1-Methylcytosinate anion

The uracilate and thyminate anions simultaneously bind the metals through N(3) and 0(4), whereas the 1-methylcytosinate anions do so through N(3) and the deprotonated amino group N(4) [14]. The neutral cytosine was found also to act as bridging ligand through N(3) and 0(2) [33]. 

Figure 8, Binding of [(NHs)2Pt(OH)2Pt(NHs)2P at N3 of 1-methylcytosine and subsequent reaction to form the 1-methylcytosinate anion bound to two platinum...

Somewhat more loosely related to platinum antitumor drugs were EHMO calculations performed on heterobimetallic Pt-Pd complexes with a bridging methylcytosinate anion by Mealli, Randaccio, Lippert, and coworkers [31][32], The calculations served to elucidate the metal-metal and metal-ligand binding interactions, and yielded a qualitative interpretation of the 195Pt-NMR chemical shifts. 

The reaction mechanism of the DNA (cytosine-5)-methyltransferase-catalyzed cytosine methylation was investigated at the MP2 and DFT levels [98JA12895]. This system has been modeled by 1-methylcytosine 117, methylthiolate, and trimethylsulfonium. The cytosine methylation is initiated by an attack of the anionic methylthiolate at Cg of the cytosine ring (Scheme 77). The formation of the methylthiolate adduct 118 of the neutral 117 was found to be endothermic in the gas phase and in solution. However, the MP2 and DFT results differ... 

Huttermann J, Ward JF, Myers LS Jr (1971) Electron spin resonance studies of free radicals in irradiated single crystals of 5-methylcytosine. Int J Radiat PhysChem 3 117-129 Huttermann J, Ohlmann J, Schaefer A, Gatzweiler W (1991) The polymorphism of a cytosine anion studied by electron paramagnetic resonance spectroscopy. Int J Radiat Biol 59 1297-1311 Hwang CT, Stumpf CL, Yu Y-Q, Kentamaa HI (1999) Intrinsic acidity and redox properties of the adenine radical cation. Int J Mass Spectrom 182/183 253-259 Ide H, Otsuki N, Nishimoto S, Kagiya T (1985) Photoreduction of thymine glycol sensitized by aromatic amines in aqueous solution. J Chem Soc Perkin Trans 2 1387-1392 Idris Ali KM, Scholes G (1980) Analysis of radiolysis products of aqueous uracil + N20 solutions. J Chem Soc Faraday Trans 176 449-456... 

These ideas have been illustrated in a recent study of the co-crystalline complex of l-MethylCytosine 5-FluoroUracil [34], Using model calculations it was shown how the hydrogen bonding network of the crystal is able to sustain a proton shuttle which leads to the selective formation of certain radicals. Calculations were able to predict that the site of reduction would be the cytosine base (yielding the N3 protonated cytosine anion C(N3+H) ), while the uracil base would be the site of oxidation (yielding the N1 deprotonated uracil cation U(N1-H) ). These are indeed the primary radiation induced species observed experimentally [34, 88], The results also nicely agree with the model proposed for radical trapping by Bernhard [11],... 

Singlet-singlet transition energies of the minor pyrimidine bases have been calculated in a few papers (tt-SCF MO Cl calculations isocytosine 104,156,188,189 jjg anioii and cation, 2-thiothymine, - 2-(S -methylcytosine and 4-jS-methylisocytosine and anions of thio-oytosine and isothiocytosine, 2-thio, 4-thio, 2,4-dithiouracil, thiocytosine, and isothiocytosine and several methyl derivatives of rare pyrimidines and their anions ). 

Figure 6. Base/base and base/PtNi, conformational drawings for the PFe and NOs salts of [Pt(en)(l,3,9-trimethylxanthine)2p and the anhydrate and trihydrate of cis-[Pt(NHs)i(l-methylcytosine)(N 1-deprotonated thymine anion)]. ...

---