Pyrimidines radical substitution

The phenylation of pyridazine and quinoxaline has been carried out using dibenzoyl peroxide, iV-nitrosoacetanilide, and benzenedia-zonium hydroxide as the sources of phenyl radical, the first two methods giving very much better yields than the third.63 The most reactive positions in these ring systems are the 4-position in pyridazine and the 2-position in quinoxaline. Phthalazine has been phenylated with iV-nitrosoacetanilide, giving a low yield of 5-phenylphthalazine, but the main product from cinnoline in this reaction was 4,4 -bicin-nolyl, although a small quantity of 4-phenylcinnoline was obtained.63 Pyrimidine has been arylated only with the 4-nitrophenyl radical, substitution occurring at the 2- and 4-positions.12... 

Pyrido[3,4-d]pyrimidine-2,4-dione synthesis, 3, 215 Pyridopyrimidines, 3, 201 iV-alkylations, 3, 206 biological activity, 3, 260-261 1-electron reductions, 3, 207 IR spectra, 3, 204 mass spectra, 3, 204 MO calculations, 3, 204 NMR, 3, 202, 203 nucleophilic substitution, 3, 213 8-nucleosides synthesis, 3, 206 physical properties, 3, 201-205 protonation, 3, 206 radical reactions, 3, 215 reactions with water, 3, 207 reduced... 

Brown has also predicted, from localization energy calculations, that pyrrole and glyoxaline should react with radicals mainly at the 2-position, whereas pyrazole should be most reactive at the 3-position. Browm and Heffernan s calculation that the orientation in pyrimidine substitution should be 4 > 2 > 5 is in agreement with the results from the p-nitrophenylation of pyrimidine. ... 

The 6-yl radicals produced by (the selective) [23, 24] addition of OH to C(5) of the C(5)/(6) double bond of naturally occurring pyrimidine bases, nucleosides and nucleotides or those formed by H-abstraction from C(6) of 5,6-dihydro-pyrimidines [25] react with para-substituted nitrobenzenes by addition (k 6xl0 to 2 X s ) to yield nitroxyl-type radicals which were... 

At pH < 7 the nitroxyl radicals do not undergo an observable heterolysis (khs 10 s ), but decay by bimolecular reactions. However, in basic solution an OH -catalyzed heterolysis takes place to yield the radical anion of the nitrobenzene and an oxidized pyrimidine. In the case of the nitroxyls substituted at N(l) by H (i.e. those derived from the free bases), the OH catalysis involves deprotonation at N(l) which is adjacent to the reaction site [= C(6)] (cf. Eq. 15) [26] ... 

Aminopyrazolo[3,4-d]pyrimidines 257 were converted into the corresponding 4-aryl substituted derivatives 259 via treatment with alkyl nitrites and boiling in aromatic solvent. The isomer distribution of 259 prepared by these route was that predicted for a radical intermediate (ortho, meta, and para). The structure of isomers was established by H-NMR. Unusual fragmentation products were isolated these probably result from collapse of the radical intermediate 258 (83JOC4605). Methylation of 257 takes place at either N-1 or N-2. Further methylation affords methylamino derivatives structures of the products were established by C-NMR as well as by chemical methods (75JOC1822). 

Unusual features of riboflavin as recorded by some researchers include (1) High levels in liver inhibit tumor formation by azo compounds in animals (2) free radicals are formed by light or dehydrogenation flavine semiquinone dihydroflavin+ (3) free vitamin is found only in retina, urine, milk, and semen (4) substitution of adenine by other purines and pyrimidines destroys activity of flavin adenine dinucleotide (FAD) ... 

Hildenbrand K (1995) Spin-trapping studies of the reaction of the sulfate radical ion with N1-substituted pyrimidine bases. Comparison with continuous-flow electron paramagnetic resonance experiments.) Chem Soc Perkin Trans 2 2153-2162 Hildenbrand K, Schulte-Frohlinde D (1997) Time-resolved EPR studies on the reaction rates of per-oxyl radicals of polyfacrylic acid) and of calf thymus DNA with glutathione. Re-examination of a rate constant for DNA. Int J Radiat Biol 71 377-385 Hildenbrand K, Behrens G, Schulte-Frohlinde D, Herak JN (1989) Comparison of the reaction OH and S04- radicals with pyrimidine nucleosides. An electron spin resonance study in aqueous solution. J Chem Soc Perkin Trans 2 283-289... 

LukeTL, Mohan FI, Manoj VM, Manoj P, Mittal JP, Aravindakumar CT (2003) Reaction of oxide radical ion (O -) with substituted pyrimidines. Res Chem Intermed 28 303-312 Luo W, Muller JG, Rachlin EM, Burrows CJ (2000) Characterization of spiroiminodihydantoin as a product of one-electron oxidation of 8-oxo-7,8-dihydroguanosine. Org Lett 2 613-616 Luo W, Muller JG, Burrows CJ (2001a) The pFI-dependent role of superoxide in riboflavin-catalyzed photooxidation of 8-oxo-7,6-dihydroguanosine. Org Lett 3 2801-2804 Luo W, Muller JG, Rachlin EM, Burrows CJ (2001b) Characterization of hydantoin products from one-electron oxidation of 8-oxo-7,8-dihydroguanosine in a nucleoside model. Chem Res Toxicol 14 927-938... 

Naumov S, Beckert D (2002) Reply to the Comment on A Fourier transform EPR study of uracil and thymine radical anions in aqueous solution)/ by DM Close. Phys Chem Chem Phys 4 45 Naumov S, Barthel A, Reinhold J, Dietz F, Geimer J, Beckert D (2000) Calculation of spin densities of radicals of pyrimidine-type bases by density functional theory. Influence of solvent and comparison with EPR results. Phys Chem Chem Phys 2 4207-4211 Naumov S, Hildenbrand K, von Sonntag C (2001) Tautomers of the N-centered radical generated by reaction of SO4 - with N(1)substituted cytosines in aqueous solution. Calculation of isotropic hyperfine coupling constants by a density functional method. J Chem Soc Perkin Trans 2 1648-1653... 

In 1993 free-radical formation in adenosine and some pyrimidines was investigated by ESR spectroscopy after bombardment with heavy ions at 100 K <93MI 711-02). Spectra were observed at 77 K, after irradiation at 100 K, upon annealing to 300 K and storage at 300 K. Individual radical patterns were isolated from the spectra by computer manipulation and assigned to structures by powder simulation based on literature data. Adenosine exhibits two H-addition radicals at C-2 and C-8. Reactions of C-6 and N-9 substituted purines with OH radicals have been studied by pulse radiolysis <87JPC4138>. 

Diketones of the selenophene series are used to synthesize various heterocyclic systems isoxazole, pyrazole, and pyrimidine, as well as a-substituted bis-/3-diketones. Thus, /3-diketones with hydrazine hydrates yielded the corresponding disubstituted pyrazoles.130,131 The presence of the selenienyl radical as a substitutent substantially reduced the basicity of a pyrazole ring (see Section V,C) the electron-accepting ability of the selenien-2-yl radical is especially great.121 The reaction of selenophene /3-diketones with ureas gives substituted pyrimidines.125... 

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