The reduction of activated C=C double bonds is an important reaction in synthetic chemistry owing to the potential formation of up to two new stereogenic centers. Artificial nicotinamide cofactors were recently presented as alternative suppliers of hydride equivalents needed for alkene reduction. To study the effect of cofactors on the reduction of activated alkenes, a set of N‐substituted synthetic nicotinamide cofactors with differing oxidation potentials were synthesized and their electrochemical and kinetic behavior was studied. The effects of the synthetic cofactors on enzyme activity of four ene reductases are outlined in this study, where the cofactor mimic with an N‐substituted 4‐hydroxy‐phenyl residue led to a sixfold higher vmax relative to the natural cofactor NADH.

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Using bis(3‐methyl‐2‐pyridyl)‐1,2,4,5‐tetrazine 1, 3‐(2‐pyrimidyl)‐6‐methyl‐1,2,4,5‐tetrazine 2 and bis(2‐pyrimidyl)‐1,2,4,5‐tetrazine=bmtz as ligands, the complexes 3=[Ru(acac)2(1)], 4={[Ru(acac)2]2(1)], 5={[Ru(acac)2]2(bmtz)], and 6={[Ru(acac)2]2(2)] were prepared and identified by structure analysis of crystallized material. The one‐electron oxidized form 6(PF6) was also studied structurally, suggesting a Class II mixed‐valent situation. The neutral dinuclear systems exhibit two reversible oxidation processes with comproportionation constants 109.2

The Cover shows a running track and three competing cofactors on their way to an enzyme. The goal is the flavin in the active side of the enzyme NADH‐dependent cyclohexenone reductase (NCR) from Zymomonas mobilis. Two of the three cofactors are artificial mimics presented in the Full Paper of S. Löw et al. Besides the electrochemical characterization of the mimics, the authors screened their activity with several enzymes and substrates. The NCR was found to be very efficient in utilizing cofactor mimics. Kinetic comparison of NADH and the mimic HPNAH with NCR and Z‐citral as a substrate revealed a sixfold higher vmax for HPNAH. This is indicated on the figure by HPNAH winning the race to the enzyme. More information can be found in the Full Paper by Löw et al. on page 911 in Issue 5, 2016 (DOI: 10.1002/cctc.201501230).