Biological and Medicinal Chemistry

Amide-to-ester substitution as a strategy for optimizing PROTAC permeability and cellular activity

Authors

Abstract

Bifunctional PROTAC degraders belong to "beyond Rule of 5" chemical space, and criteria for predicting their drug-like properties are underdeveloped. PROTAC components are often combined via late-stage amide couplings, due to the reliability and robustness of amide bond formation. Amides, however, can give rise to low cellular permeability and poor ADME properties. We hypothesized that a bioisosteric replacement of an amide with a less polar ester could lead to improvements in both physicochemical properties and bioactivity. Using a library of model compounds, bearing either amides or esters at various linker-warhead junctions, we identify parameters for optimal compound lipophilicity and permeability. We next applied these learnings to design a set of novel amide-to-ester substituted, VHL-based BET degraders with increased permeability. Our ester-PROTACs remarkably retained intracellular stability, were overall more potent degraders than their amide counterparts and showed an earlier onset of the hook effect. These enhanced cellular features were found to be driven by greater cell permeability rather than improvements in ternary complex formation. This largely unexplored amide-to-ester substitution therefore provides a simple and practical strategy to enhance PROTAC permeability and degradation performance. Such approach could prove equally beneficial to other classes of beyond Ro5 molecules. 

Content

Thumbnail image of PROTAC_Permeability_Manuscript_ 03-07-21_ Final version.pdf

Supplementary material

Thumbnail image of PROTAC_Permeability_SI_01-07-21_final verson.pdf
Supporting Information
Supporting Information containing Supplementary Tables 1-4, Supplementary Figures 1-4, Supplementary Experimental Methods, and NMR and LC/MS spectra for new compounds