Photoaffinity ligands are useful tools for the isolation, purification, and characterization of proteins. As a step toward the goal of producing a photoaffinity probe for the dopamine transporter, isocyanato and azido derivatives of 3-[(phenylcarbamoyl)oxy]ecgonine methyl ester were synthesized and tested for their ability to interact with the cocaine receptor of mammalian brain via two different assays. The ability of two isothiocyanato (N=C=S) (para and meta) and two azido (N3) (para and meta) derivatives, as well as (-)-cocaine, to inhibit [3H]cocaine binding and [3H]dopamine uptake and to covalently interact with the cocaine-binding site was tested. The p-N=C=S was the most potent, with IC50 values of 0.23 and 0.49 microM for [3H]cocaine binding and [3H]dopamine uptake. The m-N3 and p-N3 inhibited [3H]cocaine binding with IC50 values of 0.63 and 1.00 microM and inhibited [3H]dopamine uptake with IC50 values of 5.08 and 1.32 microM, respectively. Preincubation of synaptosomal membranes with the m- or p-N=C=S isomer either in reduced lighting or under ultraviolet light followed by two washes resulted in inhibition of 70% and 85% of [3H]cocaine binding, respectively, indicating the highly reactive properties of these compounds. After preincubation in reduced lighting, m-N3 and p-N3 inhibited 0% and 13% of [3H]cocaine binding, while following preincubation under ultraviolet light, the inhibition increased to 61% and 68%, respectively. Thus, the isothiocyanato derivatives appear to bind irreversibly to the cocaine receptor in the presence or absence of ultraviolet light, whereas the azido derivatives are photoreactive compounds which may prove useful in the purification of the receptor.