1. Laboratory of Aquatic Natural Products Chemistry,
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
2. Misaki Marine Biological Station, The University of Tokyo, Miura, Kanagawa 238-0225,
Japan
3. Faculty of Fisheries, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521,
Japan