Novel indole and azaindole (pyrrolopyridine) cannabinoid (CB) receptor agonists: design, synthesis, structure-activity relationships, physicochemical properties and biological activity

The discovery, synthesis and structure-activity relationship (SAR) of a novel series of cannabinoid 1 (CB(1)) and cannabinoid 2 (CB(2)) receptor ligands are reported. Based on the aminoalkylindole class of cannabinoid receptor agonists, a biphenyl moiety was introduced as novel lipophilic indole 3-acyl substituent in 11-16. Furthermore, the 3-carbonyl tether was replaced with a carboxamide linker in 17-20 and the azaindole (pyrrolopyridine) nucleus was designed as indole bioisostere with improved physicochemical properties in 21-25. Through these SAR efforts, several high affinity CB(1)/CB(2) dual cannabinoid receptor ligands were identified. Indole-3-carboxamide 17 displayed single-digit nanomolar affinity and ~80 fold selectivity for CB(1) over the CB(2) receptor. The azaindoles displayed substantially improved physicochemical properties (lipophilicity; aqueous solubility). Azaindole 21 elicited potent cannabinoid activity. Cannabinoid receptor agonists 17 and 21 potently modulated excitatory synaptic transmission in an acute rat brain slice model of cannabinoid receptor-modulated neurotransmission.