Rhodanine as a scaffold in drug discovery: a critical review of its biological activities and mechanisms of target modulation.

INTRODUCTION: Rhodanine-based compounds have been associated with numerous biological activities. After many years of research in drug discovery, they have gained a reputation as being pan assay interference compounds (PAINS) and frequent hitters in screening campaigns. Rhodanine-based compounds are also aggregators that can non-specifically interact with target proteins as well as Michael acceptors and interfere photometrically in biological assays due to their color. AREAS COVERED: The authors review the recently reported biological activities of rhodanine-based compounds. Furthermore, the article provides details of their synthesis and occurrence in compound libraries through high-throughput screening (HTS) and virtual high-throughput screening (VHTS). Additionally, the authors provide the reader with possible mechanisms of non-specific target modulation, analysis of the crystal structures of enzyme-rhodanine complexes and a comparison of rhodanine and thiazolidine-2,4-dione moieties. EXPERT OPINION: The biological activity of compounds possessing a rhodanine moiety should be considered very critically despite the convincing data obtained in biological assays. In addition to the lack of selectivity, unusual structure-activity relationship profiles and safety and specificity problems mean that rhodanines are generally not optimizable.