Showing papers on "Pyranose published in 2006"

Energetics of xylose decomposition as determined using quantum mechanics modeling.

Abstract: The decomposition of xylose has been studied using quantum mechanical calculations supported by NMR data. Proposed mechanisms for the decomposition of xylose have been investigated by obtaining the structures and energies of transition states and products. The intent of this study was to understand the experimentally observed formation of furfural and formic acid that occurs during the decomposition of xylose in mildly hot acidic solutions. A mechanism of furfural formation involving the opening of the pyranose ring and subsequent dehydration of the aldose was compared to a direct intramolecular rearrangement of the protonated pyranose. Energies were determined using CBS-QB3, and it was shown that the barriers for dehydration of the aldose were high compared to intramolecular rearrangement. This result suggests that the latter mechanism is a more likely mechanism for furfural formation. The intramolecular rearrangement step results from protonation of xylose at the O2 hydroxyl group. In addition, it has b...

Traceless Staudinger ligation of glycosyl azides with triaryl phosphines: stereoselective synthesis of glycosyl amides.

Abstract: Alpha-glycosyl amides can be synthesized from the corresponding O-benzyl-alpha-glycosyl azides using a traceless Staudinger ligation with diphenylphosphanyl-phenyl esters 4. All the phosphines employed and their phenol precursors are stable to air at 4 degrees C for months. Fast intramolecular trapping of the reduction intermediates results in the direct formation of the amide link, which, in turn, prevents epimerisation and allows retention of configuration at the anomeric carbon. Yields and alpha-selectivity are high when the reaction is performed in polar aprotic solvents. Removal of the benzyl ether protecting groups is achieved by catalytic hydrogenation. Alpha-glycosyl amides represent a class of virtually unexplored nonhydrolyzable monosaccharide derivatives that may find a useful application as sugar mimics. Conformational studies by NMR spectroscopy confirm that deprotected alpha-glycosyl amides in the gluco, galacto, and fuco series retain the normal pyranose conformation of the monosaccharide. The reaction of phosphines 4 with tetra-O-acetyl-glycosyl azides is nonstereoconservative, and beta-glycosyl amides are obtained in good yields and with complete stereoselectivity starting from both alpha and beta azides.

Temperature scanning FTIR analysis of hydrogen bonding states of various saccharides in amorphous matrixes below and above their glass transition temperatures.

Abstract: Temperature scanning Fourier transform infrared, TS-FTIR, spectroscopy of various amorphous sugar matrixes was conducted to investigate the relationship between the glass transition temperature, T(g), of an amorphous sugar matrix and the nature of the hydrogen bonds in the matrix. An amorphous sugar matrix was prepared by air-drying an aqueous solution of sugar, and the degree of formation of hydrogen bonds in the matrix was evaluated at different temperatures using the peak positions of the IR band corresponding to the O-H stretching vibration at around 3400 cm(-1). The T(g) value increased with increasing peak position of the O-H stretching vibration at T(g) and were correlated reasonably well with the magnitude of the peak shift by the temperature increase (from 25 degrees C) to the T(g) value. This demonstrates that the amorphous sugar matrix, in which the segments are fixed by fewer hydrogen bonds, has a higher thermal resistance. The glycosidic linkage largely contributes to the restriction of the segments, pyranose ring, rather than a hydrogen bond. As the degree of polymerization of pyranose rings increases, the degree of hydrogen bond formation needed to hold the matrix in a fixed position decreases. However, the magnitude of the restriction of pyranose rings by a glycosidic linkage changes depending on the type: the restrictions imposed by alpha-1,1 and -1,6 glycosidic linkages are the tightest and most flexible of all of the types of glycosidic linkages, respectively.

Retardation film, polarizing plate and liquid crystal display device

Abstract: A retardation film containing (a) at least one cellulose derivative selected from the group consisting of methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, cellulose acetate trimellitate and cellulose nitrate, wherein the cellulose derivative has a total acyl group substitution degree of 20 to 28; and (b) an esterified compound in which all or a part of the OH groups in a compound (A) or in a compound (B) are esterified by at least one aromatic monocarbolyxic acid, wherein the compound (A) comprises one of a furanose structure and a pyranose structure, and the compound (B) comprises two to twelve of at least one of a furanose structure and a pyranose structure, which are bonded in the compound (B)

New biotransformations of some reducing sugars to the corresponding (di)dehydro(glycosyl) aldoses or aldonic acids using fungal pyranose dehydrogenase

Abstract: The fungal enzyme pyranose dehydrogenase (PDH) (EC 1.1.99.29) purified to apparent homogeneity from culture media of Agaricus meleagris catalyzed the substrate-dependent C-1, C-2, C-3, C-1,3′ or C-2,3(′) (di)oxidation of a number of mono- and disaccharides with 1,4-benzoquinone as an electron acceptor. d -Ribose, d -allose, d -gulose and d -talose were oxidized to the corresponding aldonic acids. l -Arabinose was converted exclusively to 2-dehydro- l -arabinose ( l -erythro-pentos-2-ulose) whereas d -xylose underwent competing C-2 and C-3 oxidation followed by dioxidation to 2,3-didehydro- d -arabinose ( d -glycero-pentos-2,3-diulose). The major final oxidation products of maltose and cellobiose were the novel compounds 2,3′-didehydromaltose and 2,3′-didehydrocellobiose (α- and β- d -ribo-hexos-3-ulopyranosyl-(1 → 4)- d -arabino-hexos-2-ulose), formed via 2- and 3′-monooxidation intermediates. Minor concomitant (di)oxidation at C-1,(3′) to the corresponding bionic acids also took place. Maltotriose was preferentially oxidized at C-3″ of the terminal glucopyranosyl unit and at C-1 of the reducing moiety. The structures of these sugar oxidation products were established by in situ 1D and 2D NMR spectroscopy and ESI–MS. Based on HPLC analysis, conversions of (glycosyl)aldoses in non-buffered systems were nearly quantitative within 3–24 h, depending on the substrate. As the enzyme allows an easy access to highly reactive di- or tricarbonyl sugars, it might become a useful catalyst in carbohydrate chemistry.

Dehydrative Glycosylation in Water Using a Bronsted Acid-Surfactant-Combined Catalyst

Abstract: Bronsted acid-surfactant-combined catalyst, dodecylbenzenesulfonic acid (DBSA), was used in catalytic dehydrative glycosylation reactions in water. 1-Hydroxy sugars, such as O-benzyl-protected furanose and pyranose, reacted with alcohols and a nitrogen nucleophile in the presence of a catalytic amount of DBSA to afford the desired adducts in good yields. Detailed study of the glycosylation of 2-deoxy-D-ribofuranose showed that hydrophobicity of the substrates was important to attain higher yields. Regarding the α/β selectivities, D-ribose and D-mannose derivatives gave the products in high β- and α-selectivities, respectively.

Reaction Geometry and Thermostable Variant of Pyranose 2-Oxidase from the White-Rot Fungus Peniophora sp.

Abstract: Pyranose 2-oxidase catalyzes the oxidation of a number of carbohydrates using dioxygen; glucose, for example, is oxidized at carbon 2. The structure of pyranose 2-oxidase with the reaction product 2-keto-β-d-glucose bound in the active center is reported in a new crystal form at 1.41 A resolution. The binding structure suggests that the α-anomer cannot be processed. The binding mode of the oxidized product was used to model other sugars accepted by the enzyme and to explain its specificity and catalytic rates. The reported structure at pH 6.0 shows a drastic conformational change in the loop of residues 454−461 (loop 454−461) at the active center compared to that of a closely homologous enzyme analyzed at pH 4.5 with a bound acetate inhibitor. In our structures, the loop is highly mobile and shifts to make way for the sugar to pass into the active center. Presumably, loop 454−461 functions as a gatekeeper. Apart from the wild-type enzyme, a thermostable variant was analyzed at 1.84 A resolution. In this v...

Pectin isolated from white cabbage – structure and complement-fixing activity

Abstract: This study was done to investigate whether white cabbage contained polysaccharides with immunostimulatory activity using the complement-fixing test as an indicator. The main polysaccharide isolated was of pectin nature. Methanolysis and (13)C-NMR showed that the polymers consisted of highly esterified alpha-galactopyranoside (alpha-GalpA), significant amounts of alpha-arabinose furanoside (alpha-Araf), beta-Galp and lesser amounts of rhamnose in the pyranose form (Rhap) and xylose in the pyranose form (Xylp). Linkage analyses showed that the alpha-GalpA residues were mainly 1,4-linked with small amounts of 1,3,4-linkages. The alpha-Araf residues were mainly terminally (t)- and 1,5-linked, whereas beta-Galp was t-, 1,3-, 1,6-, and 1,3,6-linked. Positive Yariv reaction indicated polymers with arabinogalactan type 2 like structures. alpha-Rhap was mainly present as 1,2- and 1,2,4-linked residues and Xylp was t- and 1,4-linked. The molecular weight varied greatly and was from 10 to 150 kDa. Cabbage polymers had biological activity and this complement-fixing activity was greatly affected by hydrolytic removal of Araf from pectic side chains.

Palladium-catalyzed P-arylation of hydrophosphoryl derivatives of protected monosaccharides

Abstract: Palladium-catalyzed arylation of hydrophosphorylated protected monosaccharides of the pyranose and furanose series gave the corresponding P-aryl derivatives.

Haircare Use Of C-Glycoside Derivatives

Abstract: The present invention relates to the cosmetic use of at least one compound of general formula (I), in which: - X represents a radical chosen from the groups, with R1, R2 and R3 representing, independently of each other, a hydrogen atom, an OH group or a radical R with R as defined below, - R represents an alkyl radical, a polyfluoroalkyl or perfluoroalkyl radical or an aryl radical, - S represents a monosaccharide or a polysaccharide comprising upto 20 sugar units, in pyranose and/or furanose form and of L and/or D series, and - the bond S-C represents a bond of C-anomeric nature, or a salt or isomer thereof, for increasing the mechanical strength of keratin fibers.

Hetero‐Diels–Alder Reaction with Thiazolyl Oxabutadienes—Model Studies Toward the Synthesis of Directly Linked C‐Disaccharide

Abstract: A method for the construction of substituted pyranoses by means of the hetero-Diels–Alder (HDA) reaction of ethyl vinyl ether with 1-oxabuta-1,3-dienes bearing a thiazolyl ring at C-2 is described. The cycloaddition with 1-(thiazol-2-yl)-2-penten-1-one (2) occurred with good endo/exo selectivity to give cis- and trans-3,4-dihydro-2H-pyrans 3a and 3b in a ca. 9:1 ratio and 91% overall yield. The elaboration of 3a through the conversion of the thiazole ring into the formyl group and reduction of the latter to alcohol, followed by hydroxylation of the double bond through hydroboration–oxidation led to the ethyl 2,3-dideoxypyranoside 8. The asymmetric version of this synthetic sequence started from the HDA cycloaddition of the same alkene with the chiral oxabutadiene 10 bearing the D-galacto-pentopyranosid-5-yl moiety at C-3. This reaction afforded a mixture of the four diastereomeric cycloadducts—3,4-dihydro-2H-pyrans 11a,b and 12a,b—in 97% overall yield. The reaction was moderately endo and face selective. A high level of endo selectivity (96%) was obtained by the use of catalytic Eu(fod)3. The elaboration of the endo cycloadducts 11a and 12a by the same synthetic sequence as that developed for 3a (i.e. thiazolyl-to-formyl conversion and hydroxylation of the double bond) gave the uncommon C-disaccharides 15 and 16 featuring two directly linked pyranose rings.

Synthesis of urea-tethered disaccharides in water.

Abstract: A new method for the synthesis of urea-linked disaccharides in aqueous media has been developed. The key feature of our approach is two strained Steyermark-type gluco- and galactopyranosyl oxazolidinones. Each oxazolidinone is attached to a pyranose ring in a di-equatorial trans-annulation framework. Reaction of these oxazolidinones with 4-aminohexopyranose in water proceeded smoothly to afford the urea-tethered cellobiose and lactose analogues. The galactose-type oxazolidinone proved to be more reactive than the glucose-type, which is explained by the presence of an axial hydroxy group at C4 in the former.

A stereoselective synthesis of 6,6,6-trifluoro-L-daunosamine and 6,6,6-trifluoro-L-acosamine

Abstract: A short synthesis of 6,6,6-trifluoro-L-acosamine 15 and 6,6,6-trifluoro-L-daunosamine 19 has been accomplished. The pyranose ring system of these carbohydrate analogues was formed by a hetero-Diels–Alder reaction of vinylogous imide 11 and ethyl vinyl ether which gave adduct 12a in 40% yield. Hydroboration gave 13 and subsequent hydrogenolytic removal of the (R)-2-phenylethyl chiral auxiliary gave ethyl 6,6,6-trifluoro-L-acosaminide 14. Acid hydrolysis furnished target 15. Glycoside 13 was N-trifluoroacetylated to give 16, the structure was confirmed by single crystal X-ray diffraction. The C-4 stereochemistry of 16 was inverted by Swern oxidation of the 4-OH group, and subsequent borohydride reduction to give 17. Hydrogenolytic removal of the auxiliary gave ethyl-6,6,6-trifluoro-L-daunosaminide 18. Acid hydrolysis provided 19.

Chemistry of carbohydrate aziridines.

Abstract: Publisher Summary This chapter discusses the chemistry of carbohydrate aziridines, with emphasis being placed on surveying preparative methods and ring-opening reactions. Carbohydrate aziridines or epimines are derivatives in which an aziridine ring is fused to a pyranose or furanose ring or to an exocyclic part of a carbohydrate molecule. From the mechanistic point of view, the reported syntheses of carbohydrate aziridines are based almost exclusively on S N 2 intramolecular nucleophilic substitution. The nucleophile is a nitrogen-containing group, often free or an N -substituted amino group, which can be generated in situ by the reduction of an azido or cyano group, or by the Michael addition of amines to a double bond with appropriate substitution. The neighboring leaving group is typically an alkyl (aryl)sulfonyloxy group, or is generated in situ , which is the case with the Mitsunobu reaction. The aziridine-ring closure invariably proceeds with the inversion of configuration at the atom bearing the leaving group. The stereochemistry of S N 2 nucleophilic substitution strongly favors the antiperiplanar disposition of the participating groups in the transition state. This chapter describes the methods for the synthesis of carbohydrate aziridines. It also explains the general properties of carbohydrate aziridines and elaborates the reactions of carbohydrate aziridines.

Synthesis of Some Protected 6-O-Acyl-Galactopyranose Derivatives

Abstract: O-Pivaloyl, 6-O-benzoyl, 6-O-(2-chlorobenzoyl), 6-O-(4-chlorobenzoyl) and 6-O- benzenesylfonyl derivatives (5-9) of 1,2:3,4-di-O-isopropylidene-a-D-galactopyranose (4) were synthesized in reasonably high yields. All the compounds (5-9) showed distortion from the regular pyranose ring of galactose due to the presence of two five-membered isopropylidene rings as evident from 1 H NMR spectra.

Catalytic, Stereoselective Glycosylation - Spiroketalization of 3,4,5-Tri-O-benzyl-b-D-fructopyranose Generating Di-D-fructopyranose- 1,2’:2,1’-dianhydride

Abstract: α-D-Fructopyranose β-D-fructopyranose-1,2':2,1'- dianhydride has been stereoselectively synthesized by tandem catalytic glycosylation-spiroketalization of 3,4,5-tri-O-benzyl-β-D-fructo- pyranose. Of the several protic acid catalysts which exist, 0.3 molar equivalent trifluoromethane sulfonic acid in toluene was found to be most effective to afford the dianhydride in good yield.

New C-glycoside compounds are tyrosinase inhibitors used in depigmenting and/or bleaching skin or hair

Abstract: C-Glycoside compounds (I), are new. C-Glycoside compounds of formula (I) and their salts, solvates and isomers, are new. S1monosaccharide or polysaccharide having up to 20 sugar units, in pyranose and/or furanose form and L and/or D series, where the mono- or poly-saccharide has at least one free OH group and/or optionally protected amino group, and S1 is connected by a C-glycosidic bond; X : H, -OR1, -NR1R2 or (=O); Y1-OR3, -NR1R2 or -OSi(R4)3; Z : F, 1-6C alkyl, 3-6C cycloalkyl, -OR1, -NR1R2, -COR1, -CO2R1, -CONR1R2 or -CF3; m : 0-4; R1, R2H, 1-6C alkyl, 3-6C cycloalkyl, aralkyl or phenyl; R3R1, R2, -SO3H, -PO3H2 or -COR1, and R41-6C alkyl, 3-6C cycloalkyl or phenyl, provided that when m is 0, then Y1 is -OCH3 and S1 is not D-(or L-)glucose, L-fucose, D-(or L-)xylose and D- (or L-)maltose. An independent claim is also included for a composition (II) comprising (I). [Image] ACTIVITY : Dermatological. MECHANISM OF ACTION : Tyrosinase inhibitor.