach and pyloric ceca only. In pyloric ceca, the sulfated monoside 'asterosaponin' P(1) was identified as a main polar steroid, whereas 6-sodium sulfate of cholestane-3beta,4beta,6alpha,7alpha,8,15beta,16beta,26-octaol predominated in the stomach. Probable biological functions of polar steroids and free sterols in this starfish were discussed. It was suggested that some polyhydroxysteroids and related monoglycosides play the same biological role as bile alcohols and bile acids do in vertebrates.

Animals↗
PubMed2003

Biological activities of steroid glycosides from starfish.

Glycosides of polyhydroxysteroids from starfish were compared with regard to hemolytic activities on mouse red blood cells and cytotoxicity on developing eggs of sea urchin Strongylocentrotus intermedius. Mediasteroside M(1) from Mediaster murrayi with a 2-O-methyl group at a xylose residue exerted lower activity than mediasteroside M(2) without this group. Ceramasteroside C(2) from Ceramaster patagonicus having a 2,4-di-O-Me-Xylp residue had more activity in comparison with ceramasteroside C(3) with 2-O-Me-Xylp. Activities of rathbuniosides R(1) (four OH-groups) and R(2) (five OH-groups) from Asterias rathbuni, and culcitosides C(2) (six OH-groups) and C(3) (five OH-groups) from Culcita novaeguineae were inversely proportional to the number of hydroxyl groups of the aglycon. There was a correlation between cytotoxic and hemolytic activities. The results indicated that salt concentration, temperature and pH values are important for the hemolytic activity of steroid glycosides.

Animals↗
PubMed2005

Effect of bioactive compounds from Sainfoin ( Onobrychis viciifolia Scop.) on the in vitro larval migration of Haemonchus contortus: role of tannins and flavonol glycosides.

Anthelmintic bioactivity against gastrointestinal nematodes has been associated with leguminous forages supporting the hypothesis of a role of condensed tannins. However, the possibility that other compounds might also been involved has received less consideration. Using bio-guided fractionation, the current study aimed at characterizing the biochemical nature of the active compounds present in sainfoin (Onobrychis viciifolia ), previously identified as an anthelmintic leguminous forage. The effects of sainfoin extracts were evaluated on 3rd-stage larvae (L3) of Haemonchus contortus by using a larval migration inhibition (LMI) assay. Comparison of extracts obtained with several solvent systems showed that the bioactivity was associated with the 70ratio30 acetone/water extract. Further fractionation of the later allowed the separation of phenolic compounds. By use of a dialysis method, compounds were separated with a molecular weight cut-off of 2000 Da. The in vitro anthelmintic effect of the fraction with condensed tannins was confirmed. In the fraction containing molecules of MW <2000 Da, 3 flavonol glycosides were identified as rutin, nicotiflorin and narcissin. At 1200 mug/ml, each inhibited significantly the migration of larvae. Addition of polyvinyl pyrrolidone (PVPP) to both fractions before incubation restored larval migration. These results confirmed the role of both tannins and flavonol glycosides in the anthelmintic properties of sainfoin.

Animals↗
PubMed1995

NMR solution structure of a nonanucleotide duplex with a dG mismatch opposite a 10S adduct derived from trans addition of a deoxyadenosine N6-amino group to (+)-(7R,8S,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene: an unusual syn glycosidic torsion angle at the modified dA.

A nonanucleotide, d(G1G2T3C4[BaP]A5C6G7A8G9), in which (+)-(7R,8S,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (7-hydroxyl group and epoxide oxygen are trans) is covalently bonded to the exocyclic N6-amino group of deoxyadenosine (dA5) through trans addition at C10 of the epoxide (to give a 10S adduct) has been synthesized. The solution structure of the duplex, d(G1G2T3C4[BaP]A5C6G7A8G9).d(C10T11C12G13G14G15A16C17C18+ ++), containing a dG mismatch opposite the modified dA (designated 10S-[BaP]dA.dG 9-mer duplex) has been investigated using a combination of 1D and 2D (including COSY, PECOSY, TOCSY, NOESY, and indirect detection of 1H-31P HETCOR) NMR spectroscopies. The NMR results together with restrained molecular dynamics/energy minimization calculations show that the modified dA5 adopts a syn glycosidic torsion angle whereas all other nucleotide residues adopt anti glycosidic torsion angles. The sugar ring of dA5 is in the C3'-endo conformation, and the sugar rings of the other residues are in the C2'-endo conformation. The hydrocarbon attached at dA5 orients toward the 3' end of the modified strand (i.e., dC6 direction) and intercalates between and parallel to bases of dG13 and dG14 of the complementary strand directly opposite dC6 and dA5, respectively. The edge of the hydrocarbon bearing H11 and H12 is positioned between the imino protons of dG13 and dG14 in the interior of the duplex, whereas H4 and H5 at the opposite edge are positioned near the sugar H1' and H2" protons of dG13 and facing the exterior of the duplex. The mismatched AG base pair is stabilized by dAsyn-dGanti base pairing in which the imino proton and the O6 of dG14 are hydrogen bonded to N7- and the single N6-amino proton, respectively, of the modified dA5. The modified DNA duplex remains in a right-handed helix, which bends at the site of intercalation about 20 to 30 degrees away from the helical axis and toward the direction of the modified strand.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1983

Photoaffinity labeling of the sodium- and potassium-activated adenosinetriphosphatase with a cardiac glycoside containing the photoactive group on the C-17 side chain.

The synthesis and properties of a radiolabeled glycoside photoaffinity probe, [3H]-(3 beta,5 beta,14 beta, 20E)-24-azido-3-[(2,6-dideoxy-beta-D-ribo-hexopyranosyl) oxy]-14-hydroxy-21-norchol-20(22)-en-23-one, containing the photoactive group at the C-17 side chain of the steroid moiety are reported. The molecule binds to the sodium- and potassium-activated adenosinetriphosphatase from porcine kidney outer medulla under type II binding conditions [5 mM MgCl2, 3 mM phosphate, 2 mM ethylenediaminetetraacetic acid, 30 mM tris(hydroxymethyl)aminomethane, pH 7.2, 37 degrees C] in the dark with an equilibrium dissociation constant of (1.4 +/- 0.3) X 10(-7) M. Ultraviolet irradiation of a solution of enzyme plus 3H-labeled probe, followed by analysis of covalently incorporated radiolabel, shows ouabain-displaceable labeling exclusively of the alpha subunit of the sodium- and potassium-activated adenosinetriphosphatase. These data indicate that the binding site of the C-17 side group of cardiac glycosides is located on or near the alpha subunit of this enzyme.

Affinity Labels↗
PubMed1980

Alkyl glycoside detergents: a simpler synthesis and their effects on kinetic and physical properties of cytochrome c oxidase.

Octyl glucoside is an effective, nonionic, solubilizing agent for membrane proteins with the advantage of ease of removal by dialysis. In order to study the detergent-sensitive activity of cytochrome c oxidase, we chose this detergent because of its simple structure and the possibility of synthesizing analogues to test the structural dependence of the detergent specificity. A procedure was therefore developed that facilitates large-scale preparation of octyl glucoside and related alkyl glycosides, improving on previous methods by eliminating crystallization steps and employing a one-step purification of the final product on Dowex 1. This new purification procedure is particularly important for achieving the level of purity required to obtain the disaccharide, longer alkyl chain detergents in soluble form. Of the alkyl glycosides prepared (octyl beta-D-glucopyranoside, octyl beta-D-lactopyranoside, dodecyl beta-D-lactopyranoside, dodecyl beta-D-cellobiopyranoside, and dodecyl beta-D-maltopyranoside), lauryl (dodecyl) maltoside was found to be the most successful as an activator of purified beef and Neurospora cytochrome oxidase, giving two- to tenfold higher activities than octyl glucoside and other commercially available detergents, Tween-20 and Triton X-100. Kinetic studies using two different steady-state assay systems indicate that the activity changes are not the result of altered binding of the substrate but rather reflect a detergent effect on the state of association of the enzyme (as a monomer, dimer, or polymer) as well as on its intrinsic activity. By gel filtration procedures, lauryl maltoside and octyl glucoside were found to exist as monodisperse populations of micelles of 50 000 and 8000 daltons, respectively. The small uniform micelles and chemically well-defined structures of lauryl maltoside and octyl glucoside make them superior to other nonionic detergents for the study of membrane proteins in general and cytochrome oxidase in particular, since its activity in lauryl maltoside most closely approaches that of the physiological state.

Animals↗
PubMed1977

Anthroylouabain: a specific fluorescent probe for the cardiac glycoside receptor of the Na-K ATPase.

Anthroylouabain (AO) was synthesized by reaction of anthracene-9-carboxylic chloride with ouabain. Nuclear magnetic resonance spectroscopy of AO suggests that the anthracene is esterfied to the rhamnose in the glycoside. AO inhibits Na-K ATPase from human red cells, eel electroplax and rabbit and dog kidney with a KI less than 1muM. AO bound to rabbit or dog kidney Na-K ATPase shows enhanced fluorescence and characteristic spectral shifts. AO binding requires Mg and is optimum in the presence of Mg + Pi or MgATP + Na; ouabain prevents AO binding and fluorescence enhancement if added before AO or reverses it if added after AO is bound. Na inhibits AO binding in the presence of Mg + Pi and K inhibits it in the presence of MgATP + Na. AO binding and dissociation rate constants measured by fluorescence agree qualitatively with reported measurements for ouabain, using other methods, although AO shows faster kinetics than ouabain. Dissociation constants obtained from kinetic measurements are 1.5 X 10(-7) and 1.8 X 10(-7) M for the MgATP + Na complex and Mg + Pi complex, respectively. KD from fluorescence titrations is 2.3 X 10(-7) M for the latter. The enzyme has 2-2.5 nmol of AO binding sites/mg of protein. No differences in the fluorescence parameters of the Mg + Pi or MgATP + Na complexes were observed, suggesting that the same enzyme conformation binds AO under both ligand conditions. Comparison of the AO fluorescence parameters in the enzyme with those of model systems suggests that the binding site is hydrophobic and/or viscous and shielded from H2O. The results indicate that AO is a specific fluorescent probe of the cardiac glycoside receptor of the Na-K ATPase. Possible applications are discussed.

Adenosine Triphosphatases↗
PubMed2006

Mechanistic analysis of the unusual redox-elimination sequence employed by Thermotoga maritima BglT: a 6-phospho-beta-glucosidase from glycoside hydrolase family 4.

"Classical" glycosidases utilize either direct or double-displacement mechanisms involving oxocarbenium ion-like transition states to catalyze the hydrolysis of glycosidic bonds. By contrast, the mechanism of the glycosidases in glycoside hydrolase family 4 has been recently proposed to involve NAD+-mediated redox steps along with alpha,beta-elimination and addition steps via anionic intermediates. Support for this mechanism in BglT, a 6-phospho-beta-glucosidase in family 4, has been provided through mechanistic and X-ray crystallographic analyses [Yip, V. L.Y., et al. (2004) J. Am. Chem. Soc. 126, 8354-8355] in which primary deuterium kinetic isotope effects for the hydride abstraction at C3 and for the alpha-proton abstraction at C2 indicate that these two steps are both partially rate-limiting. Current data reveal that there is no secondary deuterium kinetic isotope effect associated with the rehybridization of the C1 sp3 center to a sp2 center. Furthermore, a flat linear free energy relationship was established with a series of aryl 6-phospho-beta-D-glucosides of varying leaving group abilities. Taken together, these data indicate that cleavage of the C1-O1 linkage does not occur during a rate-limiting step. Since the deprotonation at C2 is slow and partially rate-limiting while the departure of the leaving group is not, a stepwise E1(cb)-type mechanism rather than an E1 or a concerted E2-syn mechanism is proposed. Direct evidence for the role of NAD+ was obtained by reduction in situ using NaBH4 leading to an inactive enzyme that could be reactivated by the addition of excess NAD+. This was accompanied by the expected UV-vis spectrophotometric changes.

Catalysis↗
PubMed1997

Solution structure of the minor conformer of a DNA duplex containing a dG mismatch opposite a benzo[a]pyrene diol epoxide/dA adduct: glycosidic rotation from syn to anti at the modified deoxyadenosine.

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants whose metabolism in mammals results in deleterious cell transformation. Covalent modification of DNA by diol epoxides metabolically formed from PAHs such a benzo[a]pyrene (BaP) provides a mechanism for the genotoxicity, mutagenicity, and carcinogenicity of PAHs. We had previously reported NMR evidence for a minor conformer of the duplex d(G1G2T3C4A5*C6G7A8G9).d(C10T11C12G13G14G15A16C17C18) containing a dG14 mismatch opposite a dA5* residue modified at the exocyclic amino group by trans addition to (+)-(7R,8S,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a] pyrene [Yeh, H.J.C., Sayer, J.M., Liu, X., Altieri, A.S., Byrd, R.A., Lashman, M.K., Yagi, H., Schurer, E.J., Gorenstein, D.G., & Jerina, D.M. (1995) Biochemistry 34, 13570-13581]. In the present work, we describe the structure of this minor conformer (ca. 17% of the total conformer population). This represents the first structural determination of a minor conformer of a carcinogen-lesion DNA adduct. Two-dimensional NOESY, ROESY, TOCSY, and exchange-only spectra at 750 MHz allowed nearly complete sequential assignment of both conformers. In the minor conformer, the adducted base assumes an anti-glycosidic torsion angle whereas in the major conformer it assumes an unusual syn-glycosidic torsion angle. The aromatic hydrocarbon in the minor conformer is intercalated between dG13 and dG14, preserving the energetically favorable stacking interactions found in the major conformer. The major structural differences between the two conformers appear to be near the lesion site as evidenced by the large chemical shift differences between major and minor conformer protons near the lesion site; away from this site, the chemical shifts of the major and minor conformer protons are nearly identical. Because any of the conformations of benzo[a]pyrene diol epoxide-modified DNA may contribute to tumorigenic activity, structural determination of all conformations is essential for the elucidation of the mechanism of cell transformation initiated by covalent modification of DNA by PAHs.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1998

Snapshots along an enzymatic reaction coordinate: analysis of a retaining beta-glycoside hydrolase.

The enzymatic hydrolysis of O-glycosidic linkages is one of the most diverse and widespread reactions in nature and involves a classic "textbook" enzyme mechanism. A multidisciplinary analysis of a beta-glycoside hydrolase, the Cel5A from Bacillus agaradhaerens, is presented in which the structures of each of the native, substrate, covalent-intermediate, and product complexes have been determined and their interconversions analyzed kinetically, providing unprecedented insights into the mechanism of this enzyme class. Substrate is bound in a distorted 1S3 skew-boat conformation, thereby presenting the anomeric carbon appropriately for nucleophilic attack as well as satisfying the stereoelectronic requirements for an incipient oxocarbenium ion. Leaving group departure results in the trapping of a covalent alpha-glycosyl-enzyme intermediate in which the sugar adopts an undistorted 4C1 conformation. Finally, hydrolysis of this intermediate yields a product complex in which the sugar is bound in a partially disordered mode, consistent with unfavorable interactions and low product affinity.

Bacillus↗
PubMedDate not supplied

Accelerated biodegradation of poly(vinyl alcohol) by glycosidations of the hydroxyl groups or addition of sugars.

Biodegradabilities of N-acetyl-d-glucosamine (GlcNAc)- (1) and chitobiose-substituted (2) poly(vinyl alcohol)s (PVA)s in a soil suspension (pH 6.5) were investigated at 25 degrees C for 40 days. Biochemical oxygen demand of 1 with a degree of substitution of 0.2-0.3 (DP = 430-480) was higher than that of PVA under the degradation condition. Size exclusion chromatography, (1)H NMR, and Fourier-transform infrared measurements of the recovered sample indicated that biodegradation of the PVA main chain was accelerated by partial glycosidation of hydroxyl groups in PVA. Similar acceleration was observed in a PVA/GlcNAc (50:50, w/w) mixture. Microbes which relate with degradation of the glycosidated polymers were grown in a culture medium including the soil suspension and the polymer as the carbon source. Polyacrylamide gel electrophoresis (SDS-PAGE) and IR measurements indicated that a cell-free extract derived from GlcNAc-substituted PVA was different from that in the PVA/GlcNAc mixture. The results suggested that the PVA main chain in GlcNAc-substituted PVA was cleaved by a different microorganism or via a mechanism different from that in the mixture. Chitobiose-substituted PVA 2 showed more enhanced acceleration, indicating that the sugar length influenced the degradability.

Biodegradation, Environmental↗
PubMed2002

Conformational selection of glycomimetics at enzyme catalytic sites: experimental demonstration of the binding of distinct high-energy distorted conformations of C-, S-, and O-glycosides by E. Coli beta-galactosidases.

We show that the conformational features of the molecular complexes of E. coli beta-galactosidase and O-glycosides may differ from those formed with closely related compounds in their chemical nature, such as C- and S-glycosyl analogues. In the particular case presented here, NMR and ab initio quantum mechanical results show that the 3D-shapes of the ligand/inhibitor within the enzyme binding site depend on the chemical nature of the compounds. In fact, they depend on the relative size of the stereoelectronic barriers for chair deformation or for rotation around Phi glycosidic linkage.

Binding Sites↗
PubMed2003

DFT analysis of NMR scalar interactions across the glycosidic bond in DNA.

The relationship between the glycosidic torsion angle chi, the three-bond couplings (3)J(C2/4-H1') and (3)J(C6/8-H1'), and the one-bond coupling (1)J(C1'-H1') in deoxyribonucleosides and a number of uracil cyclo-nucleosides has been analyzed using density functional theory. The influence of the sugar pucker and the hydroxymethyl conformation has also been considered. The parameters of the Karplus relationships between the three-bond couplings and chi depend strongly on the aromatic base. (3)J(C2/4-H1') reveals different behavior for deoxyadenosine, deoxyguanosine, and deoxycytidine as compared to deoxythymidine and deoxyuridine. In the case of (3)J(C6/8-H1'), an opposite trans to cis ratio of couplings is obtained for pyrimidine nucleosides in contrast to purine nucleosides. The extremes of the Karplus curves are shifted by ca. 10 degrees with respect to syn and anti-periplanar orientations of the coupled nuclei. The change in the sugar pucker from S to N decreases (3)J(C2/4-H1') and (3)J(C6/8-H1'), while increasing (1)J(C1'-H1') for the syn rotamers, whereas all of the trends are reversed for the anti rotamers. The influence of the sugar pucker on (1)J(C1'-H1') is interpreted in terms of interactions between the n(O4'), sigma*(C1'-H1') orbitals. The (1)J(C1'-H1') are related to chi through a generalized Karplus relationship, which combines cos(chi) and cos(2)(chi) functions with mutually different phase shifts that implicitly accounts for a significant portion of the related sugar pucker effects. Most of theoretical (3)J(C2/4-H1') and (3)J(C6/8-H1') for uracil cyclo-nucleosides compare well with available experimental data. (3)J(C6/8-H1') couplings for all C2-bridged nucleosides are up to 3 Hz smaller than in the genuine nucleosides with the corresponding chi, revealing a nonlocal aspect of the spin-spin interactions across the glycosidic bond. Theoretical (1)J(C1'-H1') are underestimated with respect to the experiment by ca. 10% but reproduce the trends in (1)J(C1'-H1') vs chi.

DNA↗
PubMed2003

2,3-anhydrosugars in glycoside bond synthesis. NMR and computational investigations into the mechanism of glycosylations with 2,3-anhydrofuranosyl glycosyl sulfoxides.

We report here the combined use of computational chemistry and low-temperature NMR spectroscopy to probe the mechanism of a highly stereoselective glycosylation reaction employing 2,3-anhydrofuranosyl glycosyl sulfoxides (2 and 4). The reaction involves a two-step process that is carried out in one pot. In the first step, the sulfoxide is reacted with triflic anhydride leading to the formation of a single intermediate. Using NMR spectroscopy, we have established the structure of this intermediate as a glycosyl triflate. In the second step, the acceptor alcohol is added to the reaction mixture, which leads to the highly stereocontrolled formation of the glycoside product. The structure of the major product is consistent with a pathway involving an S(N)2-like displacement of the triflate by the alcohol. In the predominant intermediate that is formed, there is a trans relationship between the triflate group and epoxide. Therefore, in the glycoside product there is a cis relationship between the epoxide and the aglycone. In addition to providing insight into these reaction pathways, these investigations have also allowed us to identify conditions under which the glycosylations can be made to proceed with even greater stereoselectivity and in higher yield.

Cold Temperature↗
PubMed2003

Regioselective synthesis of unsymmetrical C-aryl glycosides using silicon tethers as disposable linkers.

Silicon tethers were employed to control the regiochemistry of Diels-Alder reactions between substituted benzynes and glycosyl furans as a key step in the syntheses of unsymmetrical representatives of three major groups of C-aryl glycosides. The cycloaddition precursors were readily prepared by O-alkylation of substituted phenols with various sugar-substituted furylsilane derivatives. Selective deprotonation on the benzene ring of these ethers led to a benzyne that underwent an intramolecular Diels-Alder reaction to give bridged cycloadducts. Fluoride-induced removal of the silicon tether and acid-catalyzed ring opening of the oxabicycloheptadiene subunit yielded the desired C-aryl glycosides as single isomers.

Benzene Derivatives↗