The invention relates to compounds of the general formula (I) and their pharmaceutically acceptable salts (in which formula R1 represents a hydrogen atom, lower alkyl group, lower alkenyl group, lower cycloalkyl group, aryl group, aralkyl group or heterocyclic group, wherein, the above groups are optionally substituted in ortho, meta and/or para position with 1, 2, 3 or 4 electron withdrawing groups or electron donating groups； R2 represents a hydrogen atom, lower alkyl group, aryl group, aralkyl group or heterocyclic group wherein the above groups are optionally substituted with one or more halogen atoms； R3 represents a lower alkyl group, aryl group, aralkyl group or heterocyclic group wherein the above groups are optionally substituted in ortho, meta or para position with 1, 2, 3 or 4 electron withdrawing groups or electron donating groups； R4 represents a hydrogen atom, lower alkyl group or any acidic functional group； n is 1 or 2). The compounds according to the invention can be used in the medicine mainly for the treatment of diseases associated with neurological and/or oxidative stress.
