1. Institute of Pharmaceutical Sciences, Hiroshima University School of Medicine, 1–2-3 Kasumi, Minamiku, Hiroshima 734
2. Osaka University of Pharmaceutical Sciences, 2–10-65 Kawai, Matsubara, Osaka 560, Japan
3. Pharmaceutical Chemistry Laboratories, University of Kansas, 2065 Constant Avenue, Lawrence, Kansas 66046, USA