Theoretical evaluation of new nucleic acid bases. II. Ab initio study on tautomerism of pyrazolo[4,3-d]pyrimidine-5,7 (4H,6H)-dione

✍ Scribed by Jerzy Leszczyński

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 470 KB
• Volume: 181
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(91)90343-8

✦ Synopsis

The four most important tautomers of the title compound were studied by the ab initio LCAO-MO method at the MP2/ 6-31G**//HF/3-21G level. All calculated structures are minima at the HF/3-2 1G potential energy surface with the dioxo tautomer 1 being the global minimum. 41~0 in a polar environment 1 is predicted to be a predominant form. The second most stable species, oxo-hydroxy tautomer 2 has a relative energy of 38.7 kJ mol-' (MP2/6-31G** t 0.9 ZPE). For the l-2 transition the calculated energy gap corresponds to an equilibrium constant of IO-' which is only one order larger than the estimated frequency threshold of spontaneous mutations and it strongly suggests that II is a new purine base with reduced probability of spontaneous mutations.