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Glycosans

Condensation of a hemiacetal hydroxyl with another hydroxyl group in the same molecule produces an anhydro sugar (glycosan) which can be considered as an intramolecular glycoside. The most common glycosans may be classified, by their skeletal structures, as 1,2-anhydro- and 1,6-anhydro-pyranoses, and 1,6-anhydrofuranoses. The ether anhydro derivatives are considered in Chapter VII. [Pg.220]

2-Anhydro-D-glucopyranose is obtained as its triacetate by the action of ammonia in benzene on 3,4,6-t i-0-acetyl-2-0-t ichlo oacetyl-i8-D-gluco-py anosyl chloride 53). [Pg.221]

The mechanism of the reaction has been studied by McCloskey and Coleman 121). It appears that a 1,2-anhydride may be an intermediate in the formation of 1,6-anhydro-jS-D-glucopyranose because the reaction is blocked by the presence of a methoxyl group at carbon 2 whereas the presence of methoxyl groups at carbons 3 and 4 does not prevent the reaction. This reaction course does not explain the formation of 1,6-anhydro-jS-D-mannopyranose from the phenyl /3-D-anomer and the corresponding [Pg.221]

D-galactose derivative from the phenyl a-D-anomer. The reaction is discussed by Lemieux 16) who suggests other possible reaction paths. [Pg.222]

The quaternary salt formed from tetra-O-acetyl-a-D-galactopyranosyl bromide and trimethylamine yields l,6-anhydro-/3-D-galactopyranose on treatment with barium hydroxide 122). During treatment of tri-O-acetyl-5-0-trityl-D-ribofuranose with hydrogen bromide, a trityl and an acetyl group are removed with the formation of 2,3-di-0-acetyl-l,5-anhydro-D-ribofuranose 123) (shown by other workers to be dimeric). [Pg.222]


The compounds usually known as monosaccharide anhydrides or glycose anhydrides (earlier glycosans ), formation of which involves the anomeric hydroxy group, are named by the same procedure. In these cases the order of preference of ring size designators is pyranose > furanose > septanose. However, three- or four-membered rings should normally be cited as anhydro if there is a choice. [Pg.119]

VI. Anhydro Sugars of the Glycosan Type 1. Preparative Methods for 1,6-Anhydro Hexoses... [Pg.81]

An outline of the evidence on which the constitution of levoglucosan is based has been given in Section I. Hudson and coworkers have more recently employed the powerful weapon of attack elaborated by them, namely oxidation with per-iodic acid, to establish on the firmest basis the type of ring structures present in the glycosans.7 71> 8 64... [Pg.83]

The 2,5-anhydrides of 2-ketoses constitute a special case, in which the hemiacetalic carbon atom is involved in the anhydride bridge. Such anhydrides more closely resemble the 1,6-anhydroaldoses (glycosans) than the 2,5-anhydroaldoses. An example of a 2,5-anhydride of a 2-hexulose is obtained by the action of base on a D-fructosyl fluoride derivative treatment of l-0-methyl-/3-D-fructopyranosyl fluoride at 90° with concentrated, aqueous sodium hydroxide leads,80 in poor yield, to 2,5-anhydro-l-0-methyl-/3-D-fructopyranose. [Pg.203]

Two representatives of a remarkable new class of glycosans containing the < 1,4 > < 1,6 > (1,6-anhydrohexofuranose) ring system recently have been isolated as additional products of the pyrolytic vacuum distillation of carbohydrates. From starch, Dimler, Davis and Hilbert7 obtained... [Pg.38]

Outside of the glycosan series the stabilizing effect of an anhydro-ring on furanosides has been observed in the case of the 3,6-anhydro-D-glucose derivatives studied by Haworth, Owen and Smith.23 The methyl... [Pg.45]

Glycolic acid, III, 141, 149 from inositol oxidation, III, 52 Glycolic acid, effect on conductivity of boric acid, IV, 195 Glycols, from sucrose, IV, 301 Glycoproteins, II, 162 Glycopyranoside, III, 130 Glycosans, II, 64... [Pg.364]


See other pages where Glycosans is mentioned: [Pg.54]    [Pg.54]    [Pg.57]    [Pg.57]    [Pg.58]    [Pg.64]    [Pg.72]    [Pg.72]    [Pg.73]    [Pg.81]    [Pg.81]    [Pg.83]    [Pg.86]    [Pg.158]    [Pg.161]    [Pg.9]    [Pg.122]    [Pg.167]    [Pg.37]    [Pg.39]    [Pg.43]    [Pg.44]    [Pg.44]    [Pg.45]    [Pg.46]    [Pg.49]    [Pg.49]    [Pg.328]    [Pg.35]    [Pg.53]    [Pg.207]    [Pg.227]    [Pg.737]   
See also in sourсe #XX -- [ Pg.64 ]

See also in sourсe #XX -- [ Pg.35 ]

See also in sourсe #XX -- [ Pg.64 ]

See also in sourсe #XX -- [ Pg.27 , Pg.54 ]




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Anhydro Sugars of the Glycosan Type

Glycosan Type

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