1. Molecular Cancer Research Center, Korean Research Institute of Biosciences and Biotechnology, Daejeon 305-333, Korea, Laboratory of Natural Products, College of Pharmacy, Chungnam National University, Daejeon 305-764, Korea, Department of Biochemistry, College of Natural Sciences, Kangwon National University, Chuncheon 200-701, Korea, and Division of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 136-713, Korea