1. Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, and Aventis Pharmaceuticals, Inc., 1041 U.S. Route 202-206, Bridgewater, New Jersey 08807