Overview on the Rule of Five

In the mid‐ to late 1990s, because of the drug discovery paradigm shift from phenotypic screens to combinatorial chemistry and high‐throughput screening, the physicochemical properties of exploratory drug molecules displayed a dramatic shift toward higher molecular weight and lipophilicity. In response, Lipinski and coworkers reported an analysis of compounds that successfully navigated Phase I and entered into Phase II clinical studies, and correlated the computed physicochemical properties of these molecules to their aqueous solubility, permeability, and oral bioavailability. In doing so, the authors created the “Rule of Five,” a mnemonic tool for medicinal chemists to use to quickly assess compounds during the drug discovery and optimization process with respect to the compounds' likelihood to display good solubility and permeability profiles. This overview outlines the basis for the Rule of Five, the ways in which it has been applied, and its impact on drug discovery and development. Curr. Protoc. Pharmacol. 49:9.12.1‐9.12.8. © 2010 by John Wiley & Sons, Inc.