Calculated H-bonding descriptors

Considerable interest is focused on the calculahon of H-bonding capability in the design of combinatorial libraries, for assessing the potenhal for oral absorphon and permeability [16, 62-65]. A number of different descriptors for H-bonding have been discussed [66], one of the simplest being the count of the number of H-bond forming atoms [67]. 

Poorly absorbed compounds have been identified as those with a PSA 140Af Considering more compounds, considerable more scatter was found around the sigmoidal curve observed for a smaller set of compounds [74]. This is partly due to the fact that many compounds do not show simple passive diffusion only, but are affected by active carriers, efflux mechanisms involving P-glycoprotein (P-gp) and other transporter proteins, and gut wall metabohsm. These factors also con- 

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