Amine, and Hydrazide Derivatives

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 cross-linking agent (Chapter 5). 

This type of modification process has been used to form sulfhydryl-reactive dextran polymers by coupling amine spacers with cross-linkers containing an amine-reactive end and a thiol-reactive end (Noguchi et al., 1992 Brunswick et al., 1988). The result was a multivalent sulfhydryl-reactive dextran derivative that could couple numerous sulfhydryl-containing molecules per polymer chain. 

Hgure 388 An amine terminal derivative of dextran may be prepared through a two-step process involving the reaction of chloroacetic acid with the hydroxyl groups of the polymer to create carboxylates. Next, ethylene diamine is coupled using a carbodiimide-mediated reaction to give the primary amine funaional groups. 

Another approach uses reactive alkyl halogen compounds containing a terminal carboxylate group on the other end to form spacer arms off the dextran polymer. In this manner, Brunswick et al. (1988) used chloroacetic acid to modify the hydroxyl groups of dextran, forming the carboxymethyl derivative. The carboxylates were then aminated with ethylene diamine to create an amine-terminal derivative (Inman, 1985). The amine was then modified with iodoacetate to form a sulfhydryl-reactive polymer (Fig. 388). 

In a somewhat similar scheme, Noguchi etal. (1992) prepared a carboxylate spacer arm by reacting 6-bromohexanoic acid with the dextran polymer. The carboxylate was then aminated with ethylene diamine to form an amine-terminal spacer (Fig. 389). This dextran derivative was finally reacted with SPDP (Chapter 5, Section 1.1) to create the final sulfhydryl-reactive polymer (Section 2.4). 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. 

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It should be noted that furoxan amides and hydrazides could only be prepared in aqueous solution. In ether solution, reaction of diethyl furoxandicarboxylate with amines and hydrazine derivatives have been shown to give isoxazolones 93 (Scheme 45) (08CB3512, 09LA52, 09LA80). 

The functional groups present in glycosides allow these derivatives to be used as substrates, aldehyde, or as amine reagents of the Mannich reaction. Thus, amide and hydrazide derivatives of D-galacturonic acid are employed as substrates of-type 479,... 

Hydrazides of vicinal acetylene-substituted derivatives of benzoic and azole carboxylic acids are important intermediate compounds because they can be used for cyclization via both a- and /3-carbon atoms of a multiple bond involving both amine and amide nitrogen atoms (Scheme 131). Besides, the hydrazides of aromatic and heteroaromatic acids are convenient substrates for testing the proposed easy formation of a five-membered ring condensed with a benzene nucleus and the six-membered one condensed with five-membered azoles. 

Addition of a nucleophile to the C-6 position of cytosine often results in fascile displacement reactions occurring at the N4 location. With hydroxylamine attack, nucleophilic displacement causes the formation of an N4-hydroxy derivative. A particularly important reaction for bioconjugate chemistry, however, is that of nucleophilic bisulfite addition to the C-6 position. Sulfonation of cytosine can lead to two distinct reaction products. At acid pH wherein the N-3 nitrogen is protonated, bisulfite reaction results in the 6-sulfonate product followed by spontaneous hydrolysis. Raising the pH to alkaline conditions causes effective formation of uracil. If bisulfite addition is done in the presence of a nucleophile, such as a primary amine or hydrazide compound, then transamination at the N4 position can take place instead of hydrolysis (Fig. 38). This is an important mechanism for adding spacer arm functionalities and other small molecules to cytosine-containing oligonucleotides (see Chapter 17, Section 2.1). 

Ushakov and Panarin synthesized polymeric salts of vinyl amine and vinyl alcohol copolymers and amides and hydrazides of penicillin derivatives. The coupled water-soluble, stable polymeric penicillin derivatives were found to have the same activity as the parent drugs. 

Sulfonyl chlorides (51) are important intermediates in the synthesis of a range of sulfonyl derivatives since the chlorine atom is readily replaced by nucleophilic reagents such as amines, alcohols and hydrazine to give the corresponding sulfonamides (57), sulfonates (58) and hydrazides (59) (Scheme 35). 

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