o-Naphthalenedicarboxaldehyde derivative of 7'-aminonaltrindole as a selective delta-opioid receptor affinity label.

Incorporation of a naphthalene-dialdehyde moiety into the delta antagonist, 6'-aminonaltrindole afforded a potent, selective, irreversible delta-agonist 1. However, flow cytometry studies revealed no time-dependent specific fluorescence, suggesting that both Lys214 and Cys216 at the recognition site are not involved in covalent binding. Molecular simulation studies suggest that compound 1 may form a Schiff base with the epsilon-amino group of Lys214, which could explain its irreversibility and transformation into a delta-agonist through a conformational change of TM5.