Compounds useful in the treatment of Alzheimer's disease, senile dementia, or memory disorders which have the formula ##STR1## in which R represents a hydrogen atom, a linear, branched or cyclic alkyl radical, saturated or unsaturated, containing up to 8 carbon atoms, possibly substituted by a free or esterified carboxy radical or R represents an aralkyl radical containing up to 10 carbon atoms and R' represents a linear or branched, saturated or unsaturated, alkyl radical, containing up to 8 carbon atoms, a radical --COalk.sub.1 or a radical --(CH.sub.2).sub.2 N(alk.sub.2).sub.2, alk.sub.1 and alk.sub.2 representing an alkyl radical containing up to 8 carbon atoms, as well as their addition salts with acids. Also compositions containing the same, method of preparation and method of treatment using the same.