1. Research and Development Division, Yamasa Corporation, 2−10−1 Araoicho, Choshi, Chiba 288, Japan, Cancer Research Institute, Kanazawa University, 13−1 Takara-machi, Kanazawa 920, Japan, and Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12, Nishi-6, Kita-ku, Sapporo 060, Japan