Structural modifications and in vitro pharmacological evaluation of 4-pyridyl-piperazine derivatives as an active and selective histamine H receptor ligands.

A novel series of 4-pyridylpiperazine derivatives with varying alkyl linker length and eastern part substituents proved to be potent histamine H receptor (hHR) ligands in the nanomolar concentration range. While paying attention to their alkyl linker length, derivatives with a six methylene linker tend to be more potent than their five methylene homologues. Moreover, in the case of both phenoxyacetyl- and phenoxypropionyl- derivatives, an eight methylene linkers possess lower activity than their seven methylene homologues. However, in global analysis of collected data on the influence of alkyl linker length, a three methylene homologues appeared to be of highest hHR affinity among all described 4-pyridylpiperazine derivatives from our group up to date. In the case of biphenyl and benzophenone derivatives, compounds with para- substituted second aromatic ring were of higher affinity than their meta analogues. Interestingly, benzophenone derivative 18 showed the highest affinity among all tested compounds (hHR K = 3.12 nM). The likely protein-ligand interactions, responsible for their high affinity were demonstrated using molecular modeling techniques. Furthermore, selectivity, intrinsic activity at HR, as well as drug-like properties of selected ligands were evaluated using in vitro methods.