Polysaccharide oxidation with

Polysaccharides.—Very few oxidations of polysaccharides have been carried out with lead tetraacetate, a situation in marked contrast to the voluminous literature on polysaccharide oxidations with periodate.22 The main reason for this discrepancy has undoubtedly been the fact that polysaccharides are insoluble in the solvents generally used for lead tetraacetate oxidation. 

In polysaccharides oxidized with periodic acid, one molar proportion of each individual, oxidized monosaccharide reacts with only one mole of... 

The carbonyl-reactive group on these crosslinkers is a hydrazide that can form hydrazone bonds with aldehyde residues. To utilize this functional group with carbohydrate-containing molecules, the sugars first must be mildly oxidized to contain aldehyde groups by treatment with sodium periodate. Oxidation with this compound will cleave adjacent carbon-carbon bonds which possess hydroxyl groups, as are abundant in polysaccharide molecules (Chapter 1, Sections 2 and 4.4). 

Figure 10.3 Antibody molecules oxidized with sodium periodate to create aldehyde groups on their polysaccharide chains can be modified with PDPH to produce thiols after reduction of the pyridyl disulfide. Direct labeling of the sulfhydryls with "Tc produces a radioactive complex.

Figure 20.9 Polysaccharide groups on antibody molecules may be oxidized with periodate to create aldehydes. Modification with biotin-hydrazide results in hydrazone linkages. The sites of modification using this technique often are away from the antibody-antigen binding regions, thus preserving antibody activity.

A second method of immunotoxin preparation by reductive amination involves the use a polysaccharide spacer. Soluble dextran may be oxidized with periodate to form a multifunctional crosslinking polymer. Reaction with antibodies and cytotoxic molecules in the presence of a reducing agent forms multivalent immunotoxin conjugates. The following sections discuss these options. 

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). 

The reaction of these aldehydes, derived from periodate oxidation, with carbonyl reagents has also been investigated. Studies 147 148 were made on oxidized laminarin, a (1 —> 3)-linked polysaccharide, in which only the terminal residues had been oxidized. The addition of phenylhydrazine acetate detached the remainder of the terminal residue as glyoxal phenyl-osazone. When the aldehydic compounds derived from the periodate oxidation of raffinose and trehalose818a were reacted with p-nitrophenylhydrazine, the authors were surprised to find that one molecule of oxidized raffinose, containing six aldehydic functions, reacts with only three molecules of the reagent, and that the four aldehydic functions of the oxidized trehalose molecule react with only two. The reactions of periodate-oxidized carbo-... 

A few polymerizations leading to nonhydrolyzable polysaccharides have been reported. The first was a base-catalyzed polymerization of 5,6-anhydro-l,2-0-isopropylidene-3-0-methyl-a-D-glucofuranose.u The polymerization was initiated most successfully with solid potassium or cesium hydroxide, and the d.p. achieved was —25. Hydrolysis gave a free, methylated, nonhydrolyzable polysaccharide, which was oxidized with hypoiodite to the poly(D-gluconic acid.)... 

Uronic acid degradation of the fully methylated Klebsiella type 47 capsular polysaccharide120 results in a partially methylated polysaccharide having a disaccharide repeating-unit (see Section IV,2, p. 218), in which the hydroxyl groups at C-3 in the L-rhamnose residues are free. Oxidation with ruthenium tetraoxide consequently gave the product 82, which, on treatment with base, followed by... 

BODIPY 530/550 C3 hydrazide is 4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl hydrazide, a derivative of the basic BODIPY structure, which contains two phenyl rings off the No. 5 and 7 carbon atoms and a propionic acid hydrazide group on the No. 3 carbon atom (Molecular Probes). The hydrazide functional group reacts with aldehyde- or ketone-containing molecules to form hydrazone linkages (Fig. 229). The compound may be used to label glycoproteins or other carbohydrate-containing molecules after oxidation of their polysaccharide portions with sodium periodate to yield aldehyde residues. 

J. Hoffman, B. Lindberg, and S. Svensson, Determination of the anomeric configuration of sugar residues in acetylated oligo- and polysaccharides by oxidation with chromiun trioxide in acetic acid, Acta. Chem. Scand., 26 (1972) 661-666. 

The action of chlorine in alkaline media is much slower than that of bromine. Lewin29 reported that the rate of oxidation of D-glucose at pH 9.8 by hypobromite is 1360 times higher than that by hypochlorite at the same pH. For cellulose, the ratio is much smaller (33 to 1). The complexity of the latter system is, however, revealed by the variability of this ratio over the pH range of 8-13 at pH 6-7, the action of hypochlorite is actually slightly faster than that of hypobromite. Maltodextrins and starch have been oxidized with alkaline sodium hypochlorite. The resulting oxidized polysaccharide formed stable complexes with calcium cations.30... 

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