2.2.2.  Veber rule
For oral bioavailability, membrane permeability is an important factor. Polar surface area and number of rotatable bonds are two critical considerations for a compound to behave as a potential drug candidate. With a reduction in polar surface area, permeation increases and with the increase in number of rotatable bonds permeation decreases significantly (Veber et al., 2002). The following two criteria should be met by a potential drug candidate in order to obey Veber rules:≤10 rotatable bonds;
Polar surface area ≤140Å2 (or 12 or fewer H-bond donors and acceptors).