New esters of heteryl acetic and mercaptoacetic acids. Synthesis and H1-antihistaminic evaluation.

Synthesis of esters containing 2 (N,N-dialkylamino) ethanolic and 2-alkoxyethanolic groups with heteroaryl acids was carried out. Three series of such esters: (2-substituted-3,4-dihydro-4-oxo-quniazolin-3-yl) acetates, S-(3-aryl-3,4-dihydro-4-oxo-quinazolin-2-yl) mercaptoacates and S-(1H-benzimidazol-2-yl) mercaptoacetates were synthesized from their respective acids/acid chlorides using appropriate alcohols. Their in vivo H1-antihistaminic potencies were evaluated using isolated guinea pig ileum method. The IC50 values indicate higher potencies of quinazolinonyl mercaptoacetates than the other two series, in general. Presence of an aryl group at position 3, with an electron-releasing substituent appears to enhance the antihistaminic activity. Similarly 2 (N,N-diethylamino) ethyl esters were found to be more active than the other type of esters tested.