1. Department of Chemistry, University of Aberdeen, Old Aberdeen, AB24 3UE, U.K., Institute of Applied Sciences, Faculty of Science and Technology, University of the South Pacific, P.O. Box 1168, Suva, Fiji Islands, Australian Institute of Marine Science, Townsville 4810, Queensland, Australia, and Laboratoire de Biologie Moléculaire et Cellulaire du Cancer, Hôpital Kirchberg, 9, Rue Edward Steichen, L-2540 Luxembourg, Luxembourg