eteroaryl, heteroarylalkyl, or aryloxy; or R1 is a group of the structure ##STR460## wherein p is 1 to 8 and R17 and R18 are each independently H, alkyl, alkenyl, aryl, arylalkyl, heteroaryl, heteroarylalkyl, cycloalkyl or cycloalkylalkyl at least one of R17 and R18 being other than H; or R1 is a group of the structure ##STR461## wherein R19 is aryl or heteroaryl; R20 is aryl or heteroaryl; R21 is