Structures of the five most potent inhibitors. NSC 619196, N4-(12-((5-amino-6-chloro-4-pyrimidinyl)amino)dodecyl)-6-chloro-4,5-pyrimidinediamine; NSC 619195,N4-(12-((2-amino-6-chloro-4-pyrimidinyl)amino)dodecyl)-6-chloro-2,4-pyrimidinediamine; NSC 629621, N4-(10-((2-amino-6-chloro-4-pyrimidinyl)amino)decyl)-6-chloro-2,4-pyrimidinediamine; NSC 668602, 1-(12-(3-formyl-1H-indol-1-yl)dodecyl)-1H-indole-3-carbaldehyde; and NSC 618296,2-((9-((7-oxo-1,3,5-cycloheptatrien-1-yl)amino)nonyl)amino)-2,4,6-cycloheptatrien-1-one.