Selective N-15-Labeling and Analysis of C-13-N-15 J Couplings as an Effective Tool for Studying the Structure and Azide-Tetrazole Equilibrium in a Series of Tetrazolo[1,5-b][1,2,4]triazines and Tetrazolo[1,5-a]pyrimidines

[摘要]：Two general methods for the selective incorporation of an N-15-label in the azole ring of tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines were developed. The first approach included treatment of azinylhydrazides with N-15-labeled nitrous acid, and the second approach was based on fusion of the azine ring to [2-N-15]-5-aminotetrazole. The synthesized compounds were studied by H-1, C-13, and N-15 NMR spectroscopy in both DMSO and TFA solution, in which the azide-tetrazole equilibrium is shifted to tetrazole and azide forms, respectively. Incorporation of the N-15-label led to the appearance of C-13-N-15 J coupling constants (J(CN)), which can be measured easily using either 1D C-13 spectra with selective N-15 decoupling or with amplitude modulated 1D C-13 spin-echo experiments with selective inversion of the N-15 nuclei. The observed J(CN) patterns permit unambiguous determination of the type of fusion between the azole and azine rings in tetrazolo[1,5-b][1,2,4]triazine derivatives. Joint analysis of J(CN) patterns and N-15 chemical shifts was found to be the most efficient way to study the azido-tetrazole equilibrium.

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