Amino acids in peptides

A great many protective groups have been developed for the amino group, including carbamates (>NC02R), used for the protection of amino acids in peptide and protein syntheses, and amides (>NCOR), used more vv idely in syntheses of alkaloids and for the protection of the nitrogen bases adenine, cytosine, and guanine in nucleotide syntheses. 

Kohn, J., and Danger, R., Backbone modification of synthetic poly-o-L-amino acids, in Peptides (G. R. Marshall, ed)., Escom, Leiden, Netherlands, 1988, pp. 658-660. 

Coupling constants are routinely used to determine the side-chain conformation of amino acids in peptides and proteins. Whereas proteins nowadays are almost exclusively studied as C- and N-labeled isotopomers, peptides usually have these isotopes in natural abundance, i.e. the magnetically active heteronuclei are highly diluted. Most amino acids contain a methylene group at the ji-position for which the X angle is determined by the conformation of the Ca—Cp bond. Two vicinal Jhh coupling constants can be measured Ha to and H to Usually... 

Zhao, Q., Sannier, F., Garreau, I., Lecoeur, C., and Piot, J. M., Reversed-phase high-performance liquid chromatography coupled with second-order derivative spectroscopy for the quantitation of aromatic amino acids in peptides application to hemorphins, /. Chromatogr. A, 723, 35, 1996. 

Racemization of the native L-amino acid in peptides and proteins to the D-enantiomer generally results... 

The importance of the thioesters was realized at the beginning of the 1950s by Theodor Wieland from the University of Frankfurt am Main (Wieland and Pflei-derer, 1957), who used aminoacyl mercaptans as activated amino acids in peptide syntheses (see Sect. 5.3). Thus, 30 years later, this area of basic research came to be useful for prebiotic chemistry. 

Racemisation is a chemical reaction, and its rate is different for each type of amino acid. An important fact is that this process is affected by many factors that influence the rate of change of the amino acids stereochemistry [106]. The main parameters affecting the racemisation process include the amino acid structure, the sequence of amino acids in peptides, the bound state versus the free state of the amino acids, the pH in the environment, the concentration of buffer compounds, the contact of the sample with clay surfaces... 

PCI and PC2 cleave at selected pairs of basic amino acids in peptide precursors Lys-Arg, Arg-Arg, Lys-Lys and Arg-Lys. PCI may also catalyze cleavages at selected single Arg sites present in some precursors, such as prosomatostatin and procholecystokinin. Cleavages in LDCVs by PCs are tightly controlled, often occurring in a very orderly fashion (Fig. 18-7). The initial cleavages of POMC... 

Gilbertson used the diversity available from the use of the 20 natural amino acids in peptides by creating two new phosphine-containing amino acids 9 a and b these were incorporated in the form of their thiooxides 8 into random peptide sequences (Fig. 36.4) [29]. 

F Weygand, A Prox, W Konig. Racemisation of the second last carboxyl-containing amino acid in peptide synthesis. Chem Ber 99, 1446, 1966. 

Onorato, J. J., Palczewski, K., Regan, J. W., Caron, M. G., Lefkowitz, R. J., and Benovic, J. L. (1991) Role of acidic amino acids in peptide substrates of the beta-adrenergic receptor kinase and rhodopsin kinase. Biochemistry. 30, 5118-5125. 

Peptide chains have a direction and therefore two different ends. The amino terminus (N terminus) of a peptide has a free ammonium group, while the carboxy terminus (C terminus) is formed by the carboxylate group of the last amino acid. In peptides and proteins, the amino acid components are usually linked in linear fashion. To express the sequence of a peptide, it is therefore suf cient to combine the three-letter or single-letter abbreviations for the amino acid residues (see p. 60). This sequence always starts at the N terminus. For... 

Evolution is tireless in the development of natural toxins. A vast number of variations are possible with even a small number of amino acids in peptides, and peptides make up only one of a broad array of toxic compounds. For example, the predatory marine snail genus Conus is estimated to include at least 500 different species. Each species kills or paralyzes its prey with a venom that contains 50-200 different peptides or proteins. Furthermore, there is little duplication of peptides among Conus species. Other animals with useful toxins include snakes, frogs, spiders, bees, wasps, and scorpions. Plant species with toxic (or therapeutic) substances are too numerous to mention here they are referred to in many chapters of this book. 

S ATP -I- peptide <3> (<3> synthetic [9,13,14] <3> e.g. Leu-Glu-Glu-Ser-Ser-Ser-Ser-Asp-His-Ala-Glu-Arg-Pro-Pro-Gly or Arg-Arg-Arg-Glu-Glu-Glu-Glu-Glu-Ser-Ala-Ala-Ala, role of acidic amino acids in peptide substrates, preference for negatively charged amino acids localized to the N-terminal side of a Ser- or Thr-residue, Ser-containing peptides are 4fold better than Thr-containing [9] <3> /1-ARK 1 and 2 prefer peptide substrates with acidic amino acids N-terminal to a Ser-residue [13] <3> /)-ARK 1 prefers peptides containing acidic residues on the N-terminal side of a serine or threonine, presence of activated receptor enhances peptide phosphorylation [14]) (Reversibility <3> [9,13,14]) [9, 13, 14]... 

All free amino acids plus charged amino acids in peptide chains can serve as buffers. 

Activated Cyclic Derivatives of Amino Acids in Peptide Synthesis J. C. Sheehan, Ann. N.Y. Acad. Sci., 1960, 88, 665-668. 

The high reactivity of di- and trinitrophenyl fluorides towards nucleophiles has been used for the arylation of various N-nucleophiles. A method was developed for the determination of N-terminal amino acids in peptides. Thus, nucleophilic attack of the amino acid nitrogen at Sanger s reagent (2,4-dinitrophenyl fluoride, 4), hydrolysis and subsequent analysis of the N-(2,4-dinitrophenyl)amino acid allows determination of the amino acid.162,163 Although this method has been replaced by more efficient procedures, it marked a milestone in the elucidation of peptide structures (Nobel Prize 1958). A variety of N-nuclcophilcs (no amino acids) which have been used in the nucleophilic substitution of 2,4-dinitrophcnyl fluoride is listed. 

The retention times of peptides with fewer than 20 residues in reversed-phase chromatography can be predicted with a high degree of accuracy based on their amino acid composition and the characteristics of their N-terminal and C-terminal amino acids. A number of researchers (66 -75) have studied the role of amino acids in peptide retention and have established retention coefficients for the different amino acids. The retention coefficient value of each amino acid is normally calculated by regression analysis of the retention times for peptides of known composition. 

The formation of methyl- (MTH) or phenylthiohydantoin (PTH) amino acids is a valuable technique for sequencing of amino acids in peptides and proteins by the Edman degradation procedure [1], HPLC is very useful for the separation of MTH- or PTH-amino acids as adsorption [2,3], reversed-phase [4] and ion-exchange [S] chromatography. 

The tert-butoxycarbonyl (i-BOC) group is often used for protection of the amino, hydroxy, and sulfhydryl groups. This kind of defense is usual in the protection of amino acids in peptide synthesis. 

Table 6.2 The use of oligonucleotides to encode amino acids in peptide synthesis...

Spatola, A. F. (1983) Peptide backbone modifications in chemistry and biochemistry of amino acids, in Peptides and Proteins (Weinstein, B ed.), Marcel Dekker, New York, pp. 267-357. 

We are currently designing special recognition tips in our new hosts for nonpolar and acidic amino acids in peptides. We are also covalently connecting two or more of the modules to achieve predictable sequence-selective recognition of larger peptides (for another approach to peptide receptors see Chapters 2.3 and 3.1). This... 

Protonated binations of amino acids in peptide linkages, that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur Having protons added to a base... 

Table III. Protection and Deprotection of Amino Acids in Peptide Synthesis...

This technique relies on the clean coupling of amino acids in peptide synthesis, the ability to easily remove reactants and solvents and wash the products between each stage of the synthesis and the ability to protect and deprotect reactive groups on the sohd support as necessary. 

P. F. Butskus, Russ. Chem. Rev. (English Transl.) 31, 283 (1962). Cyclic derivatives of amino acids in peptide synthesis ... 

The 4.4,4-trifluoro-3-oxobut-l-enyl group has been proposed as a suitable group for the protection of the N —H terminal of amino acids in peptide synthesis. Chiral amino acids react with 4-etnoxy-1,l,l-trifluorobut-3-en-2-one (59) to give the N-prolected amino acids (e.g., 60) in good yields and with retention of chirality. The protecting group can be removed by acidic... 

Table 13.24 Results of PLS regression for prediction of the aging times in wines from five amino acids in peptides <700 Da fraction...

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