Molecular properties, including chameleonicity, as essential tools for designing the next generation of oral beyond rule of five drugs.

Background and purpose: The classical drug discovery toolbox continually expands beyond traditional rule of five (Ro5)-compliant small molecules to include new chemical modalities for difficult-to-drug targets. The paper focuses on the molecular properties essential to drive oral bioavailability within the bRo5 framework.

Experimental approach: The first part outlines the concept and methodologies for characterizing bRo5 physicochemical properties, including considerations on chameleonicity; in particular, the paper summarizes the content of the last author's talk presented during the IAPC-10 Meeting held in Belgrade in September 2023 (https://iapchem.org/index.php/iapc-10-home). The second part of the manuscript presents novel experimental and computational data on three proteolysis targeting chimeras (PROTACs) currently in clinical trials.

Key results: Molecular descriptors of ARV-110, ARV-471, and DT-2216 are reported and the main limitations of the applied experimental approaches are discussed. Moreover, a simple computational method shows how predicting the presence of chameleonic effects.

Conclusion: A full complete physicochemical characterization of three degraders in clinical trials is reported to highlight the differences in physicochemical descriptors between PROTACs dosed orally and intravenously.