The present invention provides compounds represented by general formula (I): or pharmaceutical acceptable salts thereof, wherein R.sup.1 and R.sup.2 are each hydrogen or lower alkyl; R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each hydrogen, halogen, lower alkyl or lower alkoxy; R.sup.7 and R.sup.8 are each hydrogen, halogen, lower alkyl, halo-lower alkyl, lower alkoxy, cycloalkyl, aryl, heteroaryl, cyano, a hydroxyl group, lower acyl, carboxy or the like; R.sup.9 is --C(O)--R.sup.10, -A.sup.1-C(O)--R.sup.10, --O-A.sup.2-C(O)--R.sup.10 or a tetrazol-5-yl group, which exhibit potent and selective .beta.3-adrenoceptor stimulating activities. The present invention also provides pharmaceutical compositions containing said compound, and uses thereof.