1. Contribution from the Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan, Division of Medicinal Chemistry, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan, Rigaku Corporation X-ray Research Laboratory, 3-9-12 Matsubaracho, Akishima, Tokyo 196-8666, Japan, and Faculty of Integrated Arts and Sciences, Hiroshima University,1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan