Protein-protein interactions (PPIs) play pivotal roles in a range of cellular processes including proliferation, differentiation, metabolism and apoptosis. Dysregulations of certain PPIs can lead to the development and progression of human cancers. In particular, the overexpression of the anti-apoptotic BCL-2 family members, specifically Mcl-1, have been linked to pancreatic, colorectal and lung cancers as well as leukemia and lymphoma. When over-expressed, MCL-1 prevents cell death by binding and sequestering the BH3 "death" domain of its pro-apoptotic counterpart, such as Bim. Mcl-1 has become an important target for the development of novel antineoplastics. As with many, helix-mediated PPIs, several key residues are hydrophobic and located on one face of the BH3 α-helix, specifically at the i, i + 3/4, i + 7 residues. In addition to exhibiting a hydrophobic face, Asp67 on the "other" face of the Bim-BH3 helix forms a salt bridge with the protein (Arg263). In an improved effort to develop more potent and more selective agents to disrupt the MCL-1-BH3 PPI, we used structure-based design, and developed two complementary strategies: synthetic α-helix (purine based) and BH3 mimetics (naphthoate based). Both scaffolds yielded molecules that disrupted the MCL-1-BIM PPI consistently, and subsequent studies were undertaken towards second-generation molecules. The designed molecules were subjected to biological assays and further structure-activity relationship (SAR) studies to increase affinity and potency in an effort to translate in vitro activity to on target cell activity. It is expected anticipated that the SAR developed in the present study will facilitate the development of novel therapeutics capable of inhibiting Mcl-1 will be identified, which can be advanced to preclinical evaluation.