Compounds of formula(I) ##STR1## wherein R.sub.1 is nitro, halo, cyano and R.sub.2 is a group selected from ##STR2## wherein Y is oxygen or sulfur; X.sub.1 is NR wherein R is hydrogen, C.sub.1-8 alkyl or phenyl and pharmaceutically acceptable salts thereof are useful in the prevention or treatment of tissue damage induced by lipid peroxidation.