Hexo

Derivatives of 6-deoxy-hex-5-enopyranosides are important intermediates in the synthesis of dicarbonyl sugars, namely hexos-5-uloses. For... 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

Figure 5.9 Models of hexo-kinase in space-filling and wireframe formats, showing the cleft that contains the active site where substrate binding and reaction catalysis occur. At the bottom is an X-ray crystal structure of the enzyme active site, showing the positions of both glucose and ADP as well as a lysine amino acid that acts as a base to deprotonate glucose.

D-arab/no-Hexos-3-ulose Methyl p-o-xy/o-hexopyranosid-4-ulose... 

Example CH=N-NHPh 1 CH = N—NHPh HOCH HCOH HCOH i ch2oh D-araib/no-Hexos-2-ulose bis(phenylhydrazone)... 

D-arab/no-Hexos-2-ulose phenylosotriazole or (1 fl)-1-(2-phenyl-2H-1,2,3-triazol-4-yl))-D-erythritol or 2-phenyl-4-(D-arab/no-1,2,3,4-tetrahydroxybutyl)-2H-1,2,3-triazole... 

Deoxy-D-arafa/no-hexos-2-id-2-yl or 2-deoxy-D-arab/no-hexopyranos-2-ylidene radical anion... 

T ri-0-benzyl-a-D-arab//Jo-hexos-2-ulo-2,6-pyranosyl bromide or 3,4,5-tri-0-benzyl-a/de/iydo-a-D-arab/no-hexos-2-ulopyranosyl bromide... 

Two branched-chain sugars, methyl 3-azido-4,6-0-benzylidene-2,3,-dideoxy-3-C-(fluoromethyl)-a-D-flraZ)/ o-hexopyranoside and methyl 2-azido-4,6-0-benzylidene-2,3-dideoxy-2-C-(fluoromethyl)-) -D-r/to-hexo-pyranoside have been prepared through the usual displacement reactions. 

The type-specific capsular polysaccharide from Streptococcus pneumoniae type 5 contains 2-acetamido-2,6-dideoxy- -D-x>>/o-hexopyranosyl-4-ulose residues (17). Sugar nucleotides of hexos-4-uloses are important intermediates in the transformation of sugars during the biosynthesis, but this is the only known example of such a sugar as a polysaccharide component. 

The structures of the a-D-aldo-pento and -hexo-pyranose monosaccharides are shown in Pig. 1. In all cases, these sugars will be studied as the six-membered-ring tautomer, as shown. 

C -CP-MAS NMR provides subtle information about the degree of solvation of the polymer chains of a CFP in a given solvent and consequently it may be qualitatively correlated with the nanometer scale morphology of the polymer matrix. In fact, the prerequisite that enables a polymer framework to develop a nanoporosity is the ability of the polymer chains and its pendants to be suitably solvated by the liquid medium [26-28]. Therefore, C -CP-MAS NMR spectra provide the basis for a first level screening of the possibility of a CFP in a given solvent to be employed as an hexo-template, able to accommodate metal nanoclusters chemically produced in its interior (see below and Ref. [29]). 

C16HS0O6 Methyl 3-C-acetyl-4,6-0-benzylidene-2-deoxy-cr-D-rii>o-hexo-pyranoside MABRHP 43 243... 

Esterification of several methyl 4,6-O-benzylidene-D-hexo-pyranosides with one molar equivalent of benzoyl chloride-triethylamine in an inert solvent was found to occur with good selectivity, mainly affording 2-benzoates from the a-D-gluco, a-D-allo, and a-D-altro compounds, and the 3-benzoate from the j8-D-gluco compound.52... 

From the reactions shown in Scheme 5, it is obvious that only those uronic acid derivatives whose elimination proceeds with the formation of enolic or aldehydic groups, or both, afford products capable of reducing the Cu(II) ion. Although such structures can be expected from hexo- and hepto-furanuronic, as well as from hep-topyranuronic, acid derivatives, glycosides of pentofuranuronic and of hexopyranuronic acid derivatives do not exhibit reducing properties. However, in view of this generalization, the zero reducing power observed for compound 26 requires a different explanation. 

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