Laccases are oxidases that only require O 2 as a terminal oxidant. Thus, they provide an attractive green alternative to established alcohol oxidation protocols. However, laccases typically require catalytic amounts of mediator molecules to serve as electron shuttles between the enzyme and desired substrate. Consequently, laccase-mediator systems are defined by a multitude of parameters such as, e. g., the choice of laccase and mediator, the respective concentrations, pH, and the oxygen source. This complexity and a perceived lack of comparable data through-out literature represent an entry burden into this field. To provide a solid starting point, particularly for organic chemists, we herein provide a time-resolved, quantitative laccase and mediator screening based on the oxidation of anis alcohol as model reaction. We measured the redox potentials of mediators under the reaction conditions to relate them to their performance. Lastly, for particularly efficient laccase-mediator pairs, we screened important reaction parameters, resulting in an optimized setup for mediator-assisted laccase catalyzed oxidations.

Examples of strong substrate governance and tuning of selectivity between two borderline scenarios by successful catalyst design are reported.

Aldoses exist predominantly in the cyclic hemiacetal form, which is in equilibrium with the open‐chain aldehyde form. The small aldehyde content hampers reactivity when chemistry addresses the carbonyl moiety. This low concentration of the available aldehyde is generally difficult to ascertain. Herein, we demonstrate a new kinetic determination of the (minute) open‐chain content (OCC) of aldoses. This kinetic approach exploits the aldehyde‐selectivity of 2‐aminobenzamidoxime (ABAO), which furnishes a strongly UV‐active adduct. Simple formation curves can be measured in a photometer or plate reader for high‐throughput screening. Under pseudo‐first order kinetics, these curves correlate with a prediction model yielding the relative OCC. The OCCs of all parent aldoses (pentoses and hexoses) were determined referencing against the two tetroses with exceptionally high OCCs and were in very good agreement with literature data. Additionally, the assay was extended towards higher‐carbon sugars with unknown OCC and also applied to rationalise a lack of reactivity observed in a recent synthetic investigation.

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The Front Cover shows two fishermen fishing for the rare fish, eager for the risky treat. Various species are differently eager to give in to temptation, much like various aldoses substantially differ in their open‐chain content (OCC) and consequently in their ease to react as aldehydes. The OCC represents the very small proportions of the aldehyde form (<1%), which is in equilibrium with the dominant ring forms. Accurate measurement of these OCCs was now accomplished by an operationally simple UV‐based kinetic (ABAO) assay which furnished OCC values of all native parent aldoses in full consistency with the more complicated literature gold standard. Cover image designed and illustrated by Thomas Blaukovitsch. More information can be found in the Communication by C. Stanetty et al.