1. Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan, Procyon Pharmaceuticals, Inc., 165 New Boston Street, Woburn, Massachusetts 01801, Max-Delbück Laboratorium, Carl-von-Linné-Weg 10, D-5000 Köln 30, Germany, and Institute of Medicinal Molecular Design, 5-24-5, Hongo, Bunkyo-ku, Tokyo 113, Japan