Expanding the scope of enzymatic carboligation reactions in flow-mode: production of optically active tertiary alcohols with packed-bed micro-bioreactors

Acetylacetoin synthase (AAS) from Bacillus licheniformis has been partially purified and immobilized on a silica support and its activity was tested under batch conditions in the homo-coupling of a set of alpha-diketones leading to valuable alpha-hydroxy ketone derivatives displaying a chiral tertiary alcohol functionality at the alpha-position. Next, the effectiveness of AAS heterogeneous catalysis has been evaluated under continuous-flow conditions by fabricating the corresponding packed-bed microreactors (pressure- resistant stainless-steel columns). It has been demonstrated that the covalent immobilization on a silica support and the flow regime synergistically contribute to preserve the enzyme activity over time, thus permitting the long-term operation (up to 15 days) of the prepared bioreactors for the production of the 25 chiral targets via the umpolung strategy.