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 China