Informing Efforts to Develop Nitroreductase for Amine Production.

Anne-Frances Miller,Jonathan Park,Kyle Ferguson,Warintra Pitsawong,Andreas Bommarius

doi:10.3390/molecules23020211

Anne-Frances Miller, Jonathan Park + Show 3 more

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https://doi.org/10.3390/molecules23020211

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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.

Highlights

Numerous efforts are underway to develop nitroreductase enzymes to activate prodrugs [1,2], remediate pollutants [3,4,5,6,7] and generate building-blocks for high-value pharmaceuticals [8]
We suggest that the capacious active sites of members of the NfsA, Frm2 and primitive HUB NR subgroups will be good sources of enzymes for use in combination with substrates that have large aromatic π systems activated by electron withdrawing groups, for production of aromatic amines
Just as theofprodigious chemical represented in this superfamily can be traced the large repertoire the cofactor, a flavin,variety we propose that stabilization of the dimer chemical repertoire of the cofactor, a flavin, we propose that stabilization of the dimer

Summary

Introduction

Numerous efforts are underway to develop nitroreductase enzymes to activate prodrugs [1,2], remediate pollutants [3,4,5,6,7] and generate building-blocks for high-value pharmaceuticals [8]. The yield of desired amines is commonly diminished by incomplete reduction to the nitroso and hydroxylamino products [11,12,13] (Figure 1). These partially-reduced compounds react with one-another to form additional by-products that can be toxic, and require expensive purification steps (reviewed in [14]). Inorganic catalysts have shown promise but produce. Molecules 2018, 23, 188 compounds react with one-another to form additional by-products that can be toxic, and require expensive purification steps (reviewed in [14]). Inorganic catalysts have shown promise but produce byproducts and must be quantitatively removed before the product can find pharmaceutical [15]

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