5-methyluracil. thymine

CI. l-(2-Deoxy-p-D-ribofuranosyl)-5-methyluracil. Thymine 2-desoxyriboside. Thymosine. NSC 21548 [50-89-5]... 

MO methods have calculated that the bond order of the C(5)-C(6) bond in the first triplet of a series of pyrimidines is lower than in the first excited singlets of the corresponding molecules, and have concluded that dimerization of the bases occurs via the triplet state. They divided the pyrimidines into three groups the pyrimidines which are known to be easily dimerizable (uracil, 6-methyluracil, thymine, orotic acid—for these molecules the Pse values in their T state are of the order of 0.09-0.12), those which dimerize not so easily (5-aminouracil, cytosine, 5-methylcytosine—Pge 0.13-0.17), and the bases which do not dimerize at all or only with considerable difficulty (2-thiothymine, Pgg = 0.31 isocytosine, Pgg = 0.39 and 5-nitrouracil). The relative distribution of the bases within groups leads sometimes to only limited agreement with available experimental data. For instance, as the Pgg = 0.085 in T of uracil is lower than Pgg = 0.106 in T of thymine, uracil should dimerize more easily than thymine, a conclusion in disagreement with experiment. ... 

The common naturally occurring pyrimidines are cytosine, uracil, and thymine (5-methyluracil) (Figure 11.3). Cytosine and thymine are the pyrimidines typically found in DNA, whereas cytosine and uracil are common in RNA. To view this generality another way, the uracil component of DNA occurs as the 5-methyl variety, thymine. Various pyrimidine derivatives, such as dihydrouracil, are present as minor constituents in certain RNA molecules. 

Thymine (5-methyluracil) and related 5-substituted uracils do not yield isolable dihydropyrimidines under similar irradiation conditions [507,515,520]. Uptake of a water molecule was at first discounted [521]. Subsequent study... 

Several of the oxo forms of the pyrimidines are particularly important in biological systems, and are normally referred to by their nonsystematic names such as cytosine [4-aminopyrimidin-2(l//)-one] 5, uracil [2,4(1//,3//)-pyrimidinedione] 6, and thymine (5-methyluracil) 7. Their nucleoside derivatives are also normally referred to by their nonsytematic names such as cytidine (l-/3-D-ribofuranosylcytosine) 8 and thymidine [l-(2-deoxy-/3-D-ribofur-anosyl)-5-methyluracil] 9. 

Cytosine and thymine were first isolated by hydrolysis of calf thymus tissue by Albrecht Kossel (1853-1927) and A. Neumann during 1893-1894. Thymine s structure was published in 1900 and confirmed over the next several years when it was synthesized by several investigators. In 1903, cytosine was synthesized by Henry Lord Wheeler (1867-1914) and Treat B. Johnson, confirming its structure. Uracil was first isolated in 1900 from yeast nucleic acid found in bovine thymus and herring sperm. The methylation of uracil produces thymine thymine is also called 5-methyluracil because methylation takes place at the fifth carbon in uracil to produce thymine. 

Cytosine (2-hydroxy-6-amino-pyrimidine), uracil (2,6-dihydroxypyrimidine), and thymine (5-methyluracil) are pyrimidine derivatives adenine (6-aminopurine), guanine (2-amino-6-hy-droxypurine), and xanthine (2,6-dihydroxypurine) are purine derivatives (Fig. 5). 

Since DNA contains thymine (5-methyluracil) as a major base instead of uracil, the synthesis of thymidine monophosphate (dTMP, or thymidylate) is essential to provide dTTP (thymidine triphosphate), which is needed for DNA replication together with dATP, dGTP, and dCTP. 

Identification of the nitrogenous bases (aglycons) of pyrimidine nucleosides began at the turn of the century, when Kossel and Neumann18 isolated thymine (5-methyluracil) from nucleic acid and showed this pyrimidine to be identical with the nucleosin previously described by Miescher.19 The isolation of cytosine20 [4-amino-2()//)-pyrimidinone] and uracil21 [2,4(1, 3 )-pyrimidinedione] from the nucleic acids came shortly there-... 

We have studied the direct allylation of uracil 190, thymine 191, and 6-methyluracil 192 (Scheme 43) under Pd(0) catalysis and forcing conditions (93T1457). The results are summarized in Table V. Uracil and thymine... 

Thymine Uracil 5-Bromouracil 5-Aminouracil (Adenine) (Hypoxanthine) (6-Methyluracil ) (Purine ) Thymine Uracil 5-Bromouracil 5-Aminouracil 5-Bromouracil Adenine Guanine Hypoxanthine 6-Methyluracil Uracil Adenine Hypoxanthine Purine (Adenine)... 

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]. 

Thymine can also be described as 5-methyluracil. Other methylated pyrimidines are found in some nucleic acids. 

Thymine is 5-methyluracil. The fluorine atom is much smaller in size than the methyl group, but the bromine atom is similar in size to it. 5-Bromouracil can be readily incorporated into DNA through the action of the enzyme DNA polymerase (Chap. 16), while 5-fluorouracil cannot. 

Much of the early UV resonance Raman spectroscopy and determination of the excited-state structure of uracil was also performed by Peticolas [96, 113, 114, 117, 118], using a similar approach to that described above for thymine. In addition to uracil, the calculated and experimental UV resonance Raman spectra of 1-methyluracil and... 

The experimental apparatus, as shown in Figure 11-1, was a standard molecular beam machine with a heated pulsed valve for vaporization of the non-volatile species and for supersonic cooling. Samples of 1-methyluracil, 1,3-dimethyluracil and thymine were purchased from Aldrich Co. and used without further purification. The sample 1,3-dimethylthymine was synthesized from thymine following a literature procedure [33], and its purity was checked by nuclear magnetic resonance (NMR) and infrared absorption (IR) spectroscopy. The heating temperatures varied for different samples 130°C for DMU, 150°C for MU, 180°C for DMT, and 220°C for thymine. No indication of thermal decomposition was observed at these... 

Fig. 15.1. The four bases found in the nucleic acids. Uracil occurs in RNA and is substituted by the analogous thymine (5-methyluracil) in DNA. Uracil is the keto tautomer of 2,4-dihydroxy pyrimidine with two donors N(1)H, N(3)H and two acceptors 0(2), 0(4). Cytosine is the keto tautomer of 4-amino, 2-hydroxy pyrimidine with three donors N(4)H2, N(1)H and two acceptors 0(2), N(3). Adenine is 6-aminopurine with three donors N(6)H2, N(9)H and three acceptors N(l), N(3), N(7). Guanine is the keto tautomer of 2-amino, 6-hydroxy purine with three donors N(2)H2, N(9)H and three acceptors, N(3), N(7), 0(6). In the nucleosides, pyrimidine N(l) and purine N(9) are substituted by ribose or deoxyribose (see Fig. 17.1)...

The centrosymmetrical UU12 configuration (Fig. 16.2) occurs frequently as in thymine [THYMIN] thymine monohydrate [THYMMH] Dihydrouracil [DHU-RAC10] dihydrothymidine [DHTHYD10] 6-methyluracil-5-acetic acid [MUR-CAC] 5,6-dihydro-2-thiouracil [DHTURC] 6-methyl-5,6-dihydrouracil [MDH-URC10] 2,4-dithiouracil [DTURAC]. 

Several MO methods have been applied to calculate the 7T-electronic bond orders (or total bond overlap populations) of uracil, thymine, and some of their derivatives. They can be found in the following papers tt-HMO calculations on uracils and thymines, see reviews ° ° 7T-SC HMO (w-technique) calculations on forms 32 and 28 of uracil and thymine, 1-methyluracil and 1-methylthymine tt-SCF MO calculations on uracil forms 27,29-31,i ... 

---