This invention thus includes, among others, compounds of the following formulas, as well as those exemplified elsewhere herein: ##STR8## where R1 is an aryl, arylalkyl or arylcycloalkyl group such as are illustrated above; R4 is an alkyl or aryl group and is preferably a C1-6 aliphatic group such as methyl, ethyl, n-propyl, i-propyl, allyl and so forth; Raa is H or an aryl or alkyl group and is pr