Sixteen derivatives (2-17) synthesized from the naphthoquinone lapachol (1), were tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), as a test for potential cancer chemopreventive agents. They exhibited a variety of inhibitory activities from very high to moderate, which allow us to suggest structure-activity relationships. Ten of these derivatives are reported for the first time, their structures being thoroughly determined by spectroscopic methods.