Amino acid specific compounds

Amino acids N-containing protein components See Lewis acid carboxylic acid fatty acid amino acid specific compounds. 

The gastropods account for the majority of chemistry reported for the phylum. Of the total reported for the phylum, 497 (86%) were isolated from the class Gastropoda. The subclass Opistho-branchia accounts for 378 compounds, 76% of the total reported from gastropods. More specifically, 317 compounds (55%) were isolated from nudibranchs and sea hares. For the order Nudibranchia, 159 compounds have been reported, of which 137 (86%) are isoprenoids. The subclass Prosobran-chia (snails) is one of the few groups that have yielded mainly amino acid derived compounds. A total of 72 compounds have been reported for prosobranchs, and 51% are derived from amino acids. A large number of groups within the phylum are underrepresented statistically with respect to reported chemistry. 

Bacteria require specific enzymes, called racemases, to interconvert d- and L-amino acids. Mammals do not use D-amino acids, so compounds that block racemases do not affect mammals and show promise as antibiotics. 

Tripp, J.A., McCuUagh, J.S.O., and Hedges, R.E.M. Preparative separation of underiva-tized amino acids for compound-specific stable isotope analysis and radiocarbon dating of hydrolyzed bone collagen. J. Sep. Sci. 2006, 29, 41-48. 

The stable C isotopic (5 C) signature of organic compounds is commonly employed for source apportionment, but few studies have applied this strategy for specific compounds within DOM. Recently, in an effort to identify specific HMWDOM sources McCarthy et al. (2004) compared the 5 C signature of individual amino acids in HMWDOM to those amino acids isolated from a variety of autotrophic and heterotrophic organisms. Based on patterns of amino acid-specific 8 C values these authors concluded that amino acids in HMWDOM were derived from an autotrophic source. However, this study focused on a Hmited sample set and considerable variations in 8 C signature of amino acids was apparent. 

Values of specific rotation are expressed as in equation (3) for the amino acid cysteine (compound 30 in the Problems section of this chapter) ... 

The rate-limiting step of the mass transfer for the separated compound(s) in such systems depends on the concentration of the surfactant used [121]. Hebrant and Tondre [120] studied the extraction of tryptophan and p-iodophenylalanine through the reverse-micelle ELM composed of isooctane and the aqueous solution of Aerosol OT, that is, the sodium salt of bis (2-ethylnexyl)sulfosuccinate, as the stripping phase. The extraction efficiencies and transport rates were shown to be amino acid specific. 

Some Amino Add-Specific Compounds. As listed in Table I, there were three pyrrolizines and one pyridoimidazole identified in the model systems. Pyrrolizines are a very in rtant class of volatile conpounds generated by the reaction of proline with reducing sugars. 2-Acetyl-pyrido(3,4-d)imidazole was another amino acid-specific Maillard reaction product identified in the model systems, which was derived fi om the reaction of histidine with dicaibonyls. 

Although the term N. p. is now used almost exclusively for specific organic compounds of natural origin, in the past substances of mineral origin were also included. Natural products can be classified, for example, according to a) their chemical structure e. g., alkaloids, amines, amino acids, aromatic compounds, fatty acids. 

Vacuoles also have a second principal function they stock metabolites before their use. In fact, tliey contain a quarter of the pool of the amino acids of the cell, including a lot of arginine as well as 5-adenosyl methionine. In this organelle, there is also potassium, adenine, isoguanine, uric acid and polyphosphate crystals. These are involved in the fixation of basic amino acids. Specific permeases ensure the transport of these metabolites across the vacuolar membrane. An ATPase linked to the tonoplast furnishes the necessary energy for the movement of stocked compounds against the concentration gradient. It is different from the plasmic membrane ATPase, but also produces a proton efflux. 

The colour test is not specific for a-amino acids other primary amino compounds and also ammonia give a blue colouration with ninhydrin. 

By analogy, a great many of other functionalized styrenes, including carboxyHc acids, amino acids, Schiff bases, or specific compounds, eg, l-DOPA, have successfully been appHed as print templates. Moreover, it has also been shown that siUca gel can be imprinted with similar templates, and that the resulting gel has specific recognition sites determined by the print molecule (162—164). 

A useful source of details such as likely impurities, stability and tests for homogeneity of amino acids is Specifications and Criteria for Biochemical Compounds, 3rd edn. National Academy of Sciences, USA, 1972. 

In contrast, there are fewer limitations from the chemical point of view. The preparation of large, well-defined, libraries that involve amino acid building blocks has been demonstrated many times. Carefully optimized reaction conditions for the preparation of other mixed libraries can also ensure that each desired compound is present in sufficient amount. However, the reaction rates of some individual selectors with the activated solid support may be lower than that of others. As a result, the more reactive selectors would occupy a majority of the sites within the beads. Since the most reactive selectors may not be the most selective, testing of a slightly larger number of specifically designed CSPs may be required to reduce the effect of falsenegative results. 

Amino acid separations represent another specific application of the technology. Amino acids are important synthesis precursors - in particular for pharmaceuticals -such as, for example, D-phenylglycine or D-parahydroxyphenylglycine in the preparation of semisynthetic penicillins. They are also used for other chiral fine chemicals and for incorporation into modified biologically active peptides. Since the unnatural amino acids cannot be obtained by fermentation or from natural sources, they must be prepared by conventional synthesis followed by racemate resolution, by asymmetric synthesis, or by biotransformation of chiral or prochiral precursors. Thus, amino acids represent an important class of compounds that can benefit from more efficient separations technology. 

The substrate specificity of ACE is low. ACE cleaves a variety of pairs of amino acids from the carboxy-terminal part of several peptide substrates. The conversion of ANGI to ANGII and the degradation of bradykinin to inactive fragments are considered the most important functions of ACE. Both peptides have profound impact on the cardiovascular system and beyond. ACE is thus an important target for ACE inhibitors. These compounds are frequently and efficiently used in the treatment of hypertension and cardiac failure. 

Recently Turner and coworkers have sought to extend the deracemization method beyond a-amino acids to encompass chiral amines. Chiral amines are increasingly important building blocks for pharmaceutical compounds that are either in clinical development or currently licensed for use as drugs (Figure 5.7). At the outset of this work, it was known that type II monoamine oxidases were able to catalyze the oxidation of simple amines to imines in an analogous fashion to amino acid oxidases. However, monoamine oxidases generally possess narrow substrate specificity and moreover have been only documented to catalyze the oxidation of simple, nonchiral... 

Enzyme preparations from liver or microbial sources were reported to show rather high substrate specificity [76] for the natural phosphorylated acceptor d-(18) but, at much reduced reaction rates, offer a rather broad substrate tolerance for polar, short-chain aldehydes [77-79]. Simple aliphatic or aromatic aldehydes are not converted. Therefore, the aldolase from Escherichia coli has been mutated for improved acceptance of nonphosphorylated and enantiomeric substrates toward facilitated enzymatic syntheses ofboth d- and t-sugars [80,81]. High stereoselectivity of the wild-type enzyme has been utilized in the preparation of compounds (23) / (24) and in a two-step enzymatic synthesis of (22), the N-terminal amino acid portion of nikkomycin antibiotics (Figure 10.12) [82]. 

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