Uracils, 1-alkylation xanthines

Abnormal bases (uracil, hypoxanthine, xanthine) alkylated bases in some other organisms, pyrimidine dimers... 

In the early days of meteorite analysis, it was difficult to detect N-heterocycles later, the Murchison meteorite was shown to contain xanthine, hypoxanthine, guanine, adenine and uracil (about 1.3 ppm in total). This meteorite seems to contain various classes of basic and neutral N-heterocycles, as well as isomeric alkyl derivatives. 

Potentially tautomeric pyrimidines and purines are /V-alkylated under two-phase conditions, using tetra-n-butylammonium bromide or Aliquat as the catalyst [75-77], Alkylation of, for example, uracil, thiamine, and cytosine yield the 1-mono-and 1,3-dialkylated derivatives [77-81]. Theobromine and other xanthines are alkylated at N1 and/or at N3, but adenine is preferentially alkylated at N9 (70-80%), with smaller amounts of the N3-alkylated derivative (20-25%), under the basic two-phase conditions [76]. These observations should be compared with the preferential alkylation at N3 under neutral conditions. The procedure is of importance in the derivatization of nucleic acids and it has been developed for the /V-alkylation of nucleosides and nucleotides using haloalkanes or trialkyl phosphates in the presence of tetra-n-butylammonium fluoride [80], Under analogous conditions, pyrimidine nucleosides are O-acylated [79]. The catalysed alkylation reactions have been extended to the glycosidation of pyrrolo[2,3-r/]pyrimidines, pyrrolo[3,2-c]pyridines, and pyrazolo[3,4-r/]pyrimidines (e.g. Scheme 5.20) [e.g. 82-88] as a route to potentially biologically active azapurine analogues. 

N2O3 formed by a third order reaction, can deaminate DNA bases yielding uracil from cytosine, xanthine from guanine, methyl cytosine from thymine and hypoxanthine from adenine [ 56 ]. Furthermore, it can react with secondary amines to yield carcinogenic N-nitrosoamines, which can damage DNA by alkylation, [57]. 

---