1. Drug Discovery and Biomedical Sciences College of PharmacyUniversity of South Carolina Columbia SC 29208 USA
2. Present Address: NCI Shady Grove Rockville MD 20850-9702 USA
3. Present Address: Department of ChemistryWake Forest University Winston-Salem NC 27109 USA
4. Present Address: University of California San Francisco San Francisco CA 94115 USA
5. John Wayne Cancer Institute and Pacific Neuroscience Institute Providence Saint John's Health Center Santa Monica, CA USA