Heterocyclic aromatic compounds pyrimidine

Actinomycetes can metabolize a wide variety of organic substrates, including organic compounds that are generally not metabolized, such as phenols and steroids. They are also important in the metabolism of heterocyclic compounds such as complex nitrogen compounds and pyrimidines [42,49]. The breakdown products of their metabolites are frequently aromatic, and these metabolites are important in the formation of humic substances and soil humus [42,49]. 

The bases that occur in nucleic acids are aromatic heterocyclic compounds derived from either pyrimidine or purine. Five of these bases are the main components of nucleic acids in all living creatures. The purine bases adenine (abbreviation Ade, not A ) and guanine (Gua) and the pyrimidine base cytosine (Cyt) are present in both RNA and DNA. In contrast, uracil (Ura) is only found in RNA. In DNA, uracil is replaced by thymine (Thy), the 5-methyl derivative of uracil. 5-methylcyto-sine also occurs in small amounts in the DNA of the higher animals. A large number of other modified bases occur in tRNA (see p. 82) and in other types of RNA. 

The bases occurring in nucleic acids are derivatives of the aromatic heterocyclic compounds purine and pyrimidine (see p. 80). The biosynthesis of these molecules is complex, but is vital for almost all cells. The synthesis of the nucleobases is illustrated here schematically. Complete reaction schemes are given on pp. 417 and 418. 

Pyrimidine is a six-membered aromatic heterocyclic compound that contains two nitrogen atoms, separated by a carbon atom, in the ring. Nucleic acids, DNA and RNA, contain substituted purines and pyrimidines. Cytosine, uracil, thymine and alloxan are just a few of the biologically significant modified pyrimidine compounds, the first three being the components of the nucleic acids. 

The monofunctional complexes [PtCl(dien)]+, [PtCl(NH3)3]+, and the active d.v-compounds cA-[PtCl(NH3)2 (Am)]+, where Am is an heterocyclic or aromatic amine ligand like pyridine, pyrimidine, purine, or aniline, only form stable monoadducts with DNA [50][51]. However, when Am = A-methyl-2,7-diazapyrenium (a strong intercalator), the monoadduct is stable only on single-stranded DNA. On double-stranded DNA it is hydrolyzed with release of c T-[Pt(NH3)2(Am)(H20)]3+ or of Am generating the aqua monoadduct of cisplatin [52],... 

In 1975 the anion of T was observed in a mass spectrometer, indicating a positive valence-state Ea for T. In 1990 the Ea of AGCUT were predicted using substitution, replacement, and conjugation effects [10-14], In order to estimate the Ea of substituted compounds, that of the parent compounds is required. In 1974 I. Nenner and G. J. Schulz estimated the AEa of quinoline (0.36 eV), pyradazine (0.40 eV), pyrimidine (0.00 eV), pyrazine (0.40 eV), and s-triazine (0.45 eV) from electron transmission spectra and half-wave reduction potentials [15]. No adiabatic electron affinities of aromatic nitrogen heterocyclic compounds were measured in the gas phase before 1989 [16]. 

There is, for example, no end-of-text chapter entitled Heterocyclic Compounds. Rather, heteroatoms are defined in Chapter 1 and nonaromatic heterocyclic compounds introduced in Chapter 3 heterocyclic aromatic compounds are included in Chapter 11, and their electrophilic and nucleophilic aromatic substitution reactions described in Chapters 12 and 23, respectively. Heterocyclic compounds appear in numerous ways throughout the text and the biological role of two classes of them—the purines and pyrimidines—features prominently in the discussion of nucleic acids in Chapter 27. 

Acetylenecarboxylic acids, reactions with heterocyclic compounds, 1, 125 Aminochromes, 5, 205 Anthranils, 8, 277 Aromatic quinolirines, 5, 291 Aza analogs, of pyrimidine and purine bases, 1, 189... 

Ring systems containing two heteroatoms tend to feature less in the vapor-phase literature. This is partly because of the greater reactivity (i. e. reduced aromaticity) of these heterocyclic compounds. In addition, there has been less commercial incentive to develop catalyzed processes for these smaller-volume niche products. As an example, both pyrimidine (26) [51] and pyrazine (27) [52] can be made by catalyzed vapor-phase methods they can also be recovered from the pyri-dine- ff-picoline reaction. In principle, pyrimidine and pyrazine could then serve as platforms-much like pyridine does-for preparing a wide range of derivatives. The market for these derivatives is, however, best met by traditional convergent syntheses in the liquid phase. 

Quinoline, indole, imidazole, purine, and pyrimidine are other examples of heterocyclic aromatic compounds. The heterocyclic compounds discussed in this section are examined in greater detail in Chapter 21. 

Pyrimidine derivatives are synthesized from TV-substituted lactams and Viehes salt with a short reaction sequence, good yields of the targeted heterocyclic compounds, as well as their convenient isolations and purifications. Addition of dry DMF to the reaction mixture proved to be highly beneficial in increasing the yields of the targeted heterocycles. This may be attributed to the improved solubility of amidines in the toluene/DMF (2 1) solvent mixture. Pyrimidines reacted with A-methylbenzylamine in dry DMF at 140 °C in a sealed-tube to furnish products of formal nucleophilic aromatic substitution of the N-Me2 group. 

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