The synthesis of chiral compounds
through dynamic kinetic resolution
has shown improved results with the presence of racemization. Integrating
the reaction media for biocatalytic kinetic resolution and base-catalyzed
racemization pose challenges in chiral separation due to its alkaline
environment. Base-catalyzed racemization of (R)-ibuprofen
ester has been separately studied in isooctane, isooctane–water,
and isooctane–DMSO media. A rapid racemization rate of (R)-ibuprofen ester was obtained in isooctane-DMSO medium
as compared with the other two media with racemization rate constants
(k
rac) of 0.292 and 0.001 h–1, respectively. An investigation carried out on sodium hydroxide
and Amberlyst A26 (OH– resin) as base catalysts
has shown that Amberlyst A26 gave a better performance compared to
that of sodium hydroxide. Additionally, the rate of racemization increases
at higher reaction temperatures, but shows otherwise at a higher concentration
of substrate. The kinetic model of the base-catalyzed racemization
was developed and experimentally validated. The model incorporates
two main contributing factors in the racemization reaction: a base
catalyst and initial substrate concentrations. Base-catalyzed racemization
was conducted in the proposed packed-bed reactor, where the racemization
rate was faster with an increased velocity of feed flow rate. The
absolute rate constants of racemization (k
abs) obtained were 0.112 and 0.275 h–1 for feed flow
rates of 0.6 and 1.2 mL·min–1, respectively.
The packed-bed reactor was then proposed to be coupled with a membrane
reactor as an integrated dynamic kinetic resolution reactor of chiral
compounds.
A simple procedure involving simultaneous adsorption and fixation was developed to immobilize β-galactosidase (β-Gal) from Aspergillus oryzae on a polysulfone hollow-fiber membrane module for converting lactose to galactooligosaccharides. Polyethylenimine was used as a polyelectrolyte intermediate layer to provide a positively charged character for β-Gal adsorption. β-Gal adsorbed on polyethylenimine layer was then fixed with cross-linking by glutaraldehyde. The concentrations of polyethylenimine, glutaraldehyde, and β-Gal were significant parameters to achieve high activity yield. The optimum concentration of polyethylenimine and glutaraldehyde were determined as 5% (w/v) and 15% (v/v), respectively. The activity yield on the membrane surface increases as the concentration of β-Gal used during adsorption and fixation increased. The highest activity yield obtained was 1.26 IU cm −2 at 5 mg mL −1 of β-Gal concentration. The activity yield is proportionally dependent on the concentration of the β-Gal employed. Moreover, the immobilized β-Gal exhibited higher specific productivity and stable transgalactosylation activity compared with free β-Gal during the lactose-catalyzed conversion reaction.
Ibuprofen (isobutyl-propanoic-phenolic
acid) is a chiral drug well-known
for its analgesic, antipyretic, and anti-inflammatory effects. In
the present work, an enzymatic membrane reactor (EMR) has been developed
for the production of optically pure (S)-ibuprofen
acid. The EMR is equipped with a multitubular fixed bed racemization
unit to enhance the enzymatic deracemization of (R,S)-ibuprofen ester. Several process parameters
such as enzyme loading, racemization catalyst loading, reaction temperature,
buffer pH, as well as the flow rate were investigated. These experimental
results were then compared with the proposed process model. It was
found that the experimental data were in good agreement with the theoretical
results. The optimum condition of the lipase-catalyzed dynamic kinetic
resolution (DKR) using the EMR could give 96–98% conversion
with 97–99% of product enantiomeric excess (ee
p).
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