Synthesis and pharmacology of highly selective carboxy and phosphono isoxazole amino acid AMPA receptor antagonists

Article abstract of DOI:10.1021/jm950826p

(RS)-2-Amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA, 5) and the selective AMPA receptor antagonist (RS)-2-amino-3-[3- (carboxymethoxy)-5-methyl-4-isoxazolyl]propionic acid (AMOA, 7) have been used as leads for the design and synthesis of

Full text of DOI:10.1021/jm950826p

1682
J . Med. Chem. 1996, 39, 1682-1691
Syn th esis a n d P h a r m a cology of High ly Selective Ca r boxy a n d P h osp h on o
Isoxa zole Am in o Acid AMP A Recep tor An ta gon ists
Ulf Madsen,* Benny Bang-Andersen,† Lotte Brehm, Inge T. Christensen, Bjarke Ebert, Inge T. S. Kristoffersen,
Yolande Lang, and Povl Krogsgaard-Larsen
PharmaBiotec Research Center, Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, DK-2100
Copenhagen, Denmark, and Medicinal Chemistry Research, H. Lundbeck A/ S, DK-2500 Valby-Copenhagen, Denmark
Received November 8, 1995X
(RS)-2-Amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA, 5) and the selective
AMPA receptor antagonist (RS)-2-amino-3-[3-(carboxymethoxy)-5-methyl-4-isoxazolyl]propionic
acid (AMOA, 7) have been used as leads for the design and synthesis of a number of potential
AMPA receptor antagonists. Two parallel series of AMOA analogs were synthesized, containing
either a distal carboxylic acid (compounds 8b-g and 11b) or a phosphonic acid (compounds
9a -g, 10c, and 11c). Pharmacological characterization of the synthesized compounds was
carried out using a series of receptor binding assays and by in vitro electrophysiological
experiments using the rat cortical slice model. The two analogs with a tert-butyl substituent,
(RS)-2-amino-3-[5-tert-butyl-3-(carboxymethoxy)-4-isoxazolyl]propionic acid (ATOA, 8b) and the
corresponding phosphonic acid analog ATPO (9b), were the most potent and selective AMPA
antagonists within each series. ATOA and ATPO showed IC50 values of 150 and 28 µM,
respectively, toward AMPA-induced depolarizations in the cortical slice model compared to
IC50 ) 320 µM for the parent compound, AMOA. These two new competitive AMPA antagonists
were significantly more selective than AMOA, showing no antagonism (up to 1 mM) toward
NMDA-induced responses, whereas AMOA (at 1 mM) showed weak (19%) inhibition toward
NMDA-induced responses. The structure-activity relationships for the two series of compounds
revealed considerable differences with respect to the substituents effects, and the phosphonic
acid analogs generally exhibited significantly higher potencies compared to the carboxylic acid
analogs.
In tr od u ction
ity studies on ATPA (6b) and other AMPA analogs with
different substituents in the 5-position of the isoxazole
ring, including the phenyl analog 6f, have given rise to
the hypothesis that the AMPA receptors contain a
lipophilic cavity capable of accommodating substituents
of a certain size.14-16
(S)-Glutamic acid (Glu, 1) is the major excitatory
amino acid (EAA) neurotransmitter in the central
nervous system.1-3 The N-methyl-D-aspartic acid (NMDA,
2) and (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl-
)propionic acid (AMPA, 5) subtypes of EAA receptors
are the subject of extensive exploration as potential
targets for drug intervention in different neurodegen-
erative diseases.1,4,5 The availability of a broad spec-
trum of phosphono amino acids showing potent and
highly selective competitive antagonism of NMDA re-
ceptor function has played a crucial role in the charac-
terization of this subtype of EAA receptors.6,7 The
pharmacology of the NMDA receptors is closely associ-
ated with this particular class of amino acids, notably,
(R)-2-amino-5-phosphonovaleric acid8 (AP5, 3) and (R)-
[3-(2-carboxypiperazin-4-yl)propyl]phosphonic acid9 (CPP,
4).
AMPA has previously been converted into the AMPA
receptor antagonist (RS)-2-amino-3-[3-(carboxymethoxy)-
5-methyl-4-isoxazolyl]propionic acid (AMOA, 7), which
shows neuroprotective properties.17,18 AMOA is a rela-
tively weak antagonist at AMPA receptors and also
shows very weak antagonist activity toward NMDA-
induced responses.17 In order to investigate the impor-
tance of the substituent in the 5-position of the isoxazole
ring, a number of AMOA analogs, compounds 8b-g,
have been synthesized and pharmacologically charac-
terized.
Since a distal phosphonic acid is an important, though
not essential, structural element of competitive NMDA
antagonists,6,7 and since many AMPA receptor ligands,
including AMOA (7), contain an isoxazole nucleus, we
designed “structural hybrids” containing both of these
elements as novel EAA receptor antagonists. Thus, in
parallel with the series of AMOA analogs (compounds
8b-g), we describe the synthesis and pharmacological
characterization of compounds 9a -g containing a distal
phosphonic acid.
AMPA (5) and a number of structurally related
isoxazole amino acids, including (RS)-2-amino-3-(5-tert-
butyl-3-hydroxy-4-isoxazolyl)propionic acid (ATPA, 6b),
are potent and selective AMPA receptor agonists.3,10,11
Although ATPA (6b) is somewhat weaker than AMPA
as an AMPA agonist, the observation that ATPA is
active after systemic administration to animals makes
this compound an important tool for studies of the
pharmacology of AMPA receptors.12,13 Structure-activ-
* Address correspondence to this author at PharmaBiotec Research
Center, Department of Medicinal Chemistry, The Royal Danish School
of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
Phone: (+45) 35370850, ext. 243. Fax: (+45) 35372209. E-mail:
ulf@medchem.dfh.dk.
The potent and selective AMPA agonist (RS)-3-
hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-
carboxylic acid19 (10a ) has previously been converted
into the carboxymethyl analog 10b, which quite surpris-
ingly was shown to be an NMDA antagonist.20 We here
† H. Lundbeck A/S.
X Abstract published in Advance ACS Abstracts, March 15, 1996.
0022-2623/96/1839-1682$12.00/0 © 1996 American Chemical Society

Carboxy and Phosphono AMPA Receptor Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1683
tected distal acid functionalities were introduced at an
earlier step of the synthetic sequences. This procedure
provided, in most cases, a better yield as compared to
the alkylation of the acetamidomalonate derivatives
12a ,c-e, as described above. The low yields (15-59%)
of the alkylation reactions probably reflect the formation
and subsequent decomposition of an N-alkylated prod-
uct in analogy with earlier observations.17,23 Introduc-
tion of the acetamidomalonate group in compounds
16b,g and 17b,f,g was performed via regioselective NBS
bromination under free radical conditions followed by
a Sorensen synthesis. Different variants of the So-
rensen synthesis were performed, including the use of
dimethyl or diethyl acetamidomalonate and sodium
hydride, potassium tert-butoxide (Scheme 1), or sodium
ethoxide (Scheme 2) as the base. For the synthesis of
compound 8b, it proved essential to use the Boc-
protected intermediate 20b in order to produce the final
product 8b in reasonable yield and with satisfactory
purity. Compound 20b was synthesized from 18b using
diethyl [N-(tert-butyloxycarbonyl)amino]malonate24 and
sodium hydride. Final deprotection was carried out in
NaOH followed by HCl under reflux.
For the synthesis of compounds 8f, 10c, and 11b,c,
modified versions of the above strategies were used
(Scheme 2). Protection of the amino acid moiety of
compound 6f15 followed by O-alkylation gave the inter-
mediate 23, which was deprotected in two steps. For
the synthesis of compound 10c, a fully protected inter-
mediate, compound 25,25 was NBS brominated, and
subsequent cyclization was accomplished with sodium
hydride.
Compounds 11b,c were synthesized from 5-methyl-
3-isoxazolol (tachigaren, 29)26 by O-alkylation followed
by NBS bromination, Sorensen synthesis, and depro-
tection, in analogy with the preparation of compounds
8b,g and 9b,f,g.
In Vitr o P h a r m a cology. The compounds 8b-g,
9a -g, 10c, and 11b,c were studied in different receptor
binding assays. For the determination of affinity for
AMPA receptors, the ligands [3H]AMPA27 and [3H]-6-
cyano-7-nitroquinoxaline-2,3-dione ([3H]CNQX)28 were
used (Table 1). None of the compounds described
showed significant affinity in the [3H]kainic acid binding
assay29 (IC50 > 100 µM), and only compounds 10b,20c
showed significant affinity for [3H]CPP binding sites9
(Table 1).
F igu r e 1. Structures of Glu (1) and ligands at either NMDA
receptors (2-4) or AMPA receptors (5-7). The compounds
synthesized (8b-g, 9a -g, 10c, and 11b,c) are depicted in the
box.
All new compounds were studied electrophysiologi-
cally, using the rat cortical slice model.32 The phospho-
nic acid analog of AMOA, (RS)-2-amino-3-[5-methyl-3-
(phosphonomethoxy)-4-isoxazolyl]propionic acid (AMPO,
9a ), showed markedly increased antagonist potency
toward AMPA-induced responses, as compared to AMOA
(7) (Table 1). The tert-butyl analog of AMOA, (RS)-2-
amino-3-[5-tert-butyl-3-(carboxymethoxy)-4-isoxazolyl]-
propionic acid (ATOA, 8b), also exhibited a more potent
antagonist effect than AMOA. (RS)-2-Amino-3-[5-tert-
butyl-3-(phosphonomethoxy)-4-isoxazolyl]propionic acid
(ATPO, 9b) was the most potent compound, showing
more than 10-fold increase in potency as compared to
AMOA as an AMPA antagonist. All compounds listed
in Table 1 with significant AMPA antagonist potencies
(IC50 < 1 mM) gave parallel rightward shifts of the
AMPA dose-response curve, as illustrated in Figure 2
for ATPO (9b). The antagonist profiles of ATOA (8b),
describe the synthesis and pharmacology of the phos-
phonic acid analog of 10b, compound 10c, and com-
pounds 11b,c, derived from the AMPA agonist homoi-
botenic acid (11a ).10
Resu lts
Ch em istr y. Two different strategies were used for
the syntheses of the target compounds (Scheme 1).
Alkylation of the hydroxy group at the 3-position of the
isoxazole ring of 12a ,c-e21,22 with either chloroacetic
acid ester or {[(p-tolylsulfonyl)oxy]methyl}phosphonate
ester followed by full deprotection using 1 M hydrochlo-
ric acid gave the desired carboxy or phosphono amino
acids, compounds 8c-e and 9a ,c-e, respectively. For
the synthesis of compounds 8b,g and 9b,f,g, the pro-

1684 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Madsen et al.
Sch em e 1a
a
(i) ClCH2COOEt, K2CO3; (ii) CH3(C6H4)SO3CH2PO3Et2, NaH; (iii) 1 M HCl; (iv) CH3SO3CH2PO3Et2, K2CO3; (v) NBS; (vi)
BocNHCH(COOEt)2, NaH; (vii) AcNHCH(COOEt)2, (CH3)3COK; (viii) AcNHCH(COOMe)2, NaH; (ix) 2 M NaOH; (x) (CH3)3SiBr.
AMPO (9a ), and ATPO (9b) are compared with that of
AMOA (7) in Figure 3. Not only are these compounds
more potent as AMPA antagonists, as compared to
AMOA, but they also show a higher degree of selectivity.
In the case of ATOA (8b) and ATPO (9b) (Figure 3), no
significant antagonism of NMDA responses are observed
even at concentrations of 1 mM, whereas AMOA (7) and
AMPO (9a ) did show a weak inhibitory effect at 1 mM
toward NMDA-induced responses (19 ( 7% and 31 (
4% inhibition, respectively) (see Figure 3). For com-
pounds showing a significant AMPA receptor antagonist
effect (IC50 < 1 mM), a weak antagonism of kainic acid
responses was generally observed at 1 mM concentra-
tions of the antagonist (Figure 3). This probably reflects
that kainic acid shows weak AMPA receptor agonist
effects in addition to its agonism at kainic acid recep-
tors.3 The bicyclic compound 10c showed a selective
NMDA antagonist effect comparable with that described
for the carboxylic acid analog 10b20 (Table 1). The two
compounds derived from the AMPA agonist homoi-
botenic acid (11a ), compounds 11b,c, were completely
inactive in the studies performed (Table 1).
distal acidic moiety (Figure 1). In electrophysiological
experiments antagonist potencies of the new compounds
varied considerably, and all compounds showing AMPA
antagonist activity (IC50 < 1 mM) gave parallel right-
ward shifts of the AMPA dose-response curves, indica-
tive of competitive antagonism. The results of [3H]-
AMPA binding studies showed weak inhibition by the
more potent antagonists AMOA (7), ATOA (8b), AMPO
(9a ), and ATPO (9b) with IC50 values ranging from 31
to 90 µM. Using the [3H]CNQX binding assay, a better
correlation between the electrophysiological data and
the binding data was demonstrated, although AMOA
does show some anomaly. The fairly low affinities
observed in the [3H]AMPA and [3H]CNQX binding
assays for the antagonists described may reflect a
difference in binding mode for these antagonists as
compared to the binding mode for the agonist AMPA
as well as for the quinoxalinedione antagonist CNQX.
The observed affinities may also reflect dissimilar
binding to different subtypes of AMPA receptors.
Among the carboxylic acid analogs, only ATOA (8b)
showed higher AMPA antagonist potency than AMOA
(7). All of the analogs 8c-g were virtually inactive (IC50
> 1 mM). Generally, the phosphonic acid analogs 9a -g
showed higher potency than the corresponding carboxy-
lic acid analogs (7 and 8b-g), ATPO (9b) being the most
potent AMPA antagonist. Concomitantly with the
potency increase, ATOA (8b) and ATPO (9b) also
showed improved selectivity toward AMPA receptors,
as compared with AMOA (7). In contrast to AMOA,
Discu ssion
A series of “structural hybrids” of the AMPA receptor
antagonist AMOA (7) and the NMDA antagonists AP5
(3) and CPP (4) were synthesized and characterized
pharmacologically in vitro. These analogs contain dif-
ferent substituents in the 5-position of the isoxazole ring
and either a carboxylic acid or a phosphonic acid as the

Carboxy and Phosphono AMPA Receptor Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1685
Sch em e 2a
a
(i) HCl/EtOH; (ii) BocOBoc, TEA; (iii) ClCH2COOEt, K2CO3; (iv) HCl/EtOAc; (v) TEA; (vi) CH3(C6H4)SO3CH2PO3Et2, NaH; (vii) NBS;
(viii) NaH; (ix) 1 M HCl; (x) AcNHCH(COOEt)2, C2H5ONa; (xi) AcNHCH(COOMe)2, NaH.
Ta ble 1. Receptor Binding and Electrophysiological Data (Mean ( SEM, n ) 3-6)
IC50 (µM)
compd
[3H]AMPA
[3H]CNQX
[3H]CPP
[3H]KAIN
>100
electrophysiologya
AMOAb (7)
ATOA (8b)
90 ( 14
33 ( 6
>100
>100
>100
>100
>100
31 ( 3
35 ( 3
>100
>100
>100
>100
>100
>100
>100
>100
>100
8.0 ( 0.7
12 ( 5
87 ( 20
63 ( 18
>100
320 ( 25
150 ( 14
>1000c
>1000d
>1000
>1000
>1000
60 ( 7
28 ( 3
140 ( 14
350 ( 38
>1000e
>1000
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
8c
8d
8e
8f
>100
>100
>100
8g
AMPO (9a )
ATPO (9b)
9c
6.9 ( 2.6
5.7 ( 3.2
18 ( 6
nt
9d
9e
9f
9g
35 ( 10
>100
>100
360 ( 64
170 ( 10g
135 ( 18g
>1000
10bf
10c
11b
nt
16.4
22 ( 6
>100
>100
25h
0.050 ( 0.025
>100
>100
>100
>100
11c
>1000
CNQX
CPP (4)
KAIN
0.37 ( 0.04
>100
4.0 ( 0.9
0.038 ( 0.004
1.5h
nt
0.016 ( 0.004
0.6i
nt
1.6i
100j
agonist
a
b
d
Antagonism of AMPA-induced responses. Reference 17. c 29 ( 7% inhibition at 1000 µM 8c. 45 ( 4% inhibition at 1000 µM 8d .
e 43 ( 3% inhibition at 1000 µM 9e. f Reference 20. Antagonism of NMDA-induced responses. Reference 30. Ki value. Reference 31.
nt, not tested.
g
h
i
j
neither ATOA nor ATPO showed any antagonist activity
at 1 mM concentrations toward NMDA-induced re-
sponses (Figure 3).
to different sites at the AMPA receptors and/or different
conformations of the receptors.
For the bicyclic phosphonic acid analog 10c, which is
an analog of compound 10b, previously shown to be a
selective NMDA antagonist,20 equal NMDA antagonist
effects were observed. The comparable potency of 10b,c
as NMDA antagonists is somewhat surprising, since
conversion of NMDA antagonists containing a distal
carboxylic acid into the corresponding phosphonic acid
analogs generally results in a significant increase in
antagonist potency.6,7 AMOA (7), 8b-g, and 9a -g, as
well as 10b,c, all have the same chain length as the
The increased antagonist potency for the two tert-
butyl analogs 8b and 9b is interesting, as the opposite
effect on agonist activity is observed for AMPA (5) and
the AMPA analog with a tert-butyl substituent, AT-
PA11,33 (6b), showing EC50 values of 3.5 and 48 µM,
respectively. Such discrepancies in structure-activity
relationships for AMPA agonists versus antagonists
may indicate a difference in binding mode, possibly
reflecting that these two categories of compounds bind

1686 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Madsen et al.
organic phases was performed with MgSO4, and evaporations
were performed under vacuum on a rotary evaporator at 15
mmHg. Tachigaren (29) was kindly supplied by Cheminova
A/S, Denmark.
Gen er a l P r oced u r e A: P r ep a r a tion of 3-[(Eth oxyca r -
bon yl)m eth oxy]isoxa zoles (Com p ou n d s 13c-e, 16g, 23,
a n d 30). A mixture of 3-hydroxyisoxazole 12c-e, 15g, 22b,
or 29, K2CO3 (2 equiv), and acetone was stirred for 30 min at
60 °C. Ethyl chloroacetate (3 equiv) was added and stirring
continued for 5 h at 60 °C. After cooling the reaction mixture
was filtered and evaporated.
Gen er a l P r oced u r e B: P r ep a r a tion of 3-[(Dieth oxy-
p h osp h or yl)m eth oxy]isoxa zoles (Com p ou n d s 14a ,c-e,
17b, 26, a n d 31). Sodium hydride (1.1 equiv) was suspended
in DMF under nitrogen, and 3-hydroxyisoxazole 12a ,c-e, 15b,
25, or 29 dissolved in DMF was added dropwise. Diethyl
{[(p-tolylsulfonyl)oxy]methyl}phosphonate (1.5 equiv) dissolved
in DMF was added, and the reaction mixture was stirred at
room temperature for 3 days and then evaporated to dryness
(l mmHg). H2O was added to the residue and extracted with
EtOAc. The EtOAc phase was dried and evaporated.
Gen er a l P r oced u r e C: P r ep a r a tion of ω-Ca r boxy or
ω-P h osp h on o r-Am in o Acid s (Com p ou n d s 8c-e,g, 9a -
g, 10c, a n d 11b,c). The protected intermediate 13c-e, 20g,
14a ,c-e, ethyl 2-acetamido-2-(ethoxycarbonyl)-3-[5-phenyl-3-
(phosphonomethoxy)-4-isoxazolyl]propionate, ethyl 2-aceta-
mido-2-(ethoxycarbonyl)-3-[3-(phosphonomethoxy)-5-(2-thienyl)-
4-isoxazolyl]propionate, or 34 was boiled under reflux in 1 M
HCl for 12-72 h (monitored by TLC and ninhydrin spray
reagent) and then evaporated and reevaporated twice from
H2O.
Gen er a l P r oced u r e D: P r ep a r a tion of Isoxa zole Br o-
m om eth yl Der iva tives (Com p ou n d s 18b,g, 19b,f,g, 27, 32,
a n d 33). A solution of starting material 16b,g, 17b,f,g, 26,
30, or 31 in CCl4 was treated under reflux with NBS (1.05
equiv) and benzoyl peroxide (0.1 equiv) over a period of 4-8
h. NBS and benzoyl peroxide were added in four equal
portions at 1-2 h intervals. After cooling of the reaction
mixture, filtration and evaporation gave crude brominated
product.
F igu r e 2. Dose-response curves as determined in the rat
cortical slice preparation for AMPA (5) alone and AMPA
coapplied with 100 µM ATPO (9b).
potent and selective NMDA antagonist CPP (4). The
pharmacological selectivities of the compounds under
study seem to indicate that only compounds 10b,c can
adopt conformations recognizable by the “antagonist
conformation” of the NMDA receptor. For the other
analogs, the AMPA structural element may mediate the
AMPA receptor selectivity. The two compounds 11b,c,
derived from the weak AMPA agonist homoibotenic acid
(11a ),10 were inactive, indicating that the introduction
of a carboxymethyl or a phosphonomethyl group on the
3-hydroxyisoxazole moiety of AMPA agonists is not a
generally applicable principle for the design of AMPA
receptor antagonists.
In conclusion, a number of AMPA receptor antago-
nists, containing either a distal carboxylic acid or a
phosphonic acid moiety, has been synthesized. The
antagonist effects of the compounds were highly de-
pendent on the substituents on the molecules as well
as on the nature of the distal acidic moiety, phosphonic
acids generally being more potent than the correspond-
ing carboxylic acids. The phosphonic acid analog ATPO
(9b) was markedly more potent and selective than the
parent compound, AMOA (7), as an AMPA receptor
antagonist.
Met h yl 2-Acet a m id o-3-{5-b u t yl-[3-(et h oxyca r b on yl)-
m et h oxy]-4-isoxa zolyl}-2-(m et h oxyca r b on yl)p r op ion -
a te (13c). 13c was prepared from 12c14 according to general
procedure A and purified by CC [tol-EtOAc (3:1)] and recrys-
tallization (EtOAc-light petroleum), which gave 13c as color-
1
less crystals (400 mg, 31%): mp 67-68 °C; H NMR (CDCl3,
200 MHz) δ 7.03 (s, 1H), 4.76 (s, 2H), 4.26 (q, 2H, J ) 7 Hz),
3.79 (s, 6H), 3.41 (s, 2H), 2.51 (t, 2H, J ) 7 Hz), 1.99 (s, 3H),
1.60 (m, 2H), 1.4-1.2 (m, 5H), 0.91 (t, 3H, J ) 7.2 Hz). Anal.
(C19H28N2O9) C, H, N.
Meth yl 2-Aceta m id o-3-{3-[(eth oxyca r bon yl)m eth oxy]-
5-(1-p r op ylbu tyl)-4-isoxa zolyl}-2-(m eth oxyca r bon yl)p r o-
p ion a te (13d ). 13d was prepared from 12d 22 according to
general procedure A and purified by CC [tol-EtOAc (2:1)
containing 1% AcOH] and recrystallization (tol-light petro-
leum), which gave 13d as colorless crystals (660 mg, 47%): mp
Exp er im en ta l Section
1
95-96.5 °C; H NMR (CDCl3, 200 MHz) δ 4.75 (s, 2H), 4.25
Ch em istr y. Melting points were determined in capillary
tubes and are uncorrected. Column chromatography (CC) was
performed on Merck silica gel 60 (70-230 mesh, ASTM) and
flash chromatography on Merck silica gel 60 H. Elemental
analyses were performed by Mr. G. Cornali, Microanalytical
Laboratory, Leo Pharmaceutical Products, Denmark, Mr. P.
Hansen, Department of General and Organic Chemistry,
University of Copenhagen, or Analytical Research Department,
H. Lundbeck A/S, Denmark, and are within (0.4% of the
calculated values unless otherwise stated. 1H NMR spectra
were recorded on a Varian EM 360L (60 MHz), a Bruker AC-
200F (200 MHz), or a Bruker AC 250 (250 MHz) instrument
using TMS or 1,4-dioxane, unless otherwise stated, as internal
standard for spectra recorded in organic or aqueous solvents,
respectively. Compounds containing the 3-hydroxyisoxazole
moiety were visualized on TLC plates using UV light and a
FeCl3 spraying reagent (yellow colors). Compounds containing
amino groups were visualized using a ninhydrin spraying
reagent, and all compounds under study were also detected
on TLC plates using a KMnO4 spraying reagent. Drying of
(q, 2H, J ) 7 Hz), 3.75 (s, 6H), 3.45 (s, 2H), 2.7 (m, 1H), 1.95
(s, 3H), 1.55 (m, 4H), 1.30 (t, 3H, J ) 7 Hz), 1.20 (m, 4H), 0.9
(t, 6H, J ) 7 Hz). Anal. (C22H34N2O9) C, H, N.
Meth yl 2-Aceta m id o-3-{3-[(eth oxyca r bon yl)m eth oxy]-
5-(2,2-d im eth ylp r op yl)-4-isoxa zolyl}-2-(m eth oxyca r bon -
yl)p r op ion a te (13e). 13e was prepared from 12e22 according
to general procedure A, purified by CC [tol-EtOAc (2:1)
containing 1% AcOH], and recrystallized (tol-light petroleum)
to give 13e as colorless crystals (34 mg, 48%): mp 127-128
°C; 1H NMR (CDCl3, 200 MHz) δ 4.75 (s, 2H), 4.25 (q, 2H, J )
7 Hz), 3.8 (s, 6H), 3.45 (s, 2H), 2.4 (s, 2H), 2.0 (s, 3H), 1.3 (t,
3H, J ) 7 Hz), 0.95 (s, 9H). Anal. (C20H30N2O9) C, H, N.
Meth yl 2-Aceta m id o-3-{3-[(d ieth oxyp h osp h or yl)m eth -
oxy]-5-m eth yl-4-isoxa zolyl}-2-(m eth oxyca r bon yl)p r op i-
on a te (14a ). 14a was prepared from 12a 21 according to
general procedure B, purified by CC [tol-EtOAc (1:3) contain-
ing 1% AcOH], and recrystallized (EtOAc-light petroleum) to
give 14a as a colorless powder (410 mg, 15%): mp 96.5-98.0
°C; 1H NMR (CDCl3, 200 MHz) δ 6.81 (s, 1H), 4.53 (d, 2H, J )

Carboxy and Phosphono AMPA Receptor Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1687
F igu r e 3. Effects of AMOA (7) (A), AMPO (9a ) (B), ATOA (8b) (C), and ATPO (9b) (D) on rat cortical depolarizations induced
by NMDA, AMPA, or kainic acid (KAIN). Normalized responses ( SEM; n ) 3-6.
8.6 Hz), 4.22 (q, 2H, J ) 7.0 Hz), 4.18 (q, 2H, J ) 7.0 Hz), 3.82
(s, 6H), 3.37 (s, 2H), 2.21 (s, 3H), 2.04 (s, 3H), 1.35 (t, 6H, J )
7.0 Hz). Anal. (C17H27N2O10P) C, H, N.
3.9 (m, 1H), 2.9 (m, 2H), 2.6 (t, 2H, J ) 7 Hz), 1.5 (m, 2H), 1.2
(m, 2H), 0.76 (t, 3H, J ) 7 Hz). Anal. (C12H18N2O6‚2H2O) C,
N; H: calcd, 6.87; found, 6.25.
Meth yl 2-Aceta m id o-3-{5-bu tyl-3-[(d ieth oxyp h osp h o-
r yl)m et h oxy]-4-isoxa zolyl}-2-(m et h oxyca r b on yl)p r op i-
on a te (14c). 14c was prepared from 12c22 according to
general procedure B, purified by CC [tol-EtOAc (1:1) contain-
ing 1% AcOH], and recrystallized (EtOAc-light petroleum) to
give 14c as colorless crystals (310 mg, 17%): mp 94-95 °C;
1H NMR (CDCl3, 200 MHz) δ 6.86 (s, 1H), 4.54 (d, 2H, J ) 8.5
Hz), 4.22 (q, 2H, J ) 7.0 Hz), 4.18 (q, 2H, J ) 7.1 Hz), 3.81 (s,
6H), 3.37 (s, 2H), 2.52 (t, 2H, J ) 7.6 Hz), 2.04 (s, 3H), 1.56
(m, 2H), 1.42-1.25 (m, 2H), 1.35 (t, 6H, J ) 7.1 Hz), 0.91 (t,
3H, J ) 7.2 Hz). Anal. (C20H33N2O10P) C, H, N.
(RS)-2-Am in o-3-[3-(car boxym eth oxy)-5-(1-pr opylbu tyl)-
4-isoxa zolyl]p r op ion ic Acid Zw itter ion (8d ). 8d was
prepared from 13d according to general procedure C. Recrys-
tallization (H2O) gave 8d (104 mg, 60%): mp 214-216 °C dec;
1H NMR (DMSO-d6, 200 MHz) δ 4.65 (s, 2H), 3.6 (t, 1H, J )
7 Hz), 2.9-2.7 (m, 3H), 1.6 (m, 4H), 1.25 (m, 4H), 0.9 (t, 6H,
J ) 7 Hz). Anal. (C15H24N2O6) H, N; C: calcd, 54.87; found,
54.42.
(RS)-2-Am in o-3-[3-(ca r boxym eth oxy)-5-(2,2-d im eth yl-
p r op yl)-4-isoxa zolyl]p r op ion ic Acid Zw itter ion (8e). 8e
was prepared from 13e according to general procedure C.
Recrystallization (H2O) gave 8e (11.5 mg, 56%): mp 228-231
°C dec; 1H NMR (D2O, 200 MHz) δ 4.65 (s, 2H), 3.9 (dd, 1H, J
) 7, 5.5 Hz), 2.9 (m, 2H), 2.5 (d, 1H, J ) 15 Hz), 2.4 (d, 1H, J
) 15 Hz), 0.85 (s, 9H). Anal. (C13H20N2O6) C, H, N.
(RS)-2-Am in o-3-[5-m et h yl-3-(p h osp h on om et h oxy)-4-
isoxa zolyl]p r op ion ic Acid Zw itter ion (9a ). 9a was pre-
pared from 14a according to general procedure C. Recrystal-
lization (H2O) afforded 9a (220 mg, 75%): mp 225-230 °C dec;
1H NMR (D2O, 200 MHz) δ 4.29 (d, 2H, J ) 9.6 Hz), 4.05 (t,
1H, J ) 6.4 Hz), 2.95 (d, 2H, J ) 6.4 Hz), 2.24 (s, 3H). Anal.
(C8H13N2O7P) C, H, N.
(RS)-2-Am in o-3-[5-bu tyl-3-(ph osph on om eth oxy)-4-isox-
a zolyl]p r op ion ic Acid Zw itter ion (9c) Hyd r a te. 9c was
prepared from 14c according to general procedure C. The
residue was dissolved in H2O-EtOH (1:2) and the pH adjusted
to ca. 2.5. Recrystallization (H2O) of the obtained precipitate
afforded 9c (44 mg, 22%): mp 177-180 °C dec; 1H NMR (D2O,
200 MHz) δ 4.25 (d, 2H, J ) 9 Hz), 4.05 (t, 1H, J ) 6.3 Hz),
2.95 (d, 2H, J ) 6.3 Hz), 2.55 (t, 2H, J ) 7 Hz), 1.5 (quintet,
2H, J ) 7 Hz), 1.2 (sextet, 2H, J ) 7 Hz), 0.75 (t, 3H, J ) 7
Hz). Anal. (C11H19N2O7P‚1.5H2O) C, H, N.
Meth yl 2-Aceta m id o-3-{3-[(d ieth oxyp h osp h or yl)m eth -
oxy]-5-(1-p r op ylbu tyl)-4-isoxa zolyl}-2-(m eth oxyca r bon -
yl)p r op ion a te (14d ). 14d was prepared from 12d 22 according
to general procedure B, purified by CC [tol-EtOAc (1:1)], and
recrystallized to give 14d as a colorless powder (164 mg,
24%): mp 92-93 °C; 1H NMR (CDCl3, 200 MHz) δ 6.83 (s,
1H), 4.54 (d, 2H, J ) 8.2 Hz), 4.22 (q, 2H, J ) 7.1 Hz), 4.18 (q,
2H, J ) 7.1 Hz), 3.80 (s, 6H), 3.40 (s, 2H), 2.65 (m, 1H), 2.02
(s, 3H), 1.6 (m, 4H), 1.4-1.2 (m, 4H), 1.35 (t, 6H, J ) 7.1 Hz),
0.87 (t, 6H, J ) 7.0 Hz). Anal. (C23H39N2O10P) C, H, N.
Meth yl 2-Aceta m id o-3-{3-[(d ieth oxyp h osp h or yl)m eth -
oxy]-5-(2,2-d im eth ylp r op yl)-4-isoxa zolyl}-2-(m eth oxyca r -
bon yl)p r op ion a te (14e). 14e was prepared from 12e22
according to general procedure B, purified by CC [tol-EtOAc
(1:1) containing 1% AcOH], and recrystallized (EtOAc-light
petroleum) to give 14e as colorless crystals (310 mg, 31%): mp
1
163-164 °C; H NMR (CDCl3, 200 MHz) δ 6.95 (s, 1H), 4.55
(d, 2H, J ) 8.4 Hz), 4.22 (q, 2H, J ) 7.1 Hz), 4.19 (q, 2H, J )
7.1 Hz), 3.80 (s, 6H), 3.40 (s, 2H), 2.43 (s, 2H), 2.03 (s, 3H),
1.35 (t, 6H, J ) 7.1 Hz), 0.96 (s, 9H). Anal. (C21H35N2O10P)
C, H, N.
(RS)-2-Am in o-3-[5-b u t yl-3-(ca r b oxym et h oxy)-4-isox-
a zolyl]p r op ion ic Acid Zw itter ion (8c) Dih yd r a te. 8c was
prepared from 13c according to general procedure C. The
residue was dissolved in H2O and EtOH and the pH adjusted
to ca. 3 by addition of TEA. Recrystallization of the precipi-
tate, first from AcOH and then from H2O, afforded 13c (102
(RS)-2-Am in o-3-[3-(p h osp h on om et h oxy)-5-(1-p r op yl-
bu tyl)-4-isoxazolyl]pr opion ic Acid Zwitter ion (9d) Mon o-
h yd r a te. 9d was prepared from 14d according to general
procedure C. The residue was dissolved in H2O-EtOH (1:2)
and the pH adjusted to ca. 2.5. Recrystallization (H2O) of the
precipitate gave 9d (30 mg, 29%): mp 218-220 °C dec; 1H
NMR (D2O, 200 MHz) δ 4.25 (d, 2H, J ) 9 Hz), 3.95 (br t, 1H,
1
mg, 50%): mp 215-217 °C dec; H NMR (D2O, 200 MHz) δ

1688 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Madsen et al.
J ) 7 Hz), 2.95-2.75 (m, 3H), 1.5 (m, 4H), 1.1 (m, 4H), 0.75
(t, 6H, J ) 7 Hz). Anal. (C14H25N2O7P‚H2O) C, H, N.
Hz), 1.41 (s, 9H), 1.35 (t, 6H, J ) 7 Hz). The crude product
was used in the next step without further characterization.
Dieth yl {{[4-(Br om om eth yl)-5-ph en yl-3-isoxazolyl]oxy}-
m eth yl}p h osp h on a te (19f). 19f was prepared from 17f
according to general procedure D. Crude product (3.0 g, 100%)
was used in the next step without further purification: 1H
NMR (CDCl3, 250 MHz) δ 7.85-7.74 (m, 2H), 7.60-7.50 (m,
3H), 4.69 (d, 2H, J ) 8.8 Hz), 4.42 (s, 2H), 4.29 (q, 2H, J ) 7.1
Hz), 4.26 (q, 2H, J ) 7.1 Hz), 1.39 (t, 6H, J ) 7.1 Hz).
Dieth yl {{[4-(Br om om eth yl)-5-(2-th ien yl)-3-isoxa zolyl]-
oxy}m eth yl}p h osp h on a te (19g). 19g was prepared from
17g according to general procedure D. Crude product (3.7 g,
100%): 1H NMR (CDCl3, 250 MHz) δ 7.65-7.58 (m, 2H), 7.21
(dd, 1H, J ) 5.0, 3.8 Hz), 4.67 (d, 2H, J ) 8.8 Hz), 4.44 (s,
2H), 4.28 (q, 2H, J ) 7.1 Hz), 4.25 (q, 2H, J ) 7.1 Hz), 1.39 (t,
6H, J ) 7.1 Hz). The crude product was used in the next step
without further purification.
Eth yl 3-{5-ter t-Bu tyl-3-[(eth oxyca r bon yl)m eth oxy]-4-
isoxa zolyl}-2-[N-(ter t-bu tyloxyca r bon yl)a m in o]-2-(eth ox-
yca r bon yl)p r op ion a te (20b). To a suspension of NaH (1.6
g, 60% suspension, 41 mmol) in DMF (37 mL) was added a
solution of diethyl [N-(tert-butyloxycarbonyl)amino]malonate24
(11.2 g, 41 mmol) in DMF (37 mL). After stirring for 15 min,
a solution of 18b (11.8 g, 37 mmol) in DMF (15 mL) was added.
The reaction mixture was stirred for 18 h at room temperature
and evaporated. An ice-cold solution of the residue in CHCl3
(300 mL) was washed with ice-cold H2O (100 mL), dried, and
evaporated. CC (tol containing 0-50% EtOAc) of the residue
gave crude 20b as an oil (16 g, 84%): 1H NMR (CDCl3, 200
MHz) δ 6.22 (s, 1H), 4.72 (s, 2H), 4.40-4.05 (m, 6H), 3.52 (s,
2H), 1.41 (s, 9H), 1.34 (s, 9H), 1.25 (t, 9H, J ) 7.2 Hz). The
crude product was used in the next step without further
characterization.
Eth yl 2-Aceta m id o-2-(eth oxyca r bon yl)-3-{3-[(eth oxy-
c a r b o n y l)m e t h o x y ]-5-(2-t h ie n y l)-4-is o x a z o ly l}p r o -
p ion a te (20g). A mixture of diethyl acetamidomalonate (3.5
g, 16.2 mmol) and potassium tert-butoxide (1.9 g, 17 mmol) in
N-methylpyrrolidone (30 mL) was stirred at room temperature
for 30 min. Compound 18g (2.8 g, 8.1 mmol) in N-methylpyr-
rolidone (5 mL) was added, and the resulting mixture was
stirred for 1 h and then poured into H2O (250 mL) at 0 °C.
The aqueous phase was extracted with ether (3 × 200 mL),
and the combined organic phases were washed with brine (200
mL), dried, and evaporated. Flash chromatography [n-hep-
tane-EtOAc-MeOH (20:10:1)] followed by another flash chro-
matography [CH2Cl2-EtOAc (7:1)] gave crude 20g as a
greenish oil (2.3 g, 59%). A small sample was recrystallized
(EtOH) to give 20g: mp 92-94 °C; 1H NMR (CDCl3, 250 MHz)
δ 7.51 (dd, 1H, J ) 3.7, 1.0 Hz), 7.47 (dd, 1H, J ) 5.1, 1.0 Hz),
7.13 (dd, 1H, J ) 5.1, 3.7 Hz), 7.07 (br s, 1H), 4.81 (s, 2H),
4.29 (q, 2H, J ) 7.1 Hz), 4.29-3.90 (m, 4H), 3.73 (s, 2H), 1.81
(s, 3H), 1.32 (t, 3H, J ) 7.1 Hz), 1.17 (t, 6H, J ) 7.1 Hz). Anal.
(C21H26N2O9S) C, H, N.
Meth yl 2-Aceta m id o-3-{5-ter t-bu tyl-3-[(d ieth oxyp h os-
p h or yl)m eth oxy]-4-isoxa zolyl}-2-(m eth oxyca r bon yl)p r o-
p ion a te (21b). To a suspension of NaH (32 mg, 60% disper-
sion, 0.78 mmol) in DMF (10 mL) under nitrogen was added a
solution of dimethyl acetamidomalonate (135 mg, 0.84 mmol)
in DMF (2 mL). After stirring for 15 min a solution of 19b
(250 mg, 0.71 mmol) in DMF (3 mL) was added and stirring
continued for 18 h. The reaction mixture was evaporated (1
mmHg), H2O added, and extraction performed with EtOAc.
The organic phase was dried and evaporated and the residue
purified by CC [tol-EtOAc (1:4)] and recrystallized (EtOAc-
light petroleum) to give 21b (185 mg, 53%): mp 88-89 °C; 1H
NMR (CDCl3, 200 MHz) δ 7.52 (s, 1H), 4.53 (d, 2H, J ) 8.1
Hz), 4.24 (q, 2H, J ) 7.1 Hz), 4.20 (q, 2H, J ) 7.1 Hz), 3.75 (s,
6H), 3.61 (s, 2H), 2.03 (s, 3H), 1.36 (t, 6H, J ) 7.1 Hz), 1.35 (s,
9H). Anal. (C20H33N2O10P) C, H, N.
(RS)-2-Am in o-3-[5-(2,2-d im et h ylp r op yl)-3-(p h osp h o-
n om eth oxy)-4-isoxa zolyl]p r op ion ic Acid Zw itter ion (9e)
Hyd r a te. 9e was prepared from 14e according to general
procedure C. The residue was dissolved in H2O-EtOH (1:2)
and the pH adjusted to ca. 2.5. Recrystallization (H2O) of the
precipitate gave 9e (45 mg, 25%): mp 217-220 °C dec; 1H
NMR (D2O, 200 MHz) δ 4.26 (d, 2H, J ) 9.2 Hz), 4.13 (t, 1H,
J ) 6.6 Hz), 3.00 (m, 2H), 2.53 (d, 1H, J ) 14.7 Hz), 2.47 (d,
1H, J ) 14.7 Hz), 0.86 (s, 9H). Anal. (C12H21N2O7P‚0.75H2O)
C, H, N.
Eth yl {[4-Meth yl-5-(2-th ien yl)-3-isoxa zolyl]oxy}a ceta te
(16g). 16g was prepared from 15g34 according to general
procedure A and purified by flash chromatography [n-hep-
tane-EtOAc-MeOH (20:10:1)] to give an oil, which crystal-
lized upon standing (8.7 g, 59%). A small sample was
recrystallized (1-propanol) to give 16g as colorless crystals: mp
1
69-71 °C; H NMR (CDCl3, 250 MHz) δ 7.50-7.43 (m, 2H),
7.14 (dd, 1H, J ) 4.8, 3.9 Hz), 4.86 (s, 2H), 4.28 (q, 2H, J )
7.1 Hz), 2.15 (s, 3H), 1.31 (t, 3H, J ) 7.1 Hz). Anal. (C12H13
NO4S) C, H, N.
-
Dieth yl {[(5-ter t-Bu tyl-4-m eth yl-3-isoxazolyl)oxy]m eth -
yl}p h osp h on a te (17b). 17b was prepared from 15b11 ac-
cording to general procedure B and purified by CC [tol-EtOAc
(1:1) containing 1% AcOH] to give a colorless oil (350 mg, 59
mg). Distillation (15 mmHg, 230-240 °C) of a small sample
gave 17b: 1H NMR (CDCl3, 200 MHz) δ 4.55 (d, 2H, J ) 8.7
Hz), 4.25 (q, 2H, J ) 7.1 Hz), 4.21 (q, 2H, J ) 7.1 Hz), 1.95 (s,
3H), 1.36 (t, 6H, J ) 7.1 Hz), 1.34 (s, 9H). Anal. (C13H24NO5P)
C, H, N.
Dieth yl {[(4-Meth yl-5-ph en yl-4-isoxazolyl)oxy]m eth yl}-
p h osp h on a te (17f). A mixture of 15f15 (5.0 g, 29 mmol), K2-
CO3 (7.9 g, 57 mmol), and DMF (100 mL) was stirred at 80 °C
for 30 min. Diethyl {[(methylsulfonyl)oxy]methyl}phosphonate
(14 g, 57 mmol) dissolved in DMF (25 mL) was added and the
reaction mixture stirred at 80 °C for 3.5 h. After cooling, the
mixture was poured into H2O (400 mL) at 0 °C and extracted
with ether. The organic phase was dried and evaporated.
Flash chromatography [n-heptane-EtOAc-TEA (10:10:1)]
afforded 17f as a colorless oil (2.6 g, 28%): 1H NMR (CDCl3,
250 MHz) δ 7.76-7.65 (m, 2H), 7.55-7.40 (m, 3H), 4.64 (d,
2H, J ) 8.6 Hz), 4.35-4.15 (m, 4H), 2.13 (s, 3H), 1.37 (t, 6H,
J ) 7.1 Hz). Anal. (C15H20NO5P) H, N; C: calcd, 55.38; found,
54.74.
Diet h yl {{[4-Met h yl-5-(2-t h ien yl)-3-isoxa zolyl]oxy}-
m eth yl}p h osp h on a te (17g). 17g was prepared from 15g34
(5.0 g, 28 mmol) by the method described for the synthesis of
17f. Flash chromatography [n-heptane-EtOAc (1:2)] gave 17g
(3.0 g, 33%) as a yellow oil, which was used in the next step
without further characterization: 1H NMR (CDCl3, 250 MHz)
δ 7.50-7.44 (m, 2H), 7.15 (dd, 1H, J ) 4.8, 3.8 Hz), 4.63 (d,
2H, J ) 8.6 Hz), 4.26 (q, 2H, J ) 7.1 Hz), 4.23 (q, 2H, J ) 7.1
Hz), 2.11 (s, 3H), 1.37 (t, 6H, J ) 7.1 Hz).
Eth yl {[4-(Br om om eth yl)-5-ter t-bu tyl-3-isoxazolyl]oxy}-
a ceta te (18b). 18b was prepared from 16b 23 according to
general procedure D, yielding crude 18b (12.0 g, 100%).
A
small sample was distilled (128-131 °C, 0.2 mmHg) to give
18b: 1H NMR (CDCl3, 200 MHz) δ 4.85 (s, 2H), 4.38 (s, 2H),
4.27 (q, 2H, J ) 7.1 Hz), 1.41 (s, 9H), 1.30 (t, 3H, J ) 7.1 Hz).
Anal. (C12H18BrNO4) C, H, N.
E t h yl {[4-(Br om om et h yl)-5-(2-t h ien yl)-3-isoxa zolyl]-
oxy}a ceta te (18g). 18g was prepared from 16g according to
general procedure D. Crude 18g (2.8 g, 88%) crystallized upon
standing: mp 79-84 °C; 1H NMR (CDCl3, 250 MHz) δ 7.62
(dd, 1H, J ) 3.8, 1.1 Hz), 7.57 (dd, 1H, J ) 5.1, 1.1 Hz), 7.19
(dd, 1H, J ) 5.1, 3.8 Hz), 4.90 (s, 2H), 4.47 (s, 2H), 4.27 (q,
2H, J ) 7.1 Hz), 1.30 (t, 3H, J ) 7.1 Hz). The crude product
was used for the next step without further characterization.
Dieth yl {{[4-(Br om om eth yl)-5-ter t-bu tyl-3-isoxa zolyl]-
oxy}m eth yl}p h osp h on a te (19b). 19b was prepared from
17b according to general procedure D and purified by CC
[cyclohexane-EtOAc (1:1)] to give crude 19b (1.1 g, 87%) as a
colorless oil: 1H NMR (CDCl3, 200 MHz) δ 4.59 (d, 2H, J ) 9
Hz), 4.34 (s, 2H), 4.27 (q, 2H, J ) 7 Hz), 4.23 (q, 2H, J ) 7
Eth yl 2-Aceta m id o-2-(eth oxyca r bon yl)-3-{3-[(d ieth ox-
y p h o s p h o r y l)m e t h o x y ]-5-p h e n y l-4-is o x a z o ly l}p r o -
p ion a te (21f). 21f was prepared from 19f (3.0 g, 7.4 mmol)
by the procedure described for compound 20g. Flash chroma-
tography [n-heptane-EtOAc (1:4)] and recrystallization
(EtOAc-n-heptane) gave 21f (1.6 g, 40%) as colorless crys-
1
tals: mp 89-91 °C; H NMR (CDCl3, 250 MHz) δ 7.70-7.60

Carboxy and Phosphono AMPA Receptor Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1689
(m, 2H), 7.53-7.42 (m, 3H), 6.67 (br s, 1H), 4.61 (d, 2H, J )
8.5 Hz), 4.32-4.09 (m, 6H), 3.99-3.84 (m, 2H), 3.70 (s, 2H),
1.64 (s, 3H), 1.37 (t, 6H, J ) 7.1 Hz), 1.15 (t, 6H, J ) 7.1 Hz).
Anal. (C24H33N2O10P) C, H, N.
(RS)-2-Am in o-3-[3-(p h osp h on om eth oxy)-5-(2-th ien yl)-
4-isoxa zolyl]p r op ion ic Acid Zw itter ion (9g) Mon oh y-
d r a te. 9g was prepared from compound 21g (1.0 g, 1.9 mmol)
by the procedure described for ethyl 2-acetamido-2-(ethoxy-
carbonyl)-3-[5-phenyl-3-(phosphonomethoxy)-4-isoxazolyl]pro-
pionate followed by general procedure C. The residue was
dissolved in H2O and the pH adjusted to ca. 2.5 with 0.1 M
NaOH. Treatment of the precipitate with H2O gave 9g (420
mg, 66%): mp 220-221 °C dec; 1H NMR (DMSO-d6, CF3-
COOH, 250 MHz) δ 7.90 (d, 1H, J ) 4.8 Hz), 7.65 (d, 1H, J )
3.3 Hz), 7.29 (t, 1H, J ) 4.3 Hz), 4.44 (d, 2H, J ) 8.6 Hz), 4.11
(br s, 1H), 3.28-2.99 (m, 2H). Anal. (C11H13N2O7PS‚H2O) C,
H, N.
E t h yl 2-Acet a m id o-2-(et h oxyca r b on yl)-3-{3-[(d iet h -
oxyp h osp h on yl)m e t h oxy]-5-(2-t h ie n yl)-4-isoxa zolyl}-
p r op ion a te (21g). 21g was prepared from 19g (3.7 g, 9.1
mmol) by the procedure described for compound 20g. Flash
chromatography [n-heptane-EtOAc (1:4) followed by EtOAc]
gave crude 21g (2.8 g, 60%). A small sample was recrystallized
1
(2-propanol) to give 21g: mp 104-105 °C; H NMR (CDCl3,
250 MHz) δ 7.55-7.46 (m, 2H), 7.14 (dd, 1H, J ) 5.1, 3.8 Hz),
6.91 (br s, 1H), 4.60 (d, 2H, J ) 8.4 Hz), 4.31-3.95 (m, 8H),
3.70 (s, 2H), 1.82 (s, 3H), 1.37 (t, 6H, J ) 7.1 Hz), 1.17 (t, 6H,
J ) 7.1 Hz). Anal. (C22H31N2O10PS) C, H, N.
Eth yl (RS)-2-Am in o-3-(3-h ydr oxy-5-ph en yl-4-isoxazolyl)-
p r op ion a te Hyd r och lor id e (22a ). To a solution of acetyl
chloride (26 mL, 366 mmol) in EtOH (130 mL) was added 6f23
(1.40 g, 5.64 mmol). The reaction mixture was boiled under
reflux for 1.5 h, evaporated, and reevaporated twice from tol.
Recrystallization (EtOH) gave 22a (1.46 g, 83%): mp 200-
(RS)-2-Am in o-3-[5-ter t-bu tyl-3-(car boxym eth oxy)-4-isox-
a zolyl]p r op ion ic Acid Zw itter ion (8b) Hem ih yd r a te. To
a solution of 20b (16 g, 31 mmol) in MeOH (110 mL) was added
2 M NaOH (5.55 mL), and the mixture was boiled under reflux
for 3 h and then evaporated. The residue was dissolved in 1
M HCl (148 mL), boiled under reflux for 30 min, and evapo-
rated. The residue was dissolved in H2O and the pH adjusted
to ca. 3.5 by addition of TEA. Recrystallization (H2O) of the
obtained precipitate afforded 8b (6.2 g, 68%): mp 233-235
1
201 °C dec; H NMR (D2O, 200 MHz, CH3CN δ 2.0) δ 7.65-
7.45 (5H, m), 4.28 (t, 1H, J ) 13.1 Hz), 4.1-3.8 (2H, m), 3.25
(dd, 1H, J ) 6.2, 15.5 Hz), 3.16 (dd, 1H, J ) 6.9, 15.5 Hz),
1.02 (t, 3H, J ) 7.2 Hz). Anal. (C14H17ClN2O4) C, H, N.
E t h yl (RS)-2-[N-(ter t-Bu t yloxyca r b on yl)a m in o]-3-(3-
h yd r oxy-5-p h en yl-4-isoxa zolyl)p r op ion a te (22b). To an
ice-cold solution of 22a (700 mg, 2.24 mmol) in EtOH (30 mL)
were added TEA (937 µL, 6.72 mmol) and a solution of di-tert-
butyl dicarboxylate (BocOBoc) (1.30 mL, 5.57 mmol) in EtOH
(5 mL), and the mixture was stirred at 0 °C for 1.5 h. The
reaction mixture was evaporated, and H2O (40 mL) and EtOAc
(40 mL) were added. The mixture was cooled on ice and, while
stirring, acidified with AcOH. The phases were separated, and
the aqueous phase was extracted with EtOAc (2 × 40 mL).
The combined and dried organic phases were filtered and
evaporated. Recrystallization (EtOAc) gave TLC-pure 22b
(640 mg, 76%). A small sample was recrystallized (EtOAc) to
1
°C dec; H NMR (D2O, CF3COOD, 200 MHz) δ 4.87 (s, 2H),
4.26 (br t, 1H, J ) 7.4 Hz), 3.24 (dd, 1H, J ) 15.5, 6.7 Hz),
3.08 (dd, 1H, J ) 15.5, 7.9 Hz), 1.30 (s, 9H). Anal. (C12H18
N2O6‚0.5H2O) C, H, N.
-
(RS)-2-Am in o-3-[3-(ca r b oxym et h oxy)-5-(2-t h ien yl)-4-
isoxa zolyl]p r op ion ic Acid Zw itter ion (8g) Hyd r a te. 8g
was prepared from 20g according to general procedure C.
Treatment of the residue with H2O gave 8g as colorless
1
crystals (1.0 g, 71%): mp 228-230 °C dec; H NMR (DMSO-
d6, 250 MHz) δ 7.86 (d, 1H, J ) 5.0 Hz), 7.69 (d, 1H, J ) 3.8
Hz), 7.26 (dd, 1H, J ) 5.0, 3.8 Hz), 4.69 (s, 2H), 3.79 (t, 1H, J
) 7 Hz), 3.15 (dd, 1H, J ) 15.2, 5.7 Hz), 2.97 (dd, 1H, J )
15.2, 8.2 Hz). Anal. (C12H12N2O6S‚1.25H2O) C, H, N.
1
give 22b: mp 128.5-129.0 °C; H NMR (CDCl3, 200 MHz) δ
7.71 (m, 2H), 7.49 (m, 3H), 6.38 (br s, 1H), 5.44 (br d, 1H, J )
8 Hz), 4.55 (m, 1H), 4.25-3.90 (m, 2H), 3.11 (m, 2H), 1.40 (s,
9H), 1.18 (t, 3H, J ) 7 Hz). Anal. (C19H24N2O6) C, H, N.
Eth yl (RS)-2-[N-(ter t-Bu tyloxyca r bon yl)a m in o]-3-{3-
[(et h oxyca r b on yl)m et h oxy]-5-p h en yl-4-isoxa zolyl}p r o-
p ion a te (23). 23 was prepared from 22b according to general
procedure A and purified by CC [tol-EtOAc (2:1)] to give a
colorless solid (330 mg, 54%). A small sample was recrystal-
lized (EtOAc-light petroleum) to give 23 as colorless crys-
tals: mp 72.5-73.5 °C; 1H NMR (CDCl3, 200 MHz) δ 7.69 (m,
2H), 7.48 (m, 3H), 5.5 (br d, 1H, J ) 8.5 Hz), 4.95 (d, 1H, J )
16 Hz), 4.84 (d, 1H, J ) 16 Hz) 4.58 (m, 1H), 4.29 (q, 2H, J )
7.15 Hz), 4.20-3.85 (m, 2H), 3.12 (d, 2H, J ) 6.3 Hz), 1.37 (s,
9H), 1.32 (t, 3H, J ) 7.15 Hz), 1.16 (t, 3H, J ) 7.15 Hz). Anal.
(C23H30N2O8) C, H, N.
Eth yl (RS)-2-Am in o-3-{3-[(eth oxyca r bon yl)m eth oxy]-
5-p h en yl-4-isoxa zolyl}p r op ion a te Hyd r och lor id e (24). To
an ice-cold solution of HCl in EtOAc (10 mL, 2.7 M) was added
23 (240 mg, 0.52 mmol), and the mixture was stirred at 0 °C
for 2 h. The reaction mixture was evaporated, reevaporated
twice from tol, and dried. The crude crystalline product was
recrystallized (EtOAc) to give 24 (156 mg, 75%): mp 132.0-
132.5 °C; 1H NMR (D2O, 200 MHz, DOH δ 4.7) δ 7.60 (m, 2H),
7.50 (m, 3H), 4.91 (s, 2H), 4.29 (t, 1H, J ) 6.4 Hz), 4.22 (q,
2H, J ) 7.2 Hz), 4.00-3.65 (m, 2H), 3.27 (m, 2H), 1.20 (t, 3H,
J ) 7.2 Hz), 0.95 (t, 3H, J ) 7.2 Hz). Anal. (C18H23ClN2O6)
C, H, N.
(RS)-2-Am in o-3-[3-(ca r boxym eth oxy)-5-p h en yl-4-isox-
a zolyl]p r op ion ic Acid Zw itter ion (8f). A mixture of 24
(150 mg, 0.38 mmol), TEA (300 µL, 2.15 mmol), and H2O (5
mL) was stirred at room temperature overnight. The reaction
mixture was evaporated and reevaporated twice from tol. The
residue was dissolved in H2O, the pH was adjusted to ca. 3.5
with 0.1 M HCl, and the solution was left at 5 °C. Crude 8f
(80 mg, 69%) precipitated, and recrystallization (H2O) afforded
8f: mp 236-238 °C dec; 1H NMR (D2O, NaOD, 200 MHz, CH3-
CN δ 2.00) δ 7.70 (m, 2H), 7.50 (m, 3H), 4.61 (s, 2H), 3.46 (dd,
1H, J ) 6.0, 8.5 Hz), 2.93 (dd, 1H, J ) 6.0, 14.7 Hz), 2.73 (dd,
1H, J ) 8.5, 14.7 Hz). Anal. (C14H14N2O6) C, H, N.
(RS)-2-Am in o-3-[5-ter t-bu tyl-3-(p h osp h on om eth oxy)-4-
isoxa zolyl]p r op ion ic Acid Zw itter ion (9b) Mon oh yd r a te.
9b was prepared from 14b according to general procedure C.
The residue was dissolved in H2O-EtOH (1:2) and the pH
adjusted to ca. 2.5. Recrystallization (H2O) of the obtained
precipitate gave 9b as a colorless powder (99 mg, 50%): mp
1
218-220 °C dec; H NMR (D2O, 200 MHz) δ 4.25 (d, 2H, J )
9 Hz), 4.1 (t, 1H, J ) 7 Hz), 3.15 (dd, 1H, J ) 15, 7 Hz), 2.9
(dd, 1H, J ) 15, 7 Hz), 1.25 (s, 9H). Anal. (C11H19N2O7P‚H2O)
C, H, N.
Eth yl 2-Aceta m id o-2-(eth oxyca r bon yl)-3-[5-p h en yl-3-
(p h osp h on om eth oxy)-4-isoxa zolyl]p r op ion a te. A solution
of compound 21f (1.2 g, 2.2 mmol) and trimethylsilyl bromide
(1.5 mL, 11 mmol) in CH3CN (25 mL) was stirred at room
temperature for 24 h. The mixture was boiled under reflux
for 30 min and then evaporated to dryness. After addition of
H2O (25 mL) and acetone (30 mL), the mixture was stirred at
room temperature for 1 h and the acetone was evaporated.
The aqueous phase was extracted with EtOAc and the organic
phase washed with brine. After drying and evaporation, ethyl
2-a cet a m ido-2-(et h oxyca r bon yl)-3-[5-ph en yl-3-(ph osph o-
nomethoxy)-4-isoxazolyl]propionate (1.07 g, 99%) was ob-
tained: mp 167-169 °C dec; 1H NMR (CDCl3, DMSO-d6, 250
MHz) δ 7.70-7.57 (m, 2H), 7.53-7.41 (m, 3H), 6.96 (br s, 1H),
4.56 (d, 2H, J ) 9.2 Hz), 4.18-4.02 (m, 2H), 3.91-3.75 (m,
2H), 3.69 (s, 2H), 1.74 (s, 3H), 1.11 (t, 6H, J ) 7.1 Hz). Anal.
(C20H25N2O10P) C, H, N.
(RS)-2-Am in o-3-[5-p h en yl-3-(p h osp h on om et h oxy)-4-
isoxa zolyl]p r op ion ic Acid Zw itter ion (9f) Mon oh yd r a te.
9f was prepared from ethyl 2-acetamido-2-(ethoxycarbonyl)-
3-[5-phenyl-3-(phosphonomethoxy)-4-isoxazolyl]propionate ac-
cording to general procedure C. The residue was dissolved in
H2O and the pH adjusted to ca. 3 by addition of 0.1 M NaOH,
which afforded 9f (500 mg, 63%) as a colorless precipitate: mp
231-232 °C dec; 1H NMR (DMSO-d6, CF3COOH, 250 MHz) δ
7.77-7.66 (m, 2H), 7.64-7.51 (m, 3H), 4.45 (dd, 2H, J ) 8.8,
1.1 Hz), 4.14 (br s, 1H), 3.25-3.00 (m, 2H). Anal. (C13H15
N2O7P‚H2O) C, H, N.
-

1690 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Madsen et al.
Eth yl 2-Aceta m id o-2-(eth oxyca r bon yl)-3-{3-[(d ieth ox-
y p h o s p h o r y l)m e t h o x y ]-5-m e t h y l-4-is o x a zo ly l}p r o -
p ion a te (26). 26 was prepared from compound 2525 (2.0 g,
6.1 mmol) according to general procedure B, purified by CC
[tol-EtOAc (1:4)], and recrystallized (EtOAc-light petroleum)
to give 26 (0.8 g, 27%) as colorless crystals: mp 68-70 °C; 1H
NMR (CDCl3, 200 MHz) δ 6.8 (br s, 1H), 4.53 (d, 2H, J ) 8.5
Hz), 4.35-4.10 (m, 8H), 3.36 (s, 2H), 2.21 (s, 3H), 2.04 (s, 3H),
1.34 (t, 6H, J ) 7.1 Hz), 1.26 (t, 6H, J ) 7.1 Hz). Anal.
(C19H31N2O10P) H, N; C: calcd, 47.69; found, 48.11.
Eth yl 2-Aceta m id o-3-{5-(br om om eth yl)-3-[(d ieth oxy-
p h osp h or yl)m eth oxy]-4-isoxa zolyl}-2-(eth oxyca r bon yl)-
p r op ion a te (27). 27 was prepared from 26 according to
general procedure D, purified by CC [tol-EtOAc (4:1)], and
recrystallized (EtOAc-light petroleum) to give 27 (360 mg,
41%): mp 66-67 °C; 1H NMR (CDCl3, 200 MHz) δ 6.9 (s, 1H),
4.55 (d, 2H, J ) 8.4 Hz), 4.29 (s, 2H), 4.35-4.12 (m, 8H), 3.46
(s, 2H), 2.06 (s, 3H), 1.35 (t, 6H, J ) 7.1 Hz), 1.26 (t, 6H, J )
7.1 Hz). Anal. (C19H30BrN2O10P) C, H, N.
with ice-cold 1 M NaOH, dried, and evaporated. Flash
chromatography [tol-EtOAc (3:1)] gave, after recrystallization
(tol-cyclohexane), 31 (666 mg, 15%): mp 85-86 °C; 1H NMR
(CDCl3, 60 MHz) δ 6.8 (br s, 1H), 5.7 (s, 1H), 4.8 (s, 2H), 4.2
(q, 6H, J ) 7 Hz), 3.8 (s, 2H), 2.0 (s, 3H), 1.3 (t, 9H, J ) 7 Hz).
Anal. (C17H24N2O9) C, H, N.
Meth yl 2-Aceta m id o-3-{3-[(d ieth oxyp h osp h or yl)m eth -
oxy]-5-isoxa zolyl}-2-(m eth oxyca r bon yl)p r op ion a te (35).
35 was prepared from 33 (1.0 g, 3 mmol) by the method
described for compound 21b. Recrystallization (2-propanol)
afforded 35 (802 mg, 61%): mp 106-107 °C; 1H NMR (CDCl3,
200 MHz) δ 6.77 (s, 1H), 5.72 (s, 1H), 4.51 (d, 2H, J ) 9.0 Hz),
4.24 (q, 2H, J ) 7.1 Hz), 4.20 (q, 2H, J ) 7.1 Hz), 3.84 (s, 6H),
3.79 (s, 2H), 2.05 (s, 3H), 1.36 (t, 6H, J ) 7.1 Hz). Anal.
(C16H25N2O10P) C, H, N.
(RS)-2-Am in o-3-[3-(ca r boxym eth oxy)-5-isoxa zolyl]p r o-
p ion ic Acid Zw itter ion (11b). 11b was prepared from 34
according to general procedure C. Recrystallization (H2O)
afforded 11b (125 mg, 69%): mp 252-255 °C dec; 1H NMR
(D2O, NaOD, 60 MHz) δ 6.2 (s, 1H), 4.7 (s, 2H), 3.7 (dd, 1H, J
) 7.5, 5.5 Hz), 3.1 (m, 2H). Anal. (C8H10N2O6) C, H, N.
Eth yl 6-Acetyl-5-(eth oxyca r bon yl)-3-[(d ieth oxyp h os-
p h or yl)m eth oxy]-4,5,6,7-tetr a h yd r oisoxa zolo[5,4-c]p yr i-
d in e-5-ca r boxyla te (28). A solution of 27 (360 mg, 0.65
mmol) in CH3CN (5 mL) was added to a suspension of NaH
(51 mg, 60% dispersion, 1.3 mmol) in CH3CN at 0 °C. The
mixture was stirred at room temperature for 1 h and then
acidified with AcOH and evaporated to dryness. H2O was
added and extraction performed with EtOAc. After drying,
evaporation, and CC [tol-EtOAc (4:1)], recrystallization
(EtOAc-light petroleum) afforded 25 (213 mg, 69%): mp 71-
(RS)-2-Am in o-3-[3-(p h osp h on om eth oxy)-5-isoxa zolyl]-
p r op ion ic Acid Zw itter ion (11c). 11c was prepared from
35 according to general procedure C. The residue was dis-
solved in H2O-EtOH (1:2) and the pH adjusted to ca. 2.5.
Recrystallization (H2O) of the precipitate gave 11c (89 mg,
1
35%): mp 209-210 °C dec; H NMR (D2O, 200 MHz) δ 6.05
(s, 1H), 4.25 (m, 1H), 4.20 (d, 2H, J ) 8.9 Hz), 3.31 (br d, 1H,
J ) 6.1 Hz). Anal. (C7H11N2O7P) C, H, N.
1
72 °C; H NMR (CDCl3, 200 MHz) δ 4.66 (br s, 2H), 4.56 (d,
Recep tor Bin d in g Assa ys. Affinity for AMPA receptors
was determined using the ligands [3H]AMPA27 and [3H]-
CNQX,28 and for determination of NMDA and kainic acid
receptor affinities, [3H]CPP9 and [3H]kainic acid,29 respectively,
were used. The membrane preparations used in all the
receptor binding experiments were prepared according to the
method of Ransom and Stec.35
2H, J ) 8.9 Hz), 4.3-4.1 (m, 8H), 3.24 (br s, 2H), 2.24 (s, 3H),
1.36 (t, 6H, J ) 7.1 Hz), 1.26 (t, 6H, J ) 7.1 Hz). Anal.
(C19H29N2O10P) C, H, N.
(RS)-3-(P h osp h on om et h oxy)-4,5,6,7-t et r a h yd r oisox-
a zolo[5,4-c]p yr id in e-5-ca r boxylic Acid Zw itter ion (10c).
10c was prepared from 28 according to general procedure C.
The residue was dissolved in H2O-EtOH (1:2) and the pH
adjusted to ca. 2.5. Recrystallization (H2O) of the precipitate
In Vitr o Electr op h ysiology. A rat cortical slice prepara-
tion for determination of excitatory amino acid-evoked depo-
larizations described by Harrison and Simmonds32 was used
in a slightly modified version. Wedges (500 µm thick) of rat
brain, containing cerebral cortex and corpus callosum, were
placed through a grease barrier for electrical isolation with
each part in contact with an Ag/AgCl pellet electrode. The
cortex and corpus callosum parts were constantly superfused
with a Mg2+-free oxygenated Krebs buffer at room tempera-
ture. The test compounds were added to the cortex superfu-
sion medium, and the potential difference between the elec-
trodes was recorded on a chart recorder. For determination
of IC50 values, inhibition curves were constructed. The depo-
larization induced by 5 µM AMPA was inhibited with increas-
ing concentrations of the antagonist in question, and for
compounds 10b,c, the depolarizations induced by 10 µM
NMDA were inhibited. Application of agonists were done for
90 s, and for antagonist experiments, the antagonists were
applied alone for 90 s followed by coapplication of the agonist
and antagonist for another 90 s.
1
gave 10c (34 mg, 29%): mp 228-230 °C dec; H NMR (D2O,
200 MHz) δ 4.4 (d, 1H, J ) 16 Hz), 4.25 (m, 3H), 4.12 (dd, 1H,
J ) 10.5, 5 Hz), 3.05 (dd, 1H, J ) 16, 5 Hz), 2.75 (dd, 1H, J )
16, 10.5 Hz). Anal. (C8H11N2O7P) C, H, N.
Eth yl [(5-Meth yl-3-isoxa zolyl)oxy]a ceta te (30). 30 was
prepared from tachigaren26 (29) according to general procedure
A and purified by flash chromatography [tol-EtOAc (19:1)]
to give an oil (2.8 g, 30%). A small sample was distilled (0.2
mmHg, 85-86 °C) to give 30 as a colorless oil: 1H NMR (CCl4,
60 MHz) δ 5.6 (s, 1H), 4.7 (s, 2H), 4.2 (q, 2H, J ) 7 Hz), 2.35
(s, 3H), 1.3 (t, 3H, J ) 7 Hz). Anal. (C8H11NO4) H, N; C: calcd,
51.88; found, 51.47.
Dieth yl {[(5-Meth yl-3-isoxa zolyl)oxy]m eth yl}p h osp h o-
n a te (31). 31 was prepared from tachigaren26 (29) according
to general procedure B and purified by CC [CH2Cl2-EtOAc
(6:1)] to give 31 (3.1 g, 25%) as a pale yellow oil, which was
used in the next step without further purification: 1H NMR
(CDCl3, 200 MHz) δ 5.70 (s, 1H), 4.54 (d, 2H, J ) 8.9 Hz),
4.24 (q, 2H, J ) 7.1 Hz), 4.20 (q, 2H, J ) 7.1 Hz), 2.34 (s, 3H),
1.36 (t, 6H, J ) 7.1 Hz).
Ack n ow led gm en t. This work was supported by
grants from the Lundbeck Foundation, EEC (BIO2-
CT93-0243), and The Danish State Biotechnology Pro-
gramme (1991-1995). The technical assistance of Ulla
Geneser, J ørgen S. J ohansen, and Brian Rosenberg is
gratefully acknowledged.
Dieth yl {{[5-(Br om om eth yl)-3-isoxa zolyl]oxy}m eth yl}-
p h osp h on a te (33). 33 was prepared from 31 according to
general procedure D and purified by CC [CH2Cl2-EtOAc (6:
1)] to give crude 33 (1.0 g, 27%), which was used in the next
step without further purification: 1H NMR (CDCl3, 200 MHz)
δ 6.04 (s, 1H), 4.56 (d, 2H, J ) 8.9 Hz), 4.34 (s, 2H), 4.24 (q,
2H, J ) 7.1 Hz), 4.20 (q, 2H, J ) 7.1 Hz), 1.36 (t, 6H, J ) 7.1
Hz).
Eth yl 2-Aceta m id o-2-(eth oxyca r bon yl)-3-{3-[(eth oxy-
ca r bon yl)m eth oxy]-5-isoxa zolyl}p r op ion a te (34). From
30 was, according to general procedure D, prepared crude ethyl
{[5-(bromomethyl)-3-isoxazolyl]oxy}acetate (32) (3.0 g, 100%).
To a solution of sodium ethoxide prepared from Na (265 mg,
11.5 mmol) and EtOH (30 mL) was added diethyl acetami-
domalonate (2.5 g, 1.5 mmol). To this mixture was added a
solution of 32 (3.0 g, 11.5 mmol) in EtOH (20 mL) followed by
reflux for 4 h. After evaporation, H2O was added and extrac-
tion performed with CH2Cl2. The organic phase was extracted
Refer en ces
(1) Greenamyre, J . T.; Porter, R. H. P. Anatomy and physiology of
glutamate in the CNS. Neurology 1994, 44, 7-13.
(2) Simon, R. P., Ed. Excitatory Amino Acids; Thieme: New York,
1992.
(3) Watkins, J . C.; Krogsgaard-Larsen, P.; Honore´, T. Structure-
activity relationships in the development of excitatory amino acid
receptor agonists and competitive antagonists. Trends Pharma-
col. Sci. 1990, 11, 25-33.
(4) Bowen, D. M. Treatment of Alzheimer’s disease. Br. J . Psychiat.
1990, 157, 327-330.

Carboxy and Phosphono AMPA Receptor Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1691
(5) Meldrum, B. S. The role of glutamate in epilepsy and other CNS
disorders. Neurology 1994, 44 (Suppl.), 14-23.
(20) Madsen, U.; Andresen, L.; Poulsen, G. A.; Rasmussen, T. B.;
Ebert, B.; Krogsgaard-Larsen, P.; Brehm, L. Excitatory amino
acid receptor antagonists: synthesis and pharmacology of 3-(car-
boxymethoxy)isoxazoles derived from AMPA. Bioorg. Med. Chem.
Lett. 1993, 3, 1649-1654.
(21) Begtrup, M.; Sløk, F. A. Equilibrium control in bromomethyla-
tion: an expedient route to 2-amino-3-(3-hydroxy-5-methylisox-
azol-4-yl)propionic acid (AMPA). Synthesis 1993, 861-863.
(22) Sløk, F.; Lenz, S.; Ebert, B.; Krogsgaard-Larsen, P.; Madsen U.
Unpublished results.
(23) Brehm, L.; Madsen, U.; J ohansen, J . S.; Krogsgaard-Larsen, P.
Chemistry of 3-oxygenated isoxazoles. Formation and X-ray
analysis of ethyl (RS)-6-tert-butyl-5-methyl-4-oxo-2,3-dihydro-
4H-1,3-oxazine-2-carboxylate, an isoxazol-3(2H)-one rearrange-
ment product. J . Chem. Soc., Perkin Trans. I 1991, 2009-2013.
(24) Holy, A.; Rosenberg, I. Preparation of 5′-O-phosphonylmethyl
analogues of nucleoside-5′-phosphates, 5′-diphosphates and 5′-
triphosphates. Collect. Czech. Chem. Commun. 1982, 47, 3447-
3463.
(25) Madsen, U.; Nielsen, E. Ø.; Curtis, D. R.; Beattie, D. T.;
Krogsgaard-Larsen, P. Synthesis and single cell pharmacology
of potential heterocyclic bioisosteres of the excitatory amino acid
antagonist glutamic acid diethyl ester. Acta Chem. Scand. 1990,
44, 96-102.
(6) Ornstein, P. L.; Klimkowski, V. J . Competitive NMDA receptor
antagonists. In Excitatory Amino Acid Receptors: Design of
Agonists and Antagonists; Krogsgaard-Larsen, P., Hansen, J . J .,
Eds.; Ellis Horwood: Chichester, 1992; pp 183-200.
(7) Watkins, J . C. Structure/activity relations of competitive NMDA
receptor antagonists. In Excitatory Amino Acid Antagonists;
Meldrum, B. S., Ed.; Blackwell Scientific Publications: London,
1991; pp 84-100.
(8) Davies, J .; Francis, A. A.; J ones, A. W.; Watkins, J . C. 2-Amino-
5-phosphonovalerate (2-APV): a potent and selective antagonist
of amino acid and synaptic activation. Neurosci. Lett. 1981, 21,
77-82.
(9) Murphy, D. E.; Schneider, J .; Boehm, C.; Lehmann, J .; Williams,
K. Binding of [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic
acid to rat membranes. A selective high affinity ligand for
N-methyl-D-aspartate receptors. J . Pharmacol. Exp. Ther. 1987,
240, 778-783.
(10) Krogsgaard-Larsen, P.; Honore´, T.; Hansen, J . J .; Curtis, D. R.;
Lodge, D. New class of glutamate agonist structurally related
to ibotenic acid. Nature (London) 1980, 284, 64-66.
(11) Lauridsen, J .; Honore´, T.; Krogsgaard-Larsen, P. Ibotenic acid
analogues. Synthesis, molecular flexibility, and in vitro activity
of agonists and antagonists at central glutamic acid receptors.
J . Med. Chem. 1985, 28, 668-672.
(12) Arnt, J .; Sa´nchez, C.; Lenz, S. M.; Madsen, U.; Krogsgaard-
Larsen, P. Differentiation of in vivo effects of AMPA and NMDA
receptor ligands using drug discrimination methods and con-
vulsant/anticonvulsant activity. Eur. J . Pharmacol. 1995, in
press.
(13) Turski, L.; J acobsen, P.; Honore´, T.; Stephens, D. N. Relief of
experimental spasticity and anxiolytic/anticonvulsant actions of
the R-amino-3-hydroxy-5-methyl-4-isoxazolepropionate antago-
nist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline. J .
Pharmacol. Exp. Ther. 1992, 260, 742-747.
(14) Brehm, L.; J ørgensen, F. S.; Hansen, J . J .; Krogsgaard-Larsen,
P. Agonists and antagonists for central glutamic acid receptors.
Drug News Perspect. 1988, 1, 138-144.
(15) Christensen, I. T.; Reinhardt, A.; Nielsen, B.; Ebert, B.; Madsen,
U.; Nielsen, E. Ø.; Brehm, L.; Krogsgaard-Larsen, P. Excitatory
amino acid agonists and partial agonists. Drug. Des. Delivery
1989, 5, 57-71.
(16) Madsen, U.; Frølund, B.; Lund, T. M.; Ebert, B.; Krogsgaard-
Larsen, P. Design, synthesis and pharmacology of model com-
pounds for indirect elucidation of the topography of AMPA
receptor sites. Eur. J . Med. Chem. 1993, 28, 791-800.
(17) Krogsgaard-Larsen, P.; Ferkany, J . W.; Nielsen, E. Ø.; Madsen,
U.; Ebert, B.; J ohansen, J . S.; Diemer, N. H.; Bruhn, T.; Beattie,
D. T.; Curtis, D. R. Novel class of amino acid antagonists at non-
N-methyl-D-aspartic acid excitatory amino acid receptors. Syn-
thesis, in vitro and in vivo pharmacology, and neuroprotection.
J . Med. Chem. 1991, 34, 123-130.
(26) J acobsen, N.; Kolind-Andersen, H.; Christensen, J . Synthesis of
3-isoxazolols revisited. Diketene and â-ketoesters as starting
materials. Can. J . Chem. 1984, 62, 1940-1944.
(27) Honore´, T.; Nielsen, M. Complex structure of quisqualate-
sensitive glutamate receptors in rat cortex. Neurosci. Lett. 1985,
54, 27-32.
(28) Honore´, T.; Drejer, J .; Nielsen, E. Ø.; Nielsen, M. Non-NMDA
glutamate receptor antagonist 3H-CNQX binds with equal
affinity to two agonist states of quisqualate receptors. Biochem.
Pharmacol. 1989, 38, 3207-3212.
(29) Braitman, D. J .; Coyle, J . T. Inhibition of [3H]kainic acid receptor
binding by divalent cations correlates with ion affinity for the
calcium channel. Neuropharmacology 1987, 26, 1247-1251.
(30) Honore´, T.; Davies, S. N.; Drejer, J .; Fletcher, E. J .; J acobsen,
P.; Lodge, D.; Nielsen, F. E. Quinoxalinediones: Potent competi-
tive non-NMDA glutamate receptor antagonists. Science 1988,
241, 701-703.
(31) Ebert, B.; Madsen, U.; Lund, T. M.; Lenz, S. M.; Krogsgaard-
Larsen, P. Molecular pharmacology of the AMPA agonist (S)-2-
amino-3-(3-hydroxy-5-phenyl-4-isoxazolyl)propionic acid [(S)-
APPA] and the AMPA antagonist, (R)-APPA. Neurochem. Int.
1994, 24, 507-515.
(32) Harrison, N. L.; Simmonds, M. A. Quantitative studies on some
antagonists of N-methyl-D-aspartate in slices of rat cerebral
cortex. Br. J . Pharmacol. 1985, 84, 381-391.
(33) Ebert, B.; Madsen, U.; Lund, T. M.; Holm, T.; Krogsgaard-
Larsen. P. Molecular Pharmacology of cortical and spinal AMPA
receptors. Mol. Neuropharmacol. 1992, 2, 47-49.
(18) Frandsen, A.; Krogsgaard-Larsen, P.; Schousboe, A. Novel
glutamate receptor antagonists selectively protect against kainic
acid induced neurotoxicity in cultured cerebral cortex neurones.
J . Neurochem. 1990, 55, 1821-1823.
(19) Krogsgaard-Larsen, P.; Brehm, L.; J ohansen, J . S.; Vinzents,
P.; Lauridsen, J .; Curtis, D. R. Synthesis and structure-activity
studies on excitatory amino acids structurally related to ibotenic
acid. J . Med. Chem. 1985, 28, 673-679.
(34) Lenz, S. M.; Falch, E.; Ebert, B.; Bregnedal, B.; Nielsen, B.;
Bøgesø, K. P.; Krogsgaard-Larsen, P. Unpublished results.
(35) Ransom, R. W.; Stec, N. L. Cooperative modulation of [3H]MK-
801 to the N-methyl-D-aspartate receptor ion channel complex
by L-glutamate, glycine and polyamines. J . Neurochem. 1988,
51, 830-836.
J M950826P