Dihydropyrrolopyrazol-6-one MCHR1 antagonists for the treatment of obesity: Insights on in vivo efficacy from a novel FLIPR assay setup

Our investigation of the structure–activity and structure–liability relationships for dihydropyrrolopyrazol-6-one MCHR1 antagonists revealed that off-rate characteristics, inferred from potencies in a FLIPR assay following a 2h incubation, can impact in vivo efficacy. The in vitro and exposure profiles of dihydropyrrolopyrazol-6-ones 1b and 1e were comparable to that of the thienopyrimidinone counterparts 41 and 43 except for a much faster MCHR1 apparent off-rate. The greatly diminished dihydropyrrolopyrazol-6-one anti-obesity response may be the consequence of this rapid off-rate.