The studies of tautomerism in 6-mercaptopurine derivatives by 1H-13C, 1H-15N NMR and 13C, 15N CP/MAS-experimental and quantum chemical approach

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Authors

PAZDERSKI Leszek LAKOMSKA Iwona WOJTCZAK Andrzej SZLYK Edward SITKOWSKI Jerzy KOZERSKI Lech KAMIEŃSKI Bohdan KOŹMIŃSKI Wiktor TOUŠEK Jaromír MAREK Radek

Year of publication 2006
Type Article in Periodical
Magazine / Source Journal of Molecular Structure
MU Faculty or unit

Faculty of Science

Citation
Web http://www.sciencedirect.com/science?_ob=JournalURL&_cdi=5262&_auth=y&_acct=C000045159&_version=1&_urlVersion=0&_userid=835458&md5=94c7f6972ea3add66a0adb8beebaee23
Field Physical chemistry and theoretical chemistry
Keywords 6-mercaptopurine; tautomerism; 15N NMR; 15N CPMAS; HECADE
Description Tautomerism in 6-mercaptopurine (6mpH), 2,6-dimercaptopurine (2,6dmp) and 6-mercaptopurine-9-riboside (6mp-9rb) was studied in the solution with 2D NMR methods-1H-13C HMBC and 1H-15N HMQC. The 15N NMR signals were assigned and the distribution of mobile protons proposed on the basis of 13C, 15N chemical shifts and JHC, JHN coupling constants, determined with HECADE. These heterocycles appear in DMSO-d6 as the thionic species with predominance of the following tautomers: N(1)H, N(7)H for 6mpH; N(1)H, N(3)H, N(7)H for 2,6dmp; N(1)H for 6mp-9rb. Quantum-chemical NMR calculations by GIAO method(RHF/6-31G**//B3LYP/6-31G**) allowed to evaluate the ratios of N(7)H, N(9): N(7), N(9)H tautomeric forms as ca. 3:1 for 6mpH and nearly 10:0 for 2,6dmp. The 13C and 15N CPMAS spectra were measured for solid 6mpHH2O, anhydrous 6mpH, 2,6dmp and 6-mercaptopurinium chloride (6mpH2Cl), confirming the thionic character of all compounds. The 15N chemical shifts in the solid phase were calculated (B3LYP/631G**) for 6mpHH2O and 6mpH2Cl, basing on the re-determined single crystal X-ray data (optimised with RHF/3-21G**).
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