1H, 13C and 15N NMR observations on the protonation of 1- and 3-deazapurine |
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| Authors: | J C Lindon J M Williams P Barraclough |
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| Institution: | 1. Department of Physical Chemistry, Wellcome Research Laboratories, Langley Court, Beckenham, Kent BR3 3BS, UK;2. Department of Medicinal Chemistry, Wellcome Research Laboratories. Langley Court, Beckenham, Kent BR3 3BS, UK |
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| Abstract: | Using 1H, 13C and 15N NMR it has been concluded that 3-deazarpurine protonates exclusively at N-1 with a pK of about 5.6. The base exhibits rapid tautomerism with proportions of 70:30, with the N–7-H tautomer in the majority. The salt exists predominantly as the N-7-H tautomer. 1-Deazapurine protonates essentially in a 1:1 ratio at N-3 and at the imidazole ring, with a pK of about 3.1. This base also exhibits rapid tautomerism with proportions of 30:70, this time with the N-9-H in the majority. The salt also exists in a tautomcric mixture with approximately equal proportions. One form has N-3 and N-9 bearing hydrogens and the other has N-7 and N-9 bearing hydrogens. |
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