1. Laboratory of Medicinal Chemistry, CCR, NCI-Frederick, NIH, Bldg. 376 Boyles St., Frederick, Maryland 21702, Protein Chemistry Laboratory, SAIC-Frederick, Inc., Frederick, Maryland 21702, HIV Drug Resistance Program, CCR, NCI-Frederick, Frederick, Maryland 21702, U.S. Army Medical Research Institute for Infectious Diseases, Frederick, Maryland 21702