CASREACT System

Bob Dana and colleagues at Chemical Abstracts Service presented a poster on the machine generation of multi-step reactions for the CASREACT system on STN International. The online version of FIZ s Cheminform database will be available on STN International also. Alex Parlow gave a poster presentation on the creation of Cheminform both as an electronic database (for onhne and in-house use) and as a printed product. 

Substructure searching of explicit reaction schemes has been implemented in the CASREACT system by enumerating all the individual reactions and indexing them individually. The application of reaction substructure searching techniques to query implicit reaction schemes (where the product of one reaction is the reactant of another in the database) and analogous reaction schemes (where the reaction center of a reactant in one reaction is present in the product of another) has also been explored. ... 

The major commercially available reaction indexing programs are REACCS (Molecular Design Limited), SYNLIB (started by Clark Still, developed by Smith, Kline and French and now sold by Dan Chodosh), ORAC (developed at the University of Leeds) and DARC-RMS (Telelsystemes). Pfizer s in-house system CONTRAST is noteworthy but is not available outside Pfizer. The release of CASREACT by Chemical Abstracts is awaited with interest. 

It is planned to produce an online version of the database, which will be implemented on STN International. For this purpose, a data file in standard format that can be used under Messenger software will be derived from the base file. (Stereochemical information will be kept in this file, even though Messenger cannot handle this information at present). The enhancements to Messenger developed at CAS for CASREACT, the online reaction retrieval system developed by CAS, will also be used for this database. The display capability of Messenger will, in this configuration, also allow for the display of the whole (multi-step) reaction schemes. 

The first commercial computer system to store, search and retrieve reaction schemes was ChemBase (see Figure 1). ChemBase could represent and display linear schemes, but was limited in its ability to perform scheme-oriented structure searches (see below). The Chemical Abstracts Service (CAS) has announced the availability of their reaction file (CASREACT)," organised with reaction schemes in mind. Although at present the scheme searching capabilities available at the user interface are limited, CASREACT appears to represent schemes in a more rigorous manner internally, allowing further user interface refinements in the future. 

Surprisingly, Fugmann expected the prior-registration approach to be infeasible, in spite of announcements and demonstrations by Chemical Abstracts of a system using that method. A likely explanation is that Fugmann assumed redundant storage of connection tables, not necessary in either REACCS or CASREACT. 

The results of the study indicate that the best method of searching explicit schemes in REACCS is by exhaustive enumeration and prior registration of all possible subschemes, analogous to the method adopted by the developers of CASREACT. The same conclusion may not be made for all reaction indexing systems, however both CASREACT and REACCS maintain a separate molecule registry, which hmits the growth of the database when prior registration is used. 

Current awareness of new chemical reactions can. in principle. be organized in databases as for other types of queries, with search profiles that are automatically executed at each database update ( alerts . SDls ). Because of the frequency of updating (see Section 3.2), at present this only makes sense for CASREACT. Although the printed current awareness journals, such as the Journal of Synthetic Methods, Current Chemical Reactions, Methods in Organic Synthesis, and Cheminform RX are all available in electronic form, both as in-house databases for MDL s REACCS or ISIS system, and, with the exception of Current Chemical Reactions and Methods in... 

Many producers and public hosts offer reduced rates for academics or full academic programs , making expensive retrieval systems and databases affordable for academic institutions (e.g., MDL, retrieval system ISIS plus several databases Beilstein Information Systems, CrossFire FIZ Chemie, reduced rates for both Cheminform RX in house and at the host STN Springer/Infochem Synopsys). However, CASREACT is unfortunately not included at this time in the otherwise very useful CAS academic program. ... 

The use of selective reactions, in the sense that certain functionalities present in the reactant must not participate in/interfere with the desired reaction, is often needed. Retrieval is possible in all systems by specifying bonds as nonreaction centers . In CASREACT and DJSMONLINE this kind of restriction can also be entered via keywords (see Section 4.7). 

The in-house systems REACCS, ISIS, and CrossFire handle aromaticity and tautomerism satisfactorily a user can enter structures as any chemist normally would without having to worry about the bond conventions used internally by the database system. This is not yet true for CASREACT and other reaction databases offered under STN Messenger. Here the user has to know the definition and use of normalized bonds, a special bond type defined to handle aromaticity and tautomerism in a formal way. This, unfortunately, corresponds only partially to these concepts ias used by chemists. CAS is working on Ais problem the SciFinder interface already offers a solution for exact structures, but not yet for substructures, falling into this category (see Structure Representation). 

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