(2S,1′S,2′R,3′R)-2-(2′-Carboxy-3′ -hydroxymethylcyclopropyl) Glycine Is a Highly Potent Group 2 and 3 Metabotropic Glutamate Receptor Agonist with Oral Activity

Article abstract of DOI:10.1021/jm030967o

The asymmetric synthesis and biological activity of (2S, 1′S,2′R,3′R)-2-(2′-carboxy-3′ -hydroxymethylcyclopropyl) glycine ((+)-3) is described. This novel C-3′ substituted carboxy cyclopropyl glycine is a highly potent group 2 and group 3 mGluR agonist that has proven to be orally active in both fear potentiated startle (animal model for anxiety) and PCP-induced motor activation (animal model for psychosis) assays in rats.

Full text of DOI:10.1021/jm030967o

456
J . Med. Chem. 2004, 47, 456-466
(2S,1′S,2′R,3′R)-2-(2′-Ca r boxy-3′-h yd r oxym eth ylcyclop r op yl) Glycin e Is a High ly
P oten t Gr ou p 2 a n d 3 Meta botr op ic Glu ta m a te Recep tor Agon ist w ith Or a l
Activity
Iva´n Collado,*,† Concepcio´n Pedregal,*,† Ana Bele´n Bueno,† Alicia Marcos,† Rosario Gonza´lez,†
J aime Blanco-Urgoiti,‡ J avier Pe´rez-Castells,‡ Darryle D. Schoepp,§ Rebecca A. Wright,§ Bryan G. J ohnson,§
Ann E. Kingston,§ Eric D. Moher,§ David W. Hoard,§ Kelly I. Griffey,§ and J oseph P. Tizzano§,|
Lilly, SA, Avda. de la Industria 30, 28108 Alcobendas, Madrid, Spain, Facultad de Ciencias Experimentales y de la Salud,
Universidad San PablosCEU, Urb. Montepr´ıncipe, 28668 Boadilla del Monte, Madrid, Spain, and Lilly Research
Laboratories, Indianapolis, Indiana 46285
Received J uly 22, 2003
The asymmetric synthesis and biological activity of (2S,1′S,2′R,3′R)-2-(2′-carboxy-3′-hydroxy-
methylcyclopropyl) glycine ((+)-3) is described. This novel C-3′ substituted carboxy cyclopropyl
glycine is a highly potent group 2 and group 3 mGluR agonist that has proven to be orally
active in both fear potentiated startle (animal model for anxiety) and PCP-induced motor
activation (animal model for psychosis) assays in rats.
In tr od u ction
CCG-I) (Chart 1 and Table 1) is a selective and nano-
molar potent agonist for group 2 mGluRs and some
group 3 mGluRs (mGluR6 and mGluR8 subtypes) with
micromolar potency at group 1 mGluRs and the rest of
group 3 mGluRs (mGluR4 and mGluR7 subtypes).7,8
The corresponding gem-difluoro-substituted L-F2CCG-I
is a more potent agonist at mGluR2; however, its
activity at other mGluR subtypes has not been re-
ported.9 Further investigation of the effect of substitu-
tion at the 3′-position of L-CCG-I has led to the
identification of additional potent group 2 mGluR ago-
nists with equal potency but with improved selectivity.
Thus, both (2S,1′S,2′R,3′R)-2-(2′-carboxy-3′-methoxy-
methylcyclopropyl) glycine (cis-MCG-I) (Chart 1) and
trans-MCG-I maintain the agonist activity at mGluR2
compared to L-CCG-I but have increased selectivity
versus group 1 mGluR subtypes.10 (2S,2′R,3′R)-2-(2′,3′-
Dicarboxycyclopropyl) glycine (DCG-IV) also displays
potent group 2 activity. However, it has agonist activity
at the NMDA receptor and unexpectedly mGluR an-
tagonist activity at group 3 (Table 1).11,12 We have very
recently reported that compound (2S,1′S,2′S,3′R)-2-(2′-
carboxy-3′-methylcyclopropyl) glycine (1), in which a
methyl group in the 3′-position is on the same face to
the R-amino acid, is the most potent and selective group
2 mGluR agonist belonging to the carboxycyclopropyl
glycine family known to date.13
It has been over 45 years since the excitatory and
neurotoxic actions of L-glutamate (Glu) were initially
described. Glu is the major excitatory neurotransmitter
in the mammalian central nervous system (CNS).1,2 Glu
receptors are subdivided into ionotropic (GluRs) and
metabotropic receptors (mGluRs).3,4 The mGluRs are
members of the type 3 G protein coupled receptors
(GPCRs), which also include GABAB, calcium-sensing,
and certain pheromone receptors.5 There are currently
eight distinct mGluR proteins (mGluR1-8) which have
been pharmacologically distinguished into three groups
based on amino acid sequence homology, signal trans-
duction mechanisms, and agonist pharmacology. Group
1 mGluRs (mGluR1 and 5) are positively coupled to
phospholipase C activation and groups 2 (mGluR2 and
3) and 3 (mGluR4 and 6-8) are negatively coupled to
adenylate cyclase. With the cloning of mGluR subtypes,
the pharmacology of mGluRs began to progress more
rapidly. Previously discovered and newly discovered
mGluR active agents can be fully characterized for their
affinity and/or functional activity across the cloned
mGluRs. A number of potent and selective compounds
for subtypes as well as subgroups of mGluRs have been
discovered as useful radioligands or pharmacological
tools to explore the biochemical and behavioral conse-
quences of mGluR modulation.6
On the other hand, Pellicciari et al. have demon-
strated that the stereoselective introduction of a bulky,
hydrophobic group such as a phenyl ring in the 3′-
position confers antagonism to the corresponding CCG
analogue, (2S,1′S,2′S,3′R)-2-(2′-carboxy-3′-phenylcyclo-
propyl) glycine (PCCG-4, Chart 1).14 Furthermore, the
same authors have also shown that compounds with
other tethered bulky substituents at the same position
like 9-xanthenylmethyl-CCG (XM-CCG-I) and 9-xan-
thenylethyl-CCG (XE-CCG-I) have the same antagonis-
tic effect.15
Among the several classes of Glu analogues, carboxy-
cyclopropylglycines (CCGs) represent a valuable source
of both potent and selective agonist and antagonist
ligands for the various members of the Glu receptor
family. (2S,1′S,2′S)-2-(2′-Carboxycyclopropyl) glycine (L-
* To whom correspondence should be addressed. For Dr. Iva´n
Collado: phone, +34-91-6633409; fax, +34-91-6633411; e-mail,
collado_ivan@lilly.com. For Dr. Concepcio´n Pedregal: phone, +34-91-
6633426; fax, +34-91-6633411; e-mail, pedregal_concepcion@lilly.com.
† Lilly, SA.
‡ Universidad San Pablo-CEU.
§ Lilly Research Laboratories.
Finally, it should be pointed out that our laboratories
have reported that a substituent R to the amino acid
| Current address: DOV Pharmaceuticals Inc., Hackensack, NJ
07601.
10.1021/jm030967o CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/09/2003

Metabotropic Glutamate Receptor Agonist
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2 457
Ch a r t 1
equilibrium with its aldehyde form (()-6a , classical
methods of amino acid synthesis techniques would
convert (()-6 to the desired product. The only limitation
of this approach was that the amino acid would be
presumably obtained as a mixture of diastereoisomers.
The synthesis of (()-6 was straightforward in two steps
starting from butenolide 4 after cyclopropanation reac-
tion with ethyl(dimethylsulfuranylidene)acetate (EDSA),
generated in situ by treatment of ethyl dimethylsulfo-
nium acetate bromide and a base, and further chemose-
lective reduction of the lactone. Unfortunately, under
the best reaction conditions for the cyclopropanation of
4 (EtO2CCH2SMe2Br, Cs2CO3, DMF, rt), lactone (()-5
was obtained with a poor 22% yield (Scheme 1). This
limitation prompted the development of an alternative
approach for the synthesis of (()-6 from cycloadduct 8.
Thus, 8 was obtained as a single diastereoisomer by
rhodium-catalyzed cyclopropanation of ethyl diazoace-
tate with cis-4,7-dihydro-1,3-dioxepin (7). Cleavage of
the acetal provided diol 9, which was isolated with a
63% combined yield from 7. Conversion of diol 9 to the
corresponding lactol (()-6 was possible by oxidation
with a variety of common oxidizing reagents (TPAP,
TEMPO, Swern conditions). However, it has to be noted
that overoxidation of (()-6 to the lactone (()-5 was the
major side product in these cases. Fortunately, partial
oxidation of 9 with MnO2 afforded exclusively hemiketal
(()-6 as only one of the two possible epimers in a very
high yield.
center (2 position) converts an agonist into an antago-
nist (LY341495, Chart 1).16 Interesting enough, we have
also demonstrated some time ago that the combination
of both effects, R (C-2) and C-3′ disubstitution, retains
the antagonist effect,17 indicating that, at least in 2, the
C-2 and not the C-3′ substitution drives the pharmacol-
ogy of the compound.
We felt that substituted CCGs are a very versatile
platform that has not been widely enough explored, and
therefore, it is still not well understood what structural
features are driving the agonism-antagonism profile as
well as the activity across all mGluRs. In the aim to
further explore the effect of substituents on the C-3′
position of the L-CCG-I and to develop novel, potent,
and selective agonists for mGluRs, we designed and
prepared the 3′-cis-hydroxymethyl analogue 3, which
has the additional possibility of acting as both hydrogen
bond donor and acceptor.
On the basis of absolute stereochemistry of the highly
potent and selective group 2 mGluR agonist 1 deter-
mined by us (2S,1′S,2′S,3′R) and taking into account
that of the 16 possible isomers for MCGs the high-
est agonist activity for mGluR2 was that observed for
the cis-MCG-I, with the same stereochemistry pat-
tern (2S,1′S,2′R,3′R), we decided to synthesize the
corresponding enantiomerically pure analogue of 3,
(2S,1′S,2′R,3′R)-2-(2′-carboxy-3′-hydroxymethylcyclo-
propyl) glycine. Herein, we describe the asymmetric
synthesis and biological activity of (+)-3 (Chart 2, Table
1).
Conversion of lactol (()-6 to the amino acid using the
Strecker reaction was initially investigated. As pre-
dicted, poor stereoselectivity was observed. Treatment
of (()-6 with potassium cyanide and ammonium chlo-
ride in the presence of alumina under sonication gave
a 2:1 mixture of the two possible racemic aminonitriles
(()-10 (Scheme 2). Further transformation of this
mixture to their corresponding N-Boc-aminodiesters by
treatment with a saturated solution of HCl in EtOH and
subsequent protection of the nitrogen afforded a 2:1
mixture of isomers (()-11 and (()-12, respectively, in
good yield. The isomers were separated by column
chromatography, and their relative configurations were
assigned based on nuclear Overhauser effect (NOE)
measurements on their corresponding pyroglutamate
derivatives (()-13 and (()-14, obtained by J ones oxida-
tion of (()-11 and (()-12, respectively. The correspond-
ing relative configurations (1SR,5RS,6RS) in both (()-
13 and (()-14 at the three cyclopropyl carbons were
assigned through coupling constant analysis. All the
proton and carbon resonances were assigned through
the combination of 1D and 2D experiments (1H, COSY,
HSQC, 1D-NOESY). Since it is well-known that for
18
cyclopropane derivatives J cis > J trans
,
the coupling
constant values (J H5-H6 ) 3.2 Hz for (()-13 and 3.3 Hz
for (()-14, J H1-H6 ) 2.9 Hz for (()-13 and 2.8 Hz for
(()-14, J H1-H5 ) 6.4 Hz for (()-13 and 6.5 Hz for (()-
14) indicate that H1 is cis to H5 and trans to H6 in both
cases. To elucidate the relative stereochemistry of the
substituent at the C-2 position in both (()-13 and (()-
14, ROESY-2D experiments were performed (Figure 1).
For (()-13, the ROESY-2D spectrum showed a cross-
peak between H2 and H6, whereas for (()-14 it was not
detected and instead a relevant NOE effect was present
between H2 and H1 and H2 and H.5 These NOE patterns
Ch em istr y
As a first goal, we decided to develop a racemic
diastereoselective synthesis for 3. In a retrosynthetic
analysis, lactol (()-6 was envisioned as its plausible
precursor (Scheme 1). Since this lactol would exist in

458 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2
Collado et al.
Ta ble 1. Potency and Subtype Selectivity of Human MGluR Agonists Reported in NM Values
group 1a
group 2b
group 3b
compd
L-CCG-I
L-F2CCG-I
cis-MCG-I
trans-MCG-I
DCG-IV
1
mGluR1
mGluR5
mGluR2
mGluR3
mGluR4
mGluR6
mGluR7
mGluR8
23000
NTe
17000
NTe
300c
600
NTe
4,000
NTe
600c
NTe
47,000
NTe
400
NTe
90c
>100000
>100000
>100000c
>100000
>100000
>500000
32000
>100000
>100000
389000c
>100000
>100000c
>500000
>100000
>100000
NTe
100
NTe
NTe
NTe
NTe
NTe
300
NTe
NTe
NTe
NTe
NTe
300c
200c
23000c,f
>100000
320
40000c,f
1198
55
40000c,f
>100000
175000
185000
>100000
NTe
32000c,f
1320
60
8
38
S-AP4
448000
>300000
>100000
5
>100000
>200000
>100000
11
(RS)-PPG
(S)-3,4-DCPG
(()-3
(-)-3
(+)-3
5200
4700
3600
NTe
210
8800
31
>100000
NTe
NTe
NTe
>100000
>100000
NTe
NTe
NTe
>100000
>100000
>100000
>100000
4
7
1800
147
10
a
b
Assay used: EC50/PI hydrolysis in nonneuronal cells. Assay used: EC50/inhibition of forskolin c-AMP in nonneuronal cells. c For
rat subreceptors. Reference 11. e NT: not tested. f Antagonist.
d
1
Ch a r t 2
raphy. H NMR analysis of the mixture proved that its
major component was the desired isomer (()-12.
The racemic N-Boc diester (()-12 was then subjected
to basic hydrolysis followed by treatment with 2 N HCl
to afford the corresponding hydrochloride salt. The
zwitterion of the final amino acid (()-3 was obtained
by treatment of the hydrochloride with propylene oxide
in methanol (Scheme 3).
Sch em e 1a
To identify the active enantiomer of (()-3, chiral
HPLC separation of the racemate (()-12 was performed
prior to its hydrolysis to the final zwitterions. Each
antipode was then separately submitted to a sequential
treatment with TFA and further hydrolysis with 3 N
sodium hydroxide. Finally, both isomers were isolated
after precipitation with concentrated HCl. Affinity of
(+)-3 and (-)-3 for group 2 mGluR was then evaluated.20
As a result, the binding assay showed that isomer (+)-3
had a very high affinity for both mGluR2 and mGluR3
(mGluR2, Ki ) 23 nM; mGluR3, Ki ) 3nM) whereas
(-)-3 demonstrated to be inactive in the same assay
(mGluR2, Ki > 10000 nM; mGluR3, Ki > 10000 nM).
Thus, it was concluded that the affinity for group 2
mGluRs resided in the (+)-3 isomer and it was profiled
for agonist and antagonist activity at all of the known
mGluR subtypes (vide infra).
a
(a) EtO2OCH2SMe2Br, Cs2CO3, DMF, room temperature; (b)
DIBAL-H, THF, -78 °C; (c) N2CHCO2Et, Rh2(OAc)4, CH2Cl2,
reflux; (d) 0.5 N HCl/EtOH, reflux; (e) MnO2, CH3CN, room
temperature.
To determine the absolute stereochemistry of (+)-3,
we developed a new enantioselective synthesis based on
the asymmetric intramolecular cyclopropanation of al-
lylic and homoallylic diazoacetates using Doyle cata-
lysts.21 This new synthesis started with the commer-
cially available cis-4-benzyloxy-2-buten-1-ol (16) as
starting material (Scheme 4). By use of a general
procedure for preparing diazoacetates, 16 was trans-
formed into the corresponding acetoacetic ester 17 using
diketene. Subsequent diazo transfer followed by base-
induced deacylation of the intermediate R-diazo aceto-
acetic ester afforded diazoacetate 18. Enantiose-
lective intramolecular cyclopropanation of 18 catalyzed
by Rh2(4S-MPPIM)4,22 followed by alkaline hydrolysis
and further esterification with diazomethane of the
(1R,5S,6R)-cyclopropyl lactone (-)-19 (ee >95%)23 af-
forded the intermediate (1S,2R,3S)-hydroxyester (-)-
20. Subsequent protection of the hydroxyl group, and
further epimerization of the methoxycarbonyl moiety of
(-)-21 afforded epimer (-)-22 upon removal of the TBS
group. After oxidation of alcohol (-)-22 to (1S,2S,3R)-
aldehyde (+)-23 by treatment with tetra-n-propylam-
monium perruthenate (TPAP) in the presence of N-me-
confirmed a relative stereochemistry of (2RS, 1′SR,
2′RS, 3′RS) for alcohol (()-11 and (2SR, 1′SR, 2′RS,
3′RS) for alcohol (()-12.
Comparison of the relative stereochemistry of (()-11
(2RS,1′SR,2′RS,3RS) and (()-12 (2SR,1′SR,2′RS,3RS)
to that of cis-MCG-I and 1 allowed us to believe that
(()-12 was the direct precursor of (()-3. Considering
that (()-12 was the minor isomer in the Strecker
reaction, we decided to investigate other methods for
the installation of the amino acid moiety that might
enhance the steroselectivity of the desired isomer.
Toward this end, we next ran a Bucherer-Bergs reac-
tion for the generation of the amino acid center, which
is generally known to produce the opposite stereochem-
ical effect of a Strecker reaction.19 Thus, hydrolysis of
lactol (()-6 followed by treatment with an excess of
sodium cyanide and ammonium carbonate afforded a
1:2.3 mixture of hydantoins (()-15. Further hydrolysis
of hydantoins with 1 N sodium hydroxide to the amino
acids and their subsequent esterification and nitrogen
protection furnished a mixture of (()-11 and (()-12 in
a 1:2.3 ratio that was separated by column chromatog-

Metabotropic Glutamate Receptor Agonist
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2 459
Sch em e 2a
a
(a) KCN, NH4Cl, CH3CN, ultrasound; (b) i. HCl/EtOH (satd), H2O, room temperature, ii. Boc2O, NaHCO3 (satd), dioxane, room
temperature; (c) J ones reagent, acetone, 0 °C to room temperature; (d) i. 1 N NaOH, EtOH, 60 °C, ii. NaCN, (NH4)2CO3, H2O, reflux; (e)
i, 1 N NaOH, reflux, ii. 1 N HCl/EtOH, iii. Boc2O, NaHCO3 (satd), dioxane, room temperature.
ee), followed by nucleophilic addition of cyanide to the
Schiff base, afforded the expected mixture of the two
possible R-amino nitrile derivatives in a 9:1 ratio, in
which the major component (-)-24 was separated by
medium-pressure chromatography in 86% isolated yield.
Since R-(-)-R-phenylglycinol preferentially induces op-
posite chirality in the newly formed asymmetric cen-
F igu r e 1. NOE correlations for compounds 13 and 14.
ter,24 the absolute configuration of the more abundant
Sch em e 3a
constituent of the mixture of glycinonitriles was as-
signed as (2S,1′S,2′R,3′R)-[(R)-(phenylglycinyl)])-ami-
nonitrile ((-)-24). After oxidative cleavage of (-)-24 with
lead tetraacetate and further acidic hydrolysis, N-Boc-
aminodiester (+)-25 was obtained by treatment of the
corresponding amino diacid with a saturated solution
of HCl in EtOH and subsequent protection of the
nitrogen. Deprotection of the hydroxyl group afforded
(+)-12 in 8% overall yield. Further basic hydrolysis of
(+)-12 followed by hydrolysis with 2 N HCl and subse-
quent treatment of the hydrochloride salt with propy-
lene oxide in methanol afforded the zwitterion of the
final amino acid (+)-3, which possesses identical phys-
icochemical properties to the one synthesized through
the first method reported herein (Scheme 3).
P h a r m a cology
Racemic and enantiomerically purecompounds (()-3
and (+)-3 were evaluated in adult rat cerebral cortical
slices for their ability to influence forskolin-stimulated
c-AMP formation (group 2 and 3 mGluRs)25 or basal [3H]-
IP formation (group 1 mGluR).26 The data (EC50) are
shown in Table 1 along with other known CCG agonists
and some representative group 3 mGluR selective
agonists: L-1-amino-4-phosphonobutyric acid (L-AP4),
a
(a) i. 2.5 N LiOH, THF, room temperature, ii. 2 N HCl, room
temperature, iii. propylene oxide. MeOH, room temperature; (b)
chiral HPLC separation; (c) i. TFA, CH2Cl2, room temperature, ii.
3 N NaOH, room temperature.
thylmorpholine N-oxide (NMO), a diastereoselective
Strecker synthesis was performed.24 Condensation of
(+)-23 with optically active R-(-)-R-phenylglycinol (99%

460 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2
Collado et al.
Sch em e 4a
F igu r e 2. Effect of mGlu 2/3 and mGlu8 agonist (+)-3 on fear
potentiated startle. Diazepam (0.6 mg/kg) was given ip 30 min
prior to testing. (+)-3 was administered orally 60 min prior to
testing. *P < 0.05.
pure enantiomer (+)-3 is the most potent cyclopropyl
glycine thus far known for these mGluRs (2, 3, 6, and
8).
Beh a vior a l P h a r m a cology Stu d ies
The recent years have seen a growing interest in the
field of mGluR agonists, due to the intriguing thera-
peutic opportunities offered by their modulation. It is
hoped that drugs targeted at mGluRs hold new promise
to safely and effectively treat a wide range of psychiatric
and neurological disorders. In particular, there is an
accumulation of experimental evidence which implicates
both groups 2 and 3 mGluRs in the treatment of
schizophrenia,28 anxiety,29 drug withdrawal,30 depres-
sion,31 neuroprotection,32 pain,33 Alzheimer’s disease,34
epilepsy,35 and Parkinson’s disease.36
We studied the oral potencies of (+)-3 in two mGluR2
linked therapeutic animal models: the fear-potentiated
startle and PCP-induced hyperactivity assays in rats.
The rat fear-potentiated startle was specifically cho-
sen, as it is highly sensitive to mGluR2 agonists and
served as the basis for developing therapeutic agents
for anxiety disorders in humans.29 Diazepam (0.6 mg/
kg i.p.) was used as a positive control in each experi-
ment, and all experiments were performed in fed rats.
As shown in Figure 2, (+)-3 dose dependently blocked
the fear-potentiated startle response in rats with a MED
of 0.0003 mg/kg.
a
(a) Diketene, AcONa, THF, reflux; (b) i. p-AcNHC6H4SO2N3,
Et3N, CH3CN, room temperature, ii. LiOH, H2O, room tempera-
ture; (c) Rh2(4S-MPPIM)4, CH2Cl2, reflux; (d) i. 2.5 N LiOH, THF,
room temperature, ii. CH2N2, Et2O, 0 °C; (e) TBSCl, imidazole,
DMF; room temperature; (f) i. KHMDS, THF, -78 to -10 °C, ii.
TBAF, THF, 0 °C; (g) TPAP, NMO, mol sieves (4A), CH2Cl2; room
temperature; (h) i. (R)-phenylglycinol, MeOH, room temperature,
ii. TMSCN, room temperature; (i) i. Pb(AcO)4, CH2Cl2, MeOH, 0
°C, ii. HCl/EtOH satd, H2O, room temperature, iii. Boc2O, NaHCO3
satd, dioxane, room temperature; (j) H2, 5% Pd/C, MeOH, room
temperature; (k) i. 2.5 N LiOH, THF, room temperature, iii. 2 N
HCl, room temperature, iii. propylene oxide, MeOH, room tem-
perature.
Ch a r t 3
Drugs such as phencyclidine (PCP) and ketamine
produce schizophrenia-like symptoms in humans.28i It
was reported that group 2 agonists suppressed PCP-
induced excitatory behaviors (hyperlocomotion, ambu-
lations, stereotypy) in rats.28a As shown in Figure 3, oral
administration of (+)-3 attenuated PCP-induced ambu-
lations (ED50 ) 1.82 mg/kg), fine motor movements
(MED ) 3 mg/kg), and decreased time at rest (MED )
3 mg/kg) in rats. Similarly observed with previous
ligands, the difference in potency detected for (+)-3 in
the fear-potentiated startle and the PCP in vivo animal
models is due to their different sensitivity to group 2
mGluR selective agonists.29a,28c
In conclusion, we have shown that enantiomerically
pure (2S,1′S,2′R,3′R)-2-(2′-carboxy-3′-hydroxymethyl-
cyclopropyl) glycine ((+)-3) is a highly potent agonist
at mGluR2, 3, 6, and 8. Furthermore, (+)-3 has been
demonstrated to possess potent oral activity in animal
models of anxiety and psychosis. Further studies di-
rected at expanding the structure-activity relationship
for this novel mGluR agonist platform will be reported
in due course.
(RS)-4-phosponophenylglycine ((RS)-PPG), and (S)-di-
carboxyphenylglycine ((S)-3,4-DCPG) (see Chart 3).27
The molecular pharmacology of group 3 mGluR is not
as developed as that for groups 1 and 2. This is partially
due to the greater diversity of receptor subtypes within
this class and partially to the paucity of pharmacological
tools developed to study these targets.
As shown in Table 1, compound (+)-3 was identical
to L-CCG-I in its biological profile through all mGluRs
although 90-fold more potent for mGluR2/3 and 4- and
40-fold for mGluR6 and mGluR8, respectively. There-
fore, the presence of the hydroxymethyl group in the
same face as the amino acid center could be enhancing
the population of the active conformation needed for
effective interaction with the binding site of mGluR2,
3, 6, and 8, and/or providing an additional direct (e.g.,
H-bond) interaction with the receptor. Lack of data for
group 3 mGluR for the methoxy analogue cis-MCG-1
precludes defining the role of a hydrogen bond interac-
tion of the hydroxy functionality of compound (+)-3. The

Metabotropic Glutamate Receptor Agonist
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2 461
Indianapolis, IN. Animals were group housed (maximum eight
rats per cage) under standard laboratory conditions (12 h light/
dark cycle) with ad libitum access to water and feed for at least
1 day prior to overnight fasting for use in oral dosing studies.
E t h yl (2SR,3RS)-2,3-Dih yd r oxym et h ylcyclop r op a n e
Ca r boxyla te (9). To a solution of cis-4,7-dihydro-1,3-dioxepin
(10.0 g, 99.9 mmol) in CH2Cl2 (50 mL) was added Rh2(OAc)4
(442 mg, 1.0 mmol). The resulting suspension was allowed to
stir vigorously at reflux while a solution of ethyl diazoacetate
(22.0 mL, 209.7 mmol) in CH2Cl2 (100 mL) was added dropwise
over a period of 5-6 h. After the addition was completed, the
reaction was allowed to stir for 15 min followed by cooling to
room temperature and filtering through a plug of silica gel.
The filtrate was concentrated in vacuo, and the residue was
purified by column chromatography (AcOEt/hexane 1:10 and
then 1:5) to afford 17.5 g of an inseparable mixture of
cyclopropanated product 8 and both isomers of EtO2CCHd
CHCO2Et. This mixture was taken into 0.5 N HCl/EtOH (400
mL, 200 mmol) and allowed to stir under reflux for 2-3 h (until
TLC showed no starting material) at which time the solvent
was removed in vacuo. The residue was dissolved in EtOH (200
mL) and concentrated to dryness in vacuo. The residue was
taken up again in EtOH (200 mL), and the resulting solution
was neutralized with NaHCO3 (solid). The mixture was
allowed to stir for 30 min, filtered, and concentrated. The
resulting residue was purified by column chromatography
(AcOEt/hexane 1:1 and then 3:1) to give diol 9 (11.0 g, 63%)
1
as colorless oil. H NMR (200 MHz, CDCl3): 1.23 (t, J ) 7.1
Hz, 3H), 1.49 (t, J ) 3.5, 1H), 1.89-2.00 (m, 2H), 2.72 (br s,
2H), 3.31-3.42 (m, 2H),4.05-4.16 (m, 2H) and 4.10 ppm (c, J
) 7.1 Hz, 2H). 13C NMR (50 MHz, CDCl3): 14.0, 23.8, 27.1
(2C), 60.3 (2C), 60.8 and 172.8 ppm. Anal. (C8H14O4) C; H.
E t h yl (1RS,5SR,6RS)-2-H yd r oxy-3-oxa b icyclo[3.1.0]-
h exa n e-6-ca r b oxyla t e ((()-6). To
a solution of ethyl
(2SR,3RS)-2,3-dihydroxymethylcyclopropane carboxylate (9)
(10.5 g, 60.3 mmol) in CH3CN (150 mL) at room temperature
was added activated MnO2 (29.1 g mL, 301.5 mmol) followed
by stirring for 24 h at which time additional MnO2 (29.1 g,
301.5 mmol) was added followed by stirring an additional 24
h. The mixture was poured onto a stirring suspension of silica
gel (20 g) in AcOEt (450 mL), and the resulting mixture was
filtered through a plug of Celite. After removal of the solvent
under reduced pressure, the residue was purified by column
chromatography (AcOEt/hexane 1:2 and then 1:1) to afford
F igu r e 3. Effect of mGlu 2/3 and mGlu8 agonist (+)-3 on PCP
(5 mg/kg) evoked behaviors. (+)-3 or vehicle was administered
orally 2 h prior to PCP or vehicle s.c. injection. Behaviors were
monitored over
a 60 min time period immediately after
injection of PCP. Data (mean + S.E.) are presented as total
number of behaviors expressed during 60 min; n ) 8 rats. *P
< 0.05. When compared to saline/PCP control EC50 calculated
(nonlinear regression sigmoidal dose response variable slope)
is amount of drug to inhibit the PCP-evoked response of
ambulations by 50%. Emax is the maximum percent effect of
the compound.
1
lactol (()-6 (8.7 g, 83%). H NMR (200 MHz, CDCl3): 1.23 (t,
J ) 7.1 Hz, 3H), 1.43 (t, J ) 3.3 Hz, 1H), 2.21-2.23 (m, 2H),
2.76 (d, J ) 3.0 Hz, 1H), 3.85 (d, J ) 8.7 Hz, 1H), 4.06 (d, J )
8.7 Hz, 1H), 4.10 (c, J ) 7.1 Hz, 2H), and 5.32 (d, J ) 3.0 Hz,
1H). 13C NMR (50 MHz, CDCl3): 14.1, 22.1, 25.0, 31.2, 60.8,
67.3, 97.8, and 171.9 ppm.
Exp er im en ta l Section
Eth yl (2RS,1′SR,2′RS,3′RS)-N-(ter t-Bu toxyca r bon yl)-2-
(2′-et h oxyca r b on yl-3′-h yd r oxym et h ylcyclop r op yl) Gly-
cin a te (11); a n d Eth yl (2SR,1′SR,2′RS,3′RS)-N-(ter t-Bu -
toxyca r bon yl)-2-(2′-eth oxyca r bon yl-3′-h yd r oxym eth ylcy-
clop r op yl) Glycin a te ((()-12). Meth od A. A suspension of
NH4Cl (2.42 g, 45.3 mmol) and neutral aluminum oxide (1.4
g) in CH3CN (50 mL) was ultrasonicated for 1 h. A solution of
ethyl (1RS,5SR,6RS)-2-hydroxy-3-oxabicyclo[3.1.0]-hexane-6-
carboxylate ((()-6) (780 mg, 4.53 mmol) in CH3CN (20 mL)
was added to the mixture, and the reaction was ultrasonicated
for 1 h at which time finely powdered KCN (3.54 g, 54.36
mmol) was added and the mixture was allowed to react for 15
h. Additional aluminum oxide (3.2 g) was added to the reaction
mixture, and it was ultrasonicated for an additional 4 days.
The mixture was then filtered through a plug of Celite, and
the inorganics were washed with CH3CN to give 710 mg of a
2:1 mixture of the two possible racemic aminonitriles (()-10
as a yellow oil that was used without further purification. A
solution of (()-10 (380 mg, 1.92 mmol) in HCl/EtOH (satu-
rated) (20 mL) and H2O (0.10 mL, 5.75 mmol) was stirred for
1 h at 0 °C and for 48 h at room temperature. The solvent
was removed in vacuo, and the residue was dissolved in
absolute EtOH (25 mL). The resulting solution was evaporated
under reduced pressure, and the residue was taken up again
Gen er a l. All solvents and reagents were purchased from
commercial sources and used as received, unless otherwise
indicated. Tetrahydrofuran (THF) was distilled from sodium
benzophenone ketyl prior to use. All reactions were performed
under a positive pressure of nitrogen. H NMR and 13C NMR
1
data were recorded on a Bruker AC-200P (200 MHz), Brucker
AM-300 (300 MHz), or Brucker Avance 500-DRX (500 MHz)
spectrometer. Chemical shifts are reported as ppm (δ) relative
to TMS as internal standard. Melting points were determined
on a Bu¨chi apparatus and are not corrected. Optical rotations
were measured with a Perkin-Elmer 241 polarimeter and with
a Bellingham Stanley ADP-220. Analytical TLC was performed
on Merck TLC glass plates precoated with F254silica gel 60 (UV,
254 nm and phosphomolibdic acid). Chromatographic separa-
tions were performed by using 230-400 mesh silica gel
(Merck). Elemental analyses were performed in the Univer-
sidad Complutense Analytical Centre (Facultad de Farmacia),
Madrid. PCP was obtained from Sigma (St. Louis, MO).
An im a ls. All experiments were performed in accordance
with Eli Lilly and Company animal care and use policies, each
animal being used on only one occasion. Male Sprague Dawley
rats (225-274 g) were obtained from Harlan Industries,

462 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2
Collado et al.
in absolute EtOH (25 mL). This procedure was repeated three
times followed by neutralization with NaHCO3 (solid), stirring
for 1 h, filtering through a plug of Celite, and concentra-
tion to dryness. A dioxane (20 mL) solution of the resulting
residue was treated with a saturated aqueous solution of
NaHCO3 (5 mL) followed by a solution of di-tert-butyl dicar-
bonate (500 mg, 2.3 mmol) in dioxane (5 mL). The mixture
was allowed to stir overnight, at which time the layers were
separated and the aqueous layer was extracted with AcOEt.
The combined organic layers were dried (Na2SO4), filtered, and
concentrated to dryness. The residue was purified by column
chromatography (AcOEt/hexane 1:2) to give 400 mg (61%
overall yield) of a 2:1 mixture of racemic diastereoisomers (()-
11 and (()-12. After separation of both isomers by column
chromatography (Et2O/hexane 1:1), the more abundant con-
stituent of the mixture was determined to be racemic ethyl
(2RS,1′SR,2′RS,3′RS)-N-(tert-butoxycarbonyl)-2-(2′-ethoxycar-
bonyl-3′-hydroxymethylcyclopropyl) glycinate ((()-11) whereas
the minor diastereoisomer (with lower Rf) was assigned as the
desired racemic ethyl (2SR,1′SR,2′RS,3′RS)-N-(tert-butoxy-
carbonyl)-2-(2′-ethoxycarbonyl-3′-hydroxymethylcyclopropyl) gly-
cinate ((()-12).
Meth od B. A solution of ethyl (1RS,5SR,6RS)-2-hydroxy-
3-oxabicyclo[3.1.0]-hexane-6-carboxylate ((()-6) (6.8 g, 39.5
mmol) in EtOH (95 mL) and 1 N NaOH (47.4 mL, 47.4 mmol)
was allowed to stir at 60 °C for 2 h. To the resulting solution
was added a suspension of (NH4)2CO3 (34.3 g, 355.5 mmol) and
NaCN (9.7 g, 197.5 mmol) in H2O (50 mL). The mixture was
allowed to stir under reflux for 3 days and then cooled to room
temperature. The EtOH was removed in vacuo and the
resulting aqueous solution was cooled to 0 °C while the pH
was adjusted to ∼6 by the addition of 1 N KHSO4. The solution
was evaporated to dryness in vacuo to give a residue that was
dissolved in 1 N NaOH (400 mL, 400 mmol) followed by
stirring under reflux for 48 h. Upon cooling to 0 °C the pH
was adjusted to 1-2 by addition of 1 N HCl followed by
removal of the solvent in vacuo. The resulting residue was
dissolved in a 1 N HCl/EtOH (400 mL, 400 mmol), and the
mixture was stirred for 2 days at room temperature. The
solvent was removed in vacuo and residue taken into EtOH
(200 mL). After solvent was removed in vacuo, the residue was
again taken into EtOH (200 mL) and the solution was
neutralized with NaHCO3 (solid) and stirred for 1 h. The
inorganics were filtered off and the solvent was removed in
vacuo. The residue was dissolved in dioxane (300 mL) at room
temperature, and a saturated aqueous solution of NaHCO3
(∼100 mL) was added (until pH was adjusted to ∼8). The
mixture was treated with a dioxane (100 mL) solution of di-
tert-butyl dicarbonate (10.4 g, 47.4 mmol) dropwise followed
by vigorous stirring at room temperature overnight. The
mixture was diluted with AcOEt, and the layers were sepa-
rated. The aqueous layer was extracted with AcOEt (2×), and
the combined organic layers were dried (Na2SO4), filtered, and
concentrated to dryness. The residue was purified by column
chromatography (AcOEt/hexane 1:2) to give 8.1 g (60% overall
yield) of a 1:2.3 mixture of racemic diastereoisomers (()-11
and (()-12, respectively. After separation of both isomers by
column chromatography (Et2O/hexane 1:1), the more abundant
constituent of the mixture (with lower Rf) was determined to
be the desired racemic ethyl (2SR,1′SR,2′RS,3′RS)-N-(tert-
butoxycarbonyl)-2-(2′-ethoxycarbonyl-3′-hydroxymethylcyclo-
propyl) glycinate ((()-12) whereas the minor diastereoisomer
was the racemic ethyl (2RS,1′SR,2′RS,3′RS)-N-(tert-butoxy-
carbonyl)-2-(2′-ethoxycarbonyl-3′-hydroxymethylcyclopropyl) gly-
cinate ((()-11).
(()-12: Eth yl (2SR,1′SR,2′RS,3′RS)-N-(ter t-Bu toxyca r -
bon yl)-2-(2′-eth oxyca r bon yl-3′-h yd r oxym eth ylcyclop r o-
p yl) Glycin a te. H NMR (200 MHz, CDCl3): 1.25 (t, J ) 7.1
Hz, 3H), 1.32 (t, J ) 7.1 Hz, 3H), 1.45 (s, 9H), 1.70-1.81 (m,
2H), 1.91-2.11 (m, 1H), 3.17 (dd, J ) 3.1, 10.1 Hz, 1H), 3.54-
3.67 (m, 1H), 3.95-4.33 (m, 5H), and 5.20 (br d, J ) 7.3 Hz,
1H). 13C NMR (50 MHz, CDCl3): 14.0, 14.1, 22.5, 28.2 (3C),
28.9, 29.2, 52.3, 60.8, 61.0, 62.5, 80.4, 155.3, 171.8, and 172.4
ppm. Anal. (C16H27NO7) C, H, N.
1
Eth yl (1SR,2RS,5RS,6RS)-3-(ter t-Bu toxyca r bon yl)-4-
oxo-3-a za bicyclo[3.1.0]h exa n e-2,6-d ica r boxyla te ((()-13).
To a solution of ethyl (2RS,1′SR,2′RS,3′RS)-N-(tert-butoxy-
carbonyl)-2-(2′-ethoxycarbonyl-3′-hydroxymethylcyclopropyl) gly-
cinate ((()-11) (74 mg, 0.21 mmol) in acetone (2 mL) at 0 °C
was added J ones reagent (0.63 mL, previously cooled to 0 °C)
dropwise. The reaction mixture was stirred for 1 h at 0 °C and
2 h at room temperature after which time H2O (2 mL) and
iPrOH (2 mL) were added followed by extraction with AcOEt
(3 × 5 mL). The combined organic layers were dried (MgSO4),
filtered, and evaporated under reduced pressure. The residue
was purified by flash chromatography (AcOEt) to give (()-13
(68 mg, 97%) as white solid. 1H NMR (500 MHz, CDCl3) δ:
1.26 (t, 3H, J ) 7.1 Hz), 1.31 (t, 3H, J ) 7.1 Hz), 1.46 (s, 9H),
1.95 (dd, 1H, J 1 ) 3.2 Hz, J 2 ) 2.9 Hz), 2.42 (dd, 1H, J 1 ) 6.4
Hz, J 2 ) 2.9 Hz), 2.53 (dd, 1H, J 1 ) 6.4 Hz, J 2 ) 3.2 Hz), 4.16
(q, 2H, J ) 7.1 Hz), 4.21-4.32 (m, 2H), and 4.57 (s, 1H) ppm.
13C NMR (75 MHz, CDCl3) δ: 14.4, 14.5, 22.6, 25.7, 28.2 (3C),
29.0, 60.3, 62.1, 62.6, 84.4, 149.4, 169.3, 169.4, and 169.9 ppm.
Mp 78-81 °C. Anal. (C16H23NO7) C, H, N.
Eth yl (1SR,2SR,5RS,6RS)-3-(ter t-Bu toxyca r bon yl)-4-
oxo-3-a za bicyclo[3.1.0]h exa n e-2,6-d ica r boxyla te ((()-14).
To a solution of ethyl (2SR,1′SR,2′RS,3′RS)-N-(tert-butoxy-
carbonyl)-2-(2′-ethoxycarbonyl-3′-hydroxymethylcyclopropyl) gly-
cinate ((()-12) (100 mg, 0.29 mmol) in acetone (2 mL) at 0 °C
was added J ones reagent (0.87 mL, previously cooled to 0 °C)
dropwise. The reaction mixture was stirred for 1 h at 0 °C and
2 h at room temperature after which time H2O (2 mL) and
iPrOH (2 mL) were added followed by extraction with AcOEt
(3 × 5 mL). The combined organic layers were dried (MgSO4),
filtered, and evaporated under reduced pressure. The residue
was purified by flash chromatography (AcOEt) to give (()-14
(92 mg, 97%) as white solid. 1H NMR (500 MHz, CDCl3) δ:
1.27 (t, 3H, J ) 7.1 Hz), 1.34 (t, 3H, J ) 7.1 Hz), 1.49 (s, 9H),
2.36 (dd, 1H, J 1 ) 3.3 Hz, J 2 ) 2.8 Hz), 2.56 (dd, 1H, J 1 ) 6.5
Hz, J 2 ) 2.8 Hz) 2.65 (dt, 1H, J 1 ) 6.5 Hz, J 2 ) 3.3 Hz), 4.13-
4.21 (m, 2H), 4.26-4.34 (m, 2H), and 4.76 (d, 1H, J ) 6.5 Hz)
ppm. 13C NMR (75 MHz, CDCl3) δ: 13.5, 13.6, 21.5, 21.7, 27.3
(3C), 28.6, 58.1, 61.4, 61.7, 83.3, 148.1, 168.1, 168.7, and 168.9
ppm. Mp 78-80 °C. Anal. (C16H23NO7) C, H, N.
(2SR,1′SR,2′RS,3′RS)-2-(2′-Ca r boxy-3′-h yd r oxym eth yl-
cyclop r op yl) Glycin e ((()-3). To a solution of ethyl
(2SR,1′SR,2′RS,3′RS)-N-(tert-butoxycarbonyl)-2-(2′-ethoxycar-
bonyl-3′-hydroxymethylcyclopropyl) glycinate ((()-12) (145 mg,
0.42 mmol) in THF (3.5 mL) was added 2.5 N LiOH (6.7 mL,
16.8 mmol). The mixture was vigorously stirred overnight. The
organic layer was separated and discarded, and the aqueous
layer was washed with Et2O. After the aqueous solution was
adjusted to pH ∼1 by addition of 1 N HCl at 0 °C, it was
extracted four times with AcOEt, and the combined organic
layers were dried (Na2SO4) and evaporated under reduced
pressure. A solution of the residue in 2 N HCl (3.5 mL) was
stirred overnight. The solvent was then removed in vacuo, and
the resulting solid was washed with Et2O. The resulting
hydrochloride salt was dissolved in MeOH (3 mL), and pro-
pylene oxide (10 mL) was added. The mixture was stirred
overnight and the resulting insoluble solid was filtered and
washed with Et2O to give (()-3 (55 mg, 69% overall yield) as
(()-11: Eth yl (2RS,1′SR,2′RS,3′RS)-N-(ter t-Bu toxyca r -
bon yl)-2-(2′-eth oxyca r bon yl-3′-h yd r oxym eth ylcyclop r o-
1
1
a white solid. H NMR (200 MHz, D2O): 1.77-2.11 (m, 3H),
p yl) Glycin a te. H NMR (300 MHz, CDCl3): 1.18 (t, J ) 7.1
3.62 (d, J ) 11.0 Hz, 1H), 3.66 (dd, J ) 8.6, 12.5 Hz, 1H), and
3.90 ppm (dd, J ) 6.0, 12.5 Hz, 1H). 13C NMR (50 MHz, D2O):
25.0, 27.7, 29.1, 54.8, 61.0, 173.9, and 177.9 ppm. Mp 154-
156 °C. Anal. (C7H11NO5) C, H, N.
Hz), 3H, 1.25 (t, J ) 7.1 Hz, 3H), 1.40 (s, 9H), 1.57-1.65 (m,
1H), 1.70 (t, J ) 4.9 Hz, 1H), 1.84-1.92 (m, 1H), 3.49 (t, J )
10.4 Hz, 1H), 3.97-4.30 (m, 6H), 5.60 (br d, J ) 7.7 Hz, 1H).
13C NMR (75 MHz, CDCl3): 14.0, 14.1, 21.6, 28.2 (3C), 28.4,
29.6, 50.9, 59.4, 60.7, 61.9, 81.1, 155.9, 171.1, 172.3. Mp <50
°C. Anal. (C16H27NO7) C, H, N.
(2R,1′R,2′S,3′S)-2-(2′-Ca r boxy-3′-h yd r oxym eth ylcyclo-
p r op yl) Glycin e ((-)-3) a n d (2S,1′S,2′R,3′R)-2-(2′-Ca r boxy-

Metabotropic Glutamate Receptor Agonist
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2 463
3′-h yd r oxym eth ylcyclop r op yl) Glycin e ((+)-3). The cor-
responding enantiomers of ethyl (2SR,1′SR,2′RS,3′RS)-N-(tert-
butoxycarbonyl)-2-(2′-ethoxycarbonyl-3′-hydroxymethylcyclo-
propyl) glycinate ((()-12) were separated by chiral HPLC
using the following analytical method: Chiralpak AD 4.6 ×
250 mm column; eluent, 10% MeOH, 10% IPA in heptane; flow,
1.0 mL/min; UV, 220 nm. Retention time for (-)-12: 5.5 min.
Retention time for (+)-12: 7.0 min. Once both isomers were
separated, they were further purified by silica gel chromatog-
raphy (AcOEt/hexane 1:1).
was purified by column chromatography (AcOEt/hexane 1:5)
to afford (-)-19 (1.03 g, 65% overall yield, 86% conversion, ee
>95%) as a colorless oil. [R]20 ) -24.2° (c 0.50, CHCl3). 1H
D
NMR (300 MHz, CDCl3): 1.77-1.87 (m,1H), 2.27 (dd, 1H, J 1
) 8.8 Hz, J 2 ) 6.0 Hz), 2.38 (dd, 1H, J 1 ) 12.6 Hz, J 2 ) 6.0
Hz), 3.42 (dd, 1H, J 1 ) 10.4 Hz, J 2 ) 8.8 Hz), 3.69 (dd, 1H, J 1
) 10.4 Hz, J 2 ) 6.6 Hz), 4.20 (d, 1H, J ) 9.9 Hz), 4.39 (dd,
1H, J 1 ) 9.9 Hz, J 2 ) 4.9 Hz), 4.49 (d, 1H, J ) 11.5 Hz), 4.56
(d, 1H, J ) 11.5 Hz), 7.33 (s, 5H). 13C NMR (75 MHz, CDCl3):
21.2, 22.2, 22.3, 64.6, 66.3, 73.2, 127.7, 127.8,. 128.4, 137.6,
174.2. Anal. (C13H14O3) C, H.
To a stirred solution of either (-)-12 or (+)-12 (1 equiv) in
CH2Cl2 (2 mL/mmol) at 2 °C was added TFA (10 equiv) over a
few minutes, maintaining the temperature below 5 °C. The
mixture was allowed to warm to room temperature with
stirring for 2.5 h. The mixture was evaporated under reduced
pressure to give a faint yellow oil. The oil was dissolved in
CH2Cl2 (1.2 mL/mmol), and the volatiles were evaporated (3×).
This process was repeated using EtOH (3 × 1.3 mL/mmol) to
afford a faint yellow oil which was dissolved in 3 N NaOH (5
equiv) using a water bath to maintain the temperature slightly
above ambient temperature. The faint yellow homogeneous
mixture was stirred for 1.25 h before the pH was slowly
lowered to 3.5 using concentrated HCl. Once crystallization
initiated, the pH was adjusted to 2.55 over 10 min using
concentrated HCl. The suspension was cooled to 2 °C and
allowed to stir for 2.25 h before the white solid was collected
and washed with cold water (1 × 12 mL, 2 × 5 mL). The
material was dried in vacuo for several hours at 38 °C and for
2.5 days at room temperature, affording (-)-3 from (-)-12 or
Meth yl (1S,2R,3S)-2-ben zyloxym eth yl-3-h yd r oxym eth -
ylcyclop r op a n e Ca r boxyla te ((-)-20). To a solution of
(1R,5S,6R)-6-benzyloxymethyl-3-oxabicyclo[3.1.0]hexan-2-
one ((-)-19) (0.70 g, 3.2 mmol) in anhydrous THF (20 mL) was
added 2.5 N LiOH (51.1 mL, 127.7 mmol). After being stirred
at room temperature for 2 h, the mixture was neutralized with
5% citric acid and extracted with AcOEt. The organic layer
was then dried (MgSO4), filtered, and concentrated in vacuo.
A solution of the residue in Et2O (30 mL) at 0 °C was treated
with a recently prepared CH2N2 solution in Et2O at 0 °C (until
the yellow color is retained). The mixture was stirred for 1 h
and concentrated in vacuo. Purification of the crude residue
by column chromatography (AcOEt/hexane 1:5) afforded (-)-
20 (0.65 g, 81%) as coloroless oil. [R]20 ) -14.3° (c 0.35,
D
CHCl3). 1H NMR (300 MHz, CDCl3): 1.75-1.83 (m, 2H), 1.90-
1.96 (m, 1H), 3.65 (s, 3H), 3.76-3.89 (m, 2H), 3.94-4.05 (m,
2H), 4.53 (s, 2H), 7.33 (s, 5H). 13C NMR (75 MHz, CDCl3): 20.7,
22.6, 25.3, 51.5, 56.9, 64.2, 73.0, 127.6, 127.7, 128.3, 137.5,
171.6. Anal. (C14H18O4) C, H.
(+)-3 from (+)-12 (87% yield). (-)-3: [R]20 -4.1 (c 1.1, 1 N
D
NaOH). (+)-3: [R]20 +3.3 (c 1.1, 1 N NaOH).
D
Meth yl (1R,2R,3S)-2-Ben zyloxym eth yl-3-(ter t-bu tyldim e-
th ylsilyl)oxym eth ylcyclop r op a n e Ca r boxyla te ((-)-21).
To a solution of methyl (1S,2R,3S)-2-benzyloxymethyl-3-hy-
droxymethylcyclopropane carboxylate ((-)-20) (0.65 g, 2.6
mmol) in DMF (20 mL) was added imidazole (0.44 g, 6.5 mmol)
and tert-butyldimethylsilil chloride (1.42 g, 9.0 mmol). The
mixture was stirred at room temperature for 2 h, and a
mixture of ice-water and Et2O (30 mL) was then added. The
organic layer was washed with H2O (3 × 30 mL), dried
(MgSO4), filtered, and concentrated in vacuo. Purification of
the crude residue by column chromatography (AcOEt/hexane
cis-4-Ben zyloxy-2-bu ten -1-yl Acetoa ceta te (17). To a
solution of cis-4-benzyloxy-2-buten-1-ol (16) (5.0 g, 28.1 mmol)
in anhydrous THF (20 mL) was added sodium acetate (0.14 g,
1.7 mmol). The mixture was heated at reflux, and a solution
of freshly distilled diketene (2.4 mL, 31.5 mmol) in anhydrous
THF (10 mL) was added dropwise over 1 h. The reaction
mixture was refluxed for an additional 30 min upon completion
of the addition. The mixture was cooled and Et2O (30 mL) and
saturated aqueous sodium chloride (50 mL) were added. The
organic layer was extracted, dried (MgSO4), filtered, and
concentrated in vacuo. The residue was purified by column of
chromatography (AcOEt/hexane 1:4) to afford product 17 (6.70
g, 91% overall yield) as a colorless oil. 1H NMR (300 MHz,
CDCl3): 2.24 (s, 3H), 3.44 (s, 2H), 4.12 (d, 2H, J ) 5.5 Hz),
4.51 (s, 2H), 4.69 (d, 2H, J ) 6.6 Hz), 5.66-5.74 (m, 1H), 5.80-
5.88 (m, 1H), and 7.33 (s, 5H). 13C NMR (75 MHz, CDCl3):
30.0, 49.7, 60.9, 65.4, 72.3, 125.8, 127.5, 127.6, 128.3, 131.2,
137.8, 166.7, and 200.2. Anal. (C15H18O4) C, H.
1:99) afforded (-)-21 (0.83 g, 88%) as coloroless oil. [R]20
)
D
-7.0° (c 0.28, CHCl3). 1H NMR (300 MHz, CDCl3): 0.20 (s,
3H), 0.21 (s, 3H), 1.04 (s, 9H), 1.85-1.94 (m, 2H), 2.03-2.09
(m, 1H), 3.80 (s,3H), 3.98 (dd, 1H, J 1 ) 10.4 Hz, J 2 ) 7.1 Hz),
4.08 (dd, 2H, J 1 ) 9.3 Hz, J 2 ) 6.0 Hz), 4.18 (dd, 1H, J 1 ) 10.4
Hz, J 2 ) 6.0 Hz), 4.66 (dd, 2H, J 1 ) 15.4 Hz, J 2 ) 11.5 Hz),
7.43-7.50 (m, 5H). 13C NMR (75 MHz, CDCl3): -5.4, 18.1, 19.8,
23.6, 25.7, 26.1, 51.3, 57.1, 64.2, 72.8, 127.4, 127.6, 128.2, 138.3,
171.6.
cis-4-Ben zyloxy-2-bu ten -1-yl d ia zoa ceta te (18). To a
solution of cis-4-benzyloxy-2-buten-1-yl acetoacetate (17) (4.78
g, 18.2 mmol) in anhydrous CH3CN (50 mL) was added Et3N
(3.2 mL, 23.5 mmol). The reaction mixture was treated with a
solution of p-acetamidobezenesulfonyl azide (5.7 g, 23.7 mmol)
in anhydrous CH3CN (50 mL) dropwise over 30 min. After the
mixture was stirred for 2.5 h at room temperature, 3 N LiOH
(19.8 mL, 59.4 mmol) was added and the mixture was stirred
overnight at room temperature. The reaction mixture was
extracted with Et2O/AcOEt 2:1 (2 × 60 mL). The combined
organic layers were washed with a saturated aqueous solution
of NaCl (50 mL), dried (MgSO4), filtered, and concentrated in
vacuo. The residue was purified by column chromatography
(AcOEt/hexane 1:10) to afford product 18 (3.73 g, 83% overall
yield) as a yellow oil. 1H NMR (300 MHz, CDCl3): 4.12 (d, 2H,
J ) 6.0 Hz), 4.51 (s, 2H), 4.71 (d, 2H, J ) 6.6 Hz), 4.74 (s,
1H), 5.66-5.74 (m, 1H), 5.79-5.87 (m, 1H), 7.73 (s, 5H). 13C
NMR (75 MHz, CDCl3): 46.1, 60.5, 65.5, 72.4, 126.5, 127.6,
127.7, 128.3, 130.9, 137.9, 160.5.
Meth yl (1R,2R,3S)-2-Ben zyloxym eth yl-3-h yd r oxym e-
th ylcyclop r op a n e Ca r boxyla te ((-)-22). To a solution of
methyl (1R,2R,3S)-2-benzyloxymethyl-3-(tert-butyldimethyl-
silil)oxymethylcyclopropane carboxylate ((-)-21) (0.45 g, 1.22
mmol) in anhydrous THF (40 mL) at -78 °C under nitrogen
was added a 0.5 M KHMDS solution in toluene (2.8 mL, 1.4
mmol). The mixture was stirred for 2.5 h and then allowed to
react by warming to -10 °C. After 10 min at -10 °C, the
reaction was cooled again to -78 °C and quenched with a
saturated aqueous solution of NH4Cl (25 mL). The aqueous
layer was extracted twice with AcOEt, and the combined
organic layers were dried (MgSO4), filtered, and evaporated
under reduced pressure. The resulting residue was dissolved
in anhydrous THF (25 mL), and tetrabuthylamonium fluoride
(2.5 mL, 1 M) was added at 0 °C. The reaction mixture was
stirred for 2 h at 0 °C. After hexane (10 mL), Et2O (20 mL),
and H2O (50 mL) were added, the organic layer was separated,
dried (MgSO4), filtered, and concentrated in vacuo. The residue
was purified by column chromatography (AcOEt/hexane 1:4)
to afford (-)-22 (0.22 g, 70%) as a colorless oil. [R]20D ) -23.2°
(1R,5S,6R)-6-Ben zyloxym eth yl-3-oxabicyclo[3.1.0]h exan -
2-on e ((-)-19). To a suspension of Rh2(4S-MPPIM)4 (47.8 mg,
0.034 mmol) in anhydrous CH2Cl2 (50 mL) under reflux was
added a solution of cis-4-benzyloxy-2-buten-1-yl diazoacetate
(18) (1.8 g, 7.3 mmol) in anhydrous CH2Cl2 (100 mL) dropwise
overnight. The solvent was removed in vacuo, and the residue
1
(c 0.44, CHCl3). H NMR (300 MHz, CDCl3): 1.51 (t, 1H, J )
4.4 Hz), 1.95-1.98 (m, 2H), 3.24-3.35 (m, 2H), 3.65 (s, 3H),
3.85-3.93 (m, 2H), 4.49 (d, 1H, J ) 11.5 Hz), 4.58 (d, 1H, J )
11.5 Hz), and 7.29-7.35 (m, 5H). 13C NMR (75 MHz, CDCl3):

464 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2
Collado et al.
23.8, 24.4, 27.7, 51.8, 60.6, 67.9, 73.0, 127.8, 127.9, 128.4, 136.9,
172.7. Anal. (C14H18O4) C, H.
E t h yl (2S,1′S,2′R,3′R)-N-(ter t-Bu t oxyca r b on yl)-2-[2′-
et h oxyca r b on yl-3′-h yd r oxym et h ylcyclop r op yl] Glyci-
n a te ((+)-12). To a solution of ethyl (2S,1′S,2′R,3′R)-N-(tert-
butoxycarbonyl)-2-[3′-benzyloxymethyl-2′-(ethoxycarbonyl)-
cyclopropyl] glycinate ((+)-25) (0.030 g, 0.07 mmol) in MeOH
(3 mL) was added Pd (C) 5% (0.006 g, 20 wt %). The mixture
was stirred under hydrogen (balloon) at room temperature for
6 h and filtered through Celite, and the solvent was evaporated
Meth yl (1S,2S,3R)-3-Ben zyloxym eth yl-2-for m ylcyclo-
p r op a n e Ca r boxyla te ((+)-23). To a solution of methyl
(1R,2R,3S)-2-benzyloxymethyl-3-hydroxymethylcyclopro-
pane carboxylate ((-)-22) (0.22 g, 0.86 mmol) in CH2Cl2 (10
mL) at room temperature and under argon was added molec-
ular sieves (4 Å) (0.4 g). After the mixture was stirred for 5
min, NMO (0.15 g, 1.3 mmol) and TPAP (0.006 g, 0.02 mmol)
were added and the mixture stirred overnight at which time
the reaction was filtered through a plug of Celite and the
solvent was removed in vacuo. The residue was purified by
column chromatography (AcOEt/hexane 1:4) to afford (+)-23
in vacuo to afford (+)-12 (0.023 g, 96%) as a colorless oil. [R]20
D
) +32.6° (c 0.46, CHCl3). 1H NMR (300 MHz, CDCl3): 1.25 (t,
3H, J ) 7.1 Hz), 1.32 (t, 3H, J ) 7.1 Hz), 1.45 (s, 9H), 1.70-
1.81 (m, 2H), 1.91-2.11 (m, 1H), 3.17 (dd, 1H, J 1 ) 10.1 Hz,
J 2 ) 3.1 Hz), 3.54-3.67 (m, 1H), 3.95-4.33 (m, 6H), 5.20 (br
d, 1H, J ) 7.3 Hz). 13C NMR (75 MHz, CDCl3): 14.0, 14.1,
22.5, 28.2, 28.9, 29.2, 52.3, 60.8, 61.0, 62.5, 80.4, 155.3, 171.8,
172.4.
(0.19 g, 89%) as coloroless oil. [R]20 ) +58.9° (c 0.83, CHCl3).
D
1H NMR (300 MHz, CDCl3): 2.27-2.36 (m, 1H), 1.51 (t, 1H, J
) 6.0 Hz), 2.56-2.62 (m, 1H), 3.47 (dd, 1H, J 1 ) 10.4 Hz, J 2
)
(2S,1′S,2′R,3′R)-2-(2′-Ca r boxy-3′-h yd r oxym eth ylcyclo-
p r op yl) Glycin e ((+)-3). Isolated as a white solid in 71% yield
7.7 Hz), 3.70 (s, 3H), 3.78 (dd, 1H, J 1 ) 10.4 Hz, J 2 ) 5.5 Hz),
4.45 (t, 2H, J ) 12.6 Hz), 7.26-7.32 (m, 5H), 9,58 (d, 1H, J )
2.2 Hz). 13C NMR (75 MHz, CDCl3): 25.4, 30.0, 34.3, 52.1, 65.4,
72.9, 127.6, 127.7, 128.3, 137.4, 171.0, 196.9.
from (+)-12 according to the same procedure described for
1
preparing (()-3. [R]20 +3.4 (c 1.1, 1 N NaOH). H NMR (200
D
MHz, D2O): 1.77-2.11 (m, 3H), 3.62 (d, J ) 11.0 Hz, 1H), 3.66
(dd, J ) 8.6, 12.5 Hz, 1H), and 3.90 ppm (dd, J ) 6.0, 12.5 Hz,
1H). 13C NMR (50 MHz, D2O): 25.0, 27.7, 29.1, 54.8, 61.0,
173.9, and 177.9 ppm. Mp 155-156 °C. Anal. (C7H11NO5) C,
H, N.
(2S,1′S,2′R,3′R,1′′R)-N-[(2′′-Hyd r oxy-1′′-p h en yl)et h yl]-
2-[3′-b en zyloxym et h yl-2′-(m et h oxyca r b on yl)cyclop r o-
p yl] Glycin on it r ile ((-)-24). To a solution of methyl
(1S,2S,3R)-3-benzyloxymethyl-2-formylcyclopropane carboxy-
late ((+)-23) (0.15 g, 0.6 mmol) in MeOH (5 mL) was added
(R)-R-phenylglycinol (0.08 g, 0.62 mmol). The resulting solution
was stirred at room temperature for 2 h and then cooled to 0
°C. Trimethylsilylcyanide (0.12 g, 1.2 mmol) was added, and
the resulting mixture was stirred at room temperature over-
night. The solvent was removed in vacuo to afford a mixture
of diastereomeric aminonitriles (0.20 g, 91%). The major
diastereoisomer (-)-24 was separated and purified by column
chromatography (AcOEt/hexane 1:2) to give 0.18 g as colorless
Biologica l Assa y. 1. Recep tor F u n ction a l Assa y.13 2.
F ea r P oten tia ted Sta r tle Assa y.13 3. P CP -In d u ced Motor
Activa tion Assa y. Compound (+)-3 was tested against PCP-
induced motor activation (ambulations) in rats. Behavioral
parameters were monitored in transparent, shoebox cages that
measured 45 × 25 × 20 cm, with a 1 cm depth of wood chips
on the cage floor and a metal grill on top of the cage.
Rectangular photocell monitors (Hamilton Kinder, Poway, CA)
with a bank of 12 photocell beams (8 × 4 formation) sur-
rounded each test cage. A lower rack of photocell beams was
positioned 5 cm above the cage floor to enable detection of the
location of the animals body, while an upper bank positioned
10 cm above the first tabulated rearing activity. Ambulations
(locomotor activity) and rearing were recorded by the computer
and stored for each test session. Male Sprague-Dawley rats
were generally food-fasted 12-18 h prior to the experiment.
In some experiments, rats were allowed food and water ad
libitum prior to the experiment. On the test day animals were
placed in the test cage for a 30-min habituation period before
testing to allow for acclimation to the test cage environment.
Following this habituation period, animals were administered
challenges of PCP (5 mg/kg s.c.) or 0.9% NaCl vehicle (1 mL/
kg) and behavioral assessment began immediately following
their administration. Animals were monitored over a 60 min
period in all instances. Compound (+)-3 or vehicle were
administered at various pretreatment times prior to the PCP
challenge.37 Statistical analysis was carried out using the
GraphPad PRISM statistical/graphing package (GraphPad,
San Diego, CA). Data were analyzed using a one-way analysis
of variance (ANOVA) and post-hoc comparisons were per-
formed using Dunnett’s multiple comparisons test. Significance
from PCP control is indicated by an asterisk, *p < 0.05.
oil. [R]20 ) -70.5° (c 1.12, CHCl3). 1H NMR (300 MHz,
D
CDCl3): 1.86 (t, 1H, J ) 4.9 Hz), 1.95-2.00 (m, 2H), 3.45-
3.60 (m, 3H), 3.63-3.69 (m, 4H), 3.69-3.80 (m, 1H), 4.04 (dd,
1H, J 1 ) 8.8 Hz, J 2 ) 3.8 Hz), 4.42 (s, 2H), 7.22-7.54 (m, 10H).
13C NMR (75 MHz, CDCl3): 23.5, 24.9, 27.3, 46.1, 52.0, 62.7,
66.2, 67.0, 72.7, 118.7, 127.4, 127.7, 127.8, 128.1, 128.3, 128.7,
137.2, 137.9, 172.5. Anal. (C23H26 N2O4) C, H, N.
E t h yl (2S,1′S,2′R,3′R)-N-(ter t-Bu t oxyca r b on yl)-2-[3′-
ben zyloxym eth yl-2′-(eth oxyca r bon yl)cyclop r op yl] Gly-
cin a te ((+)-25). Lead tetraacetate (0.18 g, 0.42 mmol) was
added to a solution of the (2S,1′S,2′R,3′R,1′′R)-N-[(2′′-hydroxy-
1′′-phenyl)ethyl]-2-[3′-benzyloxymethyl-2′-(methoxycarbonyl)-
cyclopropyl] glycinonitrile ((-)-24) (0.15 g, 0.39 mmol) in a 1:1
mixture of CH2Cl2-MeOH (10 mL) at 0 °C followed by stirring
for 10 min. The mixture was treated with H2O (10 mL) and
passed through Celite. The filtrate was concentrated in vacuo,
and the residue was dissolved in HCl/EtOH (saturated) (15
mL) at 0 °C followed by treatment with H2O (0.21 mL, 1.17
mmol). After the mixture was stirred at room temperature for
18 h, the solvents were evaporated under reduced pressure
leaving behind a residue that was taken into EtOH. The
solution was neutralized with NaHCO3 (solid) and concetrated
in vacuo to give a residue which was taken into dioxane (15
mL) at room temperature and treated with
a saturated
aqueous solution of NaHCO3 (until pH was adjusted to ∼8). A
solution of di-tert-butyl dicarbonate (0.1 g, 0.47 mmol) in
dioxane (3 mL) was added dropwise, and the mixture was
vigorously stirred at room temperature overnight followed by
dilution with AcOEt and layer separation. The aqueous layer
was extracted with AcOEt (2×), and the combined organic
layers were dried (Na2SO4), filtered, and concentrated to
dryness. The residue was purified by column chromatography
Ack n ow led gm en t. We thank Dr. J ames A. Monn
and Dr. J uan F. Espinosa for their helpful collaboration.
Refer en ces
(1) Osborne, H. B.; Egebjerg, J .; Nielsen, E.; Madsen, U.; Krogs-
gaard-Larsen, P. Ligands for Glutamate Receptors: Design and
Therapeutic Prospects. J . Med. Chem. 2000, 43, 2609-2645.
(2) Cunningham, M. D.; Ferkany, J . W.; Enna, S. J . Excitatory
Amino Acid Receptors: A Gallery Of New Targets For Pharmo-
cological Intervention. Life Sci. 1994, 54, 135-148.
(3) Hollmann, M.; Heinemann, S. Cloned Glutamate Receptors.
Annu. Rev. Neurosci. 1994, 17, 31-108.
(4) Nakanishi, S.; Masu, M. Molecular Diversity And Functions Of
Glutamate Receptors. Annu. Rev. Biophys. Biomol. Struct. 1994,
23, 319-348.
(5) Bockaert, J .; Pin, J . P. Molecular Tinkering of G protein-coupled
Receptors: an Evolutionary Success. EMBO J . 1999, 18, 1723-
1729.
(AcOEt/hexane 1:4) to give 0.11 g (65% overall yield) of product
1
(+)-25 as a yellow oil. [R]20 ) +28.7° (c 0.8, CHCl3). H NMR
D
(300 MHz, CDCl3): 1.21-1.28 (m, 6H), 1.42 (s, 9H), 1.71-1.94
(m, 3H), 3.60 (dd, 1H, J 1 ) 10.4 Hz, J 2 ) 6.6 Hz), 3.80 (dd,
1H, J 1 ) 9.9 Hz, J 2 ) 4.9 Hz), 4.09-4.22 (m, 5H), 4.51-4.55
(m, 2H), 5.31 (d, 1H, J ) 8.2 Hz), 7.29-7.36 (m, 5H). 13C NMR
(75 MHz, CDCl3): 14.0, 14.1, 23.7, 26.3, 28.2, 28.5, 52.2, 60.8,
61.4, 61.6, 72.9, 80.1, 127.7, 127.8, 128.4, 137.8, 155.2, 172.2,
172.7. Anal. (C23H33 NO7) C, H, N.

Metabotropic Glutamate Receptor Agonist
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2 465
(6) For reviews see: (a) Watkins, J . C.; Collingridge, G. L. Phenyl-
glycine derivatives as antagonists of metabotropic glutamate
receptors. Trends Pharmacol. Sci. 1994, 15, 333-342. (b) Pin,
J . P.; Duvoisin, R. The metabotropic glutamate receptors:
structure and functions. Neuropharmacology 1995, 34, 1-26. (c)
Roberts, P. J . Pharmacological tools for the investigation of
metabotropic glutamate receptors (mGluRs): phenylglycine
derivatives and other selective antagonists: un update. Neu-
ropharmacology 1995, 34, 813-819. (d) Conn, P. J .; Pin, P. J .
Pharmacology and functions of metabotropic glutamate recep-
tors. Annu. Rev. Pharmacol. Toxicol. 1997, 37, 205-237. (e) Pin,
J . P.; De Colle, C.; Bessis, A. S.; Acher, F. New perspectives for
the development of selective metabotropic glutamate receptor
ligands. Eur. J . Pharmacol. 1999, 375, 277-294. (f) Schoepp,
D. D.; J ane, D. E.; Monn, J . A. Pharmacological agents acting
at subtypes of metabotropic glutamate receptors. Neurophar-
macology 1999, 38, 1431-1476.
(7) Nakagawa, Y.; Saitoh, K.; Ishihara, T.; Ishida, M.; Shinozaki,
H. (2S,3S,4S)-R-(Carboxycyclopropyl) glycine is a novel agonist
of metabotropic glutamate receptors. Eur. J . Pharmacol. 1990,
184, 205-206.
(8) Hayashi, Y.; Tanabe, Y.; Aramori, I.; Masu, M.; Shimamoto, K.;
Ohfune, Y.; Nakanishi, S. Agonist analysis of 2-(carboxy-
cyclopropyl) glycine isomers for cloned metabotropic glutamate
receptor subtypes expressed in chinese hamster ovary cells. Br.
J . Pharmacol. 1992, 107, 539-543.
(20) Sorensen, U. S.; Bleisch, T. J .; Kingston, A. E.; Wright, R. A.;
J ohnson, B. G.; Schoepp, D. D.; Ornstein, P. L. Synthesis and
Structure-Activity Relationship Studies of Novel 2-Diarylethyl
Substituted (2-Carboxycycloprop-1-yl) Glycines as High-Affinity
Group II Metabotropic Glutamate Receptor Ligands. Bioorg.
Med. Chem. 2003, 11, 197-205.
(21) (a) Doyle, M. P.; Austin, R. E.; Bailey, A. S.; Dwyer, M. P.;
Dyatkin, A. B.; Kalinin, A. V.; Kwan, M. M. Y.; Liras, S.;
Oalmann, C. J .; Pieters, R. J .; Protopova, M. N.; Raab, C. E.;
Roos, G. H. P.; Zhou, Q.-L.; Martin, S. F. Enantioselective
intramolecular cyclopropanations of allylic and homoallylic
diazoacetamides using chiral dirhodium(II) carboxamide cata-
lysts. J . Am. Chem. Soc. 1995, 117, 5763-5775. (b) Doyle, M.
P.; Zhou, Q.-L. Enantioselective catalytic intramolecular cyclo-
propanation of allylic R-diazopropionates optimized with dirhod-
ium(II) tetrakis[methyl 2-oxazolidinone-4(S or R)-carboxylate].
Tetrahedron: Asymmetry 1995, 6, 2157-2160. (c) Doyle, M. P.;
Dyatkin, A. B.; Ruppar, D. A. Enhancement of enantiocontrol/
diastereocontrol in catalytic intramolecular cyclopropanation and
carbon-hydrogen insertion reactions of diazoacetates with Rh2-
(4S-MPPIM)4. Tetrahedron Lett. 1995, 36, 7579-7582. (d)
Martin, S. M.; Oalmann, C. J .; Liras, S. Enantioselective,
rhodium catalyzed intramolecular cyclopropanations of homoal-
lylic diazoacetates. Tetrahedron Lett. 1992, 33, 6727-6730.
(22) Doyle, M. P.; Peterson, C. S.; Zhou, Q.-L.; Nishiyama, H.
Comparative evaluation of enantiocontrol for intramolecular
cyclopropanation of diazoacetates with chiral CuI, RhII and RuII
catalysts. Chem. Commun. 1997, 211-212.
(9) Shibuya, A.; Sato, A.; Taguchi, T. Peparation of difluoro ana-
logues of CCGs and their pharmacological evaluations. Bioorg.
Med. Chem. Lett. 1998, 8, 1979-1984.
(10) Shimamoto, K.; Ohfune, Y. Inversion of cis-substituted R-cyclo-
propyl acyl anion. Stereoselective entry to the synthesis of a
potent metabotropic glutamate agonist, (2S,1′S,2′S)-2-(carboxy-
cyclopropyl) glycine (L-CCG-I), and its 3′-substituted analogues.
SynLett 1993, 919-920.
(23) The absolute configuration of lactone 19 was assigned by analogy
to the one described by Doyle et al. obtained under the same
conditions.20 The enantiomeric excess of the (1R,5S,6R)-cyclo-
propyl lactone 19 was determined to be >95% by integration of
suitable enantiotopic protons in the 1H NMR (500 MHz) spec-
trum ((2%) with the chiral shift reagent Eu(tfc)3 in C6D6 of the
corresponding monoacetate obtained by reaction of 19 with
methyllithium and subsequent acetylation.21a
(11) Brabet, I.; Parmentier, M. L.; De Colle, C.; Bockaert, J .; Acher,
F.; Pin, J . P. Comparative effect of L-CCG-I, DCG-IV and
γ-carboxy-L-glutamate on all cloned metabotropic glutamate
receptor subtypes. Neuropharmacology 1998, 37, 1043-1051.
(12) Mutel, V.; Adam, G.; Chaboz, S.; Kemp, J . A.; Klingelschmidt,
A.; Messer, J .; Wichmann, J .; Woltering, T.; Richards, J . G.
Characterization of (2S,2′R,3′R)-2-(2′,3′-[3H]-Dicarboxycyclopro-
pyl) Glycine Binding in Rat Brain. J . Neurochem. 1998, 71(6),
2558-2564.
(13) Collado, I.; Pedregal, C.; Mazo´n, A.; Espinosa, J . F.; Blanco-
Urgoiti, J .; Schoepp, D.; Wright, R. A.; J ohnson, B.; Kingston,
A. (2S,1′S,2′S,3′R)-2-(2′-Carboxy-3′-methylcyclopropyl) glycine is
a potent and selective Metabotropic Group 2 Receptor Agonists
with Anxiolytic Properties. J . Med. Chem. 2002, 45, 3619-3629.
(14) (a) Pellicciari, R.; Marinozzi, M.; Natalini, B.; Costantino, G.;
Luneia, R.; Giorgi, G.; Moroni, F.; Thomsen, C. Synthesis and
Pharmacological Characterization of All Sixteen Stereoisomers
of2-(2′-Carboxy-3′-phenylcyclopropyl)glycine.Focuson (2S,1′S,2′S,3′R)-
2-(2′-Carboxy-3′-phenylcyclopropyl) glycine, a Novel and Selec-
tive Group II Metabotropic Glutamate Receptors Antagonist. J .
Med. Chem. 1996, 39, 2259-2269. (b) Marinozzi, M.; Natalini,
B.; Constantino, G.; Tijskens, P.; Thomsen, C.; Pellicciari, R.
Asymmetric Synthesis of Enantiomerically Pure (2S,1′S,2′S,3′R)-
Phenylcarboxycyclopropylglycine (PCCG-4): A Potent and Selec-
tive Ligand at Group II Metabotropic Glutamate Receptors.
Bioorg. Med. Chem. Lett. 1996, 6, 2243-2246.
(15) Pellicciari, R.; Costantino, G.; Marinozzi, M.; Macchiarulo, A.;
Amori, L.; Flor, P. J .; Gasparini, F.; Kuhn, R.; Urwyler, S.
Design, Synthesis and Preliminary Evaluation of Novel 3′-
Substituted Carboxycyclopropylglycines as Antagonists at Group
2 Metabotropic Glutamate Receptors. Bioorg. Med. Chem. Lett.
2001, 11, 3179-3182.
(16) Ornstein, P. L.; Bleisch, T. J .; Arnold, M. B.; Wright, R. A.;
J ohnson, B. G.; Schoepp, D. D. 2-Substituted ((1SR,2SR)-2-
Carboxycycloprop-1-yl) glycines as Potent and Selective antago-
nist of group II metabotropic receptors. 1. Effects of alkyl,
arylalkyl, and diarylalkyl substitution. J . Med. Chem. 1998, 41,
346-357.
(24) Chakraborty, T. K.; Azhar Hussain, K.; Venkat Reddy, G.
R-Phenylglycinol as chiral auxiliary in diastereoselective Streck-
er synthesis of R-amino acids. Tetrahedron 1995, 51, 9179.
(25) Schoepp, D. D.; J ohnson, B. G.; Salhoff, C. R.; Valli, M. J .; Desai,
M. A.; Burnett, J . P.; Mayne, N. G.; Monn, J . A. Selective
inhibition of forskolin-stimulated cyclic AMP formation in rat
hippocampus by a novel mGluR agonist, 2R,4R-4-amino-pyrro-
lidine-2,4-dicarboxylate. Neuropharmacology 1995, 34, 843-850.
(26) Schoepp, D. D.; J ohnson, B. G.; Salhoff, C. R.; McDonald, J . W.;
J ohnston, M. V. In vitro and in vivo pharmacology of trans- and
cis-(()-1-amino-1,3-cyclopentanedicarboxylic acid: dissociation
of metabotropic and ionotropic excitatory amino acid receptor
effects. J . Neurochem. 1991, 56, 1789-1796.
(27) (a) Flor, P. J .; Lindauer, K.; Puttner, I.; Ruegg, D.; Lukic, S.;
Kno¨fel, R.; Kuhn, R. Molecular cloning, functional expression
and pharmacological characterization of the human metabotropic
glutamate receptor type 2. Eur. J . Neurosci. 1995, 7, 622-629.
(b) Flor, P. J .; Henrich-Noack, P.; Sabelhaus, C. F.; Prass, K.;
Dirnagl, U.; Gasparini, F.; Sauter, A.; Rudin, M.; Reymann, K.
G. Distinct influence of the group III metabotropic glutamate
receptor agonist (R,S)-4-phosphonophenylglycine on different
forms of neuronal damage. Neuropharmacology 2000, 39, 911-
917. (c) Thomas, N. K.; Wright, R. A.; Howson, P. A.; Kingston,
A. E.; Schoepp, D. D.; J ane, D. E. (S)-3,4-DCPG, a potent and
selective mGlu8a receptor agonist, activates metabotropic
glutamate receptors on primary afferent terminals in the
neonatal rat spinal cord. Neuropharmacology 2001, 40, 311-
318.
(28) (a) Moghaddam, B.; Adams, B. W. Reversal of Phencyclidine
Effects by a Group II Metabotropic Glutamate Receptor Agonist
in Rats. Science 1998, 281, 1349-1352. (b) Aghajanian, G. K.;
Marek, G. J . Serotonin-Glutamate Interactions: A New Target
for Antipsychotic Drugs. Neuropsychopharmacology 1999, 21
(S6), S122-S133. (c) Cartmell, J .; Monn, J . A.; Darryle, D. D.
The Metabotropic Glutamate 2/3 Receptor Agonists LY354740
and LY379268 Selectively Attenuate Phencyclidine versus d-
Amphetamine Motor Behavours in Rats. J . Pharmacol. Exp.
Ther. 1999, 291, 161-170. (d) Cartmell, J .; Monn, J . A.; Darryle,
D. D. Attenuation of specific PCP-evoked behaviors by the potent
mGlu2/3 receptor agonist, LY379268 and comparison with the
atypical antipsychotic, clozapine. Psychopharmacology 2000,
148, 423-439. (e) Schreiber, R.; Lowe, D.; Voerste, A.; De Vry,
J . LY354740 Affects Startle Responding but not Sensorimotor
Gating or Discriminative Effects of Phencyclidine. Eur. J .
Pharmacol. 2000, 388, R3-R4. (f) Cartmell, J .; Monn, J . A.;
Schoepp, D. D. The mGlu2/3 receptor agonist LY379268 selec-
tively blocks amphetamine ambulations and rearing. Eur. J .
Pharmacol. 2000, 400, 221-224. (g) Cartmell, J .; Kenneth, W.
P.; Salhoff, R. C.; Monn, J . A.; Schoepp, D. D. The Potent,
Selective mGlu2/3 Receptor Agonist LY379268 Increases Extra-
cellular Levels of Dopamine, 3,4-Dihydroxyphenylacetic Acid,
Homovanillic Acid and 5-Hydroxyindole-3-Acetic Acid in the
(17) Pedregal, C.; Mazo´n, A.; Collado, I.; Yruretagoyena, B.; Ezquerra,
J .; Wright, R. A.; J ohnson, B. G.; Schoepp, D. D.; Kingston, A.;
Tomlinson, R. 2,3′-Disubstituted 2-(2′-Carboxycyclopropyl) Gly-
cine as Potent and Selective Antagonists of Metabotropic
Glutamate Receptors. Bioorg. Med. Chem. Lett. 1998, 8, 2849-
2854.
(18) Pretsch, E.; Buhlmann, P.; Affolter, C. Tables of spectral data
for structure determination, 3rd ed.; Verlag: Berlin, Heidelberg,
New York, 2000.
(19) Edward, J . T.; J itrangsri, C. Stereochemistry of the Bucherer-
Bergs and Strecker Reactions of 4-tert-Butylcyclohexanone. Can.
J . Chem. 1975, 53, 3339-3350.

466 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 2
Collado et al.
Medial Prefrontal Cortex of the Freely Moving Rat. J . Neuro-
chem. 2000, 75, 1147-1154. (h) Schoepp, D. D.; Maker, G. J .
Preclinical Pharmacology of mGlu2/3 Receptor Agonists: Novel
Agents for Schizophrenia? Curr. Drug Targets 2002, 1, 215-
225. (i) Lahti, A. C.; Weiler, M. A.; Michaelidis, T.; Parwani, A.;
Tamminga, C. A. Effects of Ketamine in Normal and Schizo-
phrenic Volunteers. Neuropsychopharmacology 2001, 25, 455-
466.
Fratkin, J . D.; Rhodes, P. G. Protection of Neonatal Rat Brain
from Hypoxic-ischemic Injury by LY379268, a Group II Metabo-
tropic Glutamate Receptor Agonist. Neurochem. Int. 1999, 10,
3927-3931. (f) Kingston, A. E.; O′Neill, Lam, A.; Bales, K. R.;
Monn, J . A.; Schoepp, D. D. Neuroprotection by Metabotropic
Glutamate Receptor Agonists: LY354740, LY379268 and
LY389795. Eur. J . Pharmacol. 1999, 377, 155-165. (g) Pizzi,
M.; Benarese, M.; Boroni, F.; Goffi, F.; Valerio, A.; Spano, P. F.
Neuroprotection by Metabotropic Glutamate Receptor Agonists
on Kainate-Induced Degeneration of Motor Neuron in Spinal
Cord Slices from Adult Rat. Neuropharmacology 2000, 39, 903-
910. (h) Bond, A.; J ones, N. M.; Hicks, C. A.; Whiffin, G. M.;
Ward, M. A.; O′Neill, M. F.; Kingston, A. E.; Monn, J . A.;
Ornstein, P. L.; Schoepp, D. D.; Logde, D.; O’Neill, M. J .
(29) (a) Helton, D. R.; Tizzano, J . P.; Monn, J . A.; Schoepp, D. D.;
Kallman, M. J . Anxiolytic and side-effects profile of LY354740:
A potent, highly selective, orrally active agonist for group II
metabotropic glutamate receptors. J . Pharmacol. Exp. Ther.
1998, 284, 651-660. (b) Klodzinska, A.; Chojnacka-Wojcik, E.;
Palucha, A.; Branski, P.; Popik, P.; Pilc, A. Potential anti-
anxiety, anti-additive effects of LY354740, a selective group 2
glutamate metabotropic receptors agonist in animal models.
Neuropharmacology 1999, 38, 1831-1839. (c) Benvenga, M. J .;
Overshiner, C. D.; Monn, J . A.; Leander, J . D. Disinhibitory
Effects of LY354740, a New mGluR2 Agonist, on Behaviors
Suppressed by Electric Shock in Rats and Pigeons. Drug Dev.
Res. 1999, 47, 37-44. (d) Shekhar, A.; Keim, S. R. LY354740, a
potent group II metabotropic glutamate receptor agonist pre-
vents lactate-induced panic-like response in panic-prone rats.
Neuropharmacology 2000, 39, 1139-1146. (e) Pilc, A.; Chojnacka-
Wo´jcik, E.; Tatarczynska, E.; Borycz, J .; Kroczka, B. Stimulation
of group II metabotropic glutamate receptor or inhibition of
group I ones exerts anxiolytic-like effects in rats. Amino Acids
2000, 19, 81-86. (f) Tizzano, P. J .; Griffey, K. I.; Schoepp, D. D.
The anxiolytic action of mGlu2/3 receptor agonist, LY354740,
in the fear-potentiated startle in rats is mechanistically distinct
from diazepam. Pharmacol., Biochem. Behav. 2002, 73, 367-
374.
Neuroprotective Effects of LY379268,
a Selective mGlu2/3
Receptor Agonist: Investigations into Possible mechanism of
Action In Vivo. J . Pharm. Exp. Ther. 2000, 294, 800-809. (i)
Mills, C. D.; Xu, G. Y.; McAdoo, D. J .; Hulsebosch, C. E.
involvement of metabotropic glutamate receptors in excitatory
amino acid and GABA release following spinal cord injury in
rat. J . Neurochem. 2001, 79, 835-848.
(33) (a) Dolan, S.; Nolan, A. M. Behavioural evidence supporting a
differential role for group I and II metabotropic glutamate
receptors in spinal nociceptive transmission. Neuropharmacology
2000, 39, 1132-1138. (b) Maione, S.; Oliva, P.; Marabese, I.;
Palazzo, E.; Rossi, F.; Berrino, L.; Rossi, F.; Filippelli, A.
Periaqueductal gray matter metabotropic glutamate receptors
modulate formalin-induced nociception. Pain 2000, 85, 183-189.
(c) Popik, P.; Kozela, E.; Pilc, A. Selective agonist of group II
glutamate metabotropic receptors, LY354740, inhibits tolerance
to analgesic effects of morphine in mice. Br. J . Pharmacol. 2000,
130, 1425-1431. (d) Simmons, R. M. A.; Webster, A. A.; Balra,
A. B.; Iyengar, S. Pharmacol., Biochem. Behav. 2002, 73, 419-
427.
(30) Vardergriff, J .; Rasmussen, K. The selective mGlR2/3 receptor
agonist LY354740 attenuates morphine-withdrawal-induced
activation of locus coeruleus neurons and behavioral signs of
morphine withdrawal. Neuropharmacology 1999, 38, 217-222.
(31) (a) Marek, G. J .; Wright, R. A.; Schoepp, D. D.; Monn, J . A.;
Aghajanian, G. K. Physiological Antagonism between 5-Hydroxy-
tryptamine 2A and Group II Metabotropic Glutamate Receptors
in Prefrontal Cortex. J . Pharmacol. Exp. Ther. 2000, 292 (1),
76-87. (b) Gewirtz, J . C.; Marek, G. J . Behavioral Evidence for
(34) Abe, K.; Saito, H. L-Glutamate Suppresses Amyloid â-Protein-
Induced Stellation of Cultured Rat Cortical Astrocytes. J .
Neurochem. 2000, 74 (1), 280-286.
(35) (a) Attwell, P. J . E.; Kaura, S.; Sigala, G.; Bradford, H. F.;
Croucher, M. J .; J ane, D. E.; Watkins, J . C. Blockade of both
epileptogenesis and glutamate release by (1S, 3S)-ACPD, a
presynaptic glutamate receptor agonist. Brain Res. 1995, 698,
155-162. (b) Abdul-Ghani, A. S.; Attwell, P. J . E.; Kent, N. S.;
Bradford, H. F.; Croucher, M. J .; J ane, D. E. Anti-epileptogenic
and anticonvulsant activity of L-2-amino-4-phosphonobutyrate,
a presynaptic glutamate receptor agonist. Brain Res. 1997, 755,
202-212. (c) Klodzinska, A.; Chojnacka-Wojcik, E.; Pilc, A.
Selective group II glutamate metabotropic receptor agonist
LY354740 attenuates pentetrazole- and picrotoxin-induced sei-
zures. Pol. J . Pharmacol. 1999, 51, 543-545. (d) Moldrich, R.
X.; J effrey, M.; Talebi, A.; Beart, P. M.; Chapman, A. G.;
Meldrum, B. S. Anti-epileptic activity of group II metabotropic
glutamate receptor agonists (-)-2-oxa-4-aminobicyclo[3.1.0.]-
hexane-4,6-dicarboxylate (LY389795). Neuropharmacology 2001,
41, 8-18.
Interactions between
a Hallucinogenic Drug and Group II
Metabotropic Glutamate Receptors. Neuropsychopharmacology
2000, 23 (5), 569-576. (c) Gewirtz, J . C.; Chen, A. C.; Terwilliger,
R.; Duman, R. C.; Marek, G. J . Modulation of DOI-induced
increases in cortical BDNF expression by group II mGlu recep-
tors. Pharmacol., Biochem. Behav. 2002, 73, 317-326. (d)
Klodzinska, A.; Bijak, M.; Tokarski, K. Pilc, A. Group II mGlu
receptor agonists inhibit behavioural and electrophysiological
effects of DOI in mice. Pharmacol., Biochem. Behav. 2002, 73,
327-332. (e) Krystal, J . H.; Sanacora, G.; Blumberg, H.; Anand,
A.; Charney, D. S.; Marek, G.; Epperson, C. N.; Goddard, A.;
Mason, G. F. Glutamate and GABA systems as targets for novel
antidepressant and mood-stabilizing treatments. Mol. Psychiatry
2002, 7, S71-S80.
(36) (a) Konieczny, J .; Ossowska, K.; Wolfarth, S.; Pilc, A. LY354740,
a group 2 metabotropic glutamate receptor agonist with potential
antiparkinsonian properties in rats. Naunyn-Schmiedeberg’s
Arch. Pharmacol. 1998, 358, 500-502. (b) Wolfarth, S.; Koniecz-
ny, J .; Lorenc-Koci, E.; Ossowska, K.; Pilc, A. The role of
metabotropic glutamate receptor (mGluR) ligands in parkinso-
nian muscle rigidity. Amino Acids 2000, 19, 95-101. (c)
Greenamyre, J . P. Glutamatergic Influences on the Basal
Ganglia. Clin. Neuropharmacol. 2001, 24 (2), 65-70. (d) Murray,
T. K.; Messenger, M. J .; Ward, M. A.; Woodhouse, S.; Osborne,
D. J .; Duty, S.; O′Neill, M. J . Evaluation of the mGluR2/3 agonist
LY379268 in rodent models of Parkinson’s disease. Pharmacol.,
Biochem. Behav. 2002, 73, 455-466.
(32) (a) Kingston, A. E.; O’Neill, M. J .; Bond, A.; Bruno, V.; Battaglia,
G.; Nicoletti, F.; Harris, J . R.; Clark, B. P.; Monn, J . A.; Lodge,
D.; Schoepp, D. D. Neuroprotective Actions of Novel and Potent
Ligands of Group
I and Group II Metabotropic Glutamate
Receptors. Ann. New York Acad. Sci. 1999, 438-449. (b) Bat-
agglia, G.; Bruno, V.; Ngomba, R. T.; Di Grezia, R.; Copani, A.;
Nicoletti, F. Selective Activation of Group II Metabotropic
Glutamate Receptors is Protective Against Excitotoxic Neuronal
Death. Eur. J . Pharmacol. 1998, 356, 271-274. (c) Lam, A. G.
M.; Soriano, M. A.; Monn, J . A.; Schoepp, D. D.; Lodge, D.;
McCulloch, J . Effects of the Selective Metabotropic Glutamate
Agonist LY354740 in a Rat Model of Permanent Ischaemia.
Neurosci. Lett. 1998, 254, 121-123. (d) Behrens, M. M.; Strasser,
U.; Heidingen, V.; Lobner, D.; Yu, S. P.; McDonald, J . W.; Won,
M.; Choi, D. W. Selective Activation of Group II mGlu receptors
with LY354740 does not Prevent Neuronal Excitotoxicity. Neu-
ropharmacology 1999, 38, 1621-1630. (e) Cai, Z.; Xiao, F.;
(37) (a) Cartmell, J . J . Pharmacol. Exp. Ther. 1999, 291, 161-170.
(b) Cartmell, J . Naunyn-Schmiedeberg’s Archives Pharmacology
2000, 361, 39-46.
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