1. Contribution from the Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, Genomics Institute of the Novartis Research Foundation, 10675 John J. Hopkins Drive, San Diego, California 92121, Department of Chemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, and Department of Chemistry, University of California, Berkeley, California 94720