![]() Since cascades with two steps are numerous, these cascades are subdivided whether they encompass two, one, or no redox step in case a redox step is part of the cascade, the order and type of the redox steps were considered, whereby hydrogen-borrowing cascades and deracemization are treated separately. Importantly, it was also distinguished between cascades performed in vitro and in vivo. Then the cascades have been grouped based on the criteria whether the steps of the sequence can be performed simultaneously or the reaction has to be divided into stages performed sequentially. If they need a catalyst, it has been differentiated between cascades requiring exclusively enzymes and such cascades combining enzymes and other types of catalysts or chemical steps. The review suggests a possible classification of cascades ( section 1.3) and is then structured following the classification proposed: first, according to the number of enzymes involved in the linear sequence next, whether the subsequent reactions are spontaneous or need a catalyst. The focus is on the development of such cascades over the last 10 years. The review covers artificial linear cascades with at least one biocatalyzed step thus, other steps might be catalyzed by chemical catalysts or performed with stoichiometric amounts of reagent or may be spontaneous. Furthermore, this classification differentiates between cascades where all reaction steps are performed simultaneously, sequentially, or in flow. ![]() Since the number of examples involving two enzymes is predominant, the two enzyme cascades are further subdivided according to the number, order, and type of redox steps. The review introduces a systematic classification of the cascades according to the number of enzymes in the linear sequence and differentiates between cascades involving exclusively enzymes and combinations of enzymes with non-natural catalysts or chemical steps. Additionally, cascades performed in vivo and in vitro are discussed separately, whereby in vivo cascades are defined here as cascades relying on cofactor recycling by the metabolism or on a metabolite from the living organism. A cascade is defined as the combination of at least two reaction steps in a single reaction vessel without isolation of the intermediates, whereby at least one step is catalyzed by an enzyme. The review compiles artificial cascades involving enzymes with a focus on the last 10 years.
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