5-((4-Chlorophenyl)sulfonyl)imidazo[2',1':6,1]pyrido[2,3-b]quinoxalin-4-amine 5-((4-Chlorophenyl)sulfonyl)imidazo[2',1':6,1]pyrido[2,3-b]quinoxalin-4-ylamine AIDS-140908 AIDS140908 NSC654903