An efficient new enzymatic method for the preparation of β-aryl-β-amino acid enantiomers

Article abstract of DOI:10.1016/j.tetasy.2008.08.009

An efficient synthesis of β-aryl-β-amino acid enantiomers has been developed via the lipase-catalysed enantioselective hydrolysis of the corresponding racemic ethyl esters in an organic solvent. High enantioselectivities (E >100) were observed when the lipase PS-catalysed reactions were performed with H₂O (0.5 equiv) in diisopropyl ether at 45 °C. The products could be easily separated and were obtained in good yields of ≥40%.

Full text of DOI:10.1016/j.tetasy.2008.08.009

Tetrahedron: Asymmetry 19 (2008) 2072–2077
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An efficient new enzymatic method for the preparation of b-aryl-b-amino
acid enantiomers
a
a,
a,b,
*
*
}
Gábor Tasnádi , Eniko Forró , Ferenc Fülöp
a Institute of Pharmaceutical Chemistry, University of Szeged, H-6720 Szeged, Eötvös u. 6, Hungary
b Research Group for Stereochemistry, Hungarian Academy of Sciences, University of Szeged, H-6720 Szeged, Eötvös u. 6, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient synthesis of b-aryl-b-amino acid enantiomers has been developed via the lipase-catalysed
enantioselective hydrolysis of the corresponding racemic ethyl esters in an organic solvent. High enantio-
selectivities (E >100) were observed when the lipase PS-catalysed reactions were performed with H2O
(0.5 equiv) in diisopropyl ether at 45 °C. The products could be easily separated and were obtained in
good yields of P40%.
Received 17 July 2008
Accepted 6 August 2008
Available online 29 August 2008
Ó 2008 Published by Elsevier Ltd.
1. Introduction
NS5B polymerase inhibitors against the hepatitis C virus,15 anti-
inflammatory bradykinin B1 receptor antagonists,16 anticancer
b-Amino acids, including b-aryl-substituted b-amino acids, are
widely used in drug research, and their pharmacological signifi-
cance has been described.1 There are several methods for the syn-
thesis of enantiopure b-aryl-b-amino acids, such as (i) the
enantioselective reduction of a b-enamino ester;2 (ii) the addition
of a chiral sulfoxide to a substituted N-sulfonylimine;3 (iii) an
asymmetric catalytic Mannich reaction;4 (iv) the conjugate addi-
matrix metalloproteinase (MMP-12) inhibitors17 or analgesic
endomorphin-1 analogue tetrapeptides.18 (S)-b-Phenylalanine 7a
has been applied in the synthesis of novel antibiotics.19 In addition
to b-phenylalanine, we set out to prepare b-amino acid enantio-
mers with pharmaceutical potential. (S)-3-Amino-3-(3-fluoro-
phenyl)propanoic acid 7b was used to obtain chemokine receptor
(CCR5) antagonists with anti-inflammatory and anti-HIV effects.20
The (R)-isomer of 3-amino-3-(3,5-dichlorophenyl)propanoic acid
tion of a chiral lithium amide to a b-aryl
a
,b-unsaturated ester;5
(v) the reaction of a Reformatsky reagent with an imine;6 or (vi)
the preparation of a diastereomeric salt.7 In addition to asymmetric
synthetic routes,2–7 enzyme-catalysed processes have been devel-
oped through (i) the transesterification of an N-protected ester in
isobutanol;8 (ii) stereoselective degradation of a racemic amino
acid;9 (iii) hydrolysis of a racemic b-amino ester;10 (iv) hydrolysis
of a racemic N-acetylated b-amino acid;11 or (v) an aminomutase-
6c was investigated as part of an integrin receptor avb3 antago-
nist.21 This receptor is an interesting therapeutic target in the
treatment of osteoporosis, restenosis, cancer growth and metasta-
sis formation. Several VLA-4 integrin receptor antagonists have
been synthetized, including the (S)-3-amino-3-(3,4-dimethoxy-
phenyl)propanoic acid 7d unit, and used against inflammatory
and autoimmune diseases.22 One non-peptide bradykinin B1
receptor antagonist with anti-inflammatory and analgesic effects
contains an (R)-3-amino-3-benzo[1,3]dioxol-5-ylpropanoic acid
6e moiety.23
catalysed a
,b-rearrangement12 in aqueous medium.
We recently reported some direct and indirect enzymatic meth-
ods for the preparation of enantiomers of b-phenylalanine or its
derivatives from racemic b-lactams.13 Previously, we devised the
first direct enzymatic highly enantioselective (E >100) hydrolysis
of carbocyclic b-amino esters in i-Pr2O with Lipolase at 60 °C.14
Herein, our goal was to extend this method to b-aryl-substi-
tuted b-amino esters, hydrolysing them to enantiopure b-aryl-b-
amino acids. b-Phenylalanine was chosen as the model compound.
There are complex structures which include an (R)- or (S)-b-phen-
ylalanine 6a or 7a moiety. For example, 6a has been inserted into
2. Results and discussion
2.1. Syntheses of ethyl 3-amino-3-arylpropanoates 3a–e
The racemic compounds 2a–e were first synthesized by a mod-
ified Rodionov synthesis from the corresponding 1a–e through
condensation with malonic acid and in the presence of NH4OAc,
the mixture was heated at reflux in EtOH (Scheme 1).11c Com-
pounds 3a–eꢀHCl were prepared by the esterification of 2a–e in
the presence of SOCl2. The free bases 3a–e were then liberated
by treatment of 3a–eꢀHCl with aqueous KOH.
* Corresponding authors. Tel.: +36 62 545564; fax: +36 62 545705 (F.F.).
E-mail addresses: Forro.Eniko@pharm.u-szeged.hu (E. Forró), fulop@pharm.
u-szeged.hu (F. Fülöp).
0957-4166/$ - see front matter Ó 2008 Published by Elsevier Ltd.
doi:10.1016/j.tetasy.2008.08.009

G. Tasnádi et al. / Tetrahedron: Asymmetry 19 (2008) 2072–2077
2073
COOH
NH2
Next, we analysed the effect of the solvent (Table 2). All the sol-
vents tested proved to be suitable for the enantioselective (E >200)
hydrolysis of 3a, with significant differences in the reaction rate.
The highest reaction rates were observed in i-Pr2O, t-BuOMe and
n-hexane (entries 1, 2 and 4), while the hydrolysis was slowest
in CHCl3 (entry 7). We chose to continue our experiments with i-
Pr2O.
COOEt
NH2
NH4OAc
CH2(COOH)2
O
1. SOCl2, EtOH
2. aq. KOH
EtOH, reflux
Ar
Cl
Ar
H
Ar
1a-e
2a-e
3a-e
Ar:
MeO
O
O
MeO
Table 2
Effect of solvents on the hydrolysis of 3aa
F
Cl
c
a
b
d
e
b
c
Entry
Solvent (1 mL)
Conv. (%)
ees (%)
eep (%)
E
Scheme 1. Synthesis of 3a–e.
1
2
3
4
5
6
7
8
9
i-Pr2O
t-BuOMe
Et2O
n-Hexane
Toluene
1,4-Dioxane
CHCl3
49
48
39
50
38
26
4
96
92
63
98
60
34
4
>99
>99
>99
>99
>99
>99
>99
>99
>99
>200
>200
>200
>200
>200
>200
>200
>200
>200
2.2. Lipase-catalysed enantioselective ring cleavage of 3a–e
Previous results14 on the lipase-catalysed enantioselective
hydrolysis of carbocyclic b-amino esters suggested the possibility
of the enantioselective hydrolysis of 3a–e with 0.5 equiv of H2O
in the presence of Lipolase (CAL-B) in i-Pr2O at 60 °C. Since Lipolase
did not exhibit any selectivity towards 3a, further enzymes were
screened, including lipase PS (Pseudomonas cepacia), PPL (porcine
pancreatic lipase), lipase AK (Pseudomonas fluorescens), lipase AY
(Candida rugosa) and Chirazyme L-5 (lipase A from Candida antarc-
tica) (Table 1).
THF
Me2CO
14
13
16
15
0.05 M substrate, 0.5 equiv. of H2O, 50 mg mLꢁ1 lipase PSd, after 5 h.
According to GC after derivatization.
According to GC after double derivatization.
a
b
c
d
Contains 20% (w/w) lipase adsorbed on Celite in the presence of sucrose.
The reaction rate for the hydrolysis of 3a clearly increased as
the amount of enzyme was increased (Table 3). The highest reac-
tion rate was observed in the presence of 75 mg mLꢁ1 lipase PS
(entry 6). However, for economic reasons, 30 mg mLꢁ1 lipase PS
was chosen for the preparative-scale resolutions of 3a–e.
Table 1
Conversion and enantioselectivity of the hydrolysis of 3aa
b
c
Entry
Enzyme
H2O
T (°C)
t (h)
Conv.
(%)
ees
(%)
eep
(%)
E
(50 mg mLꢁ1
)
(equiv)
1
2
3
4
5
6
7
8
PPL
0.5
0.5
0.5
0.5
—
1
2
5
45
45
25
45
45
45
45
45
5
5
6
5
2
2
2
2
43
43
49
49
46
48
50
50
66
67
92
96
85
93
99
>99
88
89
31
Table 3
lipase AKd
Lipase PSd
Lipase PSd
Lipase PSd
Lipase PSd
Lipase PSd
Lipase PSd
35
>200
>200
>200
>200
>200
>200
Effect of the quantity of lipase PS on the hydrolysis of 3aa
>99
>99
>99
>99
>99
>99
Lipase PSd (mg mLꢁ1
)
Conv. (%)
ees (%)
eep (%)
E
b
c
Entry
1
2
3
4
5
6
10
20
30
40
50
75
17 (45 after 24 h)
20
36
45
54
60
82
>99
>99
>99
>99
>99
>99
>200
>200
>200
>200
>200
>200
27
31
35
38
45
a
0.05 M substrate, 1 mL i-Pr2O.
According to GC after derivatization (Section 4).
According to GC after double derivatization (Section 4).
b
c
a
0.05 M substrate, 0.5 equiv of H2O, 1 mL i-Pr2O, after 1 h.
According to GC after derivatization.
According to GC after double derivatization.
d
b
c
Contains 20% (w/w) lipase adsorbed on Celite in the presence of sucrose.
d
Contains 20% (w/w) lipase adsorbed on Celite in the presence of sucrose.
A key issue was to develop a simple analytical method allowing
the progress of the reactions to be followed. The unreacted amino
ester and the product amino acid were detected in the same run by
GC on a chiral column, where the hydrolysed amino acid was
derivatized (Section 4).
All enzymes were active in the presence of 0.5 equiv of H2O in i-
Pr2O at 45 °C, but lipase AY and Chirazyme L-5 did not exhibit any
selectivity towards 3a, while PPL and lipase AK catalysed the reac-
tion with moderate enantioselectivities (entries 1 and 2). Lipase PS
directed the hydrolysis with excellent enantioselectivity (E >200)
(entry 4). When the lipase PS-catalysed hydrolysis of 3a was per-
formed at 25 °C, a slight decrease in the reaction rate was observed
(entry 3).
Next, we analysed the effects of the amount of added H2O on
the enantioselectivity and the reaction rate. The added H2O
amount (1–5 equiv) apparently did not affect the enantioselectivi-
ty (E >200) or the reaction rate (Table 1, entries 6, 7 and 8), but
when an i-Pr2O/H2O 1/1 (v/v) mixture was used, a dramatic de-
crease in the enantioselectivity was observed (E = 30). In a small-
scale experiment, the hydrolysis of 3a was complete, even without
the addition of H2O (entry 5). In this case, the H2O originated from
the reaction medium (<0.1%) or from the enzyme preparation
(<5%).
In view of the results of the preliminary experiments, the
preparative-scale resolutions of 3a–e were performed with
0.5 equiv of H2O in the presence of lipase PS in i-Pr2O at 45 °C.
The products were characterized by a good enantiomeric excess
at close to 50% conversion. The results are reported in Table 4
and in Section 4.
2.3. Transformations of the enantiomers
The transformations involving the hydrolysis of 4a–e with
aqueous HCl afforded 6a–eꢀHCl (ee P 97%) (Scheme 2). Treatment
of 5a–e with 22% HCl/EtOH resulted in the corresponding enantio-
pure 7a–eꢀHCl (ee >99%).
The absolute configurations in the cases of 5a, 5d and 5c were
proved by comparing the [a] values with literature data (Section
4), while for 5b and 5c the chromatograms analysed indicated
the same enantiopreference for all the enzymes applied. Thus,
the absolute configurations indicated the (S)-selective hydrolysis
of 3a–e. Although the enantiomers 5b10c and the ethyl ester of
5c24 have been prepared, physical data for them (specific rotations
and melting points) have not been described. It should be

2074
G. Tasnádi et al. / Tetrahedron: Asymmetry 19 (2008) 2072–2077
Table 4
Lipase PS-catalysed hydrolysis of 3a–ea
Time (h)
Conv. (%)
E
b-Amino acidꢀHCl (6a–e)
b-Amino acid (5a–e)
Yield (%)
Isomer
eeb (%)
½
a 2D5
ꢂ
(H2O)
Yield (%)
Isomer
eec (%)
½
a 2D5
ꢂ
(H2O)
3a
3b
3c
3d
3e
22
23
74
18
16
50
49
50
50
52
>200
>200
139
>200
110
44
40
43
41
44
(R)
(R)
(R)
(R)
(R)
>99
>99
>99
>99
97
ꢁ4d
44
40
44
41
46
(S)
(S)
(S)
(S)
(S)
>99
>99
>99
>99
>99
ꢁ8e
ꢁ6.5f
ꢁ5.1h
ꢁ7.9i
ꢁ8.4k
ꢁ1.8g
ꢁ5.5g
+1.3j
+4d
a
b
c
d
e
f
30 mg mLꢁ1 enzyme in i-Pr2O, 0.5 equiv H2O, 45 °C.
According to GC after derivatization.
According to GC after double derivatization.
c = 0.3.
c = 0.27.
c = 0.31.
c = 0.38.
c = 0.34.
c = 0.32.
c = 0.51.
c = 0.33.
g
h
i
j
k
fermentation of a genetically modified Aspergillus oryzae microor-
ganism and adsorbed on a macroporous resin) and PPL (type II)
were from Sigma, and Chirazyme L-5 (lipase B from C. antarctica)
was from Novo Nordisk. Before use, lipase PS, lipase AK and CAL-
A (5 g) were dissolved in Tris–HCl buffer (0.02 M; pH 7.8) in the
presence of sucrose (3 g), followed by adsorption on Celite (17 g)
(Sigma). Substituted benzaldehydes were from Aldrich, except for
3,5-dichlorobenzaldehyde, which was from Fluorochem. The sol-
vents were of the highest analytical grade.
H2O
lipase PS
COOEt
NH2
COOEt
NH2
HOOC
H2N
(R)
(S)
Ar
5a-e
+
i-Pr2O
45 ºC
Ar
Ar
3a-e
4a-e
18% aq. HCl
Δ
22% HCl/EtOH
Optical rotations were measured with a Perkin–Elmer 341
polarimeter. 1H NMR and 13C NMR spectra were recorded on a
Bruker Avance DRX 400 spectrometer. Melting points were
determined on a Kofler apparatus. Elemental analyses (CHN)
corresponded closely (within 3%) with the calculated ones in all
cases.
COOEt
HOOC
(R)
(S)
Ar
Ar
NH2·HCl
HCl·H2N
6a-e
7a-e
The ee values for the unreacted b-amino ester and the b-amino
acid enantiomers produced were determined by GC on a Chirasil-L-
Val column (20 m) after double derivatization with (i) CH2N2 [Cau-
tion! derivatization with CH2N2 should be performed under a well-
working hood]; (ii) Ac2O in the presence of 4-dimethylaminopyri-
dine and pyridine [100 °C for 10 min?150 °C (temperature rise
10 °C minꢁ1), 140 kPa; retention times (min); 4a: 23.16 (antipode:
23.65); 5a: 21.11 (antipode: 20.80); 120 °C for 10 min?190 °C
(temperature rise 10 °C minꢁ1), 140 kPa; 4b: 16.32 (antipode:
16.45); 5b: 15.81 (antipode: 15.69); 130 °C for 10 min?160 °C
(temperature rise 10 °C minꢁ1), 140 kPa; 4c: 40.59 (antipode:
42.29); 5c: 37.60 (antipode: 36.06); 4d: 56.58 (antipode: 58.20);
5d: 48.42 (antipode: 47.39); 4e: 43.33 (antipode: 45.00); 5e:
38.17 (antipode: 37.06)].
Scheme 2. Lipase PS-catalysed enantioselective hydrolysis of 3a–e (for the
meanings of a–e, see Scheme 1).
mentioned that lipase PS demonstrated the opposite selectivity in
the hydrolysis of 3a–e as compared with the CAL-B-catalysed
enantioselective ring-opening of 4-aryl-substituted b-lactams,
which was R-selective.13c
3. Conclusions
A simple and efficient direct enzymatic method has been devel-
oped for the synthesis of pharmacologically valuable, optically
active b-aryl-substituted b-amino acids via the enantioselective
hydrolysis of the corresponding racemic b-amino esters in an
organic medium. The lipase PS-catalysed (S)-selective hydrolysis
of 3a–e with H2O (0.5 equiv) as a nucleophile in i-Pr2O at 45 °C
led to enantiomers of 4a–e (ee P 97%) and 5a–e (ee >99%) with
high enantioselectivities (E >100) in good chemical yields
(40–46%). The products could be easily separated. Transformations
of 4a–e with 18% aqueous HCl resulted in the enantiomers of
6a–eꢀHCl (ee P 97%).
4.2. General procedure for the syntheses of racemic b-amino
acids 2a–e
Compounds 2a–e were prepared by a slightly modified litera-
ture method11c based on the modified Rodionov synthesis from
the corresponding 1a–e (5 mmol) through condensation with
malonic acid (2 equiv) in the presence of NH4Ac (2 equiv) in EtOH
at reflux for 6 h. The resulting precipitated crystals were filtered
off, washed with Me2CO and recrystallized from H2O and Me2CO.
4. Experimental
4.1. Materials and methods
4.2.1. ( )-3-Amino-3-phenylpropanoic acid 2a
Yield: 0.46 g (56%); mp 235–235 °C (lit.25 mp 220–222 °C). The
1H NMR and 13C NMR data are in accordance with those reported in
the literature.2
Lipase PS and lipase AK were from Amano Pharmaceuticals,
Lipolase (lipase B from C. antarctica was produced by submerged

G. Tasnádi et al. / Tetrahedron: Asymmetry 19 (2008) 2072–2077
2075
4.2.2. ( )-3-Amino-3-(3-fluorophenyl)propanoic acid 2b
Yield: 0.52 g (57%); mp 237–239 °C. The 1H NMR and 13C NMR
data are in accordance with those reported in the literature.10c
CH2CO), 4.05–4.11 (2H, m, CH2CH3), 4.68–4.70 (1H, t, J = 7.48 Hz,
CH), 5.96 (2H, s, OCH2O), 6.88–6.94 (3H, m, Ar). 13C NMR
(100.62 MHz, D2O) d (ppm): 13.2, 37.9, 51.5, 62.5, 101.6, 107.3,
121.5, 128.6, 148.2, 171.6.
4.2.3. ( )-3-Amino-3-(3,5-dichlorophenyl)propanoic acid 2c
Yield: 0.51 g (44%); mp 225–228 °C. 1H NMR (400 MHz, DMSO-
d6) d (ppm): 2.74–2.88 (2H, m, CH2), 4.59–4.63 (1H, m, CH), 7.41
(2H, m, Ar), 7.53 (1H, m, Ar). 13C NMR (100.62 MHz, DMSO-d6) d
(ppm): 40.2, 51.7, 125.6, 129.0, 134.9, 139.5, 176.7.
4.4. Typical small-scale enzyme tests
Racemic 3a (0.05 M solution) in an organic solvent or H2O
(1 mL) was added to the enzyme tested (10, 20, 30, 40, 50 or
75 mg mLꢁ1), followed by H2O (0, 0.5, 1, 2 or 15 equiv). The mix-
ture was shaken at either 3, 25, 45 or 60 °C. The progress of the
reaction was followed by taking samples from the reaction mixture
at intervals and analysing them by GC.
4.2.4. ( )-3-Amino-3-(3,4-dimethoxyphenyl)propanoic acid 2d
Yield: 0.52 g (46%); mp 238–240 °C (lit.26 mp 248–249 °C). The
1H NMR and 13C NMR data are in accordance with those reported in
the literature.27
4.2.5. ( )-3-Amino-3-benzo[1,3]dioxol-5-ylpropanoic acid 2e
Yield: 0.54 g (52%); mp 230–233 °C. The 1H NMR and 13C NMR
data are in accordance with those reported in the literature.5b
4.5. General procedure for the preparative-scale resolutions of
3a-e
Racemic compounds 3a–e (3 mmol) were dissolved in i-Pr2O
(25 mL). Lipase PS (0.75 g, 30 mg mLꢁ1) and H2O (27
lL, 1.5 mmol)
4.3. General procedure for the syntheses of racemic b-amino
esters 3a–e
were added and the mixture was shaken in an incubator shaker at
45 °C for 16–74 h (Table 4). The reaction was stopped by filtering
off the enzyme at 50% conversion. The solvent was evaporated
off and the residues (R)-4a–e were immediately hydrolysed by
refluxing (5 h) with 18% aqueous HCl solution (6 mL) to give (R)-
6a–eꢀHCl (in the case of 3e, the unreacted 4e was hydrolysed by
shaking at room temperature for 12 h with 3.6% aqueous HCl solu-
tion). The filtered off enzyme was washed with distilled H2O
(3 ꢃ 15 mL), and the H2O was evaporated off, yielding the crystal-
line (S)-5a–e.
To 40 mL of EtOH was added dropwise 0.55 mL of SOCl2, with
the temperature being kept under –10 °C with saline ice. To this
solution, 2a–e (5 mmol) were added. The mixture was stirred at
0 °C for 30 min, and then at room temperature for 3 h, and finally
heated at reflux for 1 h. The solvent was evaporated off and the
resulting 3a–eꢀHCl were recrystallized from EtOH and Et2O. Treat-
ment of 3a–eꢀHCl with aqueous KOH resulted in the free 3a–e as
pale-yellow oils.
When (S)-5a–e (50 mg) were treated with 22% HCl/EtOH (5 mL),
(S)-7a–eꢀHCl were obtained.
4.3.1. Hydrochloride salt of ethyl ( )-3-amino-3-phenyl-
propanoate 3aꢀHCl
Yield: 1.05 g (91%); mp 141–144 °C (lit.25 mp 138–141 °C). The
1H NMR and 13C NMR data are in accordance with those reported in
the literature.25
4.5.1. Hydrochloride salt of (R)-3-amino-3-phenylpropanoic
acid 6a
Yield: 266 mg (44%); recrystallized from EtOH and Et2O;
½
a 2D5
ꢂ
¼ ꢁ4 (c 0.3, H2O) {lit.13c
½
a 2D5
ꢂ
¼ ꢁ3 (c 0.3, H2O)}; mp 195–
4.3.2. Hydrochloride salt of ethyl ( )-3-amino-3-(3-fluoro-
phenyl)propanoate hydrochloride 3bꢀHCl
198 °C (lit.13c mp 195–198 °C); ee >99%. The 1H NMR data for 6a
are in accordance with those reported in the literature.13c 13C
NMR (100.62 MHz, D2O) d (ppm): 38.3, 52.0, 127.5, 129.8, 130.1,
135.6, 174.1.
Yield: 1.14 g (92%); mp 148–151 °C. The 1H NMR data are in
accordance with those reported in the literature.28 13C NMR
(100.62 MHz, D2O) d (ppm): 13.6, 38.4, 51.5, 62.9, 114.5, 114.7,
116.9, 117.1, 131.8, 131.8, 137.2, 161.5, 164.0, 171.3.
4.5.2. (S)-3-Amino-3-phenylpropanoic acid 5a
4.3.3. Hydrochloride salt of ethyl ( )-3-amino-3-(3,5-
dichlorophenyl)propanoate hydrochloride 3cꢀHCl
Yield: 218 mg (44%); recrystallized from H2O and Me2CO;
½
a 2D5
ꢂ
¼ ꢁ8 (c 0.27; H2O) {lit.13c
½
a 2D5
ꢂ
¼ þ7 (c 0.27, H2O) for (R)-
Yield: 1.22 g (82%); mp 180–185 °C. 1H NMR (400 MHz, D2O) d
(ppm): 1.13–1.17 (3H, t, J = 7.16 Hz, CH3), 3.06–3.21 (2H, m,
CH2CO), 4.08–4.15 (2H, m, CH2CH3), 4.77–4.81 (1H, t, J = 7.27 Hz,
CH), 7.44–7.45 (2H, m, Ar), 7.54 (1H, m, Ar). 13C NMR
(100.62 MHz, D2O) d (ppm): 13.6, 38.2, 51.0, 62.9, 126.4, 130.1,
135.8, 138.7, 171.5.
5a}; mp 251–253 °C (lit.13c mp 242–246 °C); ee >99%. The 1H
NMR (400 MHz, D2O) and 13C NMR (100.62 MHz, D2O) d (ppm)
data for 5a are similar to those for 2a.
4.5.3. Hydrochloride salt of (S)-3-amino-3-phenylpropanoic
acid 7a
Quantitative yield; ½a D25
ꢂ
¼ þ4 (c 0.3, H2O) {lit.13c
½
a 2D5
ꢂ
¼ þ3 (c
4.3.4. Hydrochloride salt of ethyl ( )-3-amino-3-(3,4-
0.28; H2O)}; mp 197–200 °C (lit.13c mp 197–201 °C); ee >99%.
The 1H NMR (400 MHz, D2O) and 13C NMR (100.62 MHz, D2O) d
(ppm) data for 7a are similar to those for 6a.
dimethoxyphenyl)propanoate hydrochloride 3dꢀHCl
Yield: 1.27 g (88%); mp 218–221 °C (lit.29 mp 206–208 °C). 1H
NMR (400 MHz, D2O) d (ppm): 1.10–1.14 (3H, t, J = 7.15 Hz, CH3),
3.05–3.21 (2H, m, CH2CO), 3.84 (1H, s, OCH3), 3.86 (1H, s, OCH3),
4.07–4.12 (2H, m, CH2CH3), 4.73–4.76 (1H, t, J = 7.44 Hz, CH),
7.04–7.09 (3H, m, Ar). 13C NMR (100.62 MHz, D2O) d (ppm): 13.1,
37.9, 51.1, 55.8, 62.2, 110.5, 112.2, 120.5, 128.1, 148.6, 171.4.
4.5.4. Hydrochloride salt of (R)-3-amino-3-(3-fluoro-
phenyl)propanoic acid 6b
Yield: 264 mg (40%); recrystallized from EtOH and Et2O;
½
a 2D5
ꢂ
¼ ꢁ6:5 (c 0.31, H2O); mp 181–190 °C (slow melting); ee
>99%. The 1H NMR data for 6b are in accordance with those re-
ported in the literature.30 13C NMR (100.62 MHz, D2O) d (ppm):
38.1, 51.5, 114.4, 114.7, 116.8, 117.1, 123.4, 131.7, 131.8, 137.9,
164.3, 173.9.
4.3.5. Hydrochloride salt of ethyl ( )-3-amino-3-
benzo[1,3]dioxol-5-ylpropanoate hydrochloride 3eꢀHCl
Yield: 1.26 g (92%); mp 189–191 °C. 1H NMR (400 MHz, D2O) d
(ppm): 1.10–1.13 (3H, t, J = 7.15 Hz, CH3), 3.00–3.15 (2H, m,

2076
G. Tasnádi et al. / Tetrahedron: Asymmetry 19 (2008) 2072–2077
4.5.5. (S)-3-Amino-3-(3-fluorophenyl)propanoic acid 5b
4.5.14. (S)-3-Amino-3-benzo[1,3]dioxol-5-ylpropanoic acid 5e
Yield: 220 mg (40%); recrystallized from H2O and Me2CO;
Yield: 289 mg (46%); recrystallized from H2O and Me2CO;
½
a 2D5
ꢂ
¼ ꢁ1:8 (c 0.38, H2O); mp 226–229 °C; ee >99%. The 1H NMR
½
a 2D5
ꢂ
¼ þ4 (c 0.3, H2O) {lit.5b
½
a 2D5
ꢂ
¼ þ42:4 (c 0.3, H2O)}; mp 231–
(400 MHz, D2O) and 13C NMR (100.62 MHz, D2O) d (ppm) data
for 5b are similar to those for 2b.
234 °C (lit.5b mp 219–220 °C); ee >99%. The 1H NMR (400 MHz,
D2O) and 13C NMR (100.62 MHz, D2O) d (ppm) data for 5e are sim-
ilar to those for 2e.
4.5.6. Hydrochloride salt of (S)-3-amino-3-(3-fluoro-
4.5.15. Hydrochloride salt of (S)-3-amino-3-benzo[1,3]dioxol-5-
phenyl)propanoic acid 7b
Quantitative yield; ½a D25
¼ þ5:7 (c 0.31, H2O); mp 185–194 °C
ꢂ
ylpropanoic acid 7e
Quantitative yield; ½a D25
¼ þ8:9 (c 0.33, H2O); mp 204–208 °C;
ꢂ
(slow melting); ee >99%. The 1H NMR (400 MHz, D2O) and 13C
NMR (100.62 MHz, D2O) d (ppm) data for 7b are similar to those
for 6b.
ee >99%. The 1H NMR (400 MHz, D2O) and 13C NMR (100.62 MHz,
D2O) d (ppm) data for 7e are similar to those for 6e.
Acknowledgements
4.5.7. Hydrochloride salt of (R)-3-amino-3-(3,5-dichloro-
phenyl)propanoic acid 6c
The authors acknowledge receipt of OTKA Grants K 71938 and T
049407 and a Bolyai Fellowship for E.F.
Yield: 349 mg (43%); recrystallized from EtOH and Et2O;
½
a 2D5
ꢂ
¼ ꢁ5:1 (c 0.34, H2O); mp 208–210 °C; ee = 97%. 1H NMR
(400 MHz, D2O) d (ppm): 3.07–3.13 (2H, m, CH2), 4.74–4.78 (1H,
t, J = 7.04 Hz, CH), 7.45 (2H, m, Ar), 7.56 (1H, m, Ar). 13C NMR
(100.62 MHz, D2O) d (ppm): 37.7, 50.8, 125.8, 129.7, 135.2, 138.5,
173.4.
References
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2181; (c) Fülöp, F.; Martinek, T. A.; Tóth, G. K. Chem. Soc. Rev. 2006, 35, 323.
2. Cimarelli, C.; Palmieri, G.; Volpini, E. Synth. Commun. 2001, 31, 2943.
3. Sivakumar, A. V.; Babu, G. S.; Bhat, S. V. Tetrahedron: Asymmetry 2001, 12, 1095.
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2006, 17, 1793; (b) Davies, S. G.; Mulvaney, A. W.; Russel, A. J.; Smith, A. D.
Tetrahedron: Asymmetry 2007, 18, 1554.
4.5.8. (S)-3-Amino-3-(3,5-dichlorophenyl)propanoic acid 5c
Yield: 309 mg (44%); recrystallized from H2O and Me2CO;
½
a 2D5
ꢂ
¼ ꢁ5:5 (c 0.38, H2O); mp 219–221 °C; ee >99%. The 1H NMR
(400 MHz, D2O) and 13C NMR (100.62 MHz, D2O) d (ppm) data
for 5c are similar to those for 2c.
6. Lange, B.; Elsenberg, H. L. M.; Broxterman, Q. B.; van der Slius, M.; Uiterweerd,
P. G. H. Patent WO 06069798, 2006.
7. (a) Muller, G. W.; Chen, R. S. Patent WO 04045597, 2004; (b) Muller, G. W.;
Chen, R. S. Patent WO 04054501, 2004.
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629.
4.5.9. Hydrochloride salt of (S)-3-amino-3-(3,5-
dichlorophenyl)propanoic acid 7c
Quantitative yield; ½a D25
¼ þ5:7 (c 0.34, H2O); mp 212–214 °C;
ꢂ
ee >99%. The 1H NMR (400 MHz, D2O) and 13C NMR (100.62 MHz,
9. Mano, J.; Ogawa, J.; Shimizu, S. Biosci. Biotechnol. Biochem. 2006, 70, 1941.
10. (a) Faulconbridge, S. J.; Holt, K. E.; Sevillano, L. G.; Lock, C. J.; Tiffin, P. D.;
Tremayne, N.; Winter, S. Tetrahedron Lett. 2000, 41, 2679; (b) Ogawa, J.; Mano,
J.; Shimizu, S. Appl. Microbiol. Biotechnol. 2006, 70, 663; (c) Yamamoto, Y.;
Miyata, H.; Konegawa, T.; Sakata, K. U.S. Patent 0,178,433, 2006.
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V.; Sorochinsky, A. E.; Kukhar, V. P. Tetrahedron: Asymmetry 1995, 6, 1601; (b)
Groger, H.; Trauthwein, H.; Buchholz, S.; Drauz, K.; Sacherer, C.; Godfrin, S.;
Werner, H. Org. Biomol. Chem. 2004, 14, 1977; (c) Kawasaki, H.; Koyama, K.;
Kurokawa, S.; Watanabe, K.; Nakazawa, M.; Izawa, K.; Nakamatsu, T. Biosci.
Biotechnol. Biochem. 2006, 70, 99; (d) Nakamatsu, T.; Kawasaki, H.; Watanabe,
K.; Nakazawa, M.; Izawa, K. E. U. Patent 1,624,052, 2006.
12. Mutatu, W.; Klettke, K. L.; Foster, C.; Walker, K. D. Biochemistry 2007, 46,
9785.
13. (a) Forró, E.; Fülöp, F. Tetrahedron: Asymmetry 2001, 12, 2351; (b) Park, S.;
Forró, E.; Grewal, H.; Fülöp, F.; Kazlauskas, R. J. Adv. Synth. Catal. 2003, 345, 986;
(c) Forró, E.; Paál, T.; Tasnádi, G.; Fülöp, F. Adv. Synth. Catal. 2006, 348, 917.
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D2O) d (ppm) data for 7c are similar to those for 6c.
4.5.10. Hydrochloride salt of (R)-3-amino-3-(3,4-
dimethoxyphenyl)propanoic acid 6d
Yield: 322 mg (41%); recrystallized from EtOH and Et2O;
½
a 2D5
ꢂ
¼ ꢁ7:9 (c 0.32, H2O); mp 178–181 °C; ee >99%. 1H NMR
(400 MHz, D2O) d (ppm): 2.98–3.14 (2H, m, CH2), 3.79–3.80 (3H,
d, J = 3.3 Hz, OCH3), 3.81–3.82 (3H, d, J = 2.1 Hz, OCH3), 4.68–4.70
(1H, m, CH), 7.02–7.04 (3H, m, Ar). 13C NMR (100.62 MHz, D2O) d
(ppm): 38.3, 51.8, 56.2, 56.3, 111.0, 112.6, 120.7, 128.6, 148.9,
149.4, 174.1.
15. Yan, S.; Larson, G.; Wu, J. Z.; Appleby, T.; Ding, Y.; Hamatake, R.; Hong, Z.; Yao,
N. Bioorg. Med. Chem. Lett. 2007, 17, 63.
4.5.11. (S)-3-Amino-3-(3,4-dimethoxyphenyl)propanoic acid 5d
Yield: 277 mg (41%); recrystallized from H2O and Me2CO;
16. D’Amico, D. C.; Aya, T.; Human, J.; Fotsch, C.; Chen, J. J.; Biswas, K.; Riahi, B.;
Norman, M. H.; Willoughby, C. A.; Hungate, R.; Reider, P. J.; Biddlecome, G.;
Lester-Zeiner, D.; Van Staden, C.; Johnson, E.; Kamassah, A.; Arik, L.; Wang, J.;
Viswanadhan, V. N.; Groneberg, R. D.; Zhan, J.; Suzuki, H.; Toro, A.; Mareska, D.
A.; Clarke, D. E.; Harvey, D. M.; Burgess, L. E.; Laird, E. R.; Askew, B.; Ng, G. J.
Med. Chem. 2007, 50, 607.
½
a 2D5
ꢂ
¼ þ1:3 (c 0.51, H2O) {lit.5b
½
a 2D5
ꢂ
¼ þ0:9 (c 0.7, H2O)}; mp
224–229 °C (lit.5b mp 216–219 °C); ee >99%. The 1H NMR
(400 MHz, D2O) and 13C NMR (100.62 MHz, D2O) d (ppm) data
for 5d are similar to those for 2d.
17. Dublanchet, A.-C.; Ducrot, P.; Andrianjara, C.; O’Gara, M.; Morales, R.; Compère,
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4.5.12. Hydrochloride salt of (S)-3-amino-3-(3,4-
dimethoxyphenyl)propanoic acid 7d
Quantitative yield; ½a D25
¼ þ7:2 (c 0.315, H2O); mp 177–181 °C;
ꢂ
ee >99%. The 1H NMR (400 MHz, D2O) and 13C NMR (100.62 MHz,
D2O) d (ppm) data for 7d are similar to those for 6d.
21. Nagarajan, S. R.; Devadas, B.; Malecha, J. W.; Lu, H.; Ruminski, P. G.; Rico, J. G.;
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4.5.13. Hydrochloride salt of (R)-3-amino-3-benzo[1,3]dioxol-
5-ylpropanoic acid 6e
Yield: 324 mg (44%); recrystallized from EtOH and Et2O;
½
a 2D5
ꢂ
¼ ꢁ8:4 (c 0.33, H2O); mp 203–207 °C; ee = 97%. The 1H NMR
data for 6e are in accordance with those reported in the litera-
ture.31 13C NMR (100.62 MHz, D2O) d (ppm): 38.0, 51.5, 101.9,
107.5, 109.2, 121.7, 129.4, 148.4, 173.8.

G. Tasnádi et al. / Tetrahedron: Asymmetry 19 (2008) 2072–2077
2077
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´
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