Synthesis of novel allosteric modulators of the G-protein coupled receptor CB1

CB1 allosteric modulators provide new opportunities to specifically regulate biological responses mediated by CB1 receptor. This approach is an attempt to infer information about the mode of binding interactions and signaling efficacy produced by allosteric modulators. Indole-2- carboxamide, ORG27569 (5-chloro-3-ethyl-N-(4-piperidin-1-yl)phenethyl)-1H-indole-2- carboxamide) and GBR12909 exhibits allosteric modulation on the CB1 receptor and ORG27569 regulates the CB1 receptor in pathway specific manner. To better understand the interaction of these compounds with the allosteric site on CB1 receptor, we synthesized analogs of ORG27569 and GBR12909 and were further characterized for their allostery on CB1 receptor. The presence of the indole ring in indole-2-carboxamide is preferred for modulator’s binding affinity (KB) to the allosteric site, but not necessary for allosteric modulation on the orthosteric site. Through structural modification, we identified a robust CB1 allosteric modulator ICAM-b, which showed an equilibrium constant KB of 469.9 nM with a markedly high cooperativity factor (= 17.6). Similarly, our hypothesis that 4-fluoro benzhydryl moiety of GBR12909 analogs can produce allosteric effects on CB1 receptor has also been proved