Heterocycles pyrimidine

The condensation of various heterocycles (pyrimidine or purine) with allyl bromide has been effected in the presence of KI. This selectively afforded N-1 isomers with pyrimidines, but N-9, N-3 or N-9, N-7 isomer mixtures with purines (88MIP1 89MI12 91 Mil). Alkyl esters of 3-adenin-9-yl-2-hydroxypropanoic acids were reported as broad-spectrum antiviral agents (85JMC282). 

Indeed, the similarity of the molecules from space and the molecules of Earth is striking. For example, several aliphatic carboxylic acids up to Cg were detected, (Knenvolden et al, 1970), as well as alkyl phosphonates (Yuen and Knenvolden, 1973 Cooper et al, 1992 Pizzarello, 1994) and also heterocyclic pyrimidines (Hayatsu et al, 1975 Stocks and Schwarz, 1982). 

The purine ring system represents a fusion of the two aromatic heterocycles pyrimidine and imidazole. As a logical consequence, appropriately substituted pyrimidines or imidazoles have been used as precursors followed by a cyclization reaction. The purine heterocycle can also be formed from simple acyclic precursors. The most widely used method to synthesize purine is the addition of an imidazole ring to a functionalized pyrimidine moiety (Traube synthesis). The alternative route for the formation of the purine system by the annulation of the pyrimidine ring to a substituted imidazole relates back to a method of Sarasin and Wegmann, and these synthetic protocols principally follow the biosynthetic pathway of purine synthesis. 

Syntheses of six-membered heterocycles (pyrimidines, pyridines, quinolines, pyrans and others) using reactions of functionally substituted alkoxyethylenes with nucleophiles 03ZOR807. 

Each of the diazines can be constructed from an appropriate source of two nitrogens and a dicarbonyl compound. In the case of pyridazines, the nitrogen source is, of course, hydrazine and this in combination with 1,4-dicarbonyl compounds readily produces dihydro-pyridazines, which are very easily dehydrogenated to the aromatic heterocycle. Pyrimidines result from the interaction of a 1,3-dicarbonyl component and an amidine (as shown) or a urea (giving 2-pyrimidones) or a guanidine (giving 2-amino-pyrimidines), without the requirement for an oxidation step. 

Although pyridazine and pyrazine A-oxides can be readily prepared by oxidation of the parent heterocycles, pyrimidine A-oxides are more difficult to obtain in this way, but they can conveniently be prepared by ring... 

Possible metabolic transformations are given for sulfadiazine 43 in Scheme 3193. They include iV4-acetylation to 54, hydroxylation of the heterocyclic pyrimidine ring at the 4- or 5-position to yield 55, depending on the species investigated, combination of... 

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