Novel highly potent serotonin 5-HT 7 receptor ligands: Structural modifications to improve pharmacokinetic properties Enza Lacivita a,⇑ , Pantaleo Di Pilato a , Madia Letizia Stama a , Nicola Antonio Colabufo a , Francesco Berardi a , Roberto Perrone a , Bianca De Filippis b , Giovanni Laviola b , Walter Adriani b , Mauro Niso a , Marcello Leopoldo a a Università degli Studi di Bari ‘Aldo Moro’, Dipartimento di Farmacia-Scienze del Farmaco, via Orabona, 4, 70125 Bari, Italy b Behavioral Neuroscience Section, Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, viale Regina Elena 299, I-00161 Rome, Italy article info Article history: Received 26 July 2013 Revised 5 September 2013 Accepted 9 September 2013 Available online 17 September 2013 Keywords: 5-HT 7 receptors Arylpiperazines Serotonin Microsomial S9 fraction abstract Here we report the synthesis, pharmacological and pharmacokinetic evaluation of a pilot set of com- pounds structurally related to the potent and selective 5-HT 7 ligand LP-211. Among the studied com- pounds, N-pyridin-3-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (4b) showed high affinity for 5-HT 7 receptors (K i = 23.8 nM), selectivity over 5-HT 1A receptors (>50-fold), in vitro metabolic stability (82%) and weak interaction with P-glycoprotein (BA/AB = 3.3). Compound 4b was injected ip in mice to preliminarily evaluate its distribution between blood and brain. Ó 2013 Elsevier Ltd. All rights reserved. The 5-HT 7 subtype is the most recently discovered receptor in the serotonin (5-HT) receptor family and it has been cloned from several species including humans. 1 Since its identification, the 5- HT 7 receptor has been the subject of intense research efforts driven by its presence in functionally relevant regions of the brain. These receptors have been proposed as a therapeutic target for schizo- phrenia and mood disorders because several antipsychotics and antidepressants currently on the market bind to 5-HT 7 receptors with high affinity. 2–4 Several studies using selective 5-HT 7 receptor antagonists, such as 1 (SB-269970) (Fig. 1), or mice lacking the 5- HT 7 receptor have further supported a role for these receptors in depression. 5–7 Moreover, 5-HT 7 receptors have been implicated in other Central Nervous System (CNS) functions, including circa- dian rhythm, rapid eye movement sleep, thermoregulation, anxi- ety, epilepsy, learning and memory. 8 Recent data suggest that the activation of 5-HT 7 receptors have a prominent role in regulating the neuronal cytoarchitecture of behaviorally relevant neuronal networks in an age-dependent manner suggesting new approaches in modulating CNS connectiv- ity. 9,10 In fact, murine striatal and cortical neuronal cultures evi- denced significant neurite outgrowth after treatment with 5-HT 7 agonists 8-OH-DPAT and 2 (LP-211). 11 Finally, recent studies have suggested that selective activation of 5-HT 7 receptors may represent a novel therapeutic strategy in the treatment of Fragile X syndrome, the most common form of inherited intellectual dis- ability and autistic spectrum disorder. 12 On such basis, the identi- fication of 5-HT 7 -acting molecules with good brain penetrance is of key importance in view of proof-of-concept studies in animal models. Our research group has been involved for several years in the study of structure–activity relationships (SARs) of 4-substituted- 1-arylpiperazine derivatives, the so-called ‘long-chain’ arylpipera- zines. 13–17 Our studies have led to the identification of 2 which showed high 5-HT 7 receptor affinity (K i = 15.1 nM), good selectivity over 5-HT 1A (K i = 379 nM) and agonist properties in an ex vivo as- say of 5-HT 7 receptor activation. Disposition studies in mice evi- denced that 2 is brain penetrant and showed a half-life of 69 min. 18 Various studies have demonstrated that 2 is a valuable tool for studying the pharmacology of 5-HT 7 receptors in vitro 11,12 0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bmcl.2013.09.025 ⇑ Corresponding author. Tel.: +39 080 5442750; fax: +39 080 5442231. E-mail address: enza.lacivita@uniba.it (E. Lacivita). NC HN O N N 2 (LP-211) S OH N O O N 1 (SB-269970) Figure 1. Structure of selective 5-HT 7 ligands. Bioorganic & Medicinal Chemistry Letters 23 (2013) 6083–6086 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl 155