Compounds of formula (I): ##STR1## wherein: A represents a CH-NO.sub.2 group or a N-CN group; B represents CH.sub.2, O, S or a direct bond; R represents a bicyclic or polycyclic residue, variously substituted and functionalized; R.sup.1 and R.sup.2, which may be the same or different, are hydrogen or C.sub.1 -C.sub.4 alkyl groups; and n and m, which may be the same or different, are 0, 1, 2, 3 or 4; are valuable pharmacological agents.