In accordance with the present invention, it has been discovered that introduction
of hydrophilic sulfoalkyl substituents and/or hydrophilic linkers derived from
homocysteic acid, cysteic acid, glycine peptides, tetraethylene oxide, and the
like, offset the hydrophobicity of the acridinium ring system to produce a more
soluble label which can be attached to an antibody at higher loading before precipitation
and aggregation problems are encountered. Additional compounds described herein
contain linkers derived from short peptides and tetraethylene oxide which increase
aqueous solubility due to hydrogen bonding with water molecules. The present invention
also embraces reagents for multiple acridinium labeling for signal amplification
composed of a peptide bearing several acridinium esters with sulfonate groups at
regularly spaced intervals for increased solubility. The invention also embraces
assays employing the above-described compounds.
