1. Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (USA), Fax: (+1) 858‐784‐7375
2. Graduate School of Pharmaceutical Sciences, Chiba University, 1‐33 Yayoi‐cho, Inage‐ku, Chiba 263‐8522 (Japan)