1. Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan, Research Laboratory, Taito Co., Ltd., 1-26 Higashi Shiriike-shinmachi, Nagata-ku, Kobe 653, Japan, and Research Laboratories, Yoshitomi Pharmaceutical Industries, Ltd., 7-25 Koyata 3-chome, Iruma-shi, Saitama 358, Japan