Studies on 1-substituted 4-(1,2-diphenylethyl)piperazine derivatives and their analgesic activities. 2. Structure-activity relationships of 1-cycloalkyl-4-(1,2-diphenylethyl)piperazines.

Forty-six 1-cycloalkyl-4-(1,2-diphenylethyl)piperazines were synthesized. The influence of substituents on phenyl groups of 1-cycloalkyl-4-(1,2-diphenylethyl)piperazines 4a-c on the analgesic activity was investigated in experimental animals. The most active compounds, 5a-c, in this series had a m-hydroxyl group on the 2-phenyl group of 4a-c, while morphine has a phenolic hydroxyl group para to th- aminoethyl moiety. Their activities were 23-56 and 23-38 times those of their original compounds 4a-c and morphine, respectively, tested by the D'Amour-Smith method after subcutaneous administration.