1. Department of Chemistry, Western Maryland College, Westminster, Maryland 21157, ABL-Basic Research Program, NCI−Frederick Research and Development Center, P.O. Box B, Frederick, Maryland 21702-1201, Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, and Janssen Research Foundation, CMD, Antwerpsesteenweg 37, B-2350 Vosselaar, Belgium