Compounds of the formula (I):
and pharmaceutically acceptable salts thereof, wherein
R1 is isopropyl or tertiary-butyl;
R2 is hydrogen, C1-4alkyl, C1-4alkoxy, hydroxy or amino; and
R3 is hydrogen or methyl; are described for use as β-adrenoceptor antagonists. Pharmaceutical compositions containing them are disclosed as are processes for their preparation and intermediates therefor.