(2R,1'S,2'R,3'S)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine (PCCG-13), the first potent and selective competitive antagonist of phospholipase D- coupled metabotropic glutamate receptors: Asymmetric synthesis and preliminary biological properties

Article abstract of DOI:10.1021/jm990128v

The asymmetric synthesis of(2R,1'S,2'R,3'S)-2-(2'-carboxy-3'- phenylcyclopropyl)glycine (PCCG-13), a trisubstituted carboxycyclopropylglycine endowed with unusual stereochemical features, is described. Preliminary biological evaluation demonstrates PCCG-1

Full text of DOI:10.1021/jm990128v

2716
J . Med. Chem. 1999, 42, 2716-2720
(2R,1′S,2′R,3′S)-2-(2′-Ca r boxy-3′-p h en ylcyclop r op yl)glycin e (P CCG-13), th e F ir st
P oten t a n d Selective Com p etitive An ta gon ist of P h osp h olip a se D-Cou p led
Meta botr op ic Glu ta m a te Recep tor s: Asym m etr ic Syn th esis a n d P r elim in a r y
Biologica l P r op er ties
Roberto Pellicciari,*,† Maura Marinozzi,† Gabriele Costantino,† Benedetto Natalini,† Flavio Moroni,‡ and
Domenico Pellegrini-Giampietro‡
Istituto di Chimica e Tecnologia del Farmaco, Universita` di Perugia, Via del Liceo, 1-06123 Perugia, Italy, and Dipartimento
di Farmacologia Preclinica e Clinica, Universita` di Firenze, Viale G. Pieraccini, 6-50139 Firenze, Italy
Received March 18, 1999
The asymmetric synthesis of (2R,1′S,2′R,3′S)-2-(2′-carboxy-3′-phenylcyclopropyl)glycine (PCCG-
13), a trisubstituted carboxycyclopropylglycine endowed with unusual stereochemical features,
is described. Preliminary biological evaluation demonstrates PCCG-13 as a very potent and
selective competitive antagonist for the novel class of metabotropic glutamate (mGlu) receptors
coupled to the activity of phospholipase D (PLD). PCCG-13 is therefore a useful tool for the
exploration of the physiopathological role of this novel class of receptors.
Ch a r t 1
In tr od u ction
A variety of physiological functions of glutamate, the
major excitatory neurotransmitter in the mammalian
central nervous system (CNS), are mediated by two
families of receptors: namely, ionotropic glutamate
receptors (iGlu), which contain integral cation-specific
ion channels and are divided into NMDA, AMPA, and
KA receptors, and metabotropic glutamate receptors
(mGlu), which are coupled, through G-proteins, to a
number of effector systems. On the basis of sequence
homology, agonist pharmacology, and signal transduc-
tion mechanisms, the eight cloned mGlu receptors are
classified into three groups: group I (mGlu1 and
mGlu5), group II (mGlu2 and mGlu3), and group III
(mGlu4, mGlu6, mGlu7, and mGlu8).1 When expressed
in heterologous systems, cloned mGlu receptors couple
to two main signal transduction pathways, namely, to
the activation of phospholipase C (PLC) (group I mGlu
receptors) which hydrolyzes phosphatidylinositols to
inositol triphosphate and diacylglycerol, and to the
inhibition of the activity of adenylyl cyclase (groups II
and III mGlu receptors) thus decreasing the intracel-
lular concentration of cAMP. Recent reports have dem-
onstrated that other signal transduction mechanisms
may be operative upon stimulation of mGlu receptors.
Indeed, it has recently been shown that the nonselective
mGlu receptor agonist (1S,3R)-ACPD (1; Chart 1)
stimulates in neonate and adult hippocampal slices the
activity of phospholipase D (PLD).2,3 This novel trans-
duction mechanism (Scheme 1) involves the hydrolysis
of membrane phosphatidylcholine (PC) leading to the
formation of choline and phosphatidic acid (PA). PA,
itself a potential second messenger, can be converted
by a phosphohydrolase to a diacylglycerol (DG) struc-
turally different from that produced by PLC-activated
metabolism of phosphoinositides. These distinct DG
structural species may activate different phosphokinase
C (PKC) isoforms, among the variety that is known to
exist in the brain.4 Interestingly, in the presence of
primary alcohols, such as ethanol, PLD activates a
transphosphatidyl reaction leading to the formation of
the corresponding phosphatidyl alcohols (Scheme 1,
pathway b).
In neonate tissue, the glutamatergic activation of PLD
appears to be indirectly mediated by group I mGlu
receptors via activation of PKC,5,6 whereas in adult
hippocampus the pharmacology of PLD-coupled mGlu
receptors does not correspond to that of any of the
known subtypes coupled to PLD or AC,7,8 thus pointing
out the possibility of the existence of a new, not yet
molecularly characterized, receptor subtype. PLD-
coupled mGlu receptors share pharmacological charac-
teristics with group I mGlu receptors (i.e., quisqualate
is the most potent agonist) but also bear a number of
unique features, such as the selective activation of
L-cysteinesulfinic acid7 and the nonselective and non-
competitive antagonism by 3,5-DHPG (2),8,9 which is
also known to be a selective agonist of group I mGlu
* To whom correspondence should be addressed: Roberto Pellicciari,
Universita` di Perugia. Tel: ++39-075-46640. Fax: ++39-075-5855124.
E-mail: rp@unipg.it.
† Universita` di Perugia.
‡ Universita` di Firenze.
10.1021/jm990128v CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/18/1999

Synthesis and Biological Properties of PCCG-13
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 14 2717
block easily obtained in four steps from (S)-serine,17 was
submitted to Wittig reaction with benzyltriphenylphos-
phonium bromide to give a 2.3:1 mixture of (E)-olefin 7
and (Z)-olefin 8, respectively, which were separated by
medium-pressure chromatography. Dirhodium(II) tet-
raacetate-catalyzed addition18 of ethyl diazoacetate to
(E)-olefin 7, followed by flash chromatography of the
reaction mixture, afforded, as the only product, tert-
butyl 4(R)-[(1′S,2′R,3′S)-2′-(ethoxycarbonyl)-3′-phenyl-
cyclopropyl]-2,2-dimethyl-1,3-oxazolidine-3-carboxy-
late (9) as the only cyclopropane derivative (GC-MS)
in 26% isolated yield. 9 was then submitted to acidic
hydrolysis (p-TSA, MeOH, room temperature) and the
alcohol 10 thus obtained was oxidized with 8 N J ones
reagent (acetone, room temperature) followed by acidic
treatment (6 N HCl, 80 °C). Ion-exchange chromatog-
raphy (Dowex 8×2-200, 1 N AcOH) afforded in 78%
yield (2R,1′S,2′S,3′R)-PCCG-13 (5), with analytical data
(1H NMR, 13C NMR, mp, and [R]D20) identical with that
of an authentic sample.12 NMR spectra (Bruker DRX400)
of a Mosher amide derived from (R)-(+)-R-methoxy-
(trifluoromethyl)phenylacetyl cloride (R-(+)-MPTA) re-
vealed an enantiomeric enrichment of >95%.19
Sch em e 1
The remarkably high selectivity of the key rhodium-
(II)-catalyzed cyclopropanation of olefin 7 leading to
intermediate 9, in which three new chiral centers are
generated in a single step, was a most gratifying,
unpredicted result that can be rationalized according
to the following considerations (Figure 1). In our case,
the stereochemical outcome is consistent with a dias-
tereofacial attack of the rhodium(II) carbethoxy car-
benoid on the more vulnerable (1si-2si)-face of conformer
a , the (E)-7 conformer shown to be the most stable
according to molecular mechanics calculations (see
Figure 1). In this case, the (1re-2re)-face of the double
bond is faced toward and hindered by the bulky N-Boc
moiety, and the cyclopropane with (1′S,2′S)-configura-
tion is the only product. It is worth to note, however,
that the energy difference between conformer a and
conformer b is very low and the highly selective stere-
ochemical outcome could not be predicted solely on these
bases.
The exclusive formation of the exo-isomer b over the
endo-a ((R)-configuration at C′3, see Figure 1), on the
other hand, can be rationalized with the steric effect
exerted by the phenyl ring. It is known that less
encumbered cyclopropanes are highly favored products
of rhodium(II)-catalyzed cyclopropanations. In our case,
the resulting cyclopropane is substituted by two groups,
the phenyl ring and the oxazolidine moiety, both of them
exerting a strong steric effect. The exclusive formation
of isomer 9-a (exo-isomer), where the phenyl ring is
trans to the carbethoxy moiety, infers that is the
aromatic portion to play a more demanding steric role.
receptors coupled to PLC activation.10,11 The widely used
group I/group II mGlu receptor antagonist (+)-MCPG
(3) also displays peculiar features, in that it is a mixed
agonist/antagonist on PLD-coupled mGlu receptors in
adult hippocampal slices.8
The clarification of the physiological role and the
possible involvement in pathological conditions of this
novel class of PLD-coupled receptors requires new
ligands, much more potent and selective than those
currently available. We have previously reported the
synthesis and activity on a variety of mGlu receptor
subtypes of 16 diastereoisomeric 2-(2′-carboxy-3′-phe-
nylcyclopropyl)glycines (PCCG-1-PCCG-16), among
which (2S,1′S,2′S,3′R)-PCCG-4 (4) was identified as a
potent and selective antagonist of mGlu2 receptors.12,13
With the aim to find new tools for the characterization
of the intriguing PLD-coupled class of mGlu receptors,
this stereolibrary of constrained L-glutamate analogues
was tested on the PLD-specific transphosphatidylation
reaction (see pathway b, Scheme 1) that is stimulated
by (1S,3R)-ACPD (1) and results in the formation of [3H]-
phosphatidylethanol ([3H]PEt), a commonly employed
assay for detecting PLD activity in intact cells.14,15 It
was discovered, as a result, that the (2R,1′S,2′R,3′S)-
2-(2′-carboxy-3′-phenylcyclopropyl)glycine (PCCG-13, 5)
antagonizes the formation of [3H]PEt induced by 100
µM (1S,3R)-ACPD (1) in adult rat hippocampal slices
in a dose-dependent manner and with a much lower IC50
(25 nM) when compared to 3,5-DHPG (2), thus revealing
compound 5 to be the first potent, selective, and
competitive antagonist of PLD-coupled mGlu receptors.9
Because of its relevance as a new tool for the charac-
terization of PLD-coupled mGlu receptors, it became of
interest to devise a practical, enantioselective synthesis
of PCCG-13 (5). The results are herein described.
P h a r m a cology
Deter m in a tion of P LC a n d P LD Activity. PLC
and PLD activities were determined in adult rat hip-
pocampal slices (350 µm thick) as previously described.8
Briefly, phosphoinositide hydrolysis was monitored by
measuring the agonist-induced formation of [3H]inositol
phosphates (IP1, IP2, and IP3) from slices preincubated
with [3H]inositol. Following 10-min stimulation, water-
soluble [3H]IPs were transferred to Dowex AG 1×8
Ch em istr y
Garner’s aldehyde (6; Scheme 2),16 a chiral building

2718 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 14
Pellicciari et al.
Sch em e 2a
a
(a) i. Ph(CH2)PPh3Br, n-BuLi, hexane, rt, ii. mpc; (b) EDA, Rh2(OAc)4, CH2Cl2, rt; (c) p-TSA, MeOH, rt; (d) i. 8 N J ones reagent,
acetone, rt, ii. 6 N HCl, 80 °C, iii. Dowex 1X8-200, 1 N AcOH.
Ta ble 1. Summary of EC50 and IC50 Values of the Agonist and
Antagonist Activities of (1S,3R)-ACPD (1), 3,5-DHPG (2),
(+)-MCPG (3), and PCCG-13 (5) on PLC and PLD Activity in
Adult Rat Hippocampal Slices
PLC activity
PLD activity
EC50 (µM) IC50 (µM) EC50 (µM)
IC50 (µM)
antagonist
compd
agonist
antagonist
agonist
(1S,3R)-ACPD (1)
(+)-MCPG (3)
3,5-DHPG (2)
PCCG-13 (5)
50 ( 2
30 ( 2
110 ( 10
150 ( 10
>300
530 ( 60
70 ( 3
0.025 ( 0.002
65 ( 2
>300
than water to the phosphatidyl moiety of phosphatidyl-
choline, producing PEt in place of PA. Slices were
incubated with [3H]glycerol for 2 h and then stimulated
with agonists [(1S,3R)-ACPD (1) or 3,5-DHPG (2)] for
1 h in the presence of 170 mM ethanol. The lipid phase
was extracted and spotted on silica gel plates. [3H]PEt
was separated from major phospholipids by thin-layer
chromatography using the upper phase of the solvent
system ethyl acetate/2,2,4-trimethylpentane/acetic acid/
water (12:5:1:10). Spots were visualized with iodine
vapor, and [3H]PEt was identified by comparison with
the PEt standard. The region corresponding to [3H]PEt
was scraped off, and radioactivity was counted by liquid
scintillation spectrometry. The formation of [3H]PEt was
expressed as the percentage of radioactivity incorpo-
rated into the total lipids present in the organic phase.
Agonist dose-response and antagonist inhibition curves
were analyzed by nonlinear regression, and EC50 and
IC50 values were calculated with the PRISM software
package (GraphPad Software, San Diego, CA).
F igu r e 1. Olefin 7 can exist in two main conformations.
Conformer a is predicted by molecular mechanics calculation
(Tripos force field) to be more stable by about 1 kcal/mol. In
conformer a the (1si,2si)-side of the double bond is less
hindered by the bulky N-Boc group (top). Attack of the ethyl
diazoacetate-dirhodium(II) tetraacetate complex leads pref-
erentially to the exo isomer b, endowed with a less encumbered
cyclopropane ring (bottom).
anion-exchange resin columns and eluted with 1 M
ammonium formate, 0.1 M formic acid. The dpm was
determined by liquid scintillation spectrometry, and
data are expressed as percentage of incorporation of
label into [3H]IPs occurring under agonist-free condi-
tions. PLD activity was determined by making use of
the transphosphatidylation reaction between phosphati-
dylcholine and primary alcohols specifically catalyzed
by PLD. Thus, in the presence of exogenously added
ethanol, PLD preferentially transfers the alcohol rather
Resu lts a n d Discu ssion
Table 1 shows that (1S,3R)-ACPD (1) is an agonist
on mGlu receptors coupled to both PLC and PLD,
whereas (+)-MCPG (3) is an antagonist on receptors
coupled to phosphoinositide hydrolysis but a mixed
agonist/antagonist on PLD-coupled mGlu receptors.8
Consistent with previous findings,11 the group I mGlu

Synthesis and Biological Properties of PCCG-13
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 14 2719
tagonists prevents us from defining a clear structure-
activity relationship for PLD-coupled mGlu receptor
antagonism. The unusual structural features and the
high potency of PCCG-13 (5), however, permit to an-
ticipate that the recognition site of PLD-coupled mGlu
receptors is endowed with a peculiar environment
among mGlu receptors that can be instrumental in the
design of structurally novel ligands. In particular, it can
be speculated that the (R)-configuration at the amino
acidic center projects the distal carboxylate groups
toward an accessory site inaccessible to quisqualate or
(1S,3R)-ACPD (1) and characterized by a hydrophobic
pocket able to accommodate the phenyl ring. Whether
the presence of the phenyl ring is necessary for antago-
nism (in analogy with group II mGlu antagonists) or
the (R)-configuration is sufficient to this aim is not
predictable at the moment and will be the object of
further studies. In conclusion, mGlu receptors coupled
to PLD are likely to play an important role in the CNS.
Developmental plasticity, synaptogenesis, long-lasting
production of diacylglycerol, and activation of PKC are
among the events that could be promoted by glutamater-
gic activation of these receptors. The potent, selective,
and competitive antagonist PCCG-13 (5) should provide
an excellent tool to explore their function in future
studies.
F igu r e 2. Schild plot of PCCG-13’s competitive antagonism
upon mGlu receptors coupled to PLD in adult rat hippocampus.
Slices were labeled with [3H]glycerol, washed, and incubated
for 1 h at 37 °C in buffer with 170 mM ethanol in the presence
of increasing concentrations of quisqualate. Quisqualate dose-
response curves for [3H]PEt formation were performed in the
absence and presence of PCCG-13 (0.1, 0.3, and 1 µM), which
was added 10 min before the agonist. EC50 values calculated
from these curves were used to construct the Schild plot, where
DR ) (EC50 for quisqualate in the presence of PCCG-13)/(EC50
for quisqualate alone). The pA2, r, and slope values were
calculated by linear regression analysis.
receptor antagonist 3,5-DHPG (2) induced a dose-
dependent accumulation of [3H]IPs in adult rat hippoc-
ampal slices, with an EC50 of 65 ( 2 µM (Table 1). On
the contrary, PCCG-13 (5) was unable to elicit a PLC
response up to a concentration of 300 µM (see also ref
13). When tested on the formation of [3H]PEt, neither
3,5-DHPG (2) nor PCCG-13 (5) stimulated the formation
of [3H]PEt up to 300 µM, but both inhibited the
activation of PLD induced by the broad-spectrum mGlu
receptor agonist (1S,3R)-ACPD (1) (100 µM). PCCG-13
(5) not only displayed pure antagonist activity but was
also much more potent than 3,5-DHPG (2): their IC50’s
were 0.025 ( 0.002 and 70 ( 3 µM, respectively (Table
1).
Moreover, PCCG-13 (5) clearly produced a parallel
rightward shift in the dose-response curve obtained by
stimulating the formation of [3H]PEt with quisqualate.9
The inhibition of quisqualate-induced PLD activation
was surmounted by increasing the concentration of the
agonist. The Schild plot analysis of PCCG-13 (5) re-
vealed a pA2 value of 7.05 (r ) 0.991) with a slope of
0.89 ( 0.12, suggesting a competitive antagonism for
this compound (Figure 2).
These results indicate that PCCG-13 (5) is the first
competitive antagonist of PLD-coupled mGlu receptors,
endowed with a remarkably high potency and selectiv-
ity. Despite the presence of the pharmacophoric ele-
ments usually required for the interaction with glutamate
receptors, PCCG-13 (5) bears some structural features
that make it unique among the so far described mGlu
receptor ligands. First of all, PCCG-13 (5) is endowed
with an unnatural (R)-configuration at the amino acidic
center. While the (R)-configuration at the amino acidic
center is a common motif of competitive NMDA antago-
nists, it appears as absolutely unusual for metabotropic
glutamate receptor. The other point of interest is the
presence of a cis disposition of the amino acidic moiety
and the distal carboxylate group. Again, while this
topological arrangement is required for interaction with
the NMDA receptor site, no other significant examples
are found among mGlu receptor ligands. The absence
of other competitive PLD-coupled mGlu receptor an-
Exp er im en ta l Section
Gen er a l Meth od s. Melting points were determined by the
capillary method on a Bu¨chi 535 electrothermal apparatus.
1H and 13C NMR spectra were taken on a Brucker AC 200
spectrometer unless otherwise stated. The abbreviations used
are as follows: s, singlet; d, doublet; t, triplet; q, quartet; m,
multiplet; dd, double doublet; br s, broad signal. Mass spectra
were recorded on a Hewlett-Packard 6890/5973 MSD instru-
ment equipped with a GC-mass coupling (30-m × 0.25-mm,
0.25-µm capillary HP-1 column): injection temperature, 250
°C; detection temperature, 230 °C; column temperature, 70 °C
(1 min), 70-150 °C (7 °C/min), 150-300 °C (5 °C/min), 300 °C
(10 min). Specific rotations were recorded on a J asco Dip-360
digital polarimeter.
ter t-Bu tyl (E)- a n d (Z)-2,2-Dim eth yl-4-(2′-p h en ylvin yl)-
3-oxa zolid in eca r boxyla tes (7) a n d (8). To a suspension of
benzyltriphenylphosphonium bromide (12.70 g, 29.30 mmol)
in dry hexane (49 mL) was added 2.5 M n-butyllithium in
hexane (12 mL) dropwise in 20 min. Stirring was continued
for 30 min after which a solution of 6 (6.60 g, 28.80 mmol) in
dry hexane (29 mL) was added dropwise in 30 min. Stirring
was continued overnight after which the reaction mixture was
diluted with water (30 mL), the organic phase was separated,
and the aqueous layer was extracted with diethyl ether (3 ×
60 mL). The combined organic phases were washed with brine
(50 mL) and dried (Na2SO4), and after evaporation of the
solvent, the residue was submitted to flash chromatography;
elution with light petroleum ether-AcOEt (80:20) afforded 7
1
(42%): mp 78-80 °C; H NMR (CDCl3) δ 1.40 (9H, s, t-Bu),
1.60 (3H, s, Me), 1.77 (3H, s, Me), 3.57 (1H, dd, J ) 2.6, 8.8
Hz, oxazolidine), 3.79 (1H, dd, J ) 6.2, 8.8 Hz, oxazolidine),
4.30 (1H, br s, oxazolidine), 6.12 (1H, dd, J ) 7.8, 15.8 Hz,
dCH), 6.53 (1H, d, J ) 15.8 Hz, dCH-Ph), 7.00-7.30 (5H,
m, aromatics); [R]20D -50° (c 2.0, CHCl3). Elution with the same
1
solvents gave 8 (18%): mp 72-4 °C; H NMR (CDCl3) δ 1.34
(9H, s, t-Bu), 1.56 (3H, s, Me), 1.73 (3H, s, Me), 3.61 (1H, dd,
J ) 3.4, 8.5 Hz, oxazolidine), 3.81 (1H, dd, J ) 6.6, 8.5 Hz,
oxazolidine), 4.80 (1H, br s, oxazolidine), 5.69 (1H, dd, J )
9.2, 11.7 Hz, dCH), 6.37 (1H, d, J ) 11.7 Hz, dCH-Ph), 7.10-
7.20 (5H, m, aromatics); [R]20 +40° (c 1.2, CHCl3).
D
ter t-Bu t yl 4(R)-[(1′S,2′R,3′S)-2′-(E t h oxyca r b on yl)-3′-
p h en ylcyclop r op yl]-2,2-d im eth yl-1,3-oxa zolid in e-3-ca r -
boxyla te (9). A solution of ethyl diazoacetate (3.83 g, 33.50

2720 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 14
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mmol) in dry dichloromethane (220 mL) was added via syringe
pump over 30 h to a magnetically stirred solution of the olefin
7 (2.55 g, 8.40 mmol) and Rh2(OAc)4 (0.41 g, 0.92 mmol) in
dry dichloromethane (50 mL). The reaction mixture was
evaporated to dryness and the residue submitted to flash
chromatography; elution with light petroleum ether-EtOAc
(70:30) gave the title compound 9 (26%): 1H NMR (CDCl3) δ
1.25 (3H, t, J ) 7.0 Hz, CO2 CH2CH3), 1.40 (9H, s, t-Bu), 1.50-
1.70 (1H, m, 1′-CH), 1.90-2.00 (1H, m, 2′-CH), 3.00 (1H, m,
3′-CH), 3.75 (1H, d, J ) 9.5 Hz, oxazolidine), 3.95 (1H, dd, J
) 6.1, 9.5 Hz, oxazolidine), 4.15 (2H, q, J ) 7.0 Hz, CO2CH2-
CH3), 4.30 (1H, m, 4-CH), 7.00-7.40 (5H, m, aromatics); 13C
NMR (CDCl3) δ 14.2, 23.1, 27.4, 28.4, 32.8, 56.3, 60.6, 68.5,
79.9, 94.0, 126.6, 126.8, 127.3, 139.5, 152.0, 171.6; GC-MS
m/z (%) 289, 333 (7), 274 (36), 189 (100), 115 (27), 57 (20).
E t h yl (1R,2S,3S)-2-(1′-ter t-Bu t oxyca r b on yla m in o-2′-
h yd r oxyeth yl)-3-p h en yl-1-cyclop r op a n eca r boxyla te (10).
p-Toluensulfonic acid monohydrate (0.01 g, 0.06 mmol) was
added to a magnetically stirred solution of 9 (0.30 g, 0.77
mmol) in methanol (20 mL). After 5 h, sodium acetate (0.01
g) was added and the stirring was continued for 30 min. The
reaction mixture was concentrated in vacuo, and the residue
was submitted to flash chromatography; elution with light
petroleum ether-EtOAc (1:1) afforded the alcohol 10 (57%):
1H NMR (CDCl3) δ 1.30 (3H, t, J ) 7.0 Hz, CO2 CH2CH3), 1.45
(9H, s, t-Bu), 1.85 (1H, m, 2-CH), 2.10 (1H, dd, J ) 5.7, 9.0
Hz, 1-CH), 2.85 (1H, t, J ) 5.7 Hz, 3-CH), 3.55-3.70 (2H, m,
2′-CH2), 4.00 (1H, m, 1′-CH), 4.15 (2H, q, J ) 7.0 Hz, CO2CH2-
CH3), 5.10 (1H, br s, NH), 7.00-7.30 (5H, m, aromatics); [R]20
D
+ 46.9° (c 1.0, CH2Cl2).
(2R,1′S,2′R, 3′S)-2-(2′-Ca r boxy-3′-p h en ylcyclop r op yl)-
glycin e (5). 8 N J ones’ reagent (1.5 mL) was added to a
magnetically stirred ice-cold solution of 10 (0.15 g, 0.64 mmol)
in acetone (3 mL). The reaction mixture was allowed to come
to room temperature and stirred for 1 h. 2-Propanol (1 mL)
was added, and after 10 min, the mixture was filtered through
Celite washing with ethyl acetate. The solution was evaporated
in vacuo to give an oil which was treated with 6 N HCl (10
mL) and stirred at 80 °C for 4 h. The reaction mixture was
washed with CH2Cl2 (5 mL) and evaporated to dryness. The
residue was submitted to ion-exchange resin chromatography
(Dowex 1×8, 1 N AcOH) to give the title compound 5 (78%):
1
mp 199-200 °C; H NMR (D2O) δ 2.05 (1H, td, J ) 5.6, 9.1,
10.4 Hz, 1′-CH), 2.30 (1H, dd, J ) 5.4, 9.1 Hz, 2′ CH), 2.70
(1H, t, J ) 5.6 Hz, 3′-CH), 4.00 (1H, d, J ) 10.4 Hz, 2-CH),
7.10-7.30 (5H, m, aromatics); 13C NMR (D2O + DCl) δ 28.3,
30.8, 51.0, 126.6, 127.5, 128.9, 137.5, 170.5, 174 3; [R]20D +48.5°
(c 1.0, 2.5 N HCl).
Refer en ces
(1) Conn, P. J .; Pin, J .-P. Pharmacology and functions of metabo-
tropic glutamate receptors. Annu. Rev. Pharmacol. Toxicol. 1997,
37, 205-237.
(2) Boss, V. K.; Conn, P. J . Metabotropic excitatory amino acid
receptor activation stimulates phospholipase D in hippocampal
slices. J . Neurochem. 1992, 59, 2340-2343.
(3) Holler, T. E.; Cappel, E.; Klein, J .; Lo¨ffelholz, K. Glutamate
activates phospholipase D in hippocampal slices of newborn and
adult rats. J . Neurochem. 1993, 61, 1569-1572.
J M990128V