Dextran oxidation with sodium

Figure 25.12 Dextran polymers can be oxidized with sodium periodate to create a polyaldehyde derivative. Note that additional oxidation may occur to cleave off another carbon atom and create an aldehyde on the adjacent C—OH group.

The dextran polymer contains adjacent hydroxyl groups on each glucose monomer. These diols may be oxidized with sodium periodate to cleave the associated... 

Weissleder et al. [84] first showed that the human transferrin receptor (hTfR) can be used to internalize MRI contrast agents. The hTfR regulates cellular uptake of iron from transferrin, a plasmatic iron transport protein [85], via a receptor mediated endocytosis mechanism. Thus, MION particles (dextran coated iron oxide) were oxidized with sodium periodate. Holotransferrin was added and the resulting Schiff base adduct was reduced with sodium cyanoborohydride to give transferrin labeled MIONs, Tf-MION (Scheme 3). 

Dextran was oxidized with sodium periodate to the corresponding polyaldehyde and daunomycin was coupled with a part of the aldehydes via its amino sugar. This complex was further bound to the lysines of the antibody. This conjugate can either be used directly or stabilized by further reduction with sodium borohydride. 

The presence of three hydroxyl groups per glucose unit was shown by the preparation of a triacetate and a tribenzoate. Six or seven methyla-tions (using dimethyl sulfate and concentrated alkali) of dextran did not raise the methoxyl content above 41% (theoretical maximum 45.6%). Also, Purdie methylations (using methyl iodide and silver oxide) and methylation with thallium ethoxide and methyl iodide were ineffective in raising the methoxyl content of methylated dextran above 43.5%. The maximum theoretical methoxyl content was eventually attained by modified Muskat methylations. 6 Partially methylated dextran suspended in anisole solution was treated with sodium in liquid ammonia, and the sodium salt of methylated dextran thus formed was allowed to react with methyl iodide. The methoxyl content of the partially methylated dextran was raised by three such methylations from 42% to 45.5% and by five such methylations from 30% to 45.4%. 

Protocol for Oxidizing Dextran with Sodium Periodate... 

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 ... 

Reduced dextran dialdehydes. The reaction of dextran (D-OH) with sodium metaperiodate is a two step reaction leading to different kinds of aldehyde functions. Although the aldehyde content can not be precisely predicted from the amount of periodate added, by approximation 1.5 equivalents of periodate are required per dialdehyde structure. By varying the amount of periodate added to the polysaccharide dextran dialdehydes with variable degree of oxidation were obtained. In order to avoid interaction of the polyaldehyde (D-CH=0) with the dextranases the aldehyde groups were subsequently reduced by reaction with sodium borohydride ... 

Earlier pulse radiolysis investigations were devoted to the radiation effects of the polymers dissolved in water. The rate constants of the reactions of OH radicals with polyethylene oxide) [75, 76], polyvinylpyrolidone [75], dextran [75], and sodium polyacrylate [77] have been measured as functions of the chainlength and the polymer concentrations. The rate constant expressed in polymer unit (mol -1 dm3 s- M increased more slowly with increasing chainlength than would be expected if the reactivity of the CH2 and CH groups were additive. The reaction between small molecules and the polymer radicals produced by the reaction of OH radical with polyethylene oxide) has also been demonstrated [78]. 

Table 2. Partial oxidation of dextran with sodium periodate.

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. 

Proteins may be modified with oxidized dextran polymers under mild conditions using sodium cyanoborohydride as the reducing agent. The reaction proceeds primarily through e-amino groups of lysine located at the surface of the protein molecules. The optimal pH for the reductive amination reaction is an alkaline environment between pH 7 and 10. The rate of reaction is greatest at pH 8-9 (Kobayashi and Ichishima, 1991), reflecting the efficiency of Schiff base formation at this pH. 

Periodate Oxidation mainly of polysaccharide supports has become a popular activation technique for protein immobilization [149]. Sodium periodate (Nal04) can react with vicinal cw-hydroxyl groups on cellulose, dextran, or any other diols to produce aldehyde groups. These aldehyde groups can easily be transformed into secondary amines by reductive oxidation or to hydrazides by reaction with dihydrazine. Further attachment of ligands or spacer molecules can be performed via primary amino groups. 

Parenteral preparations are regularly prepared aseptically a short time or immediately prior to administration. Compounds susceptible to hydrolysis or oxidative decomposition in solution are preferentially stored as dry powders, concentrates under an inert atmosphere, or in combination with stabilizers. Concentrates for injections or infusions (European Pharmacopoeia, 2002) are diluted prior to administration, usually with sterilized Water for injection (European Pharmacopoeia, 2002) or sterile, isotonic solutions of sodium chloride, glucose, dextran, or buffer (see Table 14.3). Powders for injections or infusions (European Pharmacopoeia, 2002) are dissolved or suspended in the same media. Vitamins are aseptically added ex tempore to TPN preparations due to poor stability and the risk of precipitation (Hutchinson, 1998), as are trace metals that may influence the stability of the TPN formulation. A limited number of drugs may also be dissolved in the TPN infusion prior to administration (Hutchinson, 1998). 

Sodium Dodecyl Sulfate-Capillary Gel Electrophoresis (SDS-CGE). SDS-CGE is a capillary-based version of SDS-polyacrylamide gel electrophoresis (SDS-PAGE) in the slab gel format, with advantages of shorter analysis times, ease of automation, and online detection and quantitation [26, 27]. In SDS-CGE, replaceable sieving polymers, such as linear polyacrylamide, poly (ethylene oxide), dextran, or pullulan, are used to achieve reproducible separations. These polymers permit the replacement of a separation matrix for each sample, thereby eliminating cross-contamination between samples and improving reproducibility. Best results are often obtained using chemically or dynamically coated capillaries. 

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