Derivatives of 1,2,4-triazole and related heterocycles continue to attract significant attention due to their diverse biological activities and potential pharmaceutical applications.

The aim of this work is to resynthesize and perform mass spectrometric characterization of a series of 16 organic compounds – derivatives of 1,2,4-triazole and 1,3,4-oxadiazole – containing a 5-mercapto-1,2,4-triazole fragment and various substituents at the N2 atom. The objective is to investigate their fragmentation patterns and establish analytical markers for these bioactive heterocycles.

Materials and methods. The target compounds were resynthesized according to established procedures, with reagents purchased from Sigma-Aldrich. The preparation involved refluxing 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carbohydrazide with appropriate isothiocyanates or carbon disulfide, followed by purification. S-alkyl derivatives were prepared via nucleophilic substitution of haloalkanes under basic conditions. Mass spectra were recorded using liquid chromatography coupled with electrospray ionization mass spectrometry (LC-ESI-MS) in both positive and negative ion modes. Chromatographic separation was performed on a Zorbax SB-C18 column under gradient elution.

Results. Protonated molecular ions [M+H]+ were observed for all compounds, with characteristic isotopic peaks confirming the presence of sulfur. Fragmentation primarily involved cleavage at sulfur and N2 substituents, yielding prominent ions corresponding to loss of alkyl radicals as alkenes. N-phenyl derivatives showed additional fragmentation pathways, including cleavage of the phenyl group and deeper degradation of the triazole ring. A consistent fragment corresponding to the protonated 1,2,4-triazole core was identified across most spectra, serving as a useful structural marker. Substitution pattern and alkyl chain length significantly influenced fragmentation intensity and pathways.

Conclusions. LC-ESI-MS analysis revealed reproducible fragmentation trends for these heterocyclic derivatives, providing valuable insights for their structural identification and analytical profiling. These findings facilitate the development and quality control of new bioactive 1,2,4-triazole-based compounds. Further research is recommended to expand chemical diversity and conduct biological evaluations, including antimicrobial and antidiabetic activity assessments.