Cloxacepride and related compounds: a new series of orally active antiallergic compounds.

4-[[(p-Chlorophenoxy)acetyl]amino]-5-chloro-2-methoxy-N-[2-(diethylamino)ethyl]benzamide (cloxacepride, 1), exhibited substantial oral antiallergic potential in a reaginic PCA test in rats over a wide range of antigenic challenge times. Available reference compounds with oral activity, such as doxantrazole and 7-(2-hydroxyethoxy)-9-oxoxanthene-2-carboxylic acid (AH 7725, 4), were active only when administered 15 min before challenge: 4, in particular, was not consistent in effect. Oral ED50 values for cloxacepride of 46-49 mg/kg were comparable to that of theophylline and to an intravenous injection of 2 mg/kg of disodium chromoglycate (DSCG) followed by immediate challenge. Following oral ED50 doses, 1 showed slower onset and longer duration of action than theophylline. The absence of inhibition of systemic anaphylaxis and of antihistaminic activity suggests specific effect or reaginic antigen antibody reactions. Structure-activity relationships of various chemical modifications were investigated and discussed in terms of essential substituents.