• biocatalysis
• enantioselective synthesis
• enzyme immobilization
• flow chemistry
• ketoreductase

Enzyme immobilization on carriers with different properties is a strategy undertaken by many
industries interested in the optimization of enantioselective processes. Immobilized biocatalysts
can be so efficient that they could replace their soluble counterpart or even traditional chemo-
catalytic methods employed in the synthesis of chiral building blocks. This thesis is the result
of the collaboration with Enzymaster GmbH and is focused on the enantioselective synthesis
of (S )-1-(3,5-bis(trifluoromethyl)phenyl)-ethanol performed with immobilized enzymes, under
mild reaction conditions. Both enantiomers of BTPE constitute important building-blocks for
the production of Active Pharmaceutical Ingredients (APIs), such as Aprepritant. The research
was carried out in order to verfy and optimize the use of two ketoreductase enzymes supplied
by Enzymaster for the production of enantiopure BTPE. One of the two enzymes affording
the (S ) enantiomer, proved to be more performing in the reaction of interest and therefore it
was employed for the immobilization procedures. Initially, organic resins functionalized with
different groups were chosen as carriers. Immobilized enzyme samples were first used in batch
tests in order to identify the optimal reaction conditions. The reactions were carried out in a
predominantly organic solvent mixture consisting of 90% 2-propanol and 10% water at 30°C.
The selected conditions allowed an easy product recovery as a white crystalline solid, with yields
of approximately 80% within the first 24 hours and enantiomeric excess higher than 99.9%.
Afterwards the immobilized samples were tested under flow conditions with excellent results in
terms of enantioselectivity, substrate-to-product conversion and yield of the final product and
the catalytic performances of different samples were compared. In most cases five reaction cy-
cles were performed without losses of catalytic activity and enantioselectivity. Furthermore, this
procedure allowed to obtain the desired product as a white crystalline solid after 24 hours with
a simple work-up, high yields and enantiomeric excesses higher than 99.9%. Finally, prelimi-
nary studies on enzyme immobilization onto silica gel based inorganic carriers were conducted
in batch and flow conditions, with promising results.