1. Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0204, Department of Chemistry, The Scripps Research Institute, 10650 North Torrey Pines Road, La Jolla, California 92037, and The Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, California 92093