A series of substituted 5-oxo-5H-thiazolo [2, 3-b] quinazolinecarboxylic acids was prepared and evaluated in the rat PCA test for antiallergic activity. The analogues that exhibited the highest oral activity were the 7-methoxy, 7-methylthio, and 7-isopropyl in the 2-carboxylic acid series and the 2-isopropyl in the 7-carboxylic acid series.
![2-cyano-12-oxo-12H-benzothiazolo[2,3-b]quinazoline Structure](https://image.chemsrc.com/caspic/151/83350-93-0.png)
![12-oxo-[1,3]benzothiazolo[2,3-b]quinazoline-2-carboxylic acid Structure](https://image.chemsrc.com/caspic/113/83350-94-1.png)
![2-bromo-12-oxo-12H-benzothiazolo[2,3-b]quinazoline Structure](https://image.chemsrc.com/caspic/423/37752-72-0.png)
