Pyranose

About: Pyranose is a research topic. Over the lifetime, 1619 publications have been published within this topic receiving 35348 citations. The topic is also known as: pyranoses & hexopyranose.

o-Xylylene protecting group in carbohydrate chemistry: application to the regioselective protection of a single vic-diol segment in cyclodextrins.

Abstract: A systematic study of the suitability of α,α′-dibromo-o-xylene as a reagent for cyclic o-xylylene protection of vic-diols in different monosaccharide substrates is reported. The installation of this protecting group, formally equivalent to a di-O-benzylation reaction, proceeds with good regioselectivity toward 1,2-trans-diequatorial diol systems in pyranose and furanose rings. Initially, the benzyl ether-type derivative of the more acidic hydroxyl is preferentially formed. Subsequent intramolecular etherification toward the equatorial-oriented vicinal OH is kinetically favored. The methodology has been implemented for the simultaneous protection of the secondary O-2 and O-3 positions of a single d-glucopyranosyl unit in cyclic oligosaccharides of the cyclodextrin (CD) family (cyclomaltohexa-, -hepta-, and -octaose; α, β, and γCD).

Synthesis and Conformational Analysis of(6R)-[6-2H1]-1,2:3,4-Di-O-isopropylidene-.alpha.-D-galactopyranose. NMR and Molecular Modeling Studies

Abstract: The conformation preferences of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose have been determined using NMR and molecular modeling (conformational searching) techniques. The pyranose ring assumes a skew-boat conformation. Coupling constants for the C 6 side chain and hydroxyl proton indicate that the predominant conformation places the oxygen anti to C 4 (gt conformation) with the hydroxyl hydrogen aligned toward the pyranose oxygen in deuteriochloroform. A similar orientation of the C 5 -C 6 bond was observed in water and toluene. In DMSO the C 6 oxygen is anti to the pyranose oxygen (tg conformation) with the hydroxyl hydrogen anti to C 5

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.

Easy and Stereoselective One-Step Incorporation of Two Asymmetric Carbons in Pyranose Derivatives to Acyclic Epoxyamides: New, Potentially Useful Acyclic Chiral Templates.

Abstract: We reacted N,N-diethyl-2-(dimethylsulfuranylidene)acetamide with 4,6-O-alkylidene-glycopyranoses under several experimental conditions and obtained, stereoselectively, derivatives of acyclic 3-(polyhydroxyalkyl)-α,β-epoxyamides. In this way, and in one stage, we introduced, highly stereoselectively, two new chiral carbons with a substituted asymmetric epoxide group that could then be regioselectively transformed and, in addition, obtained highly functionalized acyclic structures starting from easily obtained cyclohemiacetalic monosaccharides. The configuration of the new chiral carbons of the resulting trans-epoxyamides was determined by comparing the IR, NMR, and polarimetric data with another epoxyamide of known configuration. We attempted to explain the stereochemistry of the major products by proposing a preferential conformation for the different starting aldehyde sugars in the basic reaction medium that took into account, at first, the principal electrical interactions between the carbonyl group and...