1. Department of Organic Chemistry, University of Barcelona, 08028-Barcelona, Spain, Rohm and Haas Company, PO Box 904, 727 Norristown Road, Spring House, Pennsylvania 19477-0904, Instituto de Química Orgánica de Síntesis, CONICET-Universidad Nacional de Rosario, Rosario, Argentina, RheoGene, Inc., 2650 Eisenhower Avenue, Norristown, Pennsylvania 19403, and Barcelona Biomedical Research Institute, Barcelona Science Park, University of Barcelona, 08028-Barcelona, Spain