Showing papers on "Pyranose published in 2000"

Fungal pyranose oxidases : occurrence, properties and biotechnical applications in carbohydrate chemistry

Abstract: Pyranose oxidases are widespread among lignin-degrading white rot fungi and are localized in the hyphal periplasmic space. They are relatively large flavoproteins which oxidize a number of common monosaccharides on carbon-2 in the presence of oxygen to yield the corresponding 2-keto sugars and hydrogen peroxide. The preferred substrate of pyranose oxidases is d-glucose which is converted to 2-keto-d-glucose. While hydrogen peroxide is a cosubstrate in ligninolytic reactions, 2-keto-d-glucose is the key intermediate of a secondary metabolic pathway leading to the antibiotic cortalcerone. The finding that 2-keto-d-glucose can serve as an intermediate in an industrial process for the conversion of d-glucose into d-fructose has stimulated research on the use of pyranose oxidases in biotechnical applications. Unique catalytic potentials of pyranose oxidases have been discovered which make these enzymes efficient tools in carbohydrate chemistry. Converting common sugars and sugar derivatives with pyranose oxidases provides a pool of sugar-derived intermediates for the synthesis of a variety of rare sugars, fine chemicals and drugs.

Studies of UDP-Galactopyranose Mutase from Escherichia coli: An Unusual Role of Reduced FAD in Its Catalysis

Abstract: The galactofuranose moiety found in many surface constituents of microorganisms is derived from UDP-d-galactopyranose (UDP-Galp) via a unique ring contraction reaction catalyzed by UDP-Galp mutase This enzyme, which has been isolated from several bacterial sources, is a flavoprotein where the FAD coenzyme is noncovalently bound Since its catalysis does not appear to involve a redox mechanism, whether the enzyme-bound FAD plays an active role in the reaction mechanism has been obscure To study this transformation, the corresponding E coli mutase was purified, and the ring contraction product, UDP-Galf, was chemically synthesized Using UDP-Galf as the substrate, a Km of 194 μM and a kcat of 15 s-1 for the catalysis in the reverse direction were obtained The preference of the reaction toward the pyranose product was confirmed by an equilibrium constant of 0057 in the forward direction Interestingly, when the enzyme was reduced by sodium dithionite, its catalytic efficiency was increased by more than

Synthesis of 3,7-anhydro-D-glycero-D-ido-octitol 1,5,6-trisphosphate as an IP(3) receptor ligand using a radical cyclization reaction with a vinylsilyl tether as the key step. Conformational restriction strategy using steric repulsion between adjacent bulky protecting groups on a pyranose ring

Abstract: 3,7-Anhydro-d-glycero-d-ido-octitol 1,5,6-trisphosphate (5) was designed as a novel IP3-receptor ligand having a C-glycosidic structure and was synthesized via a radical cyclization reaction with a temporary connecting vinylsilyl tether as the key step. The phenyl 2-O-dimethylvinylsilyl-3,4,6-tri-O-benzyl-1-seleno-β-d-glucopyranoside (7), in the usual 4C1-conformation, was successively treated with Bu3SnH/AIBN and under Tamao oxidation conditions to give a mixture of five C-glycosidic products. On the other hand, similar successive treatment of the corresponding 3,4-di-O-TBS-protected substrates 13 and 24, which were in an unusual 1C4-conformaion due to the steric repulsion between the bulky silyl protecting groups, gave the desired 1α-C-glycosides 18 and 25, respectively, as the major products. Thus, the course of the radical cyclization was effectively controlled by a change in the conformation of the pyranose ring into a 1C4-form due to steric repulsion between the adjacent bulky TBS-protecting groups ...

Ligand recognition by the lactose permease of Escherichia coli: specificity and affinity are defined by distinct structural elements of galactopyranosides.

Abstract: Specificity of substrate recognition in lactose permease is directed toward the galactosyl moiety of lactose. In this study, binding of 31 structural analogues of D-galactose was examined by site-directed N-[(14)C]ethylmaleimide-labeling of the substrate-protectable Cys148 in the binding site. Alkylation of Cys148 is blocked by D-galactose with an apparent affinity of approximately 30 mM. Epimers of D-galactose at C-3 (D-gulose) and C-4 (D-glucose) or deoxy derivatives at these positions exhibit no binding whatsoever, indicating that these OH groups participate in essential interactions. Interestingly, the C-2 epimer alpha-D-talose binds almost as well as D-galactose, while 2-deoxy-D-galactose affords no substrate protection, indicating that nonstereospecific H-bonding at C-2 is required for stable binding. No substrate protection is detected with D-fucose, L-arabinose, 6-deoxy-6-fluoro-D-galactose, 6-O-methyl-D-galactose, or D-galacturonic acid, suggesting that the C-6 OH is an essential H-bond donor. Both alpha- and beta-methyl D-galactopyranosides bind more strongly than galactose, supporting the notion that the cyclic pyranose conformation is the bound form and that the anomeric configuration at C-1 does not contribute to substrate specificity. However, methyl or allyl alpha-D-galactopyranosides exhibit 60-fold lower apparent K(d)'s than D-galactose, demonstrating that binding affinity is significantly influenced by the functional group at C-1 and its orientation. Taken together, the observations confirm and extend the current binding site model [Venkatesan, P., and Kaback, H. R. (1998) Proc. Natl. Acad. Sci. U.S.A. 95, 9802-9807] and indicate that specificity toward galactopyranosides is governed by H-bonding interactions at C-2, C-3, C-4, and C-6 OH groups, while binding affinity can be increased dramatically by hydrophobic interactions with the nongalactosyl moiety.

Structural analysis of the core region of lipopolysaccharides from Proteus mirabilis serotypes O6, O48 and O57.

Abstract: The structure of lipid A core region of the lipopolysaccharides (LPS) from Proteus mirabilis serotypes O6, O57 and O48 was determined using NMR, MS and chemical analysis of the oligosaccharides, obtained by mild acid hydrolysis, alkaline deacylation, and deamination of LPS: Incomplete substitutions are indicated by bold italic type. All sugars are present in pyranose form, α-Hep is the residue of lglycero-α-dmanno-Hep, α-dd-Hep is the residue of dglycero-α-dmanno-Hep, l-Ara4N is 4-amino-4-deoxy-l-arabinose, Qui4NAlaAla is the residue of 4-N-(l-alanyl-l-alanyl)-4-amino-4,6-dideoxyglucose. All sugars except l-Ara4N have d-configuration. β-GalA* is partially present in the form of amide with 1,4-diaminobutane (putrescine)-HN(CH2)4NH2 or spermidine-HN(CH2)3NH(CH2)4NH2.

Stereoselective synthesis of C-glycosylphosphonates from their ketols. Reconsideration of an abandoned route

Abstract: Isosteric phosphonate analogues of glycosyl 1-phosphates have been obtained by addition of LiCH 2 P(O)(OMe) 2 to glyconolactones followed by Et 3 SiH–TMSOTf reductive dehydroxylation of the resultant ketols. The compounds prepared include four β-linked pyranose derivatives ( d - galacto , 2-azido-2-deoxy- d - galacto , d - gluco , d - manno ) and one β-linked furanose derivative ( d - manno ). In the latter case the ketol was activated as its 2-acetate. In agreement with an observation in another laboratory, the dehydroxylation of a model ketol phosphonate failed with the use of Et 3 SiH–BF 3 ·Et 2 O.

Structure and spectroscopic properties of luminescent cyclometalated platinum(II) complexes with chiral phosphine substituted carbohydrate ligands

Abstract: A series of new chiral cyclometalated platinum(II) complexes containing carbohydrate phosphine ligands have been prepared. The reaction of [Pt(ppy)Cl]2 (Hppy = 2-phenylpyridine) with the chiral phosphines n-Hmbpa (methyl 4,6-O-benzylidene-n-deoxy-n-(diphenylphosphino)-α-D-altropyranoside, n = 2 or 3) afforded cis-[Pt(ppy)(n-Hmbpa)Cl] (n = 2 2a or 3 2b) in high yields. Treatment of 2a or 2b with an excess of NaOCH3 gave the alkoxoplatinum(II) complexes trans-[Pt(ppy)(n-mbpa)] (n = 2 3a or 3 3b). The crystal structure of 3b shows that the phosphorus atom is located trans to the nitrogen atom of the ppy ligand and the pyranose ring is in a boat conformation. Moderately intense UV-vis absorption bands assigned to metal-to-ligand charge-transfer (MLCT) transitions are shifted from ca. 376–382 to ca. 414–416 nm when the chloride ligand is substituted by the pendant alkoxide group. In solid state and 77 K MeOH–EtOH (4∶1) glass solution, complexes 2 and 3 show a vibronic structured emission in the range 450–650 nm. Complex 2 is non-emissive in fluid solution at room temperature whereas 3 shows a long-lived 3MLCT emission in both CH3CN and CH2Cl2 at room temperature.

Analysis of neutral isomeric low molecular weight carbohydrates using ferrocenyl boronate derivatization and tandem electrospray mass spectrometry

Abstract: A new analytical technique for small carbohydrates utilizing the cyclic ferrocenyl boronic esters (FcBors) of several neutral mono- and disaccharides is demonstrated. Distinction between the diastereomers of mono- and disaccharides is obtained. Analysis is by tandem electrospray-mass spectrometry (ES-MS) using a modified ion-source that promotes the preformation of ions. Selection of the molecular ion produced during single-electron oxidation of the ferrocene moiety of a specific population of saccharide isomers permits a variety of collisionally induced dissociation (CID) experiments. The resultant MS2/MS3 spectra reflect the ensemble of possible cyclic esters in equilibrium. An array of stable cross pyranose ring fragment ions representing sequential carbon loss as 30 u is observed. Consequently, the system provides an information-rich set of MSn spectra containing large amounts of structural information. Identification of D-glucose (D-Glc), its two commonly found epimers (D-mannose and D-galactose), and the two major L-diastereomers of 6-dideoxymonosaccharides, L-fucose (L-Fuc) and L-rhamnose (L-Rhm), are demonstrated. Selected pairs of disaccharides can be distinguished in terms of their anomeric linkage by reference to their MS3 spectra.

Differential Carbohydrate Recognition of Two GlcNAc-6-sulfotransferases with Possible Roles in L-Selectin Ligand Biosynthesis

Abstract: Two human GlcNAc-6-sulfotransferases, CHST2 and HEC-GlcNAc6ST, have been recently identified as possible contributors to the inflammatory response by virtue of their participation in L-selectin ligand biosynthesis. Selective inhibitors would facilitate their functional elucidation and might provide leads for antiinflammatory therapy. Here we investigate the critical elements of a disaccharide substrate that are required for recognition by CHST2 and HEC-GlcNAc6ST. A panel of disaccharide analogues, bearing modifications to the pyranose rings and aglycon substituents, were synthesized and screened for substrate activity with each enzyme. Both GlcNAc-6-sulfotransferases required the 2-N-acetamido and 4-hydroxyl groups of a terminal GlcNAc residue for conversion to product. Both enzymes tolerated modifications to the reducing terminal pyranose. Key differences in recognition of an amide group in the aglycon substituent were observed, providing the basis for future glycomimetic inhibitor design.

Synthetic Studies on Nogarol Anthracyclines. Enantioselective Total Synthesis of an Aminohydroxy Epoxybenzoxocin

Abstract: A chiral synthesis of the aminohydroxy expoxybenzoxocin 6 is described. Enantioselective Friedel-Crafts coupling using a chiral titanium catalyst was employed to produce the optically active atrolactic ester 16a from the phenol 11 and l-menthyl pyruvate (12). The phenolic group in 16a was protected as the benzyl ether and the t-alcohol functionality as the MEM ether to give 20, which after sequential reduction/oxidation provided the aldehyde 22. Addition of the acetylide anion of propargyl aldehyde diethyl acetal (23) to aldehyde 22, followed by oxidation of the resultant diastereoisomeric carbinols, gave the acetylenic ketone 24. Lindlar reduction of 24 afforded the trans-enone 26. Reaction of 26 with thiophenylate anion furnished 27, which was then cyclized to the alpha-methyl pyranoside 29. Oxidation of 29 to the sulfoxide and subsequent thermolysis afforded the hexenulose 30. Sequential epoxidation of 30, reduction of the keto epoxide 31, and reaction of the resultant epoxycarbinol 32 with dimethylamine produced the aminohydroxy pyranose 33a. Debenzylation of 33a to the phenol 33b, followed by intramolecular cyclization, completed the fabrication of the optically active aminohydroxy epoxybenzoxocin 6. The 17-step sequence from the phenol 11 to 6 was achieved in 22% overall yield.

Synthesis of a novel N-selective ester functionalized chitin derivative and water-soluble carboxyethylchitin

Abstract: A novel chitin detivative having a pendant ester function, 2-N-(2-ethoxycarbonylmethyl)chain (2), was synthesized by a Michael-type nucleophilic addition of an amino group of partially deacetylated chitin (1) to ethyl acrylate in phosphate buffer/methanol (5:3, v/v) at 40°C. N-Selective monosubstitution occurred exclusively in the polymer reaction, which was supported by a reaction of methyl 2-ammo-2-deoxy-D-glucopycanoside with ethyl acrylate to afford methyl 2-N-(2-ethexycarbonylethyl)-2-amino-2-deoxy-D-glucopyranoside. The degrees of substitution (DSs) of 2 were determined by 1 H NMR spectroscopy. T1 analysis of 2 was carried out in other to clarify differences of signal intensities of the pendant ester protons and the pyranose ring pronons. The result of the T 1 measurement suggested a relatively restricted molecular motion of the chitin backbone in comparison with the flexible pendant ethyl ester groups. Furthermore, 2-N-(2-carboxyethyl)chitin sodium salt (3) was synthesized from ethyl aorylate and 1 by the Michael addition followed by hydrolysis in 0,1 N NaOH aq, as 40°C, The DSs of 3 were varied from 0.26 to 0.88, which were almost controlled by the reaction period of the Michael reaction from 6 to 168 h. 3 showed good solubility in water. Viscosity measured on a cone-plate viscometer for the 1.0 wt.-% aqueous solution of 3 (DS, 0,26) was 0.074 Pas.sec.

Atropdiastereoisomers of ellagitannin model compounds: configuration, conformation, and relative stability of d-glucose diphenoyl derivatives

Abstract: Conformational analysis reveals a remarkable rigidity of 2,3-, 4,6-, 3,6-, and 2,4- O -( S )- and ( R )-diphenoyl (DP) bridged methyl β- d -glucosides, which were used as model compounds to evaluate the atropisomeric features of the natural ellagitannins, which possess at least one hexahydroxydiphenoyl (HHDP) moiety. The 2,3- and 4,6- O -( S )-DP bridged glucosides with 4 C 1 pyranose geometries are thermodynamically more stable than their ( R )-DP counterparts, whilst in the 3,6- and 2,4- O -linked series with 1 C 4 glucopyranose geometries the ( R )-DP configuration is preferred. The chiral scaffold of glucose exerts a strong atropdiastereoselective effect onto the diphenoyl units, which is mediated through 10- to 12-membered rings via ester linkages. The calculated results not only explain the observed ( S )-diastereoselectivity of di-esterification reactions of suitably protected racemic hexaoxydiphenic acids with 4,6-unsubstituted d -glucopyranose derivatives, but also correlate the observed configuration of axially chiral HHDP-moieties of natural ellagitannins with conformational parameters.

Synthesis and Reactions of Branched-chain Anhydrouloses with Push Pull Functionality

Abstract: The α-oxoketene dithioacetal 1 was demethylthiolated with sodium borohydride to give the branched chain anhydroulose 2 which yielded with amines the corresponding aminomethylene enuloses 3, 4 and 5. The heterocyclic anellated pyranose derivatives 6, 7 and 8 were prepared by reaction of 2 with hydrazine hydrate, methylhydrazine and hydroxylamine, respectively. By treatment of methylthiomethylene enulose 18 with guanidine, acetamidine and benzamidine the pyrimidoanellated pyranose derivatives 12—14 have been obtained.

New Synthesis with Acetylene Biscobalthexacarbonyl Complex (2)

Abstract: Following our previous review of this issue, chemistry of acetylene biscobalthexacarbonyl complex is discussed with special reference in the synthesis of natural and unnatural products. The first example is to do with protein phosphatase inhibitors; thus, okadaic acid and tautomycin are known as strong inhibitors to these enzymes with high specificity of the enzyme type. Hybrid molecules are discussed as unnatural product having enantiomeric spiro moieties. These syntheses have been achieved via enantio-switching method from the same D-glucose derivatives; namely, alkynylation of silylacetylene to sugars provides sugar acetylenes, which are convertible with or without epimerization into α or β heteroolefins leading to enantiomer to each other. Heteroconjugate addition on pyranose ring can provide either syn or anti adduct by switching the chelational anchor and metals of the nucleophile. Pauson-Khand reaction is demonstrated on the sugar acetylenes to provide tricyclic compounds with definite stereoisomer. A macrocyclic ring closure is a specific example of the cobalt complex with C-C bond formation in the critical step. Cobalt chemistry and sugar acetylene chemistry made it possible to provide both of the enantiomers of left end segments of ciguatoxin. This line also discussed to the potential methodology directed toward other portion of this marine natural toxin. These endo-cyclic complexes have reductively been decomplexed into the olefins or vinylsilanes.