1. Natural Products Research Institute, College of Pharmacy, Seoul National University, San 56-1, Shilim, Kwanak, Seoul 151-742, Korea, Marine Natural Products Laboratory, Korea Ocean Research & Development Institute, Ansan P.O. Box 29, Seoul 425-600, Korea, and Department of Agricultural Biotechnology, College of Agriculture & Life Science, Seoul National University, San 56-1, Shilim, Kwanak, Seoul 151-921, Korea