Aldehydes with Bis-Hydrazide Compounds

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). The addition of sodium cyanoborohydride to a hydrazide—aldehyde reaction drives the equilibrium toward formation of a stable covalent complex. Mallia (1992) has found that adipic acid dihydrazide derivatization of periodate-oxidized dextran (containing multiple formyl functionalities) proceeds with much greater yield when sodium cyanoborohydride is present. 

The reaction of an excess of adipic acid dihydrazide with aldehyde groups present on proteins or other molecules will result in modified proteins containing alkyl-hydrazide groups (Fig. 96). Another bis-hydrazide compound, carbohydrazide, also may be employed with similar results, except that the spacer afforded through its use is considerably shorter. Target aldehydes may be created on macromolecules according 

Protein Molecule Containing Periodate-oxidized Polysaccharides (possessing aldehyde groups) 

Hydrazone Linkage with Terminal Hydrazide Group (a hydrazide-ar ivated glycoprotein) 

Add a quantity of adipic acid dihydrazide or carbohydrazide (Aldrich) to the 

---