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.