The selective cleavage of permethylated glycopyranosiduronic acid linkages by oxidative decarboxylation with lead tetraacetate

1981 ◽  
Vol 59 (6) ◽  
pp. 935-940 ◽  
Author(s):  
Gerald Oliver Aspinall ◽  
Hany Kamal Fanous ◽  
Nimal Savitri Kumar ◽  
Velupillai Puvanesarajah
Keyword(s):  
Sodium Borohydride ◽  
Gum Arabic ◽  
Lead Tetraacetate ◽  
Oxidative Decarboxylation ◽  
Hydroxyl Groups ◽  
Reaction Sequence ◽  
Pectic Acid ◽  
Acid Methyl ◽  
Sterculia Urens ◽  
Derivatives Of

Reaction of permethylated glycopyranosiduronic acids with lead tetraacetate furnishes epimeric 5-acetoxypentopyranosides as products of oxidative decarboxylation. Glycoside cleavage then occurs on treatment with sodium borohydride which affords the corresponding pentitols with exposure of aglyconic hydroxyl groups. The reaction sequence has been performed with permethylated derivatives of methyl β-melibiosiduronic acid, methyl β-gentiobiosiduronic acid, gum arabic, leiocarpan A, Sterculia urens gum, and citrus pectic acid. The scope of the reaction sequence in polysaccharide studies is discussed.

The formation of hex-5-enopyranosides and their selective hydrolysis in methylated polysaccharides

1978 ◽  
Vol 56 (5) ◽  
pp. 680-684 ◽  
Author(s):  
Gerald Oliver Aspinall ◽  
Karl-Gunnar Rosell
Keyword(s):  
Uronic Acid ◽  
Gum Arabic ◽  
Hydroxyl Groups ◽  
Triphenyl Phosphite ◽  
Reaction Sequence ◽  
Selective Hydrolysis ◽  
Acidic Polysaccharides ◽  
Hydrolysis Of ◽  
Derivatives Of

The introduction of hex-5-enopyranoside residues into methylated acidic polysaccharides is effected by reduction of uronic acid residues, followed by reaction with triphenyl phosphite methiodide, and dehydroiodination. The selective hydrolysis of hex-5-enopyranosidic linkages with characterization of the 6-deoxyglycos-5-uloses thus formed and location of the aglyconic hydroxyl groups thus exposed has been demonstrated for methylated derivatives of birch xylan and gum arabic. The reaction sequence provides a new method for linkage analysis of acidic polysaccharides.

The role of secondary alcoholic groups of D-galacturonan in its degradation with exo-D-galacturonanase

1980 ◽  
Vol 45 (2) ◽  
pp. 427-434 ◽  
Author(s):  
Kveta Heinrichová ◽  
Rudolf Kohn
Keyword(s):  
Acetyl Derivative ◽  
Competitive Inhibitor ◽  
Hydroxyl Groups ◽  
Pectic Acid ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
The Individual ◽  
Degradation Degree ◽  
Derivatives Of

The effect of exo-D-galacturonanase from carrot on O-acetyl derivatives of pectic acid of variousacetylation degree was studied. Substitution of hydroxyl groups at C(2) and C(3) of D-galactopyranuronic acid units influences the initial rate of degradation, degree of degradation and its maximum rate, the differences being found also in the time of limit degradations of the individual O-acetyl derivatives. Value of the apparent Michaelis constant increases with increase of substitution and value of Vmax changes. O-Acetyl derivatives act as a competitive inhibitor of degradation of D-galacturonan. The extent of the inhibition effect depends on the degree of substitution. The only product of enzymic reaction is D-galactopyranuronic acid, what indicates that no degradation of the terminal substituted unit of O-acetyl derivative of pectic acid takes place. Substitution of hydroxyl groups influences the affinity of the enzyme towards the modified substrate. The results let us presume that hydroxyl groups at C(2) and C(3) of galacturonic unit of pectic acid are essential for formation of the enzyme-substrate complex.

scholarly journals The selective cleavage of glycopyranosiduronamide linkages in methylated polysaccharides

1978 ◽  
Vol 56 (5) ◽  
pp. 685-690 ◽  
Author(s):  
Gerald Oliver Aspinall ◽  
Karl-Gunnar Rosell
Keyword(s):  
Uronic Acid ◽  
Capsular Polysaccharide ◽  
Gum Arabic ◽  
Hydroxyl Groups ◽  
Selective Degradation ◽  
Derivatives Of

Hofmann degradation of glycosiduronamide linkages in methylated polysaccharides furnishes pentodialdose derivatives to which any sugar residues external to uronic acid residues remain attached together with degraded methylated polysaccharides carrying aglyconic hydroxyl groups. The selective degradation has been carried out on methylated derivatives of birch xylan, gum arabic, and the capsular polysaccharide from Klebsiella type 47. Procedures for the degradation of methylated polysaccharides in the vicinity of uronic acid residues are assessed.

scholarly journals THE LOCATION OF THE XANTHATE GROUPS IN PARTLY SUBSTITUTED CELLULOSE XANTHATES

1957 ◽  
Vol 35 (12) ◽  
pp. 1522-1533 ◽  
Author(s):  
E. P. Swan ◽  
C. B. Purves
Keyword(s):  
Cellulose Acetate ◽  
Chlorine Dioxide ◽  
Methyl Esters ◽  
Lead Tetraacetate ◽  
Degree Of Substitution ◽  
Hydroxyl Groups ◽  
Primary Position ◽  
Standard Methods ◽  
The Third ◽  
Almost All

Cellulose sodium xanthates of degree of substitution (D.S.) 0.4 to 0.66 were methylated to xanthate S-methyl esters which were then acetylated completely, the final xanthate D.S. remaining close to the original value. Dexanthation with aqueous chlorine dioxide near pH 4.5 and −5° removed almost all of the S-methyl xanthate groups, but the loss of a few acetyl groups from, and the retention of 1 to 2% of sulphur in, the resulting cellulose acetate could not be avoided. The original xanthate groups were presumably represented in this acetate as unsubstituted hydroxyl groups, and these were located by standard methods involving tosylation–iodination, tritylation, and oxidations with lead tetraacetate. Xanthate groups appeared to occupy the third and sixth, but not the second, position in the cellulose, and 53 to 61% of the substituent was in the sixth or primary position; one sample of viscose was "ripened" before the cellulose sodium xanthate was isolated, and the value was 81%. The results were of a preliminary nature, because severe technical difficulties reduced their reliability.

Proton spin–spin coupling constants and intramolecular hydrogen bonding in bromine derivatives of 1,3-dihydroxybenzene

1976 ◽  
Vol 54 (14) ◽  
pp. 2228-2230 ◽  
Author(s):  
Ted Schaefer ◽  
J. Brian Rowbotham
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

The conformational preferences in CCl4 solution at 32 °C of the hydroxyl groups in bromine derivatives of 1,3-dihydroxybenzene are deduced from the long-range spin–spin coupling constants between hydroxyl protons and ring protons over five bonds. Two hydroxyl groups hydrogen bond to the same bromine substituent in 2-bromo-1,3-dihydroxybenzene but prefer to hydrogen bond to different bromine substituents when available, as in 2,4-dibromo-1,3-dihydroxybenzene. When the OH groups can each choose between two ortho bromine atoms, as in 2,4,6-tribromoresorcinol, they apparently do so in a very nearly statistical manner except that they avoid hydrogen bonding to the common bromine atom.

Oxidative decarboxylation of the 3-methyl-2-carboxynorbornanes with lead tetraacetate

1976 ◽  
Vol 54 (8) ◽  
pp. 1222-1225 ◽  
Author(s):  
J. B. Stothers ◽  
K. C. Teo
Keyword(s):  
Carboxylic Acids ◽  
Lead Tetraacetate ◽  
Starting Material ◽  
Oxidative Decarboxylation ◽  
Methyl Group

The mixtures of isomeric acetates produced by oxidative decarboxylation of the four 3-methyl-norbornane-2-carboxylic acids with lead tetraacetate in benzene have been characterized. The composition of these products depends primarily on the configuration of the methyl group in the starting material. The results are compared with those found for the Pb(OAc)4 decarboxylation of the norbornane-, bornane-, and 2,3,3-trimethylnorbornane-2-carboxylic acids. The formation of the products is interpreted in terms of competitive cationic and SNi substitution.

scholarly journals Chemical and structural properties of reduced graphene oxide—dependence on the reducing agent

2020 ◽  
Vol 56 (5) ◽  
pp. 3738-3754
Author(s):  
B. Lesiak ◽  
G. Trykowski ◽  
J. Tóth ◽  
S. Biniak ◽  
L. Kövér ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Sodium Borohydride ◽  
Reduction Rate ◽  
Graphite Powder ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Vacancy Defects ◽  
Group Reduction ◽  
Reduced Graphene

AbstractGraphene oxide (GO) prepared from graphite powder using a modified Hummers method and reduced graphene oxide (rGO) obtained from GO using different reductants, i.e., sodium borohydride, hydrazine, formaldehyde, sodium hydroxide and L-ascorbic acid, were investigated using transmission electron microscopy, X-ray diffraction, Raman, infrared and electron spectroscopic methods. The GO and rGOs’ stacking nanostructure (flake) size (height x diameter), interlayer distance, average number of layers, distance between defects, elementary composition, content of oxygen groups, C sp3 and vacancy defects were determined. Different reductants applied to GO led to modification of carbon to oxygen ratio, carbon lattice (vacancy) and C sp3 defects with various in-depth distribution of C sp3 due to oxygen group reduction proceeding as competing processes at different rates between interstitial layers and in planes. The reduction using sodium borohydride and hydrazine in contrary to other reductants results in a larger content of vacancy defects than in GO. The thinnest flakes rGO obtained using sodium borohydride reductant exhibits the largest content of vacancy, C sp3 defects and hydroxyl group accompanied by the smallest content of epoxy, carboxyl and carbonyl groups due to a mechanism of carbonyl and carboxyl group reduction to hydroxyl groups. This rGO similar diameter to GO seems to result from a predominant reduction rate between the interstitial layers. The thicker flakes of a smaller diameter than in GO are obtained in rGOs prepared using remaining reductants and result from a higher rate of reduction of in plane defects.

scholarly journals Characteristic Flavonoids from Acacia burkittii and A. Acuminata Heartwoods and their Differential Cytotoxicit to Normal and Leukemia Cells

2009 ◽  
Vol 4 (1) ◽  
pp. 1934578X0900400
Author(s):  
Mary H. Grace ◽  
George R. Wilson ◽  
Fayez E. Kandil ◽  
Eugene Dimitriadis ◽  
Robert M. Coates
Keyword(s):  
Cell Line ◽  
Relative Concentration ◽  
Hydroxyl Groups ◽  
L1210 Cells ◽  
Green Monkey ◽  
Bioassay Guided Fractionation ◽  
Acetone Extracts ◽  
Derivatives Of ◽  
Hplc Analyses ◽  
Mouse Lymphoma

Bioassay-guided fractionation of extracts from Acacia burkittii and A. acuminata heartwoods against an L1210 (mouse lymphoma) cell line led to the isolation of two flavan-3,4-diols, melacacidin (1) and isomelacacidin (2), and three flavonoids, 3,7,8,3′,4′-pentahydroxyflavone (3), 7,8,3′,4′-tetrahydroxyflavanone (4) and 3,7,8,3′,4′-pentahydroxyflavanone (5). HPLC analyses (280 nm) of the 70% acetone extracts of the two plants showed different profiles in terms of the relative concentration of the five identified compounds. When tested against L1210, compounds 1 and 2 were the most active, giving ID50 values of 2.5 and 4.5 μg/mL, respectively. The lower activity of the other isolated compounds indicated the importance of the 3,4-hydroxyl groups for the cytotoxic activity of these flavonoids. The isolated compounds were either non-toxic or had very low toxicities against the “normal” CV-1 cell line (green monkey kidney cells). The O-methyl and O-acetyl derivatives of these compounds were inactive. Ten commercially available phenolic compounds (6-15) were also tested for their activity against both CV-1 and L1210 cell lines. Flavan-3,4-diols 1 and 2 were more cytotoxic to L1210 cells than all tested compounds, including catechin and epicatechin, the most abundant flavan-3-ols in many fruits and vegetable.

Gas Chromatographic Analysis of Amino Acids as the jV-Heptafluorobutyryl Isobutyl Esters

1987 ◽  
Vol 70 (1) ◽  
pp. 151-160 ◽  
Author(s):  
Samuel L MacKenzie
Keyword(s):  
Amino Acids ◽  
Capillary Column ◽  
Packed Column ◽  
Complex Mixture ◽  
Amino Acid Profile ◽  
Reaction Sequence ◽  
Maximum Resolution ◽  
Acid Catalyzed ◽  
Derivatives Of ◽  
Heptafluorobutyric Anhydride

Abstract The N-heptafluoroburyryl isobutyl derivatives of proteic amino acids are well resolved by gas chromatography and form the basis of a convenient, rapid assay. The derivatives are prepared by acid-catalyzed esterification at 120°C for 20 min in 3N HCl-isobutanol followed by acylation with heptafluorobutyric anhydride at 150°C for 10 min. The reaction sequence is performed without any transfers or extractions and thus is compatible with microscale analysis. A complete proteic amino acid profile can be completed in less than 20 min by using a packed column or less than 10 min by using a capillary column in combination with an elevated oven temperature program rate. Physiological sample matrixes, which frequently contain a complex mixture of components, and thus require maximum resolution, can be assayed in less than 1 h using a program rate of 4°C/min. A capillary column is recommended for this application. Capillary column chromatography, in combination with a nitrogenspecific detector, is useful for identifying and assaying nonproteic amino acids in physiological sample matrixes. Frequently, a prior cleanup of the sample can be avoided.

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