1. School of Pharmaceutical Sciences, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan, Department of Tropical Medicine and Parasitology, School of Medicine, Keio University, 35, Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan, and Pola Chemical Industries, Inc., 27-1, Takashimadai, Kanagawa-ku, Yokohama, 221-0833, Japan