Angewandte
Chemie
contributing to variability are currently being investigated.
Regardless, the observed distribution coefficients are favor-
able and show that the separated organic phase can be used to
extract product from the reaction mixture: we recovered 80%
of the 2PE product in the organic layer for both trials.
content of samples by using an Agilent GC-FID with a DB17 column
Agilent model 6890).
(
Received: March 6, 2006
Published online: June 21, 2006
By addressing concerns of reactivity, enzyme stability in
separated media, and favorable partitioning, a biocatalytic
OATS scheme for processing hydrophobic substrates with
product separation and biocatalyst recycling has been devel-
oped. Given a cycle time of three hours, 56 mm starting
concentration for PEA in buffer–dioxane (40%) OATS, and
an average of 50% conversion per cycle, we calculated a
Keywords: catalyst recycling · enzyme catalysis · green
chemistry · homogeneous catalysis
.
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volumetric productivity, expressed by the space–time yield, of
À1 À1
2
7.4 gL d . Even with an equivalent residence time of 2 h in
the reactor and assuming a best case scenario of complete
conversion, the space–time yield in a PEA-saturated (4 mm)
À1 À1
dioxane (5%) mixture cannot exceed 5.9 gL d . This is
almost five-times less than that observed in the OATS system.
The space–time yield in pure buffer will be even lower as the
substrate is nearly insoluble. Furthermore, we find that the
enzyme can be recycled with very little activity loss between
cycles. The activity loss observed is entirely due to dilution of
the enzyme and pHdecrease of the reaction medium. A
larger reaction volume, decreased sampling, and improved
pHcontrol should minimize activity loss even further. Even
better product recoveries could be obtained by using a
reaction with more hydrophobic products.
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[
[
[
Biocatalytic OATS reaction–separation schemes fulfill an
[
14]
identified need to develop new options to meet current
challenges in biochemical synthesis. By integrating reaction
and separation, simpler and simultaneously more efficient
processes with a reduced physical footprint can be designed.
The work here shows, for the first time, that biocatalysis in
OATS is feasible and can be an effective option for designing
biocatalytic processes, especially when hydrophobic sub-
strates are involved. This also opens the door to combining
OATS with other biocatalysts and their array of unique
chemistries to efficiently synthesize chiral products.
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Experimental Section
Candida antarctica lipase B (SOL-101) was a kind gift from Bio-
catalytics (Pasadena, CA) and was diluted 100 times by volume with
1
50 mm sodium phosphate buffer solution (NaH PO ; pH7.12)
2 4
before addition to reactions. Supercritical fluid chromatography
purity > 99.9999%) grade CO was purchased from Airgas (Radnor,
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(
2
PA) and used without further purification.
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OATS reaction mixtures containing the desired amount of
dioxane (99%, Sigma), PEA (99%, Alfa Aesar), and 150 mm
sodium phosphate were prepared and 1:100 diluted CALB was
added in a ratio of 0.5 mL enzyme per 9.5 mL OATS mixture. 0.25 mL
samples were removed periodically and immediately mixed 1:1 with a
mixture of 1:1 glacial acetic acid/dioxane to quench the reaction.
Reaction progress was followed by measuring the PEA and 2PE
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Angew. Chem. Int. Ed. 2006, 45, 4670 –4673
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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