Reactions of amino acids and peptides

Part 1 of this chapter is intended to provide background material for the analytical procedures described later in this chapter for amino acids and peptides, but it also provides a broad survey of the topic that can be read in isolation from the analytical context. The derivatisation of amino acids is the basis of many of the sensitive analytical amino-acid assay procedures in current use and this chapter covers the normal profile of reactions of the amino and carboxy groups, knowledge of which is an essential prerequisite for appreciating the analytical context. Reactions of peptides are also covered here (e.g. peptide and protein hydrolysis is covered in Section 4.4.7), though the coverage is restricted in scope because parts of this topic are discussed in Chapter 5, where it is relevant to sequence-determination procedures (see also Barrett, 1985). 

---

Coupling Reaction of Amino Acids and Peptides with Thiols... 

Peptide Conformations. I. Nuclear Magnetic Resonance Study of the Carbamate Reaction of Amino Acids and Peptides, R. U. Lemieux and M. A. Barton, Can. J. Chem., 49 (1971) 767-776. 

The routine category, the use of spectrometry in support of synthetic and investigative studies (verification of the course of a synthesis or of reactions of amino acids and peptides, for example) is a topic that has been covered by numerous textbooks. A thorough coverage of this topic is therefore not provided here and the reader is assumed to know the background relating to the uses of the techniques (and the reader is also assumed to be prepared to consult standard texts for any more detailed explanation that may be needed). 

Experiments with liposomes, which are more complex stmctures than micelles, point in the same direction. Liposomes consist of one (or several) lipid double layers (see Sect. 10.2), ordered concentrically around an aqueous interior. Blocher et al. (2000) carried out polycondensation reactions of amino acids and peptides using l-palmitoyl-2-oleoyl-.vn-glycero-3-phosphocholine liposomes hydrophobically activated amino acids gave chain lengths of up to 29. The linkage of dipeptides (e.g., H-Trp-Trp-OH) to give Trps-OH, i.e., an octapeptide, was also carried out using liposomes. Thus, a second possibility, as well as adsorption on mineral surfaces, was available for polymer formation via micelles and liposomes. 

The reaction of amino acids (and peptides) with ninhydrin has been known for nearly a century. Ninhydrin reacts rapidly with all primary amines to produce characteristic blue-colored spots. 

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

It is known that not all reactions proceed in the same manner on all adsorbent layers because the material in the layer may promote or retard the reaction. Thus, Ganshirt [209] was able to show that caffeine and codeine phosphate could be detected on aluminium oxide by chlorination and treatment with benzidine, but that there was no reaction with the same reagent on silica gel. Again the detection of amino acids and peptides by ninhydrin is more sensitive on pure cellulose than it is on layers containing fluorescence indicators [210]. The NBP reagent (. v.) cannot be employed on Nano-Sil-Ci8-100-UV2S4 plates because the whole of the plate background becomes colored. 

Differences in the materials employed for the layers can also become evident when chemical reactions are performed on them. Thus, Macherey-Nagel report that the detection of amino acids and peptides by reaction with ninhydrin is less sensitive on layers containing luminescent or phosphorescent indicators compared to adsorbents which do not contain any indicator [7]. 

R Schwyzer, M. Feuer, B Iselin. Activated esters. IB. Reactions of activated esters of amino acid and peptide derivatives with amines and amino acid esters. Helv Chim Acta 38, 83, 1955. 

If we treat alkoxycarbcne complexes not with phosphines but with primary or secondary amines, we observe a new kind of reaction, reminiscent of the reactions of esters. This observation led us into peptide chemistry along a path that proved to be quite surprising to a coordination chemist. We could show that the alkoxy group of alkoxy(organo) carbene complexes can be substituted not only by mono- or dialkylamino residues but also by free amino groups of amino acid and peptide esters (63, 64). The principle of this reaction is shown in Scheme 2. 

D20. Drozdz, R., Naskalski, J. W., and Sznajd, J., Oxidation of amino acids and peptides in reaction with myeloperoxidase, chloride and hydrogen peroxide. Biochim. Biophys. Acta 957, 47-52 (1988). 

Draw structures of reaction products of amino acids and peptides. 

Abstract This review provides an overview of some of the more recent work directed to exploit radical-based chemistry for the modification of some of Natures most important biomolecules, such as amino acids, peptides, and carbohydrates. Radical reactions are particularly advantageous for carrying out a variety of structural modifications on biomolecules as the reaction conditions are typically compatible with a wide variety of functional groups and solvents. An array of effective synthetic transformations will he discussed including selective side chain and backbone modifications of amino acids and peptides, along with methods for the transformation of carbohydrate substituents, as well as fragmentation and cyclizations reactions for the preparation of either structurally modified carbohydrates or chiral building blocks. 

The major precursors in meat flavors are die water-soluble components such as carbohydrates, nucleotides, thiamine, peptides, amino acids, and the lipids, and Maillard reaction and lipid oxidation are the main reactions that convert these precursors in aroma volatiles. The thermal decomposition of amino acids and peptides, and the caramelization of sugars normally require temperatures over 150C for aroma generation. Such temperatures are higher than those normally encountered in meat cooking. During cooking of meat, thermal oxidation of lipids results in the formation of many volatile compounds. The oxidative breakdown of acyl lipids involve a free radical mechanism and the formation of... 

Amines and alcohols were readily functionalized with copper-based catalysts containing TpY ligands upon reaction of several diazo compounds under very mild conditions. In the case of the former, this strategy led to the formation of amino acids and peptides, the catalyst activity competing with that of the previous rhodium-based... 

---