Showing papers on "Pyranose published in 1969"
TL;DR: In this paper, the conformations of the aldoses in solution and the compositions of the equilibrium mixtures formed from aldosing after dissolution in water, have been determined by NMR spectroscopy.
Abstract: The conformations of the aldoses in solution, and the compositions of the equilibrium mixtures formed from aldoses after dissolution in water, have been determined by NMR spectroscopy. Calculations based on non-bonded interactions and on the anomeric effect account for the observed conformations, and allow an approximate prediction of the α:β ratio of pyranoses in equilibrium and of the extent of anhydride formation from sugars in acid solution. In certain circumstances the furanose forms are more stable than the pyranose forms.
368 citations
TL;DR: The acid degradation of the aldopentoses to furfural and the degradation offurfural were followed spectrophotometrically and are first-order functions of HCI and pentose concentration and are consistent with a positive entropic effect which implies that the transition state involves ring opening.
71 citations
TL;DR: In this article, the tautomerism of D -galactose in water has been studied by using g.l.c. to separate per-O -trimethylsilyl derivatives of D-galactoses tautomers formed during the mutarotation reaction.
32 citations
TL;DR: The steric requirements indicate that a three-point attachment to the enzyme is required for substrate activity but that a two- point attachment at C-2 or C-3 or the ring oxygen (or both) is sufficient for inhibition.
30 citations
TL;DR: In this paper, the distributions of substituents in O -(2-hydroxyethyl) derivatives of starch and dextran have been examined by gas-liquid chromatography of the hydrolysates.
29 citations
TL;DR: In this article, the favored conformations of pyranose rings of several acetonated α-L-sorbo- and β-D-fructopyranoses have been revealed by proton magnetic resonance spectroscopy.
Abstract: The favored conformations of the pyranose rings of several acetonated α-L-sorbo- and β-D-fructopyranoses have been revealed by proton magnetic resonance spectroscopy. The conformations of the rings of the pyranoses are unchanged by the introduction of 1,2-O- or 1,3-O-isopropylidene groups in α-orientation of L-sorbose, but they are affected by the introduction of the 2,3-O-isopropylidene group. These findings support the fact that 2,3-O-isopropylidene-α-L-sorbopyranose was not obtained by the acetonation of L-sorbose. The rings of diacetonated D-fructopyranoses with a cis-fused acetal ring adopt a distorted conformation; however, those of diacetonated L-sorbopyranoses with a trans-fused acetal ring are only slightly distorted from the stable 1C conformation. Angyal’s anticipation of the difficult acetalation of the trans-glycol of a pyranose has been further experimentally supported.
25 citations
TL;DR: In this paper, a series of benzylxanthate esters of methyl α-d -glucopyranoside selectively methylated at various hydroxyl groups was synthesized, and their behavior was investigated under alkaline conditions typical of xanthation media.
12 citations
TL;DR: The behavior in g.l.c. of the acetates, trimethylsilyl ethers, and trifiuoroacetates of 41 D -glucosides, D -galactosides and D -mannosides in pyranose or furanose configuration was studied on several stationary phases in order to separate hexopyranoside and hexofuranoside derivatives as mentioned in this paper.
11 citations
TL;DR: In this article, the pyranose-to-furanose ring conversion (I→II) proceeds via the keto-form intermediates Vk and VIk; VIk is formed by the preferable attack of acetonating reagents on the primary hydroxyl group at the C6 of Vk followed by cyclization with the hydroxy group at C4.
Abstract: The following reaction mechanism of the acetonation of L-sorbose is proposed:(Remark: Graphics omitted.)2,3:4,6-di-O-acetal (furanose) (II). The pyranose-to-furanose ring conversion (I→II) proceeds via the keto-form intermediates Vk and VIk; VIk is formed by the preferable attack of acetonating reagents on the primary hydroxyl group at the C6 of Vk followed by cyclization with the hydroxyl group at C4. The isolation of such keto-form intermediates as were successfully obtained from the acetalations of 1-O-methyl- (X) and 1,6-di-O-methyl-L-sorboses (XVIII) gave strong support to the above mechanism. This acetonation mechanism can also be used in the other acetalations of I; however, in the case of the benzylidenation there is a possibility that the reaction might be via the pathway of 1,3-O-acetal (pyranose)\ightleftarrows1,3-O-acetal (furanose) (Vb)→1,3: 4,6-di-O-acetal (furanose).
6 citations
TL;DR: In this paper, the degradation of cellulose triacetate under the action of u.v. irradiation and the inhibition of this degradation have been investigated and shown that in the presence of oxygen and moisture, the degradation process is increased due to photo-oxidation and hydrolysis.
5 citations
TL;DR: In this article, the p.m. spectra of ethyl 3-(glycosylamino)crotonates derived from d -glucose, d -galactose and l -rhamnose, and those of their corresponding O -acetyl derivatives, have been examined.
TL;DR: In this article, the relationship between reactant and product composition is considered, and the furanoside structure is assigned to this product; previously, the structure had been assigned to α-furanoside and α-pyranoside derivatives only.
Abstract: Methylation of 2,3-O-isopropylidene-L-rhamnose with silver oxide and methyl iodide (Purdie's reagent) yields a mixture of methyl 2,3-O-isopropylidene-4-O-methyl-α- and β-L-rhamnopyranosides and methyl 2,3-O-isopropyridene-5-O-methyl-α- and β-L-rhamnofuranosides; previously the furanoside structure had been assigned to this product. Methylation in dimethylformamide (Kuhn procedure) gives the α-furanoside and α-pyranoside derivatives only. The relationship between reactant and product composition is considered.
TL;DR: In this article, the mass spectra of a series of derivatives of 2-methyl- and 2-phenyl-glyco[1′,2′:4,5]-2-oxazolines were analyzed and it was shown that furanose and pyranose derivatives can be distinguished.
TL;DR: The partial hydrolysis of the pectin of Panax ginseng gives a polygalacturonide which has a linear carbohydrate chain consisting of residues of D-galacturonic acid in the pyranose form linked by α-(1 → 4)-bonds.
Abstract: The partial hydrolysis of the pectin ofPanax ginseng C A Mey gives a polygalacturonide which has a linear carbohydrate chain consisting of residues of D-galacturonic acid in the pyranose form linked by α-(1 → 4)-bonds