Abstract: The invention concerns compounds and their enantiomers of the formula IA or IB ##STR1## and pharmaceutically acceptable salts thereof wherein each of R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.6, R.sup.7, R.sup.8, R.sup.9, R.sup.10, R.sup.11 and R.sup.12 is independently selected from hydrogen or an alkyl group containing 1-6 carbon atoms and R.sup.5 is an alkoxy group containing 1-6 carbon atoms. The invention further concerns pharmaceutical compositions comprising the active compounds and methods employing the compounds for the treatment of conditions associated with free radical formation.