Lipinski’s rule-of-five analysis
Christopher Lipinski’s rule-of-five analysis helped to raise awareness about properties and structural features that make molecules more or less drug-like. The guidelines were quickly adopted by the pharmaceutical industry as it helped apply ADME considerations early in preclinical development and could help avoid costly late-stage preclinical and clinical failures. The guidelines predict that poor absorption or permeation of a orally administered compound are more likely if the compound meets the following criteria:

* Molecular mass greater than 500 Da
* High lipophilicity (expressed as cLogP greater than 5)
* More than 5 hydrogen bond donors
* More than 10 hydrogen bond acceptors

http://www.bioscreening.net/glossary/lipinski-rule-of-five/