Chirality of amino acids

Armstrong, D.W., Kullman, J.P., Chen, X., Rowe, M. (2001). Composition and chirality of amino acids in aerosol/dust from laboratory and residential enclosures. Chirality 13, 153-158. 

The chirality of amino acids stems from the chiral, or asymmetric, center, the a-carbon atom. The a-carbon atom is a chiral center if it is connected to four different substituents. Thus glycine has no chiral center. Two of the amino acids, isoleucine and threonine, possess additional chiral centers because each has one additional asymmetric carbon. You should be able to locate these carbons by simple inspection. 

The peptides, which are composed of only a few amino acids, exhibit predictable behavior in CZE in that their mobility (electrophoretic migration) can be predicted on the basis of their size (mass) and their charge characteristics. The charge of such peptides can be predicted from the pKa values of individual amino acids contained in them. For larger peptides and proteins, the calculation of charge based on ionization constant is not trivial and can not be easily calculated based on the pKas of the free amino aids. Besides the mass-to-charge ratio, the other factors that affect mobility are hydrophobic-ity, primary sequence, conformational difference, and the chirality of amino acids. This point has been demonstrated by an investigation on several nonapeptides of identical composition but with different primary sequences ... 

Chirality of Amino Acids Section 16.1Glycine is optically inactive because it has two hydrogens on the alpha carbon (C-2). Four different groups are required for optical activity. 

Figure 11 Chirality of amino acids involved in forming heterocycles found in cyanobacterial natural products.

Metal M Substituent 1 Substituent 2 Chirality of amino acids Chirality at metallocene Ref. 

Several unmodified amino acids (1-7) have been used directly for the activation of substrates via the enamine mechanism. In such transformations, the chirality of amino acids induces stereoselectivity in the product formation. If a high level of enantioselectivity is attainable, such unmodified amino acid catalysts are certainly ideal due to their ready avaUabihty and economical nature. 

---