Page 145 - Chiral Separation Techniques

122 4 CHIRBASE: Database Current Status and Derived Research Applications using …

Some other interesting results are:
The importance of steric and hydrogen bond interactions in chiral separations of
nonaromatic samples
Chiralpak OT(+) dominates the branches built under the “spiro” and “ARO-
MATIC RING>1” molecular keys.
CTA-I and Chiralcel OJ are found under the key “AROMATIC” and “8 member
ring or larger”. If sample also contains one amino group, then the tree leads to
Chiralcel OJ.
Whelk-O 1 well predominates the aromatic samples bearing an axial chirality cre-
ated by a C–N bond.
Chiralcel OB is associated with the separation of aromatic and nonaromatic sul-
foxides and Chiralcel OD with aromatic alcohols.
Nonetheless, these results are partial and can be seen only as a test study, and
clearly many improvements will be considered. For example, the decision at each
node should not be restricted to the only use of molecular key attributes, but should
also take into account the mobile phase constituents. Future works will also extend
this approach to the full database and will probably lead to the introduction of
knowledge rules in CHIRBASE. Knowledge rules will help the users not only in the
choice of a wide range of columns but also in the selection of appropriate experi-
mental conditions.
From these initial results we have seen that this approach has exciting practical
issues. However, we have also found that it does not match the accuracy of a
database structure search, and the latter will certainly continue to be the best
approach for CSP prediction for separation of a particular structure.

4.8 Conclusions

Today, the use of CHIRBASE as a tool in aiding the chemist in the identification of
appropriate CSPs has produced impressive and valuable results. Although recent
developments diminish the need for domain expertise, today the user must possess a
certain level of knowledge of analytical chemistry and chiral chromatography. Nev-
ertheless, further refinements will notably reduce this required level of expertise.
Part of this effort will include the design of an expert system which will provide rule
sets for each CSP in a given sample search context. The expert system will also be
able to query the user about the specific requisites for each sample (scale, solubility,
etc.) and generate rules which will indicate a ranked list of CSPs as well their most
suitable experimental conditions (mobile phase, temperature, pH, etc.).
Such an expert system can also be adapted for the evaluation of data in the pub-
lished literature. However, this point raises a number of practical questions. A better
exploitation of chromatographic data in this field would require an important effort
to be made by analysts to constitute standards for quality control and interpretation