Design, Synthesis, and Evaluation of an α-Helix Mimetic Library Targeting Protein−Protein Interactions

The design and solution-phase synthesis of an α-helix mimetic library as an integral component of a small-molecule library targeting protein−protein interactions are described. The iterative design, synthesis, and evaluation of the candidate α-helix mimetic was initiated from a precedented triaryl template and refined by screening the designs for inhibition of MDM2/p53 binding. Upon identifying a chemically and biologically satisfactory design and consistent with the screening capabilities of academic collaborators, the corresponding complete library was assembled as 400 mixtures of 20 compounds (20 × 20 × 20-mix), where the added subunits are designed to mimic all possible permutations of the naturally occurring i, i + 4, i + 7 amino acid side chains of an α-helix. The library (8000 compounds) was prepared using a solution-phase synthetic protocol enlisting acid/base liquid−liquid extractions for purification on a scale that insures its long-term availability for screening campaigns. Screening of the library for inhibition of MDM2/p53 binding not only identified the lead α-helix mimetic upon which the library was based, but also suggests that a digestion of the initial screening results that accompany the use of such a comprehensive library can provide insights into the nature of the interaction (e.g., an α-helix mediated protein−protein interaction) and define the key residues and their characteristics responsible for recognition.