Drug design and the CAS ONLINE substructure search system.

CAS ONLINE, the chemical substance search and display system available directly from Chemical Abstracts Service, is a new service which is particularly useful in drug design studies. In CAS ONLINE chemists search by structures to identify chemical substances, for example, derivatives or analogs of a drug or its pharmacologically active fragment, which share user-defined features. Search questions are phrased in terms of one or more structure diagrams, each of which can include variable atoms, bonds, or positions of substitution as required by the searcher. CAS ONLINE provides access to the world's largest (more than 6 million substance records) and most current chemical structure information data base. CAS ONLINE is updated weekly with 7,000-10,000 new substance records. Substance information available from searches in CAS ONLINE include structure diagrams, systematic and common names (including trade names) for substances, molecular formulas, and the widely cited CAS Registry Numbers. The searcher may optionally request for each substance bibliographic information for the ten most recent literature references which have been cited in Chemical Abstracts since 1967.