Formic acid polysaccharides

Acyl groups are common in bacterial polysaccharides. The parent acids are fatty acids, hydroxy acids, and amino acids. The simplest acid, formic acid, has only been found as the amide. The occurrence of O-formyl groups had been reported, but proved to be incorrect. A-Formyl groups have been found in different polysaccharides for example, in the 0-specific side-chains of the LPS from Yersinia enlerocolitica 0 9, which are composed of 4,6-dideoxy-4-formamido-D-mannopyranosyl residues. The formyl group can assume two main conformations, s-cis (41) and s-trans (42), which are... 

A different technique utilizes the Warburg respirometer to measure the carbon dioxide liberated by formic acid from a dilute, sodium bicarbonate solution.84 286 Successful application of the method necessitates a pH value of 5.7, which is somewhat high for optimal periodate oxidations, but good results were reported in experiments on a number of materials, including polysaccharides. The procedure is applicable to very small amounts and does not require prior destruction of periodate. 

D-xylopyranose units. This structural concept is substantiated by estimation of the formic acid obtained when the xylan is oxidized by periodate ions. On hydrolysis of the fully oxidized xylan there is obtained a small amount of D-xylose which presumably occupied the branch points in the polysaccharide and consequently was protected from periodate oxidation by possessing no adjacent free hydroxyl groups. 

On periodate oxidation, open-chain (1— 4)-linked polysaccharides yield one molecule of formic acid from the nonreducing end and two molecules of formic acid, as well as one molecule of formaldehyde, from the reducing end. 

Formolysis and acetolysis are not common methods for cleavage of glycosidic linkages. They do have some unique applications, however. For instance, methylated polysaccharides are not generally soluble in hot water, and consequently, hydrolysis is best preceded by formolysis under these circumstances. For example, 5 mg of methylated polysaccharide is dissolved in 3 mL of 90% formic acid, and the solution is kept for 2 h at 100°. The formic acid is removed by evaporation at 40°. The residue is dissolved in 1 mL of 250 mM sulfuric acid and the solution is heated for 12 h at 100°, cooled, the acid neutralized with barium carbonate, the... 

Preliminary hydrolysis with acetic acid may be helpful in avoiding N-deacetylation,53 and certain pneumococcal polysaccharides may be hydrolyzed with formic acid.54... 

The problems inherent in the hydrolysis of methylated polysaccharides are similar to those outlined, but, in addition, the possibility of occurrence of demethylation must be considered. This matter has been studied by Croon and coworkers,102 who found that hydrogen chloride, either in water or methanol, causes a significant amount of demethylation. Formolysis in 98% formic acid caused considerable degradation, whereas 90% formic acid or sulfuric acid gave acceptable results. The hydrolysis of a methylated dextran with 90% formic acid has been described in detail.103 The methanolysis of a methylated... 

The polysaccharide component of a lipopolysaccharide can be separated from the lipid component by selective hydrolysis of the glyco-sidic linkages of the 3-deoxy-D-manno-octulosonic acid residues connecting these two components. The conditions for the hydrolysis are mild, namely, 0.1 M acetic acid for 1.5 h at 100° (Ref. 18). Similar conditions, namely, M formic acid for 1 h at 100° or 0.05 M hydrogen chloride in methanol for 1 h at 85°, were used to split off the sialic acid residues from gangliosides.19,20... 

Fig. 8-19. Peeling reaction of polysaccharides during oxygen-alkali treatment. R is polysaccharide chain. Cellulose and glucomannans (R = CH,OH) 1,3,4-Dihydroxybutanoic acid 2, glycolic acid 3, formic acid 4, glyceric acid. Xylan (R = H) 1, 3-Hydroxypropanoic acid (2-deoxyglyceric acid) 2, glycolic acid 3, formic acid 4, glyceric acid.

Hydroxymethylfurfural is not volatile by steam. It is prepared from hexoses in the presence of an acid catalyst by short heat treatment to avoid further degradation to levulinic acid. After recovery by solvent extraction hydroxymethylfurfural is purified by distillation. Levulinic acid can be prepared in good yield from hexose-based polysaccharides by heating with acids. In this reaction formic acid is liberated and levulinic acid is easily lactonized to form a- and /3-angelica lactones (Fig. 2-31). 

Several different methods are used for the hydrolysis of methylated polysaccharides. As these ethers are generally insoluble in hot water (and, sometimes, even in cold water), it is usually necessary to use a non-aqueous or only partially aqueous medium for the initial hydrolysis. Treatment with methanohc hydrogen chloride (methanolysis) and subsequent hydrolysis of the methyl glycosides formed is widely employed. Another method involves heating with concentrated or aqueous formic acid (formo-... 

Acidic polysaccharides (see Table IV) that contain uronic acid residues are, perhaps, the most prevalent type of exocellular polysaccharide. Often, these acidic biopolymers contain other sugars, including pentoses, hexoses, and heptoses, also found in neutral polysaccharides (see Tables V and VI). In many instances, these polymers possess alkali-labile O-acyl substituents, such as acetic, formic, ma-lonic, pyruvic, and succinic acids. Positively charged biopolymers that contain free amino sugars are rare, but have been found (see Table VII). More often, these amino sugars are N-acylated, generally with acetyl groups. 

A more complete extraction " of polysaccharides was attempted by refluxing the soil for two 30-minute periods with 98 % formic acid containing lithium bromide. The organic matter extracted was precipitated by the addition of isopropyl ether and was redispersed in lithium chloride solution. The colored humic substances were then precipitated with hexadecyltri-methylammonium bromide, while the acidic and neutral polysaccharides were kept in solution by the lithium chloride. The possible degradative effects of hot formic acid on soil polysaccharides have not yet been investigated. 

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. 

The Biofine process produces levulinic acid, furfural and formic acid from lignocellulose in a two-step process using dilute sulfuric acid as a catalyst [45], The first step depolymerises the polysaccharides and converts the resulting 6-carbon sugars into hydroxymethylfurfural by a dehydration reaction at 210-220 °C and 25 bar. The second step converts hydroxymethylfurfural to the products at 190-200 °C and 14 bar (Scheme 1). 

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