Structural determinants for AMPA agonist activity of aryl or heteroaryl substituted AMPA analogues. Synthesis and pharmacology

Article abstract of DOI:10.1002/1521-4184(200102)334:2<62::AID-ARDP62>3.0.CO;2-G

We have previously reported the synthesis and pharmacological characterization of analogues of 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA, 1a), in which the methyl group was replaced by a phenyl group (APPA, 1b) or heteroaryl groups. While 2b and its 3-pyridyl analogue 2-amino-3-[3-hydroxy-5-(3-pyridyl)-4-isoxazolyl]propionic acid (3-Py-AMPA, 3) show very low affinity for AMPA receptors, introduction of heteroaryl substituents containing heteroatom in the 2-position provides potent AMPA receptor agonists. We here report the synthesis and pharmacology of 2-amino-3-(3-hydroxy-5-pyrazinyl-4-isoxazolyl)propionic acid (7) (IC₅₀ = 1.2 μM; EC₅₀ = 11 μM), which is weaker as an AMPA agonist than AMPA (IC₅₀ = 0.040 μM; EC₅₀ = 3.5 μM) but comparable in potency with 2-Py-AMPA (4) (IC₅₀ = 0.57 μM; EC₅₀ = 7.4 μM), as determined in radioligand binding and electrophysiological experiments, respectively. The AMPA analogues 8a-c, containing 2-, 3-, or 4-methoxyphenyl substituents, respectively, and the corresponding hydroxyphenyl analogues, 9a-c, were also synthesized and evaluated pharmacologically. With the exception of 2-amino-3-[3-hydroxy-5-(2-hydroxyphenyl)-4-isoxazolyl]propionic acid (9a), which is a very weak AMPA agonist (IC₅₀ = 45 μM; EC₅₀ = 324 μM), none of these compounds showed detectable effect at AMPA receptors.

Full text of DOI:10.1002/1521-4184(200102)334:2<62::AID-ARDP62>3.0.CO;2-G

62
Krogsgaard-Larsen and co-workers
Structural Determinants for AMPA Agonist Activity of Aryl or
Heteroaryl Substituted AMPA Analogues. Synthesis and Pharmacology
Ulrik S. Sørensen, Erik Falch, Tine B. Stensbøl, Jerzy W. Jaroszewski, Ulf Madsen, and Povl Krogsgaard-Larsen*
Center for Drug Design and Transport and Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, 2 Universitetsparken,
DK-2100 Copenhagen, Denmark
Key Words: AMPA receptor agonists; aryl AMPA analogues; pyrazinyl-AMPA; radioligand binding;
cortical wedge electrophysiology
[12]
manner , and an important step towards design of AMPA
receptor agonists and conversion of such agonists into
antagonists on a rational basis is detailed mapping of the
structural determinants of AMPA receptor-ligand interac-
tions.
AMPA analogues containing aromatic or heteroaromatic
rings in the 5-position of the 3-isoxazolol ring show very
distinct structure-activity relationships. 2-Amino-3-(3-hy-
droxy-5-phenyl-4-isoxazolyl)propionic acid (APPA, 1b)
Summary
We have previously reported the synthesis and pharmacological
characterization of analogues of 2-amino-3-(3-hydroxy-5-methyl-
4-isoxazolyl)propionic acid (AMPA, 1a), in which the methyl
group was replaced by a phenyl group (APPA, 1b) or heteroaryl
groups. While 2b and its 3-pyridyl analogue 2-amino-3-[3-hy-
droxy-5-(3-pyridyl)-4-isoxazolyl]propionic acid (3-Py-AMPA, 3)
show very low affinity for AMPA receptors, introduction of het-
eroaryl substituents containing heteroatom in the 2-position pro-
vides potent AMPA receptor agonists. We here report the synthesis
and pharmacology of 2-amino-3-(3-hydroxy-5-pyrazinyl-4-isoxa-
zolyl)propionic acid (7) (IC50 = 1.2 µM; EC50 = 11 µM), which is
weaker as an AMPA agonist than AMPA (IC50 = 0.040 µM; EC50
= 3.5 µM) but comparable in potency with 2-Py-AMPA (4) (IC50
= 0.57 µM; EC50 = 7.4 µM), as determined in radioligand binding
and electrophysiological experiments, respectively. The AMPA
analogues 8a–c, containing 2-, 3-, or 4-methoxyphenyl substit-
uents, respectively, and the corresponding hydroxyphenyl ana-
logues, 9a–c, were also synthesized and evaluated
pharmacologically. With the exception of 2-amino-3-[3-hydroxy-
5-(2-hydroxyphenyl)-4-isoxazolyl]propionic acid (9a), which is a
very weak AMPA agonist (IC50 = 45 µM; EC50 = 324 µM), none
of these compounds showed detectable effect at AMPA receptors.
binds to AMPA receptors with an affinity much lower than
[13,14]
that of AMPA (1a)
, and its 3-pyridyl analogue 3 is
[15]
essentially inactive . On the other hand, the 2-pyridyl
[15,16]
analogue 4 is a very potent AMPA agonist
, and whereas
2-amino-3-[3-hydroxy-5-(2-methyl-2H-5-tetrazolyl)-4-isox-
azolyl]propionic acid (2-Me-Tet-AMPA, 5) is the most po-
tent AMPA agonist so far described, the isomeric compound,
[17,18]
1-Me-Tet-AMPA (6) is almost inactive
. The AMPA
analogue with an oxygen-containing heterocyclic ring in the
5-position of the 3-isoxazolol ring, 2-amino-3-[5-(2-furyl)-3-
hydroxy-4-isoxazolyl]propionic acid (2-Fu-AMPA, 2) is
[15]
only slightly weaker than 5 as an AMPA agonist
.
The molecular basis for this structure-activity relationship
is as yet unclear, but electrostatic as well as steric effects of
the 5-substituents of these compounds obviously are impor-
tant structural determinants of AMPA agonist activity. In
order to shed further light on these aspects, we now report the
synthesis and pharmacological characterization of com-
pounds 7, 8a–c, and 9a–c.
Introduction
The excitatory neurotransmitter glutamic acid (Glu) stimu-
lates central neurones by activation of a large number of
receptors, subdivided into three heterogeneous classes of
ionotropic receptors named N-methyl-D-aspartic acid
Chemistry
A key step in the synthetic sequences was the formation of
the 3-isoxazolol ring (Scheme 1). The most frequently used
(NMDA), 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)-
[1–3]
propionic acid (AMPA), and kainic acid receptors
number of subtypes of metabotropic receptors
, and a route to 3-isoxazolols is cyclization of β-ketoesters with
[3,4]
[19–22]
. These hydroxylamine
. Thus, β-ketoesters 11a–c, synthesized
receptors or perhaps their distinct subtypes may be implicated from 10a–c and methyl propionate in a Claisen condensation
in certain neurological and psychiatric diseases and are po- reaction, were cyclized with hydroxylamine to form the 3-
[3–6]
tential therapeutic targets in such diseases
.
isoxazolol derivatives 12a–c. In addition to the desired prod-
There is accumulating evidence of a role of AMPA recep- uct (41–57% yields), these cyclizations give rise to a major
[7–
tors in the mechanisms associated with cognitive functions
by-product, the isomeric 5-isoxazolone/5-isoxazolol (5–15%
9]
[19–22]
, and enhancement of AMPA receptor functions has been yields)
. The crude reaction products were subjected to
. Although column chromatography (CC), and only the desired products
AMPA receptor agonists may not be therapeutically useful 12a–c were isolated. The structures of these 3-isoxazolols
[3,10,11]
shown to facilitate learning and memory
1
13
due to potential toxicity, these observations have focused were unequivocally established on the basis of H and
C
interest on the molecular mechanisms of receptor activation, NMR spectroscopic and thin layer chromatographic (TLC)
[15,17,19–22]
and thus on the structural basis of AMPA receptor-agonist analyses as described previously
interactions. Different structural classes of receptor agonists The next step in the synthetic sequences was protection of
may interact with the AMPA recognition site(s) in a different the hydroxy groups of 12a–c. In alkylation as well as acyla-
.
Arch. Pharm. Pharm. Med. Chem.
© WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0365-6233/01/0202/0062 $17.50 +.50/0

Agonist Activity of AMPA Analogues
63
Scheme 2
Scheme 1
tion reactions, derivatization normally takes place with both
tautomeric forms of the 3-isoxazolol/3-isoxazolone units,
[23,24]
resulting in mixtures of O- and N-protected products
.
In this case, the pivaloyl (Piv) group turned out to be suitable
for preferential O-acylation (Scheme 1). This acyl group was
easily introduced to give very good (13a,c) or moderate (13b)
yields of O-protected product. Bromination of 13a–c was
accomplished using NBS in refluxing CCl , and the products
4
14a–c were obtained in 61–96% yields after CC. Treatment
of 14a–c with dimethyl acetylaminomalonate (DMAA), us-
ing sodium hydride in DMF, yielded the protected 3-isox-
azolol aminoacids15a–c. Deprotection using4 M hydrochlo-
ric acid provided the final products 8a–c, isolated as zwitter-
ions. Complete deprotection of 15a–c to give the amino acids
9a–c required treatment with 62% hydrobromic acid in order
to cleave the methoxy groups, followed by reflux of the
reaction products in 4 M hydrochloric acid in order to fully
deprotect the amino acid side chains to give 9a–c, isolated as
zwitterions.
The target compound 7 was synthesized following a similar
reaction sequence (Scheme 2), although the presence of the
pyrazinyl group generally resulted in markedly lower yields.
(3-Hydroxy-4-methyl-5-isoxazolyl)pyrazine, synthesized by
treatment of β-ketoester 17 with hydroxylamine could not be
isolated by extraction from aqueous solution. Consequently,
the evaporated crude reaction product was dissolved in DMF
and treated with Piv chloride and triethylamine (TEA) to give
18. Due to apparent instability, the brominated intermediate
Figure 1
by treatment with DMAA under conditions described above
to give 20, which was deprotected to give 7. After several
unsuccessful attempts to crystallize 7 as a zwitterion or as a
halide salt, oily 7 was finally isolated by preparative TLC
19 could not be purified, and crude 19 was converted into 20 followed by anion exchange chromatography.
Arch. Pharm. Pharm. Med. Chem. 334, 62–68 (2001)

64
Krogsgaard-Larsen and co-workers
Table 1. Receptor binding and electrophysiological data.
—————————————————————————————————————————————————————————————–
Receptor Binding (IC50, µM)
——————————————————————————
Electrophysiology
Compound
R
[3H]AMPA [3H]Kainic acid [3H]CPP
(EC50, µM)
—————————————————————————————————————————————————————————————–
1a (AMPA)
Me
0.040a)
35a)
>100b)
0.57b)
0.030c)
54c)
1.2±0.4
>100
>100a)
>100a)
>100b)
>100b)
41c)
>100c)
22c)
100a)
>100a)
>100b)
>100b)
>100c)
>100c)
n.d.
3.5a)
385a)
>1000b)
7.4b)
0.92c)
>1000c)
11±1
>1000
1b (APPA)
Ph
3 (3-Py-AMPA)
3-Pyridyl
2-Pyridyl
2-Me-5-tetrazolyl
1-Me-5-tetrazolyl
Pyrazinyl
2-MeO-Ph
3-MeO-Ph
4-MeO-Ph
2-HO-Ph
3-HO-Ph
4-HO-Ph
4 (2-Py-AMPA)
5 (2-Me-Tet-AMPA)
6 (1-Me-Tet-AMPA)
7
8a
8b
8c
9a
9b
9c
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>1000
1000
>100
45±9
>100
324±31
>100
>100
>100
>1000
>1000
>100
—————————————————————————————————————————————————————————————–
a) Data from Ebert et al. [14]; b) Data from Falch et al. [15]; c) Data from Bang-Andersen et al. [17]; d) Only one determination.
[15,16]
As exemplified by 2-Py-AMPA (4)
AMPA (5)
, 2-Me-Tet-
Results and Discussion
[17,18]
[15]
, and 2-Fu-AMPA (2) , substitution of
heterocyclic rings containing one or two heteroatoms in 2-po-
The target amino acids 7, 8a–c, and 9a–c were pharma-
sition for the phenyl group of the weak AMPA receptor ligand
cologically characterized in receptor binding assays using the
[13,14]
3
[25]
3
APPA (1b)
has been shown to markedly enhance
radioligands [ H]-AMPA , [ H]-3-(2-carboxy-4-piperaz-
3
[26]
3
AMPA agonist activity. On the other hand, the 3-pyridyl
inyl)propyl-1-phosphonic acid ([ H]-CPP) , and [ H]-
[27]
analogue, 3-Py-AMPA (3) is devoid of affinity for AMPA
kainic acid
in order to determine the affinity for AMPA,
[15]
receptors . These striking structure-activity relationships
NMDA, and kainic acid receptor sites, respectively. The
compounds were tested for agonist or antagonist effects at
prompted us to design and synthesize compound 7 as a
structural hybrid of 3 and 4. Interestingly, 7 is slightly weaker
than 2-Py-AMPA (4) as an AMPA agonist (Table 1), indicat-
ing that the presence of a nitrogen atom in the 3-position of
the substituent of 7 somehow destabilizes the interaction of
these receptors using the rat cortical wedge electrophysi-
[28]
ological assay system
.
None of the compounds displayed significant affinity for
NMDA or kainic acid receptor sites (IC > 100µM) (Ta-
50
the molecule with the AMPA receptor recognition site, in
ble 1). Among the compounds 8a–c and 9a–c, only 9a, con-
taining a 2-hydroxyphenyl substituent, showed detectable
[15]
agreement with the observation for 3-Py-AMPA (3)
.
In an attempt to shed light on the structural basis of the
pharmacological effects of the presence of ring heteroatoms
in the 5-substituted AMPA analogues, the APPA (1b) ana-
logues 8a–c and 9a–c containing oxygenated phenyl substit-
uents were synthesized and evaluated pharmacologically.
With the exception of 9a, which is a very weak AMPA
agonist, all of these compounds were inactive as AMPA
receptor agonists or antagonists (Table 1). Thus, although
steric effects of the methoxy groups of 8a–c and the weak
acidic character of the phenol groups of 9a–c may contribute
to the very weak effects of these compounds, it may be
concluded that the above-mentioned regioselective AMPA
agonist-enhancing effects of ring heteroatoms are not mim-
icked by oxygen substituents.
affinity for AMPA receptor sites (IC = 45 µM), reflecting
50
a weak AMPA agonist activity (EC = 324 µM). In contrast,
50
the pyrazinyl-containing AMPA analogue 7 showed potent
AMPA receptor affinity (IC = 1.2 µM) and AMPA agonist
50
activity (EC = 11 µM) (Table 1). None of the compounds,
50
which were inactive as AMPA agonists showed detectable
antagonist effects at AMPA, NMDA, or kainic acid receptors,
as demonstrated by the inability of the compounds under
study to significantly reduce the depolarizations induced by
the standard agonists AMPA (1a), NMDA, or kainic acid at
the respective receptors.
A number of analogues of the specific AMPA receptor
[29]
agonist AMPA (1a) , in which C2–C4 alkyl groups have
been substituted for the methyl group of 1a, have been syn-
As shown in Table 1, compound 9a and APPA (1b) are
comparable in potency as weak AMPA receptor agonists.
Interestingly, a 2-D NOESY spectrum of 9a showed strong
thesized and shown to be AMPA agonists comparable in
[30]
potency with AMPA . Replacement of the methyl group of
[30]
AMPA (1a) by larger alkyl groups abolishes the activity
.
Arch. Pharm. Pharm. Med. Chem. 334, 62–68 (2001)

Agonist Activity of AMPA Analogues
65
NMR (CDCl3) δ 52.09, 56.06, 112.19, 120.21, 120.34, 131.88, 133.77,
159.39, 167.01.
NOE between the protons of the primary amino group and the
H-6 proton of the phenyl ring. Significant NOE was also
observed between H-5 of the phenyl ring and the methylene
and methine protons of the amino acid side chain of 9a. These
observations and the fact that the NMR spectra showed no
signs of hydrogen bonding between the phenol group and the
amino acid moiety may reflect the presence of a hydrogen
bond between the phenol group and the oxygen atom of the
isoxazole ring. It must, however, be emphasized that these
NMR spectroscopic experiments were carried out using a
solution of9a in DMSO. Under these conditions the hydrogen
bond situation may be different from that of the compound in
aqueous solution.
Methyl 3-Methoxybenzoate (10b)
Colorless oil; 56.5 g, quantitative yield. 1H NMR (CDCl3) δ 3.85 (s, 3H),
3.92 (s, 3H), 7.08–7.65 (m, 4H).
Methyl 4-Methoxybenzoate (10c)
Colorless oil; 26.4 g, 86%. 1H NMR (CDCl3) δ 3.86 (s, 3H), 3.89 (s, 3H),
6.91–6.94 (m, 2H), 7.94–8.01 (m, 2H).
General Procedure for the Preparation of β-Ketoesters. Synthesis of Methyl
2-(2-Methoxybenzoyl)propionate (11a)
We postulated that a hydrogen bonding between the
charged amino acid unit and the heteroatom in the 2-position
of the ring substituents of potent AMPA agonists such as
2-Py-AMPA (4) and 2-Me-Tet-AMPA (5) stabilizes the
amino acid side chain in a receptor-active conformation. This
proposal is, however, not supported by the structure-activity
analysis of 9a. An explanation of the structure-activity rela-
tionships for AMPA analogues containing ring substituents
in the 5-position of the 3-isoxazolol unit may be provided by
computational and X-ray crystallographic studies which are
in progress.
To a stirred solution of 10a (9.78 g, 58.9 mmol) and NaH (60% in mineral
oil, 3.06 g, 76.5 mmol) in dry DMF (120 mL), methyl propionate (6.74 g,
76.5 mmol) was added dropwise under N2. After being stirred at rt for 16 h
the reaction mixture was concentrated in vacuo, and the residue treated with
saturated aqueous NaHCO3 followed by extraction with EtOAc. The com-
bined organic phases were dried (MgSO4), filtered, and concentrated in
vacuo. CC (EtOAc/hexane 1:9) yielded 11a as a colorless oil (8.17 g, 62%).
1H NMR (CDCl3) δ 1.43 (d, 3H, J = 7.2 Hz), 3.66 (s, 3H), 3.87 (s, 3H), 4.33
(q, 1H, J = 7.2 Hz), 6.94–7.04 (m, 2H), 7.44–7.52 (m, 1H), 7.77–7.82 (m,
1H). 13C NMR (CDCl3) δ 13.52, 52.17, 52.69, 55.35, 111.68, 121.14, 126.77,
131.42, 134.45, 158.77, 172.40, 197.46. Anal. (C12H14O4) C, H.
Methyl 2-(3-Methoxybenzoyl)propionate (11b)
Colorless oil; 49.3 g, 82%. 1H NMR (CDCl3) δ 1.49 (d, 3H, J = 6.9 Hz),
3.69 (s, 3H), 3.86 (s, 3H), 4.40 (q, 1H, J = 6.9 Hz), 7.12–7.58 (m, 4H). 13C
NMR (CDCl3) δ 13.96, 48.26, 52.62, 55.55, 112.94, 120.38, 121.37, 129.98,
137.32, 160.24, 171.65, 196.01.
Acknowledgement
This work was supported by grants from the Lundbeck Foundation and
The Danish State Biotechnology Programme (1995–1999). We wish to
express our gratitude to Heidi Petersen and Annette Kristensen for technical
and to Anne Nordly for secretarial assistance.
Methyl 2-(4-Methoxybenzoyl)propionate (11c)
Colorless oil; 9.75 g, 49%. 1H NMR (CDCl3) δ 1.47 (d, 3H, J = 7.2 Hz),
3.68 (s, 3H), 3.87 (s, 3H), 4.36 (q, 1H, J = 7.2 Hz), 6.93–6.96 (m, 2H),
7.95–7.98 (m, 2H). 13C NMR (CDCl3) δ 13.99, 47.85, 52.57, 55.63, 114.16,
128.91, 131.24, 164.15, 171.86, 194.67. Anal. (C12H14O4) C, H.
Experimental Part
Chemistry. General Methods
Solvents and reagents were purchased from commercial sources and used
without further purification unless otherwise stated. Melting points were
determined in open capillaries and are uncorrected. 1H and 13C NMR spectra
were recorded on a Varian Gemini 300 spectrometer. Chemical shifts are
given in ppm using TMS or DSS as internal standard. NOESY spectra were
obtained on a Bruker AMX400 instrument with mixing time of 500 ms.
Elemental analyses were performed by Analytical Research Department, H.
Lundbeck A/S, Denmark or by J. Theiner, Microanalytical Laboratory,
Institute of Physical Chemistry, University of Vienna, Austria, and results
obtainedwerewithin±0.4% of the theoretical values, unlessotherwisestated.
CC and preparative TLC were performed using silica gel 60 (0.063–
0.200 mm) and silica gel 60H (0.045 mm), respectively from Merck. Com-
pounds were visualized on TLC (silica gel 60 F254 plates; Merck) using UV
light and either a FeCl3 or a KMnO4 spraying reagent. For amino acids, a
ninhydrin spraying reagent was used. Ion exchange chromatography of
compound 7 was performed using Amberlite IR-120.
General Procedure for the Preparation of 5-Substituted 4-Methyl-3-isox-
azolols. Synthesis of 5-(2-Methoxyphenyl)-4-methyl-3-isoxazolol (12a)
Hydroxylamine hydrochloride (2.50 g, 36.0 mmol) dissolved in MeOH
(18 mL) was added to NaOH (1.44 g, 36.0 mmol) dissolved in H2O (2 mL).
The solution was cooled to 0 °C and filtered into a cold (–30 °C) mixture of
11a (4.00 g, 18.0 mmol) in MeOH (18 mL) and H2O (2 mL). The reaction
mixture was stirred at –30 °C for 3 h, and added portionwise to hot (80 °C)
concentrated HCl (40 mL). After stirring for 1.5 h the solution was cooled to
rt, concentrated in vacuo and the residue redissolved in H2O (20 mL). The
pH was adjusted to 3–4 with solid NaHCO3 and the mixture extracted with
CH2Cl2. The combined organic phases were dried (MgSO4), filtered, and
concentrated in vacuo. CC (EtOAc/hexane 1:9) yielded 12a as a white solid
1
(2.09 g, 57%); mp 167–169 °C. H NMR (CDCl3) δ 1.91 (s, 3H), 3.86 (s,
3H), 6.98–7.50 (m, 4H), 9.20 (br s, 1H). 13C NMR (CDCl3) δ 6.28, 55.15,
103.12, 111.14, 117.56, 120.33, 130.10, 131.24, 156.65, 163.21, 170.32.
Anal. (C11H11NO3) C, H, N.
General Procedure for the Preparation of Methyl Methoxybenzoates.
Synthesis of Methyl 2-Methoxybenzoate (10a)
5-(3-Methoxyphenyl)-4-methyl-3-isoxazolol (12b)
Solid; 24.2 g, 57%; mp 142–144 °C. 1H NMR (CDCl3) δ 2.18 (s, 3H), 3.87
(s, 3H), 6.98–7.45 (m, 4H), 10.25 (br s, 1H). 13C NMR (CDCl3) δ 6.78, 55.49,
101.57, 111.88, 116.01, 119.15, 129.76, 130.18, 160.09, 164.58, 171.02.
Anal. (C11H11NO3) C, H, N.
Methyl salicylate (11.8 g, 77.8 mmol) was added dropwise to a solution of
NaH (55% in mineral oil, 3.74 g, 85.6 mmol) in dry DMF (140 mL) at 0 °C.
The reaction mixture was stirred 20 min at 0 °C and methyl iodide (12.1 g,
85.6 mmol) was added slowly. After stirring for 15 h at rt the mixture was
concentrated in vacuo. Saturated aqueous NaHCO3 was added and the
solution extracted with CH2Cl2. The combined organic phases were dried
(MgSO4), filtered, and concentrated in vacuo. CC (EtOAc/toluene 1:9)
yielded 10a as a colorless oil (10.5 g, 81%). 1H NMR (CDCl3) δ 3.87 (s, 3H),
5-(4-Methoxyphenyl)-4-methyl-3-isoxazolol (12c)
Solid; 5.75 g, 41%; mp 202–204 °C. 1H NMR (CDCl3) δ 1.98 (s, 3H), 3.71
3.88 (s, 3H), 6.93–6.98 (m, 2H), 7.41–7.47 (m, 1H), 7.60–7.79 (m, 1H). 13
C
(s, 3H), 5.54 (br s, 1H), 6.83–6.86 (m, 2H), 7.48–7.51 (m, 2H). 13C NMR
Arch. Pharm. Pharm. Med. Chem. 334, 62–68 (2001)

66
Krogsgaard-Larsen and co-workers
(s, 2H), 3.87 (s, 3H), 6.36 (s, 1H), 6.98–7.11 (m, 2H), 7.42–7.58 (m, 2H).
13C NMR (CDCl3) δ 22.29, 25.44, 26.84, 39.28, 53.22, 55.47, 65.37, 104.78,
111.36, 117.64, 120.69, 130.85, 132.08, 156.60, 166.43, 167.40, 167.65,
169.28, 174.94. Anal. (C23H28N2O9) C, H, N.
(CDCl3) δ 6.73, 55.50, 100.03, 114.51, 121.21, 128.30, 161.10, 164.96,
170.80. Anal. (C11H11NO3) C, H, N.
General Procedure for Pivaloyl Protection of Substituted 3-Isoxazolols.
Synthesis of 3-Pivaloyloxy-5-(2-methoxyphenyl)-4-methylisoxazole (13a)
Methyl 2-Acetylamino-3-[3-pivaloyloxy-5-(3-methoxyphenyl)-4-isox-
azolyl]-2-(methoxycarbonyl)propionate (15b)
Pivaloyl chloride (9.52 g, 78.9 mmol) was added to compound 12a (13.5 g,
65.8 mmol) dissolved in CH2Cl2 (125 mL) under N2. TEA (7.99 g,
78.9 mmol) was added dropwise and the reaction mixture was stirred at rt
overnight. Quenching with saturated aqueous NaHCO3 was followed by
extraction withCH2Cl2. The combined organic extracts were dried (MgSO4),
filtered, and concentrated in vacuo. CC (EtOAc/toluene 1:9) yielded 13a as
a colorless oil (17.8 g, 93%). 1H NMR (CDCl3) δ 1.41 (s, 9H), 1.85 (s, 3H),
3.85 (s, 3H), 6.98–7.08 (m, 2H), 7.42–7.52 (m, 2H). 13C NMR (CDCl3) δ
6.85, 26.86, 39.14, 55.31, 106.12, 111.32, 117.29, 120.61, 130.48, 131.76,
156.80, 165.82, 166.35, 174.77. Anal. (C16H19NO4) C, H, N.
Solid; 3.20 g, 33% (reaction time 16 h) ; mp 131–133 °C. 1H NMR (CDCl3)
δ 1.40 (s, 9H), 1.66 (s, 3H), 3.51 (s, 6H), 3.62 (s, 2H), 3.86 (s, 3H), 6.41 (s,
1H), 6.98–7.42 (m, 4H). 13C NMR (CDCl3) δ 22.62, 25.09, 27.07, 39.56,
53.55, 55.57, 65.47, 102.70, 112.41, 117.01, 120.05, 129.69, 130.39, 160.11,
167.13, 167.71, 169.50, 169.87, 175.35. Anal. (C23H28N2O9) C, H, N.
Methyl 2-Acetylamino-3-[3-pivaloyloxy-5-(4-methoxyphenyl)-4-isox-
azolyl]-2-(methoxycarbonyl)propionate (15c)
Solid; 5.81 g, 50% (reaction time 16 h); mp 183–185 °C. 1H NMR (CDCl3)
δ 1.37 (s, 9H), 1.69 (s, 3H), 3.46 (s, 6H), 3.58 (s, 2H), 3.83 (s, 3H), 6.44 (s,
1H), 6.96–6.99 (m, 2H), 7.56–7.59 (m, 2H). Anal. (C23H28N2O9) C, H, N.
3-Pivaloyloxy-5-(3-methoxyphenyl)-4-methylisoxazole (13b)
Solid; 16.1 g, 50%; mp 84–88 °C. 1H NMR (CDCl3) δ 1.41 (s, 9H), 2.06
(s, 3H), 3.86 (s, 3H), 6.97–7.43 (m, 4H). 13C NMR (CDCl3) δ 7.29, 27.13,
39.45, 55.51, 104.20, 111.94, 116.00, 119.09, 129.69, 130.22, 160.12,
166.88, 167.02, 175.07. Anal. (C16H19NO4) C, H, N.
General Procedure for the Preparation of α-Amino Acids Containing the
5-Methoxyphenyl Moiety. Synthesis of (RS)-2-Amino-3-[3-hydroxy-5-
(2-methoxyphenyl)-4-isoxazolyl]propionic Acid (8a)
3-Pivaloyloxy-5-(4-methoxyphenyl)-4-methylisoxazole (13c)
Compound 15a (3.00 g, 6.30 mmol) was dissolved in 4 M aqueous HCl
(200 mL) and stirred at reflux for 16 h. The reaction mixture was cooled to
rt, concentrated in vacuo, and the residue redissolved in H2O. The solution
was washed with EtOAc and pH adjusted to 3–4 with 2 M aqueous NaOH.
Upon standing at 5 °C overnight a precipitate was formed and filtered off.
The solid was washed with H2O and dried in vacuo to afford 8a in 71% yield
(1.25 g); mp 222–225 °C (decomp). 1H NMR (DMSO) δ 2.43 (dd, 1H, J =
2.4 Hz and 15.6 Hz), 2.72 (dd, 1H, J = 8.7 Hz and 15.6 Hz), 3.53 (dd, 1H, J
= 2.4 Hz and 8.7 Hz), 3.78 (s, 3H), 7.01–7.52 (m, 4H), 9.50 (br s, 2H). 13C
NMR (DMSO-d6) δ 25.21, 52.95, 55.68, 104.42, 112.21, 117.36, 120.74,
Solid; 7.35 g, 95%; mp 96–97 °C. 1H NMR (CDCl3) δ 1.41 (s, 9H), 2.04
(s, 3H), 3.87 (s, 3H), 6.98–7.04 (m, 2H), 7.63–7.68 (m, 2H). 13C NMR
(CDCl3) δ 7.24, 27.13, 39.43, 55.48, 102.60, 114.53, 121.28, 128.22, 161.04,
166.98, 167.16, 175.10. Anal. (C16H19NO4) C, H, N.
General Procedure for Bromination of 5-Substituted 4-Methyl-3-isoxazolols.
Synthesis of 4-Bromomethyl-3-pivaloyloxy-5-(2-methoxyphenyl)isoxazole
(14a)
.
To a solution of 13a (17.6 g, 60.8 mmol) in CCl4 (450 mL) was added NBS
(16.2 g, 91.2 mmol) in two equal portions, one portion initially and one after
24 h at reflux. After a total of 3 d at reflux, during which the reaction was
130.69, 131.99, 156.88, 163.68, 171.08, 171.87. Anal. (C13H14N2O5 0.25
H2O) C, H, N.
1
followed by H NMR, the mixture was allowed to cool to rt, filtered, and
(RS)-2-Amino-3-[3-hydroxy-5-(3-methoxyphenyl)-4-isoxazolyl]propionic
Acid (8b)
concentrated in vacuo. The residue was purified by CC (EtOAc/hexane 1:9)
to afford 14a as a yellowish oil (14.9 g, 67%). 1H NMR (CDCl3) δ 1.44 (s,
9H), 3.92 (s, 3H), 4.26 (s, 2H), 7.00–7.40 (m, 4H). 13C NMR (CDCl3) δ
20.15, 26.93, 39.28, 55.53, 107.75, 111.45, 116.16, 120.96, 130.53, 132.70,
156.67, 165.53, 166.82, 174.48.
Solid; 355 mg, 64%; mp 215–217 °C (decomp). 1H NMR (DMSO) δ 2.79
(dd, 1H, J = 2.7 Hz and 15.9 Hz), 2.94 (dd, 1H, J = 8.1 Hz and 15.6 Hz), 3.65
(dd, 1H, J = 2.7 Hz and 8.1 Hz), 3.79 (s, 3H), 7.03–7.44 (m, 4H). 13C NMR
(DMSO-d6) δ 25.35, 53.00, 55.65, 103.12, 112.70, 116.01, 119.90, 130.09,
.
130.68, 159.98, 164.81, 171.85. Anal. (C13H14N2O5 0.25 H2O) C, H, N.
4-Bromomethyl-3-pivaloyloxy-5-(3-methoxyphenyl)isoxazole (14b)
Yellowish oil; 7.82 g, 61%. 1H NMR (CDCl3) δ 1.44 (s, 9H), 3.88 (s, 3H),
4.32 (s, 2H), 7.10–7.48 (m, 4H). 13C NMR (CDCl3) δ 19.45, 27.11, 39.60,
55.59, 106.31, 112.22, 117.48, 119.65, 128.23, 130.65, 160.33, 165.77,
169.02, 174.64.
(RS)-2-Amino-3-[3-hydroxy-5-(4-methoxyphenyl)-4-isoxazolyl]propionic
Acid (8c)
Solid; 340 mg, 61%; mp > 230 °C (decomp). 1H NMR (DMSO-d6) δ 2.73
(dd, 1H, J = 2.7 Hz and 15.6 Hz), 2.90 (dd, 1H, J = 8.4 Hz and 15.6 Hz), 3.64
(dd, 1H, J = 2.7 Hz and 8.4 Hz), 3.78 (s, 3H), 7.02–7.05 (m, 2H), 7.53–7.56
(m, 2H). 13C NMR (DMSO) δ 20.94, 48.93, 51.40, 97.43, 110.55, 117.04,
4-Bromomethyl-3-pivaloyloxy-5-(4-methoxyphenyl)isoxazole (14c)
Solid; 8.95 g, 96%; mp 138–140 °C (decomp). 1H NMR (CDCl3) δ 1.45
(s, 9H), 3.85 (s, 3H), 4.30 (s, 2H), 7.02–7.10 (m, 2H), 7.70–7.78 (m, 2H).
13C NMR (CDCl3) δ 20.0, 27.2, 39.8, 55.9, 104.9, 115.0, 119.9, 129.0, 162.0,
164.8, 162.2, 174.3. Anal. (C16H18NO4Br) C, H, N.
.
124.87, 156.50, 160.90, 167.45, 167.57. Anal. (C13H14N2O5 0.75 H2O) C,
H, N.
General Procedure for the Preparation of -Amino Acids Containing
the 5-Hydroxyphenyl Moiety. Synthesis of (RS)-2-Amino-3-[3-hydroxy-
5-(2-hydroxyphenyl)-4-isoxazolyl]propionic Acid (9a)
General Procedure for the Preparation of Dimethyl Acetylaminomalonate
Derivatives. Synthesis of Methyl 2-Acetylamino-3-[3-pivaloyloxy-5-(2-
methoxyphenyl)-4-isoxazolyl]-2-(methoxycarbonyl)propionate (15a)
Compound 15a (950 mg, 1.99 mmol) was dissolved in 62% aqueous HBr
(50 mL) and stirred 16 h at 55 °C. The reaction mixture was cooled to rt and
concentrated in vacuo. The residue was dissolved in aqueous 4 M HCl (75
mL) and stirred under reflux overnight. The solution was cooled to rt, washed
with EtOAc, and concentrated in vacuo. H2O was added and pH adjusted to
4 with 2 M aqueous NaOH. Upon standing at 5 °C overnight a precipitate
was formed. This solid was filtered off, washed with H2O and dried in vacuo
to afford 9a in 75% yield (395 mg); mp > 220 °C (decomp). 1H NMR
(DMSO-d6) δ 2.52 (dd, 1H, J = 2.1 Hz and 15.6 Hz), 2.74 (dd, 1H, J = 8.4
Hz and 15.6 Hz), 3.55 (dd, 1H, J = 2.1 Hz and 8.4 Hz), 6.83–7.35 (m, 4H),
Dimethyl acetylaminomalonate (7.91 g, 41.8 mmol) dissolved in dry DMF
(200 mL) was cooled to 0 °C and NaH (60% in mineral oil, 1.67 g,
41.8 mmol) was added under N2. After stirring for 20 min, a solution of 14a
(14.0 g, 38 mmol) dissolved in dry DMF (30 mL) was added. The reaction
mixture was stirred 2 d at rt and then concentrated in vacuo. Saturated
aqueous NaHCO3 was added and the solution extracted with CH2Cl2. The
combined extracts were dried (MgSO4), filtered, and concentrated in vacuo.
CC (EtOAc/hexane 1:9) yielded 15a as a crystalline solid (5.74 g, 32%); mp
170–172 °C. 1H NMR (CDCl3) δ 1.41 (s, 9H), 1.58 (s, 3H), 3.49 (s, 6H), 3.57
.
9.65 (br s, 2H). Anal. (C12H12N2O5 0.25 H2O) C, H, N.
Arch. Pharm. Pharm. Med. Chem. 334, 62–68 (2001)

Agonist Activity of AMPA Analogues
67
(RS)-2-Amino-3-[3-hydroxy-5-(3-hydroxyphenyl)-4-isoxazolyl]propionic
Acid (9b)
barrier for electrical isolation with each part in contact with an electrode. The
cortex was superfused with Mg2+-free Krebs buffer, whereas the corpus
callosum part was superfused with Mg2+- and Ca2+-free Krebs buffer, both
at 25 °C. The test compounds were added to the cortex superfusion medium,
and the induced potential difference between the electrodes was recorded.
Agonists were applied for 90 s at each concentration tested. The sensitivity
of agonist effects to the AMPA receptor antagonist, 2,3-dihydroxy-6-nitro-
7-sulpharmoylbenzo(f)quinoxaline (NBQX)[31] (5 µM) was determined at
agonist concentrations producing at least 50% of maximal responses. Under
these conditions, all of the recorded agonist responses were reversibly
reduced by at least 70%. In experiments designed to detect antagonist effects
of test compounds at 1 mM concentrations, the compounds were applied
alone for 90 s followed by coapplication of the appropriate agonist (5 µM
AMPA, 10 µM NMDA or 5 µM kainic acid) and potential antagonist for
another 90 s.
Solid, 405 mg, 77%; mp > 230 °C. 1H NMR (DMSO-d6) δ 2.82 (dd, 1H,
J = 3.3 Hz and 15.6 Hz), 2.95 (dd, 1H, J = 7.8 Hz and 15.6 Hz), 3.69 (dd,
1H, J = 3.3 Hz and 7.8 Hz), 6.88–7.35 (m, 4H), 9.90 (br s, 2H). Anal.
.
(C12H12N2O5 0.25 H2O) C, H, N.
(RS)-2-Amino-3-[3-hydroxy-5-(4-hydroxyphenyl)-4-isoxazolyl]propionic
Acid (9c)
Solid, 354 mg, 71%; mp > 230 °C. 1H NMR (DMSO-d6) δ 2.75 (dd, 1H,
J = 2.7 Hz and 15.6 Hz), 2.92 (dd, 1H, J = 8.4 Hz and 15.6 Hz), 3.66 (dd,
1H, J = 2.7 Hz and 8.1 Hz), 6.89–6.92 (m, 2H), 7.45–7.48 (m, 2H), 10.1 (br
.
s, 2H). Anal. (C12H12N2O5 H2O) C, H, N.
Methyl 2-(Pyrazinecarbonyl)propionate (17)
Method as described for 11a. Yellowish oil; 4.51 g, 42%. 1H NMR
(CDCl3) δ 1.52 (d, 3H, J = 6.9 Hz), 3.68 (s, 3H), 4.68 (q, 1H, J = 7.2 Hz),
8.64–8.65 (m, 1H), 8.78–8.79 (m, 1H), 9.28–9.29 (m, 1H). 13C NMR
(CDCl3) δ 12.93, 47.21, 52.52, 143.69, 144.51, 146.70, 148.31, 171.81,
197.00. Anal. (C9H10N2O3) C, H, N.
References
[1] H. V. Wheal, A. M. Thomson, (Eds.), Excitatory Amino Acids and
Synaptic Transmission, Academic Press, London, 1995.
[2] D. T. Monaghan, R. J. Wenthold, (Eds.), The Ionotropic Glutamate
Receptors, Humana Press, Totowa, New Jersey, 1997.
(3-Pivaloyloxy-4-methyl-5-isoxazolyl)pyrazine (18)
[3] H. Bräuner-Osborne, J. Egebjerg, E. Ø. Nielsen, U. Madsen,
P. Krogsgaard-Larsen, J. Med. Chem. 2000, 43, 2609–2645.
Cyclization of β-ketoester 17 with hydroxylamine was performed by the
general method described for 12a. The (3-hydroxy-4-methyl-5-isoxazol-
yl)pyrazine formed could not be extracted from the aqueous solution, even
at varying pH. Instead, the aqueous phase was neutralized with 2 M aqueous
NaOH and evaporated to dryness. The remaining solid was dissolved in DMF
and reacted with pivaloyl chloride as described in the general procedure, to
afford 18 as a white solid (375 mg, 9% from 17); mp 99–100 °C. 1H NMR
(CDCl3) δ 1.43 (s, 9H), 2.26 (s, 3H), 8.60–8.61 (m, 1H), 8.66–8.68 (m, 1H),
9.16 (s, 1H). 13C NMR (CDCl3) δ 6.89, 26.86, 39.25, 109.61, 142.41, 143.95,
144.15, 144.47, 162.60, 167.27, 174.65. Anal. (C13H15N3O3) C, H, N.
[4] P. J. Conn, J. Patel, (Eds.), The Metabotropic Glutamate Receptors,
Humana Press, New Jersey, 1994.
[5] C. G. Parsons, W. Danysz, G. Quack, Drug News Perspect. 1998, 11,
523–569.
[6] R. Dingledine, K. Borges, D. Bowie, S. F. Traynelis, Pharmacol. Rev.
1999, 51, 7–61.
[7] N. K. Mahanty, P. Sah, Nature 1998, 394, 683–687.
[8] S. Q. Liu, S. G. Cull-Candy, Nature 2000, 405, 454–457.
Methyl 2-Acetylamino-3-[3-pivaloyloxy-5-(pyrazinyl)-4-isoxazolyl]-
[9] H. K. Lee, M. Barbarosie, K. Kameyama, M. F. Bear, R. L. Huganir,
2-(methoxycarbonyl)propionate (20)
Nature 2000, 405, 955–959.
The general method described above for 14a was used for the NBS
bromination. However, due to an apparent instability of the product 19, the
reaction mixture was evaporated to dryness in vacuo after 2 d and used
without further purification in the reaction with DMAA according to the
method described for 15a. The title compound 20 was isolated as a solid in
29% from 18 (303 mg); mp 186–190 °C (decomp). 1H NMR (CDCl3) δ 1.42
(s, 9H), 1.86 (s, 3H), 3.64 (s, 6H), 3.83 (s, 2H), 6.82 (s, 1H), 8.61–8.67 (m,
[10] U. Staubli, G. Rogers, G. Lynch, Proc. Natl. Acad. Sci. U. S. A. 1994,
91, 777–781.
[11] G. Lynch, R. Granger, J. Ambros-Ingerson, C. M. Davis, M. Kessler,
R. Schehr, Exp. Neurol. 1997, 145, 89–92.
[12] T. B. Stensbøl, F. A. Sløk, J. Trometer, S. Hurt, B. Ebert, C. Kjøller, J.
Egebjerg, U. Madsen, N. H. Diemer, P. Krogsgaard-Larsen, Eur. J.
Pharmacol. 1999, 373, 251–262.
.
2H), 9.18–9.19 (m, 1H). Anal. (C20H24N4O8 0.5 H2O) C, H, N.
[13] I. T. Christensen, A. Reinhardt, B. Nielsen, B. Ebert, U. Madsen, E. Ø.
Nielsen, L. Brehm, P. Krogsgaard-Larsen, Drug Des. Del. 1989, 5,
57–71.
(RS)-2-Amino-3-[3-hydroxy-5-(pyrazinyl)-4-isoxazolyl]propionic Acid (7)
Reaction conditions as described for 8a. Oil, 72 mg, 52%. Purified by
preparative TLC (EtOAc/CH3OH 24:1) and subsequent ion exchange chro-
matography. 1H NMR (D2O) δ 3.25–3.37 (m, 2H), 4.40–4.55 (m, 1H),
8.56–8.66 (m, 2H), 8.90–8.98 (m, 1H). MS(FAB+) m/z 251 ([M+1]+, 9%).
HRMS: Calcd for C10H11N4O4 251.0780, found 251.0779.
[14] B. Ebert, S. M. Lenz, L. Brehm, P. Bregnedal, J. J. Hansen, K.
Frederiksen, K. P. Bøgesø, P. Krogsgaard-Larsen, J. Med. Chem. 1994,
37, 878–884.
[15] E. Falch, L. Brehm, I. Mikkelsen, T. N. Johansen, N. Skjærbæk, B.
Nielsen, T. B. Stensbøl, B. Ebert, P. Krogsgaard-Larsen, J. Med. Chem.
1998, 41, 2513–2523.
In Vitro Pharmacology
[16] T. N. Johansen, B. Ebert, E. Falch, P. Krogsgaard-Larsen, Chirality
1997, 9, 274–280.
Receptor Binding Assays
Affinity for AMPA receptors was determined using the ligand
[3H]AMPA[25]. For determination of NMDA and kainic acid receptor affini-
ties, [3H]CPP[26] and [3H]kainic acid[27], respectively, were used. The mem-
brane preparations used in all receptor binding experiments were prepared
[17] B. Bang-Andersen, S. M. Lenz, N. Skjærbæk, K. K. Søby, H. O.
Hansen, B. Ebert, K. P. Bøgesø, P. Krogsgaard-Larsen, J. Med. Chem.
1997, 40, 2831–2842.
according to the method of Ransom and Stec[29]
.
[18] S. B. Vogensen, H. S. Jensen, T. B. Stensbøl, K. Frydenvang, B.
Bang-Andersen, T. N. Johansen, J. Egebjerg, P. Krogsgaard-Larsen,
Chirality 2000, 12, 705–713.
In Vitro Electropharmacology
[19] U. Madsen, B. Frølund, T. M. Lund, B. Ebert, P. Krogsgaard-Larsen,
A rat cortical wedge preparation for determination of excitatory amino
acid-evoked depolarizations described by Harrison and Simmonds[28] was
used in a slightly modified version[15]. Wedges (500 µm thick) of rat brain,
containing cerebral cortex and corpus callosum, were placed through a grease
Eur. J. Med. Chem. 1993, 28, 791–800.
[20] F. A. Sløk, B. Ebert, Y. Lang, P. Krogsgaard-Larsen, S. M. Lenz, U.
Madsen, Eur. J. Med. Chem. 1997, 32, 329–338.
Arch. Pharm. Pharm. Med. Chem. 334, 62–68 (2001)

68
Krogsgaard-Larsen and co-workers
[21] J. Lauridsen, T. Honoré, P. Krogsgaard-Larsen, J. Med. Chem. 1985,
28, 668–672.
[26] D. E. Murphy, J. Schneider, C. Boehm, J. Lehmann, K. Williams, J.
Pharmacol. Exp. Ther. 1987, 240, 778–783.
[27] D. J. Braitman, J. T. Coyle, Neuropharmacology 1987, 26, 1247–1251.
[28] N. L. Harrison, M. A. Simmonds, Br. J. Pharmacol. 1985, 84, 381–391.
[29] R. W. Ransom, N. L. Stec, J. Neurochem. 1988, 51, 830–836.
[22] N. Skjærbæk, B. Ebert, E. Falch, L. Brehm, P. Krogsgaard-Larsen, J.
Chem. Soc. Perkin Trans. 1 1995, 221–225.
[23] I. T. Christensen, B. Ebert, U. Madsen, B. Nielsen, L. Brehm, P.
Krogsgaard-Larsen, J. Med. Chem. 1992, 35, 3512–3519.
[30] F. A. Sløk, B. Ebert, Y. Lang, P. Krogsgaard-Larsen, S. M. Lenz, U.
Madsen, Eur. J. Med. Chem. 1997, 32, 329–338.
[24] N. Skjærbæk, L. Brehm, T. N. Johansen, L. M. Hansen, B. Nielsen, B.
Ebert, K. K. Søby, T. B. Stensbøl, E. Falch, P. Krogsgaard-Larsen,
Bioorg. Med. Chem. 1998, 6, 119–131.
[31] M. J. Sheardown, E. Ø. Nielsen, A. J. Hansen, P. Jacobsen, T. Honoré,
Science 1990, 247, 571–574.
[25] T. Honoré, M. Nielsen, Neurosci. Lett. 1985, 54, 27–32.
Received: December 11, 2000 [FP534]
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