Studies on 1,2,3-triazoles. 13. (Piperazinylalkoxy) [1]benzopyrano[2,3-d]-1,2,3-triazol-9(1H)-ones with combined H1-antihistamine and mast cell stabilizing properties.

Several N-benzylpiperazino derivatives of [1]benzopyrano[2,3-d]-1,2,3-triazol-9(1H)-one and its 5-methyl homologue have been prepared and evaluated for H1-antihistamine activity on guinea pig ileum. The most potent compounds were also evaluated for their ability to stabilize mast cells in the rat passive peritoneal anaphylaxis (PPA) system and were shown to inhibit histamine release at concentrations below those required to inhibit extravasation, suggesting that this might be relevant to their antianaphylactic activity in this system. The compound tested with the most potent H1-antihistamine activity was 6-[3-[4-(4-chlorobenzyl)-1-piperazinyl]propoxy][1]benzopyrano[2,3- d]-1,2,3-triazol-9(1H)-one, 28, which had a pA2 of 9.1 against histamine on guinea pig ileum, comparable to that of mepyramine, and inhibited histamine release in the rat PPA system with an IC50 value of 5.4 X 10(-6) M.