1. Leibniz Institute for Natural Product Research and Infection Biology, HKI, Dept. of Biomolecular Chemistry, Beutenbergstr. 11a, 07745 Jena, Germany, the Friedrich Schiller University, Jena, Germany, and the Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, California, 92093-0204