Lipase-catalyzed kinetic resolution of β-borylated carboxylic esters

Article abstract of DOI:10.1016/j.tetasy.2012.08.011

The kinetic resolution of chiral β-borylated carboxylic esters via lipase-catalyzed hydrolysis and transesterification reactions was studied. The enantioselective hydrolysis catalyzed by CAL-B furnished the β-borylated carboxylic acid with reasonable enantiomeric excess (62% ee), while both methyl and ethyl β-borylated carboxylic esters were recovered with excellent ee (>99%). Meanwhile, the transesterification reaction of β-borylated carboxylic esters and several alcohols, catalyzed by CAL-B, only indicated a high selectivity when ethanol and methyl-(β-pinacolylboronate)-butanoate were used as substrates, which gave ethyl-(β-pinacolylboronate)-butanoate with >99% ee.

Full text of DOI:10.1016/j.tetasy.2012.08.011

Tetrahedron: Asymmetry 23 (2012) 1294–1300
Contents lists available at SciVerse ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Lipase-catalyzed kinetic resolution of b-borylated carboxylic esters
⇑
Joel S. Reis, Leandro H. Andrade
Institute of Chemistry, University of São Paulo, Av. Prof. Lineu Prestes, 748, CEP 05508-900 São Paulo, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2012
Accepted 17 August 2012
Available online 15 September 2012
The kinetic resolution of chiral b-borylated carboxylic esters via lipase-catalyzed hydrolysis and transe-
sterification reactions was studied. The enantioselective hydrolysis catalyzed by CAL-B furnished the
b-borylated carboxylic acid with reasonable enantiomeric excess (62% ee), while both methyl and ethyl
b-borylated carboxylic esters were recovered with excellent ee (>99%). Meanwhile, the transesterification
reaction of b-borylated carboxylic esters and several alcohols, catalyzed by CAL-B, only indicated a high
selectivity when ethanol and methyl-(b-pinacolylboronate)-butanoate were used as substrates, which
gave ethyl-(b-pinacolylboronate)-butanoate with >99% ee.
Ó 2012 Elsevier Ltd. All rights reserved.
1
. Introduction
Organoboron compounds are widely used in synthetic organic
into their acid derivatives (b-hydroxy acid or b-amino acid), which
are attractive building blocks for the synthesis of bioactive com-
8
pounds. Alternatively, the preparation of b-hydroxy esters can
chemistry. Their versatility allows them to be easily converted into
many functional groups in addition to their constant use in new
carbon–carbon bond forming reactions. Organoboron reagents in
cross-coupling reactions have been widely described in the litera-
be carried out via the reduction of the corresponding keto esters
4a,9
using isolated oxidoreductases and whole microbial cells.
thermore, enzymatic deracemization and resolution of racemic
Fur-
1
0
11
b-hydroxy esters have also been employed.
1
ture due to their high applicability. Both chiral and achiral boron
2
compounds can be prepared by several synthetic methodologies.
2
2
. Results and discussion
Focusing our attention on chiral organoboron compounds,
especially on those with a boron atom attached directly to the
stereogenic center, a literature survey revealed that the main syn-
thetic route to obtain these compounds, besides the Matteson
.1. Synthesis of b-borylated esters (RS)-2a–f
The b-borylated esters (RS)-2a–f were synthesized by the inser-
2
homologation protocol, is a reaction catalyzed by transition
tion of a Bpin group into a range of
a,b-unsaturated carboxylic
3
metals (i.e., Cu, Ni, Pd) using chiral ligands.
esters 1a–f, according to the methodology reported by Yun
3
a
Over the past few years, biocatalysis has been recognized as an
important synthetic tool for preparing enantiomerically pure or
et al. These syntheses are shown in Scheme 1.
4
enriched compounds. The application of enzymes in traditional
2
.2. Kinetic resolution of (RS)-2a–f via hydrolysis reaction
5
chemical reactions is an area of growing interest. Despite the
importance of chiral boron compounds, enzymatic routes used to
make them are rare in the literature. Recently, we have explored
the use of enzymes as catalysts of enantioselective reactions
involving organoboron compounds, which led to the study of
kinetic resolution of boron-containing chiral alcohols and amines
mediated by lipases as well as monooxygenases7 for selective
oxidations of organoboron compounds. Herein we report a new
approach to prepare chiral b-borylated carboxylic esters via kinetic
resolution through hydrolysis and transesterification reactions
catalyzed by lipases. This class of organoboron compound can be
converted into b-hydroxy esters, b-amino esters, and consequently
The first approach selected for the kinetic resolution of b-
borylated esters was the enantioselective hydrolysis reaction. We
carried out enzymatic assays in order to find an appropriate lipase
for the enantioselective hydrolysis of compound (RS)-2a. The effi-
ciency of the enzymatic assays was measured by the ee values of
the remaining b-borylated ester (RS)-2a. Lipases from Burkholderia
cepacia (BCL), Pseudomonas cepacia immobilized on diatomite
6
(
PSD-I), Pseudomonas cepacia immobilized on ceramic (PSC-II),
Candida antarctica immobilized on acrylic resin (CAL-B), Aspergillus
niger (ANL), Candida rugosa (CRL), Candida cylindracea (CCL), Mucor
miehei (MML), and Pseudomonas fluorescens (PFL) were tested.
Among the biocatalysts tested, CAL-B showed the better perfor-
mance (82% ee for 2a) while the reactions mediated by PSD-I and
PSC-II furnished the ester with low ee (<10%) after 24 h. We
⇑
Corresponding author. Tel.: +55 11 3091 2287.
E-mail address: leandroh@iq.usp.br (L.H. Andrade).
0
957-4166/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2012.08.011

J. S. Reis, L. H. Andrade / Tetrahedron: Asymmetry 23 (2012) 1294–1300
1295
Bpin
O
O
2
CuCl, NaOt-Bu
CO R2
CO R
2
2
R1
R1
Bpin =
B
DPEphos, B pin2
2
1
a-f
2a-f
MeOH, THF
1
2
1
1
1
1
1
1
a; R = Me, R = Me
2a, 91%
2b, 86%
2c, 71%
DPEphos
1
2
b; R = Me, R = Et
1
2
c; R = Me, R = n-Bu
1
2
d; R = Me, R = Oct
1
2
e; R = Me, R = Bn
2
2
2
d, 67%
e, 65%
f, 85%
1
2
O
f; R = Ph, R = Et
PPh2
PPh2
Scheme 1. b-Borylation reaction of esters 1a–f.
Table 1
Screening of lipases for enantioselective hydrolysis of (RS)-2aa
Bpin
Bpin
Bpin
Lipase
CO2Me
CO2Me
CO2H
+
*
*
H O, 32 ºC
2
(RS)-2a
2a
3
7
00 rpm, 24 h
Entry
Lipase
ee 2ab (%)
1
2
3
4
5
6
7
8
9
BCL
No reaction
<10
PSD-I
PSC-II
CAL-B
ANL
CRL
CCL
<10
c
82
No reaction
No reaction
No reaction
No reaction
No reaction
MML
PFL
a
b
c
General conditions: H
Determined by chiral GC analysis.
ee for 3 = 88%, conversion, c = 49%, enantiomeric ratio, E-value = 29. c = ee
2
O (1 mL), lipase (10 mg), (RS)-2a (0.05 mmol).
S
/(ee
S
+ ee
P
); E = ln{[ee
P S
(1 À ee )/
1
2
(
ee
P S P S P S
+ ee )]}/ln{[ee (1 + ee )/(ee + ee )]}.
extended the reaction time to 48 h but no increase in the ee value
was observed (81% ee for 2a). The other lipases did not perform the
desired hydrolysis (Table 1).
the desired hydrolysis (Table 2, entry 6). On the other hand, when
we increased the reaction temperature, we obtained excellent ee
values (ester 2a >99% ee, 3 h, Table 2, entry 7). Similarly, compound
2b was formed in >99% ee in 24 h (Table 2, entry 8). Enzymatic
hydrolysis of esters (RS)-2c–f showed low ee values or no reaction
(Table 2, entries 9–13).
In order to evaluate the effect of organic solvents on the hydro-
lysis reaction, water-miscible and water-immiscible solvents were
employed as well as different ratios between organic solvent/
water. Hexane, toluene, t-BuOMe, THF, DMF, and dioxane were
used as the organic solvents; however, no improvement was de-
tected, yielding low ee values (10–43%) for 2a. From these results,
it was possible to see the clear dependence of a large amount of
water to perform efficiently the enzymatic hydrolysis.
We suspected that the b-borylated carboxylic acid 3 could be
disturbing the reaction through lipase inactivation; thus, assays
under buffered systems were tested. The b-borylated ester 2a
was obtained with reasonable ee (48–71%), however, the values
were slightly lower than those obtained with water as the solvent.
Our protocol was extended to additional compounds (RS)-2b–f,
which present long carbon chains or steric hindrance to the car-
boxyl group. When ethyl ester (RS)-2b was submitted to enzymatic
hydrolysis conditions a very similar result to that of methyl ester
2.3. Determination of the absolute configuration for 2a,b and 3
In order to assign the absolute configuration of 2a,b and 3 and
determine the ee of acid 3 produced from the hydrolysis protocol,
preparative-scale reactions were carried out (Schemes 2 and 3).
As shown in Scheme 2, the enantioenriched ester 2a was iso-
lated with 39% yield and >99% ee, while acid 3 was isolated with
49% yield and, after esterification with diazomethane, showed an
ee value of 62%. The absolute configuration was assigned after
boron oxidation and the values of the specific rotation of the b-
hydroxy esters were compared with the literature.1
3,14
It is
important to note that this oxidation occurs with retention of con-
figuration. The b-hydroxy ester 4a obtained from ester 2a has
revealed a rotation of +19.2, representing the (S)-enantiomer
(RS)-2a was obtained (Table 2, entry 2). Meanwhile, esters with a
1
3
long carbon chain (RS)-2c–e caused either a considerable decrease
in ee values or no reaction (Table 2, entries 3–5). Ester (RS)-2f,
which contains a phenyl group at the b position, did not undergo
according to the literature. On the other hand, b-hydroxy ester
4a obtained from acid 3 revealed a rotation of À11.4, representing
1
4
the (R)-enantiomer according to the literature. Similarly, the

1
296
J. S. Reis, L. H. Andrade / Tetrahedron: Asymmetry 23 (2012) 1294–1300
Table 2
Enzymatic hydrolysis of b-borylated esters (RS)-2a–fa
Bpin
Bpin
Bpin
CO2R2
CAL-B, H2O
00 rpm, 24 h
CO2R2
CO2H
R1
R1
+
R1
*
*
7
(
RS)-2a-f
2a-f
3
Bpin
Bpin
Bpin
Bpin
Bpin
2
2
a
b
CO2Me
CO2Et
2
2
c
d
CO2n-Bu
CO2Oct
CO2Bn
CO2Et
2
2
e
f
Bpin
Ph
(
À) = Not determined due to low or no conversion.
a
General conditions: H
2
O (1 mL), CAL-B (10 mg), (RS)-2a–f (0.05 mmol).
b
Analysis after oxidation with NaBO . For entries 2–5 and 8–11, the ee was measured by chiral GC analysis after acetylation. For entries 6, 12, and 13, the ee was measured by
3
chiral HPLC analysis.
c
2 2
ee was measured by chiral GC analysis after acid derivatization with CH N .
d
e
f
c = ee
Reaction time = 3 h.
EtOH (2%) was used as the co-solvent.
S
/(ee
S
P
+ ee ); E = ln{[ee
P
S P S P S P S
(1 À ee )/(ee + ee )]}/ln{[ee (1 + ee )/(ee + ee )]}.
enantioenriched ester 2b was isolated with 41% yield and >99% ee,
while acid 3 was isolated with 29% yield and after derivatization,
revealed an ee value of 16% (Scheme 3). The specific rotation data
show that the (S)-enantiomer was recovered, whereas the (R)-
enantiomer was hydrolyzed. These data lead us to conclude that
in the enantioselective enzymatic hydrolysis of esters 2a or 2b,
CAL-B exhibits an (R)-preference. Moreover, considering the size
of the groups bonded at stereogenic center, we can conclude that
our protocol follows Kazlauskas’ rule (Scheme 4).1
reaction, while n-BuOH exhibited a very low conversion (>10%).
By changing the alcohol for EtOH, we achieved good results. The
produced ethyl ester 2b (B form) was obtained in enantiomerically
pure form using either toluene or hexane as the solvent. For the
remaining methyl ester 2a (A form), reasonable ee values (33%
and 44%, respectively) were obtained. Moreover, when employing
more concentrated media (0.45 mL of solvent and 0.05 mL of alco-
hol), similar results were observed. When the reaction was carried
out over 48 h, a slight increase in conversion was observed, but
with a decrease of ee for the produced ethyl ester 2b (B form)
(96%). By employing only EtOH as the solvent, no reaction was ob-
served. Finally, when esters (RS)-2b–e were submitted to transe-
sterification reactions, using MeOH or EtOH as the nucleophile,
we did not observe the desired products.
5
2
.4. Kinetic resolution of (RS)-2a–e via transesterification
Asan alternative tothehydrolysisreaction, wedecided to evaluate
the enzymatic transesterification reaction to obtain esters 2a–e in
enantiomerically pure form. Different organic solvents, and carbon
chains attached to the carboxylic ester and alcohols were employed
3
. Conclusion
(
(
Scheme 5). We also carried out some reactions using an additive
Lewis acid) to increase the carboxylic group reactivity (Scheme 6).
Despite the application of several reaction conditions, no
In conclusion, we have shown the lipase-catalyzed resolution of
b-borylated carboxylic esters via hydrolysis and transesterification
reactions. Enzymatic hydrolysis proved to be a better alternative
for obtaining enantiomerically pure boron-containing carboxylic
esters than the transesterification reaction. In some cases, the
enantioselective enzymatic transesterification provided the pro-
duced ester in high enantiomeric excess. However, esters with
transesterification reaction was observed at 32 °C. Thus, we in-
creased the temperature to 70 °C as applied in the hydrolysis reac-
tions and good results were obtained (Scheme 7).
When the methyl ester (RS)-2a was submitted to the transeste-
rification protocol, we observed that OctOH and BnOH gave no

J. S. Reis, L. H. Andrade / Tetrahedron: Asymmetry 23 (2012) 1294–1300
1297
Bpin
Bpin
Bpin
CAL-B, H2O
CO2Me
CO Me
2
CO2H
+
7
0 ºC, 3h
(
RS)-2a
(
S)-2a, 39% , >99% ee
(R)-3, 49% , 62% ee
[
α]D = +5.5 (c 1, CHCl3)
NaBO3
CH2N2
Et2O
THF, H2O
OH
Bpin
CO2Me
CO2Me
(S)-4a
(R)-2a, 62% ee
obs [α]D = +19.2 (c 1, CHCl3)
lit13 [α]D = +25.7 (c 0.3, CHCl3)
[α]D = -3.4 (c 1, CHCl3)
NaBO3
THF, H2O
OH
CO2Me
(
R)-4a
obs [α]D = -11.4 (c 1, CHCl3)
lit14 [α]D = -19.5 (c 1.1, CHCl3)
Scheme 2. Transformations of ester (RS)-2a.
Bpin
Bpin
Bpin
CAL-B, H2O
0 ºC, 3h
CO2Et
CO2Et
CO2H
+
7
(
RS)-2b
(S)-2b, 41%, >99% ee
(R)-3, 29%, 16% ee
[
α]D = +2.1 (c 0.5, CHCl3)
CH2N2
Et2O
Bpin
CO2Me
(R)-2a, 16% ee
[α]D = -1.8 (c 0.2, CHCl3)
Scheme 3. Transformations of ester (RS)-2b.
CO H
2
CO2H
Bpin
Bpin
CAL-B
H2O
CO2R
CO2H
O
(
R)
B
S
7
0 ºC
L
time
(R)-3
produced
acid
R = Me, (RS)-2a
R = Et, (RS)-2b
O
Favoured
Enantiomer
Scheme 4. Kazlauskas’ rule for the hydrolysis of ester 2a,b.

1
298
J. S. Reis, L. H. Andrade / Tetrahedron: Asymmetry 23 (2012) 1294–1300
2
Bpin
R OH (2 equiv.)
CAL-B (10 mg)
Bpin
*
Bpin
*
CO2R1
CO2R1
CO2R2
+
X
solvent (1mL)
(RS)-2a-c
2a-c
2a-c
(
0.05 mmol)
32 ºC, 700 rpm, 24 h
1
2
R ; R = Me, Et, n-Bu; solvent = Hexane, Toluene, THF, Dioxane, EtOH, MeOH, n-BuOH
Scheme 5. Enzymatic transesterification of (RS)-2a–c.
Bpin
Bpin
Bpin
additive (1 equiv.)
CO2Et
CAL-B (10 mg)
CO2Et
CO2Me
+
*
*
X
(
RS)-2b (0.05 mmol)
toluene (0.8 mL)
MeOH (0.2mL)
2
b
2a
3
2 ºC, 700 rpm, 24 h
additive - CaCl , ZnCl , CoCl , CuCl , NiCl , LiCl, MnCl , FeCl , AlCl , MgCl
2
2
2
2
2
2
2
3
3
Scheme 6. Enzymatic transesterification of (RS)-2b using an additive.
A
B
2
R OH (0.1 mL)
Bpin
Bpin
*
Bpin
CAL-B (10 mg)
CO R1
CO R2
CO2R1
2
2
+
solvent (0.9 mL)
*
7
0 ºC, 750 rpm, 24 h
2a-e
2a-e
(
RS)-2a-e
(
0.05 mmol)
ee A = up to 60%
ee B = up to >99%
1
Conv. = up to 32%
R = Me 2a, Et 2b, n-Bu 2c, Oct 2d, Bn 2e
2
R OH = BnOH, OctOH, n-BuOH, EtOH, MeOH
solvent = toluene, hexane, EtOH
Scheme 7. Enzymatic transesterification of (RS)-2a–e at 70 °C.
Table 3
General conditions for the determination of the enantiomeric excess of the compounds 2a–e
Compound
General conditions
Bpin
GC: Column Varian CP-Chirasil-DEX CB b-cyclodextrin (25 m  0.25 mm  0.25
l
m). Temperature of the detector and injector was 220 °C; H
2
2
as carrier gas (60 kPa). Oven 80–130 °C, rate 1.5 °C/min. Retention time of enantiomers = (R) 19.36 and (S) 19.57 min
CO2Me
CO2Et
OAc
OAc
OAc
OAc
GC: Column Varian CP-Chirasil-DEX CB b-cyclodextrin (25 m  0.25 mm  0.25 lm). Temperature of the detector and injector was 220 °C; H
as carrier gas (80 kPa). Oven 85 (maintenance for 1 min)–110 °C, rate 2.5 °C/min. Plateau of 110 °C (10 min), then heating until 180 °C, rate
0 °C/min. Retention time of enantiomers = (S) 5.89 and (R) 6.11 min
1
GC: Column Varian CP-Chirasil-DEX CB b-cyclodextrin (25 m  0.25 mm  0.25
as carrier gas (80 kPa). Oven 85 (maintenance for 1 min)–110 °C, rate 2.5 °C/min. Plateau of 110 °C (10 min), then heating until 180 °C, rate
0 °C/min. Retention time of enantiomers = 11.96 and 12.36 min
lm). Temperature of the detector and injector was 220 °C; H
2
CO2n-Bu
CO2Oct
CO2Bn
CO2Et
1
GC: Column Varian CP-Chirasil-DEX CB b-cyclodextrin (25 m  0.25 mm  0.25
l
m). Temperature of the detector and injector was 220 °C; H
2
2
as carrier gas (80 kPa). Oven 85 (maintenance for 1 min)–180 °C, rate 2.5 °C/min. Retention time of enantiomers = 24.87 and 25.32 min
GC: Column Varian CP-Chirasil-DEX CB b-cyclodextrin (25 m  0.25 mm  0.25 lm). Temperature of the detector and injector was 220 °C; H
as carrier gas (80 kPa). Oven 85 (maintenance for 1 min)–180 °C, rate 2.5 °C/min. Retention time of enantiomers = 29.03 and 29.33 min
OH
Ph
HPLC: ChiralcelÒ OB column, hexane/i-PrOH (95:5), flow = 1 mL/min, k = 220 nm. Retention time of enantiomers = 9.99 and 11.57 min

J. S. Reis, L. H. Andrade / Tetrahedron: Asymmetry 23 (2012) 1294–1300
1299
longer carbon chains or steric hindrance at the carboxyl group did
not undergo the desired reactions, even at high temperatures.
3
(50 MHz, CDCl ): d (ppm) 173.8, 83.0, 60.1, 37.6, 24.6, 24.6, 15.0,
14.2. FT-IR (KBr)
m
max = 2978, 1735, 1370, 1319, 1144, 1032, 857,
À1
+
6
1
70 cm . LRMS (EI) m/z (%) = 242(1) [M ], 227(12), 184(70),
41(50), 127(12), 113(50), 101(12), 83(100), 59(39), 41(88).
4
4
. Experimental
4
.2.5. Butyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
.1. General methods
butanoate 2c
1H NMR (200 MHz, CDCl
3
): d (ppm) 4.06 (t, J = 6.5 Hz, 2H), 2.43
Unless otherwise noted, commercially available materials were
used without further purification. All the enzymes were purchased
from the Sigma–Aldrich Chemical Company. All solvents were
(
(
0
dd, J = 16.4, 7.6 Hz, 1H), 2.34 (dd, J = 16.4, 6.8 Hz, 1H), 1.68–1.52
m, 2H), 1.42–1.28 (m, 3H), 1.24 (s, 12H), 1.00 (d, J = 7.4 Hz, 3H),
.92 (t, J = 7.2 Hz, 3H). C NMR (50 MHz, CDCl ): d (ppm) 173.9,
3
1
3
HPLC or ACS grade. THF was distilled from sodium benzophenone
ketyl under nitrogen atmosphere. A note about 13C NMR spectra:
83.1, 64.0, 37.6, 30.7, 24.6, 24.6, 19.1, 15.0, 13.6. FT-IR (KBr)
À1
m
max = 2961, 1734, 1371, 1319, 1144, 1010, 859, 670 cm . LRMS
due to the boron quadrupole, carbons directly attached to this ele-
+
ment are often not detected in 1 C NMR spectra. Optical rotations
3
16
(EI) m/z (%) = 270(1) [M ], 255(5), 212(36), 197(22), 155(69),
1
C
15(26), 101(27), 83(100), 57(53), 41(97). HRMS (ESI): Calcd for
were measured on a Perkin Elmer-343 digital polarimeter in a 1 mL
cuvette with a 1 dm path length. All values are reported in the
+
14
H27BO
4
Na [M+Na] = 293.1900. Found: 293.1893.
following format: [
solution reported in units of 10 mg sample per 1 mL, solvent used).
Gas chromatography (GC) analyses were obtained using
Shimadzu 17-A with chiral column Varian CP-Chirasil-DEX CB
b-cyclodextrin (25 m  0.25 mm  0.25 m) and H was used as
the carrier gas under an appropriate pressure.
D
a] = specific rotation (concentration of the
4
.2.6. Octyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
butanoate 2d
a
1H NMR (200 MHz, CDCl
): d (ppm) 3.95 (m, 2H), 2.45 (dd,
3
J = 16.4, 7.6 Hz, 1H), 2.34 (dd, J = 16.4, 6.8 Hz, 1H), 1.50–1.25 (m,
0H), 1.24 (s, 12H), 1.00 (d, J = 7.4 Hz, 3H), 0.95–0.80 (m, 6H). 13
NMR (50 MHz, CDCl ): d (ppm) 174.1, 83.1, 66.5, 38.7, 37.5, 30.3,
l
2
1
C
3
2
1
8.8, 24.7, 24.6, 23.6, 22.9, 15.0, 14.0, 10.9. FT-IR (KBr)
m
max = 2961,
4
.2. Synthetic procedures
À1
734, 1464, 1387, 1370, 1319, 1144, 1009, 859, 670 cm . LRMS
+
(
1
EI) m/z (%) = 281(1) [M À3 Â Me], 268(3), 197(15), 155(21),
The
a,b-unsaturated esters 1d–e were synthesized according to
29(2), 113(23), 101(46), 83(82), 57(90), 41(100). HRMS (ESI):
17
the methodology previously established.
+
Calcd for C18
4
H35BO Na [M+Na] = 349.2526. Found: 349.2525.
4
.2.1. (E)-Octyl but-2-enoate 1d
4
.2.7. Benzyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
1
3
H NMR (200 MHz, CDCl ): d (ppm) 6.96 (dq, J = 15.6 and 6.8 Hz,
butanoate 2e
1
H), 5.84 (dq, J = 15.6 and 1.6 Hz, 1H), 4.03 (m, 2H), 1.88 (dd,
1H NMR (200 MHz, CDCl
3
): d (ppm) 7.34 (s, 5H), 5.11 (s, 2H),
J = 6.8 Hz and 1.6 Hz, 3H), 1.34–1.20 (m, 8H), 1.05–0.85 (m, 7H).
2
1
.51 (dd, J = 16.4, 7.8 Hz, 1H), 2.41 (dd, J = 16.4, 6.6 Hz, 1H), 1.50–
.30 (m, 1H), 1.21 (s, 12H), 1.01 (d, J = 7.6 Hz, 3H). C NMR
1
3
C NMR (50 MHz, CDCl
3
): d (ppm) 166.7, 144.2, 122.8, 66.5,
13
3
2
8.7, 30.4, 28.9, 23.8, 22.9, 17.9, 14.0, 10.9. FT-IR (KBr)
m
max = 3052,
(
3
50 MHz, CDCl ): d (ppm) 173.6, 136.1, 128.4, 128.0, 128.0, 83.1,
À1
960, 1723, 1660, 1265, 1181, 969 cm
. LRMS (EI) m/z
6
1
5.9, 37.6, 24.6, 24.6, 15.0. FT-IR (KBr)
319, 1142, 1007, 859, 747, 697 cm . LRMS (EI) m/z (%) = 304(1)
mmax = 2977, 1735, 1370,
+
(
%) = 199(1) [M +1], 183(1), 112(54), 85(21), 84(31), 69(100),
À1
5
7(41).
+
[
M ], 289(2), 204(15), 155(29), 113(19), 101(5), 91(100), 83(60),
6
9(19), 43(45).
4
.2.2. (E)-Benzyl but-2-enoate 1e
1
3
H NMR (200 MHz, CDCl ): d (ppm) 7.42–7.30 (m, 5H), 7.02 (dq,
4
2
.2.8. Ethyl 3-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
-yl)propanoate 2f
J = 15.6 and 7 Hz, 1H), 5.89 (dq, J = 15.6 and 1.8 Hz, 1H), 5.17 (s,
2
H), 1.88 (dd, J = 7 and 1.8 Hz, 1H).
mp = 51–52 °C, uncorrected). 1H NMR (200 MHz, CDCl
(
3
): d
ppm) 7.30–7.10 (m, 5H), 4.10 (q, J = 7 Hz, 2H), 2.89 (dd, J = 13.6,
.2 Hz, 1H), 2.75 (m, 1H), 2.64 (dd, J = 13.4, 5.2 Hz, 1H), 1.22 (t,
1
3
C NMR (50 MHz, CDCl
3
): d (ppm) 166.2, 145.1, 136.1, 128.4,
max = 3033, 2946,
(
8
1
1
28.1, 128.1, 122.4, 65.9, 18.0. FT-IR (KBr)
m
À1
721, 1658, 1264, 1174, 1014, 969, 697 cm . LRMS (EI) m/z
13
J = 7 Hz, 3H), 1.23–1.16 (m, 12H). C NMR (50 MHz, CDCl
3
): d
+
(
%) = 176(10) [M ], 131(32), 107(13), 91(74), 77(15), 69(100),
(
ppm) 173.3, 141.3, 128.4, 128.1, 125.6, 83.5, 60.3, 37.3, 24.5, 24.4,
5
1(13), 41(31).
1
7
1
4.2. FT-IR (KBr)
m
max = 2982, 1730, 1371, 1139, 1022, 848, 770,
À1
+
07, 535 cm . LRMS (EI) m/z (%) = 304(21) [M ], 289(1), 233(26),
4
.2.3. Methyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
77(3), 131(33), 117(18), 104(100), 91(10), 83(57), 77(10), 55(19).
butanoate 2a
For the preparation of b-borylated esters 2a–f was employed
4
.3. General procedure for oxidation and acetylation of
the procedure reported in the literature by Yun et al.3 H NMR
(
1
1
1
1
a
1
b-borylated esters 2a–f
200 MHz, CDCl
3
): d (ppm) 3.65 (s, 3H), 2.45 (dd, J = 16.4, 7.8 Hz,
H), 2.36 (dd, J = 16.4, 6.6 Hz, 1H), 1.40–1.30 (m, 1H), 1.24 (s,
2H), 1.00 (d, J = 7.2 Hz, 3H). 13C NMR (50 MHz, CDCl
): d (ppm)
max = 2978,
To a 25 mL round-bottomed flask was added the appropriate
3
b-borylated ester (0.5 mmol), THF (2.5 mL), water (2.5 mL), and
74.2, 83.1, 51.3, 37.4, 24.6, 24.6, 15.0. FT-IR (KBr)
738, 1371, 1320, 1204, 1144, 1012, 859, 670 cm . LRMS (EI) m/
z (%) = 228(1) [M ], 213(21), 170(89), 128(74), 127(64), 112(61),
m
NaBO
for 1 h at room temperature and then extracted with ethyl acetate
2 Â 5 mL). The organic phase was rinsed with a saturated aqueous
solution of NaCl (10 mL) and dried over anhydrous MgSO . After
solvent evaporation, the crude mixture was treated with pyridine
1 mL) and Ac O (0.7 mL) and stirred for 12 h at room temperature.
3 2
Á4H O (2.5 mmol, 0.385 g). The reaction mixture was stirred
À1
+
(
1
01(12), 83(84), 59(100), 41(93).
4
4
.2.4. Ethyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
(
2
butanoate 2b
The reaction was extracted with ethyl acetate (10 mL) and the
organic phase was treated with a saturated aqueous solution of
CuSO
1H NMR (200 MHz, CDCl
3
): d (ppm) 4.12 (q, J = 7.2 Hz, 2H), 2.44
(
(
dd, J = 16.4, 7.8 Hz, 1H), 2.34 (dd, J = 16.4, 6.6 Hz, 1H), 1.42–1.30
4
(2 Â 10 mL),
a saturated aqueous solution of NaCl
1
3
m, 1H), 1.29–1.20 (m, 15H), 1.00 (d, J = 7.4 Hz, 3H). C NMR
(
2 Â 10 mL), and dried over anhydrous MgSO
4
.

1
300
J. S. Reis, L. H. Andrade / Tetrahedron: Asymmetry 23 (2012) 1294–1300
4
.4. General procedure for small-scale enzymatic hydrolysis
References
reactions
1.
(a) Martin, R.; Buchwald, S. L. Acc. Chem. Rev. 2008, 41, 1461; (b) Molander, G.
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A
2 mL microtube was charged with the appropriate b-
1995, 95, 2457; (d) Bellina, F.; Carpita, A.; Rossi, R. Synthesis 2004, 2419; (e)
borylated esters (RS)-2a–f (0.05 mmol), CAL-B (10 mg), and
ultrapurified water (1 mL, pH 6). The reaction tube was sealed
and stirred on a thermomixer (Thermomixer Comfort Eppendorf )
at 700 rpm for appropriate temperatures and times (see Tables 1
and 2). The progress of the reactions was followed by removing
Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58, 9633.
Hall, D. G. Boronic Acids: Preparation, Applications in Organic Synthesis and
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2
.
.
Ò
3
(a) Mun, S.; Lee, J.-E.; Yun, J. Org. Lett. 2006, 8, 4887; (b) Lee, J.-E.; Yun, J. Angew.
Chem., Int. Ed. 2008, 47, 145; (c) Lillo, V.; Geier, M. J.; Westcott, S. A.; Fernández,
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Fernández, E.; Guiry, P. J. Org. Biomol. Chem. 2009, 7, 2520; (e) Lillo, V.; Prieto,
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Synthesis, 2nd ed.; Wiley-VHC: Weinheim, Germany, 2006; (c) Ghanem, A.
Tetrahedron 2007, 63, 1721.
samples (30
lL of reaction mixture were added to 600 lL of
t-BuOMe) for GC or HPLC analysis (Section 4.7).
4
.5. General procedure for preparative-scale enzymatic
4
5
.
.
reactions
A 100 mL Schlenk tube was charged with the appropriate
b-borylated ester (RS)-2a or (RS)-2b (1 mmol), CAL-B (200 mg),
and ultrapurified water (20 mL, pH 6). The tube was sealed and
the reaction was stirred (magnetic stirrer) in an oil bath at 75 °C
For an excellent compilation, see the special issue Enzymes in Synthesis: Chem.
Rev. 2011, 111, 3995–4404.
6. (a) Andrade, L. H.; Barcellos, T. Org. Lett. 2009, 14, 3052; (b) Andrade, L. H.;
Barcellos, T.; Santiago, C. G. Tetrahedron: Asymmetry 2010, 21, 2419.
7
.
(a) Brondani, P. B.; de Gonzalo, G.; Fraaije, M. W.; Andrade, L. H. Adv. Synth.
Catal. 2011, 353, 2169; (b) Brondani, P. B.; Dudek, H.; Reis, J. S.; Fraaije, M. W.;
Andrade, L. H. Tetrahedron: Asymmetry 2012, 23, 703.
(
oil temperature) until the appropriate time. Next, the enzyme
was decanted, washed with t-BuOMe (2 Â 10 mL) and the water
was extracted with t-BuOMe (2 Â 10 mL). The combined organic
8. (a) Müller, H. M.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1993, 32, 477; (b)
Seebach, D.; Matthews, J. L. Chem. Commun. 1997, 2015; (c) Cheng, R. P.;
Gellman, S. H.; DeGrado, W. F. Chem. Rev. 2001, 101, 3219; (d) Levy, L. M.; Dehli,
J. R.; Gotor, V. Tetrahedron: Asymmetry 2003, 14, 2053; (e) Nascimento, M. G.;
Zanoto, S. P.; Melegari, S. P.; Fernandes, L.; Sá, M. M. Tetrahedron: Asymmetry
4
phases were dried over anhydrous MgSO and after evaporation,
the crude mixture was purified by column chromatography on
silicagel, using hexanes/EtOAc (8:2) and then EtOAc as eluent.
2003, 14, 3111. and references cited therein.
9.
(a) Richter, N.; Hummel, W. Enzyme Microb. Technol. 2011, 48, 472; (b) Ou, Z.;
Chen, X.; Ying, G.; Shi, H.; Sun, X. Biotechnol. Bioprocess Eng. 2011, 16, 320; (c)
Matsuda, T.; Yamanaka, R.; Nakamura, K. Tetrahedron: Asymmetry 2009, 20,
4
.6. General procedure for small-scale enzymatic
transesterification reactions
513; (d) Ravía, S. P.; Carrera, I.; Seoane, G. A.; Vero, S.; Gamenara, D.
Tetrahedron: Asymmetry 2009, 20, 1393; (e) He, C.; Chang, D.; Zhang, J.
Tetrahedron: Asymmetry 2008, 19, 1347; (f) Kaluzna, I. A.; Rozzell, J. D.;
Kambourakis, S. Tetrahedron: Asymmetry 2005, 16, 3682; (g) Kaluzna, I.;
Andrew, A. A.; Bonilla, M.; Martzen, M. R.; Stewart, J. D. J. Mol. Catal. B: Enzym.
2002, 17, 101; (h) Molinari, F.; Gandolfi, R.; Villa, R.; Occhiato, E. G. Tetrahedron:
Asymmetry 1999, 10, 3515; (i) Zhou, B.; Gopalan, A. S.; VanMiddlesworth, F.;
Shieh, W. R.; Sih, C. J. J. Am. Chem. Soc. 1983, 105, 5925.
A 10 mL glass tube was charged with the b-borylated esters
RS)-2a (11.5 mg, 0.05 mmol), CAL-B (10 mg), hexane (0.9 mL),
(
and EtOH (0.1 mL). The reaction tube was sealed and stirred on a
Ò
thermomixer (Thermomixer Comfort Eppendorf ) at 750 rpm, at
7
0 °C for 24 h. The progress of the reactions was followed by
removing samples (30 L of reaction mixture were added to
00 L of t-BuOMe), with derivatization as described in Section 4.3,
and then analyzed by GC or HPLC (Section 4.7).
l
10. (a) Turcu, M. C.; Kiljunen, E.; Kanerva, L. T. Tetrahedron: Asymmetry 2007, 18,
1682; (b) Ma, D. Y.; Zheng, Q. Y.; Wang, D. X.; Wang, M. X. Org. Lett. 2006, 8,
3231; (c) Padhi, S. K.; Pandian, N. G.; Chadha, A. J. Mol. Catal. B: Enzym. 2004, 29,
25; (d) Nakamura, K.; Fujii, M.; Ida, Y. Tetrahedron: Asymmetry 2001, 12, 3147;
6
l
(
e) Huerta, F. F.; Santosh Laxmi, Y. R.; Bäckvall, J.-E. Org. Lett. 2000, 1037, 2.
4
.7. Determination of the enantiomeric excess (ee)
11. (a) Xu, C.; Yaun, C. Tetrahedron 2005, 61, 2169; (b) Sharma, A.; Chattopadhyay,
S. J. Mol. Catal. B: Enzym. 2000, 10, 531; (c) Boaz, N. W. J. Org. Chem. 1992, 57,
4
289; (d) Feichter, C.; Faber, K.; Griengl, H. Tetrahedron Lett. 1989, 30, 551.
The enantiomeric excesses of the b-borylated esters and their
1
2. (a) Chen, C. S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J. J. Am. Chem. Soc. 1982, 104,
7294; (b) Straathof, A. J. J.; Jongejan, J. A. Enzyme Microb. Technol. 1997, 21, 559.
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Asymmetry 2011, 22, 47; (b) Gotor-Fernández, V.; Brieva, R.; Gotor, V. J. Mol.
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Rappaport, A. T.; Cuccia, L. A. J. Org. Chem. 1991, 56, 2656.
6. Wrackmeyer, B. Prog. NMR Spectrosc. 1979, 12, 227.
derivatives were measured by chiral HPLC or GC analysis (Table 3).
However in some cases, derivatization reactions were carried out
as described in Table 2 and Section 4.3.
1
1
1
Acknowledgment
1
1
The authors are grateful for FAPESP, CNPq, and CAPES for finan-
cial support.
7. Yadav, J. S.; Reddy, G. S.; Srinivas, D.; Himabindu, K. Synth. Comm. 1998, 28,
2337.