Informing Efforts to Develop Nitroreductase for Amine Production

Abstract

Nitroreductases (NRs) hold promise for converting nitroaromatics to aromatic amines. Nitroaromatic reduction rate increases with Hammett substituent constant for NRs from two different subgroups, confirming substrate identity as a key determinant of reactivity. Amine yields were low, but compounds yielding amines tend to have a large π system and electron withdrawing substituents. Therefore, we also assessed the prospects of varying the enzyme. Several different subgroups of NRs include members able to produce aromatic amines. Comparison of four NR subgroups shows that they provide contrasting substrate binding cavities with distinct constraints on substrate position relative to the flavin. The unique architecture of the NR dimer produces an enormous contact area which we propose provides the stabilization needed to offset the costs of insertion of the active sites between the monomers. Thus, we propose that the functional diversity included in the NR superfamily stems from the chemical versatility of the flavin cofactor in conjunction with a structure that permits tremendous active site variability. These complementary properties make NRs exceptionally promising enzymes for development for biocatalysis in prodrug activation and conversion of nitroaromatics to valuable aromatic amines. We provide a framework for identifying NRs and substrates with the greatest potential to advance.

Cofactor F420-Dependent Enzymes: An Under-Explored Resource for Asymmetric Redox Biocatalysis

“…Nitroreductases have the potential application in the reduction of a prochiral nitro group to form a chiral amine [46]. The LLHT family F 420 -dependent nitroreductase Npd from Rhodococcus catalyzes the two-electron reduction of two nitro groups in picric acid during catabolism of the explosive TNT (Table 1; Figure 4) [47].…”

Cofactor F₄₂₀-Dependent Enzymes: An Under-Explored Resource for Asymmetric Redox Biocatalysis

“…Nitroreductases have potential application in the reduction of a prochiral nitro group to form a chiral amine [49]. The LLHT family F420-dependent nitroreductase Npd from Rhodococcus catalyzes the two-electron reduction of two nitro groups in picric acid during catabolism of the explosive TNT (Table 1; Fig.…”

Synthesis and Biological Evaluation of Lipophilic Nucleoside Analogues as Inhibitors of Aminoacyl-tRNA Synthetases

“…We here opted for the 4-nitrobenzyloxycarbonyl which on reduction by NTR produces the p-hydroxylamino-benzyl carbamate. The latter is prone to hydrolytic cleavage (Scheme 1) as the transformation converts an electron-withdrawing nitro group into an electron donating group [25,26]. Likewise, esterases upon hydrolysis of 18 will provide the hydrolytically cleavable p-hydroxybenzylcarbamate leading to the active compound [27] (Scheme 1).…”

“…The second approach deals with the attachment of a promoiety at the α-amine of aaSA ( Figure 1, structure b). Two carbamate promoieties which have been shown to be cleaved intracellularly following uptake, are the 4-nitrobenzyloxycarbonyl [25,26] and 4-acetoxybenzyloxycarbonyl carbamate [27,28]. The functional group at the para-position (either nitro or acetoxy here) on activation by nitroreductase or esterase respectively, should lead to cleavage of the prodrug and release of the active aaSA.…”