1. Division of Natural Product Sciences School of Pharmacy Iwate Medical University 1-1-1 Idaidori Yahaba Iwate 028-3694 Japan
2. Current address: Research Institute of Pharmaceutical Sciences Musashino University 1-1-20 Shinmachi, Nishitokyo-shi Tokyo 202-8585 Japan
3. Department of Bioactive Molecules National Institute of Infectious Diseases 1-23-1 Toyama, Shinjuku-ku Tokyo 162-8640 Japan
4. National Institute of Health Sciences 3-25-26 Tonomachi, Kawasaki-ku Kanagawa 210-9501 Japan
5. Current address: Department of Organic Chemistry Hoshi University 2-4-41 Ebara, Shinagawa-ku Tokyo 142-8501 Japan
6. Graduate School of Pharmaceutical Sciences The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-0033 Japan
7. Cluster for Pioneering Research (CPR) Advanced Elements Chemistry Laboratory RIKEN 2-1 Hirosawa Wako-shi Saitama 351-0198 Japan