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. National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa, Yokohama 236-8648, Japan
3. Sugashima Marine Biological Laboratory, Graduate School of Science, Nagoya University, Toba, Mie 517-0004, Japan
4. Takehara Marine Science Station, Hiroshima University, Takehara, Hiroshima 725-0024, Japan