Regio- and Stereoselective Aliphatic–Aromatic Cross-Benzoin Reaction: Enzymatic Divergent Catalysis

Article abstract of DOI:10.1002/chem.201602084

The catalytic asymmetric synthesis of chiral 2-hydroxy ketones by using different thiamine diphosphate dependent enzymes, namely benzaldehyde lyase from Pseudomonas fluorescens (PfBAL), a variant of benzoylformate decarboxylase from?Pseudomonas putida (PpBFD-L461A), branched-chain 2-keto acid decarboxylase from Lactococcus lactis (LlKdcA) and a variant of pyruvate decarboxylase from Acetobacter pasteurianus (ApPDC-E469G), was studied. Starting with the same set of substrates, substituted benzaldehydes in combination with different aliphatic aldehydes, PfBAL and PpBFD-L461A selectively deliver the (R)- and (S)-2-hydroxy-propiophenone derivatives, respectively. The (R)- and (S)-phenylacetylcarbinol (1-hydroxy-1-phenylacetone) derivatives are accessible in a similar way using LlKdcA and ApPDC-E469G, respectively. In many cases excellent stereochemical purities (>98 % enantiomeric excess) could be achieved. Hence, the regio- and stereochemistry of the product in the asymmetric aliphatic–aromatic cross-benzoin reaction can be controlled solely by choice of the appropriate enzyme or enzyme variant.

Full text of DOI:10.1002/chem.201602084

DOI: 10.1002/chem.201602084
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Asymmetric Synthesis |Hot Paper|
Regio- and Stereoselective Aliphatic–Aromatic Cross-Benzoin
Reaction: Enzymatic Divergent Catalysis
Maryam Beigi,[a] Ekaterina Gauchenova,[a] Lydia Walter,[a] Simon Waltzer,[a] Fabrizio Bonina,[a]
Thomas Stillger,[a] Dçrte Rother,[b] Martina Pohl,[b] and Michael Mꢀller*[a]
Abstract: The catalytic asymmetric synthesis of chiral
2-hydroxy ketones by using different thiamine diphosphate
dependent enzymes, namely benzaldehyde lyase from
Pseudomonas fluorescens (PfBAL), a variant of benzoylformate
decarboxylase from Pseudomonas putida (PpBFD-L461A),
branched-chain 2-keto acid decarboxylase from Lactococcus
lactis (LlKdcA) and a variant of pyruvate decarboxylase from
Acetobacter pasteurianus (ApPDC-E469G), was studied. Start-
ing with the same set of substrates, substituted benzalde-
hydes in combination with different aliphatic aldehydes,
PfBAL and PpBFD-L461A selectively deliver the (R)- and (S)-2-
hydroxy-propiophenone derivatives, respectively. The (R)-
and (S)-phenylacetylcarbinol (1-hydroxy-1-phenylacetone)
derivatives are accessible in a similar way using LlKdcA and
ApPDC-E469G, respectively. In many cases excellent stereo-
chemical purities (>98% enantiomeric excess) could be
achieved. Hence, the regio- and stereochemistry of the prod-
uct in the asymmetric aliphatic–aromatic cross-benzoin reac-
tion can be controlled solely by choice of the appropriate
enzyme or enzyme variant.
Introduction
Catalytic asymmetric CÀC bond formations are key transforma-
tions in synthetic organic chemistry. Benzoin reactions, pro-
ceeding through an ‘umpolung’ of an acyl group, provide
2-hydroxy ketones (or acyloins) as valuable chiral building
blocks.[1,2] Thiamine diphosphate (ThDP)-dependent enzymes,
which catalyse, for example, the decarboxylation of 2-keto
acids and the formation of chiral 2-hydroxy ketones in nature,
can be efficiently applied in asymmetric acyloin syntheses.[3]
ThDP is imperative in carbohydrate metabolism, namely in
the oxidative decarboxylation of pyruvate resulting in acetate
or acetyl-CoA. Moreover, the "umpoled" carbonyl species a-hy-
droxyethyl-ThDP can add an electrophile such as a proton to
liberate acetaldehyde in a nonoxidative decarboxylation. When
the electrophile is benzaldehyde, phenylacetylcarbinol (PAC) is
formed (Scheme 1, b). This reaction has been used for more
than 80 years for the bulk production of ephedrine and nore-
phedrine as important pharmaceuticals and chiral auxiliaries as
well as key ligands in asymmetric catalysis.[4]
Scheme 1. Possible products in the mixed carboligation of aromatic and
aliphatic aldehydes, exemplified with benzaldehyde and acetaldehyde as
substrates; HPP: 2-hydroxypropiophenone, PAC: phenylacetylcarbinol.
products: two homocoupled and two cross-coupled products
in either enantiomeric form (Scheme 1).[5] Whereas the homo-
coupled products acetoin and benzoin (Scheme 1, c and d)
can be selectively obtained by application of either the aliphat-
ic or the aromatic substrate aldehyde, respectively, the regio-
and stereoselective formation of the aliphatic–aromatic cross-
coupled products, such as 2-hydroxypropiophenone (HPP) and
PAC (Scheme 1, a and b) is difficult to achieve.
The range of possible regio- and stereoisomeric products is
similar to that of aldol reactions of two different aldehydes.
The problem of unselective formation of side products in aldol
reactions can be circumvented by applying nonenolisable alde-
hydes, such as formaldehyde, benzaldehyde or pivaldehyde, as
one reaction partner. In benzoin reactions, this strategy is not
applicable as both reaction partners react as electrophiles.
Thus, the development of efficient enzymatic or organocatalyt-
ic systems to control the outcome in aliphatic–aromatic cross-
benzoin reactions remains a challenge. To address the prob-
lem, the steric and/or electronic features of one (or both)
In principle, carboligation of two different aldehydes in
a cross-benzoin reaction can give access to eight different
[a] Dr. M. Beigi, Dr. E. Gauchenova, L. Walter, S. Waltzer, F. Bonina,
Dr. T. Stillger, Prof. Dr. M. Mꢀller
Institute of Pharmaceutical Sciences, Albert-Ludwigs-Universitꢁt Freiburg
Albertstrasse 25, 79104 Freiburg (Germany)
E-mail: michael.mueller@pharmazie.uni-freiburg.de
[b] Jun.-Prof. Dr. D. Rother, Prof. Dr. M. Pohl
IBG-1: Biotechnology, Forschungszentrum Jꢀlich GmbH
52425 Jꢀlich (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201602084.
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substrate(s) can be chosen in such a way that one reaction
partner reacts preferentially as an acceptor (or donor) under
appropriate catalytic conditions.
cleavage.[11] (R)-HPP derivatives are obtained in high chemical
yield and stereochemical purity by carboligation starting from
the tested aromatic aldehydes as donor and acetaldehyde,
methoxyacetaldehyde or dimethoxyacetaldehyde as acceptor
substrates.[12] Further results for the PfBAL-catalysed mixed car-
boligation of substituted aromatic aldehydes with a range of
aliphatic aldehydes are summarised in Table 1 (for additional
data, for example, amount of homocoupled products, see the
Supporting Information). Reaction monitoring was performed
Alternative organocatalytic methods for aliphatic–aromatic
cross-benzoin reactions have been investigated.[6,7] Following
the lead of early approaches with a focus on electronic and
steric properties of the substrates,[8] and based on the electron-
ic and steric properties of different thiazolium and triazolium
catalysts, an achiral pentafluorophenyl-substituted triazolium
precatalyst was found to promote chemoselectivity
toward aliphatic Breslow intermediate formation, es-
Table 1. PfBAL-catalysed aromatic-aliphatic cross-benzoin reaction.[a]
pecially when ortho-substituted benzaldehydes were
used as the aromatic substrate.[9] Connon, Zeitler
et al. have introduced an asymmetric transformation
yielding enantioenriched 1-hydroxy-1-[2-trifluorome-
thylphenyl]butan-2-one (up to 81% ee).[9] Jin et al.
have described a regioselectivity switch using aro-
matic aldehydes and acetaldehyde by altering the or-
ganocatalyst: whereas a thiazolium salt predominant-
ly gave the HPP derivatives, triazolium catalysts re-
sulted in the preferential formation of the respective
PAC derivatives.[7a] In order to achieve a high propor-
tion of PAC products, a 10-fold excess of acetalde-
hyde was applied (resulting in the formation of ace-
toin as a side product).
Entry Ar
R’
Yield [%][b] Ratio [%] (ee [%])
Config.
a
b
1
Ph
CH3
70[11]
64
98 (>99)
>99 (98)
>99 (96)
70 (95)
2
–
–
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
2
3,5-(MeO)2C6H3 CH3
3
4
5[c]
6
3,5-Cl2C6H3
3-NCC6H4
2-ClC6H4
Ph
CH3
CH3
CH3
CH2CH3
43
[d]
–
30 (n.d.)
47
88
47
75 (>99) 25 (n.d.)
86 (98.5)
94 (99)
71 (93)
64 (96)
–
14 (98)
6 (n.d.)
29 (n.d.)
36 (86)
7
3,5-(MeO)2C6H3 CH2CH3
[d]
8
9
3,5-Cl2C6H3
3-NCC6H4
2-ClC6H4
Ph
CH2CH3
CH2CH3
CH2CH3
CH2OCH3
–
57
35
33
65
28
The term ‘divergent catalysis’ generally refers to
different catalytic reactions that start with the same
set of substrates under controllable conditions to
yield specific but different products with different
catalysts. As described herein, we focused on the
challenge of the chemo- and stereoselective forma-
tion of PAC and HPP derivatives in aliphatic–aromatic
cross-benzoin reactions using different ThDP-depen-
dent enzymes under otherwise identical conditions.
Our intention was to create a selective catalytic
asymmetric access to each 2-hydroxy ketone isomer
among all possible products (Scheme 1) by means of
divergent catalysis.[10]
10[c]
11
12
13
14
15
16
17
18
19
20
21
22
>99 (90)
>99 (95)
>99 (95)
>99 (79)
>99 (65)
>99 (97)
>99 (98)
>99 (90)
>99 (93)
20 (98)
71 (96)
4 (n.d.)
–
–
–
–
–
–
–
–
–
3,5-(MeO)2C6H3 CH2OCH3
3,5-Cl2C6H3
3-NCC6H4
Ph
CH2OCH3
CH2OCH3
CH(OCH3)2
[d]
–
81
86
45
43
3,5-(MeO)2C6H3 CH(OCH3)2
3,5-Cl2C6H3
3-NCC6H4
Ph
3,5-(MeO)2C6H3 cyclopropyl 12
3-NCC6H4
2-ClC6H4
CH(OCH3)2
CH(OCH3)2
cyclopropyl 69
80 (97)
29 (n.d.)
96 (92)
>99 (96)
cyclopropyl 40
cyclopropyl 58
[a] Reaction conditions: 18–27 mm substrate in 50 mm potassium phosphate buffer
(KPi) (0.1 mm ThDP, 2.5 mm MgCl2 or MgSO4, 20 vol% DMSO, pH 7.0), 308C; PfBAL
final concentration: 300 mgmLÀ1; 15 mL reaction volume. [b] Isolated yield. [c] 10-fold
excess of aliphatic aldehyde was used. [d] The reaction was performed on an analyti-
cal scale (1.5 mL reaction volume). n.d.: not determined.
In order to determine the scope and limitations of
the enzyme-catalysed aliphatic–aromatic cross-ben-
zoin reaction, different aliphatic aldehydes (acetalde-
hyde, propanal, methoxyacetaldehyde, dimethoxya-
cetaldehyde and cyclopropanecarbaldehyde) with a set of ben-
zaldehyde derivatives (3,5-dimethoxy-, 3,5-dichloro-, 3-cyano-
and 2-chlorobenzaldehyde) were chosen for this study. Several
of the reactions were carried out on a preparative scale, prov-
ing the applicability of our concept.
by proton NMR spectroscopy and GCMS. The enantiomeric
excess (ee) was determined by chiral-phase HPLC, the absolute
configuration by circular dichroism and based on mechanistic
considerations.
As was expected, the desired (R)-HPP derivatives a were
formed predominantly when acetaldehyde was used (Table 1,
entries 1–5). The combination of acetaldehyde and 2-chloro-
benzaldehyde (Table 1, entry 5) resulted in the formation of
(R)-HPP derivative (>99% ee) as the main product and (R)-PAC
derivative b as a side product (25%). This reaction required
a large excess of acetaldehyde (10 equiv) in order to obtain an
acceptable conversion of the 2-chlorobenzaldehyde. It is
known that 2-chlorobenzaldehyde reacts preferably as an
acceptor in aromatic–aromatic cross-benzoin reactions, and
therefore is expected to be a nonpreferred donor substrate in
Results and Discussion
Enzymatic mixed carboligation of aliphatic and aromatic
aldehydes: (R)-HPP formation by PfBAL catalysis
Benzaldehyde lyase from Pseudomonas fluorescens (PfBAL, E.C.
4.1.2.38) is one of the most versatile ThDP-dependent enzymes
for catalysing the enantioselective formation of (R)-benzoins
and (R)-HPP derivatives through CÀC bond formation and/or
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aliphatic–aromatic cross-benzoin reactions, shifting the forma-
tion from HPP- to PAC-derivatives.[5c]
acetaldehyde. Nevertheless, ortho-substituted benzaldehydes
are not accepted by PpBFD.[14] PpBFD-catalysed carboligation
of benzaldehyde with larger aliphatic aldehydes such as propa-
nal proceeds at a slower rate, forming a mixture of the respec-
tive HPP-, PAC- and benzoin-derivative, beside a decrease in
the S-selectivity for the HPP derivative.[13a]
Despite high enantioselectivity, reduced regioselectivity was
observed when propanal (or 3-methylbutanal, see the Support-
ing Information) was used as the substrate. These reactions led
to a mixture of (R)-HPP and (R)-PAC derivatives with a prefer-
ence for the HPP derivatives a as the main product (Table 1,
entries 6–9), except in the case of 2-chlorobenzaldehyde,
where only the PAC derivative could be detected (Table 1,
entry 10).
The reason for the S-selectivity of PpBFD has been elucidat-
ed based on the crystal structures of PpBFD and PfBAL.[15] In
the active site of PpBFD, a structural element called "S-pocket"
has been identified, which is predominantly defined by the
side chain of L461. The S-pocket in PpBFD, which has not been
found in PfBAL, allows the antiparallel approach of acetalde-
hyde toward the ThDP-bound benzaldehyde prior to CÀC
bond-formation yielding (S)-HPP.[16]
The reaction of methoxy- and dimethoxyacetaldehyde with
different benzaldehyde derivatives in the presence of PfBAL
showed very high regioselectivity, yielding the (R)-HPP deriva-
tives as the sole products (Table 1, entries 11–18).[12)
Striking results were obtained with cyclopropanecarbalde-
hyde. Here, the regioselectivity of the PfBAL-catalysed reactions
was inverted, providing the (R)-PAC derivatives b as the main
products (Table 1, entries 19, 21, 22). This had been expected
for the reaction with 2-chlorobenzaldehyde (see above), but
was also observed with 3-cyanobenzaldehyde and even with
benzaldehyde. The highly enantioenriched products were iso-
lated in good yield. In contrast, the (R)-HPP derivative was ob-
tained predominantly when 3,5-dimethoxybenzaldehyde was
used with cyclopropanecarbaldehyde (Table 1, entry 20). In aro-
matic–aromatic cross-benzoin reactions, 3,5-dimethoxybenzal-
dehyde is a preferred donor substrate.[5c] The low yield in our
case is probably due to the sterically demanding substituents
of both substrates.
Site-directed mutagenesis of PpBFD yielded variants, such as
PpBFD-L461A and PpBFD-L461G, with an increased S-pocket
size. These variants allow the selective formation of (S)-HPP
derivatives with sterically more demanding acceptors such as
propanal and butanal.[16] Thus, we focused on the potential of
PpBFD-L461A for the synthesis of functionalised (S)-HPP deriva-
tives (Table 2).
(S)-HPP derivatives were obtained in good to high enantio-
meric excess and regioselectivity when acetaldehyde or propa-
nal was reacted with aromatic aldehydes (Table 2, entries
23–31).[16,17]
Traces of the respective PAC and benzoin derivatives were
detected in the crude product mixture of the reaction of 3,5-
dimethoxybenzaldehyde or 3,5-dichlorobenzaldehyde with
acetaldehyde (Table 2, entries 24, 25), respectively. Again,
2-chlorobenzaldehyde resulted in the formation of a high pro-
portion (33%) of the PAC derivative (Table 2, entry 27), and
also with cyanobenzaldehyde a ratio of 10% PAC derivative
was gained (entry 26).
Thus, PfBAL possesses a broad substrate spectrum and ac-
cepts different aromatic aldehydes (substituted with electron-
donating as well as electron-withdrawing groups) and different
aliphatic aldehydes. PfBAL can be used preferentially for the
selective synthesis of highly enantioenriched (R)-HPP ana-
logues. Inverse or partially inverse regioselectivity
was observed, yielding (R)-PAC derivatives as the
main products, when cyclopropanecarbaldehyde as
Table 2. PpBFD-L461A-catalysed aromatic–aliphatic cross-benzoin reaction.[a]
a preferred donor or 2-chlorobenzaldehyde, 3-cyano-
benzaldehyde as a preferred acceptor were applied.
In either case, PfBAL preferentially affords R-config-
ured 2-hydroxy ketones; the S-enantiomer was not
observed as a main enantiomer in any of the PfBAL-
catalysed transformations.
Entry Ar
R’
Yield [%][b]
Ratio [%] (ee [%])
Config.
a
b
[c]
23
24
25
26
27
28
29
30
31
32
33
34
Ph
CH3
–
–
20
49
–
35
–
10
37
–
>99 (98)
–
S
S
S
S
S
S
S
S
S
S
S
S
(S)-HPP formation by PpBFD-L461A catalysis
[c]
3,5-(MeO)2C6H3 CH3
97 (99)
95 (98)
90 (97)
66 (97)
>99 (93)[d]
>99 (99)
97 (99)
>99 (98.5)[e]
>99 (93)
>99 (37)
>99 (97)
3 (n.d.)
5 (n.d.)
10 (n.d.)
33 (rac)
–
–
3,5-Cl2C6H3
3-NCC6H4
2-ClC6H4
Ph
CH3
CH3
CH3
CH2CH3
Benzoylformate decarboxylase from Pseudomonas
putida (PpBFD, E.C. 4.1.1.7) catalyses the decarboxyla-
tion of benzoylformate to benzaldehyde as the phys-
iological reaction. In mixed aliphatic–aromatic carbo-
ligation reactions, PpBFD, like PfBAL, prefers aromatic
aldehydes as a donor and aliphatic acceptors, yield-
ing HPP derivatives as the main product; however, in
contrast to PfBAL, PpBFD gives access to (S)-HPP
(with
[c]
[c]
3,5-(MeO)2C6H3 CH2CH3
3,5-Cl2C6H3
3-NCC6H4
Ph
3-NCC6H4
Ph
CH2CH3
CH2CH3
CH2OCH3
CH2OCH3
cyclopropyl
3 (n.d.)
–
–
–
–
[c]
40
–
[c]
[a] Reaction conditions: see footnote to Table 1, PpBFD-L461 A final concentration:
300 mgmLÀ1. [b] Isolated yield. [c] The reaction was performed on an analytical scale
(1.5 mL reaction volume). [d] pH of the reaction was 7.9. The ee was determined to be
88% when the pH was adjusted to 7.0. [e] Threefold excess of propanal was used.
ꢀ92% ee) when benzaldehyde and acetaldehyde are
ligated.[13] PpBFD accepts a broad range of different
aromatic aldehydes as donors for the ligation with
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The reaction of benzaldehyde with methoxyacetaldehyde or
cyclopropanecarbaldehyde delivered (S)-HPP derivatives with
good enantioselectivity (Table 2, entries 32, 34), whereas the re-
action of 3-cyanobenzaldehyde and methoxyacetaldehyde
gave a product prone to racemisation (Table 2, entry 33). More
sterically demanding aliphatic aldehydes such as 3-methylbuta-
nal and dimethoxyacetaldehyde were not accepted by the
enzyme (see the Supporting Information).
any acyloin product (Table 3, entries 36, 38 and Supporting In-
formation). In contrast, the use of propanal with benzaldehyde,
3,5-dimethoxybenzaldehyde or 3-cyanobenzaldehyde selective-
ly yielded the enantioenriched PAC derivatives (Table 3, en-
tries 39–41), while 2-chlorobenzaldehyde with propanal gave
a mixture of acyloin products (Table 3, entry 42). The desired
PAC derivative was also achieved from the reaction of benzal-
dehyde with cyclopropanecarbaldehyde (Table 3, entry 44).
In the reaction with benzaldehyde, methoxyacetaldehyde
gave a 1:1 mixture of the (R)-HPP and (R)-PAC derivatives
(Table 3, entry 43) under the tested conditions. Other aromatic
aldehydes showed low or even no activity for this reaction (see
the Supporting Information).
Thus, structure-based engineering of PpBFD afforded an S-
selective variant that partially overcomes the limitation of the
acceptance of bulky and long-chain aliphatic aldehydes as ac-
ceptors in the mixed carboligation with aromatic aldehydes.
PpBFD-L461A is able to accept a broad range of benzaldehyde
derivatives as donor substrates and shows excellent regioselec-
tivity toward the formation of (S)-HPP derivatives.
The substrate range of LlKdcA in the mixed carboligation of
substituted aromatic and aliphatic aldehydes toward the pro-
duction of (R)-PAC derivatives could be broadened by applying
the respective 2-keto acids, which are known to be preferred
substrates for this enzyme (relative to the corresponding ali-
phatic aldehydes; Table 3).[19] The chemoselectivity in the pres-
ence of LlKdcA was exclusively driven in the direction of the
(R)-PAC derivatives when pyruvate instead of acetaldehyde was
used in the reaction with benzaldehyde, 3,5-dimethoxybenzal-
dehyde or 3-cyanobenzaldehyde (Table 3, entries 35’, 36’, 38’).
This can be explained by the fact that the 2-keto acid must be
decarboxylated prior to carboligation. Therefore, it preferential-
ly serves the acyl donor role after the release of CO2. Similar
results were observed when 2-oxobutyrate instead of propanal
was used (Table 3, entries 39’, 41’, 42’). (R)-PAC derivatives of
3-cyanobenzaldehyde displayed a tendency to racemise during
workup of the reaction (Table 3, entries 38’, 41, 41’). In conclu-
sion, LlKdcA is a potent enzyme for the synthesis of PAC deriv-
atives with strict R stereoselectivity in the enzymatic cross-acy-
loin condensation, if appropriate substrates are chosen.
Hence, PpBFD-L461A and PfBAL are enantiocomplementary
biocatalysts for the formation of HPP derivatives.
(R)-PAC formation by KdcA catalysis
Branched-chain keto acid decarboxylase from Lactococcus
lactis (LlKdcA, E.C. 4.1.1.72) is known to have a broad substrate
range in the cross-benzoin reaction of aliphatic aldehydes with
benzaldehyde.[18] The regioselectivity of LlKdcA in these reac-
tions strongly depends on the substrate combination. For ex-
ample, the reaction of an equimolar mixture of acetaldehyde
with benzaldehyde gives almost equal portions of HPP and
PAC (Table 3, entry 35); however, if 3,5-dichlorobenzaldehyde is
applied as the aromatic substrate, selective formation of the
(R)-HPP derivative occurs with 96% ee (Table 3, entry 37).[18] In
order to achieve regioselective coupling, we focused on the
synthesis of the (R)-PAC derivatives by carboligation of benzal-
dehydes with acetaldehyde derivatives (Table 3).
The reaction of acetaldehyde with 3,5-dimethoxy-, 3-cyano-
(or 2-chloro-) benzaldehyde did not result in the formation of
Table 3. LlKdcA-catalysed aromatic-aliphatic cross-benzoin reaction.[a]
Entry[b]
Ar
R’
Aldehyde
Ratio [%] (ee [%])
Config.
Entry[b]
2-Keto acid
Ratio [%] (ee [%])
Config.
Yield [%][c]
Yield [%][c]
a
b
a
b
[d]
[d]
35
36
37
38
39
40
41
42
43
44
Ph
CH3
CH3
CH3
CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2OCH3
cyclopropyl
–
n.c.
–
n.c.
–
13
–
–
60 (93)
–
n.d. (96)
–
–
–
40 (92)
–
n.d.
R
R
35’
36’
37’
38’
39’
40’
41’
42’
43’
44’
–
27
n.d.
–
–
–
45
–
–
–
–
–
–
–
–
–
–
–
>99 (97)
>99 (87)
R
R
3,5-(MeO)2C6H3
3,5-Cl2C6H3
3-NCC6H4
Ph
3,5-(MeO)2C6H3
3-NCC6H4
2-ClC6H4
Ph
[d, 18]
–
[d]
–
>99 (63)
>99 (98)
R
R
[d]
[d]
>99 (98)
>99 (83)
>99 (n.d.)
80 (n.d.)
50 (71)
R
R
R
–
[d]
>99 (52)
>99 (97)
R
R
[d]
[d]
20
50 (41)
–
[d]
–
14
R
R
n.d.
–
–
–
Ph
>99 (98)
[a] Reaction conditions: see footnote to Table 1, LlKdcA final concentration: 300 mgmLÀ1. [b] Entry numbers 35–44 are for reactions using an aliphatic alde-
hyde as substrate and 35’–44’ for reactions using a 2-keto acid as the substrate. [c] Isolated yield. [d] The reaction was performed on an analytical scale
(1.5 mL reaction volume). n.c.: no conversion; n.d.: not determined.
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(S)-PAC formation by ApPDC-E469G catalysis
Table 4. ApPDC-E469G-catalysed aromatic–aliphatic cross-benzoin reaction.[a]
Acetobacter pasteurianus pyruvate decarboxylase
(ApPDC) is a central enzyme of the oxidative metabo-
lism of the obligate oxidative bacterium. The sub-
strate range of the decarboxylase reaction is broader
than for other pyruvate decarboxylases (PDC, E.C.
4.1.1.1), such as that from Zymomonas mobilis
(ZmPDC) or Saccharomyces cerevisiae (ScPDC), encom-
passing, for example, branched-chain and aromatic
2-keto acids.[20] Investigation of the substrate range
for the carboligase activity in mixed reactions with
benzaldehyde and various aliphatic aldehydes
showed that the main product is always the (R)-PAC
derivative. Nevertheless, ApPDC was not strictly enan-
tioselective (93–96% ee) under the conditions
tested.[21] The broader substrate range and the slight-
ly reduced stereoselectivity of ApPDC suggested that
Entry Ar
R’
Yield [%][b] (Conv. [%])[c] Ratio [%] (ee [%]) Config.
a
b
[d]
[d]
[d]
45
46
47
48
49
50
Ph
CH3
–
–
–
(23)
(41)
(70)
5
4
–
–
–
–
>95 (59)
96 (95)
>99 (88)
>99 (87)
>99 (98)
>99 (69)
S
S
S
S
S
S
3,5-(MeO)2C6H3 CH3
Ph CH2CH3
3,5-(MeO)2C6H3 CH2CH3 80 (90)
3,5-Cl2C6H3
2-ClC6H4
[d]
CH2CH3
CH2CH3
–
–
(10)
(45)
[d]
[a] Reaction conditions: see footnote to Table 1, ApPDC-E469G final concentration:
300 mgmLÀ1. [b] Isolated yield. [c] Determined by GCMS. [d] Reaction was performed
on an analytical scale (1.5 mL reaction volume).
its active site might slightly differ from that of ZmPDC and
ScPDC. A superposition of the crystal structures of ApPDC,
ZmPDC, LlKdcA, PfBAL and PpBFD has provided insights into
several aspects of the active-site architecture of ApPDC, includ-
ing important residues lining the donor binding site and the S-
pocket, which, similar to PpBFD, is a special region of the ac-
ceptor binding site responsible for S-selective ligation.[23] In
ApPDC, the acceptor binding site is larger than that in ZmPDC,
and the S-pocket is the largest observed so far, if just the pro-
tein backbone, excluding sterically demanding amino acid side
chains, is regarded. Modelling studies revealed that the pocket
is large enough to accommodate aromatic aldehydes, if bulky
amino acid side chains are removed, which is a prerequisite for
the formation of (S)-PAC derivatives.
ApPDC-E469G delivered predominantly (S)-PAC derivatives
with all tested substrates (Table 4). These results, although
anticipated, are remarkable since only a single amino acid resi-
due was exchanged resulting in a highly enantiocomplementa-
ry enzyme. Whereas the reaction of aromatic aldehydes with
acetaldehyde gave minor amounts of HPP besides (S)-PAC
products (Table 4, entries 45, 46), the (S)-PAC products were
regio- and stereoselectively formed with propanal as the
acceptor substrate (Table 4, entries 47–50). Hence, LlKdcA and
ApPDC-E469G are enantiocomplementary catalysts for the
formation of PAC derivatives.
Conclusions
Together with our previous studies on PfBAL and PpBFD, the
above-noted structure-function studies paved the way for the
design of ThDP-dependent enzymes for the synthesis of (S)-
PAC derivatives. L461 in PpBFD, which has been identified as
being crucial for the rejection of large aliphatic acceptor
substrates, corresponds to E469 in ApPDC.[16,23] This residue is
highly conserved among PDCs and known to be an essential
prerequisite for the release of the aldehyde upon decarboxyl-
ation, whereas the carboligase activity is not affected, as was
shown for ZmPDC.[22] A similar strategy as with PpBFD was
applied to increase the S-pocket size of ApPDC by replacing
glutamate 469 with glycine (E469G). This was expected to
result in an improved acceptance of larger acceptor substrates,
making the antiparallel arrangement of benzaldehyde in the S-
pocket of ApPDC prior to CÀC bond-formation more likely. As
anticipated, this variant lost almost its complete decarboxylase
activity, but showed remarkable carboligase activity.[23] In addi-
tion to acetaldehyde, sterically more demanding donor
substrates such as propanal and butanal as donors in combina-
tion with benzaldehyde as the acceptor also yielded the (S)-
PAC derivatives, with even higher selectivities.[23] In this study,
we focused on representative examples for the synthesis of
the (S)-PAC derivatives by carboligation of substituted benzal-
dehydes with aliphatic aldehydes.
Using a set of two R-selective and two S-selective ThDP-depen-
dent enzymes, namely PfBAL, PpBFD-L461A, LlKdcA and
ApPDC-E469G, we have demonstrated the divergent synthetic
potential of ThDP-dependent enzymes as valuable biocatalysts
providing selective access to (R)-HPP, (S)-HPP, (R)-PAC, (S)-PAC,
and derivatives thereof through mixed carboligation of aliphat-
ic and aromatic aldehydes (Table 5). Thus, by selection of the
appropriate enzyme, regio- and stereoselective formation of
the desired product in such cross-benzoin reactions is enabled;
PfBAL and PpBFD-L461A predominantly afford regioselective
formation of (R)- and (S)-HPP derivatives, respectively, while
(R)- and (S)-PAC derivatives are obtained by enantiocomple-
mentary[24] catalyses with LlKdcA and ApPDC-E469G, respective-
ly.
Enzymes can be optimised for a specific transformation
through enzyme engineering, as demonstrated exemplarily by
the application of PpBFD-L461A and ApPDC-E469G variants. In
combination with reaction engineering, such as continuous
substrate supply or the use of 2-keto acids instead of alde-
hydes, it is possible to optimise specific transformations. This
has been recently demonstrated by some of us for the produc-
tion of (S)-1-hydroxy-1-phenylbutan-2-one (Table 4, entry 47):
through reaction engineering (iterative optimisation of solvent,
temperature and pH) and the use of 2-oxobutyrate instead of
propanal, the space-time yield (61-fold increase) and ee (from
Chem. Eur. J. 2016, 22, 1 – 8
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Table 5. Regio- and stereoselective formation of the desired product in the cross-benzoin reaction of 3,5-dimethoxybenzaldehyde and propanal by appro-
priate choice of enzyme.
Enzyme[a]
(R)-a Ratio [%] (ee [%])
(S)-a Ratio [%] (ee [%])
(R)-b Ratio [%] (ee [%])
(S)-b Ratio [%] (ee [%])
PfBAL
94 (99)
–
6 (n.d.)
–
PpBFD-L461A
LlKdcA
ApPDC-E469G
–
–
–
>99 (99)
–
–
–
–
–
>99 (83)
–
>99 (87)
[a] Reaction conditions: 50 mm potassium phosphate buffer (KPi; containing 0.1 mm ThDP, 2.5 mm MgCl2·6H2O or MgSO4, 20 vol% DMSO, pH 7.0), 308C;
enzyme final concentration: 300 mgmLÀ1 in 15 mL reaction volume.
were dissolved in 3 mL DMSO (or methyl tert-butyl ether, see the
88 to 98%) for the product of the ApPDC-E469G-catalysed re-
action were significantly improved.[25]
Supporting Information). After addition of the enzyme (PfBAL,
10 mg of lyophilised crude enzyme containing 20% protein) in
The established divergent catalytic system outlined here
12 mL of potassium phosphate buffer (50 mm, pH 7.0, 2.5 mm
nicely demonstrates that, in principle, every desired 2-hydroxy
MgSO4, 0.1 mm ThDP), the reaction mixture was stirred slowly at
ketone isomer, even the thermodynamically less stable one,
308C for 24 h. The reaction mixture was extracted three times with
can be obtained selectively under kinetically controlled condi-
tions in enzymatic cross-carboligation reactions. We propose
that the range of 2-hydroxy ketones accessible by ThDP-de-
pendent enzymes is much broader than described so far. Most
recently, Giovannini et al. have shown that through the use of
methylacetoin as a donor in combination with aromatic alde-
hydes many (S)-PAC derivatives are accessible by catalysis with
ThDP-dependent acetoin:dichlorophenolindophenol oxidore-
ductase from Bacillus licheniformis.[26] Enzymatic CÀC bond liga-
tions with ketones as acceptor substrates resulted in the for-
mation of chiral acyloins of 38 alcohols.[27] Moreover, through
enzyme and reaction engineering it is possible to perform and
optimise transformation, which are difficult to realise by other
means. This concept can also be used as a blueprint for other
members of the ThDP enzyme family, such as other PDCs,
transketolases, PigD, YerE, CDH, SucA, Kgd or MenD.[28] All of
these enzymes were shown to be applied advantageously in
the asymmetric synthesis of 2-hydroxy ketones. For some of
these biocatalysts enzyme engineering already resulted in the
formation of enantiocomplementary products.[29] With the di-
vergent catalysis approach described herein it should be possi-
ble to realise many more cross-benzoin reactions in a regio-
and stereoselective manner.
ethyl acetate (25 mL) and the organic layer was washed with brine.
The solvent was evaporated and the crude product was dissolved
in diethyl ether (5 mL). The solution was washed with brine, dried
over Na2SO4 and concentrated to deliver a 70% yield of product as
a yellow solid. 1H NMR (400 MHz, CDCl3): d=1.46 (d, 3H, 3J=
6.9 Hz, CH3), 3.8 (d, 1H, 3J=6.3 Hz, CHOH), 5.17 (quin, 1H, 3J=
6.9 Hz, CHOH), 7.49–7.53 (m, 2H, ArH), 7.61–7.65 (m, 1H, ArH),
7.92–7.95 (m, 2H, ArH); 13C NMR (100 MHz, CDCl3): d=22.5 (CH3),
69.5 (CHOH), 128.8 (CHar), 129.0 (CHar), 133.4 (Cq), 134.1 (CHar),
202.5 ppm (C=O); GCMS: tR =8.05 min; MS (70 eV, EI): m/z (%): 150
(0.1) [M+], 135 (0.1), 105 (100), 77 (45); HPLC (Chiral-OM, n-hexane/
2-propanol=90:10, 0.75 mLminÀ1, 208C): tR (R)-HPP=12.62, tR (S)-
HPP=10.93 min.
Representative example for the synthesis on an analytical
scale (1.5 mL reaction volume)
(R)-3-(2-Hydroxy-3-methoxypropionyl)benzonitrile
(Table 1,
entry 14): 3-Cyanobenzaldehyde (2.9 mg, 0.022 mmol) was dis-
solved in a mixture of 0.3 mL DMSO and 1.2 mL of potassium
phosphate buffer (50 mm, pH 7.0, 2.5 mm MgSO4, 0.1 mm ThDP).
Then, methoxyacetaldehyde (2 mg, 0.027 mmol) and enzyme
(PfBAL, 0.45 mg protein) were added to the mixture. The reaction
mixture was stirred slowly at 308C for 72 h, then extracted with
CDCl3 and immediately analysed without further purification.
3
1H NMR (400 MHz, CDCl3): d=3.27 (s, 3H, OCH3), 3.71 (d, 2H, J=
4.0 Hz, CH2), 3.90 (br s, 1H, OH), 5.12 (‘t’, 1H, 3J=4.0 Hz, CHOH),
7.61 (‘t’, 1H, 3J=7.9 Hz, CH), 7.85 (d‘t, 1H, 3J=7.9 Hz, 4J=1.5 Hz,
CH), 8.15 (d‘t’, 1H, 3J=7.9 Hz, 4J=1.5 Hz, CH), 8.23 ppm (‘t’, 1H,
4J=1.5 Hz, CH); 13C NMR (100 MHz, CDCl3): d=59.7 (CH3), 73.8
(CHOH), 74.7 (CH2), 113.5 (Cq), 117.8 (Cq), 129.9 (CHar), 132.4 (CHar),
132.6 (CHar), 135.2 (Cq), 136.7 (CHar), 198.1 ppm (C=O); GCMS: tR =
9.33 min; MS (70 eV, EI): m/z (%): 130 (100), 102 (50), 75 (25), 51
Experimental Section
Representative example for the synthesis on a preparative
scale (15 mL reaction volume)
(R)-2-Hydroxy-1-phenylpropan-1-one (Table 1, entry 1): Benzalde-
hyde (28.6 mg, 0.27 mmol) and acetaldehyde (12 mg, 0.27 mmol)
(10); HPLC (Chiralcel OB, n-hexane/2-propanol 80:20, 1.0 mLminÀ1
,
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Demir, T. Dꢀnnwald, H. Iding, M. Pohl, M. Mꢀller, Tetrahedron: Asymme-
try 1999, 10, 4769–4774; c) R. Wilcocks, O. P. Ward, S. Collins, N. J. Dew-
dney, Y. Hong, E. Prosen, Appl. Environ. Microbiol. 1992, 58, 1699–1704;
d) R. Wilcocks, O. P. Ward, Biotechnol. Bioeng. 1992, 39, 1058–1063.
[14] a) T. Dꢀnnwald, A. S. Demir, P. Siegert, M. Pohl, M. Mꢀller, Eur. J. Org.
Chem. 2000, 2161–2170; b) T. Dꢀnnwald, M. Mꢀller, J. Org. Chem. 2000,
65, 8608–8612.
[15] a) M. S. Hasson, A. Muscate, M. J. McLeish, L. S. Polovnikova, J. A. Gerlt,
G. L. Kenyon, G. A. Petsko, D. Ringe, Biochemistry 1998, 37, 9918–9930;
b) T. G. Mosbacher, M. Mꢀller, G. E. Schulz, FEBS J. 2005, 272, 6067–
6076.
258C): tR (R)=28.2, tR (S)=24.5 min; (Chiralcel OD-H, n-hexane/2-
propanol 95:5, 0.75 mLminÀ1, 258C): tR (R)=29.2, tR (S)=25.0 min.
Acknowledgements
We thank the German Research Council DFG for financial sup-
port within the framework of project FOR 1296 "Diversity of
Asymmetric Thiamine Catalysis".
[16] D. Gocke, L. Walter, E. Gauchenova, G. Kolter, M. Knoll, C. L. Berthold, G.
Schneider, J. Pleiss, M. Mꢀller, M. Pohl, ChemBioChem 2008, 9, 406–412.
[17] B. Lingen, D. Kolter-Jung, P. Dꢀnkelmann, R. Feldmann, J. Grçtzinger, M.
Pohl, M. Mꢀller, ChemBioChem 2003, 4, 721–726.
Keywords: asymmetric synthesis
coupling · thiamine diphosphate · vitamin B1
·
biocatalysis
·
CÀC
[18] D. Gocke, C. L. Nguyen, M. Pohl, T. Stillger, L. Walter, M. Mꢀller, Adv.
Synth. Catal. 2007, 349, 1425–1435.
[19] a) B. A. Smit, J. Vlieg, W. J. M. Engels, L. Meijer, J. T. M. Wouters, G. Smit,
Appl. Environ. Microbiol. 2005, 71, 303–311; b) A. Yep, G. L. Kenyon, M. J.
McLeish, Bioorg. Chem. 2006, 34, 325–336.
[1] a) D. Enders, A. A. Narine, J. Org. Chem. 2008, 73, 7857–7870; b) D.
Enders, O. Niemeier, A. Henseler, Chem. Rev. 2007, 107, 5606–5655;
c) D. M. Flanigan, F. Romanov-Michailidis, N. A. White, T. Rovis, Chem.
Rev. 2015, 115, 9307–9387.
[2] P. Hoyos, J. V. Sinisterra, F. Molinari, A. R. Alcꢂntara, P. Domꢃnguez de Ma-
rꢃa, Acc. Chem. Res. 2010, 43, 288–299.
[20] D. Gocke, T. Graf, H. Brosi, I. Frindi-Wosch, L. Walter, M. Mꢀller, M. Pohl,
J. Mol. Catal. B 2009, 61, 30–35.
[3] a) M. Pohl, C. Dresen, M. Beigi, M. Mꢀller in Enzyme Catalysis in Organic
Synthesis Vol. 3 (Eds.: K. Drauz, H. Grçger, O. May), Wiley-VCH, Wein-
heim, 2012, pp. 919–946; b) M. Mꢀller, D. Gocke, M. Pohl, FEBS J. 2009,
276, 2894–2904; c) R. Kluger, K. Tittmann, Chem. Rev. 2008, 108, 1797–
1833; d) M. Pohl, C. Wechsler, M. Mꢀller, in Science of Synthesis Biocatal-
ysis in Organic Synthesis 2 (Eds. K. Faber, W.-D. Fessner, N. J. Turner),
Thieme, 2015, pp. 93–131.
[4] a) C. Neuberg, J. Hirsch, Biochem. Z. 1921, 115, 282–310; b) J. A. Groep-
er, S. R. Hitchcock, G. M. Ferrence, Tetrahedron: Asymmetry 2006, 17,
2884–2889, and references therein.
[5] a) P. Domꢃnguez de Marꢃa, M. Pohl, D. Gocke, H. Grçger, H. Trauthwein,
T. Stillger, L. Walter, M. Mꢀller, Eur. J. Org. Chem. 2007, 2940–2944; b) P.
Ayhan, S. Ilke, B. Cifci, A. S. Demir, Org. Biomol. Chem. 2011, 9, 2602–
2605; c) P. Dꢀnkelmann, D. Kolter-Jung, A. Nitsche, A. S. Demir, P. Sie-
gert, B. Lingen, M. Baumann, M. Pohl, M. Mꢀller, J. Am. Chem. Soc. 2002,
124, 12084–12085.
[6] a) I. Piel, M. D. Pawelczyk, K. Hirano, R. Frçhlich, F. Glorius, Eur. J. Org.
Chem. 2011, 5475–5484; b) C. A. Rose, S. Gundala, S. J. Connon, K. Zei-
tler, Synthesis 2011, 190–198; c) S. M. Langdon, M. M. D. Wilde, K. Thai,
M. Gravel, J. Am. Chem. Soc. 2014, 136, 7539–7542.
[7] a) M. Y. Jin, S. M. Kim, H. Han, D. H. Ryu, J. W. Yang, Org. Lett. 2011, 13,
880–883; b) M. Y. Jin, S. M. Kim, H. Mao, D. H. Ryu, C. E. Song, J. W.
Yang, Org. Biomol. Chem. 2014, 12, 1547–1550.
[8] a) W. S. Ide, J. S. Buck, Org. React. 1948, 4, 269–304; b) H. Stetter, G.
Dꢄmbkes, Synthesis 1980, 309–310.
[9] S. O’Toole, C. A. Rose, S. Gundala, K. Zeitler, S. J. Connon, J. Org. Chem.
2011, 76, 347–357.
[10] a) W. Xu, L. Li, G.-Q. Lai, Mini-Rev. Org. Chem. 2007, 4, 217–230; b) J. Ma-
hatthananchai, A. M. Dumas, J. W. Bode, Angew. Chem. Int. Ed. 2012, 51,
10954–10990; Angew. Chem. 2012, 124, 11114–11152.
[21] P. Siegert, M. J. McLeish, M. Baumann, H. Iding, M. M. Kneen, G. L.
Kenyon, M. Pohl, Protein Eng. Des. Sel. 2005, 18, 345–357.
[22] D. Meyer, L. Walter, G. Kolter, M. Pohl, M. Mꢀller, K. Tittmann, J. Am.
Chem. Soc. 2011, 133, 3609–3616.
[23] a) D. Rother, G. Kolter, T. Gerhards, C. L. Bertold Siçberg, E. Gauchenova,
M. Knoll, J. Pleiss, M. Mꢀller, G. Schneider, M. Pohl, ChemCatChem 2011,
3, 1587–1596; b) C. Vogel, M. Widmann, M. Pohl, J. Pleiss, BMC Biochem.
2012, 13, 24.
[24] For a review on enantiocomplementary enzymes, see: P. F. Mugford,
U. G. Wagner, Y. Jiang, K. Faber, R. J. Kazlauskas, Angew. Chem. Int. Ed.
2008, 47, 8782–8793; Angew. Chem. 2008, 120, 8912–8923.
[25] A. G. Baraibar, E. von Lieres, W. Wiechert, M. Pohl, D. Rother, Top. Catal.
2014, 57, 401–411.
[26] a) P. P. Giovannini, L. A. Lerin, M. Mꢀller, G. Bernacchia, M. De Bastiani, M.
Catani, G. di Carmine, A. Massi, Adv. Synth. Catal, 2016, 358, DOI
10.1002/adsc.201600359; b) P. P. Giovannini, P. Pedrini, V. Venturi, G.
Fantin, A. Medici, J. Mol. Catal. B 2010, 64, 113–117.
[27] a) P. Lehwald, M. Richter, C. Rçhr, H.-w. Liu, M. Mꢀller, Angew. Chem. Int.
Ed. 2010, 49, 2389–2392; Angew. Chem. 2010, 122, 2439–2442; b) G.
Bernacchia, O. Bortolini, M. De Bastiani, L. A. Lerin, S. Loschonsky, A.
Massi, M. Mꢀller, P. P. Giovannini, Angew. Chem. Int. Ed. 2015, 54, 7171–
7175; Angew. Chem. 2015, 127, 7277–7281.
[28] ThDP-dependent Enzyme Engineering Database (TEED, http://www.
teed.uni-stuttgart.de): M. Widmann, R. Radloff, J. Pleiss, BMC Biochem.
2010, 11, 9.
[29] a) For a review on engineering stereoselectivity of ThDP-dependent en-
zymes, see: H. C. Hailes, D. Rother, M. Mꢀller, R. Westphal, J. M. Ward, J.
Pleiss, C. Vogel, M. Pohl, FEBS J. 2013, 280, 6374–6394; b) R. Westphal,
D. Hahn, U. Mackfeld, S. Waltzer, M. Beigi, M. Mꢀller, M. Widmann, C.
Vogel, J. Pleiss, D. Rother, M. Pohl, ChemCatChem 2013, 5, 3587–3594;
c) R. Westphal, S. Jansen, C. Vogel, J. Pleiss, M. Mꢀller, D. Rother, M.
Pohl, ChemCatChem 2014, 6, 1082–1088; d) R. Westphal, C. Vogel, C.
Schmitz, J. Pleiss, M. Mꢀller, M. Pohl, D. Rother, Angew. Chem. Int. Ed.
2014, 53, 9376–9379; Angew. Chem. 2014, 126, 9530–9533; e) C.
Wechsler, D. Meyer, S. Loschonsky, L.-M. Funk, P. Neumann, R. Ficner, F.
Brodhun, M. Mꢀller, K. Tittmann, ChemBioChem 2015, 16, 2580–12584.
[11] a) A. S. Demir, M. Pohl, E. Janzen, M. Mꢀller, J. Chem. Soc. Perkin Trans.
1 2001, 633–635; b) A. S. Demir, ꢅ. S¸es¸enoglu, E. Eren, B. Hosrik, M.
Pohl, E. Janzen, D. Kolter, R. Feldmann, P. Dꢀnkelmann, M. Mꢀller, Adv.
Synth. Catal. 2002, 344, 96–103; c) T. Stillger, M. Pohl, C. Wandrey, A.
Liese, Org. Process Res. Dev. 2006, 10, 1172–1177; d) E. Janzen, M.
Mꢀller, D. Kolter-Jung, M. Kneen, M. J. McLeish, M. Pohl, Bioorg. Chem.
2006, 34, 345–361.
[12] A. S. Demir, ꢅ. S¸es¸enoglu, P. Dꢀnkelmann, M. Mꢀller, Org. Lett. 2003, 5,
2047–2050.
Received: May 3, 2016
[13] a) H. Iding, T. Dꢀnnwald, L. Greiner, A. Liese, M. Mꢀller, P. Siegert, J. Grçt-
zinger, A. S. Demir, M. Pohl, Chem. Eur. J. 2000, 6, 1483–1495; b) A. S.
Published online on && &&, 0000
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FULL PAPER
&
Asymmetric Synthesis
M. Beigi, E. Gauchenova, L. Walter,
S. Waltzer, F. Bonina, T. Stillger, D. Rother,
M. Pohl, M. Mꢀller*
&& – &&
Divergent biocatalysis: The catalytic
asymmetric synthesis of chiral 2-hydroxy
ketones using different thiamine
scheme). The results show that the
regio- and stereochemistry of the
product in the reaction can be con-
trolled solely by choice of the appropri-
ate enzyme.
Regio- and Stereoselective Aliphatic–
Aromatic Cross-Benzoin Reaction:
Enzymatic Divergent Catalysis
diphosphate dependent enzymes,
namely PfBAL, PpBFD-L461A, LlKdcA and
ApPDC-E469G, was studied (see
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ÝÝ These are not the final page numbers!