Institute of Chemical Sciences and Engineering (ISIC), Swiss Federal Institute of Technology, EPFL-BCH, CH-1015 Lausanne, Switzerland, Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-16610 Prague, Czechoslovakia, and INSERM U469, 141 Rue de la Cardonille, F-34094 Montpellier Cedex 5, France (At 2005-09-17)