(+)-cis-N-(para-, meta-, and ortho-substituted benzyl)-N-normetazocines: synthesis and binding affinity at the [3H]-(+)-pentazocine-labeled (sigma 1) site and quantitative structure-affinity relationship studies.

σ1 receptor ligands have potential pharmacological significance as antipsychotic drugs, as tools in the study of drug-induced motor function disorders, and as radiopharmaceutical imaging agents for the noninvasive imaging of malignant tumors in human subjects. A series of substituted N-benzyl-N-normetazocines were synthesized and their binding affinity at the σ1 receptor evaluated in order to examine the details of the structure-affinity relationships (SAR) of a previously determined high-affinity lead compound, (+)-cis-N-benzyl-N-normetazocine (K i = 0.67 nM). Variation in the benzyl substituents of these compounds produced a 1590-fold range in affinity at the σ1 receptor from the unsubstituted benzyl analog to the lowest affinity p-tert-butylbenzyl analog (K i = 1066 nM). The nanomolar binding affinity for the σ1 receptor of (+)-cis-N-(4-fluorobenzyl)-N-normetzocine suggests that this analog may be a useful PET imaging agent