1. Advanced Biomedical Computing Center, SAIC Frederick, P.O. Box B, National Cancer Institute at Frederick, Frederick, Maryland 21702-1201; Department of Chemistry, University of Toronto, Toronto, Ontario, Canada, M5S 3H6; Institute of Organic Chemistry, Eotvos University, 112 Budapest, P.O. Box 32 2 Pazmany Peter setany, H-1117, Hungary; and BioChemComp, Inc., 543 Sagamore Avenue, Teaneck, New Jersey 07666