One-Pot Three-Step Consecutive Transformation of L-α-Amino Acids to (R)- and (S)-Vicinal 1,2-Diols via Combined Chemical and Biocatalytic Process

Article abstract of DOI:10.1002/cctc.201901189

Optically pure vicinal 1,2-diols are versatile chiral building blocks in the fine chemical and pharmaceutical industries. L-α-amino acid is a good feedstock source for high value-added product production since it is inexpensive and renewable. However, conversion of L-α-amino acids to enantioenriched vicinal 1,2-diols remains a significant challenge. In this study, combining a simple chemical process and a three-enzyme cascade biocatalysis system, we have successfully implemented a one-pot sequential process for the transformation of L-α-amino acids into enantiopure vicinal 1,2-diols in aqueous medium. Firstly, the NaBH₄-H₂SO₄ system converted L-α-amino acids to (S)-amino alcohols via amino acid carboxyl reduction. Secondly, the three-enzyme (transaminase, carbonyl reductase and glucose dehydrogenase) cascade biocatalysis system converted amino alcohols to enantiopure vicinal 1,2-diols via amino alcohol deamination, α-hydroxy ketone asymmetric reduction and cofactor regeneration. Taking advantage of the two different reaction systems, chiral vicinal 1,2-diols could be obtained from L-α-amino acids with high yields (69–90 %) and excellent ee values (91–>99 % ee).

Full text of DOI:10.1002/cctc.201901189

Accepted Article
Title: One-Pot Three-Step Consecutive Transformation of L-α-Amino
Acids to (R)- and (S)-Vicinal 1,2-Diols via Combined Chemical
and Biocatalytic Process
Authors: Jiandong Zhang, Jian-Wei Zhao, Li-Li Gao, Jing Zhao, Hong-
Hong Chang, and Wen-Long Wei
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To be cited as: ChemCatChem 10.1002/cctc.201901189
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10.1002/cctc.201901189
ChemCatChem
COMMUNICATION
One-Pot Three-Step Consecutive Transformation of L-α-Amino
Acids to (R)- and (S)-Vicinal 1,2-Diols via Combined Chemical and
Biocatalytic Process
Jian-Dong Zhang,*[a] Jian-Wei Zhao,[a] Li-Li Gao,[b] Jing Zhao,[c] Hong-Hong Chang,[a] Wen-Long Wei[a]
Dedication ((optional))
Abstract: Optically pure vicinal 1,2-diols are versatile chiral building
blocks in the fine chemical and pharmaceutical industries. L-α-amino
acid is a good feedstock source for high value-added product
production since it is inexpensive and renewable. However,
conversion of L-α-amino acids to enantioenriched vicinal 1,2-diols
remains a significant challenge. In this study, combining a simple
chemical process and a three-enzyme cascade biocatalysis system,
we have successfully implemented a one-pot sequential process for
the transformation of L-α-amino acids into enantiopure vicinal 1,2-
diols in aqueous medium. Firstly, the NaBH4-H2SO4 system
converted L-α-amino acids to (S)-amino alcohols via amino acid
carboxyl reduction. Secondly, the three-enzyme (transaminase,
carbonyl reductase and glucose dehydrogenase) cascade
biocatalysis system converted amino alcohols to enantiopure vicinal
1,2-diols via amino alcohol deamination, α-hydroxy ketone
asymmetric reduction and cofactor regeneration. Taking advantage
of the two different reaction systems, chiral vicinal 1,2-diols could be
obtained from L-α-amino acids with high yields (69-90%) and
excellent ee values (91->99% ee).
ketones,10 enantioselective biooxidation of racemic diols11 and
enantioconvergent hydrolysis of racemic styrene oxide (SO).12
However, most of the starting materials for vicinal 1,2-diol
synthesis are expensive, uncommercialized and unrenewable.
Thus, the synthesis of chiral 1,2-diols from readily available and
renewable feedstocks remains challenging.
L-α-amino acids are renewable platform molecules that can
be obtained in
a pure form from the fermentation of
carbohydrates or produced from renewable biomass (protein).13
The easier availability of some L-α-amino acids in comparison
with other feedstocks has encouraged the development of
multistep approaches for the one-pot conversion of L-α-amino
acids into other high valuable compounds.14-15 To the best our
knowledge, to date, there is still no report in the literature for the
conversion of L-α-amino acids to enantioenriched vicinal 1,2-
diols, this is likely due to that the reaction possess a number of
synthetic challenges: reduction of carboxyl to hydroxyl,
conversion of amino group to hydroxyl and the need for regio-
and stereoselective. The combination of chemical reactions from
different fields of catalysis in one-pot represents an attractive
synthetic route with the advantages of higher yields, low costs,
high selectivity and environmental benefits. Recently, these
kinds of reactions have brought about remarkable developments,
especially for combined chemo- and biocatalysis systems which
could enable transformations that cannot be achieved by either
of the two catalysts alone.16-17 In this study, combining a simple
chemical reduction process (NaBH4-H2SO4 system) and a three-
enzyme (transaminase, carbonyl reductase and glucose
dehydrogenase) cascade biocatalysis (Scheme 1), we
implemented a one-pot, three-step sequential chemoenzymatic
transformation in aqueous medium to prepare enantioenriched
vicinal 1,2-diols with good yield and excellent enantioselectivity.
The current research provided the first example for practical
preparation of chiral vicinal 1,2-diols from L-α-amino acids.
Optically pure vicinal 1,2-diols as chiral intermediates are
important building blocks in the fine chemical and
pharmaceutical industries.1-2 The reported chemical methods for
the preparation of enantioenriched vicinal 1, 2-diols include
Sharpless dihydroxylation of alkenes,3 epoxide hydrolysis,4
asymmetric aldol addition,5 asymmetric hydrosilylation,6 and
asymmetric transfer hydrogenation.7 However, these processes
often suffer from serious drawbacks such as use of complicated,
expensive and toxic metal catalysts, or forming product with
lower enantiomeric excess (ee) and lower yield. Alternatively,
biocatalytic approaches have attracted great attention as a
sustainable and high enantioselective strategy to prepare the
enantiopure 1,2-diols. These approaches include the
stereospecific dihydroxylation of styrene,8 kinetic resolution of
racemic PED,9 enantioselective reduction of α-hydroxy
[a]
Dr. J. D. Zhang, J. W. Zhao, Dr. H. H. Chang, Prof. Dr. W. L. Wei
Department of Biological and Pharmaceutical Engineering
Taiyuan University of Technology
79 West Yingze Street, Taiyuan 030024, Shanxi (P.R. China)
E-mail: zhangjiandong@tyut.edu.cn
[b]
[c]
Dr. L. L. Gao
Department of Environmental Engineering
Taiyuan University of Technology
79 West Yingze Street, Taiyuan 030024, Shanxi (P.R. China)
Dr. J. Zhao
State Key Laboratory of Biocatalysis and Enzyme Engineering
Hubei University
Wuhan 430062, Hubei (P.R. China)
Scheme 1. Conversion of L-α-amino acids to enantioenriched vicinal 1,2-diols
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
via chemoenzymatic transformation
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901189
ChemCatChem
COMMUNICATION
In order to realize this new chemoenzymatic transformation
(Scheme 1), the first step of this new system for the reduction of
L-α-amino acid to (S)-β-amino alcohol was conducted with a
chemical reduction process. Although several methods can
realize this reaction, however they often require the use of rather
expensive reagents (such as LiBH4, BH3-SMe2), which are also
highly toxic and explosive reagents.18 In this study, a NaBH4-
H2SO4 system was selected as a promising procedure for the
reduction of L-amino acids to the corresponding amino alcohols
since the inexpensive reagents, safe and convenient
procedure.19 Consequently, we began our studies by testing the
NaBH4-H2SO4 procedure in the reduction of L-α-amino acids 1a–
f (1 mmol) to (S)-β-amino alcohol 2a-f, after reaction for 6 h with
NaBH4-H2SO4 in tetrahydrofuran (THF), methanol was added
carefully to destroy excess BH3, and the mixture was basified
with 5 N NaOH to pH10 and stirred for 1 h. Next, the mixture
was concentrated by evaporation (final volume was 5 mL, THF
and methanol were almost evaporated) and heated at 70oC for 4
h. The product (S)-β-amino alcohols 2a-f in aqueous phase were
obtained with 69.0-90.0% yields (Table S2).
The transaminase for the conversion of (S)-β-amino alcohols
to α-hydroxy ketones in the second step of the system was
selected. In our previous study,20 we have constructed a high-
throughput assay method for the discovery of amino alcohol-
specific transaminases, and a (R)-ω-transaminase (MVTA) from
Mycobacterium vanbaalenii was identified as an appropriate
enzyme with high activity and excellent enantioselectivity toward
(S)-β-amino alcohols.21 As shown in Table S3, the cell free
extract of E. coli overexpressing MVTA was used to determine
the activities of MVTA toward (S)-β-amino alcohols 2a-f. As a
result, the highest activities of MVTA were detected with (S)-2d
(4.6 U mg-1), (S)-2e (3.2 U mg-1) and (S)-2b (2.3 U mg-1),
respectively, while the moderate activities of MVTA were found
towards (S)-2a (1.2 U mg-1), (S)-2c (1.4 U mg-1) and (S)-2f (1.1
U mg-1). After 4 to 6 h reaction with 50 mM (S)-2a-f, the
conversion of amino alcohols can reach 99% (Figure S9-S14).
Therefore, MVTA was selected as a promising enzyme for
catalyzing the amino transfer step in our designed
chemoenzymatic transformation system. In the third step of the
chemoenzymatic transformation, the carbonyl reductase was
then selected for the bioreduction of corresponding α-hydroxy
ketones to chiral vicinal 1,2-diols. Previously, BDHA from
Bacillus subtilis and GoSCR from Gluconobacter oxydans were
discovered with excellent activity and enantioselectivity toward
the 2-hydroxy acetophenone.10f Herein, the substrate specificity
and enantioselectivity of the two carbonyl reductases were
further tested with extended substrates spectrum. As shown in
Table S4, BDHA exhibited high activity and excellent
enantioselectivity toward α-hydroxy ketones 3a–f. The highest
activities of BDHA were detected with 3d (2.10 U mg−1) and 3e
(2.11 U mg−1). Moderate activities of BDHA were detected with
3a-c (1.39-0.88 U mg−1). In addition, GoSCR showed relatively
low activities but excellent enantioselectivity toward α-hydroxy
ketones 3a–e (0.13 to 1.27 U mg−1) compared to BDHA.
However, no activity of GoSCR was detected toward 3f. Then,
BDHA and GoSCR were used to catalyze the carbonyl
asymmetric reduction step of the chemoenzymatic system.
Since both BDHA and GoSCR are NADH dependent carbonyl
reductases, in order to avoid the addition of expensive cofactors
(NADH), we developed an in situ cofactor regeneration system
(Scheme 1). Glucose dehydrogenase (GDH) from Bacillus
subtilis was coupled with the BDHA and GoSCR for cofactor
regeneration to recycle the NADH and simultaneously drive the
equilibrium towards the product. The GDH was co-expressed
with the two carbonyl reductases in E. coli cells, respectively,
and the recombinant E. coli cells was used to convert hydroxy
ketone 3 to diol 4. As shown in Table S4, (R)-vicinal 1,2-diols
4a-f were produced from 3a-f with lyophilized cells of E. coli
(BDHA-GDH). After 4 h reaction, the conversion reached 99%
with the product in >99% ee. (S)-vicinal 1,2-diols 4c-e were
produced in excellent ee values (>99%) from 3c-e via
asymmetric reduction with lyophilized cells of E. coli (GoSCR-
GDH). Finally, (S)-4a and (S)-4b were obtained in high ee (91%
for (S)-4a and 98% for (S)-4b) and 99% conversion.
Based on the aforementioned results, MVTA, BDHA, GoSCR
and GDH were selected as the appropriate enzymes for the new
chemoenzymatic catalytic system. The combination of the last
two steps into a simultaneous one pot style was conducted with
two modules (module 1: MVTA/BDHA/GDH and module 2:
MVTA/GoSCR/GDH) (Table 1) for the conversion of (S)-β-amino
alcohols to chiral diols. The enantioselective conversion of (S)-β-
amino alcohols (2a-f) (20-50 mM) to (R)-vicinal 1,2-diols (4a-f)
with the cell free extract of recombinant E. coli (MVTA) (2 U mL-
1), E. coli (BDHA) (10 U mL-1) and E. coli (GDH) (2 U mL-1)
reached to 99% with (R)-4a-f in >99% ee (Table 1, entry 1-6).
Additionally, the enantioselective conversion of (S)-β-amino
alcohols (2c-e) to (S)-vicinal 1,2-diols (4c-e) with the cell free
extract of E. coli (MVTA) (2 U mL-1), E. coli (GoSCR) (20 U mL-1)
and E. coli (GDH) (4 U mL-1) reached to 99% with the product
(S)-4c-e in >99% ee (Table 1, entry 9-11). For the substrates 2a
and 2b, the excellent conversions (99%) were obtained with the
product (S)-4a and (S)-4b in 91% and 98% ee (Table 1, entry 7-
8), respectively.
Table 1. One-pot conversion of (S)-amino alcohols (2a-f) to enantiopure
vicinal
diols
(4a-f)
via
transaminase/carbonyl
reductase/glucose
dehydrogenase cascade reaction
Entry
Sub.
Sub. [mM]
Module
Time
[h]
6
6
12
6
Conv.
[%][a]
99
99
99
99
99
99
99
99
99
99
99
ee of
[%][b]
4
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
50
20
50
50
50
50
20
20
50
50
50
1
1
1
1
1
1
2
2
2
2
2
>99(R)
>99(R)
>99(R)
>99(R)
>99(R)
>99(R)
91(S)
6
6
12
12
12
12
12
98(S)
9
10
11
>99(S)
>99(S)
>99(S)
Conditions: 5 mL sodium phosphate buffer (100 mM, pH 7.5), including
substrate (20–50 mM), sodium pyruvate (20-50 mM), NADH (0.002 mM), PLP
(0.1 mM) and glucose (20-50 mM) at 30oC. Module 1: MVTA (2 U mL-1)/BDHA
(10 U mL-1)/GDH (2 U mL-1), Module 2: MVTA (2 U mL-1)/GoSCR (20 U mL-
1)/GDH (4 U mL-1). [a] Conversion was determined by GC, error limit: <2% of
the state values. [b] ee value was determined by chiral GC.
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10.1002/cctc.201901189
ChemCatChem
COMMUNICATION
With the efficient three individual steps carboxyl reduction,
amino alcohol deamination, and α-hydroxy ketone asymmetric
reduction in hand, we next sought to combine the chemical
process with MVTA, BDHA or GoSCR and GDH biocatalysts in
a one-pot sequential style to directly convert L-α-amino acid 1 to
enantiopure vicinal 1,2-diol 4. As shown in Table 2, substrates
1a-f (1 mmol) possessing aliphatic and aromatic moieties were
converted to enantiopure vicinal 1,2-diols (R)-4a-f and (S)-4a-e
by the two different catalysis systems, (R)-vicinal 1,2-diols 4a−f
were produced in excellent ee values (>99%) and good
conversions (68.0-90.0%), and (S)-vicinal 1,2-diols 4c−e were
produced from L-α-amino acid 1c-e in excellent ee values
(>99%) and good conversions (71.0-89.0%). Moreover, (S)-4a−b
were obtained in 91% and 98% ee and 68.1% and 70.5%
conversion from L-α-amino acid 1a and 1b, respectively. These
results demonstrated the feasibility and efficiency of the
designed one-pot sequential process for production of
enantiopure vicinal (R)- or (S)-1,2-diols from L-α-amino acids.
successfully co-expressed in four different recombinant E. coli
BL21 (DE3) cells. The recombinant E. coli (MVTA-BDHA-GDH)
and E. coli (MVTA-GoSCR-GDH) cells showed the specific
activities of 88.3 U g-1 cdw and 93.4 U g-1 cdw toward 2e,
respectively, which is about two times higher than the E. coli
(MVTA-GDH-BDHA) (46.0 U g-1 cdw ) and E. coli (MVTA-GDH-
GoSCR) (51.7 U g-1 cdw) (Figure 1). Thus, E. coli (MVTA-BDHA-
GDH) and E. coli (MVTA-GoSCR-GDH) were selected as the
biocatalysts for further investigation. The growth and specific
activity of the two recombinant E. coli cells were monitored by
taking samples at different time points (Figure S2). E. coli
(MVTA-BDHA-GDH) cells showed the highest specific activity of
89.2 U g−1 cdw for the conversion of 2e to (R)-4e after growth for
18 h (Figure S2a). E. coli (MVTA-GoSCR-GDH) cells showed
the highest specific activity of 93.4 U g−1 cdw for the conversion
of 2e to (S)-4e after growth for 18 h (Figure S2b). The SDS-
PAGE analysis of the cell-free extracts of the E. coli cells
harvested at 6–22 h is shown in Figure S2c and S2d, and the
enzymes were clearly co-expressed in E. coli cells.
Table 2. Convert L-α-amino acids to chiral vicinal 1,2-diols with NaBH4-H2SO4
system combined with the cell free extract of E. coli (MVTA), E. coli (BDHA) or
E. coli (GoSCR) and E. coli (GDH)
Entry
Sub.
Time
[h]
16
16
16
16
16
16
24
24
24
24
24
Module
2 [%]
3 [%]
4
ee of
[%][b]
4
[%][a]
68.5
70.1
71.5
89.5
80.6
89.7
68.1
70.5
71.8
89.1
80.4
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1a
1b
1c
1d
1e
1
1
1
1
1
1
2
2
2
2
2
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
>99(R)
>99(R)
>99(R)
>99(R)
>99(R)
>99(R)
91(S)
98(S)
9
10
11
>99(S)
>99(S)
>99(S)
Figure 1. Activity of recombinant E. coli cells co-expressing of transaminase,
carbonyl reductase and glucose dehydrogenase for convert 2e to 4e. E. coli
(pMGB): E. coli (MVTA-GDH-BDHA); E. coli (pMBG): E. coli (MVTA-BDHA-
GDH); E. coli (pMGGo): E. coli (MVTA-GDH-GoSCR); E. coli (pMGoG): E. coli
(MVTA-GoSCR-GDH)
Conditions: substrate (1 mmol), sodium pyruvate (75 mM), NADH (0.003 mM),
PLP (0.15 mM) and glucose (75 mM), 30oC. Module 1: MVTA (2 U mL-
1)/BDHA (10 U mL-1)/GDH (2 U mL-1), Module 2: MVTA (2 U mL-1)/GoSCR (20
U mL-1)/GDH (4 U mL-1). For details, see the ESI Experimental section. [a]
Conversion was determined by GC, error limit: <2% of the state values. [b] ee
value was determined by chiral GC.
The success of the designed one-pot reaction system
encouraged us to further simplify the process for practical
applications. We reasoned that the recombinant E. coli strains
which co-express all necessary enzymes used for the second
and third step of the catalytic system can avoid cultivation of
multiple strains. Moreover, intact cells can help to maintain
enzyme stability, and additionally, the cofactor NAD+/NADH in
cells can be used for target reaction with cofactor recycling.
Consequently, recombinant E. coli strains co-expressing of the
three different enzymes were constructed. In order to balance
the enzyme expression in E. coli strain, different plasmids and
plasmids combination styles were investigated. Four different
recombinant E. coli cells (E. coli (MVTA-BDHA-GDH), E. coli
(MVTA-GDH-BDHA), E. coli (MVTA-GoSCR-GDH) and E. coli
(MVTA-GDH-GoSCR)) which can co-express three different
enzymes (transaminase, carbonyl reductase and GDH) were
constructed. As shown in Figure S1, all the enzymes were
Then, the chemical reduction process combined with the
resting cells of recombinant E. coli (MVTA-BDHA-GDH) or E.
coli (MVTA-GoSCR-GDH) co-expressing of the three enzymes
was employed for the conversion of aliphatic amino acids 1a–d
(1 mmol) and aromatic amino acids 1e-f (1 mmol) to chiral vicinal
1,2-diols 4a-f. As shown in Table 3, L-α-amino acids 1a, 1b and
1c were converted to (R)-4a, (R)-4b and (R)-4c in excellent ee
(>99%) and good conversion (69.0-72.0%) by the combined
NaBH4-H2SO4 and E. coli (MVTA-BDHA-GDH) resting cell (10 g
cdw L-1) system. (R)-4e was obtained in high ee (>99%) and
81% conversion. (R)-4d and (R)-4f were produced from L-α-
amino acid 1d and 1f in >99% ee and 90% conversion.
Meanwhile, to produce (S)-vicinal diols, the NaBH4-H2SO4
system combined with E. coli (MVTA–GoSCR–GDH) resting cell
(15 g cdw L-1) was used, and (S)-4a and (S)-4b were obtained in
91% and 98% ee and 69% and 71% conversion, respectively.
(S)-4c could be obtained in >99% ee and 72% conversion. (S)-
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10.1002/cctc.201901189
ChemCatChem
COMMUNICATION
1d and (S)-1e were obtained in good conversion (81% and 90%)
and excellent ee value (>99%) (Figure S15-S26). In the whole
catalytic process, no intermediates (amino alcohol and α-
hydroxy ketone) were detected in the final reaction mixtures.
These results showed that the intermediates produced in the
first and second step were quickly converted to vicinal 1,2-diol 4
by the transaminase and carbonyl reductase.
In summary, a combined chemical and biocatalytic process
for the transformation of L-α-amino acids into useful and
valuable enantioenriched vicinal 1,2-diols was developed in high
ee via amino acid carboxyl reduction, amino alcohol deamination
and α-hydroxy ketone asymmetric reduction. Combining
a
simple chemical reduction process (NaBH4-H2SO4 system) with
a three-enzyme (transaminase, alcohol dehydrogenase and
glucose dehydrogenase) cascade biocatalysis system, we
Table 3. Convert L-α-amino acids to chiral vicinal 1,2-diols with NaBH4-H2SO4
system combined with E. coli (MVTA-BDHA-GDH) (Catalyst 1) or E. coli
(MVTA-GoSCR-GDH) (Catalyst 2)
implemented
a one-pot three step sequential process in
aqueous medium to convert L-α-amino acids 1a-f to the
corresponding (R)-1,2-diols 4a-f and (S)-1,2-diols 4a-e in 91-
>99% ee and 68.0-90.0% conversion in the presence of trace
amount of NADH, Chemical reduction processing combined with
whole-cell based cascade biocatalysis was also achieved by
using the engineered recombinant E. coli cells without additional
NADH cofactor, and the produced (R)- and (S)-1,2-diols were
obtained in good conversion (69-90%) and excellent ee values
(91->99%). Preparative transformations were also demonstrated
with combined two different reaction systems, product (R)-4d-f
and (S)-4d-e were obtained in excellent ee (>99%) and good
isolated yields (70-80%). The current research provided a first
example for practical preparation of chiral vicinal 1,2-diols from
L-α-amino acids, and highlights the exciting opportunities
available for the syntheses of high valuable chiral compounds
from renewable feedstocks via combined chemical and
biocatalytic process.
Sub.
Time
(h)
Catal.
1
Catal.
2
2
[%]
3
[%]
4
[%][a]
ee of 4
[%][b]
[g cdw L-
[g cdw L-
1
1
]
]
1a
1b
1c
1d
1e
1f
1a
1b
1c
1d
1e
16
16
16
16
16
16
24
24
24
24
24
10
10
10
10
10
10
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
69.5
71.2
72.0
90.0
81.0
90.0
69.5
71.0
72.0
90.0
81.0
>99(R)
>99(R)
>99(R)
>99(R)
>99(R)
>99(R)
91(S)
15
15
15
15
15
98(S)
>99(S)
>99(S)
>99(S)
Conditions: substrate (1 mmol), sodium pyruvate (75 mM), PLP (0.15 mM)
and glucose (75 mM) at 30oC. Catalyst 1: E. coli (MVTA-BDHA-GDH) (10
g cdw L-1), Catalyst 2 E. coli (MVTA-GoSCR-GDH) (15 g cdw L-1). For
details, see the ESI Experimental section. [a] Conversion was determined
by GC, error limit: <2% of the state values. [b] ee value was determined by
chiral GC.
To further demonstrate the synthetic potential of this new
chemoenzymatic transformation system for the conversion of L-
α-amino acids to enantiopure vicinal 1,2-diols via NaBH4-H2SO4
system combined with the resting cells of E. coli (MVTA-BDHA-
GDH) (Catalyst 1) and E. coli (MVTA-GoSCR-GDH) (Catalyst 2).
A 50 mL scale preparative experiment was conducted with the
substrates 1d-f (2 mmol). As summarized in Table 4, after 16 to
24 h of reaction, all 5 useful and valuable vicinal 1,2-diols ((R)-
4d-f and (S)-4d-e) were prepared in excellent ee (>99%) and
good isolated yields (70.0-80.0%) after extraction with ethyl
acetate and flash chromatography (Figure S27-S28). These
examples demonstrated the convenient and highly efficient
application of this new type of chemoenzymatic catalysis system
for one-pot consecutive transformation of L-α-amino acids to
(R)- and (S)-vicinal 1, 2-diols in high yields.
Experimental Section
General procedure for the transformation of L-α-amino acids into
enantiopure (R)- and (S)-vicinal 1,2-diols
NaBH4 (0.2 g, 5 mmol) in THF (10 mL) was added in a 100 mL round-
bottom flask, the suspension was stirred under the condition that the
flask was immersed in an ice-water bath, L-α-amino acids (1 mmol) were
then added in the flask, a solution of conc. H2SO4 (0.132 mL) in ether
(total volume of 0.4 mL) was added dropwise at such a rate as to
maintain the reaction mixture below 20°C, then stirring of the reaction
mixture at 25oC for 6 h. Methanol (0.4 mL) was added carefully to destroy
excess BH3, and the mixture was basified with 5 N NaOH to pH10 and
stirred for 1 h. Then, the mixture was concentrated by evaporation (final
volume was 5 mL) and heated at 70oC for 4 h, cooled and neutralized
with 2 N HCl to pH7.5, then, sodium phosphate buffer (pH 7.5, 100 mM)
containing 100 mM sodium pyruvate, 100 mM glucose, and 0.2 mM PLP
was added (total volume of 20 mL) to work at a final substrate (2a-f)
concentration of 20-50 mM. The reactions were started by the addition of
the lyophilized resting cells of E. coli (MVTA-BDHA-GDH) (10 g CDW L-1)
or E. coli (MVTA-GoSCR-GDH) (15 g CDW L-1) at 30oC. The mixtures
were shaken at 250 rpm and 30oC for 6 to 12 h. Samples (0.3 mL) were
saturated with NaCl and extracted with 0.3 mL ethyl acetate containing
20 mM n-dodecane as an internal standard. The organic phase was
collected and dried over anhydrous Na2SO4. After filtration, the samples
were subjected to GC analysis.
Table 4. Preparation of (R)-4d-f and (S)-4d-e from 1d-f with NaBH4-H2SO4
system combined with E. coli (MVTA-BDHA-GDH) (Catalyst 1) or E. coli
(MVTA-GoSCR-GDH) (Catalyst 2)[a]
Sub.
Sub.
[mg]
Time
[h]
Catal. 1
[g cdw
L-1]
Catal. 2
[g cdw
L-1]
Prod.
[mg]
Yield
[%]
Prod. ee
[%][b]
1d
1e
1f
1d
1e
298
302
330
298
302
16
16
16
24
24
10
10
10
204
216
244
191
207
75.0
78.0
80.0
70.0
75.0
>99(R)
>99(R)
>99(R)
>99(S)
>99(S)
15
15
[a] Standard conditions: substrate (2 mmol), sodium pyruvate (90 mM), PLP
(0.18 mM) and glucose (90 mM), 250 rpm at 30oC. Catalyst 1: E. coli (MVTA-
BDHA-GDH) (10 g cdw L-1), Catalyst 2: E. coli (MVTA-GoSCR-GDH) (15 g
cdw L-1). For details, see the ESI Experimental section. [b] ee value was
determined by chiral GC.
Acknowledgements ((optional))
This study was financially supported by the National Natural
Science Foundation of China (Grant No. 21772141), the Shanxi
Province Science Foundation for Youths (grant No.
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Entry for the Table of Contents (Please choose one layout)
Layout 2:
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Jian-Dong Zhang*, Jian-Wei Zhao, Li-Li
Gao, Jing Zhao, Hong-Hong Chang,
Wen-Long Wei
Page No. – Page No.
One-Pot Three-Step Consecutive
Transformation of L-α-Amino Acids to
(R)- and (S)-Vicinal 1,2-Diols via
Combined Chemical and Biocatalytic
Process
A combined chemical and biocatalytic process for the transformation of L-α-amino
acids into useful and valuable enantioenriched vicinal 1,2-diols was developed in
high ee via amino acid carboxyl reduction, amino alcohol deamination and α-
hydroxy ketone asymmetric reduction.
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