In vitro prodrug activation by NTR was performed with an assay mixture containing final concentrations: 200 µM of 6, 1.5 mM NADH, 1.5 µM FMN and 250 nM NTR. Reactions were carried out in HEPES buffer (50 mM, pH 7.4) containing 2.5% DMSO as co-solvent at 37°C for 30 min at 300 rpm. At designated time aliquots from control and reaction samples were collected and the reaction was stopped by mixing 1:1 with cold acetonitrile (ACN).