1. Groupe Cycle Cellulaire, CNRS UMR 6061, IFR 97, Facult de Medecine, Universit Rennes 1, 2 Av. du Pr Leon Bernard, CS 34317, F-35043 Rennes Cedex, France, Department of Chemistry, University of Florida, Gainesville, Florida 32611, and Department of Chemistry, University of Central Florida, P.O. Box 162366, Orlando, Florida 32816-2366