Aldehydes with Ammonia or Diamines

Aldehyde groups can be converted into terminal amines by a reductive amination process with ammonia or a diamine compound. The reaction proceeds by initial formation of a Schiff base 

Reduction to Secondary Amine Linkage with Terminal Primary Amine 

This simple strategy can be used to add amine residues to polysaccharide molecules after formation of aldehydes by periodate or enzymatic oxidation (Section 4.4, this chapter). Thus, glycoconjugates or carbohydrate polymers such as dextran may be derivatized to contain amines for further conjugation reactions. 

Nitration of the tyrosine rings in the four binding pockets of avidin or streptavidin can be done to increase the steric hinderance within the biotin binding sites (Morag et al., 1996). This process yields chromogenic proteins that have reduced binding affinity for biotin, thus allowing elution of biotinylated molecules under mild conditions. 

Dissolve the protein containing tyrosine residues (or another phenolic macromolecule) in 0.02 M sodium phosphate, 0.15M NaCl, pH 7.4, at a concentration of 2-4mg/ml. 

Aldehyde groups can be converted into terminal amines by a reductive amination process with ammonia or a diamine compound. The reaction proceeds by initial formation of a Schiff base interaction—a dehydration step yielding an imine derivative. Reduction of the Schiff base with sodium cyanoborohydride or sodium bor-ohydride produces the primary amine (in the case of ammonia) or a secondary amine derivative terminating in a primary amine (for a diamine compound) (Fig. 88). 

The reaction occurs rapidly at alkaline pH (7—10), with higher pH values resulting in better yields due to faster Schiff base formation. To ensure complete conversion of available aldehydes to amines, add the ammonia or diamine compound to the reaction in at least a 10-fold molar excess over the expected number of formyl groups present. Diamines that are commonly used for this process include ethylene diamine, diamino-dipropylamine (3,3 -iminobispropylamine), 1,6-diaminohexane, and the Jeffamine derivative EDR-148 containing a hydrophilic, 10-atom chain (Texaco Chemical Co.). 

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Figure 1.98 Aldehydes may be transformed into primary amines by reaction with ammonia or a diamine in the presence of a reducing agent.

Amine concentrations can be determined by using either diamine oxidase or monoamine oxidase in which the amine is oxidized to an aldehyde, hydrogen peroxide, and ammonia with uptake of oxygen (Equation 17). 

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