Compounds of formula (I): ##STR00001## wherein: R.sub.1 represents hydrogen, alkylcarbonyloxyalkyl or alkylcarbonylthioalkyl, R.sub.2 represents hydrogen, alkylcarbonyloxyalkyl, arylcarbonylthioalkyl or optionally substituted arylalkyl, R.sub.3 represents phenyl, which is optionally substituted, or indolyl, their isomers, and addition salts thereof with a pharmaceutically acceptable acid or base.Medicinal products containing the same which are useful in the treatment of arterial hypertension and complications thereof.