1. Laboratory of Synthesis and Natural Products; Institute of Chemical Sciences and Engineering; Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-LSPN, BCH 5304; 1015 Lausanne Switzerland
2. Laboratory of Bioorganic Phosphorous Chemistry and Chemical; Biology (Ministry of Education); Department of Chemistry; Tsinghua University; Beijing 100084 P. R. China