Dextran carboxyl derivatives

Hydrazide derivatives of dextran also may be prepared from the periodate-oxidized polymer or from a carboxyl derivative by reaction with fcfs-hydrazide compounds (Chapter 4, Section 8). A hydrazide terminal spacer provides reactivity toward al-... 

Dextran derivatives containing carboxyl- or amine-terminal spacer arms may be prepared by a number of techniques. These derivatives are useful for coupling amine- or carboxylate-containing molecules through a carbodiimide-mediated reaction to form an amide bond (Chapter 3, Section 1). Amine-terminal spacers also can be used to create secondary reactive groups by modification with a heterobifunctional crosslinking agent (Chapter 5). 

Another approach uses reactive alkyl halogen compounds containing a terminal carboxylate group on the other end to form spacer arms off the dextran polymer from each available hydroxyl. In this manner, Brunswick et al. (1988) used chloroacetic acid to modify the hydroxyl groups to form the carboxymethyl derivative. The carboxylates then were aminated with ethylene diamine to create an amine-terminal derivative (Inman, 1985). Finally, the amines were modified with iodoacetate to form a sulfhydryl-reactive polymer (Figure 25.14). 

In a somewhat similar scheme, Noguchi et al. (1992) prepared a carboxylate spacer arm by reacting 6-bromohexanoic acid with a dextran polymer. The carboxylate then was aminated with ethylene diamine to form an amine-terminal spacer (Figure 25.15). This dextran derivative finally was reacted with N-Succinimidyl 3-(2-pyridyldithio)propionate (SPDP) (Chapter 5, Section 1.1) to create the desired sulfhydryl-reactive polymer (Section 2.4, this chapter). The SPDP-activated polymer then could be used to prepare an immunoconjugate composed of an antibody against human colon cancer conjugated with the drug mitomycin-C. 

Figure 25.14 An amine derivative of dextran may be prepared through a two-step process involving the reac-tion of chloroacetic acid with the hydroxyl groups of the polymer to create carboxylates. Next, ethylene diamine is coupled in excess using a carbodiimide-mediated reaction to give the primary amine functional groups.

The following protocols may be used to create carboxyl-, amine-, or hydrazide-containing derivatives of dextran. 

The ethylene diamine-dextran derivative may be used for the coupling of carboxylate-contain-ing molecules by the carbodiimide reaction, for the coupling of amine-reactive probes, or to modify further using heterobifunctional crosslinkers. The hydrazide-dextran derivative may be used to crosslink aldehyde-containing molecules, such as oxidized carbohydrates or glycoproteins. 

Finally, the hetero polysaccharide hexagluconylhexasaminoglycan sulfate was identified as an anticoagulant and antithrombotic material compared to heparin by Sederel and coworkers [521], Derivatives of the polysaccharide dextran containing sulfate, sulfonate or carboxylic groups gave antithrombotic activity due to the presence of these charged groups [483, 522-525],... 

Several chemical approaches may be used to form the amine- or carboxyl-terminal dextran derivative. The simplest procedure may be to prepare polyaldehyde dextran according to the procedure of Section 2.1, and then make the spacer arm derivative by reductively animating an amine-containing organic compound onto it. For instance, short diamine compounds such as ethylene diamine or diaminodipropylamine (3,3 -iminotepropylamine) can be coupled in excess to polyaldehyde dextran to create an amine-terminal derivative. Carboxyl-terminal derivatives may be prepared similarly by coupling molecules such as 6-aminocaproic acid or p-alanine to polyaldehyde... 

D. Abbott and H. Weigel, Studies on dextrans and dextranases. Part V. Synthesis of the three carboxylic acids derived from methyl /1-maltoside, J. Chem. Soc., (1965) 5157-5162. 

Materials. The following were obtained from commercial sources Swims medium S77, horse serum, and fetal calf serum (Grand Island Biologicals) MTX (Lederle Laboratories) was purified by DEAE cellulose prior to use (11) crystalline BSA, poly-L-lysine (M 35,000), hypoxanthine and thymidine (Sigma Chemical Co.) 1-etnyl-3-(3 -dimethylaminopropyl)carbodiimide hydrochloride (EDC) (Story Chemicals) folinic acid (ICN Pharmaceuticals) Blue Dextran (Pharmacia). The concentrations of the folate derivatives and MTX were determined by their respective extinction coefficients (13). MTX-BSA was synthesized according to a previously described procedure ( ) in which MTX is coupled via a terminal carboxyl group to -amino groups contained in the albumin molecule. 

---