Pyrolysis product, amino acid

G. Chiavari, D. Fabbri and S. Prati, Gas chromatographic mass spectrometry analysis of products arising from pyrolysis of amino acid in the presence of hexamethyldisilazane, J. 

Ouweland et al., 1978) or directly by the pyrolysis of amino acids (Fujimaki et al., 1969). Another important, if not the main, precursor of pyridines in roasted coffee is trigonelline (see Section 2.1.1.2), a product isolated by Goi ter (1910), identical to the product isolated from the seeds of Trigonella foenum-graecum. Viani and Horman (1974, 1976) identified 12 pyridinic compounds after pyrolysis of trigonelline, six of which have now been identified in roasted coffee (4-methylpyridine is noted as identified in coffee, but it is not present in the lists of quoted publications, and to our knowledge its identification has not yet been reported in the literature). The presence of four other alkyl derivatives and of two N-methylnicotinamides have not yet been confirmed in the flavor. The authors have also isolated two piperidylpyridines, 3-phenylpyridine and two of its methyl derivatives, as well as four unsubstituted and dimethyl-substituted dipyridyl compounds. 

The CYP1A subfamily plays an integral role in the metabolism of two important classes of environmental carcinogens, PAHs, and arylamines (Tables 10.3 and 10.4) (22). The PAHs commonly are present in the environment as a result of industrial combustion processes and in tobacco products. Several potent carcinogenic arylamines result from the pyrolysis of amino acids in cooked meats and can cause colon cancer in rats. Environmental and genetic factors can alter the expression of this subfamily of these enzymes. 

Other products that form from the pyrolysis of amino acids are aldehydes, which contain one less carbon atom than the parent amino acid. This process occurs via an SNi deamination mechanism. Another process that can occur is side chain stripping involving chain homolysis. The result is the production of various saturated and unsaturated compounds. Many alpha-amino acids, when pyrolyzed, form an amine fragment, a nitrile fragment, and aldehydes that contain one less carbon atom than the parent amino acid. Also, a side stripping mechanism can result in various saturated and unsaturated compounds. ... 

Understanding the product formation from the pyrolysis of amino acids is the first step in comprehending pyrolysis behavior for more complex systems, such as proteins and nucleic acids, which comprise a large quantity of the material in biological systems. Later in this chapter, in Section 10.5, proteins are discussed in more detail. 

The question of the stability of the biomolecules is a vital one. Could they really have survived the tremendous energies which would have been set free (in the form of shock waves and/or heat) on the impact of a meteorite Blank et al. (2000) developed a special technique to try and answer this question. They used an 80-mm cannon to produce the shock waves the shocked solution contained the two amino acids lysine and norvaline, which had been found in the Murchison meteorite. Small amounts of the amino acids survived the bombardment , lysine seeming to be a little more robust. In other experiments, the amino acids aminobutyric acid, proline and phenylalanine were subjected to shock waves the first of the three was most stable, the last the most reactive. The products included amino acid dimers as well as cyclic diketopiperazine. The kinetic behaviour of the amino acids differs pressure seems to have a greater effect on the reaction pathway than temperature. As had been recognized earlier, the effect of pressure would have slowed down certain decomposition reactions, such as pyrolysis and decarboxylation (Blank et al., 2001). 

Methods were described for HPLC determination of the mutagenic and carcinogenic a-carbolines (56,57), y-carbolines (58,59)155 160, and other products of amino acid pyrolysis found in cigarette smoke, diesel exhaust and cooked foods and phenazines (60, 61) present as impurities of certain pesticides161. These compounds were also determined in human plasma, urine and bile161,162. 

Nitrogen-containing analytes in a FIA system, e.g. amino acids, as they emerge from the LC column, are introduced into a pyrolysis oven under argon atmosphere. The products... 

As to the origins of the major N compounds identified, it is possible that at least a portion of some of these compounds are pyrolysis products of amino acids, peptides, proteins, [18] and porphyrins (a component of chlorophyll), [19] or originate from the microbial decomposition of plant lignins and other phenolics in the presence of ammonia. [20] Of considerable interest are the identifications aromatic and aliphatic nitriles. Nitriles can be formed from amines with the loss of 2 H2, from amides with the loss of H20, and also by reacting n-alkanoic acid with NH3. [21] The detection of long-chain alkyl- and dialkyl-nitriles points to the presence in the soil or SOM of long-chain amines... 

Presently about 20 different mutagenic and/or carcinogenic heterocyclic amines (HAs) have been isolated from various heat-processed foods. One class of these HAs is formed by pyrolysis of proteins or some amino acids. These HAs are amino-carbolines (Figure 13.7), and have been identified in grilled, broiled, baked, and fried meat and fish products, in meat sauces and bouillons, as well as in pyrolyzed proteins, glutamate, lysine, phenylalanine, tryptophan, ornithine, and creatine. 

Dean, M. A., A. S. Dhaliwal, and W. R. Jones. Effects of Zingiberaceae rhizome extract of the infectivity of cyanophage LPP-1. Trans 111 State Acad Sci Suppl 1987 80 Abstr 83. Morita, K., M. Hara, and T. Kada. Studies on natural desmutagens screening for vegetable and fruits factors active in inactivation of mutagenic pyrolysis products from amino acids. Agr Biol Chem 1978 42(6) 1235-1238. 

In its utilization of acetonitrile, the oxazoline synthesis shown in Scheme 56 resembles a Ritter reaction.The procedure is convenient, but yields are variable the pyrolysis gives starting alkene plus acetamide as by-products. Another oxazoline synthesis and subsequent conversion to a cif-amino alcohol is discussed later (Scheme 85). A recent y-hydroxy-a-amino acid synthesis incorporates the following type of transformation (Scheme 57).If a three-day equilibration with anhydrous HBr was introduced iMtween stages i and ii, almost pure trans product was obtained. The paper has many usefol references. Yet another modified Ritter reaction is shown in Scheme 58. ... 

The results for amino acids show that the main pyrolysis products are similar to the ion fragmentation that takes place upon electron impact. For the case of peptides and proteins, most of the effort has been done in obtaining ions of large fragments in order to account as much as possible for the protein structure [24]. Several mass spectra of substituted diketopiperazines obtained from peptide pyrolysis are shown in Figures 3.6.6 a to 3.6.6 f. The fragments generated in their mass spectra are similar to some small molecules obtained in amino acid pyrolysis. 

The amino acid pyrolysis is relevant for protein pyrolysis because certain compounds in the pyrolysate are the same when the substance to be pyrolysed is the amino acid or a peptide formed from that specific amino acid (see Section 13.2). The main pyrolysis products of several amino acids are given in Table 12.1.2 [3,4]. 

Table 12.1.2. The main pyrolysis products of several amino acids. 

Besides the determination of major pyrolysis products for amino acids, a special issue is the formation of several mutagenic compounds (heterocyclic amines) during pyrolysis. These types of compounds were detected in traces in the pyrolysates of amino acids, and the finding is very important as the amino acids are components of proteins and are present in food. Some of these compounds isolated from pyrolysates performed at 550 C from several amino acids [5,6] are shown below ... 

Another main type of pyrolysis products for peptides includes the diketopiperazines (DKP) and their secondary fragmentation products. The formation of DKP from oligopeptides showed that the generation of DKPs always takes place from neighboring amino acids. The mechanism of DKP formation seems to be the following ... 

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