Blues 1-methyluracil

Photolytic. When a dilute aqueous solution (1-10 mg/L) of bromacil was exposed to sunlight for 4 months, the TV-dealkylated photoproduct, 5-bromo-6-methyluracil, formed in small quantities. This compound is less stable than bromacil and upon further irradiation, the de-brominated product, 6-methyluracil was formed (Moilanen and Crosby, 1974). Acher and Dunkelblum (1979) studied the dye-sensitized photolysis of aerated aqueous solutions of bromacil using sunlight as the irradiation source. After 1 h, a mixture of diastereoisomers of 3-5ec-butyl-5-acetyl-5-hydroxyhydantoin formed in an 83% yield. In a subsequent study, another minor intermediate was identified as a 5,5 -photoproduct of 3-5ec-butyl-6-methyluracil. In this study, the rate of photooxidation increased with pH. The most effective sensitizers were riboflavin (10 ppm) and methylene blue (2-5 ppm) (Acher and Saltzman, 1980). Direct photodegradation of bromacil is not significant (Acher and Dunkelblum, 1979 Ishihara, 1963). 

A detailed study on the binding of Pt uracil blue to closed and nicked circular DNA, reported in 1978 [38], confirmed some of the salient features of the earlier study. However, it was also shown that presumably low-mo-lecular-weight Pt entities not carrying a uracil nucleobase had formed covalent adducts with DNA. Whether or not these Pt species were solvolysis products of the blue used or simply part of the complex mixture, was not obvious. Hints for a hydrolytic decomposition of another blue obtained from 1-methyluracil rather than uracil during reaction with DNA were later found [39], but there appears to be no consensus about the nature of the DNA-binding Pt species. 

A 1-methyluracil blue of distinctly different composition, containing (formally) two Ptn and a heterometal ion, Pdm, has likewise been prepared and structurally characterized by X-ray analysis (Scheme 5) [67]. It can be (reversibly) further oxidized to a PtnPdIVPtn state and also reduced to PtnP-d t11. There is no reason why Pt instead of Pd should not behave similarly, although this would require the loss of two NH3 ligands from a cis-[Pt(NH3)2(H20)2]2+entity. 

Although blues prepared from unsubstituted uracil, thymine and related bases (e.g., 6-methyluracil, 5,6-dihydrouracil etc.) were the first to be prepared and tested, their composition is the least clear. The author suspects that there is still long way to go to fully understand the nature of these blues . It is possible that there are even blues built on different principles. A main obstacle to the elucidation of Pt blues derived from the unsubstituted pyrimidine nucleobases lies in their versatility as ligands. Not only is there the possibility that these ligands bind to metal ions, specifically Pt, via N(l) or N(3) or (only with uracil) C(5), but also many possible combinations of two or more binding sites, e.g., N(l),0(2) N(3),0(2) N(3),0(4) N(1),N(3) N(3),0(2),0(4) N(1),0(2),N(3),0(4) etc. (Scheme 6). A series of these binding patterns has been established by X-ray crystal-structure analyses [68-70], and others are likely on the basis of spectroscopic studies [71] [72] or from comparison with results obtained for N(l) substituted derivatives. The possibility of different tautomers of platinated forms being... 

The work by Lippard and coworkers [2][24][25][88][95][98-100] derives its chief motivation from the understanding of the interaction between the anticancer drug cA-[PtCl2(NH3)2] and pyrimidine nucleobases. Unfortunately, the reaction of c7v-[PtCl2(NH3)2] with molecules such as uracil or thymine leads to non-crystalline dark blue materials ( platinum blues ) which are difficult to characterize. The use of a ligand with similar but more restricted number of donor sites, such as a-pyridone (hp), allowed isolation and full characterization of relevant platinum complexes. Related work has used 1-methyluracil (1-Me-urac) and 1-methylthymine (1-Me-thym) in which one of the pyrimidine nitrogens has been blocked [101]. 

An interesting route to platinum 1-methyluracil blue was reported by Lippert and Neugebauer [105]. They reacted the 1-methyluracil-bridged head-to-head compound [Pt2(NH3)4(l-Me-urac)2]2+, with silver nitrate to... 

Thymine being 5-methyluracil, electronic spectra of uracil and thymine are similar. Thus, both uracil and thymine show three absorption bands near 260, 205 and 180 nm (4.77, 6.05 and 6.89 eV, respectively). The first and third bands in thymine are generally sli tly red- and blue-shifted, respectively, with respect to the corresponding bands in yjacii 23.213.214.217.220.224.262.263 spectra reveal a composite nature of the 205 nm band corresponding to peaks near 215 and 195 nm (5.77 and 6.36 eV, respectively). The CD spectra... 

Platinum-acetamide-blue and platinum-uracil-blue compounds have been reported. The tetranuclear uracil blue [Pt4(l-MeU)4(NH3)g](N03)5-H20, where 1-MeU is the mono-anion of 1-methyluracil, has structure and properties resembling 2-pyridone-blues. Platinum blue compounds with uridine, isonicotinamide, malonamide, and biuret have been described. ... 

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