| Popis: |
15N-NMR. spectra of mono- and diaminopyridines, and mono-, di- and triaminopyrimidines including trimethoprim and other dihydrofolate reductase inhibitors have been studied in neutral and acidic media. Complete chemical shift assignments are given. Ring-nitrogen shifts are discussed in terms of β-, χ- and δ-substituent effects of amino and alkyl groups. Protonation states in TFA- and FSO3H-solution and protonation increments for the 15N-shifts of ring and amino N-atoms are determined. A linear correlation is observed between amino substituent effects (Δδ(15N)) on the ring N-atom in aminopyridines and corresponding Δδ (13C) values in aminobenzenes and, similarly, between Δδ(15N) values in aminopyrimidines and Δδ(13C) values in aminopyridines. Assignment of the 15N-NMR. spectra of pyrimidine N-oxides, pyrazine N-oxides and pyridazine N-oxides is achieved by comparison with 14N-NMR. data and with the aid of Yb(fod)3-induced shifts. One-bond 15N, 1H-coupling constants are reported for aminopyridines and aminopyrimidines and discussed in terms of conjugative interaction between NH2-group and ring system. |
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