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. Graduate School of Agricultural and Life Sciences; The University of Tokyo; Bunkyo-ku Tokyo 113-8657 Japan
3. Graduate School of Pharmaceutical Sciences; Hokkaido University; Sapporo Hokkaido 060-0812 Japan
4. Japan Agency for Marine-Earth Science and Technology (JAMSTEC); Natsushima Yokosuka Kanagawa 237-0061 Japan