📚 What is Lipinski's Rule of Five?
Lipinski's Rule of Five, also known as the Rule of Fives, is a guideline used in drug design to assess the drug-likeness or oral bioavailability of a chemical compound. It helps predict if a molecule is likely to be orally active in humans. Essentially, it filters out compounds that are unlikely to be successful drugs due to poor absorption or permeability.
📜 History and Background
Developed by Christopher A. Lipinski and his colleagues at Pfizer in 1997, the Rule of Five emerged from observing a significant number of orally administered drugs. Lipinski's team analyzed the properties of these drugs and identified common characteristics that correlated with good oral bioavailability. This empirical approach led to the formulation of the Rule of Five, which has since become a staple in the early stages of drug discovery.
🔑 Key Principles of the Rule
- ⚖️Molecular Weight: Should be less than 500 Daltons.
- 🧲LogP (Octanol-water partition coefficient): Should be less than 5. This indicates the compound's lipophilicity.
- 🤝Hydrogen Bond Donors: Should be no more than 5. These are the sum of OH and NH groups.
- acceptors.
- 🔢Molar Refractivity: This parameter is often used in computational chemistry but is not strictly part of the original rule.
A compound is considered likely to have good oral bioavailability if it violates no more than one of these rules. However, it's essential to remember that the Rule of Five is a guideline, not an absolute law, and there are exceptions.
🧪 Real-world Examples
Let's look at some examples of how Lipinski's Rule of Five applies to known drugs:
| Drug |
Molecular Weight (Da) |
LogP |
H-bond Donors |
H-bond Acceptors |
Rule Violations |
| Atorvastatin (Lipitor) |
558.6 |
5.2 |
5 |
0 |
2 |
| Aspirin |
180.2 |
1.2 |
1 |
3 |
0 |
| Metformin |
129.2 |
-2.6 |
5 |
1 |
0 |
As seen in the table, Atorvastatin violates two rules. Aspirin and Metformin adhere to the rule perfectly.
💡 Conclusion
Lipinski's Rule of Five is a valuable tool in drug design, providing a quick assessment of a compound's likelihood of oral bioavailability. While it's not a definitive predictor, it serves as an important filter in the early stages of drug discovery, helping to prioritize compounds with a higher probability of success.