The basic helix-loop-helix PER-ARNT-SIM (bHLH-PAS) proteins BMAL1 and CLOCK heterodimerize to form the master transcription factor governing rhythmic gene expression. Owing to connections between circadian regulation and numerous physiological pathways, targeting the BMAL1-CLOCK complex pharmacologically is an attractive entry point for intervening in circadian-related processes. In this study, we developed a small molecule, Core Circadian Modulator (CCM), that targets the cavity in the PASB dom...