Nitrogen heterocyclic bases

Adams, J., E. L. Atlas, and C.-S. Glam, Ultratrace Determination of Vapor-Phase Nitrogen Heterocyclic Bases in Ambient Air, Anal. Chem., 54, 1515-1518 (1982). 

Oligonucleotides are nucleic acid polymers. Each nucleic acid is assembled from a sugar, a nitrogenous heterocyclic base, and a phosphate. The specific identity of the sugar and base determines the type of nucleic acid, which in turn determines the structure and function of the oligonucleotide. 

Silver(II) Compounds. Silver(II) is stabilized by coordination with nitrogen heterocyclic bases, such as pyridine and dipyridyl. These cationic complexes are prepared by the peroxysulfate oxidation of silver(I) solutions in the presence of an excess of the ligand. An extensive review of the higher oxidation states of silver has been published (21). 

A nitrogenous heterocyclic base (either a purine or a pyrimidine) attached to the 1 -carbon atom of the sugar by an N-glycosidic bond. In DNA the purine bases are adenine (A) and guanine (G) and the pyrimidine bases are cytosine (C) and thymine (T). The bases in RNA are the same except that uracil (U), a pyrimidine, replaces thymine. 

Boger has devised numerous synthetic schemes for the synthesis of six-membered nitrogen heterocycles based upon DA addition with subsequent rDA extrusion, and has reviewed the subject. Representative examples are shown for the synthesis of substituted pyridines (equation 95), substituted pyrimidines (equation 96) ° and substituted 1,2-diazines (equation 97). ... 

Togo, Yokoyama and coworkers have developed a useful synthetic procedure for the preparation of nitrogen heterocycles based on the N-radical cyclization onto an aromatic ring [247, 656-658], For example, various iV-alkylsaccharins 626 can be conveniently prepared in moderate to good yields by the reaction of arenesul-fonamides 625 with (diacetoxyiodo)benzene in the presence of iodine under irradiation with a tungsten lamp (Scheme 3.245) [656]. A similar procedure has been applied to the synthesis of 1,2,3,4-tetrahydroquinoline derivatives [247, 657] and 3,4-dihydro-2,l-benzothiazine 2,2-dioxides [658],... 

Synthetic studies on natural products with aromatic nitrogen heterocycles based on the development of methods for the formation of aryl C-N bond 13YZ1065. 

Yamaguchi R, K-1 Fujita, Zhu M (2010) Recent progress of new catalytic synthetic methods for nitrogen heterocycles based on hydrogen transfer reactions. Heterocycles 81(5) 1093-1140... 

Borane (BH3) adducts of some nitrogen heterocyclic bases e.g. quinoline, aminopyridines) have been prepared. Halogenoboranes form boronium salts with such heterocycles, and some containing two different bases attached to a single boron atom, of the type (R -pyridine)(R -pyridine)aBH + 2I, have been identified. The syntheses and molecular structure determinations of complexes of phosphoranes with borane have been reported. The molecular structure of MejP.BCls has been determined by gas electron diffraction. ... 

The reduction of iminium salts can be achieved by a variety of methods. Some of the methods have been studied primarily on quaternary salts of aromatic bases, but the results can be extrapolated to simple iminium salts in most cases. The reagents available for reduction of iminium salts are sodium amalgam (52), sodium hydrosulfite (5i), potassium borohydride (54,55), sodium borohydride (56,57), lithium aluminum hydride (5 ), formic acid (59-63), H, and platinum oxide (47). The scope and mechanism of reduction of nitrogen heterocycles with complex metal hydrides has been recently reviewed (5,64), and will be presented here only briefly. 

Hantzsch 2 gave the name pseudo bases to those carbinols that gave salts with acids by the elimination of water and a simultaneous change of constitution. Such carbinols are common among the nitrogen heterocyclic compounds and the naturally occurring alkaloids e.g., berberine, sanguinarine, chelerythrine. 

CaveU and Chapman made the interesting observation that a difference exists between the orbital involved in the quatemization of aromatic nitrogen heterocycles and aromatic amines, which appears not to have been considered by later workers. The lone pair which exists in an sp orbital of the aniline nitrogen must conjugate, as shown by so many properties, with the aromatic ring and on protonation or quatemization sp hybridization occurs with a presumed loss of mesomerism, whereas in pyridine the nitrogen atom remains sp hybridized in the base whether it is protonated or quaternized. Similarly, in a saturated compound, the nitrogen atom is sp hybridized in the base and salt forms. 

The reversible hydration of nitrogen-containing heterocyclic bases and their hydroxy and mercapto derivatives is acid-base catalyzed and, at constant pH, the reactions obey first-order rate equations. 2 26.27-33... 

The majority of sequential radical reactions deal with cyclizations as the key steps. The constructions of carbocycles, oxygen, and nitrogen heterocycles using (TMSlsSiH as a mediator are many and represents the expansion and importance of these synthetic approaches. For example, Nicolaou and coworkers found that (TMSlsSiH serves as a superior reagent in the radical-based approach toward the synthesis of azadirachtin, an antifeedant agent currently used as an insecticide, and in other related systems. ° ° Here below we collected a number of reactions mostly from the recent work in the area of intramolecular reactions. 

Many companies spiecialize in the production of chemicals grouped in chemical trees characterized by the same chemical roots (compounds) or the same/similar method of manufacturing. Examples are the Lonza trees based upon (I) hydrogen cyanide, (2) ketene (H2C=C=0) and diketene (4-methyleneoxetan-2-one), and (3) nitrogen heterocycles. A different t3q)e of tree is that of DSM Chemie Linz, which branches out from ozonolysis as the core technology (Stinson, 1996). Wacker Chemie has developed its chemical tree leading to acetoacetates, other acylacetates, and 2-ketones (Stinson, 1997). Table 1.1 shows examples of fine chemicals. 

Palladium-catalyzed substitution can also be applied to nonbasic nitrogen heterocycles, such as indoles, in the absence of strong bases. 

In Table IV some physical data and spectral characteristics of 6,7-secoberbines are listed. Only methyl corydalate (55) is optically active. Formula 55 presents the spatial structure of this compound, deduced by Nonaka et al. (65) and confirmed by Cushman et al. by both correlation with (+)-mesotetrahydrocorysamine (72) (<5S) and total synthesis (69). It is difficult to find common characteristic features in both the mass and H-NMR spectra of these alkaloids because they differ significantly from each other in their structures. On one hand, corydalic acid methyl ester (55) incorporates a saturated nitrogen heterocycle, while the three aromatic bases (56-58) differ in the character of the side chain nitrogen. For example, in mass fragmentation, ions of the following structures may be ascribed to the most intensive bands in the spectrum of 55 ... 

Acridine is a three-ring nitrogen heterocycle, classified as polycyclic aromatic hydrocarbons (PAHs), some of which are proposed to be human carcinogens based on the evidence of carcinogenicity in experimental animals. Acridine is present in crude oil and tar pitch, as well as in emissions resulting from their combustion. 

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