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1 Polish Journal of Chemistry

1 2007

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NMR Studies of Tautomerism and Protonation Patterns in Bis(6-purinyl) Disulfide and Ionic Forms of 6-Mercaptopurine

Pazderski L., Toušek J., Sitkowski J., Kozerski L., Szłyk E

Polish Journal of Chemistry

2007

Vol. 81, nr 2

193-210

1H-13C and 1H-15N HMBC-NMR spectroscopy was applied to study tautomerism and the protonation patterns in 6-mercaptopurine (6mpH) derivatives: bis(6-purinyl) disulfide ((6puS)2), 6-mercaptopurinium cation (6mpH2 + ) and purine-6-thiolate anions (6mp–, 6mp-deH2–). 1H, 13C, 15N resonances were assigned and the respective delta 1H, delta 13C, delta 15N chemical shifts as well as JHC, JHN coupling constants determined. Quantum-chemical NMR calculations by GIAO method (B3LYP/6-31G**//RHF/6-31G*) allowed to evaluate the ratio of N(1), N(3), N(7), N(9)H : N(1), N(3), N(7)H, N(9) tautomeric forms for the DMSO-solvated (6puS)2 molecules as ca. 9:1. The existence of “semi-protonated” 6mpHźH3O+ species, intermediate between 6mpH and 6mpH2 + , and readily oxidized to (6puS)2 was suggested in the DMSO-d6 + HCl solution. Further hydrolysis and oxidation of the formed disulfide lead to the derivatives of purine-6-sulfenic and purine-6-sulfinic acid.