Recent advances in orexin receptor antagonists for the treatment of insomnia

The orexin system was discovered in 1998 with two G-protein coupled receptors (GPCRs):orexin-1 (OX₁R) and orexin-2 (OX₂R) receptors that bind the neuropeptides orexin-A (OX-A) and orexin-B (OX-B). The causal link between the orexin system and obesity, anxiety, and sleep/wake disorders as a potential therapeutic target has drawn much attention in the field of pharmaceuticals. The developments of dual antagonism of the receptors by small molecules are clinically efficacious in the treatment of insomnia, where the most advanced molecule suvorexant has been approved by FDA in August, 2014. The small molecule orexin receptor antagonists (ORA) between January 2010 and August 2017 are summarized in this review and we focus on their chemical structures, mechanism and human clinical trials.