Hydrogen cytosine adduct

The methyl group of thymine is susceptible to hydrogen abstraction resulting in a carbon-centred allyl radical. Further oxidation of this radical intermediate can yield thymine-specific products, 5-hydroxymethyluracil and 5-formyluracil. Cytosine adducts also yield unique products under further... 

Figure 3.10 Formation of cytosine adducts (43) by reaction of reactive aldehyde arising from C4 hydrogen abstraction in DNA.

Two types of addition to pyrimidine bases appear to exist. The first, the formation of pyrimidine photohydrates, has been the subject of a detailed review.251 Results suggest that two reactive species may be involved in the photohydration of 1,3-dimethyluracil.252 A recent example of this type of addition is to be found in 6-azacytosine (308) which forms a photohydration product (309) analogous to that found in cytosine.253 The second type of addition proceeds via radical intermediates and is illustrated by the addition of propan-2-ol to the trimethylcytosine 310 to give the alcohol 311 and the dihydro derivative 312.254 The same adduct is formed by a di-tert-butyl peroxide-initiated free radical reaction. Numerous other photoreactions involving the formation by hydrogen abstraction of hydroxyalkyl radicals and their subsequent addition to heterocycles have been reported. Systems studied include 3-aminopyrido[4,3-c]us-triazine,255 02,2 -anhydrouri-dine,256 and sym-triazolo[4,3-fe]pyridazine.257 The photoaddition of alcohols to purines is also a well-documented transformation. The stereospecific addition of methanol to the purine 313, for example, is an important step in the synthesis of coformycin.258 These reactions are frequently more... 

Bansal KM, Patterson LK, Schuler RH (1972) Production of halide ion in the radiolysis of aqueous solutions of the 5-halouracils. J Phys Chem 76 2386-2392 Barnes JP, Bernhard WA (1994) One-electron-reduced cytosine in acidic glasses conformational states before and after proton transfer. J Phys Chem 98 887-893 Barvian MR, Greenberg MM (1992) Independent generation of the major adduct of hydroxyl radical and thymidine. Examination of intramolecular hydrogen atom transfer in competition with thiol trapping.Tetrahedron Lett 33 6057-6060... 

The first direct synthesis of 5-fluorocytosine (15) was reported by Robins and Naik,21 in which cytosine (20) was reacted with trifluoromethyl hypofluorite followed by decomposition of the resulting adduct to provide 5-fluorocytosine in 85% yield. Some years later, Takahara disclosed that 15 could be prepared as its hydrofluoride salt in high purity when cytosine was reacted with fluorine gas in the presence of hydrogen fluoride, followed by treatment with methanol.22... 

In several platinated NpN adducts with. vyn-residues and N = DNA base, the 3 residue was found to be syn [87-89], In these cases, N was a purine. This observation of a syn orientation for only the 3 residue could be related to the 5 residue having an N-sugar in these adducts the N pucker favors an anH-orientation [90]. Also, in our AHT model of (S,R,R,S)-BipPt-(d(GpG)), there is a 3,-G NH2-phosphate hydrogen bond. This interaction could help stabilize the xyn-orientation for the 3 -G residue. In the one instance of a platinated NpN complex with a syn 5 residue, the 5 sugar pucker was N, but the 5 base was a pyrimidine, cytosine [48],... 

When (298) is irradiated in the presence of hydrogen donors (e.g., CH3OH) the reduced dimer (299) and the adduct (300) are formed, presumably via the intermediate radical (301). Irradiation of the cytosine derivatives (302) in... 

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