Tautomeric Conflicts in Forty Small-Molecule Databases.

We have analyzed 40 different databases ranging in size from a few thousand to nearly 100 million molecules, comprising a total of over 210 million structures, for their tautomeric conflicts. A tautomeric conflict is defined as an occurrence of two or more structures within a data set identified by the tautomeric rules applied as being tautomers of each other. We tested a total of 119 detailed tautomeric transform rules expressed as SMIRKS, out of which 79 yielded at least one conflict. These transformations include three types of tautomerism: prototropic, ring-chain, and valence tautomerism. The databases analyzed spanned a wide variety of types including large aggregating databases, drug collections, and structure collections based on experimental data. All databases analyzed showed intra-database tautomeric conflicts. The conflict rates as percentage of the database were typically in the few tenths of a percent range, which for the largest databases amounts to >100,000 cases per database.