The synthesis of analog of Triazavirin (Riamilovir) enriched with isotopic 13C and 15N labels, viz. monohydrate of l-arginine salt of 5-methyl-6-nitro-7-oxo-4,7-dihydro[1,2,4]triazolo[1,5-a]pyrimidine was developed. To incorporate 13C and 15N stable isotopes into its structure, [5-13C]-3-amino-1,2,4-triazole (13C, 99%), ethyl [1,2,3,4-13C4]-acetoacetate (13C, 99%), and potassium 15N-nitrate (15N, 99%) were used. The presence of 13C and 15N atoms allowed us to estimate spin—spin coupling constants for the 13C-13C and 13C-15N interactions in the NMR spectra of labeled [1,2,4]triazolo[1,5-a]pyrimidine derivatives. © Springer Science+Business Media LLC 2024.