The compound of claim 1 wherein Z is selected from the group consisting of:(1) --NR15 --, wherein R15 is selected from the group consisting of: hydrogen, --CH3, and --CH2 CH2 OCH3, (2) --CO--NR15 --, (3) --NR15 --CO--, (4) --SO2 --NR15 --, and (5) --NR15 --SO2 --, or if R3 is other than hydrogen, then Z is optionally absent. 15.