Synthesis and antiallergic activities of 1,3-oxazolo[4,5-h]quinolines

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Abstract
A series of new 1,3-oxazolo[4,5-h]quinolines was prepared. These compounds were tested as inhibitors of antigen-induced release of histamine (AIR) in vitro from rat peritoneal mast cells (RMC) and as inhibitors of IgE-mediated passive cutaneous anaphylaxis in the rat (PCA). After several modifications of the original lead, the most potent compound of the series was determined to be 5-chloro-1,3-oxazolo[4,5-h]quinoline-2-carboxylic acid methyl ester. It has an IC50 [medium inhibitory concentration] of 0.3 .mu.M in the RMC assay and an ED50 (i.v.) of 0.1 mg/kg in the PCA test, which is 10 times and 60 times more potent than disodium cromoglycate (DSCG), respectively. Of greater importance, it is orally active (ED50 = 0.5 mg/kg) as an inhibitor of the pCA test.