Biocatalytic hydrogen-borrowing cascades
The exquisite chemoselectivity and the intrinsic compatibility of enzymes have been widely exploited during the past decade for the development of multi-step biocatalytic reactions in one-pot. In this context, hydrogen-borrowing cascades permit to maximise the atom-efficiency through the internal recycling of redox equivalents, which avoids the use of additional oxidants or reductants. Here, we describe the state-of-the-art in the field of biocatalytic hydrogen-borrowing cascades and provide a future perspective for a wider implementation in organic synthesis.
Multi-step chemical reactions in one-pot offer economic as well as environmental benefits because they avoid the need for isolation and purification of intermediates along a synthetic route (1-3). For instance, that results in a reduced consumption of solvents for isolation procedures and energy for evaporation and mass transfer. In this context, biocatalytic hydrogen-borrowing cascades possess the most elevated atom-economy, since the electrons liberated in the oxidative step are quantitatively consumed in the concurrent reductive step (4).
A concurrent oxidation-reduction process in a single vessel without compartmentalisation is possible as a consequence of the exquisite chemoselectivity and intrinsic compatibility of enzymes. Such systems are inspired from Nature’s complex redox networks. This contribution aims at providing an overview in this field and a guideline for future developments.
Racemisation, isomerisation and disproportionation
The simplest biocatalytic hydrogen-borrowing reaction is the racemisation of optically active alcohols ( ...