Disclosed are compounds having the formula ##STR00001## wherein R.sup.1 is hydrogen, an alkyl group, an aryl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aralkyl group, or .dbd.O, R.sup.2 is an alkyl group, an aryl group, a cycloalkyl group, an alkenyl group, an alkynyl group, or an aralkyl group, or the pharmaceutically acceptable salt or ester thereof. Also disclosed are methods of using the compounds.