Synthesis and azido-tetrazole tautomerism of 3-azido-1,2,4-triazines

14N to 15N Isotopic Exchange of Nitrogen Heteroaromatics through Skeletal Editing

The selective modification of nitrogen heteroaromatics enables the development of new chemical tools and accelerates drug discovery. While methods that focus on expanding or contracting the skeletal structures of heteroaromatics are emerging, methods for the direct exchange of single core atoms remain limited. Here, we present a method for 14N → 15N isotopic exchange for several aromatic nitrogen heterocycles. This nitrogen isotope transmutation occurs through activation of the heteroaromatic substrate by triflylation of a nitrogen atom, followed by a ring-opening/ring-closure sequence mediated by 15N-aspartate to effect the isotopic exchange of the nitrogen atom. Key to the success of this transformation is the formation of an isolable 15N-succinyl intermediate, which undergoes elimination to give the isotopically labeled heterocycle. These transformations occur under mild conditions in high chemical and isotopic yields.

Preparation of Novel Pyrazolo[4,3-e]tetrazolo[1,5-b][1,2,4]triazine Sulfonamides and Their Experimental and Computational Biological Studies

Pyrazolo[4,3-e]tetrazolo[1,5-b][1,2,4]triazine sulfonamides constitute a novel class of heterocyclic compounds with broad biological activity, including anticancer properties. Investigated in this study, MM-compounds (MM134, MM136, MM137, and MM139) exhibited cytotoxic and proapoptotic activity against cancer cell lines (BxPC-3, PC-3, and HCT-116) in nanomolar concentrations without causing cytotoxicity in normal cells (L929 and WI38). In silico predictions indicate that tested compounds exhibit favorable pharmacokinetic profiles and may exert anticancer activity through the inhibition of BTK kinase, the AKT-mTOR pathway and PD1-PD-L1 interaction. Our findings point out that these sulfonamide derivatives may constitute a source of new anticancer drugs after optimization.

15N Chemical Shifts and JNN-Couplings as Diagnostic Tools for Determination of the Azide-Tetrazole Equilibrium in Tetrazoloazines

Selectively ¹⁵N-labeled tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines bearing one, two, or three ¹⁵N labels were synthesized. The synthesized compounds were studied by ¹H, ¹³C, and ¹⁵N NMR spectroscopy in DMSO and TFA solutions, where the azide-tetrazole equilibrium can lead to the formation of two tetrazole (T, T') isomers and one azide (A) isomer for each compound. Incorporation of the ¹⁵N-label(s) leads to the appearance of ¹⁵N-¹⁵N coupling constants (J_NN), which can be easily measured via simple 1D ¹⁵N NMR spectra, even at natural abundance between labeled and unlabeled ¹⁵N atoms. The chemical shifts for the ¹⁵N nuclei in the azole moiety are very sensitive to the ring opening and azide formation, thus providing information about the azido-tetrazole equilibrium. At the same time, the ^1-2J_NN couplings between ¹⁵N-labeled atoms in the azole and azine fragments unambiguously determine the fusion type between tetrazole and azine rings in the cyclic isomers T and T'. Thus, combined analysis of ¹⁵N chemical shifts and J_NN values in selectively isotope-enriched compounds provides an effective diagnostic tool for direct structural determination of tetrazole isomers and azide form in solution. This method was found to be the most simple and efficient way to study the azido-tetrazole equilibrium.

Nucleophile-Induced Rearrangement of 2H-Azirine-2-carbonyl Azides to 2-(1H-Tetrazol-1-yl)acetic Acid Derivatives

2H-Azirine-2-carbonyl azides undergo a rearrangement into derivatives of 2-(1H-tetrazol-1-yl)acetic acid when interacting with O- and S-nucleophiles at room temperature. The reaction is catalyzed by tertiary amines or hydrazoic acid. The reaction with primary alcohols and phenols gives alkyl/aryl 2-(1H-tetrazol-1-yl)acetates. Thiophenols react with 2H-azirine-2-carbonyl azides to afford S-aryl 2-(1H-tetrazol-1-yl)ethanethioates. The mechanism of the nucleophile-induced rearrangement of 2H-azirine-2-carbonyl azides is discussed on the basis of DFT calculations as well as kinetic and ¹⁵N labeling experiments.

15N labeling and analysis of 13C–15N and 1H–15N couplings in studies of the structures and chemical transformations of nitrogen heterocycles

This review provides a generalization of effective examples of ¹⁵N labeling followed by an analysis of J_CN and J_HN couplings in solution as a tool to study the structural aspects and pathways of chemical transformations in nitrogen heterocycles.