1. Kekulé-Institut für Organische Chemie und Biochemie; Universität Bonn; Gerhard-Domagk-Str. 1 53121 Bonn Germany
2. Current address: GlaxoSmithKline, Medicines Research Centre; Gunnels Wood Road Stevenage SG1 2NY UK
3. Current address: Dottikon Exclusive Synthesis AG; Dottikon Switzerland
4. Current address: Scripps Research Institute; La Jolla USA
5. Current address: Institute of Quality Standard and Testing Technology for Agro-products; Chinese Academy of Agricultural Sciences; Key Laboratory of Agro-food Safety and Quality; Ministry of Agriculture; Beijing China