4-Alkyl- and 4-cinnamylglutamic acid analogues are potent GluR5 kainate receptor agonists

Article abstract of DOI:10.1021/jm9911682

Enantiomerically pure (2S,4R)-4-substituted glutamic acids were prepared and tested for homomeric GluR5 and GluR6 kainate subtype receptor affinity. Some of the 4-cinnamyl analogues showed high selectivity and potency (K(i) < 25 nM) for the GluR5 receptor

Full text of DOI:10.1021/jm9911682

1958
J . Med. Chem. 2000, 43, 1958-1968
4-Alk yl- a n d 4-Cin n a m ylglu ta m ic Acid An a logu es Ar e P oten t Glu R5 Ka in a te
Recep tor Agon ists
Concepcio´n Pedregal,*,† Iva´n Collado,† Ana Escribano,† J esu´s Ezquerra,† Carmen Dom´ınguez,† Ana I. Mateo,†
Almudena Rubio,† S. Richard Baker,‡ J ohn Goldsworthy,‡ Rajender K. Kamboj,§ Barbara A. Ballyk,§
Ken Hoo,§ and David Bleakman|
Lilly, S.A., Avda. de la Industria 30, 28108 Alcobendas, Madrid, Spain, Eli Lilly and Company Limited, Lilly Research
Centre, Erl Wood Manor, Windlesham, Surrey GU20 6PH, U.K., Allelix Biopharmaceuticals Inc., 6850 Goreway Drive,
Mississauga, Ontario L4V 1V7, Canada, and Lilly Research Laboratories, Indianapolis, Indiana 46285
Received December 17, 1999
Enantiomerically pure (2S,4R)-4-substituted glutamic acids were prepared and tested for homo-
meric GluR5 and GluR6 kainate subtype receptor affinity. Some of the 4-cinnamyl analogues
showed high selectivity and potency (Ki < 25 nM) for the GluR5 receptors. The greatest
selectivity and potency were achieved with the 3-(2-naphthyl)prop-2-enyl compound. This
compound, LY339434, has negligible activity at the AMPA and kainate receptors GluR1, -2, -4
and -6. Although, LY339434 shows agonist activity at NMDA receptors in cultural hippocampal
neurons (approximate EC50 of 2.5 µM), we consider that LY339434 should be a useful
pharmacological tool for the investigation of the functional role of GluR5 kainate receptors.
Sch em e 1
In tr od u ction
L-Glutamate (Glu) is the major excitatory neurotrans-
mitter in the mammalian central nervous system (CNS).
Glutamate receptors are subdivided into ionotropic
(GluRs)1,2 and metabotropic (mGluRs) receptors.3,4 The
ionotropic receptors mediate fast synaptic transmission
through ligand-gated ion channels while metabotropic
receptors are G protein coupled and have a modulatory
role in the CNS. Ionotropic receptors have been subdi-
vided into three classes on the basis of their sensitivity
to the ligands NMDA (N-methyl-D-aspartate), KA (kain-
ate), and AMPA (R-amino-3-hydroxy-5-methyl-4-isox-
azolepropionate), from which they take their names.5
Expression studies have recently verified that there are
further subtypes for each of the aforementioned iono-
tropic receptors. Five distinct kainate binding proteins
have been identified: GluR7, KA1, and KA2 show high
affinity for kainate, and GluR5 and -6 show low
affinity.6-13 GluR5, -6 and -7, when expressed homo-
merically, can form functional ion channels activated
by kainate, domoate, or glutamate. By contrast, KA1
or KA2 expressed in homomeric form do not appear to
form functional channels. Selective kainate receptor
ligands are expected to exhibit distinct pharmacological
effects since individual receptor proteins show different
distributions within the CNS.3,14 Recent studies have
identified ligands which show selectivity for kainate
receptors including ATPA,15 5-iodowillardiine,16 and
(2S,4R)-4-methyl glutamate.17,18 All of them exhibit
high-affinity binding and functional activity at GluR5
kainate receptors. However, none of them are com-
pletely selective for kainate. In an earlier paper, we
reported that the 4-substituted glutamate analogue
LY339434 is a potent homomeric hGluR5 receptor
agonist.19 In this paper we describe the structure-
activity relationships for a number of 4-alkyl- and
4-cinnamyl glutamate analogues that are potent GluR5
agonists and show selectivity over other kainate and
AMPA receptors examined.
In an early unpublished study, we found that the
2S,4R isomers of 4-cinnamyl- (1) and 4-allylglutamate
(2) were active in a tritium-labeled kainate binding
assay using a rat forebrain membrane preparation.
With the availability of both homomeric hGluR5 and -6
expressing cell lines we decided to retest compounds 1
and 2 since the radioligands themselves were nonselec-
tive (many analogues of kainic acid (3)) (Scheme 1).20
Thus, compounds 1 and 2 showed promising subtype
selectivity, having at least 30 times greater affinity for
hGluR5 than hGluR6 receptors. A highly subtype selec-
tive GluR5 ligand would be a very valuable pharmaco-
logical tool for the characterization of this receptor. We
therefore set out to further improve the selectivity and
potency of these ligands. Although we cannot extrapo-
late the results for homomeric receptors to all kainate
receptors found in neuronal tissues, we were able to
demonstrate the functional agonist activity of com-
pounds at rat dorsal root ganglion neurons, neurons
thought to express GluR5 kainate receptors.
* To whom correspondence should be addressed. Phone: (34-91)
6633426. Fax: (34-91) 6633411. E-mail: Pedregal_Concepcion@Lilly.com.
† Lilly, S.A.
‡ Eli Lilly and Co. Ltd.
§ Allelix Biopharmaceuticals Inc.
| Lilly Research Laboratories.
10.1021/jm9911682 CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/27/2000

Potent GluR5 Kainate Receptor Agonists
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10 1959
Sch em e 2
Sch em e 3
Ch em istr y
The procedure used for the final deprotection was
dependent on the nature of the substituent at the
4-position. In the case of the cinnamyl derivatives, direct
hydrolysis with hydrochloric acid was satisfactory.
However, where the 4-substituent had an isolated
double bond, it was found that either the hydrochloric
acid itself or the 4-carboxy group would add across the
bond during the vigorous acid hydrolysis. This problem
was overcome by using a two-step hydrolysis procedure,
whereby the lactam and ester were cleaved using LiOH
in aqueous THF and the BOC group was finally re-
moved under milder acid conditions at room tempera-
ture. Even this modified procedure was unsatisfactory
for the compounds having electron-rich trisubstituted
double bonds. In this case the BOC group of the lactam
5 and 6 was removed thermally, and the lactam and
esters were cleaved using aqueous sodium hydroxide.
The disadvantage of this latter procedure was that some
epimerization occurred.
The syntheses of (2S,4R)- and (2S,4S)-4-substituted
glutamic acids (1, 2, 7, and 8) were stereoselectively
achieved starting from N-Boc protected pyroglutamate
esters 4 (Scheme 2). Thus, selective generation of the
pyroglutamate lactam enolate with LiHMDS in THF at
-78 °C and reaction with activated electrophiles (cin-
namyl halides) gave rise to thermodynamic equilibrium
mixtures of both 4-substituted pyroglutamates 5 and 6,
in moderate to good yields, without affecting the pyro-
glutamate stereogenic center21 (Scheme 2). With allyl
and propargyl bromides (Scheme 3), we found it neces-
sary to carry out inverse addition of the enolate to 4
equiv of the electrophile. The mixture of diastereomers
could then generally be separated by chromatography
and their stereochemistry established by NMR (see ref
21 for a detailed discussion). Subsequent deprotection
of the individual isomers 5 and 6 yielded the corre-
sponding free amino acids 7 and 8 (Scheme 2). The
optical purity of the final amino acids was determined
by chemical correlation (see ref 21 for more information).
Attempts to couple phenyl propargyl bromide with
protected pyroglutamate failed, so this compound was

1960 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10
Pedregal et al.
Ta ble 1. hGluR5 and hGluR6 Binding Data for the Cinnamyl
Series (calculated from an 11 point concentration inhibition
curve) (1, 9-33)
prepared by coupling the terminal acetylene with iodo-
benzene in the presence of a palladium catalyst to give
30. The cis olefins were prepared by hydrogenation of
the acetylenic amino acid in water using Lindlar
catalyst. The saturated compounds were prepared by
hydrogenation of the acetylenic amino acid using 10%
Pd on carbon catalyst at 60 psi (Scheme 3).
Ki, nM
P h a r m a cology Meth od s
ratio
stereo-
chemistry
hGlu- hGlu- hGluR6/
Liga n d Bin d in g Stu d ies a t AMP A a n d Ka in a te
Recep tor s Exp r essed in HK293 Cells. Cell mem-
branes were prepared from frozen HEK293 cells ex-
pressing either recombinant AMPA22,23 or kainate12,13
receptors by resuspending the cells in ice cold distilled
water, sonicating, and centrifuging at 50 000g for 20
min. The membrane pellets were then washed in >100
× volumes of 50 mM Tris-HCl buffer (pH 7.5) and
centrifuged to remove endogenous glutamate. Binding
reactions were performed at 4 °C for 60 min in a total
volume of 250 µL containing 50 µL of membrane
suspension (100-150 µg of protein). For kainate recep-
tor binding (hGluR5 or hGluR6), the reaction mixture
consists of 150 µL of 50 mM Tris-HCl (pH 7.5), 25 µL of
[3H]-KA (DuPont NEN), and 25 µL of unlabeled com-
petitor (10-12-10-3 M). The final [3H]-kainate concen-
tration used in the competitive inhibition experiments
was 20 nM. For AMPA binding experiments (hGluR1,
hGluR2, or hGluR4), 20 nM [3H]-AMPA (DuPont NEN)
was used for each receptor subtype and 100 mM KSCN
was added to the Tris-HCl buffer. Following the 60 min
incubation, the membranes were centrifuged at 50 000g
for 20 min to separate bound from free ligand and the
pellets washed three times in cold assay buffer. Non-
specific binding was determined by incubation in the
presence of 1 mM glutamate. All data were analyzed
by GRAFIT 2.0 software.
compd no.
Ar
R5
R6
hGluR5
1
9
Ph
Ph
E
Z
E
E
E
E
E
E
E
E
E
E
E
E
E
E
44
157
26
1580
339
59
36
2
2
10 LY339296 2-OMe-Ph
11
12
13
14
3-OMe-Ph
4-OMe-Ph
2-Cl-Ph
40
6349
22340
1404
1132
3859
7216
4375
559
161
79
6
19
504
241
28
7
284
254
60
8
30
3-Cl-Ph
15 LY339295 4-Cl-Ph
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
4-Br-Ph
4-Me-Ph
4-F-Ph
172
78
4-CF3-Ph
4-SMe-Ph
4-i-Pr-Ph
4-CN-Ph
4-CO2H-Ph
4-NO2-Ph
4-OCF3-Ph
4-Ph-Ph
3,4-DiCl-Ph
3,4-DiOMe-Ph
2,6-DiCl-Ph
Ph
52
32
58
43929
6024
27532
4491
27280
3845
11185
5650
3987
13949
1568
1000
841
191
476
12
8
65
44
42
81
26
12
3
367
3590
59
254
133
49
540
131
337
E
E
E
E
E
E
acetylene
saturated 1190 >10000
Ph
>9
980
605
32 LY339434 2-naphthyl
33 1-naphthyl
E
E
14
7
13723
4366
concentration obtained from separate cells. Curve fitting
was performed as described above.
Resu lts a n d Discu ssion
Electr op h ysiologica l Recor d in gs Usin g HEK293.
Whole-cell voltage clamp recordings were made from
HEK293 cells stably transfected with hGluR5 or hGluR6
as previously described.12,13,24 Drugs were applied to
cells via bath perfusion with exchange of solutions
occurring in less than 20 s. Experiments for both these
cell lines were performed in the presence of 2.5 mM
concanavalin A to prevent receptor desensitization.15
Results are expressed as a percentage of the maximum
inward current evoked by the ligand. Curve fitting
to the data points was based upon the equation y )
The prepared compounds can be classified in three
different categories: the cinnamyl, the straight chain
aliphatic, and the branched aliphatic compounds shown
in Table 1, 2 and 3, respectively. In all of them the activ-
ity resided in the 2S,4R stereoisomer. In the cinnamyl
series (Table 1) it was found that the introduction of a
4-chloro group (15) markedly increased the selectivity
and potency for the hGluR5 receptor compared to the
parent compound 1. The general trend was that electron-
withdrawing groups in the 4-position of the phenyl ring,
at least, kept the same range of activity. However,
attempts to further enhance the activity with more
powerful mesomeric electron-withdrawing groups e.g.
the nitrile 22 and the nitro 24 led to a decrease in
activity. Another interesting finding was that an ortho
substituent on the phenyl ring reduced the selectivity
between hGluR5 and hGluR6. This effect was most
apparent with the 2-methoxy analogue 10, where there
was little or no selectivity between hGluR5 and hGluR6,
but the effect was also detectable with the 2-chloro (13)
and 2,6-dichloro (29) analogues. A similar loss of
selectivity was also found with the Z isomer 9 and
compound 52 with a methyl group. These results may
suggest that planarity enhances hGluR5 selectivity.
However, there were also some compounds which might
be expected to be planar (e.g. 4-F, 4-CN, and 4-CO2H)
which also showed little selectivity, so there may be
R
max(Dn/(Dn + EC50n), using a slope fixed to a value of
1, where D is the drug concentration. Data for each point
were obtained from a minimum of four separate cells.
Electr op h ysiologica l Recor d in g in DRG Neu -
r on s. Whole-cell voltage clamp recordings were made
(Vh ) -70 mV) from acutely isolated dorsal root
ganglion neurons that were prepared as previously
described.25 All cells were pretreated with 10 mM
concanavalin A for 10 min prior to agonist applications.
Under these conditions, agonist-induced desensitization
is irreversibly removed, and subsequent experiments
were performed in the absence of concanavalin A.
Comparison of agonist efficacy relative to kainate was
obtained by constructing concentration-relationship
curves and comparing steady-state current magnitudes
to those of 100 µM kainate in the same cell. Data shown
represent the mean of at least three values for each

Potent GluR5 Kainate Receptor Agonists
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10 1961
Ta ble 2. hGluR5 and hGluR6 Binding Data for the Alkyl
Series (calculated from an 11 point concentration inhibition
curve) (34-48)
olefin with a chloro group 50 was not beneficial, which
is a surprise in the light of the SAR for the cinnamyl
series. The previously reported kainate ligand 4-meth-
ylglutamate17,18 52 was very potent in our hands
(hGluR5, Ki ) 3 nM) but showed little selectivity
(hGluR6, Ki ) 10 nM) (Table 3).
In Table 4, we report the binding profiles for three of
the more interesting compounds from the cinnamyl
series along with the figures for glutamate and kainate.
It should be noted that the three new compounds have
Ki values of greater than 10 µM on the AMPA receptors
GluR1, -2 and -4, making them more selective for
kainate receptors than kainate itself. Compounds 15
and 32, which show greater selectivity between hGluR5
than hGluR6, do have significant hGluR7 activity (Ki )
423 and 617 nM, respectively). The 2-OMe derivative
10 shows no selectivity among hGluR5, -6, and -7, but
still lacks AMPA and KA2 activity. Compound 10 could
thus be a tool for distiguishing the effects of homomeric
GluR5, -6, and -7 compared with homomeric KA2 in
biological systems. However, we cannot know to what
extent this can be extrapolated to biological heteromeric
systems. Additionally, compound 32, LY339434, was
shown to have activity at NMDA receptors with EC50
values of 2.5 µM in cultured hippocampal neurons. The
functional NMDA receptor activity of the other com-
pounds in this series remains to be evaluated.
ratio
hGluR6/
stereochemistry hGluR5 hGluR6 hGluR5
Ki, nM
compd no.
34
35
36
37
38
R
H
H
2S,4R acetylene
2S,4R acetylene
Me 2S,4R acetylene
Et 2S,4R acetylene
11.6
307
28.9
831
160
823
14
3
1456
10247
68547
1840
13800
5373
22529
3258
2984
2893
2450
41152
7207
50
12
19
38
11
9
141
155
19
71
20
154
3
nPr 2S,4R acetylene 3606
39 LY310214
H
H
2S,4R olefin
2S,4R olefin
Me 2S,4R,Z olefin
Et 2S,4R,Z olefin
48
1300
577
160
21
161
41
123
267
40
41
42
43 LY339180 Me 2S,4R,Z olefin
44
45
46
47
48
Et 2S,4R,E olefin
Cl 2S,4R,E olefin
2S,4R saturated
Et 2S,4R saturated
H
nPr 2S,4R saturated 2376
Ta ble 3. hGluR5 and hGluR6 Binding Data for 49-52
(calculated from an 11 point concentration inhibition curve)
In Table 5, we report the electrophysiology data using
hGluR5 and -6 expressing cells and acutely isolated rat
DRG cells. On the hGluR5 expressing cells the new
compounds are all agonists having Rmax values between
65 and 95% of that observed with kainic acid. On the
hGluR6 expressing cells the compounds were again
agonists having Rmax values in the range 110-153%
that of kainic acid. It should also be noted that the EC50
values are consistently higher than the binding Ki
values; however, the rank order of potency is very
similar. The data with the DRG cells closely parallels
that seen with the hGluR5 expressing cells but not that
seen with the hGluR6 expressing cells. We believe these
results provide additional evidence that native DRG
neurons functionally express GluR5 kainate receptors.
Figures 1 and 2 show typical dose-response curves for
the compounds listed in Table 4.
other factors at work here. Compound 31, in which the
double bond was removed, was markedly less potent at
hGluR5, as were both the Z olefin 9 and acetylene 30.
The greatest selectivity was achieved with the 2-naph-
thyl compound 32 (LY339434) which showed nearly
1000-fold selectivity for hGluR5 over hGluR6.
In the three aliphatic series, saturated, olefinic, and
acetylenic (Table 2), it was found that for R ) H the
saturated analogue 46 was less active than the equiva-
lent olefinic compound 39; however, the acetylenic
compound 34 was the most active. In the three series
the optimum activity occurred with three- or four-carbon
atom chains, with a gradual fall off of activity with
increasing chain length. Selectivity between GluR5 and
GluR6 did vary between the three classes of compounds
and with chain length; however, none of the compounds
achieved the high selectivity seen with the cinnamyl
series. The E olefin 43 is more potent and selective that
the Z isomer 41 when R ) Me. However, for R ) Et the
affinity for the E olefin 44 is just the same as that for
the Z isomer 42, and the selectivity is reversed. So no
clear conclusion can be drawn. Surprisingly, considering
the structure of the aliphatic side chain in kainic acid,
the trisubstituted olefin 49 (Table 3) was less active
than the related disubstituted analogue 43. It should
also be noted that reducing the electron density on the
Con clu sion s
The choice of 4-substituent on glutamic acid can
profoundly effect the activity of the ligand at hGluR5
and -6 receptors. Although it was not possible to fully
understand the structure-activity relationship, we have
identified compounds with large planar substituents
(compounds 15, LY339434, and 33) that can provide
very useful selectivity between hGluR5 and -6 receptors.
LY339434 has the advantage of no activity at the AMPA
receptors hGluR1, 2, and 4, although it showed some
NMDA activity.
LY339434 should be a useful pharmacological tools
for the investigation of the role of GluR5 receptors in
both normal and diseased states. Preliminary studies
show that LY339434 does cross the blood-brain barrier
following intraparitoneal administration, and its in vivo
pharmacology is now being investigated.

1962 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10
Pedregal et al.
F igu r e 1. (Left) Concentration-response curves for inward currents evoked by LY339295 at either GluR5 (∆) or GluR6 (b)
expressing HEK293 cells using whole voltage clamp electrophysiology. Approximate Rmax values and EC50 values were generated
from the curves for data expressed as a percentage of responses evoked by 100 µM kainate in the same cells. (Right) Concentration-
response curves in acutely isolated rat DRG neurons produced by LY339295 (4) and kainate (9).
Ta ble 4. Binding Profiles through the AMPA/Kainate Subreceptors
Ki, nMa
compd
GluR1
GluR2
GluR4
GluR5
GluR6
KA2
GluR7
kainate (3)
glutamate
LY339295 (15) >10000 (1)
LY339296 (10) >10000 (1)
LY339434 (32) >10000 (1)
7449 ( 2018 (3) 12221 ( 2744 (4) 1714 ( 170 (3) 177 ( 22 (3) 32 ( 13 (4)
8 ( 2 (5)
10 ( 2 (3)
1362 ( 257 (3)
940 ( 93 (3)
>10000 (1)
>10000 (1)
>10000 (1)
868 ( 219 (3)
>10000 (1)
>10000 (1)
>10000 (1)
701 ( 46 (3) 1106 ( 159 (3)
8 ( 1 (3) 4649, 3069 (2)
30 ( 13 (3) 48 ( 4 (3)
750 ( 77 (3) 789 ( 83 (3)
>10000 (1)
>10000 (1)
423 (1)
42 (1)
617 (1)
15 ( 13 (2) 15406, 12040 (2) >10000 (1)
a
In parentheses are the number of replicates.
Ta ble 5. Electrophysiology Data for Selected Compounds
hGluR5a
hGluR6a
DRG neuronsa
EC50, µM Rmax, %
compd
Ki, nM
EC50, µM
Rmax, %
Ki, nM
EC50, µM
Rmax, %
100
kainate (3)
glutamate
LY310214 (39) 56, 38 (2)
LY339180 (43) 21 ( 3 (3)
LY339295 (15) 8 ( 1 (3)
LY339434 (32) 15, 13 (2)
177 ( 22 (3) 16.2 ( 1.0 (4) 100
32 ( 13 (4)
0.7 ( 0.1 (6)
12.0 ( 0.1 (4) 100
35.2 ( 0.2 (5) 51 ( 10 (5)
701 ( 46 (3) 75.0 ( 7.5 (15) 79 ( 2 (15) 1106 ( 159 (3)
25.0 ( 2.0 (8) nd
4.4, 3.7 (2)
65, 96 (2)
86 ( 2 (6) 3258 (1)
66 ( 5 (6) 4649, 3069 (2)
1840 (1)
8.3 ( 2.7 (3)
>110 (1)
nd
nd
nd
4.5 ( 0.8 (6)
2.8 ( 0.4 (6)
2.5 ( 0.9 (3)
58.3 ( 4.2 (4) 138 ( 5 (4) nd
70.8 ( 10.7 (5) 130 ( 10 (5) 1.6 ( 0.2 (4) 55 ( 4 (4)
nd 0.8 ( 0.2 (6) 57 ( 5 (6)
153 ( 2 (5) nd nd
80 ( 1 (3) 15406, 12040 (2) >100 (5)
LY339296 (10) 30 ( 13 (3) 3.3 ( 0.4 (3)
95 ( 2 (3) 48 ( 4 (3)
1.3 ( 0.6 (5)
a
In parentheses are the number of replicates.
nitrogen atmosphere. The mixture was warmed to -40 °C and
stirred for 2 h. A saturated ammonium chloride solution was
added and the aqueous layer was extracted three times with
ether. The organic layer was dried over Na2SO4, filtered, and
concentrated in vacuo. The residue was dissolved in CH2Cl2
(8 mL) and 48% HBr (25.6 mmol) and 98% H2SO4 (12.8 mmol)
were added. The mixture was heated at 60 °C for 30 min. The
reaction mixture was washed with a saturated NaHCO3
solution. The organic layer was dried over Na2SO4, filtered,
and concentrated in vacuo. The cinnamyl bromide were used
without further purification.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. All solvents and reagents were
purchased from commercial sources and used as received,
unless otherwise indicated. Tetrahydrofuran (THF) was dis-
tilled from sodium benzophenone ketyl prior to use. All
reactions were performed under a positive pressure of argon
1
or nitrogen. H NMR and 13C NMR data were recorded on a
Bruker AC-200P or Bruker AC-300. IR spectra were obtained
on a Nicolet 510 P-FT (film and KBr). High-resolution mass
spectra (HRMS) were measured on a VG-Autospec spectrom-
eter. Melting points were determined on a Bu¨chi apparatus
and are not corrected. Optical rotations were measured with
a Perkin-Elmer 241 polarimeter. Analytical TLC was per-
formed on Merck TLC glass plates precoated with F254 silica
gel 60 (UV, 254 nm and iodine). Chromatographic separations
were performed by using 230-400 mesh silica gel (Merck).
Elemental analyses were performed by the Universidad Com-
plutense Analytical Centre (Facultad de Farmacia) Madrid.
Gen er a l P r oced u r e for P r ep a r a tion of Cin n a m yl Br o-
m id es. To a -78 °C solution of the corresponding aldehyde
(12.8 mmol) in THF (40 mL) was added a 1 M solution of
vinylmagnesium bromide in ethyl ether (14.8 mmol) under
Cin n a m yl Der iva tives (Ta ble 1). Gen er a l P r oced u r e
for Alk yla tion Rea ction s of Eth yl or Ben zyl N-BOC
P yr oglu ta m a te Ester s w ith Cin n a m yl Br om id es. To a
solution of pyroglutamate (4a or 4b ) (7.77 mmol) in THF
(40 mL) stirred at -78 °C was added a 1 M solution of lithium
hexamethyldisilazide in THF (8.55 mL, 8.55 mmol, 1.1 equiv).
After the reaction mixture was stirred at -78 °C for 1 h,
the corresponding cinnamyl bromide (9.30 mmol, 1.2 equiv)
in THF (10 mL) was added and stirring continued for 2 h. The
reaction mixture was quenched with saturated ammonium
chloride solution (50 mL) at -78 °C and extracted with ethyl

Potent GluR5 Kainate Receptor Agonists
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10 1963
F igu r e 2. (Left) Concentration-response curves for inward currents evoked by LY339296 at either GluR5 (4) or GluR6 (b)
expressing HEK293 cells using whole voltage clamp electrophysiology. Approximate Rmax values and EC50 values were generated
from the curves for data expressed as a percentage of responses evoked by 100 µM kainate in the same cells. (Right) Comparison
of LY339434 at either GluR5 (4) or at GluR6 (b) expressing HEK293 cells.
ether (3 × 20 mL). The combined organic phases were dried
over Na2SO4, filtered, and evaporated to dryness. The diastereo-
mers were separated by flash column chromatography using
EtOAc/hexane 1:4 as eluent.
174.0, 170.7, 155.8, 148.8, 141.0, 134.6, 128.1 (2C), 128.0 (2C),
127.1, 126.6, 126.0, 125.7, 125.4, 120.1, 110.3, 82.9, 66.7, 59.8,
56.6, 54.8, 41.1, 27.2 (3C), 27.1. Anal. (C27H31NO6) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(2-m eth oxyp h en yl)p r op -2-en yl]-
Gen er a l P r oced u r e for th e Hyd r olysis of 4-Su bstitu t-
ed Eth yl or Ben zyl N-BOC P yr oglu ta m a te Ester s. To a
solution of the title compounds (2 mmol) in THF (15 mL) was
added a 2.5 N aqueous solution of LiOH (14.4 mL, 36 mmol).
The mixture was stirred at room temperature for 4 h and then
acidified to pH 2 with 1 N HCl solution and extracted with
ethyl ether (3 × 20 mL). The combined organic layers were
dried over Na2SO4 and concentrated in vacuo to give an oily
residue which was reacted with a saturated HCl solution in
ethyl acetate for 1 h at room temperature. The resulting white
solid was triturated with ethyl ether (3 × 20 mL). The final
amino acids were isolated as zwitterions by treatment of a
methanolic solution of the corresponding hydrochloride with
propylene oxide.
p en ta n ed ioic a cid (10): 29% yield. Mp: 171-2 °C. [R]D )
+4.25 (c 0.4, DMSO). 1H NMR (D2O/KOD): δ 7.12 (d, 1H, J )
7.2 Hz), 6.92 (t, 1H, J ) 8.0 Hz), 6.68-6.60 (m, 2H), 6.33 (d,
1H, J ) 15.0 Hz, HCd), 5.89 (dt, 1H, J ) 15.0 and 6.9 Hz,
HCd), 3.47 (s, 3H, OCH3), 2.83 (dd, 1H, J ) 8.6 and 4.0 Hz,
H-2), 2.15-1.96 (m, 3H), 1.62-1.48 (m, 1H), 1.27-1.12 (m, 1H).
13C NMR (D2O/MeOH-d4/KOD): δ 183.0, 182.0, 154.8, 129.3,
127.7, 125.8, 125.5, 124.3, 120.5, 111.2, 54.9, 53.8, 45.2, 37.4,
35.8. IR (KBr): 3036, 1686, 1574, 1244 cm-1. Anal. (C15H19
-
NO5‚H2O) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(3-m eth oxyp h en yl)p r op -2-en yl]-
p en ta n ed ioic a cid (11): 45% yield. Mp: 148-150 °C. [R]D
)
+17.6 (c 0.3, pyridine). 1H NMR (D2O/KOD): δ 6.92 (t, 1H,
J ) 7.8 Hz) 6.70-6.64 (m, 2H), 6.49 (dd, 1H, J ) 8.0 and 2.3
Hz), 6.08 (d, 1H, J ) 15.9 Hz, HCd), 5.91 (dt, 1H, J ) 15.9
and 6.5 Hz, HCd), 3.44 (s, 3H, OCH3), 2.82 (dd, 1H, J ) 9.3
and 4.5 Hz, H-2), 2.15-1.95 (m, 3H), 1.61-1.48 (m, 1H), 1.25-
1.11 (m, 1H). IR (KBr):: 1699, 1581, 1489, 1261 cm-1. Anal.
(C15H19NO5‚H2O) C, H, N.
Eth yl (2S,4R,E)-N-BOC-4-cin n am ylpyr oglu tam ate: Hex-
ane/ethyl acetate 3:1. colorless oil. 54% yield. [R]D ) -33.3
1
(c 1, CHCl3). H NMR (CDCl3): δ 7.28-7.09 (m, 5H), 6.37 (d,
J ) 15.8 Hz, 1H), 6.05 (dt, J ) 7.1 and 15.8 Hz, 1H), 4.46 (dd,
J ) 0.7 and 9.1 Hz, 1H), 4.13 (q, J ) 7.2 Hz, 2H), 2.28-2.60
(m, 2H), 2.40-2.20 (m, 1H), 2.20-1.90 (m, 2H), 1.42 (s, 9H),
1.20 (t, J ) 7.2 Hz, 3H). 13C NMR (CDCl3): δ 174.0, 170.8,
148.9, 136.5, 132.5, 128.1, 127.0, 125.7, 125.4, 83.0, 61.2, 56.7,
41.1, 33.1, 27.4, 27.2, 13.8. IR (film): 2980, 1790, 1748, 1317,
1205 cm-1. Anal. (C21H27NO5) C, H, N.
Eth yl (2S,4R,E)-N-BOC-4-(4-m eth oxycin n a m yl)p yr o-
glu ta m a te: 30% yield. EtOAc/hexane 1:4. A pale yellow oil.
1
[R]D ) - 18.3 (c 0.6, CHCl3). H NMR (CDCl3): δ 7.18 (d, J )
8.7 Hz, 2H), 6.76 (d, J ) 8.7 Hz, 2H), 6.31 (d, J ) 15.8 Hz,
1H), 5.90 (dt, J ) 14.4 and 7.3 Hz, 1H), 5.19 (s, 2H), 4.47 (dd,
J ) 1.9 and 9.0 Hz, 1H), 4.15 (q, J ) 7.2 Hz, 2H), 3.72 (s, 3H),
2.85-2.59 (m, 2H), 2.40-1.92 (m, 3H), 1.42 (s, 9H), 1.21 (t,
J ) 7.2 Hz, 3H). 13C NMR (CDCl3): δ 174.4, 171.2, 158.9, 149.2,
132.3, 129.6, 127.1, 123.3, 113.8, 83.4, 61.6, 57.1, 55.2, 41.6,
33.4, 27.7, 14.0. IR (film): 1790, 1748, 1512, 1316, 1250, 1154.
Anal. (C22H29NO6) C, H, N.
(2S,4R,E)-2-Am in o-4-(3-p h en ylp r op -2-en yl)p en ta n ed io-
ic a cid (1): 54% yield. Mp: 158-160 °C. [R]D ) +24.2 (c 0.24,
1 N NaOH). 1H NMR (TFA-acetone-d6): δ 7.12-6.97 (m, 5H),
6.32 (d, J ) 15.8 Hz, 1H), 6.03-5.88 (td, J ) 3.0 and 15.8 Hz,
1H), 4.45-4.38 (dd, J ) 4.5 and 7.8 Hz, 1H), 2.91-2.87 (m,
1H), 2.62-2.37 (m, 3H), 2.29-2.18 (m, 1H). Anal. (C14H17NO4‚
H2O) C, H, N.
(2S,4R,6E)-2-Am in o-4-[3-(4-m eth oxyph en yl)pr op-2-en yl]-
p en t a n ed ioic a cid (12): 15% yield. Mp: 159 °C (dec).
(2S,4R,Z)-2-Am in o-4-(3-p h en ylp r op -2-en yl)p en ta n ed io-
ic a cid (9): 43% yield. Mp: 143-5 °C. [R]D ) +12.0 (c 0.15,
DMSO). 1H NMR (D2O-KOD): δ 7.50-7.30 (m, 5H, Ph), 6.55
(d, J ) 11.8 Hz, 1H), 5.70 (dt, J ) 11.8 and 3.9 Hz, 1H), 3.15
(dd, 1H, J ) 9.4 and 4.4 Hz, H-2), 2.60-2.40 (m, 3H), 2.00-
1.84 (m, 1H), 1.61-1.47 (m, 1H). 13C NMR (D2O/MeOH-d4-
KOD): δ 185.0, 183.9, 138.4, 131.7, 130.6, 129.9, 129.5, 128.0,
1
[R]D ) +25.0 (c 0.08, 12N HCl). H NMR (D2O-KOD): δ 7.00
(d, J ) 8.5 Hz, 2H), 6.55 (d, J ) 8.5 Hz, 2H), 6.03 (d, J ) 16.0
Hz, 1H), 5.75 (dt, J ) 6,5 and 16.0 Hz, 1H), 3.40 (s, 3H), 2.78
(dd, J ) 4.5 and 9.1 Hz, 1H), 2.10-1.90 (m, 3H), 1.50 (m, 1H),
1.15 (m, 1H). 13C NMR (MeOH-d4/Pyr-d5/KOD): δ 184.2, 183.0,
160.1, 132.0, 131.6, 128.2, 127.8, 114.8, 56.4, 55.8, 47.8, 40.6,
38.6. IR (KBr): 3420, 1703, 1586, 1512, 1246 cm-1. Anal.
(C15H19NO5‚H2O) C, H, N.
55.6, 47.4, 39.6, 33.0. IR (KBr): 3447, 2851, 1695, 1585 cm-1
.
Anal. (C14H17NO4‚H2O) C, H, N.
Ben zyl (2S,4R,E)-N-BOC-4-(2-m eth oxycin n a m yl)p yr o-
Ben zyl (2S,4R,E)-N-BOC-4-(2-ch lor ocin n a m yl)p yr o-
glu ta m a te: 53% yield. EtOAc/hexane 1:4. White solid. Mp:
82-4 °C. [R]D ) - 31.0 (c 0.5, CHCl3). 1H NMR (CDCl3): δ
7.47-7.13 (m, 4H), 7.33 (s, 5H), 6.78 (d, J ) 15.8 Hz, 1H),
6.08 (dt, J ) 14.4 and 7.2 Hz, 1H), 5.18 (s, 2H), 4.59 (dd, J )
1.9 and 9.2 Hz, 1H), 2.91-2.70 (m, 2H), 2.51-2.02 (m, 3H),
1
glu ta m a te: 23% yield. EtOAc/hexane 1:3. H NMR (CDCl3):
δ 7.41-7.12 (m, 7H), 6.91-6.71 (m, 3H), 6.06 (dt, 1H, J ) 15.5
and 7.0 Hz, HCd), 5.16 (AB, 2H, CO2CH2), 4.55 (dd, 1H, J )
9.3 and 1.2 Hz, H-2), 3.77 (s, 3H, OCH3), 2.81-2.65 (m, 2H),
2.44-1.92 (m, 3H), 1.39 (s, 9H, C(CH3)3). 13C NMR (CDCl3): δ

1964 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10
Pedregal et al.
1.40 (s, 9H). 13C NMR (CDCl3): δ 174.2, 171.1, 149.3, 135.0,
132.6, 129.6, 128.7, 128.5, 126.8, 83.7, 67.4, 57.1, 41.4, 33.6,
27.8. IR (KBr): 1780, 1734, 1306 cm-1. Anal. (C26H28ClNO5)
C, H, N.
6.38 (d, J ) 15.9 Hz, 1H), 6.03 (dt, J ) 14.3 and 7.2 Hz, 1H),
5.18 (s, 2H), 4.57 (dd, J ) 2.0 and 9.1 Hz, 1H), 2.90-2.65 (m,
2H), 2.45-1.96 (m, 3H), 2.31 (s, 3H), 1.40 (s, 9H). 13C NMR
(CDCl3): δ 174.3, 171.1, 149.2, 137.2, 135.0, 134.1, 132.8, 129.2,
128.6, 128.5, 126.0, 124.6, 83.6, 67.3, 57.1, 41.6, 33.4, 27.8, 27.7,
(2S,4R,6E)-2-Am in o-4-[3-(2-ch lor op h en yl)p r op -2-en yl]-
21.1. IR (KBr): 1775, 1742, 1704, 1366, 1316, 1192, 1160 cm-1
Anal. (C27H31NO5) C, H, N.
.
p en ta n ed ioic a cid (13): 20% yield. Mp: 140-1 °C. [R]D
)
1
+8.5 (c 0.42, DMSO). H NMR (pyr-d5-D2O): δ 7.25 (m, 1H),
7.6-7.3 (m, 3H), 6.95 (d, J ) 16.2 Hz, 1H), 6.44 (m, 1H), 4.19
(dd, J ) 3.5 and 9.2 Hz, 1H), 3.10-2.25 (m, 5H). 13C NMR
(pyr-d5-D2O): δ 181.7, 174.0, 134.5, 131.3, 130.5, 128.9, 127.9,
127.0, 126.6, 126.4, 53.0, 44.4, 35.8, 32.2. IR (KBr): 3400, 1699,
1584, 1418, 1200 cm-1. Anal. (C14H16ClNO4‚H2O) C, H, N.
Ben zyl (2S,4R,E)-N-BOC-4-(3-ch lor ocin n a m yl)p yr o-
(2S,4R,E)-2-Am in o-4-[3-(4-m eth ylp h en yl)p r op -2-en yl]-
p en t a n ed ioic a cid (17): 25% yield. White solid. Mp:
155-6 °C (dec). [R]D ) + 42.8 (c 0.5, 1 N HCl). 1H NMR (D2O-
pyr-d5): δ 7.44 (d, J ) 8.0 Hz, 2H), 7.25 (d, J ) 8.5 Hz, 2H),
6.86-6.46 (m, 2H), 4.35 (dd, J ) 3.2 and 9.5 Hz, 1H), 3.20-
2.41 (m, 5H), 2.41 (s, 3H). 13C NMR (D2O-pyr-d5): δ 184.2,
176.4, 150.2, 136.5, 133.3, 131.1, 129.0, 128.0, 126.1, 55.6, 47.2,
1
glu ta m a te: 50% yield. EtOAc/hexane 1:7. H NMR (CDCl3):
38.5, 34.9, 22.4. IR (KBr): 3023, 2921, 1699, 1586, 1514 cm-1
Anal. (C15H19NO4) C, H, N.
.
δ 7.35 (broad s, 5H), 7.30-7.13 (m, 4H), 6.36 (d, 1H, J ) 15.8
Hz, HCd), 6.11 (dt, 1H, J ) 15.8 and 7.0 Hz, HCd), 5.19
(AB system, 2H, CO2CH2), 4.60 (dd, 1H, J ) 9.3 and 1.8 Hz,
H-2), 2.87-2.66 (m, 2H), 2.44-1.94 (m, 3H), 1.42 (s, 9H,
C(CH3)3). 13C NMR (CDCl3): δ 174.0, 170.9, 149.1, 138.6, 134.8,
134.2, 131.5, 129.6, 128.5 (2C), 128.4, 128.3 (2C), 127.3, 127.1,
125.8, 124.2, 83.5, 67.2, 56.9, 41.3, 33.2, 29.5, 27.6 (3C). IR
(film): 1777, 1744, 1314, 1182 cm-1. Anal. (C26H28ClNO5)
C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-flu or op h en yl)p r op -2-en yl]-
p en ta n ed ioic a cid (18): 35% yield. Mp: 164-6 °C. [R]D
)
+2.4 (c 0.42, DMSO). 1H NMR (MeOH-d4-D2O-KOD): δ 7.45
(m, 2H), 7.10 (m, 2H), 6.50 (d, J ) 15.9 Hz, 1H), 6.22 (m, 1H),
3.22 (dd, J ) 4.4 and 9.3 Hz, 1H), 2.60-2.30 (m, 3H), 1.98 (m,
1H), 1.60 (m, 1H). 13C NMR (MeOH-d4-D2O-KOD): δ 185.0,
183.9, 162.8 (d, J ) 245 Hz, C-F), 134.8 (d, J ) 3 Hz), 131.0,
129.5, 128.7 (d, J ) 8.1 Hz), 116.4 (d, J ) 21.5 Hz), 55.8, 47.2,
(2S,4R,6E)-2-Am in o-4-[3-(3-ch lor op h en yl)p r op -2-en yl]-
39.4, 37.3. IR (KBr): 3410, 1705, 1586, 1508, 1231, 1208 cm-1
.
p en ta n ed ioic a cid (14): 50% yield. Mp: 146-8 °C. [R]D
)
1
Anal. (C14H16FNO4‚H2O) C, H, N.
+1.7 (c 0.41, DMSO). H NMR (D2O-KOD): δ 7.20-6.90 (m,
4H), 6.22-5.94 (m, 2H), 2.96 (d, J ) 4.3 and 9.2 Hz, 1H), 2.35-
2.15 (m, 3H), 1.70 (m, 1H), 1.32 (m, 1H). 13C NMR (D2O-
KOD): δ 184.3, 183.4, 140.0, 134.4, 130.8, 130.6, 130.3, 127.4,
126.3, 125.0, 55.3, 46.5, 38.9, 36.8. IR (KBr): 3450, 1698, 1593,
1481, 1203 cm-1. Anal. (C14H16ClNO4‚H2O) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-tr iflu or om eth ylp h en yl)p r op -
2-en yl]p en ta n ed ioic a cid (19): 43% yield. Mp: 166-8 °C.
[R]D ) +17.5 (c 0.83, DMSO). 1H NMR (MeOH-d4-D2O-
KOD): δ 7.62 (d, J ) 8.5 Hz, 2H), 7.54 (d, J ) 8.5 Hz, 2H),
6.53 (d, J ) 17.3 Hz, 1H), 6.40 (m, 1H), 3.22 (dd, J ) 4.8 and
9.3 Hz, 1H), 2.60-2.30 (m, 3H), 1.96 (m, 1H), 1.58 (m, 1H);
13C NMR (MeOH-d4-D2O-KOD): δ 185.0, 183.9, 142.3, 132.5,
130.9, 129.0 (c, J ) 31.7 Hz), 127.3, 126.5 (c, J ) 4 Hz), 125.3
(c, J ) 267 Hz, CF3), 55.8, 47.0, 39.4, 37.3. IR (KBr): 3410,
1705, 1586, 1327, 1169, 1124 cm-1. Anal. (C15H16F3NO4‚H2O)
C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-m et h ylt h iop h en yl)p r op -2-
en yl]p en ta n ed ioic a cid (20): 42% yield. Mp: 173-4 °C (dec).
[R]D ) +6.3 (c 0.52, DMSO). 1H NMR (MeOH-d4-KOD): δ 7.40
(d, J ) 8 Hz, 2H), 7.27 (d, J ) 8 Hz, 2H), 6.47 (d, J ) 16.0 Hz,
1H), 6.28 (dt, J ) 6.5 and 16.0 Hz, 1H), 3.22 (dd, J ) 4.2 and
9.1 Hz, 1H), 2.50 (s, 3H), 2.60-2.35 (m, 3H), 1.95 (m, 1H), 1.57
(m, 1H). 13C NMR (MeOH-d4-KOD): δ 185.0, 184.1, 137.3,
135.8, 131.4, 129.6, 127.8, 127.7, 55.9, 47.2, 39.5, 37.5, 15.9.
IR (KBr): 3410, 1705, 1586, 1497, 1445, 1208 cm-1. Anal.
(C15H19NO4S‚H2O) C, H, N.
Eth yl (2S,4R,E)-N-BOC-4-(4-ch lor ocin n am yl)pyr oglu ta-
m a te: 43% yield. EtOAc/hexane 1:6. Mp: 86-8 °C. [R]D
)
-30.8 (c 0.5, CHCl3). 1H NMR (CDCl3): δ 7.26 (s, 4H), 6.41
(dt, 1H, J ) 15.8 and 0.9 Hz, HCd), 6.11 (dt, 1H, J ) 15.8
and 7.0 Hz, HCd), 4.55 (dd, 1H, J ) 9.3 and 1.9 Hz, H-2),
4.23 (q, 2H, J ) 7.1 Hz, CO2CH2), 2.90-2.68 (m, 2H), 2.46-
1.97 (m, 3H), 1.50 (s, 9H, C(CH3)3), 1.29 (t, 3H, J ) 7.1 Hz,
CH2CH3). 13C NMR (CDCl3): δ 174.2, 171.2, 149.3, 135.3,
132.9, 131.7, 128.6 (2C), 127.3 (2C), 126.5, 83.6, 61.7, 57.0, 41.5,
33.4, 27.8 (3C), 27.7, 14.1. IR (film): 1779, 1720, 1315, 1149
cm-1. Anal. (C21H26ClNO5) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-ch lor op h en yl)p r op -2-en yl]-
p en ta n ed ioic a cid (15): 70% yield. Mp: 167-9 °C. [R]D
)
+7.8 (c 0.6, DMSO). 1H NMR (MeOH-d4-KOD): δ 7.30 and
7.19 (AA′BB′, 4H), 6.42-6.17 (m, 2H, HCd), 3.20 (dd, 1H,
J ) 9.5 and 3.7 Hz, H-2), 2.57-2.41 (m, 2H), 2.36-2.24 (m,
1H), 2.08-1.94 (m, 1H), 1.25-1.44 (m, 1H). 13C NMR:
δ
(2S,4R,E)-2-Am in o-4-[3-(4-isopr opylph en yl)pr op-2-en yl]-
(MeOH-d4-KOD) 184.1, 183.3, 137.9, 133.3, 131.2, 130.9, 129.5
(2C), 128.5 (2C), 56.5, 47.6, 40.6, 38.6. IR (KBr): 2999, 2924,
1697, 1585, 1491 cm-1. Anal. (C14H16ClNO4‚H2O) C, H, N.
Ben zyl (2S,4R,E)-N-BOC-4-(4-b r om ocin n a m yl)p yr o-
glu ta m a te: 58% yield. EtOAc/hexane 1:3. White solid. Mp:
p en ta n ed ioic a cid (21): 38% yield. Mp: 163-4 °C. [R]D
)
+2.2 (c 0.32, DMSO). 1H NMR (MeOH-d4-KOD): δ 7.37 (d,
J ) 8.1 Hz, 2H), 7.18 (d, J ) 8.1 Hz, 2H), 6.43 (d, J ) 15.9 Hz,
1H), 6.23 (dt, J ) 6.5 and 15.9 Hz, 1H), 3.21 (dd, J ) 3.9 and
9.3 Hz, 1H), 2.80 (sept, J ) 7 Hz, 1H), 2.60-2.25 (m, 3H), 1.95
(m, 3H), 1.57 (m, 3H). 13C NMR (MeOH-d4-KOD): δ 184.9,
184.0, 149.4, 136.3, 131.8, 129.0, 127.8, 127.2, 55.9, 47.3, 39.7,
37.6, 34.0.4, 24.4. IR (KBr): 3410, 1703, 1584, 1497, 1451, 1208
cm-1. Anal. (C17H23NO4‚H2O) C, H, N.
1
131-2 °C. [R]D ) - 27.5 (c 0.4, CHCl3). H NMR (CDCl3): δ
7.39 (d, J ) 8.5 Hz, 2H), 7.33 (s, 5H), 7.17 (d, J ) 8.5 Hz, 2H),
6.35 (d, J ) 16.0 Hz, 1H), 6.08 (dt, J ) 14.2 and 7.1 Hz, 1H),
5.18 (s, 2H), 4.57 (dd, J ) 1.8 and 9.3 Hz, 1H), 2.89-2.63 (m,
2H), 2.44-1.92 (m, 3H), 1.40 (s, 9H). 13C NMR (CDCl3): δ
174.1, 171.0, 149.2, 141.7, 135.8, 134.9, 131.6, 128.6, 128.5,
127.6, 126.6, 121.1, 83.7, 67.4, 57.0, 41.4, 27.7. IR (KBr): 1779,
1738, 1316, 1188 cm-1. Anal. (C26H28BrNO5) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-cya n op h en yl)p r op -2-en yl]-
p en ta n ed ioic a cid (22): 54% yield. Mp: 162-4 °C. [R]D
)
+1.43 (c 0.28, DMSO). 1H NMR (DMSO): δ 7.78 (d, J ) 8.5
Hz, 2H), 7.60 (d, J ) 8.5 Hz, 2H), 6.60-6.30 (m, 2H), 3.32 (m,
1H), 2.80 (m, 1H), 2.50 (m, 2H), 2.10 (m, 1H), 1.70 (m, 1H). IR
(KBr): 3410, 1694, 1605, 1576, 1414 cm-1. Anal. (C15H16N2O4‚
H2O) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-br om op h en yl)p r op -2-en yl]-
p en ta n ed ioic a cid (16): 21% yield. Mp: 158 °C (dec). [R]D
1
) +3.1 (c 0.65, DMSO). H NMR (D2O-KOD): δ 7.11 (d, J )
8.4 Hz, 2H), 6.94 (d, J ) 8.4 Hz, 2H), 6.06 (d, J ) 15.8 Hz,
1H), 5.90 (m, 1H), 3.40 (s, 3H), 2.80 (dd, J ) 4.4 and 9.0 Hz,
1H), 2.20-1.90 (m, 3H), 1.50 (m, 1H), 1.15 (m, 1H). 13C NMR
(MeOH-d4-D2O-KOD): δ 184.9, 184.0, 137.8.1, 132.7, 131.0,
130.8, 128.9, 121.3, 55.9, 47.1, 39.5, 37.4. IR (KBr): 3420, 1698,
1586, 1487 cm-1. Anal. (C14H16BrNO4‚H2O) C, H, N.
Ben zyl (2S,4R,E)-N-BOC-4-(4-m et h ylcin n a m yl)p yr o-
glu ta m a te: 35% yield. EtOAc/hexane 1:3. White solid. Mp:
88-9 °C. [R]D ) - 33.1 (c 0.9, CHCl3). 1H NMR (CDCl3): δ
7.33 (s, 5H), 7.21 (d, J ) 8.1 Hz, 2H), 7.09 (d, J ) 8.1 Hz, 2H),
Ben zyl (2S,4R,E)-N-BOC-4-(4-car boxym eth ylcin n am yl)-
p yr oglu ta m a te: 34% yield. EtOAc/hexane. Oil. [R]D ) -15.7
1
(c 4.0, CHCl3). H NMR (CDCl3): δ 7.97 (d, 2H, J ) 8.4 Hz),
7.38 (d, 2H, J ) 8.4 Hz), 6.45 (d, 1H, J ) 15.8, HCd), 6.25 (dt,
1H, J ) 15.8 and 6.9 Hz, HCd), 5.23 (AB system, 2H, J )
12.2 Hz, CH2Ph), 4.61 (dd, 1H, J ) 9.2 and 1.6 Hz, H-2), 3.91
(s, 3H), 2.87-2.71 (m, 2H), 2.48-2.02 (m, 3H), 1.42 (s, 9H,
C(CH3)3). 13C NMR (CDCl3): δ 174.1, 171.0, 166.8, 149.2, 141.3,
134.9, 129.8, 128.7, 128.6, 128.5, 126.0, 121.6, 83.6, 67.4, 57.0,
52.0, 41.4, 33.5, 27.7 (3C). Anal. (C23H29NO7) C, H, N.

Potent GluR5 Kainate Receptor Agonists
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10 1965
(2S,4R,E)-2-Am in o-4-[3-(4-ca r boxyp h en yl)p r op -2-en yl]-
113.4, 110.8, 57.4, 57.3, 55.6, 47.3, 38.4, 34.9. IR (KBr): 3420,
1705, 1586, 1516, 1264, 1138 cm-1. Anal. (C16H21NO6‚H2O)
C, H, N.
p en ta n ed ioic a cid (23): 29% yield. Mp: >200 °C. [R]D
)
1
+42.1 (c 0.21, 1 N HCl). H NMR (D2O-pyr-d5): δ 8.9 (d, J )
7.8 Hz, 2H), 7.56 (d, J ) 7.8 Hz, 2H), 6.68 (d, 15.8 Hz, 1H),
6.54 (dt, J ) 6.2 and 15.8 Hz, 1H), 4.18 (m, 1H), 3.10-2.20
(m, 5H); 13C NMR (D2O-pyr-d5): δ 184.4, 176.7, 176.6, 141.9,
136.9, 133.1, 131.6, 127.8, 126.2, 55.6, 47.1, 38.5, 34.9. IR
(KBr): 3420, 1698, 1609, 1586 cm-1. Anal. (C15H17NO6‚H2O)
C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(2,6-dich lor oph en yl)pr op-2-en yl]-
p en ta n ed ioic a cid (29): 45% yield. Mp: 184 °C. [R]D ) -16.0
1
(c 0.05, 1 N NaOH). H NMR (D2O-KOD): δ 7.08 (d, J ) 8.0
Hz, 2H), 6.86 (t, J ) 8.0 Hz, 1H), 6.12 (d, J ) 16.9 Hz, 1H),
5.88 (m, 1H), 2.91 (m, 1H), 2.40-2.00 (m, 3H), 1.64 (m, 1H),
1.33 (m, 1H). 13C NMR (D2O-pyr-d5): δ 138.6, 136.0,
135.6, 130.2, 130.1, 127.1, 55.5, 42.0, 39.0, 34.9. IR (KBr):
3410, 1705, 1586, 1504, 1429, 1208 cm-1. Anal. (C14H15Cl2NO4‚
H2O) C, H, N.
Ben zyl (2S,4R,E)-N-BOC-4-(4-n itr ocin n am yl)pyr oglu ta-
m a te: 52% yield. Colorless oil. [R]D ) -37.5 (c 0.2, CH2Cl2).
1H NMR (CDCl3): δ 8.16 (d, J ) 8.7 Hz, 2H), 7.45 (d, J ) 8.7
Hz, 2H), 7.35 (s, 5H), 6.50 (d, J ) 16.0 Hz, 1H), 6.34 (dt, J )
16.0 and 6.8 Hz, 1H), 5.20 (s, 2H), 4.61 (dd, J ) 1.6 and 7.8
Hz, 1H), 2.90-2.70 (m, 2H), 2.55-2.30 (m, 1H), 2.30-2.00 (m,
2H), 1.42 (s, 9H). 13C NMR (CDCl3): δ 173.5, 170.4, 150.4,
146.3, 143.0, 134.5, 130.8, 128.3, 128.2, 127.9, 127.7, 126.4,
123.6, 83.7, 67.1, 56.7, 40.9, 33.2, 27.9, 27.4. Anal. (C26H28N2O7)
C, H, N.
Ben zyl (2S,4R)-N-BOC-4-(3-p h en ylp r op -2-yn yl)p yr o-
glu ta m a te. To a mixture of iodobenzene (0.37 mL, 3.36 mmol)
and benzyl (2S,4R)-N-BOC-4-(prop-2-ynyl)pyroglutamate (see
below) (1 g, 2.80 mmol) in triethylamine (15 mL) was added
bis(triphenylphosphine)palladium dichloride (100 mg, 5%) and
copper iodide (33 mg, 2.5%). The reaction mixture was heated
at 70 °C under nitrogen atmosphere for 2.5 h. After this time
the solvent was evaporated and the residue chromatographed
using ethyl acetate/hexane (1:4) as eluent to yield 0.99 g, (82%)
as an oil. [R]D ) -26.5 (c 0.5, CDCl3). 1H NMR (CDCl3): δ 7.44
(s, 10H), 5.26 (AB system, 2H), 4.65 (m, 1H), 2.90 (m, 2H),
2.65 (m, 1H), 2.43 (m, 2H), 1.45 (s, 9H). 13C NMR (CDCl3): δ
173.2, 171.0, 149.2, 134.9, 131.6, 128.66, 128.63, 128.49,
128.21, 128.02, 123.05, 85.5, 83.8, 82.7, 67.4, 57.1, 41.0, 27.7,
27.6. Anal. (C26H27NO5) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(4-n itr oph en yl)pr op-2-en yl]pen -
ta n ed ioic a cid (24): 61% yield. Mp: 171-2 °C. [R]D ) +51.0
1
(c 1, 1 N HCl). H NMR (D2O-pyr-d5): δ 8.13 (d, J ) 7.6 Hz,
2H), 7.65 (d, J ) 7.6 Hz, 2H), 6.80 (m, 2H), 4.37 (m, 1H), 3.30-
2.50 (m, 5H). 13C NMR (D2O-pyr-d5): δ 184.1, 176.5, 147.7,
146.6, 136.0, 131.9, 128.8, 125.8, 55.8, 47.1, 38.7, 35.2. IR
(KBr): 3410, 1692, 1597, 1522, 1429, 1342 cm-1. Anal.
(C14H16N2O6‚H2O) C, H, N.
(2S,4R)-2-(Am in o)-4-(3-p h en ylp r op -2-yn yl)p en ta n ed io-
ic a cid (30): 71% yield. Mp: 164-6 °C. [R]D ) +13.9 (c 0.23,
(2S,4R,E)-2-Am in o-4-[3-(4-t r iflu or om et h oxyp h en yl)-
p r op -2-en yl]p en ta n ed ioic a cid (25): 54% yield. Mp: 168-9
1
DMSO). H NMR (D2O/KOD): δ 7.52-7.30 (m, 5H), 3.21 (dd,
1
°C. [R]D ) +2.0 (c 0.2, DMSO). H NMR (MeOH-d4-KOD): δ
J ) 2.8, 9.3 Hz, 1H), 2.60 (m, 2H), 2.00 (m, 2H), 1.70 (m, 1H).
13C NMR (DO2/KOD): δ 183.8, 183.7, 132.7, 129.7, 129.4,
124.0, 89.9, 82.8, 55.8, 46.4, 39.2, 23.8. IR (KBr): 3000, 1697,
1618, 1491, 1404, 1213 cm-1. Anal. (C14H17NO5) C, H, N.
7.49 (d, J ) 7.9 Hz, 2H), 7.28 (d, J ) 7.9 Hz, 2H), 6.51 (d, J )
15.9 Hz, 1H), 6.30 (m, 1H), 3.25 (dd, J ) 4.2 and 9.3 Hz, 1H),
2.65-2.37 (m, 3H), 1.98 (m, 1H), 1.60 (m, 1H). 13C NMR
(MeOH-d4-KOD): δ 184.9, 184.0, 148.8, 137.6, 130.8, 130.7,
128.5, 122.3, 121.4 (c, J ) 250 Hz, CF3), 55.9, 47.1, 39.5, 37.4,
34.0.4, 24.4. IR (KBr): 3410, 1705, 1584, 1508, 1275, 1219
cm-1. Anal. (C15H16F3NO5‚H2O) C, H, N.
Eth yl (2S,4R)-N-Boc-4-(3-ph en ylpr opyl)pyr oglu tam ate.
To a solution of ethyl (2S,4R,E)-N-BOC-4-cinnamylpyrogluta-
mate (500 mg, 1.34 mmol) in EtOAc (10 mL) was added PtO2
(30 mg) and the mixture was stirred under a hydrogen atmo-
sphere at room temperature overnight. The reaction mixture
was filtered through a pad of Celite and the solvent evapo-
rated. The crude was purified by chromatography (hexane/
ethyl acetate 4:1). 82% yield. Colorless oil. [R]D ) -26.6 (c 1,
(2S,4R,E)-2-Am in o-4-[3-(4-p h en ylp h en yl)p r op -2-en yl]-
p en ta n ed ioic a cid (26): 50% yield. Mp: 192-3 °C. [R]D
)
1
+13.4 (c 0.5, 1 N NaOH). H NMR (D2O-KOD): δ 7.55-7.10
(m, 9H), 6.35-5.94 (m, 2H), 2.95 (m, 1H), 2.32-2.00 (m, 3H),
1.70 (m, 1H), 1.32 (m, 1H). 13C NMR (D2O-KOD): δ 184.0,
183.0, 140.2, 139.2, 137.0, 130.5, 129.2, 127.7, 127.2, 126.8,
54.8, 46.2, 38.4, 36.4. IR (KBr): 3420, 1701, 1583, 1485, 1206
cm-1. Anal. (C20H21NO4‚H2O) C, H, N.
1
CHCl3). H NMR (CDCl3): δ 7.25-7.00 (m, 5H), 4.42 (dd, J )
1.4 and 9.5 Hz, 1H), 4.12 (c, J ) 7.1 Hz, 2H), 2.62-2.45 (m,
3H), 2.20-2.00 (m, 1H), 2.45-1.70 (m, 2H), 1.65-1.20 (m, 3H),
1.40 (s, 9H). 13C NMR (CDCl3): δ 174.6, 170.9, 149.0, 141.4,
128.0, 127.9, 125.4, 82.9, 61.2, 56.7, 41.1, 35.3, 29.6, 28.3, 28.0,
27.4, 13.8. Anal. (C21H29NO5) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(3,4-dich lor oph en yl)pr op-2-en yl]-
p en ta n ed ioic a cid (27): 60% yield. Mp: 145-6 °C. [R]D
)
+30.9 (c 0.42, DMSO). 1H NMR (MeOH-d4-D2O-KOD): δ
7.52-7.20 (m, 3H), 6.50-6.13 (m, 2H), 3.26 (dd, J ) 4.5 and
9.2 Hz, 1H), 2.60-2.30 (m, 3H), 1.98 (m, 1H), 1.58 (m, 1H).
13C NMR (MeOH-d4-D2O-KOD): δ 185.0, 183.9, 138.9, 132.6,
131.7, 131.3, 130.6, 129.9, 128.6, 126.6, 55.8, 47.0, 39.4, 37.3.
IR (KBr): 3436, 1696, 1588, 1474 cm-1. Anal. (C14H15Cl2NO4‚
H2O) C, H, N.
(2S,4R,E)-2-Am in o-4-(3-ph en ylpr opyl)pen tan edioic acid
h yd r och lor ic a cid (31): 67% yield. White hygroscopic solid.
1
[R]D ) +19.5 (c 1, MeOH). H NMR (MeOH-d4): δ 7.30-7.10
(m, 5H), 3.90 (dd, J ) 5.6 and 7.8 Hz, 1H), 2.75-2.55 (m, 3H),
2.42-2.20 (m, 1H), 1.95-1.80 (m, 1H), 1.80-1.50 (m, 4H). 13
C
NMR (MeOH-d4): δ 178.2, 172.2, 143.1, 129.4, 129.3, 126.8,
53.0, 42.5, 36.6, 33.4, 32.9, 29.8. IR (KBr): 3426, 1717, 1636,
1497 cm-1. Anal. (C14H19NO4.HCl) C, H, N.
Ben zyl (2S,4R,E)-N-BOC-4-(3,4-d im et h oxycin n a m yl)-
p yr oglu ta m a te: 46% yield. EtOAc/hexane 1:3. A pale yellow
Ben zyl (2S,4R,E)-N-Boc-4-(2-n aph th ylpr op-2-en yl)pyr o-
glu ta m a te: White solid. Mp: 137-8 °C. [R]D ) -24.0 (c 1,
CH2Cl2). 1H NMR (CDCl3): δ 7.90-7.25 (m, 12H), 6.60
(d, J ) 15.8 Hz, 1H), 6.23 (dt, J ) 15.8 and 7.1 Hz, 1H), 5.19
(s, 2H), 4.60 (dd, J ) 1.9 and 9.1 Hz, 1H), 2.95-2.70 (m, 2H),
2.55-2.30 (m, 1H), 2.30-2.00 (m, 2H), 1.42 (s, 9H). 13C NMR
(CDCl3): δ 174.3, 171.1, 149.3, 134.9, 134.3, 133.5, 133.1,
132.8, 128.7, 128.6, 128.5, 128.1, 127.8, 127.6, 126.2, 126.1,
125.8, 125.7, 123.4, 83.6, 67.4, 57.1, 41.6, 33.6, 27.8. Anal.
(C30H31NO5) C, H, N.
1
oil. [R]D ) - 28.0 (c 0.5, CHCl3). H NMR (CDCl3): δ 7.31 (s,
5H), 7.29-6.74 (m, 3H), 6.33 (d, J ) 15.8 Hz, 1H), 5.94 (dt,
J ) 14.5 and 7.2 Hz, 1H), 5.16 (s, 2H), 4.56 (dd, J ) 2.0 and
8.9 Hz, 1H), 3.86 (s, 3H), 3.83 (s, 3H), 2.90-2.61 (m, 2H),
2.45-1.98 (m, 3H), 1.38 (s, 9H). 13C NMR (CDCl3): δ 174.3,
171.0, 149.2, 148.9, 148.5, 134.9, 132.6, 129.9, 128.6, 128.4,
123.5, 119.1, 110.9, 108.2, 83.5, 67.3, 57.1, 55.7, 41.5, 33.3, 27.6.
IR (film): 1788, 1748, 1717, 1514, 1314, 1264, 1152 cm-1. Anal.
(C28H33NO7) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(3,4-d im eth oxyp h en yl)p r op -2-
en yl]p en ta n ed ioic a cid (28): 31% yield. Mp: 156-8 °C.
[R]D ) +35.3 (c 0.34, 1 N HCl). 1H NMR (D2O-KOD): δ 7.70-
6.45 (m, 3H), 5.96 (d, J ) 16.3 Hz, 1H), 5.81-5.63 (m, 1H),
3.41 (s, 3H), 3.39 (s, 3H), 2.75 (dd, J ) 4.1 and 10.0 Hz, 1H),
2.09-1.85 (m, 3H), 1.48 (m, 1H), 1.12 (m, 1H). 13C NMR (D2O-
pyr-d5): δ 184.5, 178.6, 150.2, 150.0 133.2, 132.9, 128.3, 121.4,
(2S,4R,E)-2-Am in o-4-[3-(2-n a p h t h yl)p r op -2-en yl]p en -
ta n ed ioic a cid (32): 77% yield. Mp: 194-5 °C. [R]D ) +4.6
(c 0.35, DMSO). 1H NMR (pyr-d5-D2O): δ 8.05-7.57 (m, 7H),
6.80 (d, J ) 15.9 Hz, 1H), 6.65 (m, 1H), 4.28 (dd, J ) 3.3 and
9.5 Hz, 1H), 3.15-2.35 (m, 5H). 13C NMR (pyr-d5-D2O): δ
184.3, 176.5, 137.0, 135.4, 134.5, 133.6, 130.7, 130.1, 129.8,
129.5, 128.4, 127.8, 127.6, 125.6, 55.7, 47.3, 38.6, 35.0. IR

1966 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10
Pedregal et al.
(KBr): 3420, 1703, 1584, 1497, 1208 cm-1. Anal. (C18H19 NO4‚
H2O) C, H, N.
Hz, 1H), 2.77 (m, 1H), 2.59 (m, 1H), 2.43 (m, 1H), 2.26 (m,
2H), 1.75 (t, J ) 2.5 Hz, 3H), 1.42 (s, 9H). 13C NMR (CDCl3):
δ 173.5, 171.1, 149.3, 135.1, 128.7, 128.6, 128.5, 83.7, 78.1, 74.7,
67.4, 57.1, 41.1, 27.8, 27.5, 19.7, 3.5. Anal. (C21H25NO5) C, H, N.
Ben zyl (2S,4R,E)-N-Boc-4-(1-n aph th ylpr op-2-en yl)pyr o-
glu t a m a t e: 53% yield. EtOAc/hexane 1:6. Mp: 96-8 °C.
[R]D ) -22.5 (c 0.2, CHCl3). 1H NMR (CDCl3): δ 8.07-7.98
(m, 1H), 7.81-7.69 (m, 2H), 7.51-7.21 (m, 10H), 7.12 (d, 1H,
J ) 15.5 Hz, HCd), 6.06 (dt, 1H, J ) 15.5 and 7.1 Hz, HCd),
5.16 (AB, 2H, CO2CH2), 4.57 (dd, 1H, J ) 9.4 and 1.7 Hz, H-2),
2.88-2.72 (m, 2H), 2.51-2.33 (m, 1H), 2.24-1.93 (m, 2H), 1.40
(s, 9H, C(CH3)3). 13C NMR (CDCl3): δ 173.9, 170.7, 148.9,
134.7, 134.4, 133.1, 130.6, 129.9, 128.8, 128.3 (2C), 128.2 (3C),
128.1, 127.4, 125.7, 125.4, 125.3, 83.1, 66.9, 56.8, 41.2, 33.5,
27.4 (3C), 27.3. IR (film): 1778, 1738, 1311, 1147 cm-1. Anal.
(C30H31NO5) C, H, N.
(2S,4R,E)-2-Am in o-4-[3-(1-n a p h t h yl)p r op -2-en yl]p en -
ta n ed ioic a cid (33): 40% yield. Mp: 150-1 °C. [R]D ) +12.0
(c 0.4, DMSO). 1H NMR (D2O-KOD): δ 7.57-7.49 (m, 1H),
7.29-7.13 (m, 2H), 7.03-6.81 (m, 4H), 6.56 (d, 1H, J ) 15.7
Hz, HCd), 5.71-5.56 (m, 1H, HCd), 2.64 (dd, 1H, J ) 9.5 and
4.3 Hz, H-2), 2.00-1.81 (m, 3H), 1.47-1.32 (m, 1H), 1.10-
0.93 (m, 1H). 13C NMR (D2O-MeOH-d4-KOD): δ 185.0, 184.1,
136.2, 134.4, 133.3, 131.7, 129.6, 129.1, 128.6, 127.5, 127.3,
125.0, 124.8, 56.0, 47.4, 39.8, 37.9. IR (KBr): 1697, 1585, 1487,
1203 cm-1. Anal. (C18H19NO4‚H2O) C, H, N.
Hyd r olysis of Acetylen ic Su bstitu ted P yr oglu ta m a tes.
To a solution of the corresponding pyroglutamate (1.1 mmol)
in tetrahydrofuran (10 mL) was added 1 M lithium hydroxide
(3.3 mL, 3.3 mmol) and the mixture stirred at ambient
temperature for 16 h. The reaction mixture was acidified to
pH 2 with 1 M hydrochloric acid and extracted three times
with diethyl ether. The combined ethereal extracts were dried
over magnesium sulfate, filtered, and evaporated in vacuo to
give (2S,4R)-2-(tert-butoxycarbonylamino)-4-(alken-2-yn-1-yl)
pentanedioic acid as a viscous oil. To a solution of this (400
mg) in moist diethyl ether (10 mL) was added, with ice-bath
cooling, trifluoroacetic acid (4 mL). The reaction mixture was
then stirred at ambient temperature for 4 h. The reaction
mixture was evaporated to dryness in vacuo, redissolved in
water, and azeotroped to remove excess trifluoroacetic acid.
The resulting white solid was purified by cation-exchange
chromatography (Dowex 50 × 8-100). The column was eluted
sequentially with water, water/THF 1:1, and water again, and
the amino acid was finally eluted with water/pyridine 9:1. The
pyridine was removed in vacuo and the residual solid redis-
solved in water and freeze-dried.
Alk yl Der iva tives (Ta ble 2). Ben zyl (2S,4R)-N-Boc-4-
(p r op -2-yn yl)p yr oglu ta m a te was prepared following the
general method for alkylation of pyroglutamates with allyl
bromide (see below). 34% Yield. Mp: 102-3 °C. [R]D ) -31.5
(2S,4R)-2-Am in o-4-(bu t-2-yn yl)p en ta n ed ioic a cid (36):
1
65% yield. Fluffy white solid. Mp: 120 °C. H NMR (D2O): δ
3.83 (dd, J ) 5.4 and 8.1 Hz, 1H), 2.74 (m, 1H), 2.53 (m, 2H),
2.33 (m, 1H), 2.06 (m, 1H), 1.78 (t, J ) 2.7 Hz, 3H). 13C NMR
(D2O): δ 181.4, 176.7, 82.4, 78.6, 55.9, 44.56, 34.47, 24.49, 5.36.
Anal. (C9H13NO4) C, H, N.
1
(c 1, CHCl3). H NMR (CDCl3): δ 7.33 (broad s, 5H), 5.16 (AB
system, 2H), 4.62 (m, 1H), 2.90-2.20 (m, 5H), 1.98 (t, J ) 2.7
Hz, 1H), 1.39 (s, 9H). 13C NMR (CDCl3): δ 172.9, 170.9, 149.1,
134.9, 128.64, 128.62, 128.4, 83.7, 79.9, 70.7, 67.4, 56.9, 40.6,
27.7, 27.3, 19.2 IR (KBr): 3280, 1790, 1744, 1311, 1215, 1148
cm-1. Anal. (C20H23NO5) C, H, N.
Ben zyl (2S,4R)-N-Boc-4-(p en t -2-yn yl)p yr oglu t a m a t e:
25% yield. 1H NMR (CDCl3): δ 7.33 (s, 5H), 5.20 (d, J )
12.1 Hz, 1H), 5.16 (d, J ) 12.1 Hz, 1H), 4.61 (t, J ) 5.2 Hz,
1H), 2.74 (m, 1H), 2.56 (m, 1H), 2.40 (m, 1H), 2.24 (m, 2H),
2.09 (m, 2H), 1.39 (s, 9H), 1.08 (t, J ) 8.2 Hz, 3H). 13C NMR
(CDCl3): δ 173.5, 171.2, 149.3, 135.1, 128.7, 128.6, 84.2,
83.6, 74.9, 67.4, 57.2, 41.2, 27.8, 27.4, 19.8, 14.1, 12.4. Anal.
(C22H27NO5) C, H, N.
(2S,4R)-2-Am in o-4-(p r op -2-yn yl)pen ta n ed ioic a cid (34):
1
32% yield. Mp: 164-5 °C. [R]D ) +16.7 (c 0.3, 1 N HCl). H
NMR (D2O-pyr-d5): δ 4.12 (dd, J ) 2.0 and 8.4 Hz, 1H), 3.00-
2.20 (m, 5H), 2.66 (t, J ) 2.4 Hz, 1H). 13C NMR (D2O-pyr-d5):
δ 183.4, 176.5, 84.6, 73.1, 55.4, 46.0, 34.4, 24.0. IR (KBr): 3100,
1697, 1622, 1505, 1406, 1215 cm-1. Anal. (C8H11NO4) C, H, N.
Ben zyl (2S,4S)-N-Boc-4-(p r op -2-yn yl)p yr oglu ta m a te:
20% Yield. Oil. [R]D ) +18.7 (c 0.48, CHCl3). 1H NMR
(CDCl3): δ 7.34 (broad s, 5H), 5.12 (s, 2H), 4.53 (dd, J ) 8.5,
7.3 Hz, 1H), 2.70-2.35 (m, 3H), 2.05-1.90 (m, 2H), 1.40 (s,
9H). 13C NMR (CDCl3): δ 173.0, 171.0, 149.1, 134.7, 128.64,
128.62, 128.5, 83.9, 80.2, 70.5, 67.3, 57.3, 41.7, 27.7, 26.5, 20.1.
IR (KBr): 3300, 1790, 1755, 1317, 1254, 1152 cm-1. Anal.
(C20H23NO5) C, H, N.
(2S,4R)-2-Am in o-4-(p en t-2-yn yl)p en ta n ed ioic a cid (37):
1
52% yield. Mp: 198-200 °C. H NMR (D2O): δ 3.17 (dd, J )
4.5 and 9.3 Hz, 1H), 2.44 (m, 1H), 2.30 (m, 2H), 2.13 (q, 2H),
1.88 (m, 1H), 1.59 (m, 1H), 1.05 (t, J ) 7.2 Hz, 3H). 13C NMR
(D2O): δ 185.8, 185.7, 87.4, 81.0, 57.6, 48.5, 40.8 25.0, 16.4,
14.6. Anal. (C10H15NO4) C, H, N.
Ben zyl (2S,4R)-N-Boc-4-(h ex-2-yn yl)pyr oglu tam ate: 14%
yield. 1H NMR (CDCl3): δ 7.33 (m, 5H), 5.23 (d, J ) 12 Hz,
1H), 5.19 (d, J ) 12 Hz, 1H), 4.64 (dd, J ) 4.2 and 7.8 Hz,
1H), 2.78 (m, 1H), 2.60 (m, 1H), 2.45 (m, 1H), 2.27 (m, 2H),
2.09 (m, 2H), 1.47 (m, 2H), 1.43 (s, 9H), 0.94 (t, J ) 7.5 Hz,
3H). 13C NMR (CDCl3): δ 173.5, 171.1, 149.1, 135.1, 128.7,
128.6, 128.4, 83.6 82.7, 75.7, 67.4, 57.1, 41.2, 27.4, 27.4, 22.3,
20.7, 19.9, 13.4. Anal. (C23H29NO5) C, H, N.
(2S,4R)-2-Am in o-4-(h ex-2-yn yl)p en ta n ed ioic a cid (38):
40% yield. Mp: 200-1 °C. 1H NMR (D2O): δ 3.16 (dd, J ) 4.8
and 9.3 Hz, 1H), 2.43 (m, 1H), 2.30 (m, 2H), 2.09 (m, 2H), 1.87
(m, 1H), 1.58 (m, 1H), 1.43 (m, 2H), 0.90 (t, J ) 7.5 Hz, 3H).
13C NMR (D2O): δ 185.8, 185.7, 86.0, 81.9, 57.6, 48.5, 40.9,
25.1, 24.7, 22.9, 15.8. Anal. (C11H17NO4) C, H, N.
Gen er a l P r oced u r e for Alk yla tion Rea ction s of Eth yl
or Ben zyl N-BOC P yr oglu ta m a te Ester s (4a , 4b) w ith
Allyl Br om id es. To a solution of the pyroglutamate (6.26
mmol) in dry tetrahydrofuran (30 mL) under argon was added
a 1 M solution of lithium hexamethyldisilazide in dry tetra-
hydrofuran (7.5 mL, 7.5 mmol) at -78 °C. After 1 h, this
solution was cannulated to a previously prepared solution of
the corresponding alkyl bromide (25 mmol) in 20 mL of dry
tetrahydrofuran at -78 °C, and stirring was continued for
2 h. The reaction mixture was quenched with saturated
ammonium chloride solution and extracted with dichloro-
methane. The organic phase was dried over anhydrous sodium
sulfate, filtered, and evaporated to dryness. The diastereomeric
mixture was evaporated and separated by flash column
chromatography.
(2S,4S)-2-Am in o-4-(p r op -2-yn yl)p en ta n ed ioic a cid (35):
37% yield. Mp: 167-8 °C. [R]D ) +10.0 (c 0.2, 1 N HCl).
1H NMR (D2O-pyr-d5): δ 3.92 (dd, J ) 5.3 and 8.4 Hz, 1H),
2.85 (m, 1H), 2.70 (m, 2H), 2.60 (m, 1H), 2.49-2.20 (m, 2H).
13C NMR (D2O-pyr-d5): δ 183.7, 177.1, 84.7, 73.2, 56.5,
47.3, 35.5, 24.2. IR (KBr): 3274, 1589, 1500, 1306 cm-1. Anal.
(C8H11NO4) C, H, N.
P r oced u r e for th e P r ep a r a tion of th e Acetylen ic
Am in o Acid s. To a solution of 4b (7.20 g, 22 mmol) in dry
tetrahydrofuran (70 mL) under positive nitrogen pressure, and
cooled to -78 °C in a dry ice/acetone bath, was added lithium
bis(trimethylsilyl)amide (25 mL of 1 M THF solution, 25
mmol). After stirring at -78 °C for 1 h, the reaction mixture
was rapidly cannulated under nitrogen pressure into a solution
of the corresponding alkynyl bromide (44 mmol) in dry
tetrahydrofuran (20 mL), also under positive nitrogen pressure
at -78 °C. The resulting mixture was then stirred at -78 °C
for 2 h. The reaction mixture was quenched at -78 °C with
saturated ammonium chloride solution and then extracted
three times with diethyl ether. The combined ethereal extracts
were dried over magnesium sulfate, filtered, and evaporated
in vacuo to give an oil. The crude oil was purified by flash
chromatography on silica (eluent hexane:diethyl ether 2:1).
Ben zyl (2S,4R)-N-BOC-4-(b u t -2yn yl)p yr oglu t a m a t e:
1
White solid. 22% yield. H NMR (CDCl3): δ 7.36 (s, 5H), 5.22
(d, J ) 12.1 Hz, 1H), 5.18 (d, J ) 12.1 Hz, 1H), 4.63 (t, J ) 5.4

Potent GluR5 Kainate Receptor Agonists
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 10 1967
E t h yl (2S,4R)-N-Boc-4-a llylp yr oglu t a m a t e: Hexane/
ethyl acetate: 4:1. Colorless oil. 34% yield. [R]D ) -31.6 (c
Gen er a l P r oced u r e for th e Hyd r ogen a tion of th e Acet-
ylen es to Z Olefin s. A solution of the acetylene amino acid
(0.75 mmol) in water (25 mL) was hydrogenated over Lindlar
catalyst (100 mg) at 8 psi in a Parr hydrogenation apparatus.
After 48 h the reaction mixture was filtered over diatomaceous
earth, and the filtrates were evaporated in vacuo to give the
product.
(2S,4R,Z)-2-Am in o-4-(bu t-2-en yl)p en ta n d ioic a cid (41):
80% yield. Mp: 200-2 °C. 1H NMR (D2O): δ 5.67 (m, 1H),
5.41 (m, 1H), 3.76 (dd, J ) 5.1 and 8.1 Hz, 1H), 2.62 (m, 1H),
2.41 (m, 2H), 2.26 (m, 1H), 1.96 (m, 1H), 1.62 (d, J ) 7.5 Hz,
3H). Anal. (C9H15NO4) C, H, N.
1
0.76, CH2Cl2). H NMR (CDCl3): δ 5.80-5.60 (m, 1H), 5.15-
5.00 (m, 2H), 4.52 (dd J ) 1.9 and 9.4 Hz, 1H), 4.20 (q, J )
7.1 Hz, 1H), 2.80-2.55 (m, 2H), 2.25-1.90 (m, 3H), 1.47 (s,
9H), 1.25 (t, J ) 7.1, 3H). 13C NMR (CDCl3): δ 174.4, 171.3,
149.4, 134.3, 117.7, 85.5, 61.6, 57.1, 41.1, 34.4, 27.8, 27.7, 14.1.
IR (film): 2980, 1748, 1717, 1319, 1254 cm-1. HRMS: calcd
for C15H23NO5 297.1576, found 297.1590.
(2S,4R)-2-Am in o-4-(p r op -2-en yl)p en ta n ed ioic a cid , h y-
d r och lor id e (39): 62% yield. White solid, mp 166-7 °C.
[R]D ) +4.5 (c 1.0, H2O). 1H NMR (D2O/MeOH-d4): δ 5.90-
5.70 (m, 1H), 5.20-5.00 (m, 2H), 3.70 (dd, J ) 2.0 and 7.0 Hz,
1H), 2.70 (m, 1H), 2.50-2.20 (m, 3H), 1.90 (m, 1H). 13C NMR
(D2O/MeOH-d4): δ 181.2, 175.0, 135.9, 118.4, 54.2, 43.8, 37.4,
(2S,4R,Z)-2-Am in o-4-[pen t-2-en yl]pen tan edioic acid (42):
1
72% yield. Mp: 250 °C (dec). H NMR (D2O): δ 5.54 (m, 1H),
5.35 (m, 1H), 3.7 (dd, J ) 3.1 and 8.7 Hz, 1H), 2.41-1.9
(m, 7H), 0.93 (t, J ) 7.5 Hz, 3H). 13C NMR (D2O): δ 185.8,
177.4, 137.3, 128.4, 56.2, 48.0, 35.5, 33.0, 22.9, 16.4. Anal.
(C10H17NO4) C, H, N.
33.0. IR (KBr): 3428-2920, 1697, 1655, 1616, 1342, 1228 cm-1
Anal. (C8H13 NO4.HCl) C, H, N.
.
E t h yl (2S,4S)-N-Boc-4-a llylp yr oglu t a m a t e: Hexane/
ethyl acetate: 4:1. Colorless oil. 16% yield. [R]D ) +1.20 (c
Ben zyl (2S,4R,E)-N-Boc-4-(3-ch lor op r op -2-en yl)p yr o-
glu t a m a t e. 3-Chloro-1-iodoprop-2(E/Z)-ene (made from
commercial available 1,3-dichloroprop-2(E/Z)-ene by reaction
with sodium iodide in acetone) was reacted with benzyl N-Boc-
4-pyroglutamate using the general procedure described above
for the preparation of acetylenic substituted pyroglutamates.
The mixture of 4R and 4S isomers (1:1) was separated by
chromatography on a silica column eluted with hexane/ether
(3:1). The first eluting 4R isomer was then recrystallized
from ether twice to give only the E isomer (mp: 109-110 °C,
yield 13%).
(2S,4R,E)-2-Am in o-4-(3-ch lor op r op -2-en yl)p en ta n d io-
ic a cid (45): 45% yield. 1H NMR (D2O): δ 6.13 (d, 1H, J )
13.3 Hz), 5.95 (m, 1H), 3.22 (dd, 1H, J ) 8.9 and 4.5 Hz),
2.27 (m, 3H), 1.93 (m, 1H), 1.55 (m, 1H). Anal. (C8H12ClNO4)
C, H, N.
1
2.44, CH2Cl2). H NMR (CDCl3): δ 5.85-5.60 (m, 1H), 5.15-
5.00 (m, 2H), 4.47 (dd J ) 6.8 and 8.8 Hz, 1H), 4.21 (q, J )
7.1 Hz, 1H), 2.70-2.55 (m, 2H), 2.55-2.38 (m, 1H), 2.30-2.10
(m, 1H), 1.80-1.60 (m, 1H), 1.48 (s, 9H), 1.28 (t, J ) 7.1, 3H).
13C NMR (CDCl3): δ 174.4, 171.3, 149.4, 117.4, 57.3, 41.9,
34.9, 27.6, 26.5, 13.9. IR (film): 2980, 1790, 1755, 1717, 1325,
1198 cm-1. HRMS: calcd for C15H23NO5 297.1576, found
297.1584.
(2S,4S)-2-Am in o-4-(p r op -2-en yl)p en ta n ed ioic a cid , h y-
d r och lor id e (40): 24% yield. White solid. Mp 140-2 °C.
1
[R]D ) +14.0 (c 1.0, H2O). H NMR (D2O/MeOH-d4): δ 5.90-
5.70 (m, 1H), 5.20-5.00 (m, 2H), 3.65 (t, J ) 7.3 Hz, 1H), 2.70
(m, 1H), 2.36 (t, J ) 6.8 Hz, 2H), 2.00 (t, J ) 6.8 Hz, 2H). 13C
NMR (D2O/MeOH-d4): δ 179.9, 174.6, 135.5, 118.5, 54.3, 43.5,
37.3, 33.5. IR (KBr): 3430-2920, 1717, 1642, 1522 cm-1. Anal.
(C8H13NO4‚HCl) C, H, N.
Eth yl (2S,4R)-N-Boc-4-p r op ylp yr oglu ta m a te: Colorless
1
oil. 99% yield. [R]D ) -30.0 (c 1.0, CHCl3). H NMR (CDCl3):
Eth yl (2S,4R,E)-N-Boc-4-(bu t-2-en yl)pyr oglu tam ate con-
taminated with the Z isomer: 66% yield. EtOAc/hexane 1:4.
[R]D ) -37.9 (c 1.0, CHCl3). 1H NMR (CDCl3): δ 5.61-5.26
(m, 2H, HCd), 4.54 (dd, 1H, J ) 9.3 and 2.1 Hz, H-2), 4.23 (q,
2H, J ) 7.1 Hz, CO2CH2), 2.77-2.49 (m, 2H), 2.23-1.92 (m,
3H), 1.65 (dq, 3H, J ) 6.2 and 1.1 Hz, CHCH3), 1.50 (s, 9H,
C(CH3)3), 1.29 (t, 3H, J ) 7.1 Hz, CH2CH3). 13C NMR (CDCl3):
δ 174.5, 171.1, 149.1, 128.2, 126.4, 83.1, 61.4, 56.9, 41.3, 32.9,
27.6 (3C), 27.4, 17.4, 13.9. IR (film): 1794, 1747, 1716, 1315,
1153 cm-1. HRMS: calcd for C16H25NO5 311.1733, found
311.1739.
δ 4.52 (dd, J ) 1.7 and 9.5 Hz, 1H), 4.21 (q, J ) 7.1 Hz, 2H),
2.65 (m, 1H), 2.30-2.10 (m, 1H), 2.05-1.70 (m, 2H), 1.62 (bs,
1H), 1.47 (s, 9H), 1.30 (m, 2H), 1.27 (t, J ) 7.1 Hz, 3H), 0.90
(t, J ) 7.6 Hz, 3H). 13C NMR (CDCl3): δ 175.2, 171.2, 149.4,
83.2, 61.5, 57.0, 41.3, 32.3, 28.4, 27.7, 20.0, 14.0, 13.8. IR
(film): 2990, 1794, 1748, 1719, 1316, 1188, 1153 cm-1
HRMS: calcd for C15H25NO5 299.1733, found 299.1739.
.
(2S,4R)-2-Am in o-4-p r op ylp en t a n ed ioic a cid h yd r o-
ch lor id e (46): 83% yield. White solid. Mp: 188-9 °C. [R]D
)
+21.0 (c 1.0, MeOH). 1H NMR (MeOH-d4): δ 3.97 (dd,
J ) 5.6 and 8.3 Hz, 1H), 2.63 (m, 1H), 2.32 (m, 1H), 1.89 (m,
1H), 1.63 (m, 2H), 1.39 (m, 2H), 0.95 (t, J ) 7.15 Hz, 3H). 13C
NMR (MeOH-d4): δ 178.1, 171.6, 52.6, 42.3, 35.5, 33.3, 21.0,
14.3. IR (KBr): 3453, 2998, 1740, 1491, 1217 cm-1. Anal.
(C8H15NO4.HCl) C, H, N.
(2S,4R,E)-2-Am in o-4-(bu t-2-en yl)pen tan edioic acid (43):
51% yield. Mp: 149-150 °C. [R]D ) +14.9 (c 0.85, DMSO). 1H
NMR (MeOH-d4-KOD): δ 5.47-5.42 (m, 2H, HCd), 3.24-
3.21 (m, 1H, H-2), 2.38-2.22 (m, 2H), 2.09-1.90 (m, 2H), 1.60
(d, 3H, J ) 4.6 Hz, CHCH3), 1.57-1.45 (m, 1H). 13C NMR
(MeOH-d4-KOD): δ 184.3, 182.7, 131.0, 130.2 (Z isomer),
126.8, 125.4 (Z isomer), 56.5, 47.5, 40.4, 38.1, 32.3 (Z isomer),
Gen er a l P r oced u r e for th e Hyd r ogen a tion of th e
Acetylen es to Alk a n es. A solution of acetylenic amino acid
(0.22 mmol) in water (30 mL) was hydrogenated over 10%
16.1, 13.1 (Z isomer). IR (KBr): 1705, 1603, 1581, 1213 cm-1
.
palladium/charcoal catalyst (20 mg) at 6 psi in
a Parr
Eth yl (2S,4R,E)-N-Boc-4-(p en t-2-en yl)p yr oglu ta m a te:
45% yield. 1H NMR (CDCl3): δ 5.50 (dt, 1H, J ) 15.4 and
6.2 Hz, HCd), 5.27 (dt, 1H, J ) 15.4 and 6.9 Hz, HCd), 4.49
(dd, 1H, J ) 9.5 and 1.8 Hz, H-2), 4.18 (q, 2H, J ) 7.1 Hz,
CO2CH2), 2.68-2.46 (m, 2H), 2.15-1.84 (m, 5H), 1.46 (s, 9H,
C(CH3)3), 1.25 (t, 3H, J ) 7.1 Hz, CH2CH3), 0.92 (t, 3H, J )
7.7 Hz, CH2CH3). 13C NMR (CDCl3): δ 174.2, 170.9, 149.1,
135.2, 124.0, 83.0, 61.2, 56.8, 41.3, 32.8, 27.5 (3C), 27.3, 25.1,
13.8, 13.4. EIMS m/e: 325 (M+, 0.3), 225 (26), 196 (10), 157
(100), 140 (10), 84 (14), 57 (65). HRMS: calcd for C17H27NO5
325.1889, found 325.1890.
hydrogenation apparatus. After 2 h the reaction mixture was
filtered over diatomaceous earth, and the filtrates were
evaporated in vacuo to give the product.
(2S,4R)-2-Am in o-4-p en tylp en ta n ed ioic a cid (47): 20%
1
yield. Mp: 160-1 °C. H NMR (D2O): δ 3.74 (dd, J ) 4.8 and
8.7 Hz, 1H), 2.56 (m, 1H), 2.24 (m,1H), 1.94 (m, 1H), 1.61 (m,
2H), 1.32 (m, 6H), 0.89 (t, 3H). 13C NMR (D2O): δ 184.0, 177.0,
56.2, 45.9, 35.5, 34.9, 33.7, 28.7, 24.6, 16.1. Anal. (C10H19NO4)
C, H, N.
(2S,4R)-2-Am in o-4-h exylp en ta n ed ioic a cid (48): 88%
1
yield. Mp: 194-6 °C. H NMR (D2O): δ 3.13 (dd, J ) 4.4 and
(2S,4R,E)-2-Am in o-4-(p en t -2-en yl)p en t a n ed ioic a cid
1
8.8 Hz, 1H), 2.29 (m, 1H), 1.84 (m, 1H), 1.48 (m, 1H), 1.48
(m, 2H), 1.24 (m, 8H), 0.83 (t, 3H). 13C NMR (D2O): δ 188.2,
186.0, 57.8, 49.1, 42.0, 35.9, 34.0, 31.5, 30.0, 25.0, 16.4. Anal.
(C11H21NO4) C, H, N.
(44): 30% yield. Mp: 153 °C. [R]D ) +5.5 (c 0.18, DMSO). H
NMR (D2O-KOD): δ 5.15 (dt, 1H, J ) 15.2 and 6.5 Hz, HCd),
4.96 (dt, 1H, J ) 15.2 and 6.3 Hz, HCd), 2.71 (dd, 1H, J ) 9.2
and 4.5 Hz, H-2), 1.98-1.81 (m, 1H), 1.73-1.34 (m, 5H), 1.06
(ddd, 1H, J ) 14.1, 9.6 and 5.3 Hz), 0.48 (t, 3H, J ) 7.4 Hz,
CH2CH3). 13C NMR (D2O-MeOH-d4-KOD): δ 185.4, 184.3,
135.8, 127.6, 55.9, 47.5, 39.5, 37.1, 26.2, 14.4. IR (KBr): 1701,
1585, 1485, 1206 cm-1. Anal. (C10H17NO4) C, H, N.
Eth yl (2S,4R)-N-Boc-4-(3-m eth ylbu t-2-en yl)p yr oglu ta -
m a te: 70% Yield. Oil. EtOAc/hexane 1:3. 1H NMR (CDCl3):
δ 5.10-5.01 (m, 1H, HCdC), 4.53 (dd, 1H, J ) 9.4 and 1.9 Hz,
H-2), 4.22 (q, 2H, J ) 7.1 Hz, CO2CH2), 2.76-2.46 (m, 2H),

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Evaluation in Cells Stably Expressing the Kainate Receptor
humGluR6. J . Med. Chem. 1996, 39, 3617-3624.
(21) Ezquerra, J .; Pedregal, C.; Rubio, A.; Yruretagoyena, B.;
Escribano, A.; Sa´nchez-Ferrando, F. Stereoselective Reactions
of Lithium Enolates Derived from N-Boc Protected Pyro-
glutamic Esters. Tetrahedron 1993, 49, 8665-8678.
(22) Kamboj, R. K.; Elliot, C.; Nutt, S. L. Amino-Hydroxy Methyl
Isoxazole-Propionate Binding to Human Glutamate Receptors.
Eur. Pat. Appl. 1993, 93304500.7.
(23) Fletcher, E. J .; Nutt, S. L.; Hoo, K. H.; Elliot, C. E.; Korczack,
B.; McWhinnie, E. A.; Kamboj, R. K. Cloning, Expression
and Pharmacological Characterization of a Human Glutamate
Receptor: hGluR4. Recept. Channels 1995, 3, 21-31.
(24) Hamill, O.; Marty, E.; Neher, E.; Sakmann, B.; Sigworth, F. An
Improved Method for High-Resolution Current Recordings from
Cells and Cell Free Patches. Pfugers Arch. 1981, 391, 85-100.
(25) Bleakman, D.; Schoepp, D. D.; Ballyk, B.; Bufton, H.; Sharpe,
E. F.; Thomas, K.; Ornstein, P. L.; Kamboj, R. K. Pharmacologi-
cal Discrimination of GluR5 and GluR6 Kainate Receptor
Subtypes by LY293558. Mol. Pharmacol. 1996, 49, 581-585.
2.24-1.87 (m, 3H), 1.69 (d, 3H, J ) 1.1 Hz, CH3), 1.61 (d, 3H,
J ) 0.8 Hz, CH3), 1.50 (s, 9H, C(CH3)3), 1.32 (t, 3H, J ) 7.1
Hz, CH2CH3). 13C NMR (CDCl3): δ 174.6, 171.3, 149.3, 134.6,
119.6, 83.2, 61.5, 56.9, 41.8, 28.2, 27.7 (3C), 27.6, 25.6, 17.7,
14.1. IR (film): 1794, 1747, 1718, 1317, 1155 cm-1. HRMS:
calcd for C17H27NO5 325.1889, found 325.1893.
Gen er a l P r oced u r e for th e Dep r otection of Com -
p ou n d s w ith Br a n ch ed Alk en yl Ch a in s. The N-BOC
protected pyroglutamate was heated neat to 150 °C under
nitrogen for up to 10 h or until the reaction was complete by
TLC. (It was found that the use of higher temperatures (185
°C) led to some epimerization of the 2S,4R isomers.) The
pyroglutamate was then hydrolyzed using 2 M aqueous sodium
hydroxide solution under nitrogen. It was found that reaction
times and temperature had to be varied for the different
substrates. Varying degrees of epimerization were observed
which could be reduced by stopping the reaction before
competion and separating the amino acid from the lactam acid
by ion exchange chromatography using Dowex 50 × 8-100
resin as described earlier. The lactam acid eluted from the
column with the THF-water wash.
(2S,4R)-2-Am in o-4-(3-m et h ylb u t -2-en yl)p en t a n ed ioic
a cid (49): Mp: >250 °C dec contained 33% of the 4-epimer
after hydrolysis for 2 days at 100 °C in 2 M aqueous sodium
hydroxide. 1H NMR (D2O): δ 5.16 (bt, 1H), 3.18 (m, 1H), 2.34-
2.16 (m, 2H), 1.89 (m, 1H), 1.77-1.66 (m, 1H), 1.69 (s, 3H),
1.62 (s, 3H), 1.57-1.48 (m, 1H). Anal. (C11H21NO4) C, H, N.
Ben zyl (2S,4S)-N-Boc-4-(2-ch lor opr op-2-en yl)pyr oglu ta-
1
m a te: 35% yield. Oil. H NMR (CDCl3): δ 7.18 (m, 10H, Ph),
5.10 (AB, 4H, OCH2), 5.18 (s, 2H), 5.01 (s, 2H), 4.58 (m, 2H,
H-2), 2.95 (m, 4H), 2.45 (m, 1H), 2.35 (m, 3H), 2.02 (m, 1H),
1.65 (m, 1H), 1.46 (s, 9H, C(CH3)3), 1.43 (s, 9H, C(CH3)3).
HRMS: calcd for C20H24ClNO5 393.1343, found 393.1340.
(2S,4S)-2-Am in o-4-(2-ch lor op r op -2-en yl)p en t a n ed io-
1
ic a cid (50): 30% yield. Mp: >250 °C dec. H NMR (D2O): δ
5.28 (s, 2H), 3.75 (m, 1H), 3.02-2.89 (m, 1H), 2.71 (m, 1H),
2.62 (m, 1H), 2.28-1.88 (m, 2H). Anal. (C8H12ClNO4) C, H, N.
(2S,4R,E)-2-Am in o-4-(2-m et h yl-3-p h en ylp r op -2-en yl)-
p en ta n ed ioic a cid (51): 48% yield. Mp: 138-140 C. [R]D
)
-14.8 (c 0.45, DMSO). 1H NMR (D2O-KOD): δ 7.06-6.83
(m, 5H, Ph), 5.95 (s, 1H, HCd), 2.81 (dd, 1H, J ) 10.5 and 4.1
Hz, H-2), 2.34-2.18 (m, 1H), 2.08-1.84 (m, 2H), 1.61-1.47
(m, 1H), 1.47 (s, 3H, CH3), 1.22-1.08 (m, 1H). 13C NMR (D2O-
MeOH-d4-KOD): δ 185.0, 183.9, 139.4, 139.0, 130.0 (2C),
129.4 (2C), 127.4, 127.1, 56.1, 45.9, 45.6, 39.9, 16.3. IR (KBr):
3022, 2926, 1695, 1581, 1489 cm-1. Anal. (C16H23NO4) C, H, N.
Su p p or tin g In for m a tion Ava ila ble: Detailed analytical
data for the compounds discussed. This material is available
free of charge via the Internet at http://pubs.acs.org.
Refer en ces
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(5) For a review, see: Bleakman, D.; Lodge, D. Neuropharmacology
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Neuron 1990, 5, 583-595.
(7) Egebjerg, J .; Bettler, B.; Hermans-Bogemeyer, I.; Heinemann,
S. Cloning of a cDNA for
a Glutamate Receptor Subunit
Activated by Kainate but not by AMPA. Nature 1991, 351, 745-
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