Anthrone reaction and

The content of galacturonic acid in the fractions, obtained by gel chromatography, was determined by the carbazole method (9), and the content of neutral monosaccharides was determined by the anthron reaction (16). 

Kohler, L.H., Differentiation of Carbohydrates by Anthrone Reaction Rate and Color Intensity, Anal. Chem. (1952) 24(10) 1576-1579. 

D-glucose, and 5-(hydroxymethyl)-2-furaldehyde with anthrone lends support to these conclusions, and further indicates the complexity of the overall reaction. In the reaction of either D-fructose or 5-(hy-droxymethyl)-2-furaldehyde with anthrone, at least nine compounds were observed, three of which were condensation products of anthrone itself. The other products had absorption maxima ranging from 490 to 770 nm (in sulfuric acid solution and under the conditions of the anthrone reaction). One of the prominent pigments, having a blue color ( max 620 nm) and a postulated structure corresponding to compound 123, was isolated and characterized by its nuclear magnetic... 

Chiral bicyclic guanidine (221) has been identified as an excellent catalyst for reactions between anthrones (219) and various dienophiles, such as (220). The catalyst can tolerate a range of substituents and substitution patterns, making several anthrone derivatives suitable for this reaction. Both Diels-Alder and Michael adducts were obtained in excellent yields, high regioselectivities, and high enantioselectivities (<99% ee). This is the first case of a highly enantioselective base-catalysed anthrone Diels-Alder reaction.263... 

Except for the formic acid extraction, < all the other methods yielded approximately the same amount of polysaccharide. However, even after more than 20 successive extractions of a Swiss brown-earth (Braunerde) with acid, water, and alkali, further extracts gave a positive anthrone reaction for sugars. " The extraction of polysaccharides is probably made difficult by their interaction with inorganic surfaces and humic substances. 

Galactose is usually estimated quantitatively by the difference in the glucose oxidase determination and the total reducing substance as determined either by the copper reduction method (Nl) or the anthrone reaction (Al). 

The use of a boron atom as a covalent template for intramolecularizing the Diels-Alder reaction has been relatively little investigated [20-22]. However Narasaka et al. have reported the use of a boronate template to control regio- and stereoselectivity in an IMDA reaction between anthrone 50 and methyl 4-hydroxybut-2-enoate 3 [20a]. Formation of the boronate tether was achieved by simply heating an equimolar mixture of phenylboronic acid with the diene and dienophile at reflux in pyridine with azeotropic removal of water. After 5 h, a single cycloadduct 51 was obtained in 81% yield. The tether was readily removed oxidatively affording the corresponding diol 52 in excellent yield (Scheme 10-19). 

The anthrone reaction is based on hydrolitic and dehydrating adion of concentrate sulphuric add on carbohydrates, in which glicosidic linkages are broken releasing free reducing sugar that are dehydrated and converted to furfural by pentoses and hydroxymethylfurfural by hexoses (Figure 1). 

Anthrones [204] and 3-substituted oxindoles [205] possess activated methylenes which have been able to react under asymmetric iminium catalysis with a,p-unsaturated aldehydes. The reaction with 3-substituted oxindoles is especially attractive, since chiral quaternary stereocenters are generated. For this purpose, chiral primary amine thiourea catalyst 132 has been demonstrated as a very efficient promoter for the addition of 3-alkyl substituted oxindoles to P-aryl substituted enals in the presence of benzoic acid as cocatalyst in toluene at rt to afford the corresponding Michael adducts in good diastereoselectivities (dr up to >19/1) and good enantioselectivities (73-93% ee) (Scheme 2.75) [205a], P-Alkyl substituted enals are not suitable partners for the reaction affording very low diastereo- and enanti-... 

Several other methods of polymer quantification in biological material have been used. In general, a polymer is usually isolated from biological material by a deproteini-zation procedure, extraction with organic solvents, etc., and then analyzed. Elemental analysis, viscosimetryturbidimetryand complexation with iodine (for PVP) in extracts were used in early studies in this field. These methods are now rarely used and have been replaced by labelling methods. Among the classical analytical techniques, the anthrone reaction for the estimation of carbohydrate polymers (e.g. dextran inulin >) has remained useful. 

Simple chiral tertiary amines (90) have been shown to catalyse the Diels-Alder reaction of anthrone (88) and maleimides (89) to yield cycloadducts (91) in excellent yields (up to 96%) and enantioselectivities (up to 95% ee) (Scheme 26). The aminocat-alytic asymmetric ex -Diels-Alder reaction of a-methylene carbonyl dienophiles with 2,4-dienals formed chiral spirocycles in moderate to excellent diastereo- and enantio-selectivity. ... 

Thiee methods for the determination of dissolved carbohydrates in sea water have been investigated by Handa (7. Oceanog. Soc. Japan, 22 1, 1966). The anthrone reaction (Antia and Lee, Fish. Res. Bd. Canada, MS Rept. Na 168,1963) and the iV-ethylcarbazole reaction (Zein-Eldin and May, Anal. Chem., 30 1935, 1958) were shown to have a greater specificity toward certain monosaccharides than the phenol-sulphuric add reaction. The method given here employs the latter reaction since, ideally, any method for total carbohydrate should give the same equivalent colour with different sugars. 

The method followed in this determination is based on the anthrone reaction as modified by Hewitt (Nature, 182 246, 1958). The choice of anthrone for the determination of carbohydrates in particulate organic material has been made on the basis of its simplicity of operation and sensitivity. The N-ethylcarbazole reaction, as modified by Zein-Elden and May (Analyt. Chem., 30 1935, 1958), has a greater sensitivity but its operation requires more skill. 

A measure of the proportion of crude fiber in the particulate carbohydrates may also be obtained by use of the anthrone reaction. Crude fiber as determined in agricultmral products is not a chemical entity but consists of the acid- and alkali-insoluble carbohydrates and lignin obtained under standardized reaction conditions. In determining microquantities of crude fiber by use of the anthrone reaction the value obtained is predominately a measure of the amount of cellulose and similar polysaccharides which may have little direct food value. 

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