Amino acids enantiomeric composition

Kullman, J.P., Chen, X., Armstrong, D.W. (1999). Evaluation of the enantiomeric composition of amino acids in tobacco. Chirality 11, 669-673. 

The influence of the mobile phase composition was also studied on the enanti-oseparation of several cycloaliphatic -substituted a-quaternary a-amino acids on a teicoplanin CSP [88,89] the study revealed two distinct enantiomeric and diastereo-meric discrimination mechanisms based on different interactions with the stationary phase. 

Yu, Y-R and Wu, W-H., Simultaneous analysis of enantiomeric composition of amino acids and A -acetyl-amino acids by enantioselective chromatography. Chirality, 13, 231, 2001. 

The fluorescence sensor can easily be used to determine the enantiomeric composition of amino acid derivative mixtures because of the linear relationship of the concentration and the fluorescence signal. 

F NMR spectroscopy is extremely sensitive in the stereochemical evaluation of MTPA amides of a wide range of amino acids (as low as 0.05% of the minor isomer detectable)HPLC analysis of diastereomeric MTPA amides may provide valuable analytical information on the enantiomeric composition of chiral primary and secondary amines. ... 

Engel M. H. and Nagy B. (1982) Distribution and enantiomeric composition of amino acids in the Murchison meteorite. Nature 296, 837-840. 

Of most concern in using the chiral carbon pool, however, is the enantiomeric homogeneity of the natural products themselves. Although it is generally accepted that most carbohydrates and amino acids are enandomerically pure, it is known that many terpenes are not. The small molecules may or not be enandomerically pure. The only sure method of avoiding a nasty surprise during the projected synthesis is to use a starting material, the enandomeric composition of which is known with certainty. 

The enantiomers of 1,8-diacridylnaphthalene derivative 23 were obtained by separation on Chiralpak AD. They were employed as a practical fluorosensor for the determination of concentration and enantiomeric composition of carboxylic acids and amino acid derivatives (06CC4242). 

More recently (I )-0-acetylmandelic acid [(/ )-99], (S)-a -methoxy-a -(trifluoro-methyl)phenylacetic acid (MTPA) [(5 )-83] and other chiral acids have been used as CSAs. These acids form diastereomeric salts soluble in benzene- /6 or chloroform-d with a wide range of amines and amino alcohols, permitting a direct measure of their enantiomeric composition. EnantiomCTs of l,l -binaphth-2,2 -diol (100) and 1,1 -binaphth-2,2 -diylphosphoric acid (101) and other derivatives of 100 and 101 have also been successfully used as CSAs in chloroform- / and benzene- /6 for the estimation of enantiomeric excesses of a number of -amino alcohols , and enantiomers of 101 have been used for cyclic secondary and tertiary amines . ... 

Parker, D. Taylor, R. J. Direct NMR Assay of the Enantiomeric Composition of Amines and jS-Amino Alcohols Using O-Acetyl Mandelic Acid as a Chiral Solvating Agent. Tetrahedron 1987, 43 (22), 5451. 

The behaviour of racemic compounds may also be influenced with the choice of pH value of the aqueous solution. The isoelectronic point of 2-phenylglycine (PG) is at neutral pH value (Ip = 7.0). The free racemic aminoacid with (S)-camphorsulfonic acid (CSA) forms a well crystallizing salt in water, but the amino acid in the precipitated diastereoisomer have almost racemic composition. When the crystallization is started from an aqueous solution containing half an equivalent amount of CSA and equivalent amount of hydrochloric acid (total 50% excess of acid to the PG as base ), the crystalline salt contains (S)-2-phenylglycine in high enantiomeric purity (and in good yield), while the almost pure (R)-2-phenylglycine was obtained from filtrate by crystallization of its hydrochloric acid salt." ... 

Recently (179), a macrocyclic antibiotic, Vancomycin, was used as a chiral mobile phase additive for TLC resolution of 6-aminoquinolyl-N-hydroxy succinimidyl carbamate (AQC) derivativatized amino acids and dansyl amino acids on chemically bonded diphenyl-P-reversed phase plates. Both the nature of stationary phase and the composition of the mobile phase have a strong influence on enantiomeric resolution typical results are given in Table 27. 

This fixed composition results from the phase rule and is also called a eutectic point. The enantiomeric composition in solution can be higher or lower than initially employed, depending on the eutectic point. In the solid phase it will be the other way roimd, as no new enantiomers are made or consumed. For amino acids in water, the whole range from a low to high eutectic point is foimd threonine is a conglomerate, which is always racemic at the eutectic point, whereas serine exhibits a eutectic point of >99% ee, being basically... 

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