Compounds of the formula: ##SPC1##And their pharmaceutically acceptable non-toxic salts, wherein R.sub.1 is alkyl of 5 to 8 carbon atoms which is straight chained or .alpha.-substituted by a methyl group or .alpha.,.alpha.-disubstituted by methyl groups and R.sub.5 is hydrogen, R.sub.6 or CO.R.sub.6 wherein R.sub.6 is alkyl of 1 to 4 carbon atoms or alkyl of 1 to 4 carbon atoms substituted by NR.sub.7 R.sub.8 wherein R.sub.7 and R.sub.8 are each hydrogen or alkyl of 1 to 4 carbon atoms or NR.sub.7 R.sub.8 is pyrrolidino, piperidino or morpholino, have been found to possess good antihypertensive activity while being of low-toxicity and substantially free of sedative side effects.