1. Department of Chemistry; Graduate School of Science; Tohoku University; Sendai 980-8578 Japan
2. Department of Organic Chemistry; Graduate School of Pharmaceutical Sciences; Kyoto University; Yoshida, Sakyo-ku, Kyoto 606-8501 Japan
3. Department of Molecular Pharmacology; Graduate School of Pharmaceutical Sciences; Kyoto University; Yoshida, Sakyo-ku, Kyoto 606-8501 Japan