1. Institut de Chimie des Substances Naturelles, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette Cedex, France, Institute of Chemistry, National Center for Science and Technology, Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam, and Centre de Recherches Pierre Fabre, Avenue Jean Moulin, Castres Cedex, France