Guanine methylated derivatives

PES has been applied to study biologically active molecules with amino groups and their constituents like nucleic bases and related compounds (e.g. adenine, guanine, thymine, cytosine, hypoxanthine and their methyl derivatives)113-120 and amino acids92,121,122 or their methyl esters123. 

The bases that occur in nucleic acids are aromatic heterocyclic compounds derived from either pyrimidine or purine. Five of these bases are the main components of nucleic acids in all living creatures. The purine bases adenine (abbreviation Ade, not A ) and guanine (Gua) and the pyrimidine base cytosine (Cyt) are present in both RNA and DNA. In contrast, uracil (Ura) is only found in RNA. In DNA, uracil is replaced by thymine (Thy), the 5-methyl derivative of uracil. 5-methylcyto-sine also occurs in small amounts in the DNA of the higher animals. A large number of other modified bases occur in tRNA (see p. 82) and in other types of RNA. 

The tRNA molecules have single chains with between 73-93 ribonucleotides. Most of the tRNA bases are adenine (A), cytosine (C), guanine (G), and uracil (U). There also are a number of unusual bases that are methylated derivatives of A, C, G, and U. 

Jurecka, R Hobza, P. True stabilization energies for the optimal planar hydrogen-bonded and stacked stmctures of guanine "cytosine, adenine-"thymine, and their 9- and 1-methyl derivatives complete basis set calculations at the MP2 and CCSD(T) levels and comparison with experiment, J. Am. Chem. Soc. 2003, 125, 15608-15613. 

The naturally occurring purines fall into 4 main groups. (1) Simple substituted derivatives of purine (1) such as adenine (2) and various 6-AT-substituted derivatives. (2) Monoxo-dihydropurines such as hypoxanthine (3), guanine (4), and isoguanine (5). f3) Dioxotetra-hydropurines such as xanthine (6) and methylated derivatives including the 3,7-dimethyl derivative theobromine (7), 1,3-dimethylxanthine or theophylline f8), and 1,3,7-trimethylxanthine or caffeine (9). (4) Trioxohexahydropurines such as uric acid (10). 

Methylation of guanine nucleosides or nucleotides with diazomethane or methyl sulfate yields 7-methylated derivatives (241, R = ribosyl). These zwitterionic derivatives are unstable in acid, neutral, and alkaline media. In alkali, (241) undergoes cleavage at the 8-9 bond, to give... 

As can be seen from Table XVIA,B the theory also predicts that the two tautomers should be characterized by very different dipole moments, that of the N(9)H tautomer being double that of the N(7)H one. Unfortunately, because of difficulties in solubilizing these substances (even when N-methylated) in nonpolar solvents, no experimental data are available. On the other hand, one notes an apparent disagreement between theory and experiment concerning the relative position of A ax in fh fwo tautomers. It must, however, be remembered that the experimental data concern N-methylated derivatives in solution. A more recent determination of A ,ax in guanine in the vapor phase places its A ,ax 293 in good... 

The NMR results show that, in the case of 3 and 5 nucleotides, the binding of metal, or at least copper, does occur at Nj for adenine and guanine and at Ni for cytosine very little binding of copper occurs in thymine, the methyl derivative of uracil. NMR studies have also shown us that in the polymeric nucleic acids binding occurs generally in the same position as in these monomers. For example, in polyadenylic acid, the binding is also at Nj, and in polycytidylic acid it is at Ni. 

M. Mons, 1. Dimicoli, F. Piuzzi, B. Tardivel, andM. Elhanine, Tautomerism of the DNA base guanine and its methylated derivatives as studied by gas-phase infrared and ultraviolet spectroscopy, J. Phys. Chem. A 106 (2002), pp. 5088-5094. 

For many years the urine has been known to contain a number of purine bases in addition to uric acid adenine, guanine, hypoxanthine, xanthine, and several methylated derivatives of the purine bases (N,2-meth-ylguanine, 1-methylguanine, 7-methylguanine, 7-methyl-8-hydroxyguanine, and 1 -methylhypoxan-... 

Robins, M. J and Robins, R K. (1969) Purine nucleosides. XXIV A new method for the synthesis of guanine nucleosides The preparation of 2 -deoxy-a- and -guanosines and the corresponding A -methyl derivatives. J Org Chem 34,2160-2163. 

Identification of the component pentose sugar confirms whether the polynucleotide chain is RNA or DNA. Both RNA and DNA contain the same two purine bases, adenine (A) and guanine (G) whereas they differ in their content of the pyrimidine bases. RNA contains cytosine (C) and uracil (U) but DNA contains cytosine and the 5-methyl derivative of uracil called thymine (T). In addition to these bases, called major bases, DNA and RNA also contain altered or less common bases called minor bases. In DNA, the minor bases are usually methylated derivatives of the major bases which play a special role in the functioning of the polynucleotide. RNAs, especially transfer RNAs, also contain minor bases, e.g. inosine, pseudouridine (in which uracil is linked through C-5, not N-1, to ribose), dihydrouridine, ribosylthymine and methylated derivatives of nucleosides (Figure 7.2). Minor bases are mainly modified versions of major bases. 

Alkylation of nucleic acid components and nucleic acids has been of considerable interest in recent years. SERS spectroscopy on Ag electrode is a useful technique for the identification of methyl derivatives of nucleic acids. The methylation of guanine leads to a specific change in the SERS spectrum. 

Table 1. Raman Band Frequencies (cm ) and Tentative Vibrational Mode Assignment of Guanine and Its Methylated Derivatives Adsorbed On A Silver Electrode Surface (Es = -0.6 V). 

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