Formula (I) compounds: 1 wherein R.sup.1 is alkyl substituted by fluorine(s); R.sup.2 is hydroxy, alkoxy, alkoxy substituted by phenyl, NR.sup.3R.sup.4, in which R.sup.3, R.sup.4 is (i) hydrogen, (ii) alkyl, (iii) phenyl, (iv) phenyl substituted by alkoxy or carboxyl, (v) heterocyclic ring containing nitrogen atom, (vi) alkyl substituted by phenyl, phenyl subsituted by alkoxy or carboxyl, heterocyclic ring containing nitrogen atom, (vii) the nitrogen bonded to R.sup.3 and R.sup.4, taken together is a saturated heterocyclic ring or amino acid residue; and non-toxic salts and acid addition salts thereof. Also, Formula (X) compounds: 2 wherein n is 0 or 1, R.sup.11 is hydrogen and chlorine, R.sup.5 is R.sup.7--CH.sub.2-- or R.sup.8, or R.sup.5 and R.sup.11, taken together is alkylidene; R.sup.6 is hydroxy, alkoxy, alkoxy substituted by phenyl, NR.sup.9R.sup.10, in which R.sup.9, R.sup.10 is (i) hydrogen, (ii) alkyl, (iii) phenyl, (iv) phenyl substituted by alkoxy or carboxyl, (v) heterocyclic ring containing nitrogen atom, (vi) alkyl substituted by phenyl, phenyl-substituted by alkoxy or carboxyl, heterocyclic ring containing nitrogen atom, (vii) the nitrogen bonded to R.sup.9 and R.sup.10, taken together is a saturated heterocyclic ring or amino acid residue, R.sup.7 is (i) F--(CH.sub.2).sub.m-- or F.sub.3C--CH.sub.2--, (ii) alkyl subsstituted by chlorine, (iii) alkyl substituted by alkoxy, cycloalkyl, phenyl, phenoxy; R.sup.8 is alkyl, alkenyl, alkoxy, alkylthio, cycloalkyl, phenyl, phenoxy. Non-toxic and acid addition salts thereof are useful to prevent and/or treat neurodegenerative disease (e.g., Alzheimer's) and neuronal dysfunction by stroke or traumatic injury (e.g., Multiple sclerosis).