Carbohydrates, acidic derivatives with pyridine

In another method for isolating the carbohydrate fraction of wood, chlorine dioxide is used, instead of chlorine, and the lignin derivatives formed are extracted out with pyridine-water. This method was first reported by Schmidt and Graumann. Several years later, Jayme modified the procedure by using sodium chlorite and acetic acid in place of the explosive, chlorine dioxide gas. Jayme s method was subsequently modified by Wise and coworkers, " and, in this form, has been used extensively in the characterization of wood. The procedure may be applied directly to air-dried wood without previous extraction, except in the case of resinous woods, where a preliminary treatment with alcohol and ether is desirable. 

Carbohydrate-derived enolones are a particular case of chiral cyclohexenes. Addition of tert-butyl radicals occurs with high stereoselectivity trans to the C-5 substituent at both x- and /f-anomers8I5. The primary adduct radical rearranges through transfer of the benzoyl group and final hydrogen atom abstraction to yield the product as a mixture of isomers at C-2. Treatment of the mixture with pyridine leads to the formation of one enolone wdth elimination of benzoic acid. 

Carbohydrates can be sulfated by treatment with chlorosulfonic acid, but with such polyhydroxy compounds, the reaction often yields a complex mixture of sulfates. However, in some cases, the use of an equimolar quantity of the reagent in chloroform or pyridine solution at low temperature may result in monosulfation, since the primary hydroxyl groups are more readily sulfated. This is generally more effectively achieved by the use of a suitably blocked carbohydrate, e.g. isopropylidene derivatives, in the sulfation reaction. ... 

F]DGal, 119, a useful tracer to measure galactose metabolism in the liver with PET162b, has been synthesized by 18F ion displacement from a triflate163-165. The protected carbohydrate 120 has been oxidized163 and then reduced by LAH to give the talose derivative 121 which, in turn with triflic anhydride and pyridine, furnished the triflate intermediate 122. [18F]fluoride displacement on the latter and deprotection by acid hydrolysis yielded 119, in 30% r.y. in 90 minutes. 

Three examples of the direct synthesis of intermolecular carbonates from carbohydrate derivatives by the action of phosgene in pyridine have been reported. Von Vargha condensed l,2 5,6-di-0-isopropylideue-D-glucofu-ranose with the calculated quantity of phosgene in a benzene-pyridine medium and selectively hydrolyzed the 5,6-0-isopropylidene group in the product XXXI with warm, 80% acetic acid, to give bis(1,2-0-isopropyli-... 

Cyclic sulfates can be prepared from cyclic but not acyclic carbohydrate units by reaction with sulfuryl chloride in pyridine [98] or phenyl chlorosulfate and sodium hydride [99]. The reactivity of cyclic sulfates is quite similar to that of epoxides. Thus, they can be used to form fluoro or azido derivatives of polysaccharides by highly regiospecific approaches, usually, but not always, leading to trans-diaxial products from which the sulfate can be easily removed by mild, acid-catalyzed hydrolysis [100,101]. 

A contamination with several C1-C4 alkylated pyrazines, cyclopentapyrazines and pyridines was discovered in the second extracts. These compounds are described in detail as primary products of the Maillard reaction, the non-enzymic browning reaction between carbohydrates and amino acids (e.g. Mulders, 1973 Chen et al., 1998). Therefore, the occurence of these specific pyrazines and pyridines suggested either contemporary degradation processes of carbohydrates with amino acids or ammonia within the deposit landfill or the emission of waste derived Maillard products generated already before deposition. 

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