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509500 
Journal Article 
NMR studies of tautomerism and protonation patterns in bis(6-purinyl) disulfide and ionic forms of 6-mercaptopurine 
Pazderski, L; Tousek, J; Sitkowski, J; Kozerski, L; Szlyk, E 
2007 
81 
2 
193-210 
English 
H-1-C-13 and H-1-N-15 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 (6mpH(2)(+)) and purine-6-thiolate anions (6mp(-), 6mp-deH(2-)).H-1, C-13, N-15 resonances were assigned and the respective delta(1H), 8130, delta(15N) chemical shifts as well as J(HC), J(HN) 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" 6mpH(.)H(3)O(+) species, intermediate between 6mpH and 6mpH(2)(+), and readily oxidized to (6puS)(2) was suggested in the DMSO-d(6) + HCl solution. Further hydrolysis and oxidation of the formed disulfide lead to the derivatives of purine-6-sulfenic and purine-6-sulfinic acid. 
6-mercaptopurine; tautomerism; N-15 NMR; HMBC; quantum-chemical NMR; calculations; nuclear-magnetic-resonance; pyrolytic-graphite electrode; polarizable; continuum model; copper(i) chloride complex; s-methyl derivatives; metal-complexes; 2,2'-bipyridine-5-sulfonic acid; electrochemical; oxidation; nitrogen-heterocycles; drug 6-mercaptopurine