1. Drug Discovery Laboratories, Welfide Corporation, 7-25 Koyata 3-chome, Iruma-shi, Saitama 358-0026, Japan, Research Laboratories, Taito Company, Ltd., 1-26 Higashi Shiriike-shinmachi, Nagata-ku, Kobe 653-0023, Japan, and Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8304, Japan