|
|
Amino Acids: |
|||||
|
Ravi Bhushan and Juergen Martens |
||||||
|
$99.75 |
March 2010 |
|||||
|
Illustrated: |
|
|||||
Preface
Amino acids are important biological
compounds that are associated with peptides and proteins, and occupy an
important position in the food and pharmaceutical industries. With their simple
structures and the ready availability of both enantiomers, amino acids not only
serve as a chiral pool for synthesis but also provide an inexpensive pool for
resolution studies as either the racemate for resolution or the chiral selector
for resolution of racemic mixtures of several other compounds. There has been
increasing interest in stereoselective synthesis based on chiral auxiliaries,
the production of which requires enantiomerically pure substances, particularly
natural substances.
Separation and identification of amino acids have always been important in
various analytical situations, including determination of primary structure of
peptides and proteins. The methods used for separation and identification have
included classic paper chromatography, using butanol档etic acid淡ter as the
solvent, and two-dimensional paper chromatography with phenol-water as the
solvent for the second run, followed by ninhydrin reaction and application of
2,4-DNFB as the derivatizing reagent. Identification using DNP derivatives in
the planar mode was achieved by Sanger to establish the amino acid sequence of insulin
(leading to his receiving the Nobel Prize in chemistry). Application of
ion-exchange columns for the separation of amino acids, followed by postcolumn
derivatization with ninhydrin and recording the absorbance, formed the basis
for early amino acid analysis. Automated Edman degradation methods were useful
specifically for se quencing. The enantiomeric resolution of amino acids has
been as challenging as that of any other chiral compound important in
pharmaceutics or the synthesis or examination of chiral purity or racemization
in immune response studies穮 particular, of peptides.
The development of analytical methods that can be applied for separation and
identification and resolution of enantiomers of chiral compounds, including the
control of optical purity, remains an area of interest and importance. Direct
enantiomeric resolution by HPLC is hindered by the very high cost of CSPs, less
durability, greater dependence on temperature, and other related problems.
Therefore, indirect HPLC methods get preference. Indirect enantioseparation in
the form of pairs of diastereomers by LC is generally simpler to perform and
may offer better results than direct separation because chromatographic
conditions can be optimized more easily and chiral derivatizing reagents (CDRs)
can provide a highly sensitive detector response, making them suitable for the
analysis of biological samples.
Chromatography has progressed from the introduction of the classical column in
1906 to capillary electrochromatography (CEC) in 2000. HPLC has passed through
many developmental phases, experiencing decreased separation time due to
reduction in particle size from >100 mm to 3 mm and improvements in
instrumentation and column materials, including fused-core particles. Although HPLC
and TLC use similar stationary and mobile phases, which have closely related
separation mechanisms, and can provide equally reliable quantitative data, the
latter method is still less frequently utilized for enantioseparations.
Nevertheless, a greater variety of stationary and mobile phases is available in
TLC, and detection methods for analytes are more flexible and varied. The
relative simplicity and low cost of TLC should make it ideal, but it is known
for having generally lower separation efficiency than fully instrumental
methods (e.g., GC, HPLC, and CE).
This book reflects our research activities over the past 30 years in the area
of separation and synthesis related to amino acids. Its significant features
are as follows
1. A unified perspective of both TLC and HPLC of amino acids for their
separation and enantiomeric resolution
2. A unified approach as a handbook as well as a source book for
separation of amino acids
3. Relevant, current information on the procedures for direct and
indirect enantioseparation of amino acids
4. A chapter exclusively on separation and enantioseparation of
nonprotein amino acids
5. Application of several CDRs, including methods of synthesis of both
the CDRs and the diastereomers
6. Impregnation of thin-layer plates by different methods and their use
for enantiomeric resolution
7. A chapter on penicillamine, which is a trifunctional nonproteinogenic
amino acid containing a thiol group
8. Details of various TLC and HPLC experiments that show how to select
an optimal method
9. Discussion and methods for determination of enantiomeric purity
without resorting to specific rotation measurements
10. Use of enantiomerically pure amino acids as chiral auxiliaries for
synthesis of various CDRs as well as chiral impregnating reagents
11. Discussion on the scope of the CDRs for their application in the
enantioseparation of compounds other than amino acids based on identical
functional reactivity
This is the first such comprehensive book, and we believe that it will be
useful as a complete guide to understanding the current and potential
applications of amino acid separations.