Novel potent (dihydro)benzofuranyl piperazines as human histamine receptor ligands - Functional characterization and modeling studies on H and H receptors.

Histamine acts through four different receptors (HR-HR), the HR and HR being the most explored in the last years as drug targets. The HR is a potential target to treat narcolepsy, Parkinson's disease, epilepsy, schizophrenia and several other CNS-related conditions, while HR blockade leads to anti-inflammatory and immunomodulatory effects. Our group has been exploring the dihydrobenzofuranyl-piperazines (LINS01 series) as human HR/HR ligands as potential drug candidates. In the present study, a set of 12 compounds were synthesized from adequate (dihydro)benzofuran synthons through simple reactions with corresponding piperazines, giving moderate to high yields. Four compounds (1b, 1f, 1g and 1h) showed high hHR affinity (pK > 7), compound 1h being the most potent (pK 8.4), and compound 1f showed the best efficiency (pKi 8.2, LE 0.53, LLE 5.85). BRET-based assays monitoring Gα activity indicated that the compounds are potent antagonists. Only one compound (2c, pK 7.1) presented high affinity for hHR. In contrast to what was observed for hHR, it showed partial agonist activity. Docking experiments indicated that bulky substituents occupy a hydrophobic pocket in hHR, while the N-allyl group forms favorable interactions with hydrophobic residues in the TM2, 3 and 7, increasing the selectivity towards hHR. Additionally, the importance of the indole NH in the interaction with Glu5.46 from hHR was confirmed by the modeling results, explaining the affinity and agonistic activity of compound 2c. The data reported in this work represent important findings for the rational design of future compounds for hHR and hHR.