Number of hydrogen bond donors
The number of hydrogen bond donors in the compound. Here we use the simplified definition in Lipinski’s RoF (Lipinski et al. Adv. Drug Deliv. Rev. (1997) 23 pp. 3-25), being the count of NH, NH2, nH and OH groups, although other, more formal, definitions are possible.
A large number of hydrogen bond donors has been associated with poor membrane permeability due to the additional desolvation energy required to break hydrogen bonds when moving from an aqueous environment to the lipid membrane.
This is defined by the following SMARTS pattern: [NH1,NH2,nH,OH]