Mimicking Nature: Synthetic Nicotinamide Cofactors for C═C Bioreduction Using Enoate Reductases

Abstract

A series of synthetic nicotinamide cofactors were synthesized to replace natural nicotinamide cofactors and promote enoate reductase (ER)-catalyzed reactions without compromising activity or stereoselectivity of the bioreduction process. Conversions and enantioselectivities of up to >99% were obtained for C=C bioreductions and the process was successfully upscaled. Furthermore, high chemoselectivity was observed when employing these nicotinamide cofactor mimics (mNADs) with crude extracts in ER-catalyzed reactions.The asymmetric reduction of conjugated C=C double bonds using enoate reductases (ERs, EC 1.3.1.31) is receiving great interest in preparative organic chemistry.1 § Both authors contributed equally.

Old Yellow Enzyme-Catalysed Asymmetric Hydrogenation: Linking Family Roots with Improved Catalysis

“…Since then, many classical OYEs were identified from proteobacteria (NCR [84], MR [85], PETNR [8]), flavobacteria (Chr-OYE2 [74]), cyanobacteria [21], yeasts (OYE1-OYE3 [86,87], CYE [62]) and plants [67], outlined in Tables 1 and 2. Nicotinamide coenzyme biomimetics (NCBs) previously used in OYE-catalysed hydrogenations to replace NAD(P)H [52,55,58].…”

“…A highly promising and elegant alternative is the use of relatively inexpensive nicotinamide coenzyme biomimetics (NCBs) [52][53][54][55][56]. The latter compounds retain the pyridine ring structure, substituted with varied functional groups either on the N1 nitrogen (NCBs 1-2, 6-7, Figure 1) or at the C3 carbon (NCBs 3-5) [55].…”

“…The latter compounds retain the pyridine ring structure, substituted with varied functional groups either on the N1 nitrogen (NCBs 1-2, 6-7, Figure 1) or at the C3 carbon (NCBs 3-5) [55]. As with the natural coenzyme, the correct positioning of the pyridine ring in the active site is crucial for optimal hydride transfer [52,57].…”

“…In a first study, YqjM, TsOYE and RmOYE were screened against NCBs 1-5 ( Figure 1) [52], followed by more extensive kinetic studies with a panel of OYEs [59]. Depending on the applied NCBs, OYEs differ in their reaction rates and the catalytic efficiency (kcat/Km) is at times even higher with NCBs than with the natural coenzyme, as discussed further in Section 4 [22,58,59].…”

New artificial fluoro-cofactor of hydride transfer with novel fluorescence assay for redox biocatalysis

“…In chemical catalysis, Hantzsch ester (HEH) successfully acts as a reductant in the asymmetric hydrogenation of benzoxazinones 6 and another artificial cofactor 9,10-dihydrophenanthridine (DHPD) has been designed for the asymmetric hydrogenation of benzoxazinones, benzoxazines, quinoxalines and quinolones, resulting in excellent activities and enantioselectivities. 7 Moreover, a widely-used artificial cofactor BNAH has been reported to react with oxidoreductases such as enoate reductases for CQC bioreduction, 8 and horse liver alcohol dehydrogenase for chiral synthesis. 9 Most notably, Nigel et al reported the cocrystal structures of flavin-containing enzyme ene reductases (ERs) from the Old Yellow Enzyme family (EC 1.3.1.31) in complex with NADH and the representative artificial cofactor, validating that both natural and artificial cofactors shared a similar p-p stacking effect and occupied the same region of the active sites.…”