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.
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.
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