A novel series of inhibitors of cancer cell proliferation, selective against p21 cell cycle checkpoint-disrupted cells vs. cells with intact p21 checkpoint, were identified by high- throughput screening. Optimization of both ends of the lead molecule to improve potency, using parallel synthesis and iterative design, is described. The 2-(1, 4-dibenzodioxane)- substituted derivative 14 was identified as a highly selective and potent agent displaying ...