1. Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1, Inohana, Chuo-ku, Chiba 260-8675, Japan
2. Department of Chemistry, Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
3. Department of Natural Medicines, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan