Ionic-surfactant-coated subtilisin: Activity, enantioselectivity, and application to dynamic kinetic resolution of secondary alcohols

Article abstract of DOI:10.1039/c7ob02181j

In this work, we explored the utility of ionic-surfactant-coated Bacillus licheniformis subtilisin (ISCBLS) as the catalyst for the dynamic kinetic resolution of secondary alcohols. ISCBLS was prepared by freeze-drying Bacillus licheniformis subtilisin wi

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COMMUNICATION
Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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Ionic-Surfactant-Coated Subtilisin: Activity, Enantioselectivity, and
Application to Dynamic Kinetic Resolution of Secondary Alcohols†
Received 00th
January 20xx,
Kyungwoo Kim,a Eungyeong Lee,a Cheolwoo Kim,a Jaiwook Park*a and Mahn-Joo Kim*a
In this work, we explored the utility of ionic-surfactant-coated Bacillus licheniformis subtilisin (ISCBLS) as the catalyst
for the dynamic kinetic resolution of secondary alcohols. ISCBLS was prepared by freeze-drying Bacillus licheniformis
subtilisin with both ionic surfactant 1 and dextrin. ISCBCL displayed 9300-fold enhanced activity relative to its native
counterpart in the transesterficaion of N-acetyl phenylalanine ethyl ester with 1-propanol in hexane and 12800-fold
enhanced activity in the transesterification of trifluoroethyl butyrate with 1-phenylethanol in THF. The enantioselecivty of
ISCBLS was examined with 50 secondary alcohols as the substrates for kinetic resolution in the presence of trifluoroethyl
butyrate. ISCBLS displayed synthetically useful enantioselecivity for most of secondary alcohols tested. The
enantioselectivity of ISCBLS was in particular good to high for m- or p-substituted 1-phenylethanols. The DKRs of these
secondary alcohols by the combination of ISCBLS and a ruthenium-based racemization catalyst provided the products of
(S)-configuration with good results (80-94% yield, 90-99% ee). It is concluded that ISCBLS is of great use as the
enantiocomplementary counterpart of (R)-selective lipase for the dynamic kinetic resolution of secondary alcohols.
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Introduction
Dynamic kinetic resolution (DKR) of racemic substrates
provides a powerful methodology for the preparation of
enantio-enriched compounds.1 DKR can provide single
enantiomeric products with high yields approaching 100%,
which is not possible for the classical kinetic resolution (KR).
Over the past two decades, we and others have explored an
approach employing an enzyme together with a metal-based
racemization catalyst for the efficient DKR. Thus, several useful
procedures have been developed, in particular, for the DKR of
secondary alcohols.2,3 These procedures require a pair of
enantio-complementary enzymes for the (R)- and (S)-selective
DKR (Scheme 1). Lipases have been the enzymes of choice for
the (R)-selective DKR of simple alkyl aryl carbinols. Among
commercially available lipases, the lipase B from Candida
antarctica (CAL-B) in the immobilized forms (brand name,
Novozym 435) has been most frequently employed for the (R)-
selective DKR owing to its good activity and excellent stability
in organic solvent.2 CAL-B, however, has been known to have
rather narrow substrate specificity. It displays satisfactory
activity toward secondary alcohols carrying at least a small
substituent at the hydroxymethine center. We recently
reported that ionic-surfactant-coated Burkholderia cepacia
lipase (ISCBCL) was highly active in organic solvent and
Scheme 1 Dynamic kinetic resolution of alkyl aryl carbinols with
lipase-metal or subtilisin-metal combination and the structure of
ionic surfactant 1 for the coating and activation of lipase and
subtilisin
displayed broader substrate specificity with excellent
enantioselectivity.4 ISCBCL was applicable to the (R)-selective
DKR of a wider range of secondary alcohols including those
carrying two bulky substituents at the hydroxymethine
center.5 These results encouraged us to explore the utility of
a Department of Chemistry, Pohang University of Science and Technology, 77
Cheongam-ro, Pohang 37673, Republic of Korea.
† Electronic Supplementary Information (ESI) available: NMR spectra and HPLC
chromatogram of DKR products. See DOI: 10.1039/x0xx00000x
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ionic-surfactant-coated Bacillus licheniformis subtilisin (ISCBLS)
as the counterpart of ISCBCL for the (S)-selective DKR. We
herein wish to report a full account of this work including the
activity, enantioselectivity, and substrate scope of ISCBLS.
Table
1
Activity of subtilisin in the presence of ionic
surfactant and/or dextrin in the transesterification of APEE
with 1-propanol in hexanea
W
e previously communicated the results from the study on
the DKR of secondary alcohols with subtilisin.6 In the previous
work, we used subtilisin treated with nonionic surfactant such
as Brij for enhancing its activity in organic solvent. The DKR
with Brij-treated subtilisin, however, was rather sluggish, thus
limiting its wider applications. In the present work, it was
found that the DKR with ISCBLS was faster and applicable to a
wider range of secondary alcohols.
Weight ratio Content
of BLS, 1,
of
Time
(h)
Conversion
(%)c
Entry
and dextrinb enzyme
(%, w/w)
1
2
3
4
5
6
7
8
9
1 : 1 : 1
1 : 2 : 1
1 : 3 : 1
1 : 1 : 2
1 : 2 : 2
1 : 3 : 2
1 : 1 : 3
1 : 2 : 3
1 : 3 : 3
1 : 3 : 3
1 : 3 : 0
1 : 4.5 : 4.5
1 : 9.5 : 9.5
33
25
20
25
20
17
20
17
14
14
25
10
5
4
4
4
4
4
4
4
4
4
3
3
3
3
57
79
81
47
78
84
36
81
90
84
80
91
98
Results and discussion
Activity of ISCBLS. Commercially available BLS was freeze-dried
with ionic surfactant 14a or both
1
and dextrin (D) to obtain
several ISCBLS preparations. The weight ratios between BLS,
1,
and D varied from 1 : 1 : 1 (the content of enzyme, 33%, w/w)
to 1 : 9.5 : 9.5 (the content of enzyme, 5%, w/w). Here we used
dextrin in order to enhance the powdery nature of enzyme
preparations for better handling. The enzymatic activity of
each BLS preparation was measured with the
transesterification of N-acetyl phenylalanine ethyl ester (APEE)
with 1-propanol in hexane at 25 °C.
10
11
12
13
a
The reactions were performed in hexane (1mL) containing
APEE (10 mM), 1-PrOH (0.85 mM) and ISCBLS (3-20 mg) at 25°C.
b
c
The amount of BLS was fixed to 1 mg. Measured by gas
chromatography.
It was found that the activity of BLS increased significantly
with increasing the amount of ionic surfactant relative to that
of BLS (compare entries 1-3, 4-6, 7-9, Table 1). On the other
hand, the activity of BLS decreased with increasing the amount
of dextrin in case that the amounts of BLS and ionic surfactant
were equal (compare entries 1, 4, and 7). The effect of dextrin
on the activity of BLS, however, was negligibly small if the
amount of ionic surfactant was two or three times greater
than that of BLS (compare entries 2, 5, and 8 and also compare
entries 10 and 11). And the activity of BLS increased gradually
with increasing the amounts of both ionic surfactant and
dextrin relative to that of BLS (compare entries 1, 5, 9, 10, 12,
and 13). This implies that the activity of BLS could reach the
almost maximum level if both ionic surfactant and dextrin are
present in extremely large amounts relative to BLS.
Table
2 The kinetic parameters of commercial and ionic
surfactant-coated subtilisin in the transesterification of APEE
with 1-propanol in hexanea
b
kcat
(s-1)
Km
kcat/Km
(s-1/M)
4.50 x 10-3
Entry
1
Subtilisin
(mM)
BLSc
3.52 x 10-4
7.82 x 10
5% (w/w)
ISCBLSd
2
6.63 x 10-1
1.59 x 10
4.18 x 10
3
2.26 x 10-1
7.40
3.07 x 10
25% (w/w)
ISCBLSe
a The Vmax and Km values were obtained from non-linear curve fit
of initial rates. b Each kcat was calculated using the equation Vmax
= kcat[E]0, where [E]0 is the total moles L-1 of enzyme (MW
27,400) suspended in the solution. c Commercial subtilisin. d The
weight ratio of BLS, 1, and dextrin = 1 : 9.5 : 9.5. e The weight
ratio of BLS, 1, and dextrin = 1 : 2 : 1.
The kinetic parameters of native and ionic surfactant-
coated BLS are described in Table 2. The data from Table 2
clearly indicate that the activity of BLS in organic solvent was
enhanced dramatically in the presence of ionic surfactant. The
5% (w/w) ISCBLS containing 5% of BLS, 47.5% (w/w) of 1, and
47.5% (w/w) of dextrin was 9300-fold more active than its
native counterpart. Such a high activity of 5% (w/w) ISCBLS
was the result from a large increase of kcat and a significant
decrease of Km. This suggests that ionic surfactant-coated
enzyme exists in the highly active form with more readily
accessible active site. Thus we guess that ionic surfactant
protected the enzyme against deactivation by the unfavorable
conformational changes and aggregation during the freeze-
drying process. In addition, ionic surfactant together with
dextrin could provide water-mimicking hydrogen bonding
network around the enzyme for more efficient catalysis in
organic solvent.
As the ISCBLS for the KR and DKR of secondary alcohols,
however, we chose 25% (w/w) ISCBLS containing 25% (w/w)
BLS, 50% (w/w) 1, and 25% (w/w) dextrin because this BLS
preparation displayed the highest activity per mg of ISCBLS
among those tested. The specific activity of 25% (w/w) ISCBCL
was 3.6 times greater than that of 5% (w/w) ISCBCL although
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Chart I The E values of ISCBLS for secondary alcohols.a
A
B
OH
OH
O
S
3
28
48
2f
2a
OH
OH
16
2g
OH
2b
OH
8
27
N
2h
2c
2d
OH
OH
OH
O
120
180
69
2i
S
OH
>200
2j
2e
C
D
E
F
OH
OH
200
116
32
4
7e
7a
OH
OH
CN
7f
7b
OH
OH
OH
3
>200
26
7g
7c
7d
a The E values were calculated using the equation: E = ln[1 - c(1 + eep)/ln[1 - c(1 - eep) where c = ees/(ees + eep).
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the activity per mg of BLS of the former was lower by 27% than enantioselectivity was observed if the polar side chain was replaced
that of the latter (compare entries 2 and 3, Table 2).
by a small alkyl ring (5e-h). The enantioselectivity was fairly good
(E = 22-71) for 1-phenyl-2-propanol (6a, Chart I-E) and its
Enantioselectivity of ISCBLS. The enantioselectivity of ISCBLS was
derivatives (6b
was high (E = >100) for 4-phenyl-2-butanol (7a, Chart I-F) and
its unsaturated analogs 7b ). In contrast to this, the
enantioselectivity for the corresponding propargyl alcohol (7d
-f). It is noteworthy that the enantioselectivity
examined
by
performing
the
ISCBLS-catalyzed
transesterification of each racemic secondary alcohol with
trifluoroethyl butyrate (TFEB) (Scheme 2). First of all, we
determined the activity and enantioselectivity of ISCBLS for 1-
phenylethanol (2a) as a standard secondary alcohol. The
activity of ISCBLS was measured as the initial rate for the
ISCBLS-catalyzed transesterification of 1-phenylethanol (0.1 M)
with trifluoroethyl butyrate (TFEB, 0.2 M) in THF at 25 °C. It was
found that the activity of ISCBLS was 94.2 U (µmol h
-1mg-1),
which was 12800-fold greater than that of its ionic surfactant-
free counterpart in the same reaction. On the other hand, the
enantioselectivity was determined as the E value using the
(
,c
)
was modest (E = 26). In case that the smaller side chain of
secondary alcohol is unsaturated, the enantioselectivity was
good (E = 32) for vinyl (7e) but low (E = 3-4) for substituted
vinyl (7f) and ethynyl (7g). Overall, 42 out of 50 secondary
alcohols tested were accepted by ISCBLS with synthetically
useful enantioselectivity (E = 20 or larger), thus proving that
ISCBLS is useful as the enzyme for the KR and DKR of a wider
range of secondary alcohols.
equation: E = ln[1 - c(1 + eep)/ln[1 - c(1 - eep) where c = ees/(ees Dynamic kinetic resolution of secondary alcohols with ISCBLS.
+ eep).7 The E value for 1-phenylethanol was 28, thus indicating First, we explored the DKR of 1-phenylethanol as the standard
that ISCBLS displayed rather modest but synthetically useful procedure. The DKR of 1-phenylethanol was carried out with a
enantioselectivity for 1-phenylethanol.
solution containing substrate (0.3 mmol), 25% (w/w) ISCBLS
(20 mg/mmol of substrate), ruthenium complex 82m (4 mol%),
TFEB (0.45 mmol), and K2CO3 (0.3 mmol) in THF at 25 oC
(Scheme 3). It proceeded smoothly to provide satisfactory
results (9 h, 95% isolated yield, 90% ee). We thus achieved the
fastest (S)-selective DKR of 1-phenylethanol.
Scheme 2 Kinetic resolution of 1-phenylethanol
Scheme 3 Dynamic kinetic resolution of 1-phenylethanol
Next, we determined the E values of ISCBLS for 9 different 1-
(hetero)arylethanols. The E values are described with that for
1-phenylethanol in Chart I. The E values were high (E = > 100) if
the (hetero)aryl group at the stereocenter was larger than
phenyl (2d, 2e, and 2j, Chart I-A) and significantly lower (E =
<20) toward if the (hetero)aryl group at the stereocenter was
Next, we carried out the DKRs of 27 additional secondary
smaller than phenyl (2f and 2g). These results thus suggest alcohols, most of which were accepted by ISCBLS with high
that ISCBLS displays high enantioselectivity for secondary enantioselectivity (E = >100). The results are described in Table
alcohols carrying a small alkyl and a large aryl substituent at 7. The DKR of 1-(1-naphthyl)ethanol proceeded rather slowly
the hydroxymethine center.
and thus required more enzyme and longer time (entry 1). The
DKR of 1-(2-naphthyl)ethanol was relatively faster so that it
was completed in shorter time with less enzyme (entry 2).
Both DKRs provided good yields and high enantiopurities. The
DKRs of 1-(2-benzofuryl)- and 1-(2-thiophenyl)ethanol
proceeded more rapidly than those DKRs and provided good
yields and high enantiopurities (entries 3 and 4).
The E values from Chart I-B indicate that ISCBLS is highly
enantioselective (E
phenylethanols 3a
=
>100) toward m-substituted 1-
(
-h
,
Chart I-B). ISCBLS is also highly
enantioselective (E = 62->200) for some of their p-substituted
counterparts (4a , Chart I-C). These results thus indicate
-c,e-h
that ISCBLS display significantly higher enantioselectivity if the
aromatic ring of 1-phenylethanol becomes sterically bulkier by
the presence of a m- or p-substituent.
The DKRs of m-substituted 1-phenylethanols proceeded
rather slowly relative to that of 1-phenylethanol and thus took
12-72 h for completion (entries 5-12). If the m-substituent of
substrate was sterically bulky, the corresponding DKR reaction
required significantly more enzyme and longer time (entries 9,
11, 12). The yields were good and the enantiopurities were
high. On the other hand, the DKRs of p-substituted 1-
phenylethanols in general were faster than those of their m-
substituted counterparts and provided good yields and high
enantiopurities in most cases (entries 13-20). As expected, the
DKRs of those with a bulky p-substituent required relatively
longer times (entries 17, 19, 20).
It is also notable that the E value was high (E = >200) for p-
Bpin-substituted 1-phenyl-1-propanol
(4j) but significantly
lower (E = 6) for p-Bpin-substituted 1-phenyl-1-butanol (4k).
These results thus suggest that alkyl aryl carbinols should carry
a small side chain (C1~C2) to be accepted by ISCBLS with high
enantioselectivity.
The enantioselectivity of ISCBLS was rather modest (E = 15-27)
for the derivatives of 1-phenylethanol with a polar substituent (Cl,
CN, and N3) on the side chain (5a-c, Chart I-D). Surprisingly, the high
4 | J. Name., 2012, 00, 1-3
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Table 3 DKR of secondary alcohols with ISCBLSa
Ph
Ru
Ph
Ph
NHiPr
Ph
OCOPr
OH
8
9
ISCBLS, or
R1 R2
R1 R2
TFEB, K2CO3, THF
25 o
Cl
OC
CO
2-7
C
2-7-Bu
9
ISCBLS
(mg/mmol)
80
Time
(h)
48
24
24
12
24
12
24
24
48
24
24
72
12
12
12
12
24
12
18
40
24
24
24
48
48
72
48
Yieldb
Eec
(%)
95
98
92
98
95
97
97
94
97
97
92
97
99
98
96
90
99
95
98
>99
96
97
91
92
98
90
>99
Entry
R1
R2
(%)
89
91
83
85
90
87
84
84
80
86
80
80
94
84
86
85
84
90
85
77
95
96
86
85
81
92
70
1
2
3
4
5
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
1-naphthyl
2-naphthyl
benzofuryl
benzothiophenyl
Ph-m-Cl
2d
2e
2i
40
30
30
40
30
40
30
80
15
80
80
20
40
40
20
40
20
40
40
30
30
40
40
80
2j
3a
3b
3c
3d
3e
3f
3g
3h
4a
4b
4c
4d
4e
4f
4g
4h
7b
7c
2b
4i
6
Ph-m-Br
7
Ph-m-NO2
Ph-m-OMe
Ph-m-Bpin
Ph-m-Me
Ph-m-Ph
8d
9
10d
11
12
13
14
15
16
17
18
19
20
21e
22e
23
24d
25f
26f
27f
Ph-m-C=CTMS
Ph-p-Cl
Ph-p-Br
Ph-p-NO2
Ph-p-OMe
Ph-p-Bpin
Ph-p-Me
Ph-p-Ph
Ph-p-C=CTMS
CH=CHPh (cis)
CH=CHPh (trans)
Ph
Et
Et
ClCH2
cPr
Ph-p-Br
Ph-p-Bpin
2-naphthyl
Ph
4j
5d
5e
40
15
a The reactions were performed with solutions containing substrate (0.3 mmol), ISCBLS (15-80 mg/mmol of substrate), 8 (4 mol%), TFEB
b
c
d
e
(0.45 mmol), and K2CO3 (0.3 mmol) in THF at 25 oC. Isolated yield. Determined by HPLC. 5 mol% of 8. The reactions were
performed with solutions containing substrate (0.3 mmol), ISCBLS (20-30 mg/mmol of substrate), 92d (5 mol%), TFEB (0.45 mmol),
Na2CO3 (0.3 mmol) and t-BuOK (6 mol%) in THF at 25 oC. f 8 mol% of 8.
The DKRs of cis- and trans-4-phenyl-3-buten-2-ol greater). The optical rotations of products from the ISCBLS-
proceeded smoothly and provided the best yields with high catalyzed DKRs of 2a, 2b, and 4d were opposite to those of the
enantiopurities (entries 21 and 22). The DKRs of 1- (R)-products from the corresponding lipase-catalyzed DKRs
phenylpropanol and p-substituted derivatives were relatively reported previously.8 Furthermore, the products from the
slower but provided satisfactory yields and enantiopurities ISCBLS-catalyzed DKRs displayed the opposite retention time
(entries 23-25). The DKR of chloromethyl(naphthyl)methanol patterns to those from the ISCBCL-catalyzed DKRs in the HPLC
was rather sluggish because both ISCBLS-catalyzed resolution analysis using the same chiral column. Thus, these
and Ru-catalyzed racemization were slow (entry 26). Finally, observations support that the ISCBLS-catalyzed DKRs provide
the DKR of cyclopropyl(phenyl)methanol was performed with the products of configuration shown in the equation of Table 3
the smallest amount of enzyme to achieve high enantiopurity and the stereochemistry of all the products except 5d-bu is S.
because the Ru-catalyzed racemization was quite slow relative As an illustrative example to show that the ISCBLS-catalyzed
to the ISCBLS-catalyzed resolution (entry 27).
DKR is straightforward on larger preparative scales, we
performed the DKR of 1-(2-naphthyl)ethanol (2e) on a gram-
scale (6 mmol), which provided the products of 96% ee in 84%
isolated yield.
Overall, the data from Table 3 indicate that all the DKR
reactions performed with ISCBLS provided satisfactory yields
(70-96%) and good to high enantiopurities (90-99% ee or
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Determination of the E values of ISCBLS for secondary
alcohols. As the representative procedure, the determination
of E value for 2a is described. 2,2,2-Trifluoroethyl butyrate (23
µL, 0.15 mmol) was added to a 4mL-vial containing 25% (w/w)
ISCBLS (2 mg), 2a (12 µL, 0.1 mmol) and anhydrous THF (200 µL,
0.5 M). The reaction mixture was shaken at 25 oC until the
reaction reached near 50% conversion. Then an aliquot was
sampled and the enantiomeric excesses of butyrate and
remaining alcohol were measured by HPLC equipped with
chiral column. The E value was then calculated from the
equation: E = ln [1 - c (1 + eep)] / ln [1- c (1 - eep)] where c = ees
/ (ees + eep).
Conclusions
We have developed ionic-surfactant-coated Bacillus
licheniformis subtilisin (ISCBLS) for the DKR of secondary
alcohols. ISCBLS was 4 orders of magnitude more active than
its native counterpart in organic solvent. Furthermore, ISCBLS
accepted
a wider range of secondary alcohols with
synthetically useful enantioselectivity. The DKR reactions of
these secondary alcohols employing ISCBLS were
straightforward and provided good results in most cases. We
thus have completed the development of a pair of procedures
employing ISCBCL and ISCBLS, respectively, for the (R)- and (S)-
selective DKR of secondary alcohols.
Dynamic kinetic resolution of secondary alcohols with ISCBLS
and ruthenium complex 8. As the representative procedure,
the DKR of 2a is described. Ru complex
8 (9.6 mg, 4 mol%),
K2CO3 (41.4 mg , 0.1 mmol) and 2a (36 µL, 0.3 mmol) were
added to a pear-shaped Schlenk-type flask with degassed THF
(600 µL, 0.5 M) under argon. The resulting mixture was stirred
Acknowledgements
This work was supported by the National Research
o
at 60 C for 30 min to activate ruthenium complex. Then the
Foundation
of
Korea
(project
numbers:
flask was cooled down to ambient temperature and 25% (w/w)
ISCBLS (6 mg) was added. 2,2,2-Trifluoroethyl butyrate (69 µL,
0.45 mmol) was added into the flask sequentially and the
2015R1D1A1A01059851 and 2015R1A2A2A01008130).
o
Experimental
reaction mixture was stirred at 25 C for 9h. The mixture was
diluted with methylene chloride, and filtered through a Celite
pad. The filtrate was concentrated and purified by column
chromatography (SiO2; hexane/diethyl ether 9:1) to give (S)-
butyrate product.
Preparation of ISCBLS. The preparation of 25% (w/w) ISCBLS is
described as the representative procedure. Commercially
available Bacillus licheniformis subtilisin (10 mg), ionic-
surfactant (
separately in deionized water (1 mL) to prepare three stock
solutions. Three aliquots (30-60 L) withdrawn from these
stock solutions were mixed to obtain an aqueous solution (120
L) containing subtilisin (0.3 mg), (0.6 mg), and dextrin (0.3
1
, 10 mg),4 and dextrin (10 mg) were dissolved
(S)-1-phenethyl butyrate ((S)-2a-Bu): 55 mg (95% yield, 90%
ee); [α]D19 = -82.8 (c = 1.0, CHCl3) [(S)-2a-Bu: lit.6a [α]D25 = -87.3
(c = 1.01, CHCl3, 92% ee); (R)-2a-Bu: lit.8 [α]D20 = +92.6 (c = 0.99,
CHCl3; 99% ee)]. The analytical data were in good agreement
with the literature values.6a
µ
µ
1
mg). The solution was then freeze-dried to obtain 25% (w/w)
(S)-1-phenylpropyl butyrate ((S)-2b-Bu): 53 mg (86% yield, 91%
ee); [α]D19 = -82.1 (c = 1.0, CHCl3) [(R)-2b-Bu: lit.8 [α]D20 = +92.1
(c = 1.01, CHCl3; >99% ee)]; 1H NMR (300 MHz, CDCl3, ppm): δ
7.36-7.26 (m, 5H), 5.68 (t, J = 6.8 Hz, 1H), 2.31 (t, J = 7.2 Hz, 2H),
ISCBLS (1.2 mg) in the powder form.
Determination of the kinetic parameters of subtilisin. The
kinetic parameters of BLS and ISBLS for the transesterification
of N-acetylphenylalanine ethyl ester were determined with
solutions containing BLS (10 mg) or 5% (w/w) ISCBLS (6 mg) or
25% (w/w) ISCBLS (1.2 mg), N-acetylphenylalanine ethyl ester
(2-10 mM), 1-propanol (0.85 M) in anhydrous hexane (1 mL).
The measurements of the initial rates were performed twice at
25 oC. In a typical procedure, the solution was shaken at 25oC.
An aliquot was sampled periodically and analyzed by HPLC to
determine the % conversion against time. The Vmax and Km
values were determined from the non-linear curve fit of the
average initial rates at four different concentrations. The kcat
values were calculated from the Vmax values.
1.97-1.76 (m, 2H), 1.69-1.57 (m, 2H), 0.95-0.86 (m, 3H+3H); 13
C
NMR (75 MHz, CDCl3, ppm): 173.0, 140.8, 128.3, 127.7, 126.5,
77.0 36.5, 29.4, 18.5, 13.7, 9.9; HPLC conditions: (R,R)-Whelk-
O1, n-hexane/2-propanol = 95/5, flow rate = 1.0 mL/mi n, UV =
217 nm; retention times: 4.60 min (S), 8.18 min (R); HRMS (EI):
m/z calcd. for [C13H18O2]+ 206.1307, found 206.1306.
(S)-1-(naphthalen-1-yl)ethyl butyrate ((S)-2d-Bu): 66mg (89%
yield, 96% ee); [α]D16 = -37.2 (c = 1.0, CHCl3); 1H NMR (300 MHz,
CDCl3, ppm): δ 8.09 (d, J = 8.1 Hz, 1H), 7.88-7.85 (m, 1H), 7.79
(d, J = 8.1 Hz, 1H), 7.60 (d, J = 6.9 Hz, 1H), 7.56-7.44 (m, 3H),
6.56 (q, J = 6.6 Hz, 1H), 2.41-2.30 (m, 2H), 1.74-1.59 (m,
2H+3H), 0.94 (t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3, ppm):
173.0, 137.6, 133.8, 130.3, 128.9, 128.4, 126.3, 125.6, 125.4,
123.2, 69.2, 36.6, 21.7, 18.5, 13.7; HPLC conditions: Chiralcel-
OD, n-hexane/2-propanol = 90/10, flow rate = 1.0 mL/min, UV
= 217 nm; retention times: 5.23 min (S), 6.06 min (R); HRMS
(EI): m/z calcd. for [C16H18O2]+ 242.1307, found 242.1307.
(S)-1-(naphthalen-2-yl)ethyl butyrate ((S)-2e-Bu): 66mg (91%
yield, 98% ee); [α]D16 = -97.1 (c = 1.0, CHCl3); 1H NMR (300 MHz,
CDCl3, ppm): δ 7.85-7.80 (m, 4H), 7.50-7.46 (m, 3H), 6.06 (q, J =
6.6 Hz, 1H), 2.34 (m, J = 7.3 Hz, 2H), 1.73-1.61 (m, 2H+3H), 0.94
Measurement of initial rates in the subtilisin-catalyzed
transesterification of 1-phenylethanol (2a). Initial rates were
measured with solutions containing 2a (0.1 M), 2,2,2-
trifluoroethyl butyrate (0.2 M), BLS (10 mg) or 25% (w/w)
ISCBLS (2 mg) in anhydrous THF (1 mL). In a typical procedure,
the solution was shaken at 25oC. An aliquot was sampled
periodically, filtered through
a short silica gel-pad, and
analyzed by HPLC to determine the conversion (%) against
time.
6 | J. Name., 2012, 00, 1-3
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ARTICLE
(t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3, ppm): 173.0, 139.2, flow rate = 1.0 mL/min, UV = 217 nm; retention times: 6.17
133.2, 133.0, 128.3, 128.0, 127.7, 126.2, 126.0, 125.0, 124.1 min (S), 9.72 min (R); LRMS (EI): m/z calcd. for [C18H20O2
72.1, 36.5, 22.3, 18.4, 13.6; HPLC conditions: Chiralcel-OD, n- OCOC3H7]+ 150, found 150.
–
hexane/2-propanol = 98/2, flow rate = 0.3 mL/min, UV = 217 (S)-1-(3-methoxyphenyl)ethyl butyrate ((S)-3d-Bu): 56 mg (84%
nm; retention times: 20.76 min (R), 22.54 min (R); HRMS (EI): yield, 94% ee); [α]D16 = -78.8 (c = 1.0, CHCl3); 1H NMR (300 MHz,
m/z calcd. for [C16H18O2]+ 242.1307, found 242.1305.
CDCl3, ppm): δ 7.29-7.24 (m, 1H), 6.95-6.89 (m, 2H), 6.84-6.80
(S)-1-(benzofuran-2-yl)ethyl butyrate ((S)-2i-Bu): 58 mg (83% (m, 1H), 5.86 (q, J = 6.6 Hz, 1H), 2.31 (t, J = 7.5, 2H), 1.72-1.58
24
1
yield, 92% ee); [α]D = -119.2 (c = 1.0, CHCl3); H NMR (300 (m, 2H), 1.52 (d, J = 6.6 Hz, 3H), 0.94 (t, J = 7.4 Hz, 3H); 13C
MHz, CDCl3, ppm): δ 7.54 (d, J = 7.7 Hz, 1H), 7.47 (d, J = 8.3 Hz, NMR (75 MHz, CDCl3, ppm): 172.9, 159.7, 143.5, 129.5, 118.3,
1H), 7.31-7.18 (m, 2H), 6.10 (q, J = 6.7 Hz, 1H), 2.33 (t, J = 7.4 113.0, 111.8, 71.9, 55.2, 36.5, 22.3, 18.5, 13.7; HPLC conditions:
Hz, 2H), 1.73-1.61 (m, 2H+3H), 0.94 (t, J = 7.4 Hz, 3H); 13C (R,R)-Whelk-O1, n-hexane/2-propanol = 90/10, flow rate = 1.0
NMR(75 MHz, CDCl3, ppm): 172.8, 156.2, 154.8, 127.9, 124.5, mL/min, UV = 217 nm; retention times: 5.24 min (S), 13.48 min
122.8, 121.2, 111.4, 104.1, 65.2, 36.3, 18.5, 18.4, 13.6; HPLC (R) ); HRMS (EI): m/z calcd. for [C13H18O3]+ 222.1256, found
conditions: (R,R)-Whelk-O1, n-hexane/2-propanol = 95/5, flow 222.1257.
rate = 1.0 mL/min, UV = 217 nm; retention times: 4.75 min (S), (S)-1-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-
6.52 min (R); HRMS (EI): m/z calcd. for [C14H16O3]+ 232.1099, ethyl butyrate ((S)-3e-Bu): 76 mg (81% yield, 98% ee); [α]D
23
=
found 232.1101.
(S)-1-(benzo[b]thiophen-2-yl)ethyl butyrate ((S)-2j-Bu): 63 mg 1H), 7.73 (d, J = 7.1 Hz, 1H), 7.45 (d, J = 7.5 Hz, 1H), 7.35 (t, J =
-56.4 (c = 1.0, CHCl3); 1H NMR (300 MHz, CDCl3, ppm): δ 7.78 (s,
24
1
(85% yield, 98% ee); [α]D = -150.2 (c = 1.0, CHCl3); H NMR 7.3 Hz, 1H) 5.90 (q, J = 6.5 Hz, 1H), 2.30 (t, J = 7.3 Hz, 2H), 1.71-
(300 MHz, CDCl3, ppm): δ 7.81-7.78 (m, 1H), 7.74-7.71 (m, 1H), 1.60 (m, 2H), 1.53 (d, J = 6.5 Hz, 3H), 1.34 (s, 12H), 0.92 (t, J =
7.36-7.28 (m, 2H), 7.25 (s, 1H), 6.24 (q, J = 6.6 Hz, 1H), 2.33 (t, J 7.3 Hz, 3H); 13C NMR (75 MHz, CDCl3, ppm): 172.9, 141.1,
= 7.4 Hz, 2H), 1.73-1.61 (m, 2H+3H), 0.94 (t, J = 7.4 Hz, 3H); 13
C
134.3, 132.4, 129.0, 127.9, 83.8, 72.1, 36.5, 24.9, 22.3, 18.4,
NMR(75 MHz, CDCl3, ppm): 172.8, 145.4, 139.4, 139.2, 124.4, 13.6; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2-propanol =
123.7, 122.4, 121.5, 67.9, 36.4, 22.0, 18.4, 13.7; HPLC 95/5, flow rate = 1.0 mL/min, UV = 217 nm; retention times:
conditions: (R,R)-Whelk-O1, n-hexane/2-propanol = 90/10, 5.04 min (S), 11.1 min (R); HRMS (EI): m/z calcd. for
flow rate = 1.0 mL/min, UV = 217 nm; retention times: 5.31 [C18H27BO4]+ 318.2006, found 318.2003.
min (S), 18.27 min (R); HRMS (EI): m/z calcd. for [C14H16O2S]+ (S)-1-m-tolylethyl butyrate ((S)-3f-Bu): 53 mg (86% yield, 97%
16
23
248.0871, found 248.0870.
ee); [α]D = -72.5 (c = 1.0, CHCl3) [lit.9a [α]D = -37.8 (c = 1.0,
(S)-1-(3-chlorophenyl)ethyl butyrate ((S)-3a-Bu): 61 mg (90% CHCl3, 85% ee)]; The analytical data were in good agreement
yield, 94% ee); [α]D16 = -74.1 (c = 1.0, CHCl3); 1H NMR (300 MHz, with the literature values.9a
CDCl3, ppm): δ 7.34 (s, 1H), 7.28-7.20 (m, 3H), 5.84 (q, J = 6.6 (S)-1-(3-phenylphenyl)ethyl butyrate ((S)-3g-Bu): 64 mg (80%
Hz, 1H), 2.32 (t, J = 7.5 Hz, 2H), 1.74-1.60 (m, 2H), 1.51 (d, J = yield, 92% ee); [α]D23 = -67.2 (c = 1.0, CHCl3); 1H NMR (300 MHz,
6.6 Hz, 3H), 0.94 (t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3, CDCl3, ppm): δ 7.58 (d, J = 7.7 Hz, 3H), 7.52-7.32 (m, 6H), 5.96
ppm): 172.8, 144.0, 134.4, 129.8, 127.9, 126.2, 124.2, 71.3, (q, J = 6.4 Hz, 1H), 2.32 (t, J = 7.3 Hz, 2H), 1.73-1.63 (m, 2H),
36.4, 22.3, 18.4, 13.6; HPLC conditions: (R,R)-Whelk-O1, n- 1.57 (d, J = 6.5 Hz, 3H), 0.94 (t, J = 7.3 Hz, 3H); 13C NMR (75
hexane/2-propanol = 95/5, flow rate = 1.0 mL/min, UV = 217 MHz, CDCl3, ppm): 172.9, 142.4, 141.5, 141.0, 128.9, 128.8,
nm; retention times: 4.21 min (S), 7.81 min (R); HRMS (EI): m/z 127.7, 127.4, 127.2, 126.7, 125.0, 72.0, 36.5, 22.4, 18.5, 13.7;
calcd. for [C12H15ClO2]+ 226.0761, found 226.0763.
HPLC conditions: (R,R)-Whelk-O1, n-hexane/2-propanol = 98/2,
(S)-1-(3-bromophenyl)ethyl butyrate ((S)-3b-Bu): 71 mg (87% flow rate = 1.0 mL/min, UV = 217 nm; retention times: 5.7 min
yield, 97% ee); [α]D18 = -95.4 (c = 1.0, CHCl3); 1H NMR (300 MHz, (S), 17.4 min (R); HRMS (EI): m/z calcd. for [C18H20O2]+
CDCl3, ppm): δ 7.49 (s, 1H), 7.30 (d, J = 7.5 Hz, 2H), 7.27-7.18 268.1463, found 268.1464.
(m, 2H), 5.83 (q, J = 6.4 Hz, 1H), 2.31 (t, J = 7.3 Hz, 2H), 1.72- (S)-1-(3-(2-(trimethylsilyl)ethylnyl)phenyl)ethyl butyrate ((S)-
23
1.59 (m, 2H), 1.50 (d, J = 6.5 Hz, 3H), 0.93 (t, J = 7.3 Hz, 3H); 13
C
3h-Bu): 69 mg (80% yield, 97% ee); [α]D = -72.5 (c = 1.0,
NMR (75 MHz, CDCl3, ppm): 172.8, 144.2, 130.9, 130.1, 129.1, CHCl3); 1H NMR (300 MHz, CDCl3, ppm): δ 7.47 (s, 1H), 7.41-
124.7, 122.6, 71.2, 36.4, 22.3, 18.4, 13.6; HPLC conditions: 7.38 (m, 1H), 7.30-7.26 (m, 2H), 5.86 (q, J = 6.5 Hz, 1H), 2.33 (t,
(R,R)-Whelk-O1, n-hexane/2-propanol = 95/5, flow rate = 1.0 J = 7.3 Hz, 2H), 1.73-1.60 (m, 2H), 1.52 (d, J = 6.5 Hz, 3H), 0.95
mL/min, UV = 217 nm; retention times: 4.05 min (S), 8.72 min (t, J = 7.3 Hz, 3H), 0.27 (s, 9H); 13C NMR (75 MHz, CDCl3, ppm):
(R); HRMS (EI): m/z calcd. for [C12H15BrO2]+ 270.0255, found 172.9, 142.1, 131.4, 129.7, 128.4, 126.4, 123.4, 104.9, 94.4,
270.0256.
71.6, 36.5, 22.2, 18.5, 13.7, 0.0; HPLC conditions: (R,R)-Whelk-
(S)-1-(3-nitrophenyl)ethyl butyrate ((S)-3c-Bu): 59 mg (84% O1, n-hexane/2-propanol = 95/5, flow rate = 1.0 mL/min, UV =
yield, 97% ee); [α]D16 = -68.3 (c = 1.0, CHCl3); 1H NMR (300 MHz, 217 nm; retention times: 4.2 min (S), 11.9 min (R); HRMS (EI):
CDCl3, ppm): δ 8.23 (m, 1H), 8.17-8.14 (m, 1H), 7.67 (d, J = 7.7, m/z calcd. for [C17H24O2Si]+ 288.1546, found 288.1549.
1H), 7.53 (t, J = 8.0, 1H), 5.95 (q, J = 6.6 Hz, 1H), 2.35 (t, J = 7.2, (S)-1-(4-chlorophenyl)ethyl butyrate ((S)-4a-Bu): 64 mg (94%
2H), 1.73-1.61 (m, 2H), 1.57 (d, J = 6.6 Hz, 3H), 0.94 (t, J = 7.4 yield, 99% ee); [α]D19 = -94.5 (c = 1.0, CHCl3) [lit.6a [α]D21 = -72.0
Hz, 3H); 13C NMR (75 MHz, CDCl3, ppm): 172.7, 144.1, 132.2, (c = 1.0, CHCl3, 92% ee)]; The analytical data were in good
129.5, 122.8, 120.9, 70.9, 36.3, 22.3, 18.4, 13.6; HPLC agreement with the literature values.6a
conditions: (R,R)-Whelk-O1, n-hexane/2-propanol = 90/10,
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(S)-1-(4-bromophenyl)ethyl butyrate ((S)-4b-Bu): 68 mg (84% (S)-1-(4-bromophenyl)propyl butyrate ((S)-4i-Bu): 73 mg (85%
16
yield, 98% ee); [α]D = -72.5 (c = 1.0, CHCl3) [lit.9a [α]D21 = -47.0 yield, 92% ee); [α]D20 = -70.8 (c = 1.0, CHCl3); 1H NMR (300 MHz,
(c = 1.0, CHCl3, 82% ee)]; The analytical data were in good CDCl3, ppm): δ 7.78 (d, J = 8.4 Hz, 2H), 7.19 (d, J = 8.4 Hz, 2H),
agreement with the literature values.9a
5.61 (t, J = 6.6 Hz, 1H), 2.31 (t, J = 8.0 Hz, 2H), 1.94-1.72 (m, 2H),
(S)-1-(4-nitrophenyl)ethyl butyrate ((S)-4c-Bu): 61 mg (86% 1.71-1.58 (m, 2H), 0.95-0.85 (m, 3H+3H); 13C NMR (75 MHz,
yield, 96% ee); [α]D16 = -76.1 (c = 1.0, CHCl3); 1H NMR (300 MHz, CDCl3, ppm): 172.9, 139.8, 131.5, 128.3, 121.6, 76.4, 36.4, 29.3,
CDCl3, ppm): δ 8.21 (d, J = 8.8 Hz, 2H), 7.51 (d, J = 8.5 Hz, 2H), 18.5, 13.7, 9.8; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2-
5.94 (q, J = 6.6 Hz, 1H), 2.37-2.32 (m, 2H), 1.73-1.61 (m, 2H), propanol = 95/5, flow rate = 1.0 mL/min, UV = 217 nm;
1.55 (d, J = 6.7 Hz, 3H), 0.94 (t, J = 7.4 Hz, 3H); 13C NMR (75 retention times: 4.21 min (S), 9.71 min (R); HRMS (EI): m/z
MHz, CDCl3, ppm): 172.7, 149.2, 126.7, 123.9, 71.0, 36.3, 22.3, calcd. for [C13H17BrO2]+ 284.0412, found 284.0412.
18.4, 13.6; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2- (S)-1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-
23
propanol = 90/10, flow rate = 1.0 mL/min, UV = 217 nm; propyl butyrate ((S)-4j-Bu): 80 mg (80% yield, 97% ee); [α]D
=
retention times: 5.92 min (S), 9.45 min (R); HRMS (EI): m/z -61.7 (c = 1.0, CHCl3); 1H NMR (300 MHz, CDCl3, ppm): δ 7.78 (d,
calcd. for [C12H15NO4]+ 237.1001, found 237.1003.
J = 7.6 Hz, 2H), 7.31 (d, J = 7.6 Hz, 2H), 5.67 (t, J = 6.6 Hz, 1H),
(S)-1-(4-methoxyphenyl)ethyl butyrate ((S)-4d-Bu): 57 mg (85% 2.31 (t, J = 7.3 Hz, 2H), 1.92-1.77 (m, 2H), 1.64 (m, 2H), 1.33 (s,
19
yield, 90% ee); [α]D = -94.5 (c = 1.0, CHCl3) [(S)-4d-Bu: lit.6a 12H), 0.89 (m, 3H+3H); 13C NMR (75 MHz, CDCl3, ppm): 176.0,
25
20
[α]D = -92.6 (c = 1.0, CHCl3, 94% ee); (R)-4d-Bu: (lit.8 [α]D
=
143.9, 134.9, 127.0, 125.8, 83.8, 36.5, 29.3, 24.9, 18.5, 13.7,
+106.4 (c = 1.00, CHCl3; >99% ee)]; The analytical data were in 9.8; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2-propanol =
good agreement with the literature values.6a
95/5, flow rate = 1.0 mL/min, UV = 217 nm; retention times:
(S)-1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)- 4.6 min (S), 11.6 min (R); HRMS (EI): m/z calcd. for [C19H29BO4]+
23
ethyl butyrate ((S)-4e-Bu): 80 mg (84% yield, 99% ee); [α]D
=
332.2162, found 332.2161.
-85.2 (c = 1.0, CHCl3); 1H NMR (300 MHz, CDCl3, ppm): δ 7.78 (d, (R)-2-chloro-1-(naphthalen-2-yl)ethyl butyrate ((R)-5d-Bu): 76
J = 7.6 Hz, 2H), 7.34 (d, J = 7.6 Hz, 2H), 5.88 (q, J = 6.4 Hz, 1H), mg (92% yield, 90% ee); [α]D26 = -63.6 (c = 1.0, CHCl3); H NMR
1
2.30 (t, J = 7.3 Hz, 2H), 1.68-1.59 (m, 2H), 1.51 (d, J = 6.5 Hz, (300 MHz, CDCl3, ppm): δ 7.87-7.84 (m, 4H), 7.52-7.44 (m, 3H),
3H), 1.33 (s, 12H), 0.92 (t, J = 7.3 Hz, 3H); 13C NMR (75 MHz, 6.14 (dd, J = 4.6, 7.8 Hz, 1H), 3.92-3.78 (m, 2H), 2.50-2.36 (m,
CDCl3, ppm): 172.9, 145.0, 135.0, 125.3, 83.8, 72.0, 36.5, 24.8, 2H), 1.77-1.64 (m, 1H), 0.96 (t, J = 7.4 Hz, 3H; 13C NMR (75 MHz,
22.3, 18.5, 13.6; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2- CDCl3, ppm): 172.6, 134.7, 133.4, 133.1, 128.6, 128.1, 127.8
propanol = 95/5, flow rate = 1.0 mL/min, UV = 217 nm; 126.5, 126.3, 123.9, 75.0, 46.5, 36.3, 18.5, 13.6; HPLC
retention times: 4.7 min (S), 12.9 min (R); HRMS (EI): m/z calcd. conditions: (R,R)-Whelk-O1, n-hexane/2-propanol = 70/30,
for [C18H27BO4]+ 318.2006, found 318.2006.
flow rate = 1.0 mL/min, UV = 217 nm; retention times: 4.89
(S)-1-p-tolylethyl butyrate ((S)-4f-Bu): 56 mg (90% yield, 95% min (S), 23.34 min (R); HRMS (EI): m/z calcd. for [C16H17ClO2]+
21
23
ee); [α]D = -52.1 (c = 1.0, CHCl3) [lit.9a [α]D = -44.5 (c = 1.0, 276.0917, found 276.0916.
CHCl3)]; The analytical data were in good agreement with the (S)-cyclopropyl(phenyl)methyl butyrate ((S)-5e-Bu): 46 mg (70%
yield, 99% ee); [α]D20 = -31.2 (c = 1.0, CHCl3); 1H NMR (300 MHz,
literature values.9a
(S)-1-(4-phenylphenyl)ethyl butyrate ((S)-4g-Bu): 68 mg (85% CDCl3, ppm): δ 7.40-7.28 (m, 5H), 5.24 (d, J = 8.7 Hz, 1H), 2.36-
yield, 98% ee); [α]D23 = -95.0 (c = 1.0, CHCl3); 1H NMR (300 MHz, 2.31 (m, 2H), 1.70-1.63 (m, 2H), 1.34-1.24 (m, 1H), 0.94 (t, J =
CDCl3, ppm): δ 7.57 (d, J = 6.9 Hz, 4H), 7.45-7.40 (m, 4H), 7.35- 7.4 Hz, 3H), 0.63-0.38 (m, 4H); 13C NMR(75 MHz, CDCl3, ppm):
7.31 (m, 1H), 5.94 (q, J = 6.4 Hz, 1H), 2.32 (t, J = 7.2 Hz, 2H), 173.0, 140.6, 128.3, 127.8, 126.6, 79.3, 36.5, 18.5, 16.6, 13.6,
1.73-1.60 (m, 2H), 1.56 (d, J = 6.6 Hz, 3H), 0.94 (t, J = 7.3 Hz, 4.0, 3.1; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2-
3H); 13C NMR (75 MHz, CDCl3, ppm): 173.0, 140.9, 140.8, 128.8, propanol = 95/5, flow rate = 1.0 mL/min, UV = 217 nm;
127.3, 127.1, 126.5, 71.8, 36.6, 32.2, 18.5, 13.7; HPLC retention times: 3.94 min (S), 6.90 min (R); HRMS (EI): m/z
conditions: (R,R)-Whelk-O1, n-hexane/2-propanol = 95/5, flow calcd. for [C14H18O2]+ 218.1307, found 218.1304.
rate = 1.0 mL/min, UV = 217 nm; retention times: 4.9 min (S), Dynamic kinetic resolution of secondary alcohols with
14.2 min (R) ); HRMS (EI): m/z calcd. for [C18H20O2]+ 268.1463, ruthenium complex 9. As the representative procedure, the
found 268.1465.
DKR of 7c is described. Ru complex 9 (9.3 mg, 5 mol%), Na2CO3
(S)-1-(4-(2-(trimethylsilyl)ethylnyl)phenyl)ethyl butyrate ((S)- (31.8 mg , 0.3 mmol) and 25% (w/w) ISCBLS (9 mg) were added
23
4h-Bu): 67 mg (77% yield, >99% ee); [α]D = -88.8 (c = 1.0, to a pear-shaped Schlenk-type flask under argon. The flask
CHCl3); 1H NMR (300 MHz, CDCl3, ppm): δ 7.45 (d, J = 8.0 Hz, evacuated and refilled with argon. Degassed THF (600 µL, 0.5
2H), 7.29 (d, J = 7.5 Hz, 2H), 5.88 (q, J = 6.4 Hz, 1H), 2.32 (t, J = M) and a solution of t-BuOK (1.0 M in THF; 15 µL, 5 mol%)
7.3 Hz, 2H), 1.72-1.60 (m, 2H), 1.52 (d, J = 6.5 Hz, 3H), 0.94 (t, J were added. The resulting mixture was stirred for 10 min. Then
= 7.3 Hz, 3H), 0.26 (s, 9H); 13C NMR (75 MHz, CDCl3, ppm): 7c (0.3 mmol) was added, and stirred for 5 min. 2,2,2-
172.8, 142.3, 132.1, 125.9, 122.6, 104.9, 94.4, 71.6, 36.5, 22.2, Trifluoroethyl butyrate (69 µL, 0.45 mmol) was added into the
18.5, 13.7, 0.0; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2- flask sequentially and the reaction mixture was stirred at 25 oC
propanol = 95/5, flow rate = 1.0 mL/min, UV = 217 nm; for 24h. The mixture was diluted with methylene chloride, and
retention times: 3.9 min (S), 12.2 min (R); HRMS (EI): m/z calcd. filtered through a Celite pad. The filtrate was concentrated
for [C17H24O2Si]+ 288.1546, found 288.1543.
and purified by column chromatography (SiO2; hexane/diethyl
ether 9:1) to give (S)-butyrate product.
8 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7OB02181J
Journal Name
ARTICLE
Gayet, C. Tababiono, C. P. Postema, V. Ritleng, M. Pfeffer, D.
B. Janssen, A. J. Minnaard, B. L. Feringa, J. G. De Vries, J. Am.
Chem. Soc. 2008, 130, 13508-13509. (f) A. Träff, K. Bogár, M.
Warner, J.-E. Bäckvall, Org. Lett., 2008, 10, 4807-4810. (g) T.
Ema, Y. Nakano, D. Yoshida, S. Kamata, T. Sakai, Org. Biomol.
Chem., 2012, 10, 6299-6308. (h) S. Kim, Y. K. Choi, J. Hong, J.
Park, M.-J. Kim, Tetrahedron Lett., 2013, 54,1185-1188.
H. Kim, Y. K. Choi, J. Lee, E. Lee, J. Park, M.-J. Kim, Angew.
Chem. Int. Ed., 2011, 50, 10944-10948.
C. Kim, J. Lee, J. Cho, Y. Oh, Y. K. Choi, E. Choi, J. Park, M.-J.
Kim. J. Org. Chem., 2013, 78, 2571-2578.
(a) M.-J. Kim, Y. I. Chung, Y. K. Choi, H. K. Lee, D. Kim, J. Park,
J. Am. Chem. Soc., 2003, 125, 11494-11495. (b) L. Borén, B.
Martín-Matute, Y. Xu, A. Córdova, J.-E. Bäckvall, Chem. Eur. J.,
2006, 12, 225-232.
(S,Z)-4-phenylbut-3-en-2-yl butyrate ((S,Z)-7b-Bu): 62 mg (95%
yield, 96% ee, 3% of (E)-form butyrate was included. It was
22
impossible to separate.); [α]D = +44.4 (c = 1.0, CHCl3); 1H
NMR (300 MHz, CDCl3, ppm): 7.38-7.27 (m, 5H), 6.52 (d, J =
11.7 Hz, 1H), 5.88-5.76 (m, 1H), 5.65 (dd, J = 11.7, 9.1 Hz, 1H),
2.25 (t, J = 7.5 Hz, 2H), 1.64 (sxt, J = 7.4 Hz, 2H), 1.37 (d, J = 6.3
Hz, 3H), 0.94 (t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3, ppm):
172.8, 136.3, 131.5, 130.9, 128.6, 128.4, 127.3, 67.6, 36.5, 20.9,
18.5, 13.6; HPLC conditions: (R,R)-Whelk-O1, n-hexane/2-
propanol = 97/3, flow rate = 1.0 mL/min, UV = 217 nm;
retention times: 5.52 min (S), 6.56 min (R).
4
5
6
(S,E)-4-phenylbut-3-en-2-yl butyrate ((S,E)-7c-Bu): 64 mg (97%
25
25
yield, 97% ee); [α]D = -110.8 (c = 1.0, CHCl3) [lit.9b [α]D = -
111.3 (c = 1.0, CHCl3, 97% ee)]; The analytical data were in
good agreement with the literature values.9b
7
8
9
C.-S. Chen, Y. Fujimoto, G. Girdaukas, C. Sih, J. Am. Chem.
Soc., 1982, 104, 7294-7299.
K. M. Verzijl, J. G. de Vries, Q. B. Broxterman, Tetrahedron:
Asymmetry, 2005, 16, 1603-1610.
(a) M.-J. Kim, H. M. Kim, D. Kim, Y. Ahn, J. Park, Green Chem.,
Gram-scale dynamic kinetic resolution of 2e. The procedure
for the g-scale DKR of 2e was practically identical to that for
the 0.3 mmol-scale DKR except the amounts of substrate and
reagents and reaction time: 2e (1.033g, 6 mmol), 25% (w/w)
2004, 6, 471-474. (b) M.-J. Kim, H. Lee, J. Park, Bull. Korean
Chem. Soc. 2007, 28, 2096-2098.
ISCBLS (240 mg), Ru complex
8 (200 mg, 4 mol%), 2,2,2-
Trifluoroethyl butyrate (1.38 mL, 9 mmol), K2CO3 (930 mg , 6
mmol), degassed THF (12 mL), and 36 h at 25 oC. The DKR
reaction provided (S)-butyrate product of 96% ee in 84%
isolated yield.
Notes and references
1
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2
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3
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