Di-aryl Sulfonamide Motif Adds π-Stacking Bulk in Negative Allosteric Modulators of the NMDA Receptor

Article abstract of DOI:10.1021/acsmedchemlett.8b00395

The N-methyl-d-aspartate receptor plays a critical role in central nervous system processes. Its diverse properties, as well as hypothesized role in neurological disease, render NMDA receptors a target of interest for the development of therapeutically re

Full text of DOI:10.1021/acsmedchemlett.8b00395

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Letter
The Di-Aryl Sulfonamide Motif Adds #-Stacking Bulk in
Negative Allosteric Modulators of the NMDA Receptor
Samantha L. Summer, Steven A. Kell, Zongjian Zhu, Rhonda Moore, Dennis C. Liotta,
Scott J Myers, George W Koszalka, Stephen F. Traynelis, and David S. Menaldino
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.8b00395 • Publication Date (Web): 04 Jan 2019
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ACS Medicinal Chemistry Letters
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The Di-Aryl Sulfonamide Motif Adds π-Stacking Bulk in
Negative Allosteric Modulators of the NMDA Receptor
Samantha L. Summer†, Steven A. Kell†§, Zongjian Zhu§, Rhonda Moore†, Dennis C. Liotta*†, Scott J.
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Myers‡§, George W. Koszalka‡, Stephen F. Traynelis*§, David S. Menaldino*†
†Department of Chemistry, Emory University, Atlanta, GA 30322
§Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322
‡NeurOp Inc., 58 Edgewood Avenue, Atlanta, GA 30303
KEYWORDS NMDA, Glutamate Receptor, Sulfonamide, GluN2C, GluN2D
ABSTRACT: The N-methyl-D-aspartate receptor plays a critical role in central nervous system processes. Its diverse properties, as
well as hypothesized role in neurological disease, render NMDA receptors a target of interest for the development of therapeutically
relevant modulators. A number of subunit-selective modulators have been reported in the literature, one of which is TCN-201, a
GluN2A-selective negative allosteric modulator. Recently, it was determined from a co-crystallization study of TCN-201 with the
NMDA receptor that a unique active pose exists in which the sulfonamide group of TCN-201 incorporates a π-π stacking interaction
between the two adjacent aryl rings that allows it to make important contacts with the protein. This finding led us to investigate
whether this unique structural feature of the di-aryl sulfonamide could be incorporated into other modulators that act on distinct
pockets. To test whether this idea might have more general utility, we added an aryl ring plus the sulfonamide linker modification to
a previously published series of GluN2C- and GluN2D-selective negative allosteric modulators that bind to an entirely different
pocket. Herein, we report data suggesting that this structural modification of the NAB-14 series of modulators was tolerated and, in
some instances, enhanced potency. These results suggest that this motif may be a reliable means for introducing a π-π stacking element
to molecular scaffolds that could improve activity if it allowed access to ligand-protein interactions not accessible from one planar
aromatic group.
The glutamate receptors are ligand-gated, cation-selective
channels expressed throughout the central nervous system and
comprise three classes: AMPA, kainate, and NMDA receptors
(NMDARs).1 The NMDAR plays an important role in nervous
system development, synaptic plasticity,2 learning, and
memory.3 In addition, NMDARs have been implicated in
various neurological disorders such as epilepsy, ischemia, and
neurodegenerative disorders.1,4,5 The NMDAR mediates a slow,
Ca2+ permeable component of excitatory synaptic transmission,
compared to the much faster and briefer synaptic currents
mediated by AMPA receptors. NMDARs are unique in that
activation requires the binding of glutamate and glycine, which
produces an inward current when coincident depolarization of
the cell relieves voltage-dependent Mg2+ block of the channel
pore. The NMDA receptor is a tetrameric assembly of two
different subunits, the glycine-binding GluN1 and glutamate-
binding GluN2 subunits. Four different GluN2 subunits exist,
referred to as GluN2A-D. These distinct subunits endow the
receptor with different response time courses and distinct
pharmacological properties, and can be targeted by different
modulators.1 Like other receptors in its class, each subunit
consists of distinct domains, each with its own function: (a) the
amino terminal domain (ATD), which controls response
properties, such as the open probability for agonist-bound
channel and deactivation time course following rapid removal
of agonists; (b) the agonist binding domain (ABD), which binds
agonists and triggers conformation changes that lead to opening
of the ion channel pore; (c) the trans-membrane domain (TMD),
O
NH2
NH2
H
Cl
H
N
N
O
3
2
1
4
HO
O
N
O
NO2
O
N
N
O
HO
N
N
O
OH
OH
Br
O
5
N
H
7
O
O
6
O
Cl
S
N
O
N
H
O
H
H
NH
N
O
N
F
N
H
O
8
9
N
F
F
N
N
N
F
10
FIGURE 1. Structures of known NMDAR channel blockers and
negative allosteric modulators; memantine (1),
dextromethorphan (2), amantadine (3), ketamine (4) ifenprodil
(5)8,9, DQP-110511 (6), QNZ-4610 (7), NAB-1415 (8), TCN-20113
(9, a GluN2A-selective negative allosteric modulator that acts
by reducing glycine affinity), and EVT-101 (10).16
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ACS Medicinal Chemistry Letters
which forms the pore of the receptor6, and (d) the intracellular
carboxy terminal domain (CTD), which may direct subcellular
localization.
Page 2 of 6
target effects.15 Structural determinants of action are in the M1
transmembrane helix, suggesting that its binding site is likely
distinct from that of TCN-201. The structure-activity
relationship for this series was relatively flat15, leading us to
consider whether introduction of the  interaction might
bring about potency-enhancing ligand-protein interactions
within the pocket that we could not access from planar di- and
tri-aryl systems linked by amide bonds.
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8
Due to the diverse properties of receptors that contain
different GluN2 subunits and the central role that the NMDAR
plays in neurological processes, this receptor is an intriguing
target for the development of subunit-selective modulators that
are therapeutically-relevant. There are multiple examples of
FDA-approved, non-selective NMDAR inhibitors that block
the channel pore of the receptor with similar potencies (see
Figure 1). These include memantine (1), dextromethorphan (2),
amantadine (3), and ketamine (4), each of which has a different
therapeutic use.6,7 Other subunit-specific NMDAR inhibitors
have been previously reported, including ifenprodil (5), a non-
competitive selective inhibitor of GluN1/GluN2B. Ifenprodil
displays over 100-fold selectivity for GluN2B over GluN2A,
GluN2C, and GluN2D.8,9. EVT-101 (10), another example of a
GluN1/GluN2B selective antagonist, was claimed by Evotec in
A
O
O
H
9
H
F
N
F
N
N
H
N
H
N
O
H
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N
O
H
O
Cl
S
O
Cl
O
26
9
a
method-of-use patent for cognitive impairment,
H
B
N
O
S
O
neurodegenerative diseases, pain, depression, attention deficit
hyperactivity disorder, and addiction16. Additionally, DQP-
1105 (6), QNZ-46 (7), and NAB-14 (8) are negative allosteric
modulators (NAMs) that display selectivity for GluN2C- and
GluN2D-containing NMDARs.
O
O
N
H
N
O
23
TCN-201 (9, Figure 1) is a GluN2A-selective NAM
identified by Bettini et al. in 2010.12 A co-crystallization study
of TCN-201 described the binding site and active pose at the
heterodimer interface between the GluN1 and GluN2A agonist
binding domains. The sulfonamide linker endows the structure
with a unique pose in which π-π-stacking between two adjacent
aryl rings is favored in the receptor pocket and allows TCN-201
to make important contacts with amino acid side chains.13,14 The
structure and binding pose of TCN-201 (9) are shown in panel
A of Figure 3. The unique shape of this biologically active pose
led us to hypothesize that it may be helpful to include it in other
planar di- and tri-aromatic compound series that bind at
different sites of the receptor and also display relatively flat
structure-activity relationships. We reasoned that perhaps these
pockets might have space for additional ligand-protein
interactions enabled by  stacking that could not be realized
by substitutions onto planar aromatic systems.
H
N
O
O
O
N
H
N
O
27
C
O
S
H
O
N
O
S
O
O
N
O
H
O
N
O
N
H
H
N
O
N
O
23
18
O
N
O
H
O
NEt2
NP11999
O
2D IC50, 6M
O
N
O
H
N
H
N
O
N
O
H
H
O
O
NEt2
O
NEt2
NP12022
2D IC50, (>100M)
NP12000
FIGURE 3. Conformational search results for TCN-201 (9) and the
di-aryl sulfonamides comparing the shapes adopted when
sulfonamide and amide linkers of two different lengths are used.
(A) The lowest-energy conformer for each TCN-201 (left) and
compound 26 (right), a compound in which the sulfonamide of
TCN-201 has been replaced with an amide. (B) The lowest-energy
conformer for each 23 (upper) and the corresponding analog 27
(lower) in which the sulfonamide is replaced by an amide. (C) All
fifty conformers resulting from the conformational search for
compound 18 containing a single methylene in the sulfonamide
linker (left) and compound 23 containing an ethylene in the
sulfonamide linker (right) are superimposed.
2D IC50, 8M
FIGURE 2. Structures and activities from first-generation
NAB-14 analogs with planar third-ring extensions. Data are for
GluN1/GluN2D (n=6 oocytes).
Recently, we described a novel N-aryl benzamide analog,
represented by NAB-14 (8, Figure 1), a GluN2C/2D-selective
NAM. This compound series displayed over 500-fold
selectivity for GluN2C/2D over GluN2A/2B, and inhibited
GluN1/GluN2C and GluN1/GluN2D with IC50 values of 1-4
µM.15 In addition, this compound series possesses improved
drug-like physicochemical properties, and achieves modest
blood brain barrier penetration in rodents with minimal off-
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Part of the SAR to probe the activity of the NAB-14 structure
The screening results of these compounds on recombinant
NMDA receptors expressed in Xenopus oocytes are shown in
Table 2. Compounds with a methylene linker (n = 1) showed
minimal activity. Compounds with an ethylene linker (n = 2)
and para-substitution showed minimal activity, except in the
case of the pyridyl sulfonamide (21). The most active
compounds in this series are those with an ethylene linker and
meta-substitution (compounds 23-25), which were up to 6-fold
more potent than the phenyl NAB analogue NP11999, which
we used as a reference point. Thus, adding the sulfonamide
linker to the scaffold not only retains activity at GluN1/GluN2C
and GluN1/GluN2D, it enhances potency over the phenyl
analog NP11999. Interestingly, reducing the length of the di-
aryl sulfonamide linker by one methylene unit decreases
activity despite its ability to better assume the favored π-π
stacking motif similar to the TCN series. The differences
between the modelled conformations of these two linker
geometries is shown in panel C of Figure 3, which reveals the
expected increased flexibility of the ethylene linker. Given the
improved potency, we interpret this increased flexibility as
better enabling the stacked rings to fit into the binding pocket
for NAB analogues. This emphasizes that there are likely
unique requirements for the optimal  stacking shape for
different pockets, as would be expected.
1
was focused on the indole, where it was first replaced with a
phenyl ring (NP11999, Figure 2). This modification showed
modest activity in the initial SAR, with an IC50 value of 6 µM
for GluN2C/D-containing NMDARs (Table 1). Further
expansion of the SAR at this position suggested that the indole
side of the NAB series could accommodate larger groups and
additional aryl rings without complete loss of activity,
depending on the substitution pattern connecting the additional
aryl ring (NP12000 and NP12022, Figure 2). We, then, began
to investigate whether replacement of the planar amide linker
connecting the additional aryl ring with a more flexible
sulfonamide linker was tolerated, and, hopefully, improved
upon activity. We reasoned that incorporating a sulfonamide
linker adjoining the additional phenyl ring should lead to a
similar U-shaped π-π stacking motif as in TCN-201, thereby
replacing the indole side of the NAB series with a larger π–π
stacked aromatic configuration. Figure 3 compares the TCN-
201 binding pose (panel A) to one of the modelled low energy
candidates binding poses for a proposed compound (panel B),
which incorporates a sulfonamide linker. Similar to TCN-201,
the proposed sulfonamide moiety endows the scaffold with
enough flexibility to obtain a “U-shape.” When the linker
contains a single methylene group like TCN-201, all modelled
poses contain this orientation of the π–π stacked rings (Fig 3C,
left panel); when the linker contains an ethylene group, most
but not all poses display π–π stacking (Fig 3C, right panel).
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To test whether the enhanced potency of this novel
sulfonamide series compared to the phenyl NAB analogue
NP11999 is due to the U-shaped motif of adjacent aromatic
rings, we reasoned that replacement of the sulfonamide linker
We chose to extend the SAR of this novel di-aryl
sulfonamide analog to include meta substitution to the extended
aryl ring because of the activity displayed in NP12022 (Figure
2), with both methylene or ethylene units included in the
sulfonamide linker. The synthesis of the sulfonamide NAB-
modified series is shown in Scheme 1. The first few steps have
been previously reported.15 Therefore, commercially available
phenol 11 was allowed to react with diethyl carbamoyl chloride
to obtain carbamate 12, which was then saponified to produce
acid 13. Acid 13 was then coupled with the appropriate aniline
intermediate to produce para and meta substituted
intermediates 14 (n = 1, 2), which were Boc-deprotected to get
the free amines 15. Compounds 15 were coupled with 0.5-1.0
equivalents of the appropriate aryl sulfonyl chloride, dependent
upon the amount of observed double addition by-product
formed, to yield final compounds 16-25 containing the desired
di-aryl sulfonamide moiety.
Table 1. Activity of Previous Compounds
I10 µM / IControl (mean ±
SEM, %) a,
IC50 (µM)b
Cmpd #
GluN2C
GluN2D
24 ± 2.1
3.7
16 ± 1.8
2.2
8
95 ± 2.1
ND
88 ± 1.4
ND
9 c
49 ± 2.1
8.6
37 ± 4.6
5.8
NP11999 d
Data are from 8-9 oocytes from 2 frogs for each compound tested.
a
The response to drug co-applied with a maximally effective
Scheme 1:
concentration of glutamate (100 M) and glycine (30 M) is given
O
O
O
as a percent of the control response to glutamate and glycine alone.
b.
a.
O
HO
O
O
O
b
IC50 values were determined by fitting the Hill equation to the
OH
O
N
O
N
11
12
average composite concentration-response curve and are reported
to two significant figures. ND indicates not determined.
c Because TCN-201 is known to be GluN2A-selective, we tested a
higher concentration, 30 M, at GluN2C and GluN2D. There was
less than 15% inhibition, which precluded determination of IC50.
13
n
d.
c.
n
O
O
H2
N
Boc NH
N
H
O
N
O
H
15
O
N
O
N
14
d Data are from unpublished results.
n
O
cIC50 values were determined by fitting the Hill equation to the
average composite concentration-response curve and are reported
to two significant figures. ND indicates not determined; see Ref
15 for methods.15
O
R
O
S
e.
NH
N
H
O
O
N
16-25
a. diethylcarbamoyl chloride, K2CO3, DMF, 24 h, 54%, b.
with an amide linker would disallow π-π stacking and eliminate
activity that is dependent on this specific pose. We first
confirmed this premise using modelling as shown in Figure 3
(panels A and B), which shows that representative amides
NaOH, MeOH, 12 h, 83%, c. aniline, HATU, DIEA 12 h, 60-89%,
d. TFA, DCM, 3-4 h, 58-91%, e. aryl sulfonyl chloride, DCM, 12
h, 19-64%
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cannot achieve the same degree of aryl ring overlap due to the
geometry of the amide bond. As a proof of principle, we tested
whether this modification altered activity in an analogue of
TCN-201 (compound 9, Figure 1) in which the sulfonamide was
replaced by the amide (compound 26, Table 3), whose structure
is shown in Figure 4. Whereas TCN-201 potently inhibited
GluN1/GluN2A, the amide-containing analogue 26 had no
detectable activity on GluN1/GluN2A receptors (Table 3),
confirming that the π-π stacked pose is essential for activity.
Page 4 of 6
compared to the parent sulfonamide 23. However, an alternative
hypothesis could be that the change in potency is due to a
change in compound geometry between the amide and the
sulfonamide, rather than a requirement of  stacking. While
this seems unlikely for the one carbon linker in TCN-201, which
primarily adopts a single conformation, it is harder to rule out
with the increased flexibility of the 2-carbon linker in 23 and
27. Moreover, there is also the possibility that the difference in
hydrogen bonding and lipophilicity (Table 3) could alter the
way the compound interacts with the receptor. Thus, there
remain caveats about our working hypothesis that will require
structural data of the ligand-bound receptor to address.
1
2
3
4
5
6
7
8
Table 2. Activity of Bi-aryl Sulfonamides a
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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45
46
47
48
49
50
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59
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O
O
O
R1
R2
S
N
H
n
N
O
H
Y
O
O
O
N
H
Cl
C
N
N
O
S
N
O
H
H
H
N
O
O
F
N
O
N
H
18
23
O
26
27
O
O
O
O
C
O
I 30 µM / I control
(mean ± SEM, %)
IC50 (µM)
S
N
N
O
N
N
O
H
H
H
H
O
N
O
N
Cmpd
#
n
R1 R2
Y
CH
GluN2C
42±2.5
22
58±4.6
35
60±2.0
45
52±1.4
34
77±2.9
ND
37±2.8
12
79±1.4
ND
9.0±2.8
2.4
GluN2D
20±2.5
10
45±3.3
24
46±2.6
29
42±1.3
23
67±4.4
ND
26±4.1
5.1
74±2.0
ND
9.0±2.3
1.7
FIGURE 4. Structures of compounds 18, 26, 23 and 27.
16
17
18
19
20
21
22
23
24
25
Para
1
1
1
1
2
2
2
2
2
2
H
H
H
H
H
H
Cl
H
H
Cl
H
H
H
H
H
H
F
Para
Meta
Meta
Para
Para
Para
Meta
Meta
Meta
N
Table 3. Comparison of Sulfonamide to Amide Linker
CH
N
IDrug / IControl (mean ± SEM,
%) a,
IC50 (µM)b
Cmpd
#
cLogPc
Drug
M
GluN2A
GluN2C
ND
GluN2D
ND
CH
N
5.1 ± 1.3
0.17
102 ± 2.2
ND
85 ± 1.2
ND
82 ± 8.6
ND
9
3.55
4.22
4.34
4.59
6
26
23
27
30
30
30
ND
ND
CH
CH
N
9.0 ± 2.8 8.9 ± 2.3
H
H
F
2.4
56 ± 1.9
37
1.7
49 ± 1.6
29
8.5±1.3
3.2
41±1.6
2.4
8.6±1.4
2.7
28±2.6
1.3
Data are from 8-9 oocytes from 2 frogs for each compound tested.
CH
a
The response to drug co-applied with a maximally effective
concentration of glutamate (100 M) and glycine (30 M) is given
as a percent of the control response to glutamate and glycine alone.
a
The response to drug co-applied with a maximally effective
concentration of glutamate (100 M) and glycine (30 M) is given
as a percent of the control response to glutamate and glycine alone.
b
IC50 values were determined by fitting the Hill equation to the
average composite concentration-response curve and are reported
to two significant figures. ND indicates not determined. cLogP
calculated using Chemicalize from ChemAxon.
c
b
Fitted IC50 values are reported to two significant figures;
inhibition in saturating test compound was set to 0 for all except
16, which was 41% for GluN2C and 27% for GluN2D. ND
indicates not determined. Data are from 8-16 oocytes from 2-3
frogs for each compound and receptor tested
The original NAB series was highly selective for GluN2C- and
GluN2D-containing NMDA receptors. We therefore, evaluated
whether one of the most active analogues in this di-aryl
sulfonamide series, compound 23, retained selectivity for
GluN1/GluN2C and GluN1/GluN2D over other receptors.
Interestingly, while this analogue retained potent activity at
GluN2C and GluN2D, it also was active at GluN2B, inhibiting
receptors with a fitted IC50 value of 7.6 µM (n=8 oocytes from 2
frogs). This result raises the possibility that the U-shaped pose of
analogue 23 allows it to access a similar pocket on GluN1/GluN2B.
Analogue 23 showed minimal activity at AMPA, kainate, and
GABA, receptors (Table 4), similar to NAB-14. However, while
the prototypical compound NAB-14 had no detectable off-target
activity at glycine, serotonin, and nicotinic receptors, analogue 23
showed a substantial degree of inhibition at these receptors (Table
We subsequently used the same strategy to test the role of π-π
stacking in the enhanced potency of compounds 23 and 25.
Therefore, we synthesized and tested an analogue of the NAB-
modified series of GluN2C/GluN2D-selective inhibitors in
which we replaced the sulfonamide group with an amide
group (Table 3, compound 27 in Figure 4). In principle, the
amide linker should minimize the ‘U-shape” binding pose due
to its linear geometry as shown in the energy-minimized
structures in Figure 3A. Indeed, consistent with this idea, amide
27 displayed reduced potency by more than 15-fold as
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4). The reduced selectivity of this compound compared to NAB-
AUTHOR INFORMATION
1
2
3
4
5
6
7
8
14, our starting reference compound, could reflect the increased
flexibility of the longer linker and the sulfonamide functionality, or
the addition of another aryl group. NAB-14 is a rigid molecule with
minimal flexibility, which may contribute to its selectivity, as it fits
into the pocket of NMDA receptors with limited ability to fit
different geometries required at other receptors. It might be useful
in future SAR studies at other targets to test both methylene and
ethylene linker that favor the U-shaped pose with different degrees
of freedom, which would be predicted to have different off-target
profiles.
Corresponding Author
*For D.S.M.: Phone, 404-727-6689, E-mail, dmenald@emory.edu
*For S.F.T.: Phone, 404-727-0357; E-mail, strayne@emory.edu
* For D.C.L.: Phone, 404-727-6602; E-mail, dliotta@emory.edu
Author Contributions
All authors designed experiments. SLS, ZZ, RLM, SAK, and DSM
carried out experiments. SLS, ZZ, RLM, SAK, DSM, SFT
analyzed data. All authors wrote the manuscript and all authors
have given approval for the final version of the manuscript.
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Table 4. Selectivity of the sulfonamide analogue 23
Receptor
I30 M / IControl (mean ± SEM, %), p, N
Funding Sources
GluN1/GluN2A
GluN1/GluN2B
GluA1
85 ± 1.2
24 ± 6.3
79 ± 2.0
95 ± 2.2
86 ± 2.7
86 ± 3.1
92 ± 3.1
80 ± 2.7
90 ± 4.9
98 ± 3.1
30± 2.7
20 ± 2.6
27 ± 0.59
p<0.001 N=8
The authors acknowledge the use of shared instrumentation
provided by grants from NSF (CHE1531620). This project was
partially supported by the ELSI Origins Network (EON), which is
supported by a grant from the John Templeton Foundation. The
study was also supported by the NIH-NINDS (NS065371 S.F.T.)
and a research grant from Janssen to Emory University (S.F.T.).
p<0.001 N=11
p=0.001 N=6
p=0.083 N=6
p=0.005 N=6
p=0.010 N=6
p=0.068 N=6
P<0.001 N=8
p=0.105 N=10
p=0.468 N=5
p<0.001 N=8
p<0.001 N=6
p<0.001 N=7
GluA2(R607Q)
GluA3(L513Y)
GluA4(L505Y)
GluK2
Notes
P2X
The authors declare the following competing financial interests:
DCL, SFT, SLS, and DSM are co-inventors on Emory-owned
intellectual property associated with allosteric modulators of
NMDA receptor function. SFT is a paid consultant for Janssen,
the principal investigator on a research grant from Janssen to
Emory University, a member of the SAB for Sage Therapeutics,
recipient of royalties from licensing software, and a co-founder
of NeurOp Inc. DCL is a member of the BOD for NeurOp Inc.
The opinions expressed in this publication are those of the
author(s) and do not necessarily reflect the views of the NIH or
the John Templeton Foundation.
GABAA 22S
GABA 
Glycine 1
Serotonin 5-HTA
Nicotinic 1
a The response to test compound co-applied with agonist is given as
a percent of the average of control and recovery current responses
to agonist alone for receptors expressed in oocytes (VHOLD -40 mV).
Agonist concentrations were 100 µM glutamate plus 30 µM glycine
for NMDA receptors, 100 µM glutamate for AMPA and kainate
receptors, 100 µM GABA for GABA receptors, 100 µM glycine
for glycine receptors, 100 µM serotonin for 5-HT3A receptors, and
9 µM ATP for P2X receptors, and 1 µM acetylcholine for nicotinic
receptors. cDNAs encoding all receptors were from rat except for
GluA2(R607Q), GluA3(L513Y), GluA4(L505Y) and P2X, which
were from human. Oocytes expressing GluK2 were incubated for
1-5 min in 1 mg/ml concanavalin A. N indicates the number of
oocytes. p values were from a paired t-test.
ACKNOWLEDGMENT
We would like to thank Phuong Le and Jing Zhang for excellent
technical assistance. We also acknowledge Kathryn Simon and
Francis X. Tavares of ChemoGenics BioPharma for the original
synthesis of analogs NP11999, NP12022, and NP12000. The
authors thank the Emory Chemical Biology Discovery Center for
their assistance.
ABBREVIATIONS
In summary, these results show that the di-aryl sulfonamide
motif promotes a “U-shape” that can be favorable for some
ligands acting at entirely distinct pockets, which for some
compounds involves substantial intramolecular π–π
interactions. We conclude that the pocket into which the NAB-
14 series binds has room to accommodate the bulky structure
and/or can make significant favorable interactions with
sulfonamide oxygen atoms. This motif, with variable linker
lengths, could be used to explore the size of the pocket for other
medicinal chemistry campaigns aimed at developing the SAR
for other druggable targets. However, longer linkers that allow
greater flexibility could bring additional off-target effects.
NMDA, N-Methyl-D-Aspartate; NMDAR, N-Methyl-D-Aspartate
Receptor; GABA, gamma aminobutyric acid; AMPA, α-amino-3-
hydroxy-5-methyl-4-isoxazolepropionic acid; ATD, amino
terminal domain; CTD, carboxy terminal domain; TMD,
transmembrane domain; LBD, ligand binding domain; NAB, N-
Aryl Benzamide; NAM, Negative Allosteric Modulator; IC50, the
half-maximal inhibitory concentration;
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