This may be detrimental to CNS activity as PSA < 90 Å 2 is desired for small molecule CNS activity with an ideal range between 40 -80 Å 2 . Related is the hydrogen-bond donors (HBD) and acceptors (HBA) counts for the prioritized analogs. The number of HBD (2 for each molecule) and HBA (7 for each molecule) are at the upper preferred limit desired for CNS active molecules. These properties are combined within QikProp to provide two predictive metrics for CNS permeability that have been benchmarked with experimental data 62 : 1) the CNS score and 2)