The invention relates to a compound of formula (I): ##STR1## wherein: A represents pyridine, pyridinium or piperidine R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined in the description R.sub.5 represents hydrogen, a nitrogen-containing heterocycle or a group of formula (II): ##STR2## R.sub.6 represents hydrogen or linear or branched (C.sub.1 -C.sub.6)alkyl. and medicinal products containing the same which are useful in treating pain or deficiencies in memory.