Page 124 - Chiral Separation Techniques

4.4 Searching the System 101

4.4 Searching the System

ISIS provides means for manipulation, comparison, search and retrieval of records.
Searches through the database can be carried out in a number of ways using:
Molecule queries (one or two associated molecules) for sample, CSP or solvent:
– Exact match
– Substructure
– Similarity
– Name
– Formula
Data queries for chromatographic data, literature references, analytical conditions
and any other text or numeric data that is associated with a separation:
– String, substring or numeric data
Multiple component queries for any combination of structures (one or two
molecules) and text or numeric data:
– Combined molecule and data components
As we have already mentioned, graphical molecule-oriented searching strategies
are the best tools to solve a chiral separation problem. Chemical substructure search-
ing (SSS) is the ability to search a structure database using any structure fragment.
The results of a SSS are the chemical structures in the database which contain the
query structure fragment. One of the major advantages of this type of search in the
chiral chromatography domain is that it allows the retrieval of a given sample of all
the derivatives, and thus a choice of the best derivatization reagent to achieve a good
resolution on a specific CSP.
Molecular similarity searching provides the possibility of finding unrelated but
functionally analogous molecules. This is a very nice feature because many distinct
structures in contact with a CSP often share the same active sites. The compounds
which have a structure similar to the structure of the sample query can be displayed
automatically in order of their similarity. The degree of similarity is measured by a
numerical value on a scale of 0 to 100 that may be included in the output form. An
example of a similarity search is shown in Fig. 4-3. In this example, a search is being
performed for the AZT with a similarity value >65 %.
The stereochemistry shown in CHIRBASE includes relative configurations, abso-
lute configurations, and geometric isomers. A chiral flag on the chiral selector of a
CSP identifies a specific enantiomer of a molecule. Up- and down- stereo bonds rep-
resent relative configurations, and together with a chiral flag, they represent the
absolute configuration of the CSP. Polymeric supports are stored as generic
monomer structures in the database. In such molecules, the pseudoatom “[” defines
the linkage that connects all the monomers of the polymer. Other searchable pseu-
doatoms may be connected to a portion of the polymer structure such as a methylene
group. For instance, the pseudoatoms “coated” or “Beads” will characterize the
preparation mode of the CSP.