Guanines, tautomerism

Nir E, Janzen C, Imhof P, Kleinermanns K, de Vries MS (2001) Guanine tautomerism revealed by UV-UV and IR-UV hole burning spectroscopy. Journal of Chemical Physics 115 4604 1611. 

ISOLATED GUANINE TAUTOMERISM, SPECTROSCOPY AND EXCITED STATE DYNAMICS... 

Section 17.81). This is the form normally present in DNA, and, as we have seen, it pairs specifically with cytosine. If guanine tautomerizes (see Section 18.2) to the lactim form, it pairs with thymine instead. Write structural formulas showing the hydrogen bonds in this abnormal base pair. 

Guanine, 9-/3-D-ribofuranosyl-, 5, 536 Guanine, 6-thio-tautomerism, 5, 509 toxicity, 1, 141 Guanine, 8-trifluoromethyl-synthesis, 5, 574 Guanines, thio-synthesis, 5, 572 Guanosine arylation, 5, 538 dipole moment, 5, 522 free radical alkylation, 5, 543 hydrobromide... 

FIGURE 11.4 The common purine bases—adenine and guanine—in die tautomeric forms predominant at pH 7. 

Langer H, Doltsinis NL (2003) Excited state tautomerism of the DNA base guanine a restricted open-shell kohn-sham study. J Chem Phys 118 5400-5407... 

Mennucci B, Toniolo A, Tomasi J (2001) Theoretical study of guanine from gas phase to aqueous solution role of tautomerism and its implications in absorption and emission spectra. J Phys Chem A 105 7126... 

Sobolewski AL, Domcke W, Hattig C (2005) Tautomeric selectivity of the excited-state lifetime of guanine/cytosine base pairs The role of electron-driven proton-transfer processes. Proc Natl Acad Sci USA 102 17903-17906... 

C. Colominas, F. J. Luque, and M. Orozco, Tautomerism and protonation of guanine and cytosine. Implications in the formation of hydrogen-bonded complexes, J. Am. Chem. Soc. 118 6811 (1996). 

The tautomerisation of the purine bases adenine and guanine and of the pyrimidine bases thymine, cytosine, and uracil has important implications in molecular biology, and the occurrence of rare tautomeric forms of these bases has been suggested as a possible cause of spontaneous mutagenesis (Lowdin, 1965 Pullman and Pullman, 1971 Kwiatowski and Pullman, 1975). Three of the most likely tautomers for cytosine are shown in [87]—[89], together with the less likely imino forms [90] and [91] (Scanlan and Hillier,... 

The amino groups are replaced with oxygen. Although here a biochemical reaction, the same can be achieved under acid-catalysed hydrolytic conditions, and resembles the nucleophilic substitution on pyrimidines (see Section 11.6.1). The first-formed hydroxy derivative would then tautomerize to the carbonyl structure. In the case of guanine, the product is xanthine, whereas adenine leads to hypoxanthine. The latter compound is also converted into xanthine by an oxidizing enzyme, xanthine oxidase. This enzyme also oxidizes xanthine at C-8, giving uric acid. 

The bases are monocyclic pyrimidines (see Box 11.5) or bicyclic purines (see Section 11.9.1), and all are aromatic. The two purine bases are adenine (A) and guanine (G), and the three pyrimidines are cytosine (C), thymine (T) and uracil (U). Uracil is found only in RNA, and thymine is found only in DNA. The other three bases are common to both DNA and RNA. The heterocyclic bases are capable of existing in more than one tautomeric form (see Sections 11.6.2 and 11.9.1). The forms shown here are found to predominate in nucleic acids. Thus, the oxygen substituents are in keto form, and the nitrogen substituents exist as amino groups. 

Lee GYC, Chan SI. Tautomerism of nucleic acid bases. 11. Guanine. J Am Chem Soc 1972 94 3218-3229. 

Tautomeric structures of adenine, guanine, cytosine, thymine and uracil are—... 

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