Neuronal nicotinic receptors have been implicated in several diseases and disorders such as autism, Alzheimer's disease, Parkinson's disease, epilepsy, and various forms of addiction. To understand the role of nicotinic receptors in these conditions, it would be beneficial to have selective molecules that target specific nicotinic receptors in vitro and in vivo. Our laboratory has previously identified novel negative allosteric modulators of human α4β2 (Hα4β2) and human α3β4 (Hα3β4) nicotinic receptors. The effects of novel sulfonylpiperazine analogues that act as negative allosteric modulators on both Hα4β2 nAChRs and Hα3β4 nAChRs were investigated. This work, through structure-activity relationship (SAR) studies, describes the chemical features of these molecules that are important for both potency and selectivity on Hα4β2 nAChRs.