Flexible 3D substructure searching

D substructure search is usually known as pharmacophore searching in QSAR. In all of the 3D search methods the conformational flexibility creates considerable difficulties. 

Most of the early systems for 3D substructure searching and those described earlier assumed that all of the molecules in the database that was to be searched were completely rigid or could be represented by a single (presumably low-energy) conformation, that is, the systems took little account of the conformational flexibility that characterized most 3D molecules. Such an approach was appropriate because the only databases that were generally available... 

The Web-based graphical user interface permits a choice from numerous criteria and the performance of rapid searches. This service, based on the chemistry information toolkit CACTVS, provides complex Boolean searches. Flexible substructure searches have also been implemented. Users can conduct 3D pharmacophore queries in up to 25 conformations pre-calculated for each compound. Numerous output formats as well as 2D and 3D visuaHzation options are supplied. It is possible to export search results in various forms and with choices for data contents in the exported files, for structure sets ranging in size from a single compound to the entire database. Additional information and down-loadable files (in various formats) can be obtained from this service. 

Comparative Molecular Field Analysis (CoMFA) Conformational Flexibility in 3D Structure Searching Conformational Search Medium-sized Molecules Conformational Search Proteins Genetic and Evolutionary Algorithms Molecular Docking and Structure-based Design Shape Analysis Structural Similarity Measures for Database Searching Structure and Substructure Searching Structure Databases. 

Because rigid pharmacophoric searching is based on the positions of explicit atoms or points, it is often difficult to pose queries based on directed vectors in space. A specialized search system, CAVEAT, has been developed that permits the specification of queries based on the relative orientation and position of bond vectors in space. If the query bond vectors have been derived from a docked flexible ligand, then when a database of rigid ring-systems (CAST-3D or CSD) is searched, CAVEAT will identify potential substructural skeletons which could act as a rigid mimic of the core substructure of the ligand. 

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