The present invention provides a compound having the structure: (structurally represented) wherein R1, R2, R3, R4, and R5 are each independently H, halogen, CF3 or C1-C4 alkyl; R6 is alkyl; A is absent or present, and when present is —C(O)— or —C(O)NH—; B is substituted or unsubstituted monocycle, bicycle, heteromonocycle, heterobicycle, benzyl, CO2H or (C1-C4 alkyl)-CO2H, wherein when B is CO2H, then A is present and is —C(O)—, or a pharmaceutically acceptable salt thereof.