Oral Druggable Space beyond the Rule of 5: Insights from Drugs and Clinical Candidates

• Oral druggable space extends far beyond the rule of 5 (bRo5)
• Peptides and natural products are the major source of oral drugs bRo5
• Intramolecular hydrogen bonding and macrocyclization are more common in bRo5 space
• Higher doses and formulations may improve oral bioavailability

The rule of 5 (Ro5) is a set of in silico guidelines applied to drug discovery to prioritize compounds with an increased likelihood of high oral absorption. It has been influential in reducing attrition due to poor pharmacokinetics over the last 15 years. However, strict reliance on the Ro5 may have resulted in lost opportunities, particularly for difficult targets. To identify opportunities for oral drug discovery beyond the Ro5 (bRo5), we have comprehensively analyzed drugs and clinical candidates with molecular weight (MW) > 500 Da. We conclude that oral drugs are found far bRo5 and properties such as intramolecular hydrogen bonding, macrocyclization, dosage, and formulations can be used to improve bRo5 bioavailability. Natural products and structure-based design, often from peptidic leads, are key sources for oral bRo5 drugs. These insights should help guide the design of oral drugs in bRo5 space, which is of particular interest for difficult targets.

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