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NMR Quantification of Tautomeric Populations in Biogenic Purine Bases
Author(s) -
Bartl Tomáš,
Zacharová Zuzana,
Sečkářová Pavlína,
Kolehmainen Erkki,
Marek Radek
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200801016
Subject(s) - tautomer , chemistry , hypoxanthine , nuclear magnetic resonance spectroscopy , proton nmr , hydrogen bond , computational chemistry , carbon 13 nmr , stereochemistry , molecule , organic chemistry , enzyme
Purine bases such as purine, adenine, hypoxanthine, and mercaptopurine are known to exist in several tautomeric forms. Characterization of their tautomeric equilibria is important not only for predicting the regioselectivity of their N ‐alkylation reactions, but also for gaining knowledge of the patterns with which these compounds of significant biological activity form hydrogen bonds with their biological targets. The tautomeric equilibria of purine and some purine derivatives in methanol and N , N ‐dimethylformamide solutions were investigated by low‐temperature 1 H and 13 C NMR spectroscopy. The N(7)H and N(9)H tautomeric forms were quantified by integrating the individual 1 H NMR signals at low temperatures. The Gibbs free energy differences were calculated and the effects of substitution on the N(7)H/N(9)H ratio discussed. A previously published theoretically predicted mechanism of the tautomeric exchange is compared with our measurements in deuteriated solvents. The influence of concentration on the temperature of coalescence indicates that supramolecular clusters play a significant role in this proton transfer process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)