RATIONAL DESIGN AND SYNTHESIS OF NOVEL POTENTIAL CB2 RECEPTOR ALLOSTERIC MODULATORS

The endocannabinoid system (ECS) is a widespread neuromodulatory system with wide-range actions. It consists of cannabinoid receptors (CB1R and CB2R), their endogenous ligands (endocannabinoids, EC) and the enzymes responsible for the synthesis and degradation of the endocannabinoids. The two main endocannabinoids produced by the human body are anandamide (AEA) and 2-arachidonoylglycerol (2-AG), while the major enzymes respon-sible for their degradation are fatty acid amide hydrolase (FAAH), monoa-cylglycerol lipase (MAGL), α/ β-Hydrolase 6 (ABHD6) and α/ β-Hydrolase 1 (ABHD12). Modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases, such as neuropathic pain, Parkinson's disease, multiple sclerosis, cancer, glaucoma and obesity. Therefore, in the past decades, the activity of many compounds capable of directly activating cannabinoid receptors has been extensively investigated. However, although CBRs agonists have shown considerable potential in the treatment of various diseases, their use has been associated with undesirable side effects, such as mood alteration (euphoria, anxiety, panic), acute psychoses, and impaired cognition and motor performance. It is now generally accepted that many of the unwanted effects of cannabinoid receptor agonists are caused by their direct activation of CB1Rs located within the brain. Among all the strategies aimed at avoiding these kind of undesirable side effects, one of the most promising consists in the allosteric modulation of CBRs. Indeed allosteric modulators, compared to orthosteric ligands, offer several unique advantages. First of all they provide selective spatial and temporal signaling, exerting their e ects only in the presence of endocannabi-noids, which are transiently released on demand and removed from their sites of action by cellular uptake. Moreover, the e ect of allosteric modulators is saturable because of their dependence on endogenous ligands for signaling, and this phenomenon increases the likelihood of on-target safety in overdose situations. Furthermore, GPCR allosteric binding sites are often less conserved than orthosteric sites, thus allosteric ligands have a greater potential for receptor subtype. Finally, they might present synergizing e ects if coadministered with other ECS modulators. More specifically, allosteric modulators can be classified in positive allosteric modulators (PAMs) and negative allosteric modulators (NAMs) when they respectively potentiate or attenuate an agonist-mediated receptor response. Moreover, compounds which bind to the allosteric site without a effcting receptor activity are classified as silent allosteric modulators (SAMs). In the laboratory where I performed my thesis molecules of general structure A and B , which showed to be CBRs orthosteric ligands, were developed. With the aim of exploring the structure activity relationships of these 2-oxopyridine-3-carboxamides derivatives, compounds C1-C5, D1-D6 and E1 were synthesized. In particular these molecules were obtained substituting the amide side chain in position C-3 of derivatives A and B with the corresponding retroamide. Following [3H]CP55940 and [35S]GTPγS binding assays, compound C2 unexpectedly turned out to be active as a positive allosteric modulator of CB2Rs. Interestingly, compound C2 was the rst CB2R PAM ever reported in the literature. With the aim to deepen the structure activity relationship (SAR) of C2, during my thesis work I designed and synthesized compounds F1-F4, G1-G2 and H1-H2. Derivatives with general structure F were obtained by replacing the cyclo-heptyl moiety of compound C2 with an aromatic or an aliphatic substituent, in order to modify the amide side chain in position C-3. Derivatives with general structure G were obtained substituting the amide function in position C-3 of C2 respectively with a carbamidic (G1) and with an ureic (G2) function. More speci cally, in compound G1 the cycloheptylic substituent of C2 was maintained, while in G2 it was replaced with a phenyl group. Finally, derivative H1 was obtained following the substitution of p- fluorobenzyl in position C-1 of compound C2 with an aliphatic chain. The O-alkylated derivative (H2) was isolated as well. Functional activity and binding affinity of all the compounds I synthesized during my master thesis will be evaluated in Professor Pertwee's lab at the University of Aberdeen