Synthesis and antagonist activities of 4-aryl-substituted conformationally restricted cyclopentenyl and cyclopentanyl-glutamate analogues

Article abstract of DOI:10.1016/j.tet.2004.12.024

The conformationally restricted glutamate analogues, 4-aryl-1-amino-2- cyclopentene-1,3-dicarboxylates and their cyclopentane analogues have been prepared in a diastereoselective manner. Biological studies of 12a and 12b indicates that both compounds are modest antagonists at mGluR2.

Full text of DOI:10.1016/j.tet.2004.12.024

Tetrahedron 61 (2005) 1803–1812
Synthesis and antagonist activities of 4-aryl-substituted
conformationally restricted cyclopentenyl and
cyclopentanyl-glutamate analogues
a,
a
a
a
Alison T. Ung,a, Stephen G. Pyne, Uta Batenburg-Nguyen, Andrew S. Davis, Azlifa Sherif,
*
*
Franc¸ois Bischoffb and Anne S. J. Lesageb
aDepartment of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia
bCNS Discovery Research, Johnson and Johnson Pharmaceutical Research and Development a Division of Janssen Pharmaceutica N.V.,
Beerse, B-2340, Belgium
Received 1 September 2004; revised 12 November 2004; accepted 9 December 2004
Available online 7 January 2005
Abstract—The conformationally restricted glutamate analogues, 4-aryl-1-amino-2-cyclopentene-1,3-dicarboxylates and their cyclopentane
analogues have been prepared in a diastereoselective manner. Biological studies of 12a and 12b indicates that both compounds are modest
antagonists at mGluR2.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
LY341495 (4), which displays antagonist activity at the
mGluR2 in the low nM range (IC50Z0.010G0.001 mM).5
[H3]LY341495 was synthesised and employed as a mGluR2
radioligand in receptor mapping studies.6 This compound
and its analogues have also been used to study the effect of
mGluR2 antagonists on locomotor activity in mice, with an
attempt to probe the function of this receptor.7 From a
consideration of these findings, we have synthesised several
4-aryl substituted derivatives of racemic 1 and 2,3-dehydro
1. We report here the diastereoselective synthesis of these 4-
aryl substituted derivatives and the activities of four of these
compounds as agonists and antagonists at mGluR2.
Considerable research efforts have been focused upon the
development of selective agonists and antagonists for the
ionotropic and metabotropic glutamate sub-type receptors.1
Such selective compounds have potential applications as
therapeutic agents for the treatment of a number neurode-
generative diseases. A variety of cyclic, conformationally
restricted glutamate analogues have been prepared in
laboratories around the world but only a few are highly
potent and sub-type selective.1 One such compound is the
conformationally restricted glutamate analogue, (1S, 3R)-1-
aminocyclopentane-1,3-dicarboxylic acid (1S, 3R-ACPD)
1, which selectively activates metabotropic glutamate
receptors (mGluR) over the ionotropic type. This com-
pound, however, is not selective for the individual eight
mGluR subtypes that are currently known.2 We recently
reported that (S)-2, the dehydro-analogue of APCD, was an
agonist at mGluR5 (EC50 18 mM) and mGluR2 (EC50
45 mM).3 (S)-4-Carboxyphenylglycine (4CPG) 3 was
reported as one of the first potent and selective mGluR2
competitive antagonists that antagonised 1S, 3R-ACPD (1)
induced inositol phosphate (IP) formation in cerebral
cortical slices.4 One approach in designing potent and
selective antagonists is by the introduction of a bulky and
lipophilic group into an agonist. This was clearly demon-
strated in the xanthylmethyl substituted compound,
Keywords: Metabotropic glutamate receptors; Antagonists; Heck reaction.
* Corresponding authors. Tel.: C61 042214388; fax: C61 042214287;
e-mail: aung@uow.edu.au
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.12.024

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A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
obtained by preparative HPLC, using a solvent system of
2. Chemistry
ethyl acetate and hexane (15:85). Using the standard Heck
conditions to prepare compounds 8c and 8d was less
efficient resulting in poor yields of these desired compounds
(Table 1). Attempts to prepare compounds 8e–8j were less
successful. However, the reactions of compound 7 with
these more hindered aryl halides under the conditions
originally developed by Jeffrey,9 using Pd(OAc)2, NaHCO3
as the base and n-Bu4NCl as a phase-transfer catalyst gave
the coupling products 8f–k in improved yields (Table 1).
The selectivity of the major and minor coupling products
was determined by 1H NMR experiments, and found to be in
the ratio of approximately 95–90:5–10, in all cases.
The initial methodology used for the synthesis of the
potential antagonists (9 and 12) was based on the palladium-
catalysed Heck coupling reaction of the Cbz-derivative rac-7
with an aryliodide.8 Compound 7 was obtained from
deprotection of the known racemic compound 5,3a followed
by reaction of the hydrochloride salt 6 with benzyl
chloroformate in the presence of saturated K2CO3 to give
7 in 78% (Scheme 1).
Table 1. Isolated yields of 8
Compounds
Method
Yield (%)
8a (RZH)
A
A
A
A
B
B
B
B
B
B
55
62
20
29
40
76
33
52
50
47
8b (RZp-CH3)
8c (RZp-OTBS)
8d (RZm-CH3)
8e (RZm-CF3)
8f (RZm-Et)
8g (RZo-CH3)
8h (RZ3,4-diMe)
8i (RZm-OCH3)
8j (RZ2-napthyl)
Method A: Heck coupling; ArX (1.3 equiv), Pd(OAc)2 (10 mol%), Ph3P
(20 mol%), Et3N (2 equiv), CH3CN, 100 8C. Method B: Jeffery–Heck
coupling condition; ArX (1.3 equiv), Pd(OAc)2 3% mol, Bu4NCl (1 equiv),
NaHCO3 (2.5 equiv), DMF, 90 8C.
Scheme 1. Synthesis of compound 7. Reagents and yields: (i) 1 M HCl,
ether, 0–25 8C, 16 h, 98%; (ii) 4 M Na2CO3, benzyl chloroformate, THF,
0 8C, 78%.
Compound 7 was treated with iodobenzene under standard
Heck conditions (10 mol% Pd(OAc)2, Ph3P, Et3N) in
acetonitrile solution at 100 8C in a sealed tube for 38 h
(Scheme 2). Purification of the crude reaction mixture by
column chromatography gave 8a as a 94:6 mixture of two
diastereomers in 55% yield (Table 1). Under similar
conditions 4-iodotoluene gave 8b in 62% yield as a 95:5
mixture of diastereomers (Table 1). Pure 8a and 8b could be
1H NMR spectroscopic analysis of the two diastereomers of
8a (RZH) indicated that the major diastereomer exhibited a
H-4 resonance (d 4.20, dd) upfield from the corresponding
resonance (d 4.47, br s) for the minor isomer (Fig. 1).
The H-5a resonance at d 3.10 of the major isomer appeared
markedly more downfield than the corresponding resonance
(d 2.73) of the minor isomer. Furthermore, the H-5b of
the major isomer exhibited a resonance at d 2.23, upfield
from the corresponding resonance (d 2.73) of the minor
isomer.
Scheme 2. Reagents: (i) ArX (1.3 equiv), Pd(OAc)2 (10 mol%), Ph3P
(20 mol%), Et3N (2 equiv), CH3CN, 100 8C, (ii) 10% aqueous HCl, [rac-
8]Z1.3 M, 100 8C, 16 h.
Figure 1. NOESY study of 8a.

A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
1805
In general, the major diastereomers 8 exhibited a H-4
chemical shift between d 4.20 and 4.36, however, for
compound 8g, this proton had a chemical shift at d 4.53. We
attribute this downfield chemical shift to the ortho methyl-
substituent on the aromatic ring. The relative stereo-
chemistry of the major isomer of 8a (RZH) was determined
from NOESY experiments. These NMR experiments
showed significant cross-peaks between H-6 and H-5b and
H-5b and H-7 on the aryl ring, which is consistent with their
relative syn stereochemistry (Fig. 1).
Table 2). The selectivity observed in this magnesium–
methanol reduction may be due to the formation of the
Mg(II) complex A, as shown in Figure 3, which upon
stereoselective protonation gives compound 10 as the major
product. Alternatively, the formation of the more stable 3,4-
anti-products (10) may be due to a based-catalysed
epimerisation during the course of the reaction.
The high diastereoselectivity and the stereochemical out-
come of these reactions may be due to formation of the aryl-
palladium(II) complex A; that could be favoured by
coordination to the electron pair of the Cbz-nitrogen
(Fig. 2). Syn b-hydride elimination from B then gives
compound 8 (Fig. 2).
Figure 3. Suggest mechanism for the stereochemistry of compounds 10a.
Complete transesterification of the ethyl ester group in 10
was observed in most cases from 1H NMR analysis. HPLC
separation of a mixture of 10a and 11a and 10b and 11b,
gave pure samples of 10a, 11a, 10b and 11b, respectively.
The relative stereochemistry of 10b was determined by
NOESY experiments that showed significant cross peaks
between H-1 and H-5b, H-6 and H-3, H-6 and H-5b, H-3
and H-2, and H-2 and H-1 which confirmed the syn
orientation of the two carboxyl groups (Fig. 4).
Figure 2. Suggest mechanism for the stereochemistry of compounds 8.
Acid hydrolysis of compounds 8a–j, with 10% aqueous HCl
at reflux gave the corresponding amino acids 9a–j as their
hydrochloride salts (Scheme 2 and Table 2).
Table 2. Isolated yields (%) of compounds 9, 10 and 12
Compounds
9
10
12
a (RZH)
100
97
81
80
78
59
100
56
89
58
73a
77a
na
63b
90b
na
b (RZp-CH3)
c (RZp-OTBS)
d (RZm-CH3)
e (RZm-CF3)
f (RZm-Et)
g (RZo-CH3)
h (RZ3,4-diMe)
i (RZm-OCH3)
j (RZ2-napthyl)
43c
95c
94c
92c
76c
86c
34c
95c
94c
98c
100c
56c
88c
33c
a Compounds 10 and 11 were separated by HPLC.
b Obtained diastereomically pure from 10a or 10b.
c These samples were ca. 5:1 mixture of diastereomers.
Figure 4. NOESY study of compound 10b (p-CH3 not shown).
Reduction of a,b-unsaturated esters and other electron
deficient alkenes using magnesium in methanol has been
described to be a selective and efficient method.10–12
Compounds 8a–j were successfully reduced using Mg-
turnings in dry methanol to selectively afford the cyclo-
pentane derivatives 10a–j and 11a–j as the major and minor
diastereomers (d.r.Z5:1), respectively (Scheme 3 and
Acid hydrolysis of compounds 10 and 11 proceeded
smoothly under the same conditions as previously described
for the hydrolysis of compounds 8a–j, to give the
hydrochloride salts 12 and 13, respectively, in good yields
(Scheme 3 and Table 2).

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A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
a C-4-aryl substituent has adverse effects on the agonist
activity of rac-1.
In summary, we have developed a diastereoselective
method for preparing 4-aryl-1-amino-2-cyclopentene-1,3-
dicarboxylates and their cyclopentane analogues. The
palladium-catalysed Heck reactions of the Cbz-derivative,
rac-7, with ortho and meta substituted aryl halides were
successfully achieved by using the Jeffrey–Heck coupling
reaction conditions. This method provided the desired aryl
derivatives in higher yields than the classical Heck coupling
reaction conditions. Compounds 12a and 12b were found to
behave selectively as antagonists at mGluR2 with modest
activities.
4. Experimental
4.1. Chemistry
Solvents and reagents were purchased from commercial
sources and used without further purification unless
otherwise stated. Unless specified, all NMR spectra were
recorded at 300 MHz (1H NMR) or 75 MHz (13C NMR) in
CDCl3 solution. 13C NMR assignments were based on
DEPT experiments. Preparative HPLC was performed using a
Waters Delta prep 4000 HPLC, on a normal phase Pre Nova-
Pakw HR Silica 6 mm 60 (25!10 mm) column. All
separations were carried out by isocratic elution, using eluents
A and B (A, in petroleum spirit; B, isopropanol) in the ratio
98:2. The flow rate was at 20 ml/min. Compounds were
detected using a Waters 486 tunable UV absorbance detector.
4.2. Biological testing
Scheme 3. Reagents: (i) Mg, MeOH, (ii) 10% HCl, reflux.
[35S]GTPgS (specific activity 37 MBq/ml) was obtained
from Amersham (Little Chalfort, UK). Dulbecco’s modified
Eagle medium (DMEM) and dialyzed fetal calf serum were
from Life technologies (Gaithersburg, MD). Scintillation
fluid Ultimaflo AF as well as the Unifilter-96 GF/B
plates were from Packard (Meriden, CT). Guanosine-50-
diphosphate dilithium salt (GDP) was from Boehringer
Manheim (Basel, Switzerland), Fluo 3-AM was from
Molecular Probes (Leiden, The Netherlands). Probenecid
was from Sigma (St Louis, MO). Black 96-well plates were
from Costar (Merck, Overijse Belgium).
3. Biological studies
The antagonist and agonist activity of the diastereomerically
pure, but racemic compounds 9a, 9b, 12a and 12b, were
investigated. Signal transduction experiments were per-
formed with CHO cells heterologously expressing human
mGluR2. Signaling at mGluR2 receptor measured by mean
of a [35S]GTPgS binding assay on membranes from these
cells.3 The results for antagonist activity are summarized in
Table 3.
Table 3. Antagonist potencies of phenyl substituted analogues for
inhibition of glutamate-induced GTPgS binding to human mGluR2
4.2.1. 3-Ethyl 1-methyl 1-amino-3-cyclopentene-1,3-
dicarboxylate hydochloride salt (6). To a stirred solution
of compound 5 (1.94 g, 5.13 mmol) in diethyl ether (10 mL)
at 0 8C, was slowly added a solution of 1 M HCl (6.6 mL).
The reaction mixture was stirred at 0 8C for 2 h and then at
RT overnight. The layers were separated and the aqueous
layer was extracted with diethyl ether. Water was removed
to give 6 as a white crystalline solid (1.08 g, 98%). 1H NMR
d: 6.69 (s, 1H), 4.18 (q, 2H), 3.85 (s, 3H), 3.28 (br s, 4H),
1.28 (s, 3H); 13C NMR d: 172.1 (CO), 164.7 (CO), 139.7
(CH), 134.2 (C), 64.2 (C), 61.9 (CH2), 54.4 (CH3), 44.6
(CH2), 43.1 (CH2), 14.5 (CH3). MS (ES) m/z 214.2 ([MC1],
100%).
Com-
pounds
Mean IC50GSD in
mM (Emax, %)
Com-
pounds
Mean IC50GSD in
mM (Emax, %)
9a
9b
O100
O100
12a
12b
32 (71%)
73 (100%)
Unlike racemic 4 and (S)-4 these compounds showed no
mGluR2 agonist activity (EC50O100 mM). Compounds 12a
and 12b, however, showed modest antagonist activities with
IC50 values of 32 and 73 mM, respectively. In contrast, 9a
and 9b were not antagonists (IC50O100 mM). These limited
results suggested that an sp3 hybridized carbon at C-2 and
C-3 and an aryl substituent at C-4 is important for
anatagonist activity in these types of compounds and that
4.2.2. 3-Ethyl 1-methyl 1-(benzyloxycarbonylamino)-3-
cyclopentene-1,3-dicarboxylate (7). To the mixture of

A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
1807
ammonium salt 6 (0.957 g, 3.83 mmol) and an aqueous
solution of 4 M Na2CO3 (9.6 mL) in THF (2.4 mL) at 0 8C
was added benzyl chloroformate (0.6 mL, 4.213 mmol) and
a solution of 4 M Na2CO3 (4.8 mL). The mixture was left to
stir at 0 8C for 2 h. THF was removed and the residue was
extracted with CHCl3 (3!20 mL) and the combined
extracts were washed with a saturated solution of NaCl
and dried over MgSO4. The solvent was removed to give a
yellow oil which was purified by column chromatography
(35% ethyl acetate/hexane) to give a colourless oil (1.30 g,
97%). 1H NMR d: 7.40–7.34 (m, 5H), 6.68 (s, 1H), 5.52 (br
s, 1H), 5.10 (s, 2H), 4.19 (q, 2H), 3.74 (s, 3H), 3.25 (dd, JZ
2.4, 16.8 Hz, 1H), 3.20 (dd, JZ1.8, 13.2 Hz, 1H), 2.91 (d,
2H), 1.28 (s, 3H). 13C NMR d: 173.8 (CO), 163.0 (CO),
155.1 (CO), 139.4 (CH), 135.9 (C), 132.7 (C), 127.8 (2 CH),
127.4 (2 CH), 126.2 (CH), 66.0 (CH2), 63.8 (C), 59.8 (CH2),
52.1 (CH3), 43.9 (CH2), 42.6 (CH2), 13.6 (CH3). MS (ES)
m/z 348.3 ([MC1], 100%).
7.36 (s, 5H), 7.15–7.09 (m, 4H), 6.79 (s, 1H), 5.73 (br s, 1H),
5.12 (s, 2H), 4.26 (ddd, JZ1.8, 6.6, 8.4 Hz, 1H), 4.05 (m, 2H),
3.79(s,3H),3.07(dd,JZ8.1.13.5 Hz,1H),2.22–2.18(m,1H),
1.12 (t, 3H). 13C NMR d: 172.3 (CO), 163.8 (CO), 154.8
(CO), 142.9 (C), 140.1 (CH), 135.9 (4C), 129.0 (2 CH), 128.3
(3 CH), 128.0 (CH), 127.9 (CH), 127.2 (2CH), 69.3 (CH2),
66.7 (C), 60.4 (CH2), 53.0 (CH3), 49.2 (CH), 45.7 (CH2), 20.9
(CH3), 13.7 (CH3). MS (ES) m/z 438.1 ([MC1]C, 100%).
HRMS calcd for C25H28O6N (MHC) 438.1917. Found
438.1904.
4.3.3. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(40-tert-butyldimethylsilyloxyphenyl)-2-cyclo-
pentene-1,3-dicarboxylate (8c). A dark yellow oil
1
(0.315 g, 20%). H NMR d: 7.35 (s, 5H), 7.11 (br d, JZ
6.6 Hz, 2H), 6.75 (br d, JZ8.1 Hz, 2H), 5.80 (s, 1H), 5.11
(s, 2H), 4.23 (t, 1H), 4.16–3.95 (m, 2H), 3.77 (s, 3H), 3.09
(dd, JZ8.4, 13.8 Hz, 1H), 2.19 (m, 1H), 1.07 (t, 3H), 0.97
(s, 9H), 0.16 (s, 6H). 13C NMR d: 172.3 (CO), 163.8 (CO),
154.8 (CO), 154.1 (C), 143.1 (C), 139.8 (2C), 135.9 (CH),
128.3 (4CH), 128.0 (2CH), 127.9 (CH), 119.8 (2CH), 69.2
(C), 66.7 (CH2), 60.3 (CH2), 52.9 (CH3), 48.9 (CH), 45.7
(CH2), 25.5 (3CH3), 13.7 (CH3), K4.6 (CH3). MS (ES) m/z
264.0 ([MC1], 30%).
4.3. General procedure for the Heck coupling reaction,
method A
A mixture of compound 7 (0.771 g, 2.22 mmol), Pd(OAc)2
(10% mol, 48 mg), Ph3P (20% mol, 0.12 g), iodobenzene
(3.33 mmol, 0.4 mL) and Et3N (0.6 mL) in dry acetonitrile
(2 mL) was heated at 100 8C in a sealed tube for 38 h. After
cooling, the reaction mixture was diluted with ethyl acetate
(50 mL) and the organic layer was washed with a saturated
solution of NaCl. The solvent was removed to give dark
thick oil, which was purified by column chromatography
(25% ethyl acetate/hexane) to give 8a as a mixture of
diastereomers 8a (0.520 g, 55%) in a ratio of 94:6 as
4.3.4. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(30-methylphenyl)-2-cyclopentene-1,3-dicar-
boxylate (8d). A yellow oil (0.686 g, 29%). 1H NMR d: 7.35
(s, 5H), 7.26–7.04 (m, 4H), 6.80 (s, 1H), 5.12 (s, 1H), 4.23 (dd,
JZ8.7, 14.7 Hz, 1H), 4.13 (q, 2H), 3.78 (s, 3H), 3.10 (dd, JZ
8.4, 8.4 Hz, 1H), 2.31 (s, 3H), 2.18 (m, 1H), 1.13 (t, 3H). 13C
NMR d: 172.0 (CO), 163.9 (CO), 154.4 (CO), 143.0 (C), 142.5
(C), 140.7 (CH), 140.0 (C), 137.6 (C), 128.31 (2CH), 127.42
(3CH), 127.36 (2CH), 126.43 (CH), 124.96 (CH), 69.1 (CH2),
66.1 (C), 60.4 (CH2), 52.9 (CH3), 49.4 (CH), 45.6 (CH2), 21.1
(CH3), 13.5 (CH3). MS (CI) m/z 438 ([MC1], 46%).
1
determined by H NMR analysis. The two diastreoisomers
were separated by HPLC (5% ethyl acetate/petroleum
spirit).
4.3.1. 3-Ethyl 1-methyl 1-(benzyloxycarbonylamino)-4-
phenyl-2-cyclopentene-1,3-dicarboxylate (8a). (1S*, 4R*)
Major isomer: a yellow oil, 1H NMR d: 7.35 (s, 5H), 7.28–
7.20 (m, 5H), 6.80 (s, 1H) 5.76 (s, 1H), 5.12 (s, 2H), 4.28
(ddd, JZ1.5, 13.2, 13.2 Hz, 1H), 4.04 (m, 2H), 3.79 (s, 3H),
3.10 (dd, JZ8.7, 14.1 Hz, 1H), 2.23 (dd, JZ6.3, 12.6 Hz,
1H), 1.08 (t, 3H). 13C NMR d: 172.3 (CO), 163.8 (CO),
154.8 (CO), 143.2 (C), 142.9 (C), 135.9 (C), 128 4 (2CH),
128.1 (2CH), 128.1 (2CH), 128.0 (2CH), 127.4 (2CH),
126.6 (2CH), 69.4 (C), 66.8 (CH2), 60.5 (CH2), 53.1 (CH3),
49.6 (CH), 45.7 (CH2), 13.7 (CH3). MS (ES) m/z 424.0
([MC1], 100%). HRMS calcd for C24H26O6N (MHC)
424.1760. Found 424.1767.
4.4. General procedure for the Jeffery–Heck coupling
reaction, method B
A solution of compound 7 (0.2 g, 0.58 mmol), Pd(OAc)2
(3% M equiv, 0.017 mmol, 4.6 mg) and NaHCO3 (0.121 g,
1.44 mmol) in dry DMF (2 mL) were added into a high-
pressure tube and the tube was purged with nitrogen. A
solution of tetrabutylammonium chloride (0.169 g,
0.576 mmol) in dry DMF (2 mL) was added to the tube
followed by 5-iodo-m-xylene (0.134 g, 0.58 mmol) and
DMF (2 mL). The reaction mixture was purged with argon
for 20 min before sealing and was heated with stirring at
90 8C for 24 h. After cooling to room temperature, the
reaction mixture was diluted with ethyl acetate (50 mL).
The mixture was washed with half-saturated NaCl (3!
100 mL) and was dried over MgSO4. The solvent was
evaporated to give a dark oil, which was purified by column
chromatography (flash silica, 15% ethyl acetate/petroleum
spirits as eluent) to give 8h as a light brown oil (136 mg,
52%). 1H NMR d: 7.24 (s, 5H), 6.73 (s, 4H), 5.68 (bs, 1H),
5.11 (s, 2H), 4.21 (dd, JZ15, 8.4 Hz, 1H), 4.09 (q, 2H), 3.77
(s, 3H), 3.09 (dd, JZ14.1, 5.4 Hz, 1H), 2.20 (s, 6H), 2.12
(dd, JZ14.1, 9.8 Hz, 1H), 1.12 (t, 3H). 13C NMR d: 172.7
(CO), 164.3 (CO), 155.3 (CO), 143.3 (2C), 140.4 (C), 138.2
(C), 128.8 (3CH), 128.4 (3CH), 125.5 (3CH), 69.7 (C), 67.2
(CH2), 60.9 (CH2), 53.4 (CH3), 49.8 (CH), 46.2 (CH2), 21.5
(1S*, 4S*) Minor isomer: a yellow oil, 1H NMR d: 7.36 (s,
5H), 7.30–7.20 (m, 5H), 6.78 (s, 1H), 5.73 (s, 1H), 4.47 (br
s, 1H), 4.13–3.93 (m, 2H), 3.80 (s, 3H), 2.73 (dd, JZ9.0,
13.8 Hz, 1H), 2.49 (dd, JZ6.3, 14.4 Hz, 1H), 1.07 (t, 3H).
13C NMR d: 169.4 (CO), 160.9 (CO), 151.7 (CO), 140.7 (C),
140.0 (C), 136.7 (HC), 132.9 (C), 125.5 (2CH), 125.4
(3CH), 125.2 (CH), 125.0 (CH), 124.4 (3CH), 123.5 (CH),
66.3 (C), 63.9 (CH2), 57.5 (CH2), 50.1 (CH3), 46.9 (CH),
42.5 (CH2), 10.8 (CH3).
4.3.2. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(40-methylphenyl)-2-cyclopentene-1,3-dicar-
boxylate (8b). A pale yellow oil (1.123 g, 62%). 1H NMR d:

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A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
(2CH3), 14.2 (CH3). MS (CI) m/z 452 ([MC1], 20%);
HRMS calcd for C26H30O6N (MHC) 452.2073. Found
452.2015.
4.4.5. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(1)-naphthalene-2-cyclopentene-1,3-dicarboxyl-
1
ate (8j). An yellow oil (0.13 g, 47%). H NMR d: 8.2–7.2
(m, 12H), 7.03 (s, 1H), 5.6 (br s, 1H), 5.1 (s, 2H), 4.05 (m,
3H, OCH2CH3 and H-5), 3.81 (s, 3H), 3.30 (dd, JZ5.1,
9.8 Hz, 1H), 2.20 (m, 1H), 1.10 (t, 3H). 13C NMR d: 172.5
(CO), 164.1 (CO), 155.0 (CO), 140.5 (C), 136.1 (C), 134.2
(C), 133.1 (C), 131.0 (C), 124–133 (C), 69.0 (C), 66.5
(CH2), 61.0 (CH2), 52.8 (CH3), 45.9 (CH2), 14.0 (CH3). MS
(CI) m/z 474 ([MC1], 100%). HRMS calcd for C28H27O6N
(MHC) 473.1838. Found 473.1815.
4.4.1. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(30-trifluoromethylphenyl)-2-cyclopentene-
1,3-dicarboxylate (8e). A yellow oil (0.94 g, 40%). 1H
NMR d: 7.57–7.40 (m, 4H), 7.35 (s, 5H), 6.81 (s, 1H), 5.94
(s, 1H), 5.11 (s, 2H), 4.34 (ddd, JZ2.1, 8.4, 8.4 Hz, 1H),
4.00 (m, 1H), 3.79 (s, 3H), 3.12 (dd, JZ8.4, 13.8 Hz, 1H),
2.28 (dd, JZ6.3, 13.2 Hz, 1H), 1.06 (t, 3H). 13C NMR d:
172.5 (CO), 163.9 (CO), 155.4 (CO), 144.3 (C), 142.4 (CH),
141.8 (2C), 136.4 (2C), 131.3 (CH), 129.3 (CH), 128.7 (2CH),
128.4 (CH), 128.3 (CH), 126.3 (CH), 122.6 (CH), 69.7 (CH2),
67.1 (C), 60.9 (CH2), 53.4 (CH3), 49.8 (CH), 45.6
(CH2), 13.9 (CH3). MS (CI) m/z 492.0 ([MC1], 30%).
HRMS calcd for C25H25O6NF3 (MHC) 429.1634. Found
492.1636.
4.5. General hydrolysis procedure for the preparation of
rac-9
Compound 8a (0.146 g, 0.345 mmol), was dissolved in 6 M
HCl (2 mL) and heated at 100 8C overnight. After cooling,
the reaction mixture was diluted with water (2 mL) and
washed with diethyl ether (2!4 mL). Water was removed
under reduced pressure to give 9a as a white solid (96 mg,
4.4.2. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(30-ethylphenyl)-2-cyclopentene-1,3-dicarboxyl-
ate (8f). A yellow oil (0.415 g, 76%). H NMR d: 7.35 (s,
1
100%). H NMR (D2O) d: 7.43 (br s, 5H), 6.96 (br s, 1H),
4.55 (br s, 1H), 3.37 (m, 1H), 2.22 (m, 1H). 13C NMR (D2O)
d: 166.8 (CO), 162.2 (CO), 141.9 (C), 137.5 (C), 124.8 (2
CH), 123.2 (3 CH), 63.7 (C), 45.4 (CH), 39.6 (CH2). MS
(ES) m/z 247.9 ([MC1], 55%). HRMS calcd for C13H14O4N
(MHC) 248.0923. Found 248.0911.
1
5H), 7.19 (m, 1H), 7.06 (m, 3H), 6.82 (s, 1H), 5.70 (br s,
1H), 5.11 (s, 1H), 4.27 (ddd, JZ2.1, 6.9, 6.9 Hz, 1H), 4.10
(m, 2H), 3.78 (s, 3H), 3.10 (dd, JZ9.0, 14.1 Hz, 1H), 2.61
(q, 2H), 2.18 (dd, JZ6.3, 14.1 Hz, 1H), 1.21 (t, 3H), 1.09 (t,
3H). 13C NMR d: 172.2 (CO), 164.3 (CO), 155.5 (CO),
144.5 (C), 143.6 (C), 143.3 (C), 140.7 (CH), 136.5 (C),
128.7 (3CH), 127.4 (2CH), 128.3 (CH), 127.4 (CH), 126.4
(CH), 125.0 (CH), 69.8 (C), 67.0 (CH2), 60.8 (CH2), 53.3
(CH3), 50.0 (CH), 46.1 (CH2), 29.0 (CH2), 15.9 (CH3), 14.1
(CH3). MS (ES) m/z 452.0 ([MC1], 40%). HRMS calcd for
C26H30O6N, (MHC) 452.2073. Found 452.2082.
4.5.1. (1S*, 4R*)-1-Amino-4-(40-methylphenyl)-2-cyclo-
pentene-1,3-dicarboxylate hydrochloride salt (9b). A
white solid (0.190 g, 97%). H NMR (D2O) d 7.15–7.08
1
(m, 4H), 6.77 (d, JZ2.1 Hz, 1H), 4.36 (dd, JZ2.4, 8.1 Hz,
1H), 3.17 (dd, JZ8.4, 14.1 Hz, 1H), 2.20 (s, 3H), 2.00 (d,
JZ8.4, 14.1 Hz, 1H). 13C NMR (D2O) d: 167.2 (CO), 162.5
(CO), 142.5 (C), 134.7 (C), 133.4 (C), 132.6 (CH), 125.6 (2
CH), 123.5 (2 CH), 64.0 (C), 45.4 (CH), 39.9 (CH2), 16.4
(CH3). MS (ES) m/z 262.1 ([MC1], 100%). HRMS calcd
for C14H16O4N (MHC) 262.1079. Found 262.1131.
4.4.3. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(20-methylphenyl)-2-cyclopentene-1,3-dicar-
boxylate (8g). A yellow oil (0.141 g, 33%). 1H NMR d: 7.34
(s, 5H), 7.12 (d, JZ10.5 Hz, 1H), 6.85 (br s, 1H), 5.70 (br s,
1H), 5.10 (s, 2H), 4.53 (ddd, JZ1.8, 6.6, 6.6 Hz, 1H), 4.06
(m, 2H), 3.79 (s, 3H), 3.16 (dd, JZ8.4, 13.8 Hz, 1H), 2.41
(s, 3H), 2.10 (m, 1H), 108 (t, 3H). 13C NMR d: 172.8
(CO), 164.3 (CO), 155.5 (CO), 143.4 (C), 142.1 (C), 140.6
(CH), 136.5 (C), 135.7 (C), 130.4 (CH), 128.7 (3CH),
128.4 (CH), 128.3 (CH), 126.7 (CH), 69.9 (C), 67.1 (CH2),
60.9 (CH2), 53.3 (CH3), 45.4 (CH), 45.1 (CH2), 20.0
(CH3), 14.1 (CH3). MS (ES) m/z 438.1 ([MC1], 40%).
HRMS calcd for C25H28O6N (MHC) 438.1917. Found
438.1909.
4.5.2. (1S*, 4R*)-1-Amino-4-(40-hydroxyphenyl)-2-cyclo-
pentene-1,3-dicarboxylate hydrochloride salt (9c). A
light grey solid (0.067 g, 81%). H NMR (D2O) d: 7.05
1
(d, JZ7.5 Hz, 2H), 6.76 (d, JZ7.5 Hz, 2H), 6.71 (s, 1H),
4.33 (t, 3H), 3.12 (dd, JZ8.1, 14.1 Hz, 1H), 1.94 (dd, JZ
8.1, 13.5 Hz, 1H). 13C NMR (D2O) d: 168.0 (CO), 163.4
(CO), 151.1 (C), 143.1 (C), 133.1 (CH), 130.5 (C), 125.3
(2CH), 112.3 (2CH), 64.4 (C), 45.5 (CH), 40.5 (CH2). MS
(ES) m/z 264.0 ([MC1], 30%).
4.5.3. (1S*, 4R*)-1-Amino-4-(30-methylphenyl)-2-cyclo-
pentene-1,3-dicarboxylate hydrochloride salt (9d). A
light grey solid (0.067 g, 80%). H NMR (D2O) d: 7.13–
4.4.4. (1S*, 4R*)-3-Ethyl 1-methyl 1-(benzyloxycarbonyl-
amino)-4-(30-methoxyphenyl)-2-cyclopentene-1,3-dicar-
boxylate (8i). A colourless oil (0.486 g, 50%). H NMR d:
1
1
6.89 (m, 4H), 6.66 (s, 1H), 4.28 (dd, JZ8.1, 15.6 Hz, 1H),
3.36 (dd, JZ7.5, 14.4 Hz, 1H), 3.10 (dd, JZ8.4, 14.4 Hz,
1H), 2.12 (s, 3H). 13C NMR (D2O) d: 173.1 (CO), 168.5
(CO), 148.2 (C), 143.8 (C), 141.0 (C), 138.7 (CH), 130.9
(CH), 129.9 (CH), 126.2 (CH), 69.8 (C), 51.5 (CH), 45.8
(CH2), 22.4 (CH3). MS (ES) m/z 169 [MK (2!CO2HC
2H)].
7.34 (s, 5H), 7.25 (t, 1H), 6.85 (s, 1H), 6.78 (2, 1H), 6.73 (m,
2H), 5.80 (br s, 1H), 5.10 (s, 2H), 4.20 (t, 1H), 4.10 (m, 2H),
3.77 (s, 3H), 3.10 (dd, JZ8.7, 10.8 Hz, 1H), 2.20 (dd, JZ
9.0, 15.3 Hz, 1H), 1.10 (t, 3H). 13C NMR d: 172.5 (CO),
164.1 (CO), 159.9 (CO), 155.1 (C), 145.2 (C), 143.1 (C),
140.7 (C), 136.3 (C), 129.7 (CH), 128.8 (2CH), 128.4 (CH),
128.3 (CH), 128.2 (CH), 120.1 (CH), 113.3 (CH), 112.5
(CH), 69.8 (C), 67.2 (CH2), 60.0 (CH2), 55.4 (CH3), 53.6
(CH3), 50.1 (C), 46.0 (C), 14.3 (CH3). MS (CI) m/z 454
([MC1], 25%). HRMS calcd for C25H28O6N (MHC)
454.1866. Found 454.1821.
4.5.4. (1S*, 4R*)-1-Amino-4-(30-trifluoromethylphenyl)-
2-cyclopentene-1,3-dicarboxylate hydrochloride salt
(9e). A white solid (0.062 g, 78%). 1H NMR (D2O) d:
7.42 (br s, 2H), 7.31 (m, 2H), 6.69 (d, JZ2.1 Hz, 1H), 4.38

A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
1809
(dd, JZ2.4, 8.1 Hz, 1H), 3.09 (dd, JZ8.1, 14.1 Hz, 1H),
1.90 (dd, JZ8.1, 14.1 Hz, 1H). 13C (D2O): 171.5 (CO),
166.1 (CO) 147.7 (C), 145.1 (C), 138.1 (C), 132.7 (CH),
130.6 (CH), 125.4 (CH), 124.9 (CH), 125.4 (CH), 111.1 (C),
69.0 (C), 51.4 (CH), 45.3 (CH2). MS (ES) m/z 317.9 ([MC
1], 100%). HRMS calcd for C14H15F3O4N (MHC)
318.0953. Found 318.0966.
m/z 298 ([MC1], 100%). HRMS calcd for C17H16NO4
(MHC) 298.1079. Found 298.1053.
4.6. General procedure for the preparation of rac-10
To a solution of 8a (0.445 mmol) in dry MeOH (8 mL)
under a nitrogen atmosphere at 0 8C was added Mg turnings
(4.45 mmol, 0.11 g). The reaction mixture was left to stir at
0 8C for 2 h then at room temperature for 3 h. Ethyl acetate
(20 mL) was then added to the reaction mixture and then
cooled to 0 8C. An ice-cold solution of 1 M HCl (10 mL)
was added to the mixture and the resulting mixture extracted
with ethyl acetate. The combined organic extracts were
washed with water and dried over MgSO4. The solvent was
removed to give an oil, which was purified by column
chromatography (ethyl acetate/petroleum spirit, 40:60) to
give a mixture of 10a and 11a. This mixture was further
separated by preparative HPLC.
4.5.5. (1S*, 4R*)-1-Amino-4-(30-ethoxylphenyl)-2-cyclo-
pentene-1,3-dicarboxylate hydrochloride salt (9f). A
white solid (0.055 g, 59%). H NMR (D2O, 300 MHz) d:
1
7.03 (d, JZ6.6 Hz, 3H), 6.91 (d, JZ6.0 Hz, 1H), 6.67 (s,
1H), 4.54 (m, 1H), 3.14 (dd, JZ8.1, 14.1 Hz, 1H), 2.18 (s,
3H), 1.77 (dd, JZ7.8, 14.1 Hz, 1H). 13C NMR (CD3OD) d:
170.8 (CO), 165.5 (CO), 147.5 (C), 144.8 (C), 142.6 (CH),
135.9 (C), 130.1, 128.6 (CH), 127.0 (CH), 126.4 (CH), 68.0
(C), 50.6 (CH), 44.5 (CH2), 28.7 (CH2), 15.1 (CH3). MS
(ES) m/z 262.0 ([MC1], 50%). HRMS Calcd for
C14H15F3O4N (MHC) 262.1079. Found 262.1119.
4.6.1. (1SR, 3RS, 4RS)-1,3-Dimethyl 1-(benzyloxycar-
bonylamino)-4-phenyl-cyclopentane-1,3-dicarboxylate
(10a). A pale yellow oil (0.23 g, 73%). 1H NMR d: 7.34 (m,
5H), 7.26 (m, 5H), 5.82 (br s, 1H), 5.11 (dd, JZ12.0,
15.3 Hz, 2H), 3.75 (br s, 3H), 3.68–3.58 (m, 1H), 3.55 (s,
3H), 3.37 (m, 1H), 2.76–2.63 (m, 2H), 2.50 (m, 1H), 2.29
(m, 1H). 13C NMR d: 174.3 (CO), 174.1 (CO), 155.2 (CO),
141.3 (C), 136.1 (C), 128.5 (CH), 128.2 (CH), 128.1 (CH),
127.2 (CH), 126.8 (CH), 66.8 (CH2), 64.4 (C), 53.0 (CH3),
51.7 (CH3), 50.7 (CH), 48.8 (CH), 45.6 (CH2), 41.5 (CH2).
MS (CI) m/z 412 ([MC1], 88%).
4.5.6. (1S*, 4R*)-1-Amino-4-(20-methylphenyl)-2-cyclo-
pentene-1,3-dicarboxylate hydrochloride salt (9g). A
grey solid (56 mg, 100%). H NMR (D2O) d: 7.19 (t, 1H),
7.06 (d, JZ9.9 Hz, 2H), 6.97 (d, JZ7.5 Hz, 1H), 6.70 (s,
1H), 4.34 (t, H), 3.09 (dd, JZ8.7, 13.8 Hz, 1H), 2.48 (q,
2H), 1.89 (dd, JZ8.4, 13.5 Hz, 1H), 1.03 (t, 3H). 13C NMR
(CD3OD) d: 170.5 (CO), 165.4 (CO), 147.9 (C), 141.1 (C),
135.7 (CH), 135.6 (C), 130.1 (CH), 126.8 (CH), 126.6 (CH),
126.2 (CH), 68.0 (C), 46.1 (CH), 43.5 (CH2), 18.6 (CH3).
MS (ES) m/z 276.0 ([MC1], 10%). HRMS calcd for
C15H18O4N (MHC) 276.1236. Found 276.1246.
1
4.6.2. (1SR, 3SR, 4RS)-1,3-Dimethyl 1-(benzyloxycar-
bonylamino)-4-phenyl-cyclopentane-1,3-dicarboxylate
4.5.7. (1S*, 4R*)-1-Amino-4-(30,40-dimethylphenyl)-2-
cyclopentene-1,3-dicarboxylate hydrochloride salt (9h).
A white solid (65 mg, 56%). 1H NMR (CD3OD) d: 6.87 (s,
3H), 6.66 (s, 1H), 4.35 (m, 1H), 3.17 (dd, JZ8.1, 13.2 Hz,
1H), 2.2 (s, 6H), 1.98 (dd, 1H, JZ8.7, 12.9 Hz, 1H). 13C
NMR (CD3OD) d: 173.4 (CO), 168.3 (CO), 149.0 (C), 145.5
(C), 139.2 (2C), 136.8 (CH), 129.3 (CH), 127.5 (2CH), 67.4
(C), 49.8 (CH), 45.4 (CH2), 21.2 (2CH3). MS (ES) m/z 276.1
([MC1], 80%).
1
(11a). A pale yellow oil (46 mg, 15%). H NMR d: 7.35–
7.16 (m, 10H), 5.86 (br s, 1H), 5.12 (s, 2H), 3.75 (br s, 3H),
3.69–3.60 (m, 1H), 3.57 (s, 3H), 3.34 (m, 1H), 2.76 (m, 2H),
2.39 (m, 1H). 13C NMR d: 174.9 (CO), 174.4 (CO), 156.0
(CO), 139.6 (C), 139.6 (C), 128.7 (CH), 128.4 (CH), 128.3
(CH), 128.1 (CH), 127.2 (CH), 67.1 (CH2), 65.1 (C), 60.6
(CH2), 53.1 (CH3), 49.3 (CH), 47.1 (CH), 42.0 (CH), 40.2
(CH2), 13.8 (CH3). MS (CI) m/z 426 ([MC1], 67%).
4.6.3. (1S*, 3R*, 4R*)-1,3-Dimethyl 1-(benzyloxycar-
bonylamino)-4-(40-methylphenyl)-cyclopentane-1,3-
dicarboxylate (10b). A pale yellow oil (0.408 g, 77%). H
4.5.8. (1S*, 4R*)-1-Amino-4-(30-methoxyphenyl)-2-
cyclopentene-1,3-dicarboxylate hydrochloride salt (9i).
A white solid (77 mg, 89%). 1H NMR (CD3OD) d: 7.25 (m,
1H), 6.70–6.9 (m, 4H), 4.30 (m, 1H), 3.70 (s, 3H), 3.05 (dd,
JZ8.7, 14.1 Hz, 1H), 1.90 (dd, JZ7.5, 13.5 Hz, 1H). 13C
NMR (CD3OD) d: 170.0 (CO), 156.8 (CO), 156.0 (C), 144.2
(C), 137.7 (C), 130.6 (CH), 120.1 (CH), 119.4 (CH), 114.4
(CH), 113.0 (CH), 68.4 (C), 55.6 (OCH3), 49.8 (CH), 44.2
(CH2). MS (ES) m/z 278.0 ([MC1], 100%). HRMS calcd
for C14H16NO5, (MHC) 278.1048. Found 278.1028.
1
NMR d: 7.36 (s, 5H), 7.18–7.06 (m, 4H), 5.67 (s, 1H), 5.12
(dd, JZ12.0, 15 .0 Hz, 1H), 4.03 (q, 2H), 3.78 (s, 3H), 3.60
(dd, JZ11.1, 16.5 Hz, 1H), 3.33 (m, 1H), 2.69 (dd, JZ7.8,
14.1 Hz, 1H), 2.67 (dd, JZ10.8, 13.5 Hz, 1H), 2.52–2.45
(m, 1H), 2.31 (s, 3H), 1.11 (t, 3H). 13C NMR d: 174.3 (CO),
173.6 (CO), 155.3 (CO), 138.2 (C), 136.2 (C), 127.1 (2!
CH), 128.4 (2!CH), 128.0 (CH), 127.6 (CH), 127.1 (2!
CH), 66.7 (CH2), 64.4 (C), 60.4 (CH2), 52.9 (CH3), 50.8
(CH), 48.4 (CH), 45.6 (CH2), 41.4 (CH2), 20.9 (CH3), 14.0
(CH3). MS (ES) m/z 439.6 ([MC1], 100%). HRMS calcd
for C25H30O6N (MHC) 440.2073. Found 440.2066.
4.5.9. (1S*, 4R*)-1-Amino-4-(1)-naphthlene-2-cyclo-
pentene-1,3-dicarboxylate hydrochloride salt (9j). A
white solid (27 mg, 58%). H NMR (CD3OD) d: 8.2 (d,
1
JZ5.4 Hz, 1H), 7.9 (d, JZ8.1 Hz, 1H), 7.8 (d, JZ8.4 Hz,
1H), 7.5 (m, 3H), 6.8 (s, 1H), 5.3 (m, 1H), 3.5 (m, 1H), 2.0
(m, 1H). 13C NMR (CD3OD) d: 170.6 (CO), 165.3 (CO),
147.6 (C), 135.9 (CH), 134.0 (C), 131.4 (2C), 128.7 (CH),
128.3 (CH), 127.4 (CH), 126.3 (CH), 125.4 (CH), 123.3
(CH), 122.9 (CH), 68.3 (C), 45.5 (CH), 44.0 (CH2). MS (ES)
4.6.4. (1S*, 3R*, 4R*)-1,3-Dimethyl 1-(benzyloxycar-
bonylamino)-4-(30-methylphenyl)-cyclopentane-1,3-
dicarboxylate (10d). A light yellow oil (0.46 g, 85%). H
NMR d: 7.36 (s, 5H), 7.26–7.04 (m, 4H), 5.62 (br s, 1H),
5.13 (dd, JZ12.3, 14.1 Hz, 2H), 4.11 (q, 2H), 3.78 (br s,
3H), 3.65 (dd, JZ11.1, 15.9 Hz, 2H), 3.58 (s, 3H), 3.37 (m,
1

1810
A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
1H), 2.88 (dd, JZ9.0, 14.4 Hz, 1H), 2.67 (dd, JZ10.5,
13.8 Hz, 1H), 2.54–2.48 (m, 1H), 2.31 (br s, 1H), 1.25 (t, 3H).
13C NMR d: 174.7 (CO), 174.5 (CO), 155.8 (CO), 141.6 (C),
138.3 (C), 136.5 (C), 128.8 (CH), 128.7 (CH), 128.5 (CH),
127.9 (CH), 127.6 (CH), 127.5 (CH), 127.1 (CH), 124.5 (CH),
66.9 (CH2), 64.7 (C), 53.2 (CH3), 52.0 (CH3), 50.8 (CH), 48.9
(CH), 21.7 (CH3). MS (CI) m/z 426 ([MC1], 24%).
4.6.9. (1S*,3R*, 4R*)-1,3-Dimethyl1-(benzyloxycarbonyl-
amino)-4-(30-methoxyphenyl)-cyclopentane-1,3-dicar-
boxylate (10i). A light yellow oil (85 mg, 86%). 1H NMR d:
7.33 (s, 5H), 7.18 (t, JZ6.57 Hz, 1H), 6.82 (s, 1H), 6.73 (dd,
JZ2.4, 3.3 Hz, 2H) 5.68 (br s, 1H), 5.10 (s, 2H), 3.75 (s, 6H),
3.73 (m, 1H), 3.57 (s, 3H), 3.38 (dd, JZ11.0, 19.0 Hz, 1H),
2.69 (dd, JZ10.5, 13.8 Hz, 2H), 2.45 (m, 1H), 2.25 (dd, JZ
9.0, 15.0 Hz, 1H). 13C NMR d: 174.5 (CO), 159.8 (2CO),
155.5 (C), 143.3 (C), 136.3 (C), 129.8–112.3 (4CH), 67.1 (C),
64.8 (CH2), 55.5 (2CH3), 53.4 (CH3), 52.2 (CH), 50.9 (CH),
45.7 (CH2), 41.8 (CH2). MS (CI) m/z 442 ([MC1], 100%).
HRMS Calcd for C24H28O7N (MHC) 442.1866. Found
442.1811.
4.6.5. (1S*,3R*,4R*)-1,3-Dimethyl1-(benzyloxycarbonyl-
amino)-4-(30-trifluoromethylphenyl)-cyclopentane-1,3-
dicarboxylate (10e). A light yellow oil (0.139 g, 95%). 1H
NMR d: 7.53–7.39 (m, 4H), 7.35 (s, 5H), 5.81 (s, 1H), 5.12
(s, 2H), 3.73 (br s, 1H), 3.72–3.65 (m, 1H), 3.58 (s, 3H),
2.77–2.63 (m, 2H), 2.54–2.36 (m, 2H). 13C NMR d: 174.5
(CO), 174.1 (CO), 155.7 (CO), 142.8 (C), 141.0 (C), 136.4
(C), 131.0 (CH), 129.4 (CH), 128.8 (3CH), 128.8 (C), 128.5
(CH), 128.4 (2CH), 128.3 (C), 124.6–124.5 (CH), 124.1–
124.0 (CH), 67.1 (CH2), 64.6 (C), 53.4 (CH3), 52.1 (CH3),
51.0 (CH), 48.8 (CH), 45.4 (CH2), 41.7 (CH2). MS (ES) m/z
494 ([MC1], 20%). HRMS calcd for C25H27O6NF3 (MHC)
494.179048. Found 494.17933.
4.6.10. (1S*, 3R*, 4R*)-1,3-Dimethyl 1-(benzyloxycar-
bonylamino)-4-(1)-naphthlene-cyclopentane-1,3-dicar-
boxylate (10j). A light yellow oil (25 mg, 34%). 1H NMR d:
8.20–7.20 (m, 12H), 5.70 (br s, 1H), 5.10 (s, 2H), 4.50 (dd,
JZ8.4, 18.9 Hz, 1H), 3.8 (s, 3H), 3.6 (m, 1H), 3.30 (s, 3H),
2.9 (dd, JZ5.4, 13.8 Hz, 1H), 2.8 (dd, JZ8.4, 18.8 Hz, 1H),
2.6 (dd, JZ6.3, 8.2 Hz, 1H), 2.2 (m, 1H). 13C NMR d: 175.0
(CO), 156.0 (CO), 136–132 (3C), 124–130 (7CH), 68.0
(CH2), 66.O (C), 50.0 (2CH3), 48.1 (CH), 46.0 (CH2), 44.2
(CH2) 42.0 (CH).
4.6.6. (1S*,3R*,4R*)-1,3-Dimethyl1-(benzyloxycarbonyl-
amino)-4-(30-ethylphenyl)-cyclopentane-1,3-dicarboxyl-
ate (10f). A light yellow oil (0.22 g, 94%). 1H NMR d: 7.37
(s, 5H), 7.22 (t, 3H), 7.10–6.99 (m, 3H), 5.62 (s, 1H), 5.13
(s, 2H), 3.80 (br s, 3H), 3.67–3.60 (m, 1H), 3.59 (s, 3H),
3.37 (m, 1H), 2.69 (dd, JZ6.3, 8.1 Hz, 2H), 2.61 (q, 2H),
2.53–2.51 (m, 1H), 2.36–2.28 (m, 1H), 1.22 (t, 3H). 13C
NMR d: 174.7 (CO), 174.5 (CO), 155.8 (CO), 144.7 (C),
141.6 (C), 135.3 (C), 128.8 (CH), 128.8 (CH), 128.7 (CH),
128.5 (CH), 128.4 (2CH), 127.3 (CH), 126.7 (CH), 124.6
(CH), 67.1 (CH2), 64.8 (C), 53.3 (CH3), 52.0 (CH3), 50.9
(CH), 49.0 (CH), 45.9 (CH2), 41.8 (CH2), 29.1 (CH2), 15.9
(CH3). MS (ES) m/z 454.1 ([MC1], 80%). HRMS calcd for
C26H32O6N (MHC) 454.2230. Found 454.2290.
4.7. General hydrolysis procedure the preparation of
rac-12 and rac-13
Compound 10b (0.168 g, 0.38 mmol), was dissolved in 6 M
HCl (2 mL) and heated at 100 8C overnight. After cooling,
the reaction mixture was diluted with water (2 mL) and
washed with ether (2!4 mL). Water was removes under
reduced pressure to give 12b as a white solid (98 mg, 90%).
1H NMR (D2O) d: 7.04 (d, JZ7.8 Hz, 2H), 6.97 (d, JZ
7.5 Hz, 2H), 3.44 (ddd, JZ6.9, 11.4, 11.4 Hz, 1H), 3.14 (dd,
JZ10.5, 19.5 Hz, 1H), 2.62 (dd, JZ10.8, 12.0 Hz, 1H),
2.57 (dd, JZ7.5, 14.1 Hz, 1H), 2.36 (dd, JZ8.7, 15.0 Hz,
1H), 2.05 (s, 3H), 2.0 (t, JZ6.9 Hz, 1H). 13C NMR (D2O) d:
173.6 (CO), 170.9 (CO), 134.6 (C), 133.0 (C), 126.1 (2!
CH), 124.3 (2!CH), 59.3 (C), 46.9 (CH), 46.0 (CH), 35.5
(CH), 41.0 (CH2), 16.9 (CH3). MS (ES) m/z 264.1 ([MC1],
100%). HRMS calcd for C14H18O4N, (MHC) 264.1236.
Found 264.1261.
4.6.7. (1S*,3R*,4R*)-1,3-Dimethyl1-(benzyloxycarbonyl-
amino)-4-(20-methylphenyl)-cyclopentane-1,3-dicarboxyl-
ate (10g). A light yellow oil (0.243 g, 92%). H NMR d:
1
7.35 (s, 5H), 7.2–7.12 (m, 4H), 5.63 (br s, 1H), 5.12 (s, 2H),
3.93 (dd, JZ10.2, 18.6 Hz, 1H), 3.79 (br s, 3H), 3.57 (s,
3H), 2.77–2.67 (m, 2H), 2.55 (m, 1H), 2.36 (dd, JZ8.4,
16.5 Hz, 1H), 2.36 (s, 3H), 2.08 (m, 1H). 13C NMR d: 174.7
(CO), 174.5 (CO), 155.7 (CO), 139.8 (C), 136.6 (C), 136.4
(2C), 130.6 (CH), 128.8 (CH), 128.8 (2CH), 128.5 (CH),
128.4 (CH), 127.1 (CH), 126.8 (CH), 125.9 (CH), 67.1
(CH2), 64.7 (C), 53.3 (CH3), 52.1 (CH3), 50.0 (CH), 46.0
(CH2), 44.5 (CH), 41.65 (CH2), 19.9 (CH3). MS (ES) m/z
440.1 ([MC1], 50%). HRMS Calcd for C25H30O6N (MHC)
440.2073. Found 440.2065.
4.7.1. (1SR, 3RS, 4RS)-1-Amino-4-phenyl-cyclopentane-
1,3-dicarboxylate hydrochloride salt (12a). A white solid
(22 mg, 63%). H NMR (D2O) d: 6.92–6.83 (m, 5H), 3.19
1
(m, 1H), 2.19 (m, 1H), 2.33 (m, 2H), 2.08 (m, 1H), 1.74 (m,
1H). 13C NMR (D2O, 75.65 MHz) d: 176.5 (CO), 173.8
(CO), 139.2 (C), 128.9 (CH), 128.7 (CH), 127.6 (CH), 127.2
(CH), 127.1 (CH), 61.9 (C), 49.5 (CH), 49.0 (CH), 43.7
(CH2), 38.2 (CH2).
4.6.8. (1S*,3R*,4R*)-1,3-Dimethyl1-(benzyloxycarbonyl-
amino)-4-(30,40-dimethylphenyl)-cyclopentane-1,3-dicar-
boxylate(10h). A light yellow oil (92 mg, 76%). 1H NMR d:
7.39 (s, 1H), 6.86 (s, 3H), 5.11 (s, 2H), 3.76 (s, 3H), 3.58 (s,
3H), 3.61 (m, 1H), 3.30 (m, 1H), 2.65 (dd, JZ10.5, 13.8 Hz,
2H), 2.48 (m, 1H), 2.20 (s, 6H), 2.08 (dd, JZ12.6, 12.9 Hz,
1H), 1.12 (t, 3H). 13C NMR d: 174.8 (CO), 155.8 (CO),
141.8 (CO), 138.2 (2C), 137.9 (C), 130.0 (CH), 128.1 (CH),
127.8 (CH), 67.0 (CH2), 65.0 (C), 53.0 (CH3), 52.0 (CH3),
50.8 (C), 49.0 (C), 46.0 (C), 41.8 (C), 21.8 (2CH3).
4.7.2. (1S*, 3R*, 4R*)-1-Amino-4-(3-methyl)-phenyl-
cyclopentane-1,3-dicarboxylate hydrochloride salt
(12d). A white solid (95 mg, 95%). 1H NMR (D2O) d:
7.18–6.93 (m, 4H), 4.50 (dd, JZ8.3, 16.0 Hz, 1H), 3.36 (dd,
JZ8.1, 11.7 Hz, 1H), 2.89 (dd, JZ7.5, 12.0 Hz, 1H), 2.54
(dd, JZ6.3, 14.1 Hz, 1H), 2.36 (dd, JZ10.2, 14.1 Hz, 1H),
2.13 (s, 3H), 1.98 (m, 1H). 13C NMR (D2O) d: 168.1 (CO),
166.5 (CO), 141.1 (C), 139.0 (C), 128.9 (CH), 128.1 (CH),
127.4 (CH), 124.3 (CH), 64.5 (C), 53.7 (CH), 50.3 (CH),
44.6 (CH2), 41.1 (CH2), 20.6 (CH3).

A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
1811
4.7.3. (1S*, 3R*, 4R*)-1-Amino-4-(3-trifluoromethyl)-
phenyl-cyclopentane-1,3-dicarboxylate hydrochloride
7.6 (d, JZ7.2 Hz, 1H), 7.5 (m, 3H), 4.6 (dd, JZ6.3, 8.2 Hz,
1H), 3.7 (dd, JZ6.1, 8.4 Hz, 1H), 2.9 (m, 2H), 2.6 (dd, JZ
6.3, 8.1 Hz, 1H), 2.2 (dd, JZ10, 13.5 Hz, 1H), 13C NMR
(CD3OD) d: 174.7 (CO), 172.9 (CO), 135.7 (C), 134.2 (C),
132.1 (C), 128.7 (CH), 127.6 (CH), 126.1 (CH), 125.6 (CH),
125.4 (CH), 122.6 (CH), 122.5 (CH), 62.3 (C), 47.9 (CH),
45.2 (CH), 45.0 (CH2), 39.6 (CH2). MS (ES) m/z 300 ([MC
1], 100%).
1
salt (12e). A white solid (87 mg, 94%). H NMR (D2O) d:
7.39 (s, 1H), 7.31–7.19 (m, 3H), 3.48 (dd, JZ12.0, 18.3 Hz,
1H), 3.14 (dd, JZ8.7, 19.5 Hz, 1H), 2.62–2.50 (m, 2H),
2.33 (dd, JZ9.0, 15.0 Hz, 1H), 1.97 (dd, JZ12.9, 12.9 Hz,
1H). 13C NMR (D2O) d: 176.4 (CO), 174.1 (CO), 140.5 (C),
130.9 (CH), 130.0 (C), 129.5 (2CH), 125.9 (C), 124.2
(2CH), 62.5 (C), 50.0 (CH), 49.0 (CH), 44.0 (CH2), 38.7
(CH2). MS (ES) m/z 317.9 ([MC1], 100%). HRMS calcd
for C14H15O4NF3 (MHC) 318.0953. Found 318.0966.
4.8. Signal transduction at mGlu2 receptors in CHO cells
Human mGluR2 (cloned and expressed in house) were
grown in DMEM/Glutamax-I to which 2 mM glutamine,
46 mg/L proline, and 10% dialyzed fetal calf serum were
added.
4.7.4. (1S*, 3R*, 4R*)-1-Amino-4-(3-ethyl)-phenyl-cyclo-
pentane-1,3-dicarboxylate hydrochloride salt (12f). A
white solid (82 mg, 98%). 1H NMR (D2O) d: 7.17 (dd, JZ
7.5, 15.0 Hz, 1H), 7.12–7.00 (m, 3H), 3.51 (ddd, JZ6.6,
11.7, 11.7 Hz, 1H), 3.22 (dd, JZ10.5, 19.8 Hz, 1H), 2.65
(m, 1H), 2.44 (m, 3H), 2.03 (t, JZ12.9 Hz, 1H), 1.00 (t,
3H). 13C NMR (D2O) d: 175.12 (CO), 173.5 (CO), 144.7
(C), 140.0 (C), 28.5 (CH), 126.9 (CH), 126.6 (CH), 124.5
(CH), 60.0 (C), 50.2 (CH), 50.2 (CH), 45.0 (CH2), 39.7
(CH2), 28.7 (CH2), 15.0 (CH3). MS (ES) m/z 278 ([MC1],
100%). HRMS calcd for C15H20O4N (MHC) 278.1392.
Found 278.1394.
4.9. [35S]GTPgS radioligand binding assay for human
mGlu2
Membrane preparation. Cells were grown to confluence.
Cells were washed twice with ice-cold PBS without Ca2C
and Mg2C, scraped off and homogenized in buffer
(EDTA mM, Hepes 20 mM). After centrifugation
(18,000 rpm, 15 min, 4 8C), the pellet was washed with
0.1 mM EDTA, 20 mM Hepes, and resuspended in the same
buffer for protein determination with the Biorad assay.
Membrane aliquots were stored at K70 8C.
4.7.5. (1S*, 3R*, 4R*)-1-Amino-4-(2-methyl)-phenyl-
cyclopentane-1,3-dicarboxylate hydrochloride salt
1
(12g). A white solid (98 mg, 100%). H NMR (D2O) d:
7.27 (d, JZ7.5 Hz, 1H), 7.14–7.10 (m, 3H), 3.69 (ddd, JZ
7.8, 12.0, 16.2 Hz, 1H), 3.06 (ddd, JZ7.2, 12.0, 16.8 Hz,
1H), 2.59 (dd, JZ7.5, 13.8 Hz, 1H), 2.42 (dd, JZ13.8,
13.8 Hz, 1H), 2.23 (dd, JZ7.5, 15.3 Hz, 1H), 2.21 (s, 3H),
1.60 (dd, JZ12.0, 13.8 Hz, 1H). MS (ES) m/z 264 ([MC1],
100%). HRMS calcd for C14H18O4N (MHC) 264.1236.
Found 264.1262.
[35S]GTPgS radioligand binding. Each incubate contained
10 mg of membrane protein in 250 mL of binding buffer
(HEPES 20 mM, NaCl 100 mM, MgCl2 3 mM, GDP 3 mM,
pH 7.4). The incubation was started by addition of an
appropriate concentration of agonist and/or antagonist.
Compounds were incubated with the membranes at 37 8C
for 30 min. Subsequently, 0.1 nM [35S]GTPgS (approxi-
mately 2!105 DPM) was added in the presence or absence
of 30 mM glutamate. The mixture was further incubated for
30 min at 37 8C. The reactions were terminated by
separating free and bound radioactivity by rapid vacuum
filtration using a Packard filtration manifold through GF/B
prewetted glass fiber filters. Filters were rapidly washed two
times with cold 10 mM.
4.7.6. (1S*, 3R*, 4R*)-1-Amino-4-(3,4-dimethyl)-phenyl-
cyclopentane-1,3-dicarboxylate hydrochloride salt (12h).
A white solid (65 mg, 56%). 1H NMR (CD3OD) d: 6.90 (s,
2H), 6.88 (s, 1H), 3.17 (dd, JZ10.2, 12.8 Hz, 1H), 2.57 (dd,
JZ10.2, 20.7 Hz, 2H), 2.3 (m, 1H), 2.2 (s, 6H), 1.98 (dd,
JZ10.3, 12.9 Hz, 1H). 13C NMR (CD3OD) d: 175.1 (CO),
173.0 (CO), 139.7 (C), 138.1 (2C), 128.6 (CH), 125.0
(2CH), 62.6 (C), 50.1 (CH), 47.3 (CH), 45.4 (CH2), 39.4
(CH2), 21.2 (2CH3). MS (ES) m/z 264.1 ([MC1], 100%).
HRMS calcd for C14H18O4N (MHC) 264.1236. Found
264.1261.
NaH2PO4/10 mM Na2HPO4 buffer, pH 7.4. Filters were
transferred to vials for subsequent counting in a scintillation
counter. Results are expressed as % of glutamate-induced
response, the latter being defined as 100%. Glutamate and
amino acids were dissolved and diluted in water. Concen-
tration–response curves were drawn on a logarithmic scale.
Sigmoidal curves of best fit were calculated by nonlinear
regression analysis using GraphPad software (San Diego,
CA). The pIC50-value referred to the concentration of a
compound producing half the maximum response.
4.7.7. (1S*, 3R*, 4R*)-1-Amino-4-(3-methoxy)-phenyl-
cyclopentane-1,3-dicarboxylate hydrochloride salt (12i).
1
A white solid (54 mg, 88%). H NMR (CD3OD) d: 7.20 (t,
1H), 6.78 (s, 1H), 6.90–6.70 (m, 2H), 3.62 (s, 3H), 3.4 (m,
1H), 3.2 (dd, JZ9.0, 19.8 Hz, 1H), 3.05 (dd, 1H, JZ9.0,
15.3 Hz, 1H), 2.61 (dd, JZ6.3, 12.6 Hz, 2H), 1.90 (dd, JZ
7.2, 11.8 Hz, 1H). 13C NMR (D2O) d: 178.0 (CO), 174.4
(CO), 155.6 (C), 141.6 (C), 130.5 (CH), 120.0 (CH), 114.6
(CH), 114.3 (CH), 63.9 (C), 55.6 (CH3), 49.7 (CH), 44.2
(CH2), 39.7 (CH2). MS (ES) m/z 280 ([MC1], 80%).
Acknowledgements
We thank Johnson and Johnson Research Pty. Limited
(Sydney, Australia) for financial support and Prof. Susan
Pond (Johnson & Johnson Research), Dr. Vic Sipido, and
Dr. John Stuart Andrews (Jannsen Pharmaceutica, Belgium)
for their encouragement and support.
4.7.8. (1S*, 3R*, 4R*)-1-Amino-4-(1)-naphthlene-cyclo-
pentane-1,3-dicarboxylate hydrochloride salt (12j). A
white solid (66 mg, 33%). 1H NMR (CD3OD) d: 8.1 (d, JZ
8.4 Hz, 1H), 7.8 (d, JZ9.3 Hz, 1H), 7.7 (d, JZ7.2 Hz, 1H),

1812
A. T. Ung et al. / Tetrahedron 61 (2005) 1803–1812
5. Ornstein, P. L.; Bleish, T. J.; Arnold, M. B.; Wright, R. A.;
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