1. Natural Products Research Laboratories, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599, Medical Center, Box 2926, SORF, Duke University, Durham, North Carolina 27710, Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung 807, Taiwan, and Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, Niigata 950-2081, Japan