By convention, the pink area represents the optimal biological range for each physiochemical property including lipophilicity (XLOGP3 range 0.7–5.0), size (MW range 150–500), polarity (TPSA range 20–130 Å2), solubility (log S ≤ 6), saturation (fraction of carbons in sp3 hybridization ≤0.25), and flexibility (≤9).