Discovery, synthesis and SAR of 2-acyl-1-biarylmethyl pyrazolidines, dual orexin receptor antagonists designed as fast and short-acting sleeping drugs

Dual orexin receptor antagonists (DORAs) are approved for the treatment of sleep onset and/or sleep maintenance insomnia. In the present disclosure, we report the discovery of a new class of DORAs designed to treat sleep disorders requiring a fast onset and a short duration of action (<4 h). We used early human pharmacokinetic-pharmacodynamic (PK-PD) predictions and in vivo experiments to identify DORAs eliciting this specific hypnotic profile. A high-throughput screening campaign revealed hits based on a rarely precedented tricyclic pyrazolidine scaffold. After unsuccessful structure–activity-relationship (SAR) studies on this hit series, a scaffold hopping exercise, aimed at reducing the molecular complexity of the tricyclic scaffold, resulted in the discovery of the 2-acyl-1-biarylmethylpyrazolidine series. SAR studies on this achiral series gave rise to the lead compound DORA 42. In vitro and in vivo parameters of DORA 42, and its PK-PD simulation for human use are detailed.