Hypertension can be treated using compounds having the formula or a basic salt thereof, wherein R.sub.1 is hydrogen, alkyl, aryl, arylalkyl or ##STR1## wherein R.sub.5 is alkyl or aryl; R.sub.2 is hydrogen or alkyl; R.sub.3 is aryl; R.sub.4 is hydrogen, alkyl or arylalkyl and n is 0, 1 or 2.