Naphthalene Dicarboxaldehyde as an Electrophilic Fluorogenic Moiety for Affinity Labeling:  Application to Opioid Receptor Affinity Labels with Greatly Improved Fluorogenic Properties

To develop ligands with fluorogenic properties amenable for following the kinetics of cross-linking to receptors, a naphthalene dicarboxaldehyde moiety has been attached to an opiate pharmacophore <b>2</b> and evaluated in μ opioid receptors. The fluorescence of the benzo[<i>f</i>]isoindole formed upon cross-linking of μ opioid receptors by <b>2</b> permitted the time-course of covalent bonding to be followed. This demonstrated proof-of-concept suggests the usefulness of naphthalene dicarboxaldehyde-containing affinity labels as kinetic probes.