Another challenge in docking is accounting for the various
tautomeric and protomeric states the molecules can
adopt. In many databases molecules such as acids or amines
are stored in their neutral forms. Considering that they are
ionized under physiological conditions it is necessary to ionize
them prior to docking. However, while standard ionization
is easy to achieve, the problem of tautomer generation is
already much more challenging: which tautomer should one
use? Or should one use more than one (or all possible)
tautomers for a given molecule? Not only for tautomers, but
also for different ionization states balanced equilibria between
the different forms provide real challenges in docking.
One (radical) approach to this would be to generate all possible
forms, subsequently to dock all of them, and to choose
the relevant form based on the scores. However, it remains to
be seen whether such an approach would be beneficial or just
generate a large number of false positives