A new perspective of cannabinoid 1 receptor antagonists: Approaches toward peripheral CB1R blockers without crossing the blood-brain barrier

Since Rimonabant was withdrawn in Europe in 2008 because of its substantial CNS risk factors including depression and anxiety, the development of anti-obesity drugs targeting CB1R in the brain has been suspended and/or terminated globally. Instead, developing peripherally restricted CB1R antagonists is actively pursued in the hope that not only could they eliminate any CNS adverse effects observed with Rimonabant, but also maintain therapeutic benefits in metabolic syndrome, including obesity, type 2 diabetes, and non-alcoholic fatty liver diseases. In this review, we summarized the most recent advances that have been made on this area, with particular emphasis on various synthetic approaches, whereby the increase in polarity, water solubility and polar surface area were centralized on, toward potential peripheralacting CB1 antagonists.