Fig. 1

¹⁹F spectra for CF₃ketones (IIIa and IIIb) with NS2B:NS3pro. Superposition of ¹⁹F spectra between − 80.5 to − 81.5 (intensities scaled up 16 times) and − 82.3 to − 83.3 ppm obtained at 25 °C. Spectra were collected: shortly after sample preparation (black), following incubation at 25 °C for 12 days (red) and for two months (blue). The signals of the free isomers of the inhibitors at − 82.83 ppm and – 82.78 ppm are assigned to (IIIa) and (IIIb), correspondingly. Impurity signals are marked with *