Amino acid, aromatic, effects

Many kinds of interactions are possible for aromatic amino acids. Aromatic aromatic (n - - n) interactions and cation n interactions [33] are well known. Weak hydrogen-bonding interactions such as CH n, NH n, OH n, and CH O play important roles in biological systems [31]. In effect aromatic amino acids can recognize a variety of structures. Moreover, as mentioned above, the high hydrophobicity of aromatic amino acids enhances binding interactions. 

It has been claimed that in trifluoroethanol the configuration of the NH2-terminal amino acid strongly effects the CD of an aromatic system (e.g., phenylalanine) in small peptides (intramolecular interaction). Presumably, the a-amino group is in interaction with the phenlalanine residue (Mehlis et aL, 1972 Muller et ai, 1972, 1973). 

Ultrasound, cleaving aromatic nuclei of amino acids, its effect being dependent on the frequency. 

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

Also the arene-arene interactions, as encountered in Chapter 3, are partly due to hydrophobic effects, which can be ranked among enforced hydrophobic interactions. Simultaneous coordination of an aromatic oc amino acid ligand and the dienophile to the central copper(II) ion offers the possibility of a reduction of the number of water molecules involved in hydrophobic hydration, leading to a strengthening of the arene-arene interaction. Hence, hydrophobic effects can have a beneficial influence on the enantioselectivity of organic reactions. This effect is anticipated to extend well beyond the Diels-Alder reaction. 

Antibiotic A201A. Antibiotic A201A (23), produced by S. capreolus is an /V -dimethyladenine nucleoside stmcturaHy similar to puromycin (19). Compound (23) which contains an aromatic acid and monosaccharide residues (1,4), inhibits the incorporation of amino acids into proteins but has no effect on RNA or DNA synthesis. Compound (23) does not accept polypeptides as does (19), and does appear to block formation of the initiation complex of the SOS subunit. It may block formation of a puromycin-reactive ribosome. 

This step is almost always performed to get rid of the coloured impurities in the fermentation broth. The method is based on the fact that amino adds (esperially the non-aromatic amino acids) do not adsorb onto activated charcoal. Although the treatment is very effective, some of the amino acid is lost during this step. 

Finally, as an old example of kinetic resolution of racemic mixtures, mention must be made on the report of Kise and Tomiuchi on the significant effect of acetonitrile on the enantioselectivity of different proteases toward the kinetic resolution of aromatic amino acid ethyl esters (5-8). For instance, (l)-DOPA (8) was obtained with 99% ee in the presence of 90% v/v acetonitrile [9]. 

Treseder, SA, Jackson, M and Jenner, P (2000) The effects of central aromatic amino acid (dopa) decarbosylase inhibition on the motor actions of L-dopa and dopamine agonists in MPTP-treated primates. Brit. J. Pharmacol. 129 1355-1366. 

Glyphosate also inhibits the activity of a form of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (13), however, this inhibition is relatively weak. Effects of glyphosate on the enzymes of aromatic amino acid synthesis have been described in more detail in recent reviews (14-17). 

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