Dextrans periodate oxidation

Aldehyde-containing macromolecules will react spontaneously with hydrazide compounds to form hydrazone linkages. The hydrazone bond is a form of Schiff base that is more stable than the Schiff base formed from the interaction of an aldehyde and an amine. The hydrazone, however, may be reduced and further stabilized by the same reductants utilized for reductive amination purposes (Chapter 3, Section 4.8). The addition of sodium cyanoborohydride to a hydrazide-aldehyde reaction drives the equilibrium toward formation of a stable covalent complex. Mallia (1992) found that adipic acid dihydrazide derivatization of periodate-oxidized dextran (containing multiple formyl functionalities) proceeds with much greater yield when sodium cyanoborohydride is present. 

Bis-hydrazide-containing molecules also can be used to activate soluble polymeric sub-stances-containing aldehyde groups. For instance, dextran may be periodate oxidized to create numerous formyl functionalities on each molecule. Subsequent reaction with a homobifunctional hydrazide in large excess results in a hydrazide-activated polymer having multivalent-binding capability toward aldehydes or ketones (Chapter 25, Section 2.2). Insoluble support matrices suitable for affinity chromatography have been activated in a similar fashion to create the hydrazide derivative (O Shannessy and Wilchek, 1990). 

Figure 21.15 A periodate-oxidized dextran polymer may be reacted with both an antibody and an intact toxin component using reductive amination to form a multivalent immunotoxin complex.

Hydrazide derivatives also may be prepared from a periodate-oxidized dextran polymer or from a carboxyl-containing dextran derivative by reaction with te-hydrazidc compounds (Chapter 4, Section 8). A hydrazide terminal spacer provides reactivity toward aldehyde- or ketone-containing molecules. Thus, the hydrazide-dextran polymer can be used to conjugate specifically glycoproteins or other polysaccharide-containing molecules after they have been oxidized with periodate to form aldehydes (Chapter 1, Section 4.4). 

With such polysaccharides110 as the dextrans,149-163 which contain primarily a-D-(l — 6) linkages, periodate oxidation has been most useful. Each (1 — 6)-linked D-glucose unit contains three contiguous hydroxyl... 

This C-13 n.m.r. analytical technique has been referenced against 27 dextrans which had been studied by periodate-oxidation and permethylation fragmentation g.l.c.-m.s. techniques (14). 

On the other hand, polymeric carriers can also be modified to introduce reactive groups. Polysaccharides such as dextran and inulin may be activated [149] by periodate oxidation to create aldehyde groups, by succinic anhydride activation to create carboxylic groups, or by p-nitrophenyl chloroformate activation to create reactive ester groups. 

The linear dextran has also been used in investigating the mechanism of the periodate oxidation of polysaccharides. The results support the proposal that inter-residue, hemiacetal formation is a general occurrence in the later stages of the oxidation.128... 

Periodate-Oxidized Dextran as Cross-linking Agent... 

Periodate oxidized dextran can be used as a protein modification or cross-linking... 

Preliminary examinations of dextran structures were conducted by optical rotation, infrared spectroscopy and periodate-oxidation reactions. More detailed results can be achieved by methylation analysis [19]. The hydroxyl groups are methylated with methyl iodide after activation with sodium methylsulfinyl carbanion (Fig. 2). The methyl dextran is hydrolysed to the corresponding different methylated monosaccharides, which are furthermore reduced and peracetylated. The resulting alditol acetates of methylated sugars are separated by gas chromatography and identified by their retention times. In particular, a combined capillary gas-liquid chromatography/mass... 

Periodate oxidation. Aldehyde groups can be easily introduced in most polysaccharides by reaction with sodium periodate. Vicinal diol structures give rise to dialdehydes. For dextran (I) having three adjacent hydroxyl groups in each non-branched anhydro glucopyranoside repeat unit the oxidation is a two step reaction ... 

Detailed studies of the periodate oxidation of dextran and inulin (4-6) have shown evidence for the occurrence of hemiacetal structures formed by reaction of aldehydes with hydroxyl groups of either the same unit (intra-residual) or a neighbouring unit (inter-residual). Inter-residual hemiacetal formation reduces the number of diol struc-... 

Structural Studies on Clinical Dextrans. Part I. Methylation and Periodate Oxidation Studies, J. K. N. Jones and K. C. B. Wilkie, Can. Biochem. Physiol., 37 (1959) 377-390. 

From this list of microorganisms capable of synthesizing dextran, it may readily be seen that one of the factors controlling the properties of the polysaccharide obtained is the strain of the particular bacterium used. This observation has been amply verified in a number of studies. Thus, immunological cross-reactions of dextrans with pnemnococcus antisera, the results of periodate oxidations, - and various physical measurements - have all demonstrated this point. 

An improved way of utilizing the method of periodate oxidation for determining the nature of the linkages in polysaccharides was provided by Smith and coworkers. They realized that, if the periodate-oxidized polysaccharide were reduced to the corresponding alcohol, the resulting fragments, on hydrolysis, would be indicative of the types of linkage present in the parent polymer. This scheme is shown in Fig. 1. Such an approach was used in a study of the dextrans from 6 different strains of L. mesente-... 

Fig. 1.—Products Resulting from Periodate Oxidation, Reduction, and Hydrolysis of (1 - 6), (1 - 4), and (1 — 3) Linkages in Dextran.

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