Acetonitrile (MeCN; Kanto Chemical, spectroscopic grade) and NH4Cl (Kanto Chemical, special grade) were used as received. Antimycin A from Streptomyces sp. (Ant A) and carbonyl cyanide 4-(trifluoromethoxy) phenylhydrozone (FCCP, 98%) were purchased from Sigma-Aldrich. Cell Counting Kit-8 (CCK-8) was purchased from Dojindo Laboratories.
1H-NMR spectra were recorded with a JEOL JNM-ECS400 (400 MHz) spectrometer in DMSO-d6. 1H-NMR chemical shifts were referenced to tetramethylsilane. The apparent resonance multiplicity was described as s (singlet), d (doublet), dd (double doublet), t (triplet), and m (multiplet). ESI–MS spectra were recorded on an Applied Biosystems API 2000 mass spectrometer.