Nicotinamide‐Dependent Ene Reductases as Alternative Biocatalysts for the Reduction of Activated Alkenes

Abstract

Four NAD(P)H‐dependent non‐flavin ene reductases have been investigated for their ability to reduce activated C=C bonds in an asymmetric fashion by using 20 structurally diverse substrates. In comparison with flavin‐dependent Old Yellow Enzyme homologues, a higher degree of electronic activation was required, because the best activities were obtained with enals and nitroalkenes rather than enones and carboxylic esters. Although FaEO from Fragaria x ananassa (strawberry) and its homologue SlEO from Solanum lycopersicum (tomato) exhibited a narrow substrate spectrum, progesterone 5β‐reductase (At5β‐StR) from Arabidopsis thaliana (thale cress) and leukotriene B4 12‐hydroxydehydrogenase (LTB4DH/PGR) from Rattus norvegicus (rat) appear to be promising candidates, in particular for the asymmetric bioreduction of open‐chain enals, nitroalkenes and α,β‐unsaturated γ‐butyrolactones. Competing nitro reduction and non‐enzymatic Weitz–Scheffer epoxidation were largely suppressed.

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

“…Although NADPH is the preferred physiological coenzyme for OYE, the dependency on this commercially expensive compound can be circumvented by established recycling systems with dehydrogenases [12,18,[42][43][44][45], with alternative sources of hydride [46,47], or through a nicotinamide-independent disproportionation coupling reaction [48][49][50][51]. A highly promising and elegant alternative is the use of relatively inexpensive nicotinamide coenzyme biomimetics (NCBs) [52][53][54][55][56].…”

Unusual CC Bond Isomerization of an α,β‐Unsaturated γ‐Butyrolactone Catalysed by Flavoproteins from the Old Yellow Enzyme Family

“…Unlike in the case of substrate 1 a , a variety of ene‐reductases were able to reduce isomer 2 a at the expense of NADH by forming the expected saturated lactone 1 b in up to 75 % yield (Table 1, left). Whereas the most active enzyme (EBP1) showed only low stereoselectivity (20 % ee ), the “slow” proteins YqjM, OPR1 and YhdA gave ( R )‐ 1 b in up to >99 % ee 36. No switch in stereoselectivity could be detected, neither could any trace of CC‐isomerization product 1 a .…”

Non-Conventional Yeasts as Sources of Ene-Reductases for the Bioreduction of Chalcones

“…The chemoselective bioreduction of α,β-unsaturated alkenes represents an important tool in the synthesis of a lot of fine chemicals and pharmaceuticals [1][2][3]. Ene-reductases (ERs) belong to the flavin-containing "Old Yellow Enzyme" family (OYE, EC 1.6.99.1), which includes a class of I flavin-dependent oxidoreductases, which have been extensively studied for their ability to catalyze the asymmetric reduction of electronically activated C=C bonds, possessing electron-withdrawing substituents in the presence of cofactor-recycling systems for NAD(P)H [4][5][6][7][8][9][10][11][12][13][14]. Intracellular ER homologues from bacteria, yeasts, filamentous fungi and higher plants have been isolated and characterized since the 1990s [15][16][17][18][19][20][21][22][23][24][25].…”