Transketolase kinetic resolution

Figure 10.37 Kinetic resolution by transketolase, and nonequilibrium C—C bond formation by decomposition of hydroxypyruvate.

The transketolase (TK EC 2.2.1.1) catalyzes the reversible transfer of a hydroxy-acetyl fragment from a ketose to an aldehyde [42]. A notable feature for applications in asymmetric synthesis is that it only accepts the o-enantiomer of 2-hydroxyaldehydes with effective kinetic resolution [117, 118] and adds the nucleophile stereospecifically to the re-face of the acceptor. In effect, this allows to control the stereochemistry of two adjacent stereogenic centers in the generation of (3S,4R)-configurated ketoses by starting from racemic aldehydes thus this provides products stereochemically equivalent to those obtained by FruA catalysis. The natural donor component can be replaced by hydroxy-pyruvate from which the reactive intermediate is formed by a spontaneous decarboxylation, which for preparative purposes renders the overall addition to aldehydic substrates essentially irreversible [42]. 

Table 9 Transketolase-Catalyzed Kinetic Resolution of 2-Hydroxy Aldehydes...

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