In this probe report, we describe the discovery and optimization of a novel more potent antagonist (120 nM by DiscoveRx) for the kappa-(κ) opioid (KOP) receptor that is >267-fold selective over the mu-(μ) (MOP) and the delta-(δ) (DOP) opioid receptors. Importantly, this probe and its analogs represent a novel chemical class compared to current literature antagonists and our previously submitted probe, ML140. Accordingly, this probe and its analogues may serve as interesting tools to advance addiction research. Additionally, this new chemotype is less complicated compared to known KOP receptor antagonist compounds. The structure contains no stereochemical centers and the short, versatile synthetic route enables both the synthesis of potential analogs and the production of the compound on larger scale.