Non-imidazole histamine H3 ligands.: Part I.: Synthesis of 2-(1-piperazinyl)- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothiazole derivatives as H3-antagonists with H1 blocking activities

New 2-(1-Piperazinyl)- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothiazoles were prepared and tested as H-1- and H-3-receptor antagonists. A number of compounds showed weak H-1-antagonistic activity, with pA(2) values ranging from 5.5 to 6.1. The simple alkyl substituted, 2-[1-(4-methyl and 4-ethyl)piperazinyl] analogues show increasing, moderate I-I,-antagonistic activity (pA(2) = 6.0, and pA(2) = 7.0). The compounds with 4-phenylalkyl substitution, for both the piperazinyl and the hexahydro-1H-1,4-diazepin-1-yl homologues series, regardless of the different physicochemical properties of the pm a substituents at the phenyl ring, showed weak H-3-antagonistic activity with pA(2) values ranging from 4.4 to 5.6. (C) 1999 Elsevier Science S.A. All rights reserved.