1. Natural Products Research Institute, College of Pharmacy, Seoul National University, San 56-1, Sillim, Gwanak, Seoul 151-742, Korea
2. Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
3. Chemical Biology Institute, Yale University, West Haven, Connecticut 06516, United States
4. Marine Natural Products Laboratory, Korea Institute of Ocean Science & Technology, P.O. Box 29, Seoul 425-600, Korea
5. Department of Biological Science, College of Life Science and Nano Technology, Hannam University, 461-6 Jeonmin, Yuseong, Daejeon 305-811, Korea
6. Department of Agricultural Biotechnology, College of Agriculture and Life Science, Seoul National University, San 56-1, Sillim, Gwanak, Seoul 151-921, Korea