Compounds of the formula: ##STR1## wherein R.sup.1 and R.sup.2 each individually are hydrogen or lower alkyl optionally substituted by aryl or C.sub.3-6 -cycloalkyl; R.sup.4 and R.sup.5 either both are hydrogen or both are halogen or one is hydrogen and the other is halogen, hydroxy, lower alkoxy, aryloxy or amino; and R.sup.3 is hydrogen or, where no primary or secondary amino group is present, alkanoyl; with the proviso that all the groups R.sup.1 through R.sup.5 cannot simultaneously be hydrogen; as well as pharmaceutically acceptable salts of compounds of formula I with acids have valuable pharmacodynamic properties as non-competitive NMDA antagonists and can accordingly be used as neuroprotectives.