[3-(Trifluoromethyl)-1H-1,2,4-triazol-5-yl]methylamine derivatives: synthesis, ways of modification and use for peptides labeling

The synthesis of new 3-(trifluoromethyl)-1H-1,2,4-triazoles is reported, starting from ethyl trifluoroacetimidate and Boc-protected amino acid hydrazides. The influence of elongation or branching of a linker between the hydrazide and amino group on cyclization of amidrazones is established. The scale-up of the synthesis of tert-butyl ((3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)methyl)carbamate (4a) starting with 1 mole of corresponding hydrazide and trifluoroacetonitrile was successfully demonstrated. Additionally, 4a and other derivatives were further elaborated, underlining their prospects as building-blocks for organic synthesis. In particular, 2-(trifluoromethyl)-5,6,7,8-tetrahydro-[1,2,4]triazolo[1,5-a]pyrazine (23) - a component in the synthesis of Fuzuloparib - was successfully obtained in good yields (56.4%). Finally, we showed that 2-(5-(aminomethyl)-3-(trifluoromethyl)-1H-1,2,4-triazol-1-yl)acetic acid hydrochloride (19) can be incorporated into short peptides using solid phase peptide synthesis, serving as a fluorinated Gly-Gly analogue for peptide ¹⁹F NMR studies.