Amino acids, natural

Sensitivity levels more typical of kinetic studies are of the order of lO molecules cm . A schematic diagram of an apparatus for kinetic LIF measurements is shown in figure C3.I.8. A limitation of this approach is that only relative concentrations are easily measured, in contrast to absorjDtion measurements, which yield absolute concentrations. Another important limitation is that not all molecules have measurable fluorescence, as radiationless transitions can be the dominant decay route for electronic excitation in polyatomic molecules. However, the latter situation can also be an advantage in complex molecules, such as proteins, where a lack of background fluorescence allow s the selective introduction of fluorescent chromophores as probes for kinetic studies. (Tryptophan is the only strongly fluorescent amino acid naturally present in proteins, for instance.)... 

Marcuse, R. (1960). Antioxidative effect of amino-acids. Nature, Vol.186, No.4728, (June I960), pp. 886-887, ISSN 0028-0836. 

The reaction was first tested with these substances as ligands but the organic molecule, in the absence of any added metal ion, proved to be the most enantioselective catalyst (library 1 19% ee vs. less than 13% ee for the best metal catalyst). The effects of selective variations of the amino acid nature and of the salicylidene moiety on the diamine structure were investigated for urea and thiourea derivatives via HTS (library 2 48 urea compounds and... 

Spectral data of these alkaloids are presented in the review works (4,8) but do not include data for bicucullinidine (110), which was discovered in 1981 (113-116). In the IR spectra of these compounds the carbonyl region generally consists of three bands. The first one is placed at 1675-1670 cm-1 and the latter two around 1625-1590 cm-1. The amino acid nature of these compounds is demonstrated by the presence of an NH band (2350 cm-1) found in the IR spectrum of bicucullinine (108) (117), as well as by the solvent-dependent position of the N(CH3)2 group in the H-NMR spectra. For instance, in the spectrum of bicucullinine (108) run in basic aqueous solution it can be found at <52.08 (118), in DMSO-d6 at <52.69 (113,116), and in CFjCOOD at <53.13 (117,119). Moreover, in H-NMR spectra the influence of the C-l carbonyl group on the chemical shift of H-8 can be observed. This proton falls in its deshielding zone and is shifted downfield around 1 ppm compared to the absorption of H-8 in spectra of monoketo acids. 

Bradbury, J. II. Improvements of the hydrazine method for determination of C-terminal amino acids. Nature 778, 912—913 (1956). 

Naturally air-fused DKPs are thermodynamically more stable, compared with their trawr-fused counterparts. This seems logical considering their biosynthetic origin, usually from two proteinogenic L-a-amino acids. Some other cis- and rntwr-functional DKPs are derived from nonproteinogenic D-a-amino acids. Naturally... 

Glutamic Acid A non-essential amino acid naturally occurring in the L-form. Glutamic acid (glutamate) is the most common excitatory neurotransmitter in the central nervous system. 

Fig.1. Chemical structures of fluorinated analogues of amino acids naturally occurring in proteins and labelled with fluorine-18.

Some functional modifications allow access to numerous analogues of amino acids, natural or not, starting from synthons prepared by the previous methods. This is illustrated by the preparation of a-trifluoromethyl arginine (Figure 5.30). ... 

This process was developed in order to synthesize unnatural a-amino acids. Naturally occurring, enantiomerically pure amino acids, as well as achiral glycine, have been used as starting materials in order to enantioselectively introduce a-substituents1 14. The resulting cyclic esters and amides have been alkylated and subjected to aldol reactions1-14. 

For the biosynthesis of inositols and of the benzene rings of aromatic a-amino acids nature employs nucleophilic centers at C-6 of a D-glucose-derived hexos-5-ulose phosphate [5] and at C-7 of a 3,7-dideoxyhept-2,6-diulosonic acid [6], respectively, ions 1 and 2... 

RT of PTH-Amino Acids (Natural and Unnatural) on an ABI Protein Sequencer"... 

Welton MGE, Pelc SR. Specificity of the stereochemical relationship between ribonucleic acid-triplets and amino-acids. Nature 1966 209 870. 

Stereochemistry of Amino Acids Naturally occurring amino acids belong to the T-family. That is, when the amino acid is drawn as a Fischer projection, with the carboxyl group at the top and the side chain at the bottom, the amino group is on the left, as shown in Figure 12.45. 

Jimenez, J.M., Rife, J., and Ortuno, R.M. (1996) Enantioselective total syntheses of cyclopropane amino acids natural... 

Finally, the search for a strategic bond is always simplified when even a first glance analysis leads to the identification of those bonds that clearly cannot be considered strategic. The latter include bonds in aromatic rings (see, however, an exception in Vollhardt s synthesis of estrone) or heteroaromatic rings, as well as bonds which are located in readily available fragments (such as monosaccharides, amino acids, natural fatty acids, etc.). 

The first use of recombinani hGH (rtiGH) was repn. in 1982. rhGH preparations were first produced itiEr -These preparations contained a terminal methionine amino acids. Natural sequence rhGH has since beenfr duced in mammalian (mouse) cell culiure. 

Sutherland, A. and Willis, C. L. (2000) Synthesis of fluorinated amino acids. Natural Product Reports, 17, 621-631. 

Poly( a-amino acid/vis a better term for peptides formed by the self-condensation of one amino acid natural examples exist, such as poly(D-glutamic acid), the protein coat of the anthrax spore (Flanby and Rydon, 1946). In early research in the textile industry, poly(a-amino acid)s showed promise as synthetic fibres, but the synthesis methodology required for the polymerisation of amino acids was complex and uneconomic. 

K8. Knight, C. S., A new two-dimensional paper chromatographic method applied to the separation of amino-acids. Nature (London) 184, 1486-1487 (1959). 

Copolymer composition (%). Abbreviations Ala, 15N-labelled L-alanine (99 atom % of l5N purity) Ala, L-alanine (natural abundance of 15N) X, other amino acids (natural abundance of 15N). 

The third mechanism is represented by nonmodular one-step peptide synthesis. Enzymes belonging to this group catalyze the biosynthesis of poly(amino acids). Naturally occurring poly(amino acids) comprise cyanophy-cin [multi-L-arginyl-poly-(L-aspartic acid) cyanophycin granule polypeptide, (CGP)], (poly-(e-lysine) (PL), and poly-(y-glutamate) (PGA). As a consequence of non-ribosomal biosynthesis these peptides reveal a polydisperse mass distribution. 

G18. Gross, D., High-voltage paper electrophoresis of non volatile organic acids and their mixture with amino acids. Nature 178, 29 (1956). 

Today a widely used artificial sweetener is a compound called aspartame, which is formed by coupling together two amino acids naturally found in humans aspartic acid and phenylalanine... 

Padmanabhan, S., Marqusee, S., Ridgeway, T., Laue, T.M. and Boldwin, R.L. (1990) Relative helix-formfing tendencies of nonpolar amino acids. Nature 344 268-270. 

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