STRUCTURE AND TAUTOMERIC PROPERTIES OF THYMINE DERIVATIVES GENERATED BY HYDROXYL RADICAL IN AEROBIC CONDITIONS

The tautomeric properties of five hydroxyl radical-induced thymine der ivatives: thymine glycol (1), 5-formyldeoxyuracil (2), 5-hydroxymethyl uracil (3), N-tatronyluridine (4) and 5-hydroxymethylhydantoine (5) we re characterised by ab initio HF (6-311G*), MP2 (6-311G**) and SCI-PC M (6-311G*) quantum chemistry calculations. Amongst all the tautomers of 1 the I-5eq6ax tautomer (the diketo form with C-5 equatorial and C -6 axial orientations of the hydroxy groups) is the most stable, in bo th polar and non-polar environments. The most stable tautomer of 2 is the diketo form with the carbonyl group oriented in such a way that th e maximum distance between O-4 and O-C'5 oxygen atoms is preserved. By analogy, the preferred tautomeric form of 3 corresponds to the diketo isomer. Among the potential 43 isomers of 4 the most stable is that i n the diketo-amino form with anti-conformation of the C-2-N-3-C-4-C-5 torsion angle and equatorial conformation of the C-5 chirality centre. Finally, the most probable structure of 5 is the diketo tautomeric fo rm.