In other preferred embodiments of the compound above, R4 is a hydrogen atom and R3 is a cyclohexyl group; R4 is a hydrogen atom and R3 is a methyoxy group; R3 and R4 each bond together to form a piperidine group; R4 is a hydrogen atom and R3 is a hydroxyl group; R4 is a hydrogen atom and R3 is a benzyloxy group; R4 is a hydrogen atom and R3 is a ??-pyridine group; R4 is a hydrogen atom and R3 is a