Tautomer search

In contrast to resonance effects where delocalization of n-electrons occur, tautomeric effects lead to isomeric structures, which differ significantly in the relative positions of their atoms. Tautomerism always involves formation and dissection a-bonds in the course of a transformation together with a change in geometry. A 

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Isomer and Tautomer Search. A search types where bond order, hydrogen counts, certain atom valences, and bond or atom stereochemistry may be allowed to vary from those specified in the query. Such searching allows re-... 

Substructure Match on all components Formula Search on all components Tautomer Search on all components... 

Third, the tautomer information from the normalised BRCT is utilised in the tautomer search option of the Softron S4 search system. Although this is not yet fully implemented, S4 uses the tautomer information to control the mapping of the query structure onto all valid tautomeric forms of candidates in the Beilstein file. 

One element of database generation that is a key consideration is whether to expand the representative compounds to include alternative tautomers, protonated and deprotonated forms of the molecule, and also to enumerate stereochemistry fully if not specified in the input. Depending on the molecules in question and the options considered, these can lead to a 10-fold increase in the size of the database to be explored. However, such an expansion is necessary if methods are used that are sensitive to such chemical precision (e.g., docking). For 3D similarity searching, it is sometimes more efficient to consider various modifications to the query, leading to multiple searches against a smaller database. 

Deduplication. When registering into a chemical structure database, the process of finding whether the given structure already exists in the database. This usually involves performing an exact match search with the given structure as the search query. Note that the definition of exact match may vary with the database, and it may even be configurable. For example, some databases may consider tautomers to be acceptable as exact matches, whereas others may require a more strict definition. 

Stereoselective substructure search, including relative and absolute stereochemistry, isomer, tautomer, any-atom, any-bond, atom lists, substituents, ring bonds, and chain bonds. 

There is some overhead in the use of indexes, constraints, triggers, etc. as discussed here. The overhead is incurred when rows are inserted or updated in the table. However, the value of this approach is that the data in the table are well validated and can be searched more reliably and efficiently. Direct lookups of canonical or stereo SMILES is simple and quick because of the index on these columns. Using the fingerprint column speeds up substructure search. Tautomers can be readily selected using the column of simple graphs. 

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