(active). Based on these calculations, analogs 16, 20, and 39 all are predicted to be CNS inactive with values of -2 for each while 38 has a predicted value of 0, indicating at least partial CNS activity. Alternatively, Madin-Darby Canine Kidney (MDCK) cells have been shown to be a viable surrogate to assess for BBB permeability. This is captured in the QPPMDCK apparent permeability (Papp) metric where a predicted Papp > 500 nm/sec is desired for CNS activity.