The studies on chemoenzymatic synthesis of Femoxetine

Article abstract of DOI:10.1016/j.molcatb.2012.06.009

The studies on enzymatic kinetic resolution of 3-phenyl-4-pentenoic acid esters were performed. The obtained results demonstrated that the careful choice of biocatalyst and a reaction type are very important for successful enzymatic kinetic resolution. Ki

Full text of DOI:10.1016/j.molcatb.2012.06.009

Journal of Molecular Catalysis B: Enzymatic 82 (2012) 96–101
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis B: Enzymatic
journal homepage: www.elsevier.com/locate/molcatb
The studies on chemoenzymatic synthesis of Femoxetine
Anna Brodzka, Dominik Koszelewski, Ryszard Ostaszewski∗
Institute of Organic Chemistry PAS, Kasprzaka 44/52, 01-224 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The studies on enzymatic kinetic resolution of 3-phenyl-4-pentenoic acid esters were performed. The
obtained results demonstrated that the careful choice of biocatalyst and a reaction type are very important
for successful enzymatic kinetic resolution. Kinetic resolution provides 3-phenyl-4-pentenoic acid (1)
with good enantioselectivity upon esterification. That product was used as a substrate for formal synthesis
of two biologically relevant compounds Femoxetine and LG 121071.
Received 20 February 2012
Received in revised form 6 June 2012
Accepted 11 June 2012
Available online 19 June 2012
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Enzymatic kinetic resolution
3-Phenyl-4-pentenoic acid
Femoxetine
1. Introduction
2. Results and discussion
The synthesis of enantiomerically pure drugs is of great impor-
tance for both academia and pharmaceutical industry [1]. Among
others 3-phenyl-4-pentenoic acid (1) is a valuable building block
for the synthesis of drugs and biologically active compounds
(Scheme 1) [2].
The enantiomerically pure acid 1 is an important substrate for
synthesis of several biologically active compounds like Femoxetine
(8) [3], (R)-3-phenylpentenoic acid (9) – the key intermediate in
synthesis of LG 121071 a modulator of androgen receptors [4] and
3-phenylGABA whose biological activity has been related to (R)-
enantiomer [5].
The aim this study was to determine the conditions for enzy-
matic kinetic resolution of 3-phenyl-4-pentenoic acid esters (2a–c)
for Femoxetine synthesis. Previously we have found that enzymes
can be used for stereocontrolled, chemoenzymatic synthesis of
unnatural peptides [10], for the kinetic resolution of the ␣-
acetoxyamides [11] and for desymmetrization of 3-arylglutaric acid
anhydrides [12]. Racemic acid 1 was obtained according to the lit-
erature procedure from cinnamyl alcohol and triethyl orthoacetate
with 86% yield [13]. The parent esters were obtained from acid
chloride and corresponding aliphatic alcohol (Scheme 2).
Enantiomer S of 3-phenyl-4-pentenoic acid is also an impor-
tant intermediate for the antitumor antibiotic methylenolactocin
[6,7]. Previously, enantiomerically pure 3-phenyl-4-pentenoic acid
(1) was synthesized by chemical routes in multistep syntheses
[2,8,6]. Enantioselective biotransformations of racemic 3-arylpent-
4-enenitriles catalyzed by Rhodococcus erythropolis AJ270 to acid
1 by a nitrile hydratase/amidase containing microbial whole-cell
catalyst was reported to proceeds with good yield but the enan-
tiomeric excess of this product did not exceed 92.5% [9]. Also the
preparation of substrate for biotransformation was cumbersome.
Despite of this, the fermentative methods are expensive and diffi-
cult to carry out in chemical laboratories.
2.1. Enzymatic hydrolysis of ethyl 3-phenyl-4-pentenoate
In the study on enzymatic kinetic resolution (EKR) of esters
2 commercially available enzymes were examined according to
Scheme 3. Reactions were conducted in buffer (pH 7.0) containing
20 vol.% of acetone, keeping enzyme/substrate ratio – 1:1.
In most cases poor results were obtained. Even for widely used
biocatalyst Novozym 435 the enantioselectivity of reaction was
close to 1 (Table 1, entry 1). More promising results were obtained
for crude biocatalyst delivered from animal tissue. Liver acetone
powders (LAP) are widely used in organic synthesis, such as the syn-
thesis of cyclohexyl based chiral auxiliaries [14], ␣-acetoxyamides
[11], ␣-hydroxy-␤,␥-unsaturated esters [15], capsaicin analogs
[16] and trans-1-acetoxy-2-aryloxycyclohexanes [17]. Also the
application of LAP for the synthesis of stereogenic carbon center
was recently reviewed [18]. In our study eight various acetone pow-
ders [pig liver acetone powder (PLAP), beef liver acetone powder
∗
Corresponding author. Tel.: +48 22 343 2120; fax: +48 22 632 66 81.
E-mail address: rysza@icho.edu.pl (R. Ostaszewski).
1381-1177/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcatb.2012.06.009

A. Brodzka et al. / Journal of Molecular Catalysis B: Enzymatic 82 (2012) 96–101
97
Scheme 1. Signification of 3-phenyl-4-pentenoic acid.
Scheme 2. Synthesis of racemic acid (1) and its esters (2a–c).
(BLAP), rabbit liver acetone powder (RLAP), wild boar liver acetone
2.2. Enzymatic esterification of 3-phenyl-4-pentenoic acid
powder (WLAP), chicken liver acetone powder (CLAP), duck liver
acetone powder (DLAP), turkey liver acetone powder (TLAP), goose
liver acetone powder (GLAP)] were screened.
The experimental data shows that in a hydrolysis reaction of
butyl ester 2b catalyzed by CLAP and WLAP acid 1 was obtained
with the highest enantioselectivity (Table 1, entries 5 and 6). When
methyl ester of compound 1 was hydrolyzed we observed decease
of enantioselectivity.
In the above studies we did not obtain satisfactory results, so we
decided to perform enzymatic kinetic resolution using the esteri-
fication reaction. In this reaction triethyl orthoacetate was used as
a donor of alcoholate group. Addition of an orthoester biases the
equilibrium in favor of the ester side, due to consumption of water
formed through hydrolysis of the orthoester. At first, the racemic
ester was obtained by this methodology [21].
Our studies on the effect of the length of ester on enantioselec-
tivity are congruent with the literature data [19].
Next, we have focused our attention on the synthesis of chi-
ral non-racemic ethyl 3-phenyl-4-pentenoate. In this study several
commercially available and one immobilized lipase [immobilized
lipase from Candida antarctica (Novo sp 435A)] together with six dif-
ferent acetone powders were screened as biocatalysts for esters (2)
synthesis. These reactions were conducted in an toluene at 40 ◦C
for 24 h (Scheme 4). The obtained results were shown in Table 2.
We found that the majority of tested enzymes exhibited enan-
tioselectivity (Table 2). A few enzymes (lipases from: Candida
rugosa; Novo sp 435 A; BLAP, WLAP) (Table 2, entries 8, 9, 13
and 16) exhibited low enantioselectivity and several enzymes
(lipases from: Penicillium roqueforti, Aspergillus, Wheat germ, Pseu-
domonas sp., Mucor miehei; TLAP, JLAP, BKAP, GLAP) (Table 2,
entries 2–4, 6, 7 and 11–14) exhibited good enantioselectivity. We
decided to scale-up selected enzymatic esterification of racemic
Table 1
Enzymatic kinetic resolution of ester 2a–c catalyzed by acetone powders.
Entry
Acetone powder
R
Time (h)
c (%)a
% eeb
Ed
(R)-2
1
2
3
4
5
6
7
8
Novozym 435
PLAP
BLAP
RLAP
WLAP
CLAP
DLAP
TLAP
GLAP
PLAP
Et
24
3
4
4
4
5
5
6
5
2
2
3
44
21
25
20
24
23
27
17
22
27
32
21
8
19
18
12
21
27c
18
13
12
1
1
8
4
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Me
Me
Me
3
24
25
3
5
3
1
2
7
9
10
11
12
WLAP
CLAP
16
19
a
Determined by HPLC on RP-C18 column.
Determined by HPLC on the Daicel Chiracel OD-H column.
b
c
(S)-1 acid [˛]D = −7.5 (c = 1.0, PhH).
d
Calculated according to Chen et al. [20], using the equation:
E = (ln[(1 − c)(1 − ees)])/(ln[(1 − c)(1 + ees)]).
Scheme 3. EKR of esters 3-phenyl-4-pentenoic acid (1).

98
A. Brodzka et al. / Journal of Molecular Catalysis B: Enzymatic 82 (2012) 96–101
Scheme 4. Enantioselective synthesis of ethyl 3-phenyl-4-pentenoate.
Table 2
Results obtained in enzymatic esterification 3-phenyl-4-pentenoic acid with triethyl
orthoacetate.a
Entry
Enzyme
Product
c (%)b
% eec
Ed
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15e
16
–
2c
11
52
23
45
15.4
37.5
40.9
30.1
57
24
54
52
25.7
25
–
90
92
93
92
93
91
90
69
90
82
83
93
97
80
83
–
Penicilium roqueforti
Aspergillus
Wheat germ
Pseudomonas cepacia
Pseudomonas sp
Mucor miehei
Candida rugosa
Novo sp 435 A
BLAP
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
(S)-2c
76
34
63
30
50
40
29
17
26
41
32
37
82
22
16
Scheme 6. Aminolysis of ethyl ester of 3-phenyl-4-pentenoic acid (2c).
block for synthesis of Femoxetine®. The reaction of optically pure
acid (S)-1 with ethyl chloroformate and benzylamine leads to
formation of amide (S)-3 in 32% yield. Several attempts were made
to optimize this reaction without satisfactory result. Reaction
of amide 3 with 9-BBN followed by oxidation (H2O2) leads to
formation of alcohol 4 in 91% yield. Next, Appel reaction provides
bromide 5 (41% yield) whose cyclization lets to formation of
(S)-N-benzyl-4-phenyl-2-piperidinone (6) in 89% yield (Scheme 5)
[22]. Specific rotation of obtained compound (+36.2) compared to
literature data (+35.0) fully confirms the absolute configuration
of our product and its enantiomeric purity [6]. Since the next
reactions leading to Femoxetine® are known in literature this is
the formal synthesis of this bioactive molecule [23,24].
TLAP
JLAPf
BKAPg
GLAP
GLAP
WLAP
50
29.1
a
Conditions: 1 (1 mmol), 4b (3 mmol), toluene (1.21 ml), the enzyme (10 mg),
35–40 ◦C, 24 h.
b
Determined by HPLC on RP-C18 column.
Determined by HPLC on the Daicel Chiracel OD-H column.
Calculated according to Chen et al. [20], using the equation:
c
d
E = (ln[1 − c(1 + eep)])/(ln[1 − c(1 − eep)]).
e
Reaction was prepared in larger scale, conditions: 1 (10 mmol), 4b (30 mmol),
toluene (12.1 ml), the enzyme (100 mg), 35–40 ◦C, 24 h.
This short and efficient synthesis of Femoxetine® based on acid
1 clearly demonstrates the synthetic potential of this chiral auxil-
iary. The formation of amide 3 from acid 1, the first step in reaction
sequence (Scheme 5) proceeds in relatively low yield what greatly
diminishes the overall yield. The same chiral product can be directly
obtained from racemic ester 2 upon enantioselective enzymatic
aminolysis. It is already known that enzymatic kinetic resolution
of ester based on aminolysis reaction is also catalyzed by liver ace-
tone powders [25]. Therefore, we examined a suitability of obtained
acetone powders in aminolysis reaction of racemic ester 2c with
benzyl amine according to Scheme 6.
f
JLAP – deer liver acetone powder.
BKAP – beef kidney acetone powder.
g
3-phenyl-4-pentenoic acid (Table 2, entry 15). Unexpectedly, the
reaction in larger scale under the same conditions proceeded with
higher rate than in small scale (Table 2, entry 14). Shortening reac-
tion time provided product with the same enantioselelctivity in
large scale.
2.3. Chemoenzymatic synthesis of Femoxetine
Efficient enzymatic kinetic resolution of esters 2 provides large
amount of chiral acid 1 which can be used as a convenient building
All reactions were conducted in tert-butylmethyl ether at 30 ◦C.
The experimental data show that enzymes which catalyze this
Scheme 5. Formal synthesis of (R)-N-benzyl-4-phenyl-2-piperidinone.

A. Brodzka et al. / Journal of Molecular Catalysis B: Enzymatic 82 (2012) 96–101
99
Scheme 7. Synthesis of (R)-3-phenylpentanoic acid (7).
reaction are present in six acetone powders (PLAP, BLAP, TLAP,
4. Experimental
RLAP, WLAP, CLAP).
Amide 3 with the highest optically purity was obtained when
pig liver acetone powder (PLAP) ([˛]D = +7.56 in CHCl3, c = 1.0) and
wild boar liver acetone powder (WLAP) ([˛]D = −7.00 in CHCl3,
c = 1.0) were used in aminolysis reaction. Comparing the value of
the specific rotation of these products to the value of specific rota-
tion of amide obtained at an earlier stage (−7.10 in CHCl3, c = 1.0,
Scheme 5) we estimated that these compounds were obtained with
enantiomeric excess over 95%.
It is interesting to note that upon proper choice of biocatalyst
both enantiomers of amide 3 are readily available. Amide (R)-3 was
obtained when PLAP was used as a biocatalyst, whereas in reaction
catalyzed by WLAP product (S)-3 was formed.
4.1. General
The HPLC analyses were performed on a Chiracel OD-H column
(4.6 mm × 250 mm, from Diacel Chemical Ind., Ltd.) equipped with
a pre-column (4 mm × 10 mm, 5 m) using an LC-6A Shimadzu appa-
ratus with UV SPD-6A detector and Chromatopac C-R6A analyser.
The elemental analyses were performed on CHN Perkin-Elmer 240
apparatus. All the reactions were monitored by TLC on Merck sil-
ica gel Plates 60 F254. The acetone powders were prepared in our
laboratory [28]. All the chemicals were obtained from commercial
chemical sources. The solvents were of analytical grade.
4.2. Synthesis of 3-phenyl-4-pentenoic acid (1)
2.4. Synthesis of (R)-3-phenylpentanoic acid (7)
3-Phenyl-4-pentenoic acid was synthesized according to the
method described by Bermejo Gonzalez and Bartlett [13]. A mix-
ture of cynnamyl alcohol (0.25 mol; 33.7 g), triethyl orthoacetate
(0.25 mol; 46.1 ml), and hexanoic acid (1.5 mmol; 0.19 ml) was
heated in an oil bath. The solution was placed in a flask with Claisen
head (for distilling off ethanol), condenser and thermometer. After
3 h 0.1 ml of hexanoic acid was added. Additional portion (0.1 ml)
hexanoic acid was added at 3.5 and 4.5 h. After 6 h the temperature
rose to 166 ◦C. After this time 27 ml of ethanol distilled off and TLC
analysis indicates that no cinnamyl alcohol remains.
Obtained, optically pure acid (S)-1 was used as a substrate to the
synthesis of (R)-3-phenylpentanoic acid (7). This acid is a building
block for synthesis of LG 121071 which is an efficient modulator of
androgen receptors [4].
Acid (S)-1 was reduced by hydrogen/palladium to (R)-3-
phenylpentanoic acid (7) (yield 77%) (Scheme 7). Specific rotation
of obtained compound was −47.3 which is almost identical to liter-
ature data (−48.0) which is observed for 99% enantiomeric excess
[26].
The mixture was cooled, and a solution of potassium hydrox-
ide (0.35 mol; 19.7 g) in water (25 ml), and methanol (75 ml) were
added. The mixture was heated under reflux for 1 h under nitro-
gen. After cooling, the solution was washed with ethyl ether and
acidified with concentrated HCl to pH 1. The acidic solution was
extracted with ethyl ether (3×) and organic layer was dried over
MgSO4, filtered and concentrated under reduced pressure.
The crude acid was purified by crystallization from hexane (86%
yield) to give product melting at 46 ◦C [13]. 1H NMR (200 MHz,
CDCl3): 2.74 (dd, J = 15.0, 7.5 Hz, 1H), 2.78 (dd, J = 15.0, 7.8 Hz,
1H), 3.90 (q, J = 7.2 Hz, 1H), 5.00–5.18 (m, 2H), 5.90–6.10 (m, 1H),
7.19–7.40 (m, 5H); 13C NMR (200 MHz, CDCl3): 40.2, 45.5, 115.3,
127.1, 127.8, 128.9, 140.2, 142.2, 178.3.
3. Conclusions
The studies on enzymatic kinetic resolution of 3-phenyl-4-
pentenoic acid were performed. Application of commercially
available enzymes as biocatalysts for enzymatic hydrolysis was
unsuccessful and respective reactions proceed with low enantios-
electivity. Home made liver acetone powders were found to be
much more efficient biocatalysts. However, the enzymatic hydroly-
sis gives better results for other class of substrates – 3-aryl alkanoic
acids [27]. The second approach – enzymatic esterification was
more efficient, the product was obtain with excellent enantiose-
lectivity. Under optimal conditions desired optically pure acid 1
was obtained in good yield and high enantiomeric excess and used
as a substrate for formal synthesis of Femoxetine and LG 121071.
Six step synthesis of lactam (R)-6, an important intermediate for
Femoxetine provide target compound proceeds in 11% overall yield.
The attempts made to shorten this synthesis by enantioselective
aminolysis of racemic ester 2c using benzyl amine and enzymes
proved to be unsuccessful.
4.3. Synthesis of 3-phenylpentanoic acid (7)
A solution of 3-phenyl-4-pentenoic acid (2.30 mmol) in ethyl
acetate (50 ml) and catalytic amount of Pd/C (5 mg) were placed
under hydrogen under pressure 50 psi. The catalyst was fil-
tered off and solvent was evaporated under vacuum. The crude
acid was purified by crystallization from hexane (77% yield) to
give product melting at 61 ◦C [27]. Elemental analysis: calcd. for
C11H14O2: C, 74.13%, H, 7.92%, found: C, 74.15%, H, 8.07%; 1H NMR
(200 MHz, CDCl3): 0.78 (t, J = 7.14, 3H), 1.40–1.80 (m, 2H), 2.61 (dd,
J = 15.0, 7.5 Hz, 1H), 2.65 (dd, J = 15.0, 7.8 Hz, 1H), 2.90–3.1 (m, 1H),
7.10–7.40 (m, 5H), 7.19–7.40; 13C NMR (50 MHz, CDCl3): 12.2, 29.4,
41.4, 43.8, 126.8, 127.7, 128.7, 143.8, 178.8.
Reduction of carbon double bond present in structure of opti-
cally pure acid 1 provides (R)-3-phenylpentanoic acid (7), an
important intermediate in LG 121071 synthesis in 77% yield.
The studies demonstrate that enzymatic procedures can be
successfully combined with chemical transformation leading to
biologically relevant compound.

100
A. Brodzka et al. / Journal of Molecular Catalysis B: Enzymatic 82 (2012) 96–101
4.4. Synthesis of (−)-(R)-3-phenylpentanoic acid ((R)-7)
solution of (R)-3-phenyl-4-pentenoic acid with 92% ee
([˛]D = −11.8, c = 0.5, PhH) (2.30 mmol) in ethyl acetate (950 ml)
and catalytic amount of Pd/C (5 mg) were placed under hydrogen
under pressure 50 psi. The catalyst was filtered off and solvent was
evaporated under vacuum. The crude acid was purified by crystal-
lization from hexane (77% yield) to give product melting at 61 ◦C
[29]. Product (R)-(−) ([˛]D = −47.3, c = 0.5, PhH).
added. The reaction mixture was stirring for 24 h at 35–40 ◦C. After
cooling, 2 M HCl was added (1.1 ml). The organic layer was washed
saturated NaHCO3 (1×) and brine (1×), and dried over anhydrous
MgSO4. The excess of reagent and solvent were evaporated under
vacuum.
The crude product was purified by silica gel flash chromatog-
raphy using hexane/ethyl acetate (99.5/0.5; v/v) as an eluent to
afford the product 2c as a colorless oil; Rf = 0.8 (hexane/EtOAc, 8:2;
v/v); HPLC analysis [hexane/i-PrOH; 9:1; ꢀ = 232 nm; 1.0 ml/min]
tR(R) = 4.30 min; tR(S) = 5.30 min.
A
4.5. Synthesis of ethyl-3-phenyl-4-pentenoate (2c)
4.10. Enantioselective synthesis of ethyl 3-phenyl-4-pentenoate
To the solution of 3-phenyl-4-pentenoic acid (1) (9.81 mmol)
in methylene chloride (3 ml) thionyl chloride was dropped
(9.87 mmol). The mixture was stirring for 2 h in room temperature.
Next, dry ethanol (85.6 mmol) was added and the mixture was stir-
ring for 3 h. The solvent excess was evaporated under vacuum. The
crude product was purified by silica gel flash chromatography using
hexane/ethyl acetate (99.5/0.5; v/v) as an eluent to afford the prod-
uct 2c as a colorless oil (92% yield); HPLC analysis [hexane/i-PrOH;
9:1; ꢀ = 232 nm; 1.0 ml/min] tR(S) = 9.77 min; tR(R) = 11.03 min. 1H
NMR (200 MHz, CDCl3): 1.16 (t, J = 7.2 Hz, 3H), 2.70 (dd, J = 15.0,
7.5 Hz, 1H), 2.74 (dd, J = 15.0, 7.8 Hz, 1H), 3.86 (q, J = 7.2 Hz, 1H),
4.06 (q, J = 7.2 Hz, 2H), 5.04 (m, 1H), 5.09 (m, 1H), 5.98 (ddd, J = 17.4,
10.2, 7.2 Hz, 1H), 7.29 (m, 5H); 13C NMR (50 MHz, CDCl3): 14.1, 40.3,
45.6, 60.3, 114.7, 126.7, 127.6, 128.5, 140.3, 142.5, 171.7 [30].
(2c) in gram scale
To the solution of 3-phenyl-4-pentenoic acid (10 mmol) in
toluene, triethyl orthoacetate (30 mmol) and GLAP (100 mg) were
added. The reaction mixture was stirring for 24 h at 35–40 ◦C. After
cooling, 2 M HCl was added (11 ml). The organic layer was washed
saturated NaHCO3 (1×) and brine (1×), and dried over anhydrous
MgSO4. The excess of reagent and solvent were evaporated under
vacuum.
The crude product was purified by silica gel flash chromatog-
raphy using hexane/ethyl acetate (99.5/0.5; v/v) as an eluent
to afford the product 2c as a colorless oil (50% yield). Elemen-
tal analysis: calcd. for C13H16O2: C, 76.44%, H, 7.90%, found: C,
76.31%, H, 7.79%; Rf = 0.8 (hexane/EtOAc, 8:2; v/v); HPLC analy-
sis [hexane/i-PrOH; 9:1; ꢀ = 232 nm; 1.0 ml/min] tR(R) = 4.30 min;
tR(S) = 5.30 min; ee = 80%. Shorter reaction time, 16 h, provide ester
with 99% ee.
4.6. Synthesis of methyl 3-phenyl-4-pentenoate (2a)
Ester 2a was obtained in the similar way as product 2c. Yield:
90%. 1H NMR (200 MHz, CDCl3): 2.74 (dd, J = 15.1, 7.7 Hz, 1H),
2.78 (dd, J = 15.1, 7.7 Hz, 1H), 3.62 (s, 3H), 3.89 (q, J = 7.7 Hz, 1H),
5.01–5.15 (m, 2H), 5.90–6.10 (m, 1H), 7.15–7.38 (m, 5H); 13C NMR
(50 MHz, CDCl3): 40.4, 45.8, 51.9, 115.1, 127.0, 127.8, 128.9, 140.5,
142.7, 172.6 [31].
4.11. Synthesis of benzyl amide of (S)-3-phenyl-4-pentenoic acid
((S)-3)
To the solution of (S)-3-phenyl-4-pentenoic acid ((S)-1),
([˛]D = −11.8, c = 0.5, PhH) (0.5 mmol) in methylene chloride (5 ml)
triethylamine (7.36 mmol) was added followed by ethyl chlorofor-
mate (1.8 mmol). The mixture was stirring in room temperature
for 3 h, filtrated through celite and benzylamine (6.31 mmol) was
added. After stirring in room temperature for 3 h. the reaction
mixture was washed with water (3 × 5 ml). The combined organic
layers were dried over MgSO4, filtered and concentrated under vac-
uum. The crude product was purified by crystallization from ethyl
acetate/hexane (32% yield).
Elemental analysis: calcd. for C18H19NO: C, 81.48%, H, 7.22%, N,
5.28%, found: C, 81.52%, H, 7.46%, N, 5.26%; 1H NMR (200 MHz,
CDCl3): 2.57–2.82 (m, 2H), 3.91–4.09 (m, 1H), 4.10–4.52 (m,
2H), 5.02–5.25 (m, 2H), 5.84–6.20 (m, 2H), 7.00–7.18 (m, 2H),
7.20–7.50 (m, 8H); 13C NMR (50 MHz, CDCl3): 43.1, 43.7, 46.3, 115.1,
127.0, 127.5, 127.8, 127.9, 128.8, 128.9, 138.3, 140.7, 142.8, 171.2;
[˛]D = −7.1 (c = 1.0, CHCl3).
4.7. Synthesis of butyl 3-phenyl-4-pentenoate (2b)
Ester 2b was obtained in the similar way as products 2a and
2c. Yield: 80%. 1H NMR (200 MHz, CDCl3): 0.94 (t, J = 7.1 Hz, 3H),
1.20–1.75 (m, 4H), 2.74 (dd, J = 15.1, 7.7 Hz, 1H), 2.78 (dd, J = 15.1,
7.7 Hz, 1H), 3.79–4.15 (m, 3H), 4.98–5.17 (m, 2H), 5.87–6.07 (m, 1H),
7.18–7.38 (m, 5H); 13C NMR (50 MHz, CDCl3): 19.3, 31.8, 40.6, 45.9,
62.3, 64.6, 115.0, 126.9, 127.8, 128.8, 140.5, 142.7, 172.6; ESI-MS
HR, [M]+, calcd for C15H20O2: 232.146, found (m/z): 232.147.
4.8. Synthesis of racemic ethyl 3-phenyl-4-pentenoate (2c)
2c was synthesized as described by Gopalan [21].
To the solution of 3-phenyl-4-pentenoic acid (1 mmol) in
toluene, triethyl orthoacetate (3 mmol) was added. The reaction
mixture was heated under reflux (110 ◦C) for 24 h. After cooling,
hydrochloric acid was added (2 M, 1.1 ml). The organic layer was
washed with saturated sodium bicarbonate (1×), brine (1×) and
dried over anhydrous MgSO4. The excess of reagents and solvent
were evaporated under vacuum. The crude product was puri-
fied by silica gel flash chromatography using hexane/ethyl acetate
(99.5/0.5; v/v) as an eluent to afford the product 2c as a colorless oil;
Rf = 0.8 (hexane/EtOAc, 8:2; v/v); HPLC analysis [hexane/i-PrOH;
9:1; ꢀ = 232 nm; 1.0 ml/min] tR(R) = 4.30 min; tR(S) = 5.3 min.
4.12. Synthesis of benzyl amide of
(+)-3-phenyl-5-hydroxypentanoic acid (4)
To the solution of benzyl amide of (S)-3-phenyl-4-pentenoic
acid ((S)-3) (0.70 mmol) in dry tetrahydrofurane (7 ml) 9-BBN
(3.44 mmol) was added and reaction mixture was stirred in room
temperature. After 12 h. solution of sodium hydroxide (2 M, 2 ml)
and hydrogen peroxide (10%, 2 ml) were dropped and the reaction
mixture was treated by ultrasound for 20 min. Then the solution
was acidified with 2 M HCl to pH 2 and distilled water (100 ml)
was added. Reaction mixture was extracted with ethyl acetate
(3 × 30 ml) and combined organic layers were dried over MgSO4
and concentrated under vacuum. The crude product was purified
by silica gel flash chromatography using hexane/ethyl acetate as an
eluent (91% yield); 1H NMR (200 MHz, CDCl3): 1.80–1.93 (m, 3H),
4.9. Enantioselective synthesis of ethyl 3-phenyl-4-pentenoate
(2c)
To the solution of 3-phenyl-4-pentenoic acid (1 mmol) in
toluene, triethyl orthoacetate (3 mmol) and enzyme (10 mg) were

A. Brodzka et al. / Journal of Molecular Catalysis B: Enzymatic 82 (2012) 96–101
101
2.24 (s, 1H), 2.37–2.62 (m, 2H), 3.20–3.40 (m, 1H), 3.40–3.60 (m,
2H), 4.00–4.40 (m, 2H), 5.68 (s, 1H), 6.88–7.00 (m, 2H), 7.09–7.32
(m, 8H); 13C NMR (50 MHz, CDCl3): 36.6, 39.3, 39.4, 43.8, 44.2,
60.7, 127.0, 127.6, 127.7, 127.8, 128.9, 129.1, 138.2, 144.1, 172.0;
[˛]D = +1.9 (c = 1.5, CHCl3).
-158/09-01, part-financed by the European Union within the Euro-
pean Regional Development Fund.
References
[1] (a) M.C. Nunez, M.E. Garcia-Rubino, A. Conejo-Garcia, O. Cruz-Lopez, M.
Kimatrai, M.A. Gallo, A. Espinos, J.M. Campos, Curr. Med. Chem. 16 (2009)
2064–2074;
(b) R.N. Patel, Coord. Chem. Rev. 252 (2008) 659–701;
(c) H. Murakami, Top. Curr. Chem. 269 (2007) 273–299;
(d) R.N. Patel, Curr. Opin. Drug Discov. Dev. 9 (2006) 741–764;
(d) R.N. Patel, Curr. Org. Chem. 10 (2006) 1289–1321.
[2] T. Ito, L.E. Overman, J. Wang, J. Am. Chem. Soc. 132 (2010) 3272–3273.
[3] G.E. Tomkins, J.L. Jackson, P.G. O’Malley, E. Balden, J.E. Santoro, Am. J. Med. 11
(2001) 54.
[4] N.S. Mani, M. Wu, Tetrahedron: Asymmetry 11 (2000) 4687.
[5] D. Koszelewski, D. Clay, K. Faber, W. Kroutil, J. Mol. Catal. B: Enzym. 60 (2009)
191–194.
[6] E. Brown, C. Deroye, J. Touet, Tetrahedron: Asymmetry 9 (1998) 1605–1614.
[7] B.K. Park, M. Nakagawa, A. Hirota, A. Nakayama, J. Antibiot. (Tokyo) 41 (1998)
751–758.
[8] K. Mitsui, T. Sato, H. Urabe, F. Sato, Angew. Chem. Int. Ed. 43 (2004) 490–492.
[9] M. Gao, D. Wang, Q. Zheng, M. Wang, J. Org. Chem. 71 (2006) 9532–9535.
[10] (a) W. Szyman´ ski, R. Ostaszewski, Tetrahedron 64 (2008) 3197–3203;
(b) W. Szyman´ ski, M. Zwolin´ ska, R. Ostaszewski, Tetrahedron 63 (2007)
7647–7653;
(c) W. Szyman´ ski, R. Ostaszewski, Tetrahedron: Asymmetry 17 (2006)
2667–2671.
[11] D. Koszelewski, A. Redzej, R. Ostaszewski, J. Mol. Catal. B 47 (2007) 51–57.
[12] (a) A. Fryszkowska, M. Komar, D. Koszelewski, R. Ostaszewski, Tetrahedron:
Asymmetry 16 (2005) 2475–2485;
4.13. Synthesis of benzyl amide of
(+)-3-(4ꢀ-fluorophenyl)-4-bromopentanoic acid (5)
To the solution of benzyl amide of (+)-3-phenyl-5-
hydroxypentanoic acid (4) (0.53 mmol) in dry methylene chloride
(5 ml) triphenylphosphine (0.63 mmol) and tetrabromomethane
(0.64 mmol) were added. The mixture was stirring in room
temperature for 24 h. and the solvent excess was evaporated
under vacuum. The crude product was purified by silica gel flash
chromatography using hexane/ethyl acetate as an eluent (41%
yield); Elemental analysis: calcd. for C18H20NOBr: C, 62.44%, H,
5.82%, N, 4.05%, found: C, 62.38%, H, 5.99%, N, 4.03%; 1H NMR
(200 MHz, CDCl3): 2.12–2.42 (m, 2H), 2.48–2.72 (m, 2H), 3.12–3.55
(m, 3H), 5.59 (s, 1H), 6.98–7.12 (m, 2H), 7.21–7.44 (m, 8H); 13C
NMR (50 MHz, CDCl3): 36.6, 39.3, 39.4, 43.8, 44.2, 60.7, 127.0,
127.6, 127.7, 127.8, 128.9, 129.1, 138.2, 144.1, 172.0; [˛]D = +20.1
(c = 1.0, CHCl3).
4.14. Synthesis of N-benzyl-(R)-4-phenyl-2-piperidinone (6)
(b) A. Fryszkowska, M. Komar, D. Koszelewski, R. Ostaszewski, Tetrahedron:
Asymmetry 17 (2006) 961–966;
To the solution of benzyl amide of (+)-3-(4ꢀ-fluorophenyl)-
4-bromopentanoic acid (5) (0.15 mmol) in dry tetrahydrofunane
(10 ml) sodium hydroxide (0.30 mmol) was added and reaction
mixture was stirred in 85 ◦C for 24 h. After that methanol was added
(2 ml) and solvent excess evaporated under vacuum. The residue
was dissolved in water and extracted with ethyl acetate (3 × 15 ml).
The combined organic layers were dried over MgSO4, filtered and
concentrated under vacuum. The crude product was purified by
crystallization from hexane/ethyl acetate (89% yield).
Elemental analysis: calcd. for C18H19NO: C, 81.48%, H, 7.22%, N,
5.28%, found: C, 81.64%, H, 7.435%, N, 5.34%; 1H NMR (200 MHz,
CDCl3): 1.80–2.15 (m, 2H), 2.48–2.90 (m, 2H), 3.00–3.20 (m, 1H),
3.21–3.40 (m, 2H), 4.65 (dd, J = 15.0, 7.0 Hz, 2H), 7.10–7.40 (m, 10H);
13C NMR (50 MHz, CDCl3): 30.5, 38.9, 39.7, 46.6, 50.3, 126.7, 127.0,
127.7, 128.4, 128.8, 128.9, 137.3, 143.6, 169.5; [˛]D = +36.2 (c = 1.12,
CHCl3).
(c) J. Frelek, A. Fryszkowska, M. Kwit, R. Ostaszewski, Tetrahedron: Asymmetry
17 (2006) 2469–2478.
[13] F. Bermejo Gonzalez, P.A. Bartlett, Org. Synth. 64 (1986) 175.
[14] D. Basavaiah, ARKIVOC (2001) 70–82.
[15] P.S. Vankar, I. Bhattacharya, Y.D. Vankar, Tetrahedron: Asymmetry 7 (1996)
1683–1694.
[16] K. Kobata, K. Yoshikawa, M. Kohashi, T. Watanabe, Tetrahedron Lett. 37 (1996)
2789–2790.
[17] D. Basavaiah, P. Rama Krishna, T.K. Bharathi, Tetrahedron Lett. 30 (1990)
434–4348.
[18] J. Nie, H.-C. Guo, D. Cahard, J.-A. Ma, Chem. Rev. 111 (2011) 455–529.
[19] T. Miyazawa, M. Shimaoka, T. Yamada, Biotechnol. Lett. 21 (1999) 309.
[20] C.S. Chen, Y. Fujimoto, G. Girdaukas, C.J. Sih, J. Am. Chem. Soc. 104 (1982) 7294.
[21] J.I. Trujillo, A.S. Gopalan, Tetrahedron Lett. 34 (46) (1993) 7355–7358.
[22] M. Ito, A. Sakaguchi, C. Kobayashi, T. Ikariya, J. Am. Chem. Soc. 129 (2007)
290.
[23] T. Senda, M. Ogasawara, T. Hayashi, J. Org. Chem. 66 (2001) 6852.
[24] S. Brandau, A. Landa, J. Franzen, M. Marigo, K.A. Jorgensen, Angew. Chem. Int.
Ed. 45 (2006) 4305.
[25] A.L. Gutman, E. Meyer, X. Yue, C. Abell, Tetrahedron Lett. 33 (1992) 3943–4394.
[26] Meyers, R. Keith Smith, C.E. Whitten, J. Org. Chem. 44 (1979) 2250.
[27] R.E. Deasy, M. Brossat, T.S. Moody, A.R. Maguire, Tetrahedron: Asymmetry 22
(2011) 47–61.
[28] K. Adachi, S. Kobayashi, M. Ohno, Chimia 40 (1986) 317.
[29] G. Gilbert, B.F. Aycock, J. Org. Chem. 22 (1957) 1013.
[30] G. Heuger, S. Kalsow, R. Gottlich, Eur. J. Org. Chem. (2002) 1848.
[31] E. Vedejs, M. Gingras, J. Am. Chem. Soc. 116 (1994) 579.
Acknowledgments
This work was supported by project “Biotransformations for
pharmaceutical and cosmetics industry”, No. POIG.01.03.01-00