Heterocyclic compounds Purine Pyridine Pyrimidine

The nitrogen-containing bases are derivatives of three families of heterocyclic compounds called the pyrimidines, purines, and pyridines. Here, the kinship with amine- or amino-type compounds becomes apparent. 

Hertz, Heinrich R., 488 Heterocyclic compounds. See also Furan Purine Pyridine Pyrimidine Pyrrole... 

The analytical data obtained, particularly by the PUMA mass spectrometer on board Vega 1 during the flyby, indicate the presence of a large number of linear and cyclic carbon compounds, such as olefins, alkynes, imines, nitriles, aldehydes and carboxylic acids, but also heterocyclic compounds (pyridines, pyrroles, purines and pyrimidines) and some benzene derivatives no amino acids, alcohols or saturated hydrocarbons are, however, present (Kissel and Krueger, 1987 Krueger and Kissel, 1987). 

Many of the simple heterocycles occur naturally within human biochemistry. For example, the amino acids proline, histidine, and tryptophan contain, respectively, a pyrrolidine, an imidazole, and an indole ring. The nucleic acids contain purine and pyrimidine rings. Vitamins are heterocyclic compounds vitamin Bg (8.8) is a substituted pyridine vitamin Bj (8.9) contains a pyrimidine ring. Simple heterocycles are therefore important to human biochemistry and thus to drug design. 

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],... 

Heterocyclic amines are compounds that contain one or more nitrogen atoms as part of a ring. Saturated heterocyclic amines usually have the same chemistry as their open-chain analogs, but unsaturated heterocycles such as pyrrole, imidazole, pyridine, and pyrimidine are aromatic. All four are unusually stable, and all undergo aromatic substitution on reaction with electrophiles. Pyrrole is nonbasic because its nitrogen lone-pair electrons are part of the aromatic it system. Fused-ring heterocycles such as quinoline, isoquinoline, indole, and purine are also commonly found in biological molecules. 

These compounds satisfy the criteria for aromaticity (planar, cyclic n system, and the Huckel number of 4n -I- 2 71 electrons) pyrrole, imidazole, indole, pyridine, 2-methylpyridine, pyrimidine, and purine. The systems with 6 7i electrons are pyrrole, imidazole, pyridine, 2-methylpyridine, and pyrimidine. The systems with 10 7i electrons are indole and purine. The other nitrogen heterocycles shown are not aromatic because they do not have cyclic 7i systems. 

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