Amino acids biological importance

Wong and co-workers have prepared various quaternary ct-nitro-ct-methyl carboxyhc acid esters by the palladium-catalyied allyhc alkyladon of ct-nitropropionate ester fEq 5 59 The products can be kmedcaUy resolved by using ct-chymotrypsin and are converted into opdciil acdve ct-methyl ct-amino acids Such amino acids are important due to the unique biological acdvity of these nonproteinogenic ct-amino acids... 

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. 

N-Acyl-a-amino acids are important compounds in both chemistry and biology. They are easily obtained in a transition metal-catalyzed, three-component domino reaction of an aldehyde, an amide, and CO. Whereas cobalt was mainly used for this process, Beller and coworkers [159] have recently shown that palladium has a... 

Enantioselective synthesis of /1-amino acids is important as they are present in various natural products and in many biologically active compounds [26,27]. Several methods exist for the enantioselective synthesis of -substituted /1-amino acids (/l3-amino acids) however, synthesis of a-substituted /1-amino acids (/l2-amino acids) is very limited [28,29]. A report on highly enantioselective hydrogen atom transfer reactions to synthesize /l2-amino acids (Scheme 9) has recently been described [30]. 

The aromatic amino acids give rise to many plant substances. The PLP-dependent decarboxylation of some amino acids yields important biological amines, including neurotransmitters. 

Unnatural amino acids in general, but especially a-amino acids being important intermediates for various biologically active compounds, have enjoyed great popularity as a growing field of interest during recent years [142]. Many enzymatic... 

It is worthwhile to apply the memory of chirality principle to asymmetric alkylation of a-amino acids because nonproteinogenic a,a-disubstituted-a-amino acids are important class of compounds in the fields of medicinal and biological chemistry.21 Typical methods for their asymmetric synthesis involve chiral auxiliary-based enolate chemistry 22-24 However, the most straightforward synthesis would be direct asymmetric a-alkylation of the parent a-amino acids in the absence of external chiral sources. Asymmetric... 

Optically active p-hydroxy-a-amino acids are important not only as constituents of biologically active peptides,5 but also as precursors to p-lactam antibiotics.6 Various synthetic approaches to compounds of this class have been reported involving the traditional resolution of racemic compounds,7 asymmetric syntheses,8 or... 

From a biological point of view with respect to life forms, only 20 amino acids are important, even though many more are found in nature. Most amino acids are optically active. With the functional groups and their chemical behavior, we can predict certain properties of amino acids such as ionization properties. Amino acids join together to form peptides. Table-1 shows the pKa values of some amino acids. 

Kimmel and Saifer (1964) have recorded the infrared spectra of the 2,4-dini-trophenyl (DNP) and 3-phenyl-2-thiohydantoin (PTH) derivatives of 27 amino acids of importance in the study of biological materials, e.g., plasma, tissues, and urine. These workers have also made a quantitative study of the intensities of the major absorption bands according to the method of Flett (1962), and showed that the infrared spectra of DNP- and PTH-amino acids are a useful means for the determination of the N-terminal residues of various peptides and proteins, especially when used in conjunction with thin-layer chromatography. 

Many important processes are thermodynamically unfavorable, or nonspontaneous. Assembling many small amino acid molecules into a large protein molecule is an example of a nonspontaneous process. Yet biological organisms do assemble proteins from amino acids. Biological organisms accomplish many similar nonspontaneous processes. How do they do this ... 

Biological infonnation is also concerned witli tire analysis of biological messages and tlieir import. The fundamental premise of tire protein-folding problem section C2.14.2.2 is tliat tire full tliree-dimensional arrangement of tire protein molecule can be predicted, given only tire amino acid sequence, together witli tire solvent composition, temperature and pressure. One test of tire validity of tliis premise is to compare tire infonnation content of tire sequence witli tire infonnation contained in tire stmcture [169]. The fonner can be obtained from Shannon s fonnula ... 

Ecample Miller and Rich investigated the conformational consequences of substitutions on an amino acid in cyclosporin A, an important immunosuppressive drug. One of the amino acids in this cyclic undecapeptide is (2, 3r, 4r, 6e)-3-Hydroxy-4-methyl-2-(methylamino)-6-octenoic acid (MeBmt). It is essential for biological activity. 

Naturally Occurring Compounds. Many derivatives of iadole are found ia plants and animals where they are derived from the amino acid tryptophan. Several of these have important biological function or activity. Serotonin [50-67-9] (12) functions as a neurotransmitter and vasoconstrictor (35). Melatonin [73-31-4] (13) production is controlled daily by the circadian cycle and its physiological level iafluences, and seasonal rhythms ia humans and other species (36). Indole-3-acetic acid [87-51-4] (14) is a plant growth stimulant used ia several horticultural appHcations (37). 

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

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