Revisiting the Quinoxalinedione Scaffold in the Construction of New Ligands for the Ionotropic Glutamate Receptors

Article abstract of DOI:10.1021/acschemneuro.7b00243

More than two decades ago, the quinoxalinedione scaffold was shown to act as an α-amino acid bioisoster. Following extensive structure-activity relationship (SAR) studies, the antagonists DNQX, CNQX, and NBQX in the ionotropic glutamate receptor field were identified. In this work, we revisit the quinoxalinedione scaffold and explore the incorporation of an acid functionality in the 6-position. The SAR studies disclose that by this strategy it was possible to tune in iGluR selectivity among the AMPA, NMDA, and KA receptors, and to some extent also obtain full receptor subtype selectivity. Highlights of the study of 44 new analogues are compound 2m being a high affinity ligand for native AMPA receptors (IC₅₀= 0.48 μM), analogues 2e,f,h,k,v all displayed selectivity for native NMDA receptors, and compounds 2s,t,u are selective ligand for the GluK1 receptor. Most interestingly, compound 2w was shown to be a GluK3-preferring ligand with full selectivity over native AMPA, KA and NMDA receptors.

Full text of DOI:10.1021/acschemneuro.7b00243

Research Article
pubs.acs.org/chemneuro
Revisiting the Quinoxalinedione Scaffold in the Construction of New
Ligands for the Ionotropic Glutamate Receptors
Charles S. Demmer, David Rombach, Na Liu, Birgitte Nielsen, Darryl S. Pickering, and Lennart Bunch*
Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100
Copenhagen OE, Denmark
ABSTRACT: More than two decades ago, the quinoxaline-
dione scaffold was shown to act as an α-amino acid bioisoster.
Following extensive structure−activity relationship (SAR)
studies, the antagonists DNQX, CNQX, and NBQX in the
ionotropic glutamate receptor field were identified. In this
work, we revisit the quinoxalinedione scaffold and explore the
incorporation of an acid functionality in the 6-position. The
SAR studies disclose that by this strategy it was possible to
tune in iGluR selectivity among the AMPA, NMDA, and KA
receptors, and to some extent also obtain full receptor subtype
selectivity. Highlights of the study of 44 new analogues are compound 2m being a high affinity ligand for native AMPA receptors
(IC50= 0.48 μM), analogues 2e,f,h,k,v all displayed selectivity for native NMDA receptors, and compounds 2s,t,u are selective
ligand for the GluK1 receptor. Most interestingly, compound 2w was shown to be a GluK3-preferring ligand with full selectivity
over native AMPA, KA and NMDA receptors.
KEYWORDS: Structure−activity relationship study, Ionotropic glutamate receptor ligands, amino acids, amino acid bioisoster
functionality remained as the amino acid bioisoster, with the
carboxylate group of the α-amino acid side chain serving to
stabilize the LBD in an open antagonist state.6 From the X-ray
structure it was also observed that the α-ammonium group did
not engage in direct interactions with any receptor residues. We
therefore decided to explore the influence on binding affinity
and receptor subtype selectivity upon altering the chemical
nature of the side chain. In total, 44 new analogues were
prepared to explore variations in chemical functionalities,
carbon chain length and flexibility (compounds 2c−x and 2aa−
2aw; Figure 2), and how these changes influence the binding
affinity profile at the iGluRs for both native and cloned
homomeric iGluR receptors.
INTRODUCTION
■
Two decades ago the two quinoxalinediones DNQX and
CNQX (Figure 1) were shown to be potent competitive
antagonists of the ionotropic glutamate receptors (iGluRs).1 By
an X-ray structural study of CNQX in the ligand binding
domain (LBD) of GluA2 (PDB code: 3B7D),2 it was later
shown that the quinoxalinedione acts as an α-amino acid
bioisoster by forming strong ionic interactions between its
dione functionality and the positively charged Arg96 residue
while its 4-NH-functionality engages in hydrogen bonding with
the carbonyl group of the Pro89 residue. Interestingly, the
carboxylate group of Glu193, which would engage in a salt-
bridge to the α-ammonium ion of an α-amino acid
functionality, now engages in a charged interaction with the
ammonium group of Lys218 via a water matrix network.
Numerous structure−activity-relationship (SAR) studies
have been carried out by introduction and/or modification of
substituents in the quinoxalinedione scaffold, which led to the
discovery of the selective AMPA/KA antagonist NBQX (Figure
1).3 However, despite extensive efforts, selectivity for one
receptor subunit within one of the three iGluR groups (AMPA
subunits GluA1−4, KA subunits GluK1−5 or NMDA subunits
GluN2A-D) has not achieved. Reported key quinoxalinediones
are non-NMDA antagonist 1a,3 NMDA antagonist 1b,4 and
glycine site NMDA antagonist 1c5 (Figure 1).
RESULTS AND DISCUSSION
■
As evidenced by the X-ray structure of 2a in the LBD of GluA2
(PDB code: 4QF9), the α-ammonium group does not
participate in direct interactions with the receptor protein.
We therefore first decided to remove this group (2c,d) which
would also bring simplicity to the synthesis. As a classical
strategy in SAR studies, the carboxylic acid functionality was
substituted with a phosphonic acid group (2e,f).7,8 To possibly
enhance binding affinity, the flexible side chains in 2a−f were
conformationally restricted by incorporation of a double bond
(2g−j). Furthermore, a sulfonamide and an secondary amine
(2k,l) were incorporated into the side chain. The four
Recently, we revisited the quinoxalinedione scaffold to
explore if it could also function as a carboxylic acid bioisoster
in the iGluRs (compounds 2a and 2b, Figure 1).6 However, the
X-ray structure of 2a in the ligand binding domain (LBD) of
GluA2 (PDB code: 4QF9) showed that the quinoxalinedione
Received: July 3, 2017
Accepted: August 24, 2017
© XXXX American Chemical Society
A
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Figure 1. Chemical structure of lead compounds 2a,b and reported key quinoxalinedione analogues DNQX, CNQX, NBQX, and 1a−c.
analogues 2m−p restrict the orientation of the carboxylic acid
group by incorporation of an aromatic ring. Finally, analogues
2q−w have a phenyl ring directly attached to the quinox-
alinedione skeleton, tethering an acid functionality.
required first reaction with BCl3 at rt overnight followed by
hydrolysis in 2 M HCl and finally saponification conditions
overnight. Saponification of intermediate 24 followed by
hydrolysis with 2 M HCl afforded target analogue 2p (Scheme
4).
Chemistry. The target analogues 2c−w were synthesized
from one of the three intermediates: bromine 6,6 alkene 7 or
boronic ester 8, which were all prepared in a convergent
manner from 4-bromo-1,2-diaminobenzene 3 (Scheme 1).
First, the quinoxalinedione ring was constructed by con-
densation of 3 with diethyl glyoxalate to give 4 in high yield.
While the dione functionality is not compatible with Pd
catalyzed cross-coupling reactions, 4 was treated with thionyl
chloride followed by potassium methoxide in methanol to give
key intermediate bromine 6. Subsequent Stille cross-coupling
with tributyl(vinyl)stannane or a Miyaura borylation reaction
led to key intermediates alkene 7 and boronic ester 8,
respectively (Scheme 1).
Synthesis of Aryl Analogues 2q−w. The synthesis of target
analogues 2q, 2r, 2v, and 2w commenced with a Suzuki
coupling reaction of bromine 6 with the appropriately
substituted arylboronic acid to give intermediates 9a−d.
Subsequent deprotection in aqueous HCl afforded analogues
2q, 2r, 2v, and 2w in good to high yield (Scheme 2).
Analogues 2s and 2u were also synthesized by a Suzuki cross-
coupling reaction, however for these two analogues with
reversed reactivity (Scheme 3). Boronic ester 8 was coupled
with the appropriate aryl halides 10 and 14, respectively, to give
products 11 and 15. Subsequent deprotection of intermediates
11 in 2 M HCl at 70 °C gave 2s, while 15 required treatment
with TMSBr in DCM followed by hydrolysis in 1 M HCl in
1,4-dioxane overnight to afford target analogue 2u in a clean
manner (Scheme 3). For the synthesis of 2t, intermediate 13
was obtained by a Suzuki cross-coupling between bromine 6
and boronic acid 12. Subsequent deprotection of intermediate
13 in 2 M HCl at 110 °C gave analogue 2t in good yield
(Scheme 3).
Synthesis of 2c−j. For the synthesis of 2c−j, bromine 6 was
coupled with either methyl 3-butenoate and ethyl acrylate to
afford intermediates 26a,b, respectively. Then, reduction of
26a−b with palladium catalyst under hydrogen atmosphere led
to compounds 27a,b. Finally, the synthesis of analogues 2c,d,
2g, and 2i were achieved by deprotection of their
corresponding intermediates with 1 M HCl (Scheme 5).
Similarly (Scheme 6), Heck cross-coupling between 6 and
diethyl vinylphosphonate or diethyl allylphosphonate afforded
the compounds 28a,b, respectively. Subsequent treatment with
TMSBr and then 1 M HCl completed the synthesis of
analogues 2h and 2j. Intermediates 28a,b were reduced with
palladium on carbon as catalyst to give corresponding saturated
analogues 29a,b, which were deprotected under the same
conditions as stated for 2h,j, to give 2e,f (Scheme 6).
The synthesis of target analogue 2l commenced by the
oxidation of 7 to aldehyde 30 in a two-step procedure by first
reaction with OsO4/NaIO4 to give the corresponding diol, then
oxidative cleavage with PhI(OAc)2. Condensation of aldehyde
30 with 3-amino propionic acid ethyl ester hydrochloride
followed by subsequent reduction led to amine 31 which was
deprotected under aqueous acidic conditions to afford the
desired analogue 2l in acceptable yield (Scheme 7).
Pharmacology. All analogues 2c−w were characterized in
binding assays at native iGluRs (rat synaptosomes) and cloned
rat homomeric GluA2 and GluK1−3 receptors (Table 1). As
anticipated, removal of the amino group (2c,d) did not lead to
a significant loss in affinity. The two phosphonic acid analogues
2e,f displayed selective affinity for the NMDA receptors,
however, only in mid-micromolar range (Ki = 55 and 56 μM,
respectively). Introduction of a double bond (2c vs 2g) did not
induce receptor subtype selectivity although the GluK3 affinity
was increased by 10-fold, whereas for compounds 2d vs 2i the
alkene resulted in a loss of affinity. Finally, for analogues 2e,f vs
2h,j, the NMDA receptor selectivity was only maintained for
compound 2j with no improved affinity (Ki = 69 μM).
Selectivity for the NMDA receptors was also observed for
sulfonamide 2k. Finally, insertion of an amine (2l) resulted in a
broad binding affinity profile at native AMPA and KA receptors
but also at cloned homomeric GluK1−3 with Ki values of 45,
37, and 19 μM, respectively (Table 1).
Synthesis of 2m−p. Analogue 2m was synthesized by a
Heck cross-coupling reaction of bromine 6 with the vinyl arene
17 (Scheme 4), which was readily obtained from 16 by a Stille
coupling reaction. Hydrolysis of 18 with 2 M HCl at 80 °C
overnight gave analogue 2m in good yield.
Following the same strategy, analogues 2n−p were obtained
by a Heck cross-coupling reaction of alkene 4 with aryl
bromides 19, 21, and 23 to give intermediates 20, 22, and 24,
respectively. Global deprotection of 20 in acidic media readily
gave target analogue 2o whereas deprotection of 22 to give 2n
B
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Figure 2. Chemical structure of all compounds undergoing pharmacological characterization.
In contrast, the ortho carboxy phenylvinyl analogue 2m
displayed enhanced binding affinity with sub-micromolar (IC50
= 0.48 μM) affinity for native AMPA receptors but also low
micromolar affinity for GluK1−3 (Ki = 1.4, 2.5, 8.9 μM,
respectively). Introduction of a hydroxyl group in the meta
position, compound 2n, did not lead to a significant change in
the binding affinity profile compared to 2m. Moving the
carboxylic acid group to the meta position, compound 2o, led
C
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a
Scheme 1. Synthesis of Bromine 6, Alkene 7, and Boronic Ester 8
a
Reagents and conditions: (a) diethyl oxalate, 96%; (b) thionyl chloride, DMF (cat.), 90%; (c) MeOK, MeOH, 93%; (d) Pd(PPh3)4,
tributyl(vinyl)stannane, toluene, 100 °C, overnight, 93%; (e) Pd(dppf)2·DCM, bis(pinacolato)diboron, AcOK, DMF, H2O, 95 °C, 44 h, 68%.
a
Scheme 2. Synthesis of analogues 2q, 2r, 2v, and 2w
a
Reagents and conditions: (a) Pd(PPh3)4, 6, Cs2CO3, DMF, H2O, 90 °C, 2 h; (b) 2 M HCl, dioxane, 80 °C, overnight.
a
Scheme 3. Synthesis of Analogues 2s−u
a
Reagents and conditions: (a) Pd(PPh3)4, Cs2CO3, DMF, H2O, 90 °C, 2 h, quant.; (b) 2 M HCl, 1,4-dioxane, 110 °C, 20 min, 50%; (c)
PdCl2(dppf)·DCM, K2CO3, 1,4-dioxane, H2O, 80 °C, overnight, 62%; (d) 2 M HCl, 1,4-dioxane, 70 °C, 3h, 69%; (e) Pd(PPh3)4, Cs2CO3, DMF,
H2O, 90 °C, 2 h, 74%; (f) TMSBr, DCM, rt, overnight, then 1 M HCl, dioxane, 70 °C, overnight, 87%.
to a general reduction in binding affinity at all iGluRs, while
substitution of the phenyl ring for a furan ring, analogue 2p,
gave a 10-fold decrease in binding affinity for AMPA receptors
and a 20-fold drop in binding affinity at GluK1.
With regard to the analogues where the phenyl ring is
directly attached to the quinoxalinedione, compounds 2q−w,
the point of substitution was of great influence on the binding
affinities. While the ortho substituted analogue 2q was without
significant affinity for any of the iGluRs, the meta-positioned
analogue (compound 2r) displayed binding affinities for all the
iGluRs in the low- to mid-micromolar range. Inducing steric
clashes by the introduction of a methyl substituent in the far
ortho position (compound 2s) led to an 8-fold preference for
GluK1 over GluK2−3 (Table 2), while a mid-micromolar
affinity remained for the AMPA receptors (IC50 = 30 μM, Table
2). Interestingly, exchanging the carboxylic acid of 2r for a
D
DOI: 10.1021/acschemneuro.7b00243
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a
Scheme 4. Synthesis of Analogues 2m−p from Key Intermediates Bromine 6 and Alkene 7
a
Reagents and conditions: (a) Pd(PPh3)4, tributyl(vinyl)stannane, toluene, 100 °C, overnight, 44%; (b) Pd(OAc)2, P(o-tol)3, 6, NEt3, DMF, 100 °C,
overnight, 43%; (c) 2 M HCl, dioxane, 80 °C, overnight, 75%; (e) Pd(OAc)2, P(o-tol)3, 7, NEt3, DMF, 100 °C, overnight, 70%; (f) 2 M HCl,
dioxane, 110 °C, 4 h, 48%; (g) Pd(OAc)2, P(o-tol)3, 7, NEt3, DMF, 100 °C, overnight, 50%; (h) 1 M BCl3 in hexane, DCM, rt, overnight; (i) 2 M
HCl, dioxane, 80 °C, 3 h; (j) 2 M NaOH, DMF, 110 °C, overnight, 38% over three steps; (k) H2SO4, dry MeOH, 2 days, reflux, 70%; (l) Pd(OAc)2,
P(o-tol)3, 7, NEt3, DMF, 100 °C, overnight, 70%; (m) 2 M NaOH, dioxane, 50 °C, overnight, 31%; (n) 2 M HCl, dioxane, 70 °C, 3 h, 79%.
a
Scheme 5. Synthesis of Analogues 2c,d, 2g, and 2i
a
Reagents and conditions: (a) Pd(OAc)2, P(o-Tol)3, NEt3, methyl 3-butenoate or ethyl acrylate, DMF, 95 °C, 3.5−6 h; (b) 1 M HCl, 1,4-dioxane,
50 °C, overnight; (c) Pd(OH)2, H2, DMF, 50 °C, 5.5−8 h; (d) 1 M HCl in 1,4-dioxane, 100 °C, 5−6 h.
phosphonic acid group gave 2u, which was shown to be a fully
selective GluK1 ligand (Ki = 12 μM). Furthermore, on
introduction of a chloro substituent in the para position
(compound 2t) the affinity for the GluK1 subtype was
enhanced by 12-fold, whereas tethering the carboxylic acid
with a methylene group (2v) led to a full selectivity for the
NMDA receptors. Finally, the para carboxylic acid analogue
(2w) was without any appreciable affinity for native iGluRs, but
a 4−7 fold preference was observed for the GluK3 subtype (Ki
= 6.6 μM, Table 2) over GluK1 or GluK2.
E
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a
Scheme 6. Synthesis of Phosphorated Analogues 2e,f, 2h, and 2j
a
Reagents and conditions: (a) Pd(OAc)2, P(o-tol)3, NEt3, diethyl vinylphosphonate or diethyl allylphosphonate, DMF, 95 °C, 7 h; (b) TMSBr,
DCM, rt, 19 h, then 1 M HCl, 1,4-dioxane, 70 °C, overnight; (c) Pd(OH)2, H2, DMF, 50 °C, 5.5−8 h.
a
Scheme 7. Synthesis of Analogue 2l
a
Reagents and conditions: (a) OsO4, NaIO4, 1,4-dioxane; (b) PhI(OAc)2 DCM, 60% over two steps; (c) 3-amino propionic acid ethyl ester
hydrochloride, NaBH3CN, AcOH, MeOH, 50%; (d) 2 M HCl, 70 °C, 3 h, 62%.
Design and Synthesis of 2aa−aw. To this date, fully
selective agonists or antagonists for the GluK3 subunit have not
yet been reported.9,10 However, SAR studies have previously
disclosed competitive amino acid based ligands as being GluK3-
preferring (5−10 fold selectivity).11 Given the attractive GluK3-
preferring binding affinity profile of 2w with full selectivity vs
native AMPA, KA and NMDA receptors (Table 2), we decided
to explore this observation in a homology model of GluK3.
Docking of 2w into an antagonist state of GluK1 (PDB: 2qs4)
(Figure 3) revealed that the para carboxylate group engages in
hydrogen bonding interaction with the OH group of Ser173.
This area of the GluK1 receptor holds residues of differ-
entiation among the GluK subunits. For both GluK2/3, Ser173
is Asn, but also Asp174 is substituted for Glu in GluK2/3.
Inspired by these differences, we set out to design new
analogues in order to explore these differences and eventually
thereby enhance selectivity for GluK3 receptor. First the
position of the carboxylic acid group was challenged
concomitant with the incorporation of additional substituents
by design of compounds 2ab−2ag including its elimination,
analogue 2aa. These analogues were intended to be
complementary to the analogues described in Table 2.
commercially available boronic acids to give intermediates
32aa−aw, followed by deprotection under aqueous acidic
conditions (Scheme 8).
Binding affinity profiles of 2aa−aw were obtained for cloned
homomeric GluK1−3 receptors at a 10 μM concentration and
percent specific (residual) binding (% SB) recorded (Tables 3
and 4). Deleting the para carboxylic acid functionality (2aa)
(Table 3), led to a complete loss of binding affinity across the
GluK1−3 receptors. When positioning the carboxylic acid
group in the meta position and concomitant introduction of
one or more substituents, the most interesting observation was
the 2,4-difluoro-3-carboxylic acid analogue 2ae, which now was
selective for GluK1 over GluK2,3 with an estimated IC50 = 10
μM. Turning to the series of para functionalized analogues
2ai−an (Table 4), the data was disappointing as none of the
analogues showed improved selectivity for GluK3 over GluK1,2
as compared with 2w. Introduction of an additional substituent
on 2w (2aq−aw) was also without success in enhancing the
selectivity for GluK3 over GluK1,2.
CONCLUSION
■
In conclusion, we designed and synthesized 44 new analogues
2c−w and 2aa−2aw of the broad-range iGluR quinoxaline-
dione antagonists 2a,b and characterized them in binding
affinity studies as ligands for the iGluRs. Highlights from the
present SAR study are compound 2m being a high affinity
ligand for native AMPA receptors (IC50= 0.48 μM), while
analogues 2e,f,h,k,v all displayed selectivity for native NMDA
receptors. Compounds 2s,t,u are selective ligands for the
GluK1 receptor, and, most interestingly, compound 2w was
shown to be a GluK3-preferring ligand with full selectivity vs
native AMPA, KA, and NMDA receptors. In all, the study
demonstrates that by introduction of a tethered acid
The analogues 2ai−an (Table 4) served to explore the
influence of various functional groups in the para position on
binding affinity, while analogues 2ao,ap explore the incorpo-
ration of an ester functionality together incorporation of a
substituent on the phenyl ring. Finally, analogues 2aq−aw
(Table 4) explore the introduction of substituents on the
phenyl ring while preserving the para carboxylic acid
functionality.
The syntheses of all analogues described above (analogues
2aa−aw) were all accomplished by Suzuki cross-coupling
reactions between bromine 6 and the corresponding
F
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Table 1. Binding Affinities of 2a−p at Native iGluRs (AMPA, KA, and NMDA Receptors) and at Cloned Homomeric Receptors
b
(GluA2 and GluK1-3)
a
b
Pharmacological data taken from ref 6. All values in μM. −: not tested. Data are mean values of at least three individual experiments performed in
a
triplicate. For AMPA and KA: pIC50 values with SEM in brackets. For NMDA: pKi values with SEM in brackets.
detector (200 and 210 nm, respectively) installed with an XTerra MS
functionality in the 6 position of the quinoxalinedione skeleton
it is possible to tune-in a wide range of binding affinity profiles
among the iGluRs.
C 18 3.5 μm, 4.6 mm × 150 mm column, using a 5 → 95% MeCN
gradient in H2O containing 0.1% TFA. 1H NMR and 13C NMR
spectra were recorded either on a 600 MHz or a 400 Hz Bruker
Avance spectrometer. MS spectra were recorded using LC-MS
performed using an Agilent 1200 series solvent delivery system
equipped with an autoinjector coupled to an Agilent 6400 series triple
quadrupole mass spectrometer equipped with an electrospray
ionization source. Gradients of 10% aqueous acetonitrile +0.05%
formic acid (buffer A) and 90% aqueous acetonitrile +0.046% formic
acid (buffer B) were employed. Melting points were measured with a
MPA 100 Optimelt Automatic Melting Point System. All purchased
chemicals were used without further purification. The purity of all
METHODS
■
General Information. All reactions involving dry solvents or
sensitive agents were performed under an argon atmosphere and
glassware was dried prior to use. Solvents were dried according to
standard procedures. Reactions were monitored by analytical thin-layer
chromatography (TLC) analysis or HPLC. TLC was carried out using
Merck silica gel 60 F254 aluminum sheets. Flash chromatography was
carried out using Merck silica gel 60A (40−63 μm). HPLC was
performed using a Dionex UltiMate 3000 pump and photodiode array
G
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a
Table 2. Binding Affinities of 6-Phenyl Analogues by Variation of the Position and Distance of Carboxylic Acid Functionality
a
−: not tested. Data are mean values of at least three individual experiments performed in triplicate. For AMPA and KA: pIC50 values with SEM in
brackets. For NMDA: pKi values with SEM in brackets.
was filtered off and washed with 2 M HCl (1.0 mL) and Et2O (1.0
mL). The solid was dried overnight at reduced pressure to afford the
1
title compounds as a white powder (42 mg, 0.17 mmol, 99%). H
NMR (600 MHz, DMSO-d6) δ 12.05 (s, 1H), 11.85 (s, 2H), 7.04 (d, J
= 8.00 Hz, 1H), 6.96−6.89 (m, 2H), 2.55 (t, J = 7.65 Hz, 2H), 2.21 (t,
J = 7.32 Hz, 2H), 1.81−1.71 (m, 2H). 13C NMR (150 MHz, DMSO-
d6, 13C−31P coupling) δ 174.7, 155.7, 155.5, 137.0, 126.0, 124.2, 123.6,
115.7, 115.0, 34.3, 33.4, 26.8; mp > 336 °C (decomposition).
3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)propanoic Acid
(2d). In a vial, ethyl-3-(2,3-dimethoxyquinoxalin-6-yl)propanoate 27a
(70 mg, 0.24 mmol, 1.0 equiv) was suspended in 1,4-dioxane (1.8 mL)
and 2 M HCl (1.8 mL) was added. The mixture was stirred for 7 h at
100 °C and then cooled to room temperature. Next, 2 M HCl (1 mL)
was added and the white precipitate filtered off and washed with 2 M
HCl (1 mL) and Et2O (1 mL). The solid was dried overnight at
reduced pressure, to give the title compound as a white powder (52
1
mg, 0.22 mmol, 93%) H NMR (600 MHz, DMSO-d6) δ 12.12 (s,
1H), 11.86 (s, 1H), 11.84 (s, 1H), 7.04−7.02 (m, 1H), 6.99−6.93 (m,
2H), 2.78 (t, J = 7.49 Hz, 2H). 1H NMR (600 MHz, MeOD-d4) δ 7.09
(m, 3H), 2.94 (t, J = 7.54 Hz, 2H); 2.63 (t, J = 7.54 Hz, 2H). 13C
NMR (150 MHz, DMSO- d6, 13C−31P coupling) δ 173.5, 155.2, 155.0,
135.8, 125.4, 123.7, 123.0, 115.0, 114.6, 35.2, 29.8; mp > 380 °C
(decomposition).
(3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)propyl)-
phosphonic Acid (2e). In a vial, diethyl (3-(2,3-dimethoxyquinoxalin-
6-yl)propyl)phosphonate 29b (85 mg, 0.23 mmol, 1.0 equiv) was
dissolved in DCM (0.60 mL). Then TMSBr (305 μL, 2.3 mmol, 10
equiv) was added and the reaction mixture stirred at room
temperature for 24 h. After removal of solvent under reduced
pressure, 1,4-dioxane and 1 M HCl (1:1) (0.4 mL) were added to the
reaction mixture which was then stirred at 70 °C overnight. The
Figure 3. Docking of 2w (green) into X-ray structure of antagonist
state of GluK1 (PDB: 2qs4) crystallized with antagonist LY466195.
solvent was removed under reduced pressure, and the solid was dried
under reduced pressure overnight to give the title compound as a
1
white solid (54 mg, 0.19 mmol, 82%). H NMR (400 MHz, DMSO-
d6) δ 11.86 (s, 1H), 11.84 (s, 1H), 7.05 (d, J = 8.04 Hz, 1H), 6.96−
6.89 (m, 2H), 2.61 (t, J = 7.46 Hz, 2H), 1.80−1.65 (m, 2H), 1.56−
1.38 (m, 2H). 13C NMR (100 MHz, DMSO-d6, 13C−31P coupling) δ
155.2, 154.9, 136.6, 125.5, 123.6, 123.2, 115.0, 114.5, 35.3, 35.2, 27.6,
26.3, 24.8, 24.8; mp = 335 °C (decomposition).
(2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)ethyl)-
phosphonic Acid (2f). In a vial, diethyl (2-(2,3-dimethoxyquinoxalin-
6-yl)ethyl)phosphonate 29a (69.0 mg, 0.19 mmol, 1.0 equiv) was
compounds was determined by HPLC254 to be >95%, unless otherwise
stated.
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)butanoic Acid
(2c). In a vial, methyl-4-(2,3-dimethoxyquinoxalin-6-yl)butanoate
27b (50 mg, 0.17 mmol, 1.0 equiv) was suspended in a mixture of
1,4-dioxane (1.0 mL) and 2 M HCl (1.0 mL). The reaction mixture
was heated at 100 °C for 6 h. The mixture was cooled to room
temperature and 2 M HCl (1.0 mL) was added. The white precipitate
H
DOI: 10.1021/acschemneuro.7b00243
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Research Article
a
Scheme 8. Synthesis of Analogues 2aa−aw
a
Reagents and conditions: (a) Pd(PPh3)4,Cs2CO3, DMF/H2O (13%−83%); (b) 2 M HCl, dioxane (34−84%).
Table 3. Binding Affinities of 2aa−ah at Cloned Homomeric
Table 4. Binding Affinity of 2ai−aw at Cloned Homomeric
a
a
GluK1-3 Subtypes
GluK1-3 Subtypes
a
Compounds tested at 10 μM and results given as means SD of %
specific binding (SB) from three experiments conducted in triplicate.
Nonspecific binding was evaluated using 1 mM (S)-glutamic acid.
dissolved in DCM (0.60 mL), and TMSBr (255 μL, 1.93 mmol, 10
equiv) was added. The mixture was stirred at room temperature for 24
h and then evaporated to dryness. Next, 1 M HCl (0.20 mL) was
added and the mixture was stirred for 7 h at 70 °C, cooled to room
temperature, and concentrated to dryness. The solid was dried under
reduced pressure overnight to give the title compound as a white solid
1
(40 mg, 0.14 mmol, 75%). H NMR (400 MHz, DMSO-d6) δ 11.86
a
Compounds tested at 10 μM and results given as means SD of %
(s, 1H), 11.84 (s, 1H), 7.04 (d, J = 8.09 Hz, 1H), 6.96 (dd, J = 1.68
Hz, 8.26 Hz, 1H), 6.94 (s, 1H), 2.73 (m, 2H), 1.76 (m, 2H). 13C
NMR (150 MHz, DMSO-d6, 13C−31P coupling) δ 155.2, 155.0, 136.9,
136.7, 125.5, 123.7, 122.8, 115.1, 114.2, 30.1, 29.2, 28.4, 28.4; mp =
355 °C (decomposition).
specific binding (SB) from three experiments conducted in triplicate.
Nonspecific binding was evaluated using 1 mM (S)-glutamic acid.
7.24−7.02 (m, 3H), 6.45 (d, J = 15.89 Hz, 1H), 6.26−6.06 (m, 1H),
3.19 (d, J = 7.06 Hz, 2H). 13C NMR (150 MHz, DMSO-d6, 13C−31P
coupling) δ 172.6, 155.1, 154.9, 131.8, 131.3, 125.8, 124.9, 122.6,
121.0, 115.3, 112.2, 37.6; mp = 310.8−311.6 °C.
(E)-(3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)allyl)-
phosphonic Acid (2h). In a vial, (E)-diethyl (3-(2,3-dimethoxyquinox-
alin-6-yl)allyl)phosphonate 28b (100 mg, 0.27 mmol, 1.0 equiv) was
dissolved in DCM (1.0 mL). Then TMSBr (360 μL, 2.7 mmol, 10
equiv) was added and the reaction mixture stirred at room
temperature for 18 h. The solvent was removed under vacuum, and
the solid redissolved in a mixture of 1,4-dioxane and 1 M HCl (1:1)
(E)-4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)but-3-enoic
Acid (2g). In a vial, (E)-methyl-4-(2,3-dimethoxyquinoxalin-6-yl)but-
2-enoate 26b (50 mg, 0.17 mmol, 1.0 equiv) was suspended in 1,4-
dioxane (1.0 mL), and 1 M HCl (1.0 mL) was added. The reaction
mixture was heated overnight at 50 °C. After cooling to room
temperature, 2 M HCl (2 mL) was added and the white precipitate
was filtered off and washed with 1 N HCl (1.0 mL) and Et2O (1.0
mL). The solid was dried under reduced pressure to afford the title
1
compound as a white powder (30 mg, 0.12 mmol, 70%). H NMR
(600 MHz, DMSO-d6) δ 12.32 (s, 1H), 11.92 (s, 1H), 11.87 (s, 1H),
I
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(1.0 mL) and then stirred at 70 °C overnight. The solvent was
removed under reduced pressure and the solid dried under reduced
pressure overnight to give the title compound as a white solid (24 mg,
125.4, 122.0, 121.9, 115.5, 112.6, 112.6; mp > 340 °C (decom-
position).
(E)-2-(2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)vinyl)-6-hy-
droxybenzoic Acid (2n). To a solution of methyl (E)-2-(2-(2,3-
dimethoxyquinoxalin-6-yl)vinyl)-6-methoxybenzoate 22 (40 mg, 0.10
mmol, 1 equiv) in dry DCM (1 mL) was added a 1 M solution of BCl3
in heptane (0.15 mL, 0.15 mmol, 1.5 equiv). The reaction mixture was
stirred overnight at room temperature then evaporated to dryness
under reduced pressure. The solid was dissolved in dioxane (0.5 mL)
and 2 M HCl (0.5 mL) was added. The reaction was stirred for 3 h at
80 °C and then cooled to room temperature and filtered. The solid
was dissolved in DMF (0.5 mL), 2 M NaOH (0.2 mL) was added, and
then the mixture heated at 110 °C overnight. It was then cooled to
room temperature followed by addition of 1 M HCl (0.5 mL). The
reaction mixture was stirred for 1 h, filtered, and dried with a vacuum
pump over the weekend to afford the title compound as a yellow solid
1
0.09 mmol, 32%). H NMR (600 MHz, DMSO-d6) δ 11.93 (s, 1H),
11.89 (s, 1H), 7.15−7.09 (m, 2H), 7.06 (d, J = 8.20 Hz, 1H), 6.41 (dd,
J = 4.37 Hz, 15.73 Hz, 1H), 6.08 (dq, J = 7.36 Hz, 14.92 Hz, 1H), 2.56
(dd, J = 7.41 Hz, 21.80 Hz, 2H). 13C NMR (150 MHz, DMSO-d6,
13C−31P coupling) δ 155.2, 155.0, 132.2, 131.7, 131.7, 131.6, 125.8,
124.7, 121.5, 121.4, 121.0, 115.3, 111.9, 33.3, 32.4; mp = 347.1−349.8
°C.
(E)-3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)acrylic Acid
(2i). In a vial, (E)-ethyl-3-(2,3-dimethoxyquinoxalin-6-yl)acrylate 26a
(59 mg, 0.20 mmol, 1.0 equiv) was suspended in 1,4-dioxane (0.7
mL), and 2 M HCl (0.7 mL) was added. The reaction mixture was
stirred overnight at 110 °C. After cooling to room temperature, the
white precipitate was filtered off and washed with 2 M HCl (1.0 mL)
and Et2O (1.0 mL). The solid was dried overnight at reduced pressure
to give the title compound as a white powder (27 mg, 0.11 mmol,
56%). 1H NMR (600 MHz, DMSO-d6) δ 12.38 (s, 1H), 12.05 (s, 1H),
11.96 (s, 1H), 7.52 (d, J = 15.92 Hz, 1H), 7.45 (dd, J = 1.57, 8.37 Hz,
1H), 7.31 (d, J = 1.34 Hz, 1H), 7.13 (d, J = 8.34 Hz, 1H), 6.35 (d, J =
15.93 Hz, 1H). 13C NMR (150 MHz, DMSO-d6, 13C−31P coupling) δ
167.4, 155.1, 155.0, 143.1, 128.9, 127.3, 126.0, 123.0, 118.1, 115.6,
114.5; mp > 143 °C (decomposition).
1
(12 mg, 38 μmol, 38%). H NMR (600 MHz, DMSO-d6) δ 13.23 (s,
1H), 11.99 (s, 1H), 11.94 (s, 1H), 10.23 (s, 1H), 7.34−7.22 (m, 4H),
7.13 (m, 3H), 6.83 (dd, J = 7.6, 1.4 Hz, 1H). 13C NMR (151 MHz,
DMSO-d6) δ 169.7, 155.5, 155.1, 154.9, 135.6, 131.9, 130.6, 129.7,
126.0, 125.4, 125.2, 121.8, 120.5, 116.2, 115.5, 114.9, 112.3; mp = 295
°C (decomposition).
(E)-3-(2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)vinyl)-
benzoic Acid (2o). To a solution of (E)-methyl 3-(2-(2,3-
dimethoxyquinoxalin-6-yl)vinyl)benzoate 20 (50 mg, 0.14 mmol, 1.0
equiv) in dioxane (0.5 mL) was added 2 M HCl (0.5 mL), and the
reaction mixture was heated at 110 °C for 4 h. A light yellow solid
precipitated, and the heterogeneous reaction mixture was cooled to
room temperature. Next, 2 M HCl (1 mL) was added and the solid
filtered off, then washed with 1 M HCl (1 mL) and diethyl ether (1
mL), and dried in a vacuum oven overnight, to give the title
(E)-(2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)vinyl)-
phosphonic Acid (2j). In a vial, (E)-diethyl-(2-(2,3-dimethoxyquinox-
alin-6-yl)vinyl)phosphonate 28a (107 mg, 0.30 mmol, 1 equiv) was
dissolved in DCM (1.0 mL) and TMSBr (360 μL, 2.7 mmol, 9 equiv)
was added. The mixture was stirred at room temperature for 19 h and
then evaporated. The solid was dissolved in a mixture of 1,4-dioxane
and 1 M HCl (1:1) (1.0 mL) and stirred at 70 °C overnight. The
white precipitate was filtered off, washed with 1 M HCl (0.20 mL),
and dried under reduced pressure overnight to give the title compound
1
compound as a light yellow solid (21 mg, 67 μmol, 48%). H NMR
(600 MHz, DMSO-d6) δ 13.03 (s, 1H), 12.00 (s, 1H), 11.99 (s, 1H),
8.14 (s, 1H), 7.88 (d, J = 7.8 Hz, 1H), 7.84 (d, J = 7.7 Hz, 1H), 7.51 (t,
J = 7.7 Hz, 1H), 7.44 (dd, J = 8.5, 1.9 Hz, 1H), 7.33 (d, J = 16.4 Hz,
1H), 7.30 (d, J = 1.9 Hz, 1H), 7.19 (d, J = 16.4 Hz, 1H), 7.14 (d, J =
8.3 Hz, 1H). 13C NMR (151 MHz, DMSO-d6) δ 167.2, 155.2, 155.0,
137.3, 131.9, 131.3, 130.4, 129.0, 128.8, 128.2, 127.2, 126.8, 125.9,
125.4, 121.3, 115.5, 113.3; mp > 400 °C (decomposition).
1
as a white solid (41.0 mg, 0.5 mmol, 50%). H NMR (600 MHz,
DMSO-d6) δ 12.01 (s, 1H), 11.94 (s, 1H), 7.37 (dd, J = 1.57 Hz, 8.35
Hz, 1H), 7.23 (d, J = 1.40 Hz, 1H), 7.12 (d, J = 8.33 Hz, 1H), 7.10
(dd, J = 4.08 Hz, 17.49 Hz, 1H), 6.30 (dd, J = 1.06 Hz, 16.19 Hz, 1H).
13C NMR (150 MHz, DMSO-d6, 13C−31P coupling) δ 155.1, 155.1,
142.0, 142.0, 130.3, 130.1, 126.6, 125.9, 122.1, 120.3, 119.1, 115.5,
113.7; mp = 256.8−260.0 °C.
(E)-2-(2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)vinyl)furan-
3-carboxylic Acid (2p). To a solution of (E)-methyl 2-[2-(2,3-
dimethoxyquinoxalin-6-yl)vinyl]furan-3-carboxylate 25 (150 mg, 0.235
mmol, 1.0 equiv) in dioxane (0.5 mL) was added 2 M NaOH (0.5
mL). The reaction mixture was heated at 50 °C overnight and then
evaporated to dryness. The crude product was purified on flash
column chromatography [EtOAc/heptanes (4:6) + 0.1% AcOH] to
give (E)-2-(2-(2,3-dimethoxyquinoxalin-6-yl)vinyl)furan-3-carboxylic
3-(((2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)methyl)amino)-
propanoic Acid (2l). To a solution of ethyl 3-(((2,3-dimethoxyqui-
noxalin-6-yl)methyl)amino)propanoate 31 (36 mg, 0.11 mmol, 1
equiv) in dioxane (1 mL) was added 2 M HCl (1 mL), and the
reaction mixture was heated at 70 °C for 3 h. The milky solution was
cooled to room temperature, filtered, washed with H2O, and dried in
vacuum oven overnight, to give the title compound as a white solid (18
1
acid as a yellow solid (24 mg, 73 μmol, 31%). H NMR (600 MHz,
1
mg, 68 μmol, 62%). H NMR (600 MHz, DMSO) δ 12.66 (s, 1H),
DMSO-d6) δ 12.93 (s, 1H), 7.91 (d, J = 1.8 Hz, 1H), 7.81−7.75 (m,
3H), 7.72 (d, J = 16.5 Hz, 1H), 7.46 (d, J = 16.5 Hz, 1H), 6.80 (d, J =
1.9 Hz, 1H), 4.06 (s, 3H), 4.05 (s, 3H). 13C NMR (150 MHz, DMSO-
d6) δ 164.2, 155.4, 150.2, 150.0, 143.0, 136.9, 134.5, 130.5, 126.7,
124.7, 124.6, 115.6, 112.3, 54.1; mp = 272.3−274.8 °C; rf = 0.51
[EtOAc/heptanes (1:1) + 0.1% AcOH]. The above purified product
(35 mg, 0.14 mmol, 1.0 equiv) was taken in dioxane (0.5 mL), and the
solution was slightly warmed to around 50 °C until all material got
dissolved. Next, 2 M HCl (0.5 mL) was dropwise added and the
reaction mixture was heated at 70 °C for 3 h. A yellow solid
precipitated, and the heterogeneous mixture was cooled to room
temperature before being filtered and dried in vacuum oven overnight.
The yellow crude solid (17 mg, 58 μmol, 79%) was pure on NMR. 1H
NMR (600 MHz, DMSO-d6) δ 12.89 (s, 1H), 12.02 (s, 1H), 11.92 (s,
1H), 7.75 (d, J = 2.0 Hz, 1H), 7.52 (d, J = 16.5 Hz, 1H), 7.38 (d, J =
1.8 Hz, 1H), 7.32 (dd, J = 8.4, 1.8 Hz, 1H), 7.25 (d, J = 16.4 Hz, 1H),
7.15 (d, J = 8.3 Hz, 1H), 6.78 (d, J = 1.9 Hz, 1H). 13C NMR (150
MHz, DMSO-d6) δ 164.2, 155.5, 155.0, 155.0, 142.8, 130.8, 130.6,
126.2, 126.1, 122.7, 115.6, 114.9, 114.1, 112.3, 112.2; mp = 339 °C
(decomposition).
12.13 (s, 1H), 12.03 (s, 1H), 9.12 (s, 2H), 7.26 (dd, J = 8.2, 1.8 Hz,
1H), 7.23 (d, J = 1.8 Hz, 1H), 7.17 (d, J = 8.2 Hz, 1H), 4.12 (br s,
2H), 3.09 (br s, 2H), 2.70 (t, J = 7.4 Hz, 2H). 13C NMR (151 MHz,
DMSO) δ 171.5, 155.2, 155.1, 126.3, 126.1, 125.6, 124.8, 116.9, 115.2,
49.6, 41.9, 30.2; mp > 372 °C (decomposition).
(E)-2-[2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)vinyl]-
benzoic Acid (2m). To a solution of (E)-methyl 2-[2-(2,3-
dimethoxyquinoxalin-6-yl)vinyl]benzoate 18 (30 mg, 86 μmol, 1.0
equiv) in dioxane (1.0 mL) was added 2 M HCl (1 mL), and the
reaction mixture was heated at 80 °C overnight. A solid precipitated,
and the heterogeneous mixture was evaporated under reduced
pressure. H2O (2 mL) was added and the solid isolated by filtration,
then dried in a vacuum oven overnight to give the title compound as a
light yellow solid (20 mg, 64 μmol, 75%). 1H NMR (600 MHz,
DMSO-d6, rotamers) δ 13.03 (br s, 1H), 11.99 (s, 1H), 11.97 (s, 1H),
7.90 (d, J = 7.9 Hz, 0.3H), 7.88−7.81 (m, 2.4H), 7.76 (d, J = 16.3 Hz,
0.3H), 7.60 (td, J = 7.7, 1.4 Hz, 0.3H), 7.56 (td, J = 7.6, 1.4 Hz, 0.7H),
7.42−7.35 (m, 1H), 7.35−7.27 (m, 2H), 7.22−7.12 (m, 2H). 13C
NMR (151 MHz, DMSO-d6, rotamers) δ 168.6, 167.3, 155.1, 155.0,
137.7, 137.6, 132.3, 132.2, 132.0, 131.8, 130.4, 130.3, 130.2, 130.0,
129.6, 128.4, 127.4, 127.3, 126.5, 126.1, 126.1, 126.0, 125.6, 125.5,
2-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic Acid (2q).
To a solution of methyl 2-(2,3-dimethoxyquinoxalin-6-yl)benzoate 9a
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(62 mg, 0.15 mmol, 1 equiv) in dioxane (0.5 mL) was added 2 M HCl
(0.5 mL) and the reaction mixture was heated at 110 °C for 4 h. A
white solid precipitated, and the heterogeneous mixture was cooled to
room temperature before addition of 2 M HCl (1 mL). The reaction
mixture was filtered and washed with 1 M HCl (1 mL) and diethyl
ether (1 mL), and then dried in vacuum oven overnight to give the
washed with 1 M HCl (1 mL). The solid was dried in a vacuum oven
overnight to give the title compound as a white solid (58 mg, 0.18
mmol, 87%). H NMR (600 MHz, DMSO-d6) δ 11.93 (s, 1H), 11.88
(s, 1H), 7.79 (dt, J = 13.8, 1.7 Hz, 1H), 7.66−7.62 (m, 1H), 7.57 (ddt,
J = 12.6, 7.5, 1.4 Hz, 1H), 7.47 (td, J = 7.7, 3.8 Hz, 1H), 7.34−7.30 (m,
2H), 7.14 (d, J = 8.1 Hz, 1H); 13C NMR (150 MHz, DMSO-d6, C−P
coupling) δ 155.6, 155.6, 139.6, 139.5, 136.1, 134.9, 130.0, 129.9,
129.5, 129.4, 129.3, 129.3, 128.8, 128.7, 126.7, 125.9, 122.0, 116.3,
113.4, 66.8; mp = 380 °C (decomposition).
1
1
title compound as a white solid (17 mg, 0.06 mmol, 40%). H NMR
(600 MHz, DMSO-d6, two conformers) δ 12.79 (s, 1H), 12.04−11.94
(m, 2H), 7.77−7.70 (m, 1H), 7.62 (td, J = 7.6, 1.6 Hz, 0.2H), 7.58 (td,
J = 7.5, 1.5 Hz, 0.8H), 7.50 (td, J = 7.6, 1.3 Hz, 0.2H), 7.47 (td, J = 7.6,
1.3 Hz, 0.8H), 7.41 (dd, J = 7.7, 1.3 Hz, 0.2H), 7.35 (dd, J = 7.5, 1.3
Hz, 0.8H), 7.19−7.14 (m, 1H), 7.09 (d, J = 1.9 Hz, 1H), 7.08−7.02
(m, 1H). 13C NMR (150 MHz, DMSO-d6, two conformers) δ 169.4,
168.0, 155.2, 155.1, 140.3, 140.2, 135.8, 135.4, 132.1, 131.4, 131.2,
131.0, 130.4, 130.3, 129.3, 129.2, 127.5, 127.4, 125.4, 125.3, 124.9,
124.8, 123.3, 123.2, 115.0, 114.9, 114.8, 114.8; mp = 327.0−328.1 °C.
3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic Acid (2r).
To a solution of ethyl 3-(2,3-dimethoxyquinoxalin-6-yl)benzoate 9b
(40 mg, 0.12 mmol, 1 equiv) in dioxane (1.5 mL) was added 2 M HCl
(1 mL) and the reaction mixture was heated at 80 °C overnight. A
white solid precipitated and the heterogeneous mixture was evaporated
under reduced pressure. H2O (2 mL) was added and the solid was
filtered, then dried in a vacuum oven overnight to give the title
2-(3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)phenyl)acetic
Acid (2v). To a solution of ethyl 2-(3-(2,3-dimethoxyquinoxalin-6-
yl)phenyl)acetate 9d (70 mg, 0.15 mmol, 1 equiv) in dioxane (0.5
mL) was added 2 M HCl (0.5 mL) and the reaction mixture was
heated at 110 °C for 4 h. A white solid precipitated and the
heterogeneous mixture was cooled to room temperature before the
addition of 2 M HCl (1 mL). The reaction mixture was filtered and
washed with 1 M HCl (1 mL) and diethyl ether (1 mL). The solid was
dried in a vacuum oven overnight to give the title compound as a white
1
solid (31 mg, 0.10 mmol, 70%). H NMR (600 MHz, DMSO-d6) δ
12.37 (s, 1H), 12.00 (s, 1H), 11.96 (s, 1H), 7.49−7.44 (m, 2H), 7.42
(t, J = 7.5 Hz, 1H), 7.40−7.36 (m, 2H), 7.26 (d, J = 7.9 Hz, 1H), 7.21
(d, J = 8.8 Hz, 1H), 3.66 (s, 2H). 13C NMR (151 MHz, DMSO-d6) δ
172.6, 155.2, 155.1, 139.4, 135.8, 135.0, 129.0, 128.5, 127.5, 126.1,
125.2, 124.7, 121.6, 115.7, 113.0, 40.7; mp > 400 °C (decomposition).
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic Acid
(2w). To a solution of ethyl 4-(2,3-dimethoxyquinoxalin-6-yl)benzoate
9c (50 mg, 0.15 mmol, 1 equiv) in dioxane (0.5 mL) was added 2 M
HCl (0.5 mL), and the reaction mixture was heated at 110 °C for 4 h.
A light yellow solid precipitated and the heterogeneous mixture was
cooled to room temperature before the addition of 2 M HCl (1 mL).
The reaction mixture was filtered and washed with 1 M HCl (1 mL)
and diethyl ether (1 mL). The solid was dried in a vacuum oven
overnight, to give the title compound (as a light yellow solid (38 mg,
1
compound as a white solid (25 mg, 0.09 mmol, 75%). H NMR (600
MHz, DMSO-d6, rotamers) δ 13.12 (s, 1H), 11.94 (d, J = 8.0 Hz, 1H),
8.13 (d, J = 1.3 Hz, 1H), 7.94 (dd, J = 11.3, 7.8 Hz, 1H), 7.87 (dd, J =
16.6, 8.4 Hz, 1H), 7.62 (dt, J = 15.4, 7.7 Hz, 1H), 7.50−7.39 (m, 2H),
7.23 (dd, J = 8.3, 3.7 Hz, 1H). 13C NMR (151 MHz, DMSO-d6) δ
167.1, 165.6, 155.1, 155.1, 139.8, 139.6, 134.0, 133.8, 131.5, 131.1,
130.7, 129.6, 129.5, 128.2, 128.0, 126.9, 126.6, 126.3, 125.6, 125.5,
121.6, 121.6, 115.8, 115.8, 113.0, 113.0; mp > 400 °C (decom-
position).
3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-4-methylbenzoic
Acid (2s). To a solution of 3-(2,3-dimethoxyquinoxalin-6-yl)-4-
methylbenzoic acid 11 (30 mg, 93 μmol, 1 equiv) in dioxane (0.5
mL) was added 2 M HCl (0.5 mL), and the reaction mixture was
heated at 110 °C for 20 min. The solution was cooled to room
temperature, filtered, and dried in a vacuum oven overnight to give the
1
0.14 mmol, 91%). H NMR (600 MHz, DMSO-d6, conformers) δ
12.98 (s, 1H), 12.04 (s, 1H), 12.00 (s, 1H), 8.07−8.00 (m, 2H), 7.74
(d, J = 8.3 Hz, 0.3H), 7.71 (d, J = 8.5 Hz, 1.7H), 7.48 (dd, J = 8.3, 2.1
Hz, 1H), 7.44 (d, J = 2.2 Hz, 1H), 7.23 (d, J = 8.4 Hz, 1H). 13C NMR
(151 MHz, DMSO-d6, conformers) δ 167.5, 166.0, 155.6, 155.6, 144.3,
144.0, 134.3, 134.1, 130.6, 130.4, 130.0, 129.1, 127.0, 126.9, 126.7,
126.7, 126.4, 126.3, 122.3, 116.3, 113.7, 113.7; mp > 400 °C
(decomposition).
General Procedure for the Synthesis of Compounds 2aa−
2aw (unless Otherwise Noted). To a solution of the corresponding
starting material in dioxane (0.5 mL) was added 2 M HCl (0.5 mL),
and the reaction mixture was heated at 110 °C for 4 h before being
cooled to rt. Next, 2 M HCl (1.0 mL) was added and the reaction
mixture was filtered and washed with 1 M HCl (1.0 mL) and diethyl
ether (1.0 mL). The solid was dried in a vacuum oil pump for 8 h, to
give the desired product.
1
title compound as an orange solid (14 mg, 46 μmol, 50%). H NMR
(600 MHz, DMSO-d6) δ 12.92 (br s, 1H), 12.02 (s, 1H), 11.95 (s,
1H), 7.84 (dd, J = 7.9, 1.9 Hz, 1H), 7.73 (d, J = 1.9 Hz, 1H), 7.44 (d, J
= 7.9 Hz, 1H), 7.22 (d, J = 8.1 Hz, 1H), 7.13 (dd, J = 8.2, 1.9 Hz, 1H),
7.10 (d, J = 1.9 Hz, 1H), 2.30 (s, 3H). 13C NMR (151 MHz, DMSO-
d6) δ 167.1, 155.2, 155.1, 140.5, 140.3, 135.0, 130.9, 130.2, 128.6,
128.2, 125.6, 124.9, 123.8, 115.3, 115.1, 20.4; mp > 400 °C
(decomposition).
2-Chloro-5-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic
Acid (2t). 2-Chloro-5-(2,3-dimethoxyquinoxalin-6-yl)benzoic acid 13
(70 mg, 0.20 mmol, 1 equiv) was dissolved in dioxane (0.5 mL) by
gentle heating. Next, 2 M HCl (0.5 mL) was then added, and the
reaction mixture was heated at 70 °C for 3 h. The solution was cooled
to room temperature, filtered, and washed subsequently with 1 M HCl
(1 mL) and Et2O (1 mL). The crude white solid was dried in vacuum
oven overnight to give the title compound as a white solid (44 mg,
6-Phenyl-1,4-dihydroquinoxaline-2,3-dione (2aa). Reaction per-
formed on a 0.218 mmol scale. The desired product was isolated as a
1
light yellow solid (33 mg, 0.139 mmol, 64%). H NMR (400 MHz,
DMSO-d6) δ: 11.97 (d, J = 6.6 Hz, 2H), 7.58 (dd, J = 8.3, 1.4 Hz, 2H),
7.47 (t, J = 8.0 Hz, 2H), 7.42−7.34 (m, 3H), 7.21 (d, J = 8.2 Hz, 1H).
13C NMR (101 MHz, DMSO-d6) δ: 155.7, 155.5, 139.9, 135.6, 129.5,
1
0.14 mmol, 69%). H NMR (600 MHz, DMSO-d6) δ 13.53 (s, 1H),
12.02 (s, 1H), 11.92 (s, 1H), 7.97 (d, J = 1.9 Hz, 1H), 7.74 (dd, J =
8.3, 2.0 Hz, 1H), 7.64 (d, J = 8.3 Hz, 1H), 7.45 (dd, J = 8.2, 1.3 Hz,
1H), 7.41 (s, 1H), 7.22 (d, J = 8.3 Hz, 1H). 13C NMR (150 MHz,
DMSO-d6) δ 166.5, 155.1, 155.1, 138.2, 132.7, 131.9, 131.4, 130.7,
130.1, 128.3, 126.3, 125.7, 121.5, 115.8, 112.9; mp > 400 °C
(decomposition).
(3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)phenyl)-
phosphonic Acid (2u). To a solution of diethyl (3-(2,3-dimethox-
yquinoxalin-6-yl)phenyl)phosphonate 15 (85 mg, 0.21 mmol, 1 equiv)
in DCM (0.6 mL) was added TMSBr (279 μL, 2.1 mmol, 10 equiv).
The reaction mixture was stirred overnight at room temperature
during which a solid was formed. The mixture was evaporated under
reduced pressure until dryness. The solid was dissolved in dioxane (0.5
mL) and 1 N HCl (0.5 mL) was added, and the reaction mixture
heated at 70 °C for 5h. After cooling to rt, the mixture was filtered and
127.9, 126.8, 126.6, 125.6, 122.1, 116.1, 113.4. mp = 375.7 °C
(decomposed). LC-MS (m/z) calcd for C14H10N2O2 [M + H]+,
238.25, found 239.1.
5-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2-methoxyben-
zoic Acid (2ab). Reaction performed on a 0.235 mmol scale. The
desired product was isolated as a light yellow solid (40 mg, 0.129
mmol, 55%). 1H NMR (400 MHz, DMSO-d6) δ: 11.98 (s, 1H), 11.90
(s, 1H), 7.85 (d, J = 2.5 Hz, 1H), 7.74 (dd, J = 8.7, 2.5 Hz, 1H), 7.42−
7.35 (m, 2H), 7.22 (dd, J = 16.4, 8.5 Hz, 2H), 3.87 (s, 3H). 13C NMR
(101 MHz, DMSO-d6) δ: 167.6, 158.1, 155.6, 155.5, 134.3, 131.6,
131.1, 128.8, 126.6, 125.4, 122.1, 121.6, 116.2, 113.7, 112.9, 56.4. mp =
303.8−304.4 °C. LC-MS (m/z) calcd for C16H12N2O5 [M − H]−,
312.28, found 311.44.
5-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2-fluorobenzoic
Acid (2ac). Reaction performed on a 0.293 mmol scale. The desired
K
DOI: 10.1021/acschemneuro.7b00243
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX

ACS Chemical Neuroscience
Research Article
product was isolated as a light yellow solid (40 mg, 0.205 mmol, 70%).
61.9, 14.6; mp = 341.1 °C (decomposed). LC-MS (m/z) calcd for
C20H18N2O6 [M + H]+, 382.37, found 383.1. HPLC254 purity > 91%.
6-(p-Tolyl)-1,4-dihydroquinoxaline-2,3-dione (2ai). Reaction per-
formed on a 0.212 mmol scale. The desired product was isolated as a
1H NMR (400 MHz, DMSO-d6) δ: 13.41 (s, 1H), 12.01 (s, 1H), 11.92
(s, 1H), 8.03 (dd, J = 7.0, 2.6 Hz, 1H), 7.85 (ddd, J = 8.6, 4.5, 2.6 Hz,
1H), 7.47−7.38 (m, 3H), 7.22 (d, J = 8.3 Hz, 1H). 13C NMR (101
MHz, DMSO-d6) δ: 165.3, 165.3, 159.8, 155.6, 155.6, 155.5, 136.1,
133.5, 132.8, 132.7, 129.8, 126.7, 125.9, 122.0, 118.4, 118.1, 116.3,
113.4. mp = 389.3 °C (decomposed). LC-MS (m/z) calcd for
C15H9FN2O4 [M + H]+, [M − H]−, 300.25, found 301.1, 299.3.
3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-5-fluorobenzoic
Acid (2ad). To a solution of the crude product of 3-(2,3-
dimethoxyquinoxalin-6-yl)-5-fluorobenzoic Acid (32d) (210 mg) in
dioxane (0.7 mL) was added 2 M HCl (0.7 mL), and the reaction
mixture was heated at 110 °C for 4 h. A light yellow solid precipitated,
and the heterogeneous mixture was cooled to rt before the addition of
2 M HCl (1 mL). The mixture was filtered, and the solid washed with
1 M HCl (1 mL), diethyl ether (1 mL), and dioxane (1 mL). The title
compound was obtained as a light yellow solid (65 mg, 66% over two
1
light yellow solid (36 mg, 0.142 mmol, 67%). H NMR (400 MHz,
DMSO-d6) δ: 11.95 (s, 2H), 7.47 (d, J = 8.0 Hz, 2H), 7.40−7.33 (m,
2H), 7.27 (d, J = 7.9 Hz, 2H), 7.19 (d, J = 8.2 Hz, 1H), 2.34 (s, 3H).
13C NMR (101 MHz, DMSO-d6) δ: 155.7, 155.5, 137.2, 137.0, 135.5,
130.1, 126.6, 126.6, 125.4, 121.8, 116.1, 113.2, 21.1. mp = 380.0 °C
(decomposed). LC-MS (m/z) calcd for C15H12N2O2 [M + H]+, [M −
H]−, 252.27, found 253.1, 251.1.
6-(4-Methoxyphenyl)-1,4-dihydroquinoxaline-2,3-dione (2aj).
Reaction performed on a 0.233 mmol scale. The desired product
1
was isolated as a light yellow solid (27.6 mg, 0.102 mmol, 44%). H
NMR (400 MHz, DMSO-d6) δ: 11.94 (d, J = 6.1 Hz, 2H), 7.51 (d, J =
8.7 Hz, 2H), 7.37−7.29 (m, 2H), 7.17 (d, J = 8.3 Hz, 1H), 7.03 (d, J =
8.7 Hz, 2H), 3.79 (s, 3H). 13C NMR (101 MHz, DMSO-d6) δ: 159.3,
155.7, 155.5, 135.4, 132.2, 127.9, 126.5, 125.0, 121.6, 116.1, 114.9,
112.9, 55.7. mp = 378.4 °C (decomposed). LC-MS (m/z) calcd for
C15H12N2O3 [M + H]+, 268.27, found 269.1.
1
steps). H NMR (400 MHz, DMSO-d6) δ: 13.44 (s, 1H), 12.04 (s,
1H), 11.92 (s, 1H), 7.99 (t, J = 1.5 Hz, 1H), 7.74 (dt, J = 2.1, 10.0 Hz,
1H), 7.65 (dt, J = 1.8, 9.0 Hz, 1H), 7.51 (dd, J = 2.0, 8.4 Hz, 1H), 7.47
(d, J = 2.0 Hz, 1H), 7.24 (d, J = 8.4 Hz, 1H). 13C NMR (101 MHz,
DMSO-d6) δ: 166.5, 166.5, 155.6, 142.6, 142.5, 134.3, 134.2, 133.0,
132.0, 131.9, 129.2, 126.7, 126.5, 123.4, 122.2, 118.0, 117.7, 116.3,
115.1, 114.8, 113.6. mp > 400 °C. LC-MS (m/z) calcd for
C15H9FN2O4 [M − H]−, 300.25, found 299.3.
3-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2,6-difluoroben-
zoic Acid (2ae). Reaction performed on a 0.260 mmol scale. The
desired product was isolated as a dark yellow solid (41 mg, 0.130
mmol, 50%). 1H NMR (400 MHz, DMSO-d6) δ: 14.04 (s, 1H), 12.03
(s, 1H), 11.98 (s, 1H), 7.65 (td, J = 8.8, 6.3 Hz, 1H), 7.35−7.20 (m,
4H). 13C NMR (101 MHz, DMSO-d6) δ: 162.6, 155.6, 155.6, 133.3,
131.6, 131.6, 128.6, 126.3, 126.2, 125.2, 125.0, 124.0, 122.5, 120.6,
115.9, 115.8, 115.7, 115.7, 113.3, 113.0, 113.0. mp = 351.7−352.8 °C.
LC-MS (m/z) calcd for C15H8FN2O4 [M + H]+, [M − H]−, 318.24,
found 319.0, 317.2.
6-(4-Fluorophenyl)-1,4-dihydroquinoxaline-2,3-dione (2ak). Re-
action performed on a 0.186 mmol scale. The desired product was
1
isolated as a light yellow solid (40 mg, 84%). H NMR (400 MHz,
DMSO-d6) δ: 11.98 (s, 2H), 7.67−7.56 (m, 2H), 7.38 (dd, J = 8.4, 2.0
Hz, 1H), 7.35−7.27 (m, 3H), 7.20 (d, J = 8.3 Hz, 1H). 13C NMR (101
MHz, DMSO-d6) δ: 163.5, 161.0, 155.7, 155.5, 136.4, 136.4, 134.6,
128.8, 128.8, 126.6, 125.6, 122.0, 116.4, 116.2, 116.2, 113.4. mp =
381.5−383.3 °C. LC-MS (m/z) calcd for C14H9FN2O2 [M + H]+, [M
− H]−, 256.24, found 257.1, 255.1.
6-(4-Chlorophenyl)-1,4-dihydroquinoxaline-2,3-dione (2al). Re-
action performed on a 0.293 mmol scale. The desired product was
1
isolated as a light yellow solid (65 mg, 0.237 mmol, 81%). H NMR
(400 MHz, DMSO-d6) δ: 11.98 (d, J = 10.9 Hz, 2H), 7.60 (d, J = 8.6
Hz, 2H), 7.52 (d, J = 8.6 Hz, 2H), 7.40 (dd, J = 8.4, 1.9 Hz, 1H), 7.35
(d, J = 1.9 Hz, 1H), 7.20 (d, J = 8.3 Hz, 1H). 13C NMR (101 MHz,
DMSO-d6) δ: 155.6, 155.5, 138.7, 134.2, 132.7, 129.5, 128.5, 126.7,
125.9, 122.0, 116.2, 113.4. mp = 383.1−384.5 °C. LC-MS (m/z) calcd
for C14H9ClN2O2 [M + H]+, [M −H]−, 272.69, found 273.0, 271.0.
6-(4-(Trifluoromethyl)phenyl)-1,4-dihydroquinoxaline-2,3-dione
(2am). Reaction performed on a 0.194 mmol scale. The desired
product was isolated as a light yellow solid (41 mg, 0.134 mmol, 69%).
1H NMR (400 MHz, DMSO-d6) δ: 12.02 (d, J = 10.1 Hz, 2H), 7.86−
3-Chloro-5-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic
Acid (2af). To a solution of the crude product of 3-chloro-5-(2,3-
dimethoxyquinoxalin-6-yl)benzoic acid (32f) (150 mg) in dioxane (1
mL) was added 2 M HCl (1 mL), and the reaction mixture was heated
at 110 °C for 4 h. A light yellow solid precipitated, and the
heterogeneous mixture was cooled to rt before the addition of 2 M
HCl (1 mL). The reaction mixture was filtered and washed with 1 M
HCl (1 mL) and diethyl ether (1 mL). According to the NMR result,
there are still some impurities. After washing with dioxane (1 mL), the
title compound was obtained as a white solid (60 mg, 58% over two
7.77 (m, 4H), 7.48 (dd, J = 8.3, 2.0 Hz, 1H), 7.43 (d, J = 1.9 Hz, 1H),
7.24 (d, J = 8.3 Hz, 1H). 13C NMR (101 MHz, DMSO-d6) δ 155.6,
155.6, 143.9, 133.8, 127.5, 126.7, 126.5, 126.4, 126.4, 126.4, 122.4,
116.3, 113.8. mp = 383.6−385.4 °C. LC-MS (m/z) calcd for
C15H9F3N2O2 [M + H]+, [M − H]−, 306.24, found 307.0, 305.0.
6-(4-Hydroxyphenyl)-1,4-dihydroquinoxaline-2,3-dione (2an).
Reaction performed on a 0.177 mmol scale. The desired product
1
steps). H NMR (600 MHz, DMSO-d6) δ: 13.49 (s, 1H), 12.04 (s,
1H), 11.91 (s, 1H), 8.07 (t, J = 1.6 Hz, 1H), 7.92 (q, J = 1.5 Hz, 1H),
7.88 (t, J = 1.7 Hz, 1H), 7.51 (dd, J = 2.0, 8.4 Hz, 1H), 7.45 (d, J = 2.0
Hz, 1H), 7.23 (d, J = 8.3 Hz, 1H). 13C NMR (151 MHz, DMSO-d6) δ:
166.4, 155.6, 142.2, 134.6, 134.0, 130.5, 128.0, 126.8, 126.5, 126.0,
122.2, 116.3, 113.7. mp > 400 °C. LC-MS (m/z) calcd for
C15H9ClN2O4 [M + H]+, [M − H]−, 316.70, found 317.1, 314.8.
5-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)isophthalic Acid
(2ag). Reaction performed on a 0.209 mmol scale. The desired
product was isolated as a dark yellow solid (23 mg, 0. 071 mmol,
1
was isolated as a light yellow solid (26 mg, 0.118 mmol, 67%). H
NMR (400 MHz, DMSO-d6) δ: 11.92 (d, J = 4.7 Hz, 2H), 9.55 (s,
1H), 7.43−7.37 (m, 2H), 7.34−7.26 (m, 2H), 7.16 (d, J = 8.2 Hz,
1H), 6.89−6.82 (m, 2H). 13C NMR(101 MHz, DMSO-d6) δ: 157.6,
155.7, 155.5, 135.8, 130.6, 127.9, 126.5, 124.7, 121.4, 116.3, 116.0,
112.7. mp > 400 °C. LC-MS (m/z) calcd for C14H10N2O3 [M + H]+,
[M − H]−, 254.25, found 255.0, 253.0.
Methyl 4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-3-fluoro-
benzoate (2ao). Reaction performed on a 0.143 mmol scale. The
desired product was isolated as a light yellow solid (19 mg, 0.060
mmol, 42%). 1H NMR (400 MHz, DMSO-d6) δ: 12.05 (s, 1H), 11.99
(s, 1H), 7.88 (dd, J = 8.1, 1.7 Hz, 1H), 7.80 (dd, J = 11.3, 1.7 Hz, 1H),
7.67 (t, J = 8.0 Hz, 1H), 7.39−7.33 (m, 2H), 7.24 (d, J = 8.3 Hz, 1H),
3.89 (s, 3H). 13C NMR (101 MHz, DMSO-d6) δ: 155.6, 155.6, 131.4,
131.4, 131.0, 128.9, 126.6, 126.4, 126.2, 126.2, 124.1, 117.3, 117.1,
116.0, 100.0, 53.0. mp = 356.9 °C (decomposed). LC-MS (m/z) calcd
for C16H11FN2O4 [M + H]+, 314.27, found 315.38. HPLC254 purity
>88%.
1
34%). H NMR (400 MHz, DMSO-d6) δ: 12.06 (s, 1H), 11.92 (s,
1H), 8.44 (t, J = 1.6 Hz, 1H), 8.35 (d, J = 1.6 Hz, 2H), 7.52 (d, J = 7.1
Hz, 2H), 7.27 (d, J = 9.0 Hz, 1H). 13C NMR (101 MHz, DMSO-d6) δ:
166.9, 155.6, 140.6, 133.4, 132.6, 131.2, 126.8, 126.4, 121.8, 118.4,
116.5, 113.6, 113.6, 111.3, 111.2. mp > 400 °C. LC-MS (m/z) calcd
for C16H10N2O6 [M − H]−, 326.26, found 325.3. HPLC254 purity >
89%.
Diethyl 5-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-
isophthalate (2ah). Reaction performed on a 0.134 mmol scale.
The desired product was isolated as a white solid (38 mg, 0.100 mmol,
1
74%). H NMR (400 MHz, DMSO-d6) δ: 12.04 (s, 1H), 11.91 (s,
1H), 8.42 (t, J = 1.6 Hz, 1H), 8.34 (d, J = 1.6 Hz, 2H), 7.52−7.46 (m,
2H), 7.25 (d, J = 8.3 Hz, 1H), 4.40 (q, J = 7.1 Hz, 4H), 1.37 (t, J = 7.1
Hz, 6H). 13C NMR (101 MHz, DMSO-d6) δ 165.2, 155.6, 155.5,
140.9, 133.0, 131.8, 131.3, 128.5, 126.8, 126.5, 122.1, 116.4, 113.6,
Methyl 4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2-me-
thoxybenzoate (2ap). Reaction performed on a 0.124 mmol scale.
The desired product was isolated as a yellow solid (33 mg, 0.100
L
DOI: 10.1021/acschemneuro.7b00243
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ACS Chemical Neuroscience
Research Article
mmol, 81%). 1H NMR (400 MHz, DMSO-d6) δ: 12.02 (s, 1H), 11.95
(s, 1H), 7.77 (d, J = 8.0 Hz, 1H), 7.51 (dd, J = 8.4, 2.0 Hz, 1H), 7.45
(d, J = 2.0 Hz, 1H), 7.30 (d, J = 1.6 Hz, 1H), 7.25−7.21 (m, 2H), 3.92
(s, 3H), 3.81 (s, 3H). 13C NMR (101 MHz, DMSO-d6) δ: 166.3,
159.3, 155.6, 145.1, 134.4, 132.1, 126.6, 126.4, 122.5, 119.0, 118.6,
116.1, 113.9, 110.9, 56.4, 52.3. mp = 330.6 °C (decomposed). LC-MS
(m/z) calcd for C17H14N2O5 [M + H]+, 326.31, found 327.1.
124.4, 116.1, 115.6. mp = 394.1 °C (decomposed). LC-MS (m/z)
calcd for C15H9ClN2O4 [M + H]+, [M − H]−, 316.70, found 317.15,
315.28.
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-3-fluorobenzoic
Acid (2av). Reaction performed on a 0.137 mmol scale. The desired
product was isolated as a dark yellow solid (30 mg, 0.100 mmol,73%).
1H NMR (400 MHz, DMSO-d6) δ: 13.30 (s, 1H), 12.05 (s, 1H), 12.00
(s, 1H), 7.86 (dd, J = 8.0, 1.6 Hz, 1H), 7.77 (dd, J = 11.3, 1.6 Hz, 1H),
7.64 (t, J = 8.0 Hz, 1H), 7.39−7.33 (m, 2H), 7.25 (d, J = 8.3 Hz, 1H).
13C NMR (101 MHz, DMSO-d6) δ: 166.5, 166.4, 160.3, 157.9, 155.6,
155.6, 132.3, 132.2, 132.1, 131.2, 131.2, 129.1, 126.5, 126.4, 126.3,
126.3, 124.1, 117.4, 117.1, 115.9, 115.8, 115.8. mp > 400 °C. LC-MS
(m/z) calcd for C15H9FN2O4 [M + H]+, [M − H]−, 300.25, found
301.06, 299.38.
2-Chloro-4-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic
Acid (2aq). To a solution of the crude product of 2-chloro-4-(2,3-
dimethoxyquinoxalin-6-yl)benzoic acid (32q) (300 mg) in dioxane
(1.0 mL) was added 2 M HCl (1.0 mL), and the reaction mixture was
heated at 110 °C for 4 h. A light yellow solid precipitated, and the
heterogeneous mixture was cooled to rt before the addition of 2 M
HCl (1 mL). The reaction mixture was filtered and washed with 1 M
HCl (1 mL) and diethyl ether (1 mL). The solid was dried in a
vacuum oil pump for 6 h, to give the mixture product of ester (50 mg).
Then the reaction was repeated with the mixture of the ester. The title
compound was obtained as a light yellow solid (40 mg, 45% over two
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2-methoxyben-
zoic Acid (2aw). Reaction performed on a 0.068 mmol scale. The
desired product was isolated as a yellow solid (11 mg, 0.035 mmol,
1
52%). H NMR (400 MHz, DMSO-d6) δ: 12.59 (s, 1H), 12.02 (s,
1
1H), 11.95 (s, 1H), 7.76 (d, J = 8.0 Hz, 1H), 7.50 (dd, J = 8.4, 2.0 Hz,
1H), 7.45 (d, J = 1.9 Hz, 1H), 7.27 (d, J = 1.6 Hz, 1H), 7.23 (d, J = 8.3
Hz, 1H), 7.20 (dd, J = 8.0, 1.6 Hz, 1H), 3.92 (s, 3H). mp = 306.9−
308.7 °C. LC-MS (m/z) calcd for C16H12N2O5 [M − H]−, 312.28,
found 311.4.
steps). H NMR (400 MHz, DMSO-d6) δ: 13.38 (s, 1H), 12.05 (s,
1H), 11.96 (s, 1H), 7.92 (d, J = 8.1 Hz, 1H), 7.74 (d, J = 1.8 Hz, 1H),
7.64 (dd, J = 8.1, 1.8 Hz, 1H), 7.51 (dd, J = 8.4, 2.0 Hz, 1H), 7.43 (d, J
= 2.0 Hz, 1H), 7.23 (d, J = 8.4 Hz, 1H). 13C NMR (101 MHz, DMSO-
d6) δ: 166.8, 155.6, 144.0, 133.2, 132.7, 132.3, 130.0, 128.6, 126.7,
126.7, 125.4, 122.4, 116.3, 113.8. mp = 390.6 °C (decomposed). LC-
MS (m/z) calcd for C15H9ClN2O4 [M + H]+, [M − H]−, 316.70,
found 317.15, 315.23.
2,3-Dimethoxy-6-vinylquinoxaline (7). To a mixture of 6-bromo-
2,3-dimethoxyquinoxaline 6 (2.0 g, 7.4 mmol, 1.0 equiv) and
Pd(PPh3)4 (86 mg, 0.15 mmol, 2 mol %) in dry toluene (21 mL)
was added tributyl(vinyl)stannane (1.3 mL, 8.9 mmol, 1.2 equiv). The
reaction mixture was heated overnight at 100 °C under argon. After
filtration through Celite, the solvent was removed under reduced
pressure, and the crude product purified by flash chromatography on
silica gel [EtOAc/heptanes (8:92)] to afford the title compound 7 as a
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2-fluorobenzoic
Acid (2ar). Reaction performed on a 0.198 mmol scale. The desired
1
product was isolated as a white solid (30 mg, 0.099 mmol, 50%). H
NMR (400 MHz, DMSO-d6) δ 13.23 (s, 1H), 12.05 (s, 1H), 11.99 (s,
1H), 7.97 (t, J = 8.0 Hz, 1H), 7.56−7.50 (m, 3H), 7.44 (d, J = 2.0 Hz,
1H), 7.23 (d, J = 8.4 Hz, 1H). 13C NMR (101 MHz, DMSO-d6) δ:
165.2, 165.2, 163.4, 160.8, 155.6, 146.2, 146.1, 133.2, 132.8, 132.8,
126.8, 126.7, 122.5, 122.5, 122.4, 118.2, 118.1, 116.3, 114.9, 114.7,
113.8. mp = 396.3−397.5 °C. LC-MS (m/z) calcd for C15H9FN2O4
[M + H]+, 300.25, found 301.1.
1
white solid (1.5 g, 6.9 mmol, 93%). H NMR (400 MHz, CDCl3) δ
7.75 (d, J = 1.9 Hz, 1H), 7.71 (d, J = 8.5 Hz, 1H), 7.59 (dd, J = 8.5, 1.9
Hz, 1H), 6.85 (dd, J = 17.6, 10.9 Hz, 1H), 5.87 (d, J = 17.6 Hz, 1H),
5.33 (dd, J = 10.9, 0.9 Hz, 1H), 4.15 (s, 6H). 13C NMR (101 MHz,
CDCl3) δ 150.8, 150.5, 137.9, 137.6, 137.0, 136.8, 127.0, 125.1, 124.8,
115.1, 54.8, 54.8; mp. = 84.9−86.1 °C (solvent: heptane); Rf = 0.45
[EtOAc/heptanes (8:92)].
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2,6-difluoroben-
zoic Acid (2as). To a solution of the crude product of 4-(2,3-
dimethoxyquinoxalin-6-yl)-2,6-difluorobenzoic acid (32s) (86 mg) in
dioxane (0.8 mL) was added 2 M HCl (0.8 mL), and the reaction
mixture was heated at 110 °C for 4 h. A light yellow solid precipitated
and the heterogeneous mixture was cooled to rt before the addition of
2 M HCl (1 mL). The reaction mixture was filtered and washed with 1
M HCl (1 mL) and diethyl ether (1 mL). The solid was dried in a
vacuum oil pump for 4 h, to give the pure product (49 mg, 41% over
2,3-Dimethoxy-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
quinoxaline (8). A flask was charged with 6-bromo-2,3-dimethox-
yquinoxaline 6 (2.0 g, 7.4 mmol), bis(pinacolato)diboron (2.8 g, 11
mmol), Pd(dppf)2 ·DCM (0.6 g, 0.74 mmol, 10 mol %), and KOAc
(2.5 g, 26 mmol). The flask was evacuated and filled back with argon
(×3). Then, dry degassed DMF (48 mL) was added and the reaction
was stirred at 95 °C for 44 h. The reaction mixture was cooled to room
temperature and poured into water (500 mL). The aqueous phase was
extracted with EtOAc (7 × 300 mL), and the combined organic phases
dried over MgSO4. The solvent was evaporated under reduced
pressure, and the crude product purified by column chromatography
[EtOAc/heptanes (1:3)] to give the title compound 8 as a greenish-
yellow solid (1.6 g, 5.0 mmol, 68%). 1H NMR (600 MHz, DMSO-d6)
δ 8.03 (d, J = 1.24 Hz, 1H), 7.74 (m, 2H), 4.06 (s, 3H), 4.04 (s, 3H),
1.33 (s, 12H). 13C NMR (150 MHz, DMSO-d6) δ 150.6, 150.0, 139.4,
136.8, 134.1, 132.2, 125.8, 84.1, 54.4, 54.3, 25.1; mp = 116.5−116.9 °C
(dec.).
Methyl 2-(2,3-Dimethoxyquinoxalin-6-yl)benzoate (9a). 6-
Bromo-2,3-dimethoxyquinoxaline 6 (135 mg, 0.50 mmol, 1 equiv),
ethyl 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate (165
mg, 0.60 mmol, 1.2 equiv), Pd(PPh3)4 (46 mg, 40 μmol, 0.08
equiv), and cesium carbonate (650 mg, 2.00 mmol, 4 equiv) were
added into a flame-dried two-neck round-bottom flask. The flask was
evacuated and filled back with argon (×3), and then dry degassed
DMF (4.5 mL) was added followed by degassed H2O (0.22 mL). The
reaction mixture was stirred at 90 °C for 2 h. The reaction mixture was
cooled to room temperature and H2O (50 mL) was added followed
and extracted with EtOAc (3 × 100 mL). The combined organic
phases were dried over MgSO4, filtered and evaporated under vacuum.
The crude product was purified by flash chromatography on silica gel
[EtOAc/heptanes (2:8)] to afford the title compound 9a as an amorph
solid (125 mg, 0.37 mmol, 74%). 1H NMR (600 MHz, CDCl3) δ 7.88
1
two steps). H NMR (400 MHz, DMSO-d6) δ: 13.87 (s, 1H), 12.06
(s, 1H), 11.98 (s, 1H), 7.53 (dd, J = 8.4, 2.0 Hz, 1H), 7.46 (d, J = 2.6
Hz, 1H), 7.44−7.41 (m, 2H), 7.22 (d, J = 8.4 Hz, 1H). 13C NMR (101
MHz, DMSO-d6) δ: 162.5, 162.5, 161.7, 161.6, 159.2, 159.1, 155.6,
155.5, 144.8, 132.0, 127.0, 126.7, 122.4, 116.2, 113.9, 110.5, 110.3,
110.3, 110.2. mp = 351.6−352.0 °C. LC-MS (m/z) calcd for
C15H8F2N2O4 [M + H]+, [M − H]−, 318.24, found 319.17, 317.25.
4-(2,3-Dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)-2-hydroxyben-
zoic Acid (2at). Reaction performed on a 0.230 mmol scale. The
desired product was isolated as a light yellow solid (55 mg, 0.184
mmol, 80%). 1H NMR (400 MHz, DMSO-d6) δ: 13.91 (s, 1H), 12.03
(s, 1H), 11.96 (s, 1H), 11.36 (s, 1H), 7.87 (d, J = 8.1 Hz, 1H), 7.47
(dd, J = 8.4, 2.0 Hz, 1H), 7.42 (d, J = 1.9 Hz, 1H), 7.22 (d, J = 8.3 Hz,
1H), 7.18−7.13 (m, 2H). 13C NMR (101 MHz, DMSO-d6) δ: 172.1,
161.9, 155.6, 146.8, 133.8, 131.5, 126.6, 126.6, 122.3, 117.8, 116.2,
114.7, 113.7, 112.3. mp = 375.2−375.4 °C. LC-MS (m/z) calcd for
C15H10N2O5 [M − H]−, 298.25, found 297.4.
3-Chloro-4-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-6-yl)benzoic
Acid (2au). Reaction performed on a 0.453 mmol scale. The desired
product was isolated as a dark yellow solid (112 mg, 0.353 mmol,
1
78%). H NMR (600 MHz, DMSO-d6) δ: 13.36 (s, 1H), 12.04 (s,
1H), 12.00 (s, 1H), 8.03 (d, J = 1.7 Hz, 1H), 7.95 (dd, J = 8.0, 1.7 Hz,
1H), 7.54 (d, J = 8.0 Hz, 1H), 7.23 (dd, J = 5.0, 3.2 Hz, 2H), 7.20 (dd,
J = 8.3, 1.8 Hz, 1H). 13C NMR (101 MHz, DMSO-d6) δ: 166.3, 155.6,
155.6, 143.5, 132.8, 132.2, 132.0, 132.0, 130.9, 128.7, 126.2, 126.0,
M
DOI: 10.1021/acschemneuro.7b00243
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ACS Chemical Neuroscience
Research Article
(d, J = 7.7 Hz, 1H), 7.80−7.72 (m, 2H), 7.55 (td, J = 7.5, 1.5 Hz, 1H),
7.49−7.40 (m, 3H), 4.17 (s, 3H), 4.15 (s, 3H), 4.09 (q, J = 7.3 Hz,
2H), 0.96 (t, J = 7.2 Hz, 3H). 13C NMR (150 MHz, CDCl3) δ 168.7,
150.3, 150.1, 141.9, 140.2, 137.0, 136.5, 131.4, 131.3, 131.0, 130.1,
127.8, 127.5, 125.9, 125.9, 61.1, 54.4, 54.4, 13.9; rf = 0.3 [EtOAc/
heptanes (2:8)].
quinoxaline 8 (100 mg, 0.32 mmol, 1.0 equiv), 3-iodo-4-methylbenzoic
acid 10 (107 mg, 0.41 mmol, 1.3 equiv), Pd(PPh3)4 (29 mg, 25 μmol,
8 mol %), and Cs2CO3 (515 mg, 1.6 mmol, 5 equiv) were added into a
flame-dried 8 mL vial. The vial was evacuated and filled back with
argon (×3), then charged with dry degassed DMF (0.3 mL) and
degassed H2O (0.15 mL). The reaction mixture was heated at 90 °C
for 4 h. After cooling to rt, H2O (3 mL) was added and the solution
extracted with Et2O (3 × 10 mL). The combined organic phases were
dried over MgSO4, and the solvent removed under vacuum. The crude
product was purified by flash chromatography on silica gel [EtOAc/
heptanes (2:8) + 1% of AcOH] to give the title compound as a yellow
Ethyl 3-(2,3-Dimethoxyquinoxalin-6-yl)benzoate (9b). 6-Bromo-
2,3-dimethoxyquinoxaline 6 (150 mg, 0.56 mmol, 1.0 equiv), 3-
ethoxycarbonylphenylboronic acid (141 mg, 0.73 mmol, 1.3 equiv),
Pd(PPh3)4 (51 mg, 45 μmol, 8 mol %), and Cs2CO3 (730 mg, 2.2
mmol, 4 equiv) were added into a flame-dried two-neck round-bottom
flask. The flask was evacuated and filled back with argon (×3), and
then dry degassed DMF (5 mL) was added followed by degassed H2O
(0.25 mL). The reaction mixture was stirred and heated at 90 °C for 2
h. The solution was cooled to room temperature and H2O (50 mL)
was added, and extracted with EtOAc (3 × 100 mL). The combined
organic phases were dried over MgSO4. The crude product was
purified by flash chromatography on silica gel [EtOAc/heptanes
(15:85)] to give the title compound 9b as a white solid (89 mg, 0.26
mmol, 47%). 1H NMR (400 MHz, CDCl3, rotamers) δ 8.42−8.39 (m,
1H), 8.07 (dd, J = 1.7, 1.1 Hz, 0.5H), 8.06−8.04 (m, 1.5H), 7.91 (dd, J
= 2.0, 1.2 Hz, 0.5H), 7.89 (dd, J = 2.0, 1.1 Hz, 0.5H), 7.87 (d, J = 0.5
Hz, 0.3H), 7.84 (d, J = 0.5 Hz, 0.7H), 7.79 (d, J = 2.1 Hz, 0.7H), 7.77
(d, J = 2.1 Hz, 0.3H), 7.55 (td, J = 7.8, 0.5 Hz, 1H), 4.43 (q, J = 7.1
Hz, 2H), 4.19 (s, 3H), 4.18 (s, 3H), 1.44 (t, J = 7.1 Hz, 3H). 13C NMR
(150 MHz, CDCl3) δ 166.7, 150.5, 150.3, 140.8, 138.7, 137.6, 137.0,
131.7, 131.3, 129.1, 128.7, 128.5, 127.0, 126.0, 124.7, 61.3, 54.5, 54.5,
14.5; mp = 124.1−125.0 °C; Rf: 0.25 [EtOAc/heptanes (15:85)].
Ethyl 4-(2,3-Dimethoxyquinoxalin-6-yl)benzoate (9c). 6-Bromo-
2,3-dimethoxyquinoxaline 6 (150 mg, 0.56 mmol, 1 equiv), 4-
ethoxycarbonylphenylboronic acid (141 mg, 0.73 mmol, 1.3 equiv),
Pd(PPh3)4 (51 mg, 45 μmol, 8 mol %), and cesium carbonate (730
mg, 2.2 mmol, 4 equiv) were added into a flame-dried two-neck
round-bottom flask. The flask was evacuated and filled back with argon
(×3), and then dry degassed DMF (5 mL) was added followed by
degassed H2O (0.25 mL), and the reaction mixture heated at 90 °C for
2 h. The solution was cooled to room temperature and H2O (50 mL)
was added followed before to be extracted with EtOAc (3 × 100 mL).
The combined organic phases were dried over MgSO4. The crude
product was purified by flash chromatography on silica gel [EtOAc/
heptanes (2:8)] to give the title compound 9c as a white solid (134
mg, 0.40 mmol, 71%). 1H NMR (600 MHz, CDCl3) δ 8.07 (d, J = 8.2
Hz, 2H), 7.97 (d, J = 2.1 Hz, 1H), 7.77 (d, J = 8.4 Hz, 1H), 7.74−7.67
(m, 3H), 4.35 (q, J = 7.2 Hz, 2H), 4.11 (s, 6H), 1.36 (t, J = 7.1 Hz,
3H); 13C NMR (150 MHz, CDCl3) δ 166.6, 150.6, 150.4, 144.9,
138.5, 137.6, 137.2, 130.3, 129.6, 127.3, 127.1, 126.0, 125.0, 77.4, 77.2,
76.9, 61.2, 54.5, 54.5, 14.5; mp = 185.7−186.4 °C (solvent: heptane);
rf = 0.38 [EtOAc/heptanes (2:8)].
Ethyl 2-(3-(2,3-Dimethoxyquinoxalin-6-yl)phenyl)acetate (9d). 6-
Bromo-2,3-dimethoxyquinoxaline 6 (143 mg, 0.54 mmol, 1 equiv), (3-
(2-ethoxy-2-oxoethyl)phenyl)boronic acid (125 mg, 0.64 mmol, 1.2
equiv), Pd(PPh3)4 (50 mg, 43 μmol, 0.08 equiv), and Cs2CO3 (700
mg, 2.15 mmol, 4 equiv) were added into a flame-dried two-neck
round-bottom flask. The flask was evacuated and filled back with argon
(×3) before dry degassed DMF (4.8 mL) was added followed by
degassed H2O (0.24 mL). The reaction mixture was heated at 90 °C
for 2 h, after which the reaction mixture was cooled to room
temperature. H2O (50 mL) was added and the solution extracted with
EtOAc (3 × 100 mL). The combined organic phases were dried over
MgSO4. Crude product was purified by flash chromatography on silica
gel [EtOAc/heptane (2:8)] to give the title compound 9d as a
colorless oil (131 mg, 0.37 mmol, 69%). 1H NMR (600 MHz, CDCl3)
δ 8.00 (d, J = 2.0 Hz, 1H), 7.81 (d, J = 8.4 Hz, 1H), 7.74 (dd, J = 8.5,
2.1 Hz, 1H), 7.67−7.59 (m, 2H), 7.43 (t, J = 7.7 Hz, 1H), 7.33−7.28
(m, 1H), 4.22−4.13 (m, 8H), 3.70 (s, 2H), 1.28 (t, J = 7.2 Hz, 3H).
13C NMR (150 MHz, CDCl3) δ 171.6, 150.4, 150.1, 140.8, 139.4,
137.5, 136.7, 134.9, 129.2, 128.5, 128.4, 126.8, 126.1, 126.1, 124.5,
61.0, 54.4, 54.3, 41.6, 14.3; rf = 0.3 [EtOAc/heptane (2:8)].
1
solid (104 mg, 0.32 mmol, 99%). H NMR (600 MHz, DMSO-d6) δ
12.88 (br s, 1H), 7.87 (dd, J = 7.9, 1.9 Hz, 1H), 7.85−7.79 (m, 2H),
7.69 (d, J = 2.0 Hz, 1H), 7.54 (dd, J = 8.4, 2.1 Hz, 1H), 7.47 (d, J = 7.9
Hz, 1H), 4.07 (s, 3H), 4.05 (s, 3H), 2.34 (s, 3H). 13C NMR (150
MHz, DMSO-d6) δ 167.1, 150.2, 150.1, 140.7, 140.4, 138.9, 136.4,
135.7, 130.8, 130.5, 128.7, 128.4, 127.9, 126.0, 54.0, 54.0, 20.4; mp =
235.6−237.5 °C; rf = 0.16 [EtOAc/heptanes (2:8) + 1% of AcOH].
2-Chloro-5-(2,3-dimethoxyquinoxalin-6-yl)benzoic Acid (13). To
a solution of 2,3-dimethoxy-6-bromoquinoxaline 6 (100 mg, 0.37
mmol, 1 equiv) in dry degassed dioxane (5 mL) and H2O (0.5 mL)
under argon was added 5-borono-2-methoxybenzoic acid (109 mg,
0.56 mmol, 1.5 equiv), K2CO3 (154 mg, 1.1 mmol, 3 equiv), and
PdCl2(dppf)·DCM (15 mg, 18.6 μmol, 5 mol %). The reaction
mixture was heated at 80 °C overnight. The mixture was cooled to
room temperature, poured into 1 M HCl (10 mL), and extracted with
AcOEt (3 × 20 mL). The collective organic phases were dried over
MgSO4 and concentrated under vacuum to give the crude product.
Purification on silica gel [EtOAc/heptanes (2:8) + 0.1% AcOH] gave
1
the title compound as a white solid (79 mg, 0.23 mmol, 62%). H
NMR (600 MHz, CDCl3) δ 8.02 (d, J = 1.9 Hz, 1H), 7.86 (d, J = 8.5
Hz, 1H), 7.82 (dd, J = 8.3, 2.4 Hz, 1H), 7.74 (dd, J = 8.9, 1.7 Hz, 1H),
7.60 (d, J = 8.3 Hz, 1H), 4.18 (s, 6H). 13C NMR (150 MHz, CDCl3) δ
168.5, 150.5, 150.3, 139.3, 137.5, 137.1, 137.0, 133.8, 131.9, 131.9,
131.0, 128.6, 127.1, 125.4, 124.5, 54.4, 54.4; Rf = 0.2 [EtOAc/heptanes
(2:8) + 0.1% AcOH].
Diethyl (3-(2,3-Dimethoxyquinoxalin-6-yl)phenyl)phosphonate
(15). 2,3-Dimethoxy-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
quinoxaline 8 (100 mg, 0.32 mmol, 1.0 equiv), diethyl (3-
bromophenyl)phosphonate 14 (120 mg, 0.41 mmol, 1.3 equiv),
Pd(PPh3)4 (29 mg, 25 μmol, 8 mol %), and Cs2CO3 (411 mg, 1.3
mmol, 4 equiv) were added into a flame-dried 8 mL vial. The vial was
evacuated and filled back with argon (×3), then charged with dry
degassed DMF (0.3 mL) and degassed H2O (0.15 mL). The reaction
mixture was heated at 90 °C for 4h. The reaction mixture was cooled
to room temperature and H2O (3 mL) was added. The solution was
extracted with Et2O (3 × 10 mL) and the combined organic phase
were dried over MgSO4, filtered, and evaporated under vacuum. The
crude product was purified by flash chromatography on silica [EtOAc/
heptanes (1:1)] to give the title compound as an amorph solid (95 mg,
1
0.24 mmol, 74%). H NMR (600 MHz, CDCl3) δ 8.17 (dt, J = 13.8,
1.7 Hz, 1H), 8.03 (d, J = 2.1 Hz, 1H), 7.89 (ddt, J = 7.8, 2.1, 1.2 Hz,
1H), 7.84 (d, J = 8.5 Hz, 1H), 7.81 (ddt, J = 13.0, 7.5, 1.3 Hz, 1H),
7.76 (dd, J = 8.5, 2.1 Hz, 1H), 7.58 (td, J = 7.7, 4.4 Hz, 1H), 4.24−4.18
(m, 2H), 4.17 (s, 3H), 4.17 (s, 3H), 4.17−4.09 (m, 2H), 1.36 (t, J =
7.1 Hz, 6H). 13C NMR (150 MHz, CDCl3) δ 150.6, 150.3, 141.0,
140.9, 138.4, 137.6, 137.0, 131.3, 131.3, 130.8, 130.8, 130.8, 130.7,
130.0, 129.3, 129.2, 128.7, 127.0, 126.0, 124.8, 62.4, 62.4, 54.5, 54.5,
16.6, 16.5; Rf = 0.23 [EtOAc/heptanes (1:1)].
Methyl 2-Vinylbenzoate (17). To a mixture of methyl 2-
iodobenzoate 16 (450 μL, 3.0 mmol, 1.0 equiv) and Pd(PPh3)4 (71
mg, 61 μmol, 2 mol %) in dry degassed toluene (8 mL) under argon
was added tributyl(vinyl)stannane (1.1 mL, 3.7 mmol, 1.2 equiv). The
reaction mixture was heated for 17 h at 100 °C, and then cooled to rt
and filtered through Celite. The solvent was removed under reduced
pressure and the residue was purified by flash column chromatography
on silica gel [Et2O/DCM (1:9)] to afford the title compound as a
white solid (214 mg, 1.3 mmol, 44%). 1H NMR (400 MHz, CDCl3) δ
7.88 (dd, J = 7.9, 0.9 Hz, 1H), 7.58 (m, 1H), 7.52−7.41 (m, 2H), 7.32
3-(2,3-Dimethoxyquinoxalin-6-yl)-4-methylbenzoic Acid (11).
2,3-Dimethoxy-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
N
DOI: 10.1021/acschemneuro.7b00243
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ACS Chemical Neuroscience
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(td, J = 7.6, 1.3 Hz, 1H), 5.65 (dd, J = 17.4, 1.3 Hz, 1H), 5.36 (dd, J =
11.0, 1.3 Hz, 1H), 3.91 (s, 3H).
flash chromatography on silica gel [EtOAc/heptanes (3:7)] to give the
title product as a white solid (430 mg, 2.1 mmol, 70%). 1H NMR (600
MHz, CDCl3) δ 7.43 (d, J = 2.2 Hz, 1H), 6.76 (d, J = 2.1 Hz, 1H),
3.86 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 162.5, 144.4, 129.2,
117.4, 112.8, 51.9; rf = 0.41 [EtOAc/heptanes (3:7)].
(E)-Methyl 2-(2-(2,3-Dimethoxyquinoxalin-6-yl)vinyl)benzoate
(18). A flame-dried 8 mL vial was charged with 2,3-dimethoxy-6-
bromoquinoxaline 6 (79 mg, 0.30 mmol, 1.0 equiv), Pd(OAc)2 (3.3
mg, 14.8 μmol, 5 mol %) and P(o-tol)3 (9.0 mg, 29.6 μmol, 10 mol %).
The vial was evacuated and filled back with argon (×3). A solution of
methyl 2-vinylbenzoate 17 (48 mg, 0.30 mmol, 1 equiv) in dry
degassed DMF (0.3 mL) was added followed by NEt3 (102.6 μL, 0.74
mmol, 2.5 equiv). The reaction mixture was heated at 100 °C
overnight, cooled to room temperature and quenched with water (5
mL). The solution was extracted with Et2O (3 × 10 mL), and the
combined organic phases were evaporated. The crude product was
purified by flash chromatography on silica gel [EtOAc/heptanes (2:8)]
to give the title compound as a white solid (45 mg, 0.13 mmol, 43%).
1H NMR (600 MHz, CDCl3) δ 8.12 (d, J = 16.2 Hz, 1H), 7.95 (dd, J =
7.8, 1.3 Hz, 1H), 7.88 (s, 1H), 7.78−7.72 (m, 3H), 7.53 (t, J = 7.4 Hz,
1H), 7.34 (t, J = 7.0 Hz, 1H), 7.13 (d, J = 16.2 Hz, 1H), 4.16 (s, 3H),
4.16 (s, 3H), 3.95 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 168.0,
150.3, 150.0, 139.3, 137.6, 137.2, 136.2, 132.4, 131.0, 130.9, 128.7,
128.2, 127.4, 127.1, 126.7, 125.3, 124.9; mp = 139.5−140.3 °C; Rf =
0.28 [EtOAc/heptanes (2:8)].
(E)-Methyl 2-[2-(2,3-Dimethoxyquinoxalin-6-yl)vinyl]furan-3-car-
boxylate (25). A flame-dried vial was charged with 2,3-dimethoxy-6-
vinylquinoxaline 7 (60 mg, 0.28 mmol, 1.0 equiv), methyl 2-
bromofuran-3-carboxylate 24 (62 mg, 0.30 mmol, 1.1 equiv),
Pd(OAc)2 (3.1 mg, 13.8 μmol, 5 mol %) and P(o-tol)3 (8.4 mg,
27.7 μmol, 10 mol %). The vial was evacuated and filled back with
argon (×3). Dry degassed DMF (0.35 mL) was added followed by
NEt3 (96 μL, 0.69 mmol, 2.5 equiv). The reaction mixture was heated
at 100 °C overnight and quenched with 1/2 saturated solution of
NH4Cl (6 mL). The solution was extracted with Et2O (3 × 12 mL)
and the combined organic phases were evaporated to dryness. The
crude product was purified by flash chromatography on silica gel
[EtOAc/heptanes (2:8)] to afford the title compound as a yellow solid
(67 mg, 0.20 mmol, 70%). 1H NMR (600 MHz, CDCl3) δ 7.92 (d, J =
1.7 Hz, 1H), 7.77 (d, J = 16.4 Hz, 1H), 7.75−7.71 (m, 2H), 7.43 (d, J
= 16.4 Hz, 1H), 7.36 (d, J = 2.0 Hz, 1H), 6.76 (d, J = 1.9 Hz, 1H), 4.17
(s, 3H), 4.16 (s, 3H), 3.91 (s, 3H). 13C NMR (150 MHz, CDCl3) δ
164.2, 157.1, 150.5, 150.3, 141.7, 137.7, 137.6, 135.1, 131.9, 126.9,
125.4, 125.3, 116.1, 114.4, 112.1, 54.5, 54.5, 51.8; mp = 165.4−166.7
°C; rf = 0.27 [EtOAc/heptanes (2:8)].
(E)-Ethyl-3-(2,3-dimethoxyquinoxalin-6-yl)acrylate (26a). A vial
was charged with Pd(OAc)2 (42 mg, 0.18 mmol, 5 mol %), P(o-Tol)3
(113 mg, 0.37 mmol, 10 mol %), and 2,3-dimethoxy-6-bromoquinoxa-
line 6 (1.00 g, 3.7 mmol, 1.0 equiv). The vial was purged twice with
argon, then dry degassed DMF (6.6 mL) was added followed by NEt3
(1.42 mL, 10.2 mmol) and ethyl acrylate (1.22 mL, 11.4 mmol, 3.0
equiv). The septum was replaced by a pressure cap and the mixture
was stirred at 100 °C for 6 h. The reaction mixture was then cooled to
room temperature and H2O (25 mL) was added. The precipitate was
filtered off and washed with H2O (3 × 5 mL). The crude product was
dried, then purified by column chromatography (EtOAc/heptanes =
1:3) to afford the title compound as a white powder (940 mg, 3.26
mmol, 88%). 1H NMR (600 MHz, DMSO-d6) δ 8.04 (d, J = 1.81 Hz,
1H), 7.92 (dd, J = 1.90 Hz, 8.54 Hz, 1H), 7.80 (d, J = 16.02 Hz, 1H),
7.73 (d, J = 8.51 Hz, 1H), 6.75 (d, J = 16.02 Hz, 1H), 4.21 (q, J = 7.10
Hz, 2H), 4.05 (s, 3H), 4.05 (s, 3H), 1.27 (t, J = 7.11 Hz, 3H). 13C
NMR (150 MHz, DMSO-d6, 13C−31P-coupling) δ 166.2, 150.4, 150.3,
143.7, 137.9, 136.6, 132.5, 127.0, 126.5, 125.6, 118.7, 60.0, 54.1, 54.0,
14.2; rf = 0.32 [EtOAc/heptanes (1:3)].
(E)-Methyl 3-(2-(2,3-Dimethoxyquinoxalin-6-yl)vinyl)benzoate
(20). A flame-dried argon filled 8 mL vial was charged with 2,3-
dimethoxy-6-vinylquinoxaline 7 (100 mg, 0.46 mmol, 1 equiv), methyl
3-bromobenzoate 19 (107 mg, 0.50 mmol, 1.1 equiv), Pd(OAc)2 (5.2
mg, 23 μmol, 5 mol %), and P(o-tol)3 (14 mg, 46 μmol, 10 mol %).
The vial was evacuated and filled back with argon (×3). Dry degassed
DMF (0.46 mL) was added followed by NEt3 (160 μL, 1.1 mmol, 2.5
equiv). The reaction mixture was heated at 100 °C overnight and
quenched with 1/2 saturated solution of NH4Cl (6 mL). The solution
was extracted with Et2O (3 × 12 mL) and the combined organic
phases evaporated to dryness. The crude product was purified by flash
chromatography on silica gel [EtOAc/heptanes (2:8)] to give the title
1
product as a pale yellow solid (124 mg, 0.35 mmol, 77%). H NMR
(600 MHz, CDCl3) δ 8.27−8.21 (m, 1H), 7.98−7.92 (m, 1H), 7.89
(d, J = 1.9 Hz, 1H), 7.76 (d, J = 8.5 Hz, 1H), 7.74−7.68 (m, 2H), 7.46
(t, J = 7.7 Hz, 1H), 7.31 (d, J = 16.3 Hz, 1H), 7.26 (d, J = 16.4 Hz,
1H), 4.17 (s, 3H), 4.16 (s, 3H), 3.96 (s, 3H). 13C NMR (150 MHz,
CDCl3) δ 167.1, 150.4, 150.1, 137.7, 137.6, 137.2, 135.7, 131.0, 130.8,
129.5, 128.9, 128.8, 128.4, 127.7, 126.8, 125.1, 124.6, 54.4, 54.4, 52.4;
mp = 131.0−131.8 °C; rf = 0.3 [EtOAc/heptanes (2:8)].
Methyl (E)-2-(2-(2,3-Dimethoxyquinoxalin-6-yl)vinyl)-6-methoxy-
benzoate (22). A flame-dried argon filled 8 mL vial was charged with
2,3-dimethoxy-6-vinylquinoxaline 7 (100 mg, 0.46 mmol, 1 equiv),
methyl 2-bromo-6-methoxybenzoate 21 (123 mg, 0.50 mmol, 1.1
equiv), Pd(OAc)2 (5.2 mg, 23.1 μmol, 5 mol %), and P(o-tol)3 (14.1
mg, 46.2 μmol, 10 mol %). The vial was evacuated and filled back with
argon (×3). Dry degassed DMF (0.46 mL) was added followed by
NEt3 (160 μL, 1.15 mmol, 2.5 equiv). The septum was replaced by a
pressure cap and the reaction mixture was heated at 100 °C overnight,
cooled to room temperature and quenched with 1/2 saturated solution
of NH4Cl (6 mL). The solution was extracted with Et2O (3 × 12 mL)
and the combined organic phases were evaporated. The crude product
was purified by flash chromatography on silica gel [EtOAc/heptanes
(2:8)] to give the title product as a pale yellow solid (87 mg, 0.23
mmol, 50%). 1H NMR (600 MHz, CDCl3) δ 7.75 (d, J = 1.8 Hz, 1H),
7.66 (d, J = 8.5 Hz, 1H), 7.56 (dd, J = 8.5, 1.8 Hz, 1H), 7.31 (t, J = 8.0
Hz, 1H), 7.26 (d, J = 7.8 Hz, 1H), 7.14 (d, J = 16.1 Hz, 1H), 7.09 (d, J
= 16.1 Hz, 1H), 6.80 (d, J = 8.1 Hz, 1H), 4.10 (s, 3H), 4.09 (s, 3H),
3.92 (s, 3H), 3.80 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 168.7,
156.8, 150.4, 150.1, 137.5, 137.3, 136.2, 135.6, 131.5, 130.7, 126.7,
125.7, 125.2, 124.8, 123.0, 117.9, 110.2, 56.2, 54.4, 52.7; rf = 0.25
[EtOAc/heptanes (2:8)].
(E)-Methyl-4-(2,3-dimethoxyquinoxalin-6-yl)but-2-enoate (26b).
A vial was charged with Pd(OAc)2 (21 mg, 93 μmol, 8 mol %),
P(o-tol)3 (57 mg, 0.18 mmol, 16 mol %), and 2,3-dimethoxy-6-
bromoquinoxaline 6 (315 mg, 1.2 mmol, 1.0 equiv). The vial was
purged twice with argon, followed by addition of dry degassed DMF
(1.5 mL), NEt3 (450 μL, 3.2 mmol) and methyl 3-butenoate (390 μL,
4.1 mmol, 3.4 equiv). The mixture was stirred at 100 °C for 3.5 h and
cooled to room temperature. H2O (10 mL) was added and the mixture
was extracted with EtOAc (3 × 20 mL). The combined organic phases
were washed with water (50 mL), brine (50 mL), dried over MgSO4,
filtered and concentrated. The crude product was purified by column
chromatography (EtOAc/heptaness = 1:5) to give the title compound
1
as a white powder (232 mg, 0.8 mmol, 67%). H NMR (600 MHz,
DMSO- d6) δ 7.74−7.63 (m, 3H), 6.68 (d, J = 15.88 Hz, 1H), 6.45 (m,
1H), 4.03 (s, 3H), 4.03 (s, 3H), 3.65 (s, 3H), 3.34 (d, J = 6.97 Hz,
2H). 13C NMR (150 MHz, DMSO- d6, 13C−31P coupling) δ 171.44,
150.08, 149.71, 136.78, 136.05, 135.27, 132.17, 126.30, 124.39, 123.70,
123.35, 53.95, 53.94, 51.63, 37.49; rf = 0.23 [EtOAc/heptanes (1:3)].
Ethyl-3-(2,3-dimethoxyquinoxalin-6-yl)propanoate (27a). In a
vial, (E)-ethyl-3-(2,3-dimethoxyquinoxalin-6-yl)acrylate 26a (140 mg,
0.49 mmol, 1.0 equiv) was dissolved in DMF (2.1 mL) and purged
with argon. Then Pd(OH)2 (20 wt % on charcoal) (34.0 mg, 48 μmol,
10 mol %) was added and the vial was purged again with argon. The
atmosphere was exchanged with H2 and the mixture was stirred at 50
°C for 8 h. The reaction mixture was poured into water (10 mL) and
extracted with EtOAc (3 × 20 mL). The combined organic phases
Methyl 2-Bromofuran-3-carboxylate (24). 2-Bromofuran-3-car-
boxylic acid 23 (600 mg, 3.0 mmol, 1.0 equiv) was added to a
flame-dried round-bottom flask. Dry MeOH (6 mL) was added
followed by 5 drops of conc. H2SO4. The reaction mixture was heated
at reflux 2 days then cooled to room temperature and carefully
evaporated under reduced pressure. The crude product was purified by
O
DOI: 10.1021/acschemneuro.7b00243
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX

ACS Chemical Neuroscience
Research Article
were dried over MgSO4, filtered, and concentrated under reduced
pressure to give the title compound as colorless oil. (127 mg, 0.44
mmol, 91%). 1H NMR (600 MHz, DMSO-d6) δ 7.66 (d, J = 8.34 Hz,
1H), 7.59 (d, J = 1.69 Hz, 1H), 7.41 (dd, J = 8.36, 1.94 Hz, 1H), 4.04
(q, J = 7.12 Hz, 2H), 4.03 (s, 3H), 4.02 (s, 3H), 3.00 (t, J = 7.53 Hz,
2H), 2.71 (t, J = 7.55 Hz, 2H), 1.14 (t, J = 7.11 Hz, 3H). 13C NMR
(150 MHz, DMSO-d6, 13C−31P coupling) δ 172.1, 149.8, 149.5, 139.4,
136.4, 135.0, 127.6, 125.8, 125.1, 59.8, 53.8, 53.8, 34.9, 30.0, 14.0.
Methyl-4-(2,3-dimethoxyquinoxalin-6-yl)butanoate (27b). In a
vial (E)-methyl-4-(2,3-dimethoxyquinoxalin-6-yl)but-2-enoate 26b
(100 mg, 0.34 mmol, 1.0 equiv) was dissolved in DMF (1.4 mL)
and then purged with argon. Then Pd(OH)2 (20 wt % on charcoal)
(24.2 mg, 34 μmol, 10 mol %) were added. The flask was evacuated
and recharged with H2 gas and the mixture was stirred at 50 °C for 5.5
h. The mixture was poured into H2O (15 mL) and extracted with
EtOAc (4 × 20 mL). The combined organic phases were dried over
MgSO4, filtered and concentrated under reduced pressure, to give the
phosphonate 28a (100 mg, 0.28 mmol, 1.0 equiv) was dissolved in
DMF (1.3 mL) and the system purged with argon. Then Pd(OH)2 (20
wt % on charcoal) (19.0 mg, 27 μmol, 10 mol %) was added, the vial
was purged again with argon and then filled with H2 gas, and the
reaction mixture was stirred at 50 °C for 8 h. The mixture was poured
into water (20 mL) and extracted with EtOAc (4 × 30 mL). The
combined organic phases were dried over MgSO4, filtered, and
concentrated under reduced pressure to give the title compound as
colorless liquid (99 mg, 0.28 mmol, 99%). 1H NMR (400 MHz,
DMSO-d6) δ 7.71−7.62 (m, 2H), 7.46 (dd, J = 1.42 Hz, 8.35 Hz, 1H),
4.00 (q, J = 7.65 Hz, 4H), 4.04 (s, 3H), 4.04 (s, 3H), 3.01−2.90 (m,
2H), 2.23−2.10 (m, 2H), 1.23 (t, J = 7.04 Hz, 6H). 13C NMR (150
MHz, DMSO-d6, 13C−31P coupling) δ 149.8, 149.4, 139.8, 139.7,
136.4, 135.0, 127.4, 125.8, 124.9, 60.9, 60.9, 53.8, 53.8, 27.8, 27.8, 26.6,
25.2, 16.2, 16.2.
Diethyl (3-(2,3-Dimethoxyquinoxalin-6-yl)propyl)phosphonate
(29b). In a vial (E)-diethyl (3-(2,3-dimethoxyquinoxalin-6-yl)allyl)-
phosphonate 28b (100 mg, 0.27 mmol, 1.0 equiv) was dissolved in
DMF (1.3 mL) and the system purged with argon. Pd(OH)2 (20 wt %
on charcoal) (19.0 mg, 27 μmol, 10 mol %) was added, and argon
atmosphere was exchanged for H2 gas. The reaction mixture was
stirred at 50 °C for 5.5 h then poured into water (20 mL) and
extracted with EtOAc (4 × 20 mL). The combined organic phases
were dried over MgSO4, filtered, and concentrated, to give the title
1
title compound as colorless oil (99 mg, 0.34 mmol, 99%). H NMR
(600 MHz, DMSO-d6) δ 7.67 (d, J = 8.31 Hz, 1H), 7.55 (d, J = 1.53
Hz, 1H), 7.38 (dd, J = 1.86 Hz, 8.33 Hz, 1H), 4.03 (s, 3H), 4.02 (s,
3H), 3.58 (s, 3H), 2.75 (t, J = 7.56 Hz, 2H), 2.33 (t, J = 7.40 Hz, 2H),
1.95−1.88 (m, 2H). 13C NMR (150 MHz, DMSO-d6, 13C−31P
coupling) δ 173.1, 149.8, 149.4, 140.2, 136.5, 134.9, 127.3, 125.9,
125.1, 53.8, 53.8, 51.2, 34.0, 32.6, 26.1.
1
compound as a colorless liquid (99 mg, 0.27 mmol, 99%). H NMR
(E)-Diethyl (2-(2,3-Dimethoxyquinoxalin-6-yl)vinyl)phosphonate
(28a). Pd(OAc)2 (42 mg, 0.18 mmol, 5 mol %), P(o-tol)3 (113 mg,
0.37 mmol, 10 mol %) and 6-bromo-2,3-dimethoxyquinoxaline 6 (1.00
g, 3.7 mmol, 1.0 equiv) were dissolved in DMF (10 mL), and the vial
purged with argon. Then NEt3 (1.41 mL, 10.2 mmol) and diethyl
vinylphosphonate (1.05 mL, 6.83 mmol, 1.8 equiv) were added under
argon. The reaction mixture was stirred at 95 °C for 7 h, then cooled
to room temperature. H2O (20 mL) was added, and the solution
extracted with EtOAc (6 × 20 mL). The combined organic phases
were washed with water (50 mL), brine (50 mL), dried over MgSO4,
filtered, and then concentrated under reduced pressure. The crude was
distilled on a bulb-to-bulb distillation apparatus (80 °C, 0.2 mbar) to
remove excess of diethyl vinylphosphonate and then purified by
column chromatography (EtOAc, 100%) to afford the title compound
(400 MHz, DMSO-d6) δ 7.68 (d, J = 8.33 Hz, 1H), 7.57 (s, 1H), 7.39
(dd, J = 1.73 Hz, 8,37 Hz, 1H), 4.11−3.89 (m, 10H), 2.82 (t, J = 7.30
Hz, 2H), 1.85 (dt, J = 8.51 Hz, 15.68 Hz, 2H), 1.78−1.63 (m, 2H),
1.21 (t, J = 7.04 Hz, 6H). 13C NMR (150 MHz, DMSO-d6, 13C−31P
coupling) δ 149.8, 149.4, 140.1, 136.5, 134.9, 127.6, 125.9, 125.2, 60.8,
60.8, 53.8, 53.8, 35.1, 35.0, 24.4, 23.9, 23.5, 16.3, 16.2.
2,3-Dimethoxyquinoxaline-6-carbaldehyde (30). To a solution of
2,3-dimethoxy-6-vinylquinoxaline 7 (500 mg, 2.6 mmol, 1 equiv) in
1,4-dioxane (100 mL) was added H2O (37,5 mL) followed by OsO4
(440 μL, 69.1 μmol, 0.03 equiv, 4 wt % in water). The reaction
mixture was stirred for 0.5 h at room temperature (black solution).
NaIO4 (147 mg, 0.69 mmol, 0.3 equiv) was added, and the reaction
mixture was stirred for 24 h at rt. EtOAc (200 mL) was added into the
reaction followed by H2O (100 mL). The organic phase was washed
with sat. Na2S2O3 (100 mL), dried over MgSO4, filtered, and
evaporated under reduced pressure. The crude was dissolved in DCM
(22 mL), and PhI(OAc)2 (764 mg, 1.1 equiv) was portion wise added
to the reaction mixture which was stirred at room temperature for 4 h
and then evaporated until dryness. The crude product was purified by
flash chromatography on silica gel [EtOAc/heptanes (1:1)] to give the
1
as a white powder (910 mg, 2.7 mmol, 72%). H NMR (600 MHz,
DMSO-d6) δ 8.04 (s, 1H), 7.90 (dd, J = 1.72 Hz, 8.53 Hz, 1H), 7.75
(d, J = 8.48 Hz, 1H), 7.53 (dd, J = 17.56 Hz, 22.61 Hz, 1H), 6.75 (t, J
= 17.57 Hz, 1H), 4.06 (s, 3H), 4.05 (s, 3H), 4.04 (q, J = 7.47 Hz, 4H),
1.27 (t, J = 7.04 Hz, 3H). 13C NMR (150 MHz, DMSO-d6, 13C−31P
coupling) δ 150.4, 150.3, 146.8, 146.8, 137.8, 136.6, 133.3, 133.2,
126.5, 126.3, 125.5, 116.3, 115.0, 61.3, 61.2, 54.1, 54.0, 16.2, 16.2; mp
=119.4−120.2 °C; rf = 0.37 (EtOAc).
1
title compound as a white solid (263 mg, 1.39 mmol, 60%). H NMR
(E)-Diethyl (3-(2,3-Dimethoxyquinoxalin-6-yl)allyl)phosphonate
(28b). Pd(OAc)2 (42 mg, 0.18 mmol, 5 mol %), P(o-tol)3 (113 mg,
0.37 mmol, 10 mol %), and 6-bromo-2,3-dimethoxyquinoxaline 6
(1.00 g, 3.7 mmol, 1.0 equiv) were dissolved in DMF (4.6 mL) and the
vial was purged with argon. Then NEt3 (774 μL, 5.6 mmol) and
diethyl allylphosphonate (704 μL, 4.09 mmol, 1.1 equiv) were added
and the vessel was purged with argon again. The reaction mixture was
stirred at 95 °C for 24 h and then cooled to room temperature. H2O
(20 mL) was added, and the solution mixture extracted with EtOAc (3
× 30 mL). The combined organic phases were washed with water (50
mL), brine (50 mL), dried over MgSO4, filtered, and concentrated
under reduced pressure. The crude product was distilled on a bulb-to-
bulb distillation apparatus (0.2 mbar, 80 °C, 20 min) to remove the
excess of the diethyl allylphosphonate. Purification by column
chromatography (EtOAc 100%) afforded the title compound as
yellow oil (817 mg, 2.2 mmol, 60%). 1H NMR (400 MHz, DMSO-d6)
δ 7.74−7.63 (m, 3H), 6.73 (dd, J = 5.02 Hz, 1H), 6.30 (td, J = 7.42,
15.08 Hz, 1H), 4.11−4.00 (m, 10H), 2.87 (dd, J = 7.58 Hz, 22.12 Hz,
2H), 1.25 (t, J = 7.01 Hz, 6H). 13C NMR (150 MHz, DMSO-d6,
13C−31P coupling) δ 150.0, 149.6, 136.7, 136.0, 135.3, 135.3, 133.2,
(600 MHz, CDCl3) δ 10.13 (s, 1H), 8.24 (s, 1H), 8.01−7.94 (m, 1H),
7.84 (d, J = 8.53 Hz, 1H), 4.18 (s, 3H), 4.17 (s, 3H); 13C NMR (150
MHz, DMSO-d6, C−P coupling) δ 155.6, 155.6, 139.6, 139.5, 136.1,
134.9, 130.0, 129.9, 129.5, 129.4, 129.3, 129.3, 128.8, 128.7, 126.7,
125.9, 122.0, 116.3, 113.4, 66.8; mp =380 °C (dec.); rf = 0.21
[EtOAc/heptanes (1:1)].
Ethyl 3-(((2,3-dimethoxyquinoxalin-6-yl)methyl)amino)-
propanoate (31). To a solution of 2,3-dimethoxyquinoxaline-6-
carbaldehyde 30 (50 mg, 0.23 mmol, 1 equiv) in MeOH (1 mL)
was added 3-amino propionic acid ethyl ester hydrochloride (53 mg,
0.35 mmol, 1.5 equiv) followed by portion wise addition of NaBH3CN
(22 mg, 0.35 mmol, 1.5 equiv) and then dropwise addition AcOH (23,
6 μL, 0.41 mmol, 1.8 equiv). The reaction mixture was stirred at room
temperature overnight, and then evaporated until dryness. DCM (3
mL) was added followed by a freshly prepared solution of NaHCO3 (3
mL). The phases were separated, and the water phase was extracted
with DCM (3 × 10 mL). The combined organic phases were dried
over MgSO4, filtered, and evaporated under reduced pressure. Crude
product was purified by flash chromatography on silica gel using pure
ethyl acetate with 1% of NEt3 as eluent to afford the title product as a
colorless oil (37 mg, 0.11 mmol, 50%). 1H NMR (400 MHz, CDCl3) δ
7.71 (m, 2H), 7.45 (dd, J = 8.3, 1.8 Hz, 1H), 4.21−4.08 (m, 8H), 3.94
(s, 2H), 2.92 (t, J = 6.4 Hz, 2H), 2.53 (t, J = 6.4 Hz, 2H), 1.24 (t, J =
7.1 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 172.8, 150.1, 149.9,
133.1, 126.3, 124.3, 123.5, 123.4, 120.7, 120.6, 61.3, 61.3, 53.9, 53.9,
30.4, 29.5, 16.3, 16.2; rf = 0.49 [EtOAc/EtOH (3:1)].
Diethyl (2-(2,3-Dimethoxyquinoxalin-6-yl)ethyl)phosphonate
(29a). In a vial, (E)-diethyl(2-(2,3-dimethoxyquinoxalin-6-yl)vinyl)-
P
DOI: 10.1021/acschemneuro.7b00243
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX

ACS Chemical Neuroscience
Research Article
139.1, 137.2, 136.3, 127.0, 126.4, 125.4, 60.5, 54.2, 53.6, 44.1, 34.9,
14.3.
3-Chloro-5-(2,3-dimethoxyquinoxalin-6-yl)benzoic Acid (32f).
Reaction performed on a 0.372 mmol scale. 6-Bromo-2,3-dimethox-
yquinoxaline (6) (100 mg, 0.372 mmol, 1.0 equiv), 3-borono-5-
chlorobenzoic acid (97 mg, 0.484 mmol, 1.3 equiv), Pd(PPh3)4 (35
mg, 0.030 mmol, 0.08 equiv), and cesium carbonate (485 mg, 1.488
mmol, 4.0 equiv) were added into a flame-dried two-neck round-
bottom flask. The flask was evacuated and filled back with argon (× 3),
then dry degassed DMF (3.4 mL) was added followed by degassed
H2O (0.16 mL), and the reaction mixture heated at 90 °C for 3h. The
solution was cooled to rt and filtered with Celite. The crude product
was purified by flash chromatograph on silica gel (EtOAc/heptane/
AcOH 1:1:0.01) to give the title compound as a white solid, which was
used in the next step without further purification. Rf 0.29 (EtOAc/
heptane/AcOH 1:4:0.05). 1H NMR (400 MHz, DMSO-d6) δ: 8.23 (t,
J = 1.6 Hz, 1H), 8.17 (t, J = 1.9 Hz, 1H), 8.09 (d, J = 2.1 Hz, 1H),
7.95−7.90 (m, 2H), 7.85 (d, J = 8.5 Hz, 1H), 4.08 (d, J = 2.1 Hz, 6H).
Diethyl 5-(2,3-Dimethoxyquinoxalin-6-yl)isophthalate (32h) and
3-(2,3-Dimethoxyquinoxalin-6-yl)-5-(ethoxycarbonyl)benzoic Acid
(32g). 6-Bromo-2,3-dimethoxyquinoxaline (6) (150 mg, 0.557
mmol, 1.0 equiv), (3,5-bis(ethoxycarbonyl)phenyl) boronic acid
(164 mg, 0.724 mmol, 1.3 equiv), Pd(PPh3)4 (52 mg, 0.045 mmol,
0.08 equiv), and cesium carbonate (726 mg, 1.23 mmol, 4.0 equiv)
were added into a flame-dried two-neck round-bottom flask. The flask
was evacuated and filled back with argon (×3), then dry degassed
DMF (5.0 mL) was added followed by degassed H2O (0.25 mL), and
the reaction mixture heated at 90 °C for 24 h, and 48h at rt. The
solution was cooled to rt and H2O (25 mL) was added and the
aqueous layer extracted with EtOAc (25 mL).The aqueous layer was
adjusted the pH to 4−5 with 2 M HCl to give the product 32ag as a
brown precipitate, which was collected by filtration and used in the
next step without further purification. The EtOAc layer concentration
on rotorvap and purified by flash chromatograph on silica gel (EtOAc/
heptane 1:10 to 1:4) to give 32h as a white solid (55 mg, 0.134 mmol,
24%); Rf 0.42 (EtOAc: heptane 1:4). 1H NMR (400 MHz, DMSO-d6)
δ: 8.52 (d, J = 1.6 Hz, 2H), 8.49 (d, J = 1.6 Hz, 1H), 8.07 (d, J = 2.0
Hz, 1H), 7.93 (dd, J = 8.5, 2.1 Hz, 1H), 7.89 (d, J = 8.5 Hz, 1H), 4.42
(q, J = 7.1 Hz, 4H), 4.09 (d, J = 3.0 Hz, 6H), 1.39 (t, J = 7.1 Hz, 6H).
1H NMR (400 MHz, DMSO-d6) δ: 8.49−8.44 (m, 3H), 8.01 (d, J =
General Procedure for the Synthesis of Compounds 32a−w
(unless otherwise noted). 6-Bromo-2,3-dimethoxyquinoxaline 6
(1.0 equiv), the corresponding boronic acid (1.3 equiv), Pd(PPh3)4 (8
mol %), and cesium carbonate (4.0 equiv) were added into a flame-
dried two-neck round-bottom flask. The flask was evacuated and filled
back with argon thrice, then dry degassed DMF (5 mL) was added
followed by degassed H2O (0.25 mL), and the reaction mixture heated
at 90 °C for 2 h. The solution was cooled to rt and H2O (25 mL) was
added and the aqueous layer extracted with EtOAc (25 mL).The
organic layer was washed with H2O (3 × 25 mL), brine (25 mL) and
dried over MgSO4. The crude product was purified by flash
chromatograph on silica gel (EtOAc/heptane) to afford the title
compound.
2,3-Dimethoxy-6-phenylquinoxaline (32a). Reaction performed
on a 0.372 mmol scale. The purified product was isolated as a white
1
solid (58 mg, 0.219 mmol, 59%); Rf 0.42 (EtOAc/heptane, 1:4). H
NMR (400 MHz, DMSO-d6) δ: 8.00 (d, J = 1.9 Hz, 1H), 7.88−7.80
(m, 4H), 7.50 (t, J = 7.6 Hz, 2H), 7.41 (d, J = 7.3 Hz, 1H), 4.07 (d, J =
3.2 Hz, 6H). 13C NMR (101 MHz, DMSO-d6) δ: 150.7, 150.4, 139.8,
139.1, 137.39, 136.5, 129.5, 128.2, 127.4, 127.1, 126.1, 124.0, 54.5. LC-
MS (m/z) calcd for C16H14N2O2 [M + H]+, 266.30, found 267.1.
5-(2,3-Dimethoxyquinoxalin-6-yl)-2-methoxybenzoic Acid (32b).
Reaction performed on a 0.557 mmol scale. The title compound was
isolated as a white solid (136 mg, 0.401 mmol, 72%); Rf 0.23 (EtOAc/
1
heptane/AcOH 1:1:0.05). H NMR (400 MHz, DMSO-d6) δ: 12.75
(s, 1H), 8.03 (d, J = 2.5 Hz, 1H), 8.00−7.96 (m, 2H), 7.87−7.80 (m,
2H), 7.26 (d, J = 8.7 Hz, 1H), 4.07 (d, J = 3.9 Hz, 6H), 3.89 (s, 3H).
13C NMR (101 MHz, DMSO-d6) δ: 170.9, 167.6, 158.2, 150.7, 150.3,
137.9, 137.4, 136.2, 131.6, 129.3, 127.1, 125.7, 123.4, 113.7, 56.4, 54.5.
LC-MS (m/z) calcd for C18H16N2O5 [M + H]+, [M − H]−, 340.34,
found 341.0, 339.2.
5-(2,3-Dimethoxyquinoxalin-6-yl)-2-fluorobenzoic Acid (32c).
Reaction performed on a 0.557 mmol scale. The crude product was
purified by flash chromatograph on silica gel (EtOAc/heptane/AcOH
1:1:0.05) to give the title compound as a white solid (152 mg, 0.401
mmol, 72%); Rf 0.49 (EtOAc/heptane/AcOH 1:1:0.05). 1H NMR
(400 MHz, DMSO-d6) δ: 8.19 (dd, J = 6.9, 2.6 Hz, 1H), 8.06 (ddd, J =
8.6, 4.5, 2.6 Hz, 1H), 8.00 (d, J = 1.9 Hz, 1H), 7.88−7.81 (m, 2H),
7.43 (dd, J = 10.6, 8.6 Hz, 1H), 4.07 (d, J = 2.5 Hz, 6H). 13C NMR
(101 MHz, DMSO-d6) δ: 165.4, 165.4, 162.5, 159.9, 150.7, 150.5,
137.4, 137.1, 136.6, 136.0, 136.0, 133.2, 133.1, 130.4, 127.2, 125.9,
124.1, 118.2, 118.0, 54.5, 54.5.
2.0 Hz, 1H), 7.89 (dd, J = 8.5, 2.1 Hz, 1H), 7.84 (d, J = 8.5 Hz, 1H),
4.40 (q, J = 7.1 Hz, 2H), 4.07 (d, J = 2.5 Hz, 6H), 1.38 (t, J = 7.1 Hz,
3H). 13C NMR (101 MHz, DMSO-d6) δ: 166.7, 165.4, 150.8, 150.7,
140.8, 137.4, 137.0, 136.9, 132.7, 132.2, 131.7, 131.6, 129.1, 127.4,
126.0, 124.5, 61.8, 54.5, 54.5, 14.6.
2,3-Dimethoxy-6-(p-tolyl)quinoxaline (32i). Reaction performed
on a 0.557 mmol scale. The title compound was isolated as a white
3-(2,3-Dimethoxyquinoxalin-6-yl)-5-fluorobenzoic Acid (32d).
Reaction performed on a 0.372 mmol scale. 6-Bromo-2,3-dimethox-
yquinoxaline (6) (100 mg, 0.372 mmol, 1.0 equiv), 3-borono-5-
fluorobenzoic acid (89 mg, 0.484 mmol, 1.3 equiv), Pd(PPh3)4 (35
mg, 0.030 mmol, 0.08 equiv), and cesium carbonate (485 mg, 1.488
mmol, 4.0 equiv) were added into a flame-dried two-neck round-
bottom flask. The flask was evacuated and filled back with argon (×3),
then dry degassed DMF (3.4 mL) was added followed by degassed
H2O (0.16 mL), and the reaction mixture heated at 90 °C for 4 h. The
solution was cooled to rt and filtered with Celite. The crude product
was purified by flash chromatograph on silica gel (EtOAc/heptane/
AcOH 1:1:0.01) to give the title compound as a white solid, which was
used in the next step without further purifications. Rf 0.26 (EtOAc/
heptane/AcOH 1:4:0.05). 1H NMR (400 MHz, DMSO-d6) δ: 8.15 (s,
1H), 8.10 (s, 1H), 8.00 (dd, J = 10.1, 2.2 Hz, 1H), 7.96 (s, 1H), 7.95−
7.91 (m, 1H), 7.86 (d, J = 8.5 Hz, 1H), 4.09 (d, J = 2.4 Hz, 6H).
3-(2,3-Dimethoxyquinoxalin-6-yl)-2,6-difluorobenzoic Acid (32e).
Reaction performed on a 0.372 mmol scale. After acidification of the
aqueous layer with 2 M HCl (pH = 4), the title compound
precipitated out as a brown solid which was collected by filtration (98
1
solid (73 mg, 0.262 mmol, 47%); Rf 0.42 (EtOAc/heptane, 1:4). H
NMR (400 MHz, DMSO-d6) δ: 7.97 (d, J = 1.9 Hz, 1H), 7.86−7.79
(m, 2H), 7.70 (d, J = 8.1 Hz, 2H), 7.31 (d, J = 8.0 Hz, 2H), 4.06 (d, J
= 3.3 Hz, 6H), 2.36 (s, 3H). 13C NMR (101 MHz, DMSO-d6) δ:
150.6, 150.3, 139.0, 137.5, 137.4, 136.9, 136.3, 130.1, 127.2, 127.0,
125.9, 123.6, 54.5, 21.1.
2,3-Dimethoxy-6-(4-methoxyphenyl)quinoxaline (32j). Reaction
performed on a 0.557 mmol scale. The title compound was isolated as
a white solid (86 mg, 0.289 mmol, 52%); Rf 0.33 (EtOAc/heptane,
1
1:4). H NMR (600 MHz, DMSO-d6) δ: 7.94 (d, J = 2.0 Hz, 1H),
7.83−7.81 (m, 1H), 7.79 (d, J = 8.5 Hz, 1H), 7.77−7.74 (m, 2H), 7.06
(d, J = 8.7 Hz, 2H), 4.06 (d, J = 6.2 Hz, 6H), 3.82 (s, 3H). 13C NMR
(101 MHz, DMSO-d6) δ: 159.6, 150.6, 150.1, 138.8, 137.4, 136.0,
132.1, 128.5, 126.9, 125.7, 123.2, 115.0, 55.7, 54.4, 54.4. LC-MS (m/z)
calcd for C17H16N2O3 [M + H]+, 296.33, found 297.1.
6-(4-Fluorophenyl)-2,3-dimethoxyquinoxaline (32k). Reaction
performed on a 0.557 mmol scale. The title compound was isolated
as a white solid (64 mg, 0.223 mmol, 40%); Rf 0.42 (EtOAc/heptane,
1
1
1:4). H NMR (400 MHz, DMSO-d6) δ: 7.99 (d, J = 1.2 Hz, 1H),
mg, 0.283 mmol, 76%). H NMR (400 MHz, DMSO-d6) δ: 14.08 (s,
7.89−7.80 (m, 4H), 7.32 (t, J = 8.8 Hz, 2H), 4.07 (d, J = 2.7 Hz, 6H).
13C NMR (101 MHz, DMSO-d6) δ: 161.3, 150.7, 150.4, 138.0, 137.4,
136.4, 136.2, 136.2, 129.5, 129.4, 127.1, 126.0, 123.9, 116.4, 116.2,
54.5. LC-MS (m/z) calcd for C16H13FN2O2 [M + H]+, 284.29, found
285.1.
1H), 7.90−7.86 (m, 1H), 7.86−7.79 (m, 2H), 7.69 (dt, J = 8.6, 1.8 Hz,
1H), 7.34 (t, J = 8.9 Hz, 1H), 4.07 (d, J = 2.6 Hz, 6H). 13C NMR (101
MHz, DMSO-d6) δ: 162.6, 150.8, 137.0, 136.7, 133.7, 133.6, 132.5,
129.2, 127.9, 127.8, 126.8, 126.7, 125.2, 125.1, 125.1, 125.0, 113.2,
113.2, 113.0, 112.9, 54.6, 54.5.
Q
DOI: 10.1021/acschemneuro.7b00243
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX

ACS Chemical Neuroscience
Research Article
6-(4-Chlorophenyl)-2,3-dimethoxyquinoxaline (32l). Reaction
performed on a 0.372 mmol scale. The title compound was isolated
as a white solid (73 mg, 0.242 mmol, 65%); Rf 0.41 (EtOAc/heptane,
1H), 8.14 (d, J = 2.1 Hz, 1H), 7.99−7.93 (m, 2H), 7.86−7.76 (m,
3H), 4.08 (d, J = 1.7 Hz, 6H). 13C NMR (101 MHz, DMSO-d6) δ:
163.4, 150.8, 150.8, 145.9, 137.4, 137.3, 136.4, 136.4, 133.0, 133.0,
127.2, 126.0, 124.8, 123.2, 123.1, 115.7, 115.4, 54.6, 54.6.
1
1:4). H NMR (400 MHz, DMSO-d6) δ: 8.00 (d, J = 2.2 Hz, 1H),
7.89−7.78 (m, 4H), 7.54 (d, J = 8.5 Hz, 2H), 4.06 (d, J = 2.3 Hz, 6H).
13C NMR (101 MHz, DMSO-d6) δ: 150.7, 150.5, 138.6, 137.7, 137.4,
136.7, 133.0, 129.4, 129.2, 127.1, 125.9, 124.1, 54.5.
4-(2,3-Dimethoxyquinoxalin-6-yl)-2,6-difluorobenzoic Acid (32s).
Reaction performed on a 0.372 mmol scale. The crude product was
purified by flash chromatograph on silica gel (EtOAc/heptane/AcOH
1:5:0.005 to 1:2:0.005) to give the title compound as a white solid,
which was used in the next step without further purification. 1H NMR
(400 MHz, DMSO-d6) δ: 13.88 (s, 1H), 8.18 (d, J = 2.1 Hz, 1H), 7.97
(dd, J = 8.6, 2.2 Hz, 1H), 7.84 (d, J = 8.6 Hz, 1H), 7.74 (d, J = 9.6 Hz,
2H), 4.08 (d, J = 1.2 Hz, 6H). LC-MS (m/z) calcd for C17H12F2N2O4
[M + H]+, [M − H]−, 346.29, found 347.0, 345.0.
4-(2,3-Dimethoxyquinoxalin-6-yl)-2-hydroxybenzoic Acid (32at).
Reaction performed on a 0.372 mmol scale. The crude product was
purified by flash chromatograph on silica gel (EtOAc/heptane/AcOH
1:1:0.05) to give the title compound as a white solid (49.5 mg, 0.152
mmol, 41%); Rf 0.12 (EtOAc/heptane/AcOH 1:4:0.05). 1H NMR
(600 MHz, DMSO-d6) δ: 8.01 (d, J = 2.1 Hz, 1H), 7.90−7.84 (m,
2H), 7.80 (d, J = 8.5 Hz, 1H), 7.38−7.32 (m, 2H), 4.06 (d, J = 3.8 Hz,
6H). 13C NMR (151 MHz, DMSO-d6) δ: 171.9, 163.7, 150.6, 150.3,
142.8, 139.3, 137.3, 136.5, 131.1, 126.9, 126.1, 123.9, 120.2, 115.2,
114.5, 54.4.
2,3-Dimethoxy-6-(4-(trifluoromethyl)phenyl)quinoxaline (32m).
Reaction performed on a 0.557 mmol scale. The title compound
was isolated as a white solid (124 mg, 0.373 mmol, 67%); Rf 0.37
1
(EtOAc/heptane, 1:4). H NMR (400 MHz, DMSO-d6) δ: 8.11 (d, J
= 2.1 Hz, 1H), 8.06 (d, J = 8.1 Hz, 2H), 7.93 (dd, J = 8.5, 2.1 Hz, 1H),
7.86 (dd, J = 9.5, 8.2 Hz, 3H), 4.08 (d, J = 1.8 Hz, 6H). 13C NMR
(101 MHz, DMSO-d6) δ: 150.8, 150.7, 137.4, 137.3, 137.1, 128.2,
127.3, 126.3, 126.3, 126.2, 126.1, 124.7, 54.6, 54.6.
4-(2,3-Dimethoxyquinoxalin-6-yl)phenol (32n). Reaction per-
formed on a 0.557 mmol scale. The title compound was isolated as
a white solid (106 mg, 0.379 mmol, 68%); Rf 0.16 (EtOAc/heptane,
1:4). 1H NMR (400 MHz, DMSO-d6) δ: 9.60 (s, 1H), 7.90 (d, J = 1.8
Hz, 1H), 7.78 (d, J = 2.9 Hz, 2H), 7.64 (d, J = 8.6 Hz, 2H), 6.88 (d, J
= 8.6 Hz, 2H), 4.06 (d, J = 4.4 Hz, 6H). 13C NMR (101 MHz, DMSO-
d6) δ: 157.8, 150.5, 150.0, 139.2, 137.4, 135.8, 130.4, 128.5, 126.9,
125.6, 122.8, 116.3, 54.4. LC-MS (m/z) calcd for C16H14N2O3 [M +
H]+, 282.30, found 283.0.
3-Chloro-4-(2,3-dimethoxyquinoxalin-6-yl)benzoic Acid (32au).
Reaction performed on a 0.734 mmol scale. After acidification of the
aqueous layer with 2 M HCl (pH = 4), the title compound
precipitated out as a brown solid which was collected by filtration (156
mg, 0.447 mmol, 61%); Rf 0.26 (EtOAc/heptane/AcOH 1:1:0.005).
1H NMR (400 MHz, DMSO-d6) δ: 8.06 (d, J = 1.6 Hz, 1H), 7.98 (dd,
J = 8.0, 1.7 Hz, 1H), 7.87−7.81 (m, 2H), 7.69−7.61 (m, 2H), 4.07 (d,
J = 6.2 Hz, 6H). 13C NMR (101 MHz, DMSO-d6) δ: 166.4, 150.9,
150.8, 143.6, 136.8, 136.7, 136.7, 132.6, 132.2, 132.1, 130.9, 128.7,
128.2, 127.0, 126.5, 54.6, 54.5.
Methyl 4-(2,3-Dimethoxyquinoxalin-6-yl)-3-fluorobenzoate (32o)
and 4-(2,3-Dimethoxyquinoxalin-6-yl)-3-fluorobenzoic Acid (32v).
6-Bromo-2,3-dimethoxyquinoxaline 6 (150 mg, 0.557 mmol, 1.0
equiv), (2-fluoro-4-(methoxycarbonyl) phenyl) boronic acid (143 mg,
0.724 mmol, 1.3 equiv), Pd(PPh3)4 (52 mg, 0.045 mmol, 0.08 equiv),
and cesium carbonate (726 mg, 2.23 mmol, 4.0 equiv) were added into
a flame-dried two-neck round-bottom flask. The flask was evacuated
and filled back with argon (× 3), then dry degassed DMF (5 mL) was
added followed by degassed H2O (0.25 mL), and the reaction mixture
heated at 90 °C. After 24 h, there are still lots of starting material. The
solution was cooled to rt, and H2O (25 mL) was added and the
aqueous layer extracted with EtOAc (25 mL). The aqueous layer was
adjusted the pH to 4−5 with 2 M HCl to give the product 32v as a
brown precipitate (25 mg, 0.076 mmol, 22%), which was collected by
filtration and used in the next step without further purification. The
EtOAc layer was purified by flash chromatograph on silica gel
(EtOAc/heptane 1:8 to 1:4) to give the title compound 32o as a white
4-(2,3-Dimethoxyquinoxalin-6-yl)-2-methoxybenzoic Acid (32w).
6-Bromo-2,3-dimethoxyquinoxaline (6) (100 mg, 0.372 mmol, 1.0
equiv), (3-methoxy-4-(methoxycarbonyl)phenyl)boronic acid (102
mg, 0.484 mmol, 1.3 equiv), Pd(PPh3)4 (35 mg, 0.030 mmol, 0.08
equiv), and cesium carbonate (485 mg, 1.488 mmol, 4.0 equiv) were
added into a flame-dried two-neck round-bottom flask. The flask was
evacuated and filled back with argon (× 3), then dry degassed DMF
(3.4 mL) was added followed by degassed H2O (0.16 mL), and the
reaction mixture heated at 90 °C for 24 h. The solution was cooled to
rt and H2O (25 mL) was added and the aqueous layer extracted with
EtOAc (25 mL). The aqueous layer was adjusted to pH 4−5 with 2 M
HCl to give the product 32w as a brown precipitate, which was
collected by filtration (16 mg, 13%).The EtOAc layer was
concentrated and purified on flash chromatography on silica gel
(EtOAc/heptane 1:8 to 1:4) to give the compound 32p as a white
1
solid (16 mg, 0.047 mmol, 13%); Rf 0.26 (EtOAc/heptane, 1:4). H
NMR (400 MHz, DMSO-d6) δ: 7.99 (t, J = 1.8 Hz, 1H), 7.93−7.88
(m, 2H), 7.85 (dd, J = 13.4, 1.9 Hz, 2H), 7.78 (dt, J = 8.5, 1.9 Hz, 1H),
4.08 (d, J = 3.2 Hz, 6H), 3.91 (s, 3H). LC-MS (m/z) calcd for
1
C18H15FN2O2 [M + H]+, 342.33, found 343.0. H NMR (400 MHz,
DMSO-d6) δ: 13.32 (s, 1H), 7.97 (t, J = 1.8 Hz, 1H), 7.88 (d, J = 1.6
Hz, 1H), 7.85 (d, J = 7.4 Hz, 1H), 7.82 (d, J = 2.0 Hz, 1H), 7.81−7.75
(m, 2H), 4.08 (d, J = 2.8 Hz, 6H).
Methyl 4-(2,3-Dimethoxyquinoxalin-6-yl)-2-methoxybenzoate
(32p). Reaction performed on a 0.372 mmol scale. The title
compound was isolated as a white solid (83 mg, 0.234 mmol, 63%);
1
solid (63 mg, 46%). H NMR (400 MHz, DMSO-d6) δ: 8.10 (d, J =
2.1 Hz, 1H), 7.93 (dd, J = 8.6, 2.1 Hz, 1H), 7.83 (d, J = 8.5 Hz, 1H),
7.76 (d, J = 7.9 Hz, 1H), 7.47 (d, J = 1.6 Hz, 1H), 7.42 (dd, J = 8.0, 1.6
Hz, 1H), 4.07 (d, J = 3.1 Hz, 6H), 3.97 (s, 3H).
Modeling. All in silico work was carried out using MOE version
2016.08.02 (Chemical Computing Group). The receptor protein was
prepared using the function “Protonate 3D”. Docking was performed
using standard setup with flexible side chains and exclusive solvent
molecules.
1
Rf 0.11 (EtOAc/heptane 1:4). H NMR (400 MHz, DMSO-d6) δ:
8.13 (d, J = 2.1 Hz, 1H), 7.95 (dd, J = 8.6, 2.1 Hz, 1H), 7.85 (d, J = 8.5
Hz, 1H), 7.77 (d, J = 8.0 Hz, 1H), 7.51 (d, J = 1.6 Hz, 1H), 7.45 (dd, J
= 8.1, 1.6 Hz, 1H), 4.08 (d, J = 2.6 Hz, 6H), 3.98 (s, 3H), 3.82 (s, 3H).
13C NMR (101 MHz, DMSO-d6) δ: 166.4, 159.3, 150.7, 150.6, 144.9,
137.9, 137.3, 137.1, 132.0, 127.1, 126.3, 124.6, 119.3, 119.1, 111.5,
56.5, 54.5, 52.3.
Radioligand Binding. Ligand affinities at native AMPA, KA, and
NMDA receptors (rat brain synaptosomes) were determined using the
radioligands [3H]AMPA, [3H]KA, and [3H]CGP-39653, respectively,
as previously described.12 Ligand affinities at recombinant homomeric
rat GluA2 were determined using [3H]AMPA. Ligand affinities at
recombinant homomeric rat GluK2 and GluK3 were determined using
[3H]KA as the radioligand as previously detailed.13 Ligand affinities at
recombinant homomeric rat GluK1 were determined using the new
radioligand [3H]-NF608 as previously described.14 Data were analyzed
using GraphPad Prism 7 (GraphPad Software, San Diego, CA) to
determine ligand IC50 and Ki values.
2-Chloro-4-(2,3-dimethoxyquinoxalin-6-yl)benzoic Acid (32q).
Reaction performed on a 0.372 mmol scale. The crude product was
purified by flash chromatograph on silica gel (EtOAc/heptane: AcOH
1:1:0.01) to give the title compound as a white solid, which was used
without further purification in the next step. Rf 0.41 (EtOAc/heptane/
AcOH 1:1:0.01).
4-(2,3-Dimethoxyquinoxalin-6-yl)-2-fluorobenzoic Acid (32r).
Reaction performed on a 0.372 mmol scale. The crude product was
purified by flash chromatograph on silica gel (EtOAc/heptane/AcOH
1:5:0.005 to 1:2:0.005) to give the title compound as a white solid (65
1
mg, 0.197 mmol, 53%). H NMR (400 MHz, DMSO-d6) δ: 13.23 (s,
R
DOI: 10.1021/acschemneuro.7b00243
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX

ACS Chemical Neuroscience
Research Article
analogues and structure-activity relationship studies at ionotropic
glutamate receptors and excitatory amino acid transporters. J. Med.
Chem. 56, 1614−28.
(13) Sagot, E., Pickering, D. S., Pu, X., Umberti, M., Stensbøl, T. B.,
Nielsen, B., Chapelet, M., Bolte, J., Gefflaut, T., and Bunch, L. (2008)
Chemo-enzymatic synthesis of a series of 2,4-syn-functionalized (S)-
glutamate analogues: new insight into the structure-activity relation of
ionotropic glutamate receptor subtypes 5, 6, and 7. J. Med. Chem. 51,
4093−103.
(14) Alcaide, A., Marconi, L., Marek, A., Haym, I., Nielsen, B.,
Møllerud, S., Jensen, M., Conti, P., Pickering, D. S., and Bunch, L.
(2016) Synthesis and pharmacological characterization of the selective
GluK1 radioligand (S)-2-amino-3-(6-[ 3 H]-2,4-dioxo-3,4-
dihydrothieno[3,2-d]pyrimidin-1(2H)-yl)propanoic acid ([ 3 H]-
NF608). MedChemComm 7, 2136−2144.
AUTHOR INFORMATION
Corresponding Author
*E-mail: lebu@sund.ku.dk.
ORCID
Lennart Bunch: 0000-0002-0180-4639
Author Contributions
C.S.D., design and synthesis of analogues. D.R., design and
synthesis of analogues. N.L., design and synthesis of analogues.
B.N., pharmacological evaluation of analogues. D.S.P.,
pharmacological evaluation of analogues. L.B., design and
synthesis of analogues, in silico modeling
■
Funding
We would like to thank H. Lundbeck A/S, the Lundbeck
Foundation, Chinese Scholarship Council for financial support.
Notes
The authors declare no competing financial interest.
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DOI: 10.1021/acschemneuro.7b00243
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX