Chem Biol Drug Des. 2017;1–13. wileyonlinelibrary.com/journal/cbdd | 1 © 2017 John Wiley & Sons A/S Received: 17 March 2017 | Revised: 16 May 2017 | Accepted: 24 June 2017 DOI: 10.1111/cbdd.13069 RESEARCH ARTICLE Novel pyrrolocycloalkylpyrazole analogues as CB 1 ligands Battistina Asproni 1 | Ilaria Manca 2 | Giansalvo Pinna 1 | Elena Cichero 3 | Paola Fossa 3 | Gabriele Murineddu 1 | Paolo Lazzari 2 | Giovanni Loriga 4 | Gérard A. Pinna 1 1 Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Sassari, Italy 2 KemoTech Srl, Pula, CA, Italy 3 Dipartimento di Farmacia, Università di Genova, Genova, Italy 4 Consiglio Nazionale delle Ricerche, Istituto di Farmacologia Traslazionale, UOS Cagliari, Pula, CA, Italy Correspondence Battistina Asproni, Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Sassari, Italy. Email: asproni@uniss.it Novel 1,4-dihydropyrazolo[3,4- a]pyrrolizine-, 4,5-dihydro-1H-pyrazolo[4,3- g]in- dolizine- and 1,4,5,6-tetrahydropyrazolo[3,4- c]pyrrolo[1,2- a]azepine-3-carboxamide- based compounds were designed and synthesized for cannabinoid CB 1 and CB 2 receptor interactions. Any of the new synthesized compounds showed high affinity for CB 2 receptor with K i values superior to 314 nM, whereas some of them showed moderate affinity for CB 1 receptor with K i values inferior to 400 nM. 7-Chloro-1-(2, 4-dichlorophenyl) -N- (homopiperidin-1-yl)-4,5-dihydro-1H-pyrazolo[4,3-g] indolizine-3-carboxamide (2j) exhibited good affinity for CB 1 receptor (K i CB 1 = 81 nM) and the highest CB 2 /CB 1 selectively ratio (>12). Docking studies carried out on such compounds were performed using the hCB 1 X-ray in complex with the close pyrazole analogue AM6538 and disclosed specific pattern of interac- tions related to the tricyclic pyrrolopyrazole scaffolds as CB 1 ligands. KEYWORDS binding affinity, cannabinoid receptors, docking studies, pyrrolocycloalkylpyrazole 1 | INTRODUCTION The cannabinoid CB 1 and CB 2 receptors (CB 1 R and CB 2 R) belong to the rhodopsin-like family of G protein-coupled re- ceptors (GPCRs) and are key components of the endocanna- binoid system. [1–3] The CB 1 R is abundantly expressed in the central nervous system (CNS) but also is present in periph- eral tissues, including lungs, liver, kidneys and adipocytes. [4] CB 2 R is found most abundantly in the periphery, predom- inantly expressed in cells of the human immune system as spleen, tonsils and thymus, [4] and to a much lesser extent in CNS. [5] CBRs are activated by terpenoid plant constituents, for example, by Δ 9 -tetrahydrocannabinol, the major psychoactive component of Cannabis sativa. [6] Recent studies have demon- strated that CB 2 Rs are involved in numerous diseases. [4,7] Several selective CB 2 R agonists exhibited analgesic activity in preclinical models of acute, inflammatory and neuropathic pain, [4,8,9] whereas CB 1 R activation mediates analgesia, stim- ulation of appetite and euphoria, among other effects, [4] and is responsible of psychotropic effects. [10] CB 1 R antagonists are potential drugs for the therapy of drug and alcohol addiction as well as for the treatment of obesity. In this regard, rimon- abant (Figure 1) was the first potent CB 1 R antagonist/inverse agonist [11] approved by European Commission as an antiobe- sity agent; however, it was soon withdrawn by EMEA for its serious psychiatric disorders including anxiety, depression and suicidal tendency. [12] Within the search for new and safe antiobesity agents, recent medicinal chemistry approaches are oriented towards the obtainment of new peripherally selective CB 1 antagonists, by designing ligands that do not cross the blood–brain barrier and have low brain penetration. [13–15] The relevance of CBRs as emerging target of pharmacotherapy is documented also by the discovery of peripherally mixed CB 1 R/CB 2 R agonists as antiglaucoma agents. [16] During the past decade, numerous ligands endowed with high affinity and subtype selectivity for both receptors were synthesized, and within each chemo-type the structure–activ- ity relationship (SAR) studies were explored.