Alkali-labile luminol derivatives as labels for quantitative binding studies with polyionic macromolecules

Acylated derivatives of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) bearing a carboxyl or amino group can be linked by amide bonds to a macromolecule requiring labelling. Though themselves of low quantum yield these compounds are alkali-labile and can be detected at a similar level of sensitivity to the parent compound luminol. These cheap, readily accessible compounds are less hydrophobic than other currently employed chemiluminescent labels. They also lack a positively charged nitrogen atom which could complicate their covalent linkage to polyanionic compounds. They thus appear well suited for labelling heparin and other macromolecules which interact with the luminal surface of blood vessels.