Synthesis and platelet-activating factor (PAF)-antagonistic activities of 1,4-disubstituted piperazine derivatives

During the screening of novel platelet-activating factor (PAF) antagonists, we found that 1-(6-methoxy-3,4-dihydro-2-naphthoyl)-4- (3,4,5-trimethoxybenzyl)piperazine and its 4-(3,4,5- trimethoxybenzoyl)piperazine derivatives (1b, 2b) exerted in vitro and in vivo PAF-antagonistic activities. Modifications of the 1-acyl group, the substituent at the 4-position and the piperazine ring of 1a and 2b were examined and from this series 1-(2,3-dimethoxy-6,7-dihydro-5H-benzocyclohepten-8-ylcarbonyl++ +)-4- (3,4,5-trimethoxybenzoyl)piperazine (2g) was found to be one of the most potent PAF antagonists.