1. Tsukuba Research Laboratories, Eisai Co., Ltd., 5-1-3 Tokodai, Tsukuba-shi, Ibaraki 300-2635, Japan
2. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
3. Kashima Plant, Eisai Co., Ltd., 22 Sunayama, Kamisu-shi, Ibaraki 314-0255, Japan