Phenolics from carbohydrates

In plants phenol biosynthesis proceeds by building the aromatic ring from carbohydrate precursors that already contain the required hydroxyl group... 

Phenol biosynthesis in plants proceeds from carbohydrate precursors whereas the pathway in animals involves oxidation of aromatic rings... 

Of the substances studied the most abundant in the Paleozoic rocks of the area are furfurals presumably derived from carbohydrates, higher molecular weight hydrocarbons, and in a few samples, amino acids. Acid and base soluble, low boiling substances having some properties of heterocyclic compounds, phenols, and organic acids exist in smaller amounts. 

Molasses. A large number of volatile and nonvolatile compounds have been identified in the flavor fractions of various types of molasses (51-621. Compound classes identified include aliphatic and aromatic acids, aldehydes, phenols, lactones, amines, esters, furans, pyrazines, and sulfides. Most of these compounds can arise from carbohydrate degradation through a number of traditional pathways especially because residual nitrogen-containing sources are present. 

The characterization of water-soluble components in slurries is one use of SPME with mixed solid-liquid samples. In one application, dried homogenized solid samples (10 mg of sewage sludge or sediment) were slurried in 4 ml of H,0 saturated with NaCl and adjusted to pH 2 with HCl for extraction for 1-15 h, which was followed by desorption into 4 1 methanol/ethanol over 2 min. The extracted compounds were either injected into a liquid chromatograph or fed directly via an electrospray ionization interface to a mass spectrometer with 1 s miz scans from 50-700 or selected-ion monitoring. The major components extracted included phthalates, fatty acids, non-ionic surfactants, chlorinated phenols and carbohydrate derivatives [235]. 

FIGURE 17. Distribution of DOC, phenols, and carbohydrates in Lake Plussee epilimnion, 1976 (from Muenster, in preparation). Algae biomass after Hickel (1978). 

From carbohydrate precursors there is another biosynthetic pathway to shikimic acid and further to gallic acid and tannins. Shikimic acid is the starting material, via chorismic acid (formed by reaction with a second molecule of pyruvic acid) which gives rise to aromatic, i.e. phenolic, amino acids. 

Fischer420 reported the preparation of mercaptals from carbohydrates the reaction can be applied to all aldoses and aliphatic thiols, but fails with thio-phenols and also with fructose and sorbose,421 so that it can be used to separate, e.g., glucose from a mixture with fructose and sorbose. 

Phenolic compounds include a wide range of secondary metabolites that are biosynthesised from carbohydrates through the shikimate pathway [14]. This is the biosynthetic route to the aromatic amino acids, phenylalanine, tyrosine, and tryptophan, and only occurs in microorganisms and plants. In the first step, the glycolytic intermediate phosphoenol pyruvate and the pentose phosphate intermediate erythrose-4-phosphate are condensed to 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP), a step catalysed by DAHP synthase. Intermediates of the shikimate pathway are 3-dehydroquinate, shikimate, and chorismate (Fig. 1). Phenylalanine is biosynthesised from chorismate, and from phenylalanine all the phenylpropanoids. Quinate is produced from 3-dehydroquinate and incorporated into chlorogenic and isochlorogenic acids (caffeoyl quinic acids) by combination with caffeic acid. Gallic acid is produced from shikimate. 

For several years our respective groups have investigated the formation of aromatic compounds from carbohydrates in aqueous solution at various pH-values under reflux or hydrothermolytic conditions. For instance, previous papers(1-6) in this series concerned the degradation of hexoses, pentoses, erythrose, dihydroxyacetone, and hexuronic acids to phenolic and enolic components. Of particular interest were the isolation and identification of catechols, an acetophenone, and chromones from pentoses and hexuronic acids at pH 4.5 (1,2). The formation of these compounds, as well as reductic acid(7),was found to be more pronounced than that of 2-furaldehyde(2) under acidic conditions. 

There were few intermediates from mod (furans from the carbohydrates and phenols from the methoxyphenols) on the way to alkenes, light aromatics, and naphthalenes ... 

In addition to the approach outlined in Scheme 4, several other approaches to the synthesis of glycofuranosides have been reported during the past year. Hanessian and Banoub have used cyclic amide acetals derived from vicinal diols as the source of the aglycone in condensations with l-0-acetyl-2,3,5-tri-0-benzoyl-jS-D-ribofuranose in the presence of stannic chloride (Scheme 5). Disaccharide derivatives are obtained when the cyclic amide acetal is derived from carbohydrate vicinal diols (Scheme 6), and selective methanolysis of the formate ester exposed an hydroxy-group that can be subjected to further manipulation or glycosylation. 2,3,5-Tri-0-benzoyl-a)8-L-arabinofuranosyl bromide or chloride has been condensed with 4-nitrophenyl 2,3-di-O-acetyl-a-L-arabinofuranoside to yield, after deacylation, 4-nitrophenyl 5-O-a-L-arabinofuranosyl-a-L-arabino-furanoside, with jS-peltatin A [isolated from podophyllin Podophyllum peltatum)] in glycosidation of the phenolic 8-OH group in an attempt to reduce... 

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