Periodate Oxidation of Glycols and Carbohydrates

Carbohydrates and other biological molecules that contain polysaccharides, such as glycoproteins, can be specifically modified at their sugar residues to produce reactive formyl functionalities. With proteins, this method often allows modification to occur only at specific locals, usually away from critical active centers or binding sites. 

Since sialic acid is a frequent terminal sugar constituent of the polysaccharide trees on glycoproteins, this method selectively forms reactive aldehydes on the most accessible parts for subsequent modifications. The carbohydrate polymer of a protein provides a long spacer arm that can be used to conjugate another large macromolecule, such as a second protein, with little steric problems. 

Oxidation of polysaccharides using 10 mM or greater concentrations of sodium periodate at room temperature results in the cleavage of adjacent hydroxyl-containing carbon-carbon bonds on other sugars besides just sialic acid residues (Lotan et al., 1975). High concentrations 

Carbon-Carbon Bond Cleavage with Oxidation to Aldehyde Residues 

Carbon-Carbon Bond Cieavage with Oxidation to Aidehyde Residues 

Quench the reaction by the addition of 0.1 ml of glycerol per milliliter of reaction solution. Alternatively, the reaction may be stopped by immediate gel filtration on a Sephadex G-25 column. The dextran beads of the chromatography support will react with sodium periodate to quench excess reagent. To quench the reaction with cellular samples, wash the cells with buffer to remove remaining traces of periodate. 

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The rate of oxidation of ethylene glycol was found268-269 to attain a broad maximum between pH 2.5 and 6. In a very complete study of the effect of pH on the periodate oxidation of carbohydrates, Neumiiller and Vasseur260 showed that the oxidation of maltose, melibiose, methyl a-D-... 

Measurement of the acidity produced in the periodate oxidation of carbohydrates is confined mainly to the determination of formic acid. Only from unsubstituted ketoses is the formation of such acids as glyoxylic and glycolic to be expected in carbohydrate chemistry.274... 

The Editors note with regret the recent passing of Louis Malaprade, University of Nancy, discoverer of the stoichiometric oxidation of glycols by periodate, a reaction that has had such profound implications in the structural investigation of carbohydrates and of Karl Freudenberg, Heidelberg, last surviving student of Emil Fischer s, pioneer of important stereochemical concepts, and a scientist whose extensive contributions to synthesis included the classic, widely used acetone derivatives (isopropylidene acetals) of the monosaccharides. 

G. O. Aspinall and R. J. Ferrier, Spectrophotometric method for the determination of periodate consumed during the oxidation of carbohydrates, Chem. Ind. (London), (1956) 1216 J. X. Khym, Direct spectrophotometric determination of iodate following periodate oxidation of a-glycol groups, Methods Carbohydr. Chem., 6 (1972) 87-93. 

Horseradish peroxidase (HRP, EC 1.11.17) was obtained from Huka. The oxidation of carbohydrate moieties of enzyme with periodic acid (0.04 mM in 0.05 mM acetate buffer, pH 5.0) was performed according to Zaborsky and Ogletree (1974). The unreacted periodic acid was removed with 0.025-ethylene glycol. The oxidized enzymes were dialyzed against 50 mM phosphate buffer with pH 6.0 for 18 h. 

Enzyme-catalyzed oxidation of the primary hydro)yl group at carbon 6 of a hexose yields a uronic acid, examples of which are common in both the plant and animal worlds. Periodic acid cleaves the carbon-carbon bond of a glycol in a reaction that proceeds through a cyclic periodic ester. This reaction was once useful in carbohydrate stmcture determination. 

The fact that periodate fission functions best in aqueous media and LTA in organic solvents makes glycol scission oxidations possible with all types of substrates. These reagents were used extensively for structural elucidation of carbohydrates before the advent of modem spectral instrumentation. Now, they are generally used in synthetic work. 

The use of oxidation by periodic acid, sodium periodate, or lead tetraacetate in structural studies on carbohydrates is well known. These reagents act on a-glycols with the production of carbonyl groups and the consumption of one molecule of oxidant for each such glycol group. Where there is a primary amino group in the position a to a hydroxyl, similar oxidation... 

For many purposes, these oxidants are interchangeable however, the fact that periodate functions best in water, and lead tetraacetate in organic solvents, makes glycol-cleavage oxidation possible with all types of carbohydrates and derivatives. For favorable examples, the behavior of the two reagents toward a given compound is sufficiently different to provide complementary information. 

Although periodate and lead tetraacetate are among the most highly specific of oxidants, they nevertheless promote a number of oxidations in the carbohydrate series besides glycol cleavage. 

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