Studies on enzymatic synthesis of chiral non-racemic 3-arylglutaric acid monoesters

Article abstract of DOI:10.1016/j.tetasy.2006.03.002

The enantioselective enzymatic desymmetrization (EED) of various 3-arylglutaric anhydrides 1 with alcohols in organic media has been studied. The effect of the solvent on the stereochemical outcome of the reaction was investigated in detail. The amount of biocatalyst was optimized, and the possibility of its re-use was tested. The first example of the EED of 3-substituted glutaric anhydrides with esters as nucleophiles is reported.

Full text of DOI:10.1016/j.tetasy.2006.03.002

Tetrahedron: Asymmetry 17 (2006) 961–966
Studies on enzymatic synthesis of chiral non-racemic
3-arylglutaric acid monoesters
Anna Fryszkowska,a Marta Komar,b Dominik Koszelewskib and Ryszard Ostaszewskia,b,
*
aFaculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
bInstitute of Organic Chemistry PAS, Kasprzaka 44/52, 01-224 Warsaw, Poland
Received 31 January 2006; accepted 7 March 2006
Available online 4 April 2006
Abstract—The enantioselective enzymatic desymmetrization (EED) of various 3-arylglutaric anhydrides 1 with alcohols in organic media
has been studied. The effect of the solvent on the stereochemical outcome of the reaction was investigated in detail. The amount of bio-
catalyst was optimized, and the possibility of its re-use was tested. The first example of the EED of 3-substituted glutaric anhydrides with
esters as nucleophiles is reported.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
Cl
Desymmetrization of meso and prochiral compounds is a
powerful approach in asymmetric synthesis.1,2 In contrast
NH
O
O
to a kinetic resolution, a maximum yield of 100% can be
achieved in a single-step reaction based on enantiofacial
or enantiotopic differentiation. A number of enantio-
selective enzymatic syntheses have been based on this
strategy.3–5 Most enzymatic enantioselective desymmetri-
zations (EEDs) catalyzed by hydrolytic enzymes use sub-
strates bearing common functional groups, such as
alcohols or esters, while examples of the desymmetrization
of anhydrides are less common.3–5
. HCl
NH2
H2N
HOOC
N
OH
N
NR
(R)-Baclofen
Cl
I
O
III GP receptor antagonist
Cl
O
NMe2
O
Cl
N
N
O
N
Me
N
OMe
Cl II NK2 receptor antagonist
Recently, we have focused our attention on the synthesis of
chiral non-racemic 3-arylglutaric acid derivatives, which
are important building blocks in the synthesis of a number
of biologically active compounds.6,7 The most prominent
examples are (R)-Baclofen I (Fig. 1)—a selective GABAB
receptor agonist8–10 and G-protein-coupled NK-receptor
antagonist II (Fig. 1).11,12 Moreover, the search for a new
glycoprotein IIb–IIIa antagonist led to the development
of compound III possessing improved pharmacokinetic
properties, bearing a 3-phenylglutaric unit.13
Figure 1. Biologically active compounds possessing the 3-arylglutaric unit.
respective prochiral diesters.9–11,14–17 The reaction usually
leads to the optically active products in good yields and
good to excellent enantioselectivities. Although highly effi-
cient, this methodology involves employing an aqueous
reaction media. Therefore, a tedious product separation
and purification is required.
A common enzymatic route toward optically active 3-aryl-
glutaric acid monoesters is an enzymatic hydrolysis of the
Recently, we reported new methodology toward the syn-
thesis of this class of compounds, based on the enzymatic
desymmetrization of 3-arylglutaric anhydrides in organic
solvents using alcohols as nucleophiles (Scheme 1).7 This
*
Corresponding author. Tel.: +48 22 632 32 21; fax: +48 22 632 66 81;
e-mail: rysza@icho.edu.pl
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.03.002

962
A. Fryszkowska et al. / Tetrahedron: Asymmetry 17 (2006) 961–966
R1
L2,C3—proved to be efficient catalysts in the desymmetri-
R1
R2
zation of 3-phenylglutaric anhydride 1a in iso-propyl
ether.7 Although the monoester (S)-2a was obtained in
approx. 80% ee, the enantiomeric excesses of other aro-
matic-ring substituted anhydrides 1b–c were lower and
the reaction times significantly longer. In order to find
more favorable conditions for desymmetrization and to
test the general applicability of the lipase-catalyzed desym-
metrization, the current studies were undertaken.
R2
O
lipase
O
R3OH or R3OAc
solvent
R3O
OH
O
O
1
O
(S)-2
1a R1 = H, R2 = H
1b R1 = Cl, R2 = H
1c R1 = Cl, R2 = Cl
2a R1 = H, R2 = H, R3 = Et
2b R1 = Cl, R2 = H, R3 = Et
2c R1 = Cl, R2 = Cl, R3 = Et
2d R1 = OMe, R2= H, R3 = Et
2e R1 = H, R2 = H, R3 = n-Pr
2f R1 = H, R2 = H, R3 = n-Bu
2g R1 = H, R2 = H, R3 = Bn
A series of 3-arylsubstituted glutaric acid anhydrides 1a–d
was prepared, as described before,7,18,19 and subjected to
an enzymatic alcoholysis reaction with Novozym 435,
according to Scheme 1. The absolute configurations of
monoesters 2 were assigned according to the previously re-
ported methodology.7 The enantiomeric excesses were
determined by HPLC using a Chiralcel OD-H column.
1d R1 = OMe, R2 = H
Scheme 1. Enzymatic desymmetrization of 3-aryl glutaric acid anhydrides
1a–d.
approach is parallel to the enzymatic hydrolysis of diesters,
but the need for aqueous media is eliminated.
2.1. The solvent effect
It is well known that the solvent almost always affects the
enantiomeric selectivity and the rate of the lipase-catalyzed
reactions.20 Our preliminary studies clearly indicated that
the use of ether solvents in the EED of anhydride 1a was
superior to other solvents.7 We extended our research to
the desymmetrization of anhydrides 1b–1d. Their enzy-
matic desymmetrizations catalyzed by Novozym 435 were
performed in organic solvents at room temperature, afford-
ing the corresponding monoesters (S)-2b–d. The reaction
times and ee values for monoesters 2b–d are summarized
in Table 1, as well as the previously reported results for
monoester 2a as a reference.
We found that the immobilized enzymes were efficient catal-
ysts for the EED of anhydrides 1, leading to the respective
monoesters 2 in quantitative yields and good enantioselec-
tivities.7 We observed that the biocatalyst had a strong
influence on both the stereoselectivity of the reaction and
its kinetics. For example, Novozym 435 (CAL-B) catalyzed
the formation of (S)-2a (78% ee), while Amano PS-C
(Pseudomonas cepacia) led to the formation of (R)-2a
(77% ee). Moreover, we have demonstrated that the use
of short aliphatic alcohols (e.g., methanol, ethanol) as
nucleophiles was advantageous for EED.
Encouraged by these results, we decided to extend this
methodology to different 3-aryl substituted glutaric anhy-
drides and to study the scope of this biocatalytic process
and the effect of solvents and nucleophile on the efficiency
and enantioselectivity of the EED reaction. The influence
of the amount of the biocatalyst and its re-use were inves-
tigated as well; this is of crucial importance for the poten-
tial applications of our methodology.
In all the cases, Novozym 435 exclusively catalyzed the for-
mation of the respective (S)-monoester. As a general trend,
the enantiomeric purities of the products obtained by the
EED of 3-phenylglutaric anhydride 1a were higher than
those for the substituted-ring anhydrides 2b–d.
EED of anhydride 1a led to monoester (S)-2a with compa-
rable enantioselectivities (75–79% ee), regardless of the
ether used. On the contrary, evaluation of various ethers
for the other anhydrides revealed that the choice of ether
was of crucial importance. The monoester (S)-2b was ob-
tained with moderate ee values (68%) in ethers having
logP = 1.9–2.9, while the ee values in more polar ethers
(logP 6 1.3) were much lower (Table 1, entries 1, 4, 5 vs
2. Results and discussion
In our previous study, immobilized lipases from Candida
antarctica type B—Novozym 435 and Chirazyme
Table 1. The effect of solvent on EED of 3-arylglutaric acid anhydrides 1a–d with ethanol catalyzed by Novozym 435a
Entry
Solvent
LogP
(S)-2a
(S)-2b
(S)-2c
(S)-2d
Timeb (days)
% eec
Timeb (days)
% eec
Timeb (days)
% eec
Timeb (days)
% eec
1
2
3
4
5
6
iso-Propyl ether
tert-Butyl methyl ether
Ethyl ether
n-Propyl ether
n-Butyl ether
2.0
1.3
0.85
1.9
2.9
3.2
2
2
3
4
2
1
78
76
79
78
75
62
5
5
17
17
3
68
56
43
68
67
6
4
22
22
11
11
—
60
3
12
10
5
22
14
—
—
—
—
69
70
—
—
—
—
Cyclohexane
3
—
a Reaction conditions: substrate 1 (0.050 mmol), solvent (1 mL), ethanol (0.075 mmol), Novozym 435 (7.6 mg), rt.
b Time required for full conversion (by TLC).
c Ee determined by HPLC using Chiracel OD-H column.

A. Fryszkowska et al. / Tetrahedron: Asymmetry 17 (2006) 961–966
963
2, 3). The best result for the monoester (S)-2c was obtained
in iso-propyl ether (Table 1, entry 1, logP = 2.0), while, for
monoester (S)-2d, the use of TBME was advantageous
(Table 1, entry 1, logP = 1.3). It is noteworthy that the rate
of EED in cyclohexane (logP = 3.2) was generally high,
although the enantioselectivities were poor (Table 1, entry
6).
ee, respectively (Table 2, entries 2 and 3). The change of
the solvent to water-miscible ethyl cyanoacetate (Table 2,
entry 6, logP = 0.02) led to a complete loss of stereo-
differentiation.
We expected to obtain better results using the acetates of
n-butyl and benzyl alcohols. These solvents are less water
miscible (logP = 1.7–1.8), which is usually advantageous
for enzymatic reactions.20 However, it was not the case
and almost no asymmetric induction was observed (Table
2, 9–14% ee, entries 4–6). Previously, we demonstrated that
short aliphatic alcohols used as nucleophiles improved the
ee values of the monoesters 2. Herein, the results may also
suggest that not only the logP, but the alkoxy group length
influence the stereochemical course of the EED reaction.
The results indicated that the reaction time and enantio-
meric excess of the product strongly depended on the struc-
ture of substrate 1. Monoesters (S)-2a–d were obtained in
moderate to good ee (60–79%). The low ee values of mono-
esters 2b–d and slower reaction rates can be at least in part
attributed to the reduced solubility of the anhydrides 1b–c
in comparison to 1a. It is also known that CAL-B lipase,
unlike other lipases, exhibits little to no interfacial activa-
tion.21 However, we found no clear correlation between
the solvent, the anhydride structure and the stereochemical
outcome of EED. Our study demonstrates that choosing
the appropriate solvent for enzymatic reaction still remains
a trial-and-error process.
Generally, the EED of glutaric anhydride 1a by transeste-
rification led to a low asymmetric induction. Moreover, the
reaction times were very long (4 weeks). These unsatisfac-
tory results can be explained by the fact that the use of
esters as solvents may decrease the activity of enzymes,
as well as an unfavorable equilibrium can be established.
Probably, the formation of acetic acid during the reaction
course can affect the enzyme activity as well. Nevertheless,
we would like to emphasize the fact that, according to our
knowledge, this is the first example of EED of 3-substituted
glutaric anhydrides by transesterification.
2.2. Studies on EED by transesterification
In an attempt to improve the enantiopurity of monoesters
2, we undertook further studies. The aim of our research
was to investigate whether it would be possible to perform
EED by transesterification, according to Scheme 1. We
envisioned that the use of esters both as alkoxy donors
and solvents would be effective. As a model reaction, the
EED of anhydride 1a with Novozym 435 was chosen.
The results are summarized in Table 2.
2.3. Enzyme quantities and enzyme re-use
Finally, the effect of amount of the biocatalyst used in EED
and possibility of its re-use were investigated. These param-
eters are crucial in terms of the potential large-scale appli-
cations of this methodology and, as a consequence, the
process economy. We investigated the desymmetrization
of anhydride 1a with ethanol in iso-propyl ether as a func-
tion of Novozym 435 quantity. The results are summarized
in Table 3.
The enzymatic transesterification of anhydride 1a led to
formation of the respective monoesters (S)-2a–g (Table 4,
entries 2–6). Without the enzyme in ethyl acetate, no prod-
uct formation was observed (Table 4, entry 1). The results
indicated that there was a correlation between logP of the
acetate used as a solvent/nucleophile and the ee values of
the monoesters 2.
Table 3. The enzyme quantity effect on EED of 1a with ethanol catalyzed
by Novozym 435 in iso-propyl ethera
Table 2. EED of 1a by transesterification catalyzed by Novozym 435a
Entry
Enzyme/anhydride 1a
(S)-2a % eeb
Timec
LogP Product % eeb Timec (weeks)
(mg/mmol)
(days/weeks)
Entry Acetate
Ethyl acetated
0.68
0.68
1.2
1.7
1.8
—
—
37
33
14
9
5
5
4
4
4
4
1
2
3
4
5
314
154
135
95
79
79
79
58
64
1/—
2/—
2.5/—
4/—
—/5d
1
2
3
4
5
6
Ethyl acetatee
n-Propyl acetate
n-Butyl acetate
Benzyl acetate
(S)-2a
(S)-2e
(S)-2f
(S)-2g
(S)-2a
13
Ethyl cyanoacetate 0.02f
0
a Reaction conditions: substrate 1a (0.050 mmol, 9.5 mg) iso-propyl ether
(1 mL), ethanol (0.075 mmol), Novozym 435, rt; TLC monitored until it
reached full conversion.
b Ee determined by HPLC using Chiracel OD-H column.
c Time required for full conversion (by TLC).
d Conversion <100%.
a Reaction conditions: 1a (0.050 mmol, 9.5 mg), acetate (1 mL), Novozym
435 (7.6 mg), rt.
b Ee determined by HPLC using Chiracel OD-H column.
c Time required for full conversion (by TLC).
d Blank reaction.
e Conversion <100%.
f Estimated.
The study revealed that the amount of enzyme does not af-
fect the stereochemical outcome of EED, unless it is higher
than 135 mg/mmol of anhydride 1a. However, the smaller
the amount of biocatalyst the longer reaction time was
required to reach a full conversion, as one could expect
(Table 3, entries 1–3). A further decrease in the amount
We observed that higher asymmetric inductions were
obtained for more polar solvents. For ethyl acetate
(logP = 0.68) and n-propyl acetate (logP = 1.2), the
respective monoesters 2 were obtained in 37% and 33%

964
A. Fryszkowska et al. / Tetrahedron: Asymmetry 17 (2006) 961–966
of the biocatalyst (Table 3, entries 4 and 5) led to an
increased reaction time, as well as to the decreased enantio-
meric purity of the monoester (S)-2a.
Our approach undoubtedly represents a new methodology
for the synthesis of chiral non-racemic glutaric acid deriv-
atives. The water-free reaction media and the simplified
work-up procedure make this process an attractive meth-
odology for industrial purposes. The use of esters for the
enzymatic desymmetrization opens new possibilities in
the synthesis of 3-aryl glutaric monoacids.
Since a substantial amount of Novozym 435 was required
for an efficient EED of 3-arylglutaric anhydrides 1, the pos-
sibility of the enzyme re-use was investigated. Again, the
desymmetrization of anhydride 1a with ethanol in iso-
propyl ether was chosen as a model reaction. The results
of the study are presented in Table 4.
4. Experimental
4.1. General
Table 4. Studies on Novozym 435 re-circulation in EED of 1a with
ethanol in iso-propyl ethera
NMR spectra were recorded in CDCl3 with TMS as an
internal standard using a 200 MHz Varian Gemini 200
spectrometer. The chemical shifts are reported in ppm (d
scale) and the coupling constants (J) are given in hertz
(Hz). The MS spectra were recorded on an API-365
(SCIEX) apparatus. The IR spectra were recorded in
CHCl3 on a Perkin–Elmer FT-IR Spectrum 2000 appara-
tus. The HPLC analyses were performed on a Chiracel
OD-H column (B 4.6 mm · 250 mm, from Diacel Chemi-
Cycle
Enzyme/anhydride 1a (S)-2a % eeb Timec
(mg/mmol)
(days/weeks)
First cycle
142
78
71
55
36
2/—
3/—
6/—
—/4
Second cycle 133
Third cycle 125
Fourth cycle 139
a Reaction conditions: 1a (0.50 mmol, 95.0 mg) iso-propyl ether (1 mL),
ethanol (0.75 mmol), Novozym 435 (70 mg), rt.
b Ee determined by HPLC using Chiracel OD-H column.
c Time required for full conversion (by TLC).
cal Ind., Ltd) equipped with
a
pre-column (B
4 mm · 10 mm, 5 lm) using LC-6A Shimadzu apparatus
with UV SPD-6A detector and Chromatopac C-R6A ana-
lyzer. Elemental analyses were performed on CHN Perkin–
Elmer 240 apparatus. Melting points are uncorrected. All
reactions were monitored by TLC on Merck silica gel
The experimental data showed that Novozym 435 could be
re-used up to three times, but in each cycle the enantio-
selectivity and activity of the biocatalyst decreased signi-
ficantly. After the first cycle, the enzyme was
approximately 10% less selective and 50% less active (Table
4, entries 1 and 2). In the next cycles, these changes were
even more pronounced (Table 4, entries 3 and 4). More-
over, approximately 5% of enzyme was lost in every cycle
due to mechanical operations.
plates 60 F254
.
Novozym 435 was purchased from Novo Nordisk. All the
chemicals were obtained from commercial sources. The sol-
vents were of analytical grade. The 3-arylglutaric anhy-
drides 1a–d were obtained in three-step methodology
from the respective aryl aldehyde, according to the litera-
ture procedures described before.7,18,19
3. Conclusions
4.1.1. Synthesis of monoesters (S)-2 by enzymatic desym-
metrization catalyzed by Novozym 435. A general proce-
dure. To a suspension of the anhydride 1 (0.50 mmol) in
ether (10 mL), lipase (75 mg), and absolute ethanol
(0.75 mmol, 70 lL) were added. The reaction was carried
out at room temperature and its progress was monitored
by TLC (CHCl3/MeOH/HCOOH; 100:2:0.05). The
enzyme was filtered off and the residue concentrated in
vacuo to give monoester (S)-2 as a colorless oil. The enan-
tiomeric excess was determined by HPLC analysis using
Chiracel OD-H column. The product was recrystallized
from Et2O/hexane.
Novozym 435-catalyzed enzymatic desymmetrization of
3-arylglutaric acid anhydrides 1 has been studied. Our
results demonstrate that immobilized CAL-B lipase cata-
lyzed the synthesis of the monoesters (S)-2 with moderate
to good enantiopurities. The solvent effect, as well as the
nucleophilic character, were investigated in an attempt to
find suitable reaction conditions. While for 3-phenylglu-
taric anhydride and its chloro-substituted derivatives 1a–
c, the enzyme showed the highest activity and enantioselec-
tivity in iso-propyl ether, the use of TBME was favorable in
the case of the 4-methoxy-substituted anhydride 1d.
The use of acetates as solvents/acetoxy group donors did
not lead to improved enantioselectivities. Nevertheless,
the first example of 3-substituted glutaric anhydride desym-
metrization by transesterification was reported.
4.1.2. Enzymatic desymmetrization of anhydride 1a with
Novozym 435 by transesterification. To a suspension of
anhydride 1a (0.05 mmol, 9.5 mg) in an appropriate acetate
(1 mL), Novozym 435 (7.5 mg) was added. The reaction
was carried out at room temperature and the reaction pro-
gress was monitored by TLC (CHCl3/MeOH/HCOOH;
100:2:0.05). The results are summarized in Table 4.
The study on the effect of the enzyme amount demon-
strated that the enantioselectivity of the reaction decreased
significantly below a certain limit (135 mg of Novozym 435
per 1 mmol of anhydride 1a). The re-use of the lipase was
limited, since each cycle was accompanied by a loss of
the enzyme enantioselectivity and the activity (from 10%
for the first cycle to 35% for the fourth one).
4.1.3. Studies on the amount of Novozym 435 in the synthesis
of (S)-2a. A general procedure. To a suspension of anhy-
dride 1a (0.05 mmol, 9.5 mg) in iso-propyl ether (1 mL),
appropriate amounts of Novozym 435, and absolute etha-

A. Fryszkowska et al. / Tetrahedron: Asymmetry 17 (2006) 961–966
965
nol (0.075 mmol, 7 lL) were added. The reaction was car-
ried out at room temperature and the reaction progress was
monitored by TLC (CHCl3/MeOH/HCOOH; 100:2:0.05).
The enantiomeric excess was determined by HPLC analysis
using Chiracel OD-H column. The enzyme quantities and
the results are summarized in Table 3.
(R) = 36.3 min] 1H NMR d 1.20 (t, J = 7.2 Hz, 3H),
2.70–2.90 (m, 4H), 3.53–3.73 (m, 1H), 3.83 (s, 3H), 4.09
(q, J = 7.2 Hz, 2H), 6.9 (d, J = 7.0 Hz, 2H), 7.19 (d,
J = 7.2 Hz, 2H); 13C NMR d 14.6, 37.3, 41.1, 41.3, 55.9,
60.9, 114.8, 129.4, 136.0, 159.4, 172.9, 174.8. Anal. Calcd
for C14H18O5: C, 63.15; H, 6.81. Found C, 63.12; H, 6.81.
4.1.4. Studies on re-circulation of Novozym 435. A general
procedure. To a suspension of anhydride 1a (0.5 mmol,
95 mg) in iso-propyl ether (10 mL), Novozym 435
(70 mg), and absolute ethanol (0.75 mmol, 75 lL) were
added. The reaction was carried out at room temperature
and the reaction progress monitored by TLC (CHCl3/
MeOH/HCOOH; 100:2:0.05). When the reaction reached
full conversion, the enzyme was filtered off, washed care-
fully with iso-propyl ether, and dried. The enzyme was
re-used for the next reaction with an appropriate amount
of the anhydride. The enantiomeric excess of product
(S)-2a was determined by HPLC analysis using Chiracel
OD-H column. The results are summarized in Table 4.
Chemical yields of all the reactions were nearly quantita-
tive (95–99%).
4.1.9. (S)-3-Phenylglutaric acid monopropyl ester (S)-
2e. White crystals: mp 32 ꢁC (Et2O/hexane); HPLC ana-
lysis: [hexane/i-PrOH/CH3COOH; 185:14:1; k = 226 nm;
1.0 mL/min; tR (S) = 7.7 min, tR (R) = 8.3 min]; 1H
NMR d 0.83 (t, J = 7.6 Hz, 3H), 1.42–1.63 (m, 2H),
2.54–2.85 (m, 4H), 3.52–3.72 (m, 1H), 3.92 (t, J = 6.6 Hz,
2H), 7.12–7.40 (m, 5H), 10.40 (s, 1H); 13C NMR d 10.6,
22.1, 38.3, 40.6, 40.9, 66.5, 127.3, 127.5, 128.9, 129.0,
142.6, 172.0, 177.9. Anal. Calcd for C14H18O4: C, 67.18;
H, 7.25. Found: C, 67.19; H, 7.24.
4.1.10. (S)-3-Phenylglutaric acid monobutyl ester (S)-
2f. White crystals: mp 41–43 ꢁC (Et2O/hexane); Rf =
0.39 (CHCl3/MeOH/HCOOH; 100:2:0.05); HPLC ana-
lysis: hexane/i-PrOH/CH3COOH; 185:14:1; k = 226 nm;
1.0 mL/min; tR (S) = 7.7 min, tR (R) = 8.2 min]. 1H
NMR d 0.91 (t, J = 7.2 Hz, 3H), 1.30 (q, J = 7.2 Hz,
2H), 1.46–1.56 (m, 2H), 2.68–2.79 (m, 4H), 3.62–3.70 (m,
1H), 4.01 (t, J = 6.5 Hz, 2H), 7.27–7.32 (m, 5H); 13C
NMR d 13.6, 19.0, 30.5, 38.0, 40.2, 40.6, 64.4, 127.0,
127.1, 127.3, 128.6, 128.7, 142.1, 171.6, 177.3. Anal. Calcd
for C15H20O4: C, 68.16; H, 7.63. Found: C, 67.75; H, 7.83;
ESI-MS HR, [M+Na]+, calcd for C15H20NaO4: 287.1254,
found (m/z): 287.1240 (100%).
4.1.5. (S)-3-Phenylglutaric acid monoethyl ester (S)-
2a. White crystals: mp 58–59 ꢁC ((Et2O/hexane; lit. 59–
6019); Rf = 0.24 (CHCl3/MeOH/HCOOH; 100:2:0.05);
HPLC analysis [hexane/i-PrOH/CH3COOH; 185:14:1;
k = 226 nm;
1.0 mL/min;
tR
(S) = 8.3 min,
tR
(R) = 8.9 min)]; 1H NMR d 1.85 (t, J = 7.1 Hz, 3H),
2.68–2.81 (m, 4H), 3.10–3.25 (m, 1H), 4.08 (q,
J = 7.1 Hz, 2H), 7.27–7.32 (m, 5H); 13C NMR d 14.0,
38.0, 40.2, 40.7, 60.5, 127.0, 127.2, 128.6, 128.7, 142.2,
171.6, 177.5; LSIMS (+, NBA): m/z = 259 ([M+Na]+,
56%), 237 ([M+H]+, 100%).
4.1.11. (S)-3-Phenylglutaric acid monobenzyl ester (S)-
2g. White crystals: mp 85–86 ꢁC (Et2O/hexane); Rf =
0.40 (CHCl3/MeOH/HCOOH; 100:2:0.05); HPLC ana-
lysis: [hexane/i-PrOH/CH3COOH; 185:14:1; k = 226 nm;
1.0 mL/min; tR (R) = 9.9 min, tR (S) = 10.9 min]; 1H
NMR d 2.18–2.32 (m, 4H), 3.70 (m, 1H), 5.06 (s, 2H),
7.15–7.40 (m, 10H); 13C NMR d 38.0, 40.2, 40.6, 66.5,
127.0, 127.2, 128.1, 128.5, 128.6, 135.6, 142.1, 171.3,
177.4. Anal. Calcd for C18H18O4: C, 72.47; H, 6.08. Found:
C, 72.39; H, 6.23.
4.1.6. (S)-3-(4-Chlorophenyl)-glutaric acid monoethyl ester
(S)-2b. White crystals: mp 56 ꢁC (Et2O/hexane); HPLC
analysis [hexane/i-PrOH/CH3COOH; 185:14:1; k = 226 nm;
1.0 mL/min; tR (S) = 9.0 min, tR (R) = 9.8 min]; 1H
NMR d 1.15 (t, J = 7.1 Hz, 3H), 2.67–2.80 (m, 4H),
3.50–3.70 (m, 1H), 4.03 (q, J = 7.1 Hz, 2H), 7.15 (d, J =
8.6 Hz, 2H), 7.34 (d, J = 8.6 Hz, 2H), 10.7 (s, 1H); 13C
NMR d 14.2, 37.3, 40.1, 40.5, 60.6, 128.6, 128.7, 128.8,
132.7, 140.6, 171.2, 177.2. Anal. Calcd for C13H15ClO4:
C, 57.68; H, 5.59. Found C, 57.59; H, 5.74.
Acknowledgment
4.1.7. (S)-3-(3,4-Dichlorophenyl)-glutaric acid monoethyl
ester (S)-2e. White crystals: mp 76–77 ꢁC (Et2O/hexane);
HPLC analysis [hexane/i-PrOH/CH3COOH; 198:1:1; k =
225 nm; 1.0 mL/min; tR (S) = 65.0 min, tR (R) = 69.8 min];
Rf = 0.16 (CHCl3/MeOH/HCOOH; 100:2:0.05); 1H
NMR d 1.20 (t, J = 7.1 Hz, 3H), 2.55–2.88 (m, 4H),
3.55–3.75 (m, 1H), 4.03 (q, J = 7.1 Hz, 2H), 7.13 (dd, J =
1.8 Hz, J = 8.2 Hz, 1H), 7.37–7.42 (m, 2H); 13C NMR d
14.1, 37.2, 40.3, 40.4, 60.8, 126.8, 129.3, 130.5, 130.9,
132.5, 142.5, 169.9, 177.0. Anal. Calcd for C13H14Cl2O4:
C, 51.17; H, 4.62. Found: C, 51.16; H, 4.78.
This work was supported by the Polish State Committee
for Scientific Research, grant PZB-MIN-007/P04/2003.
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