Benzo[7]annulene-based GluN2B selective NMDA receptor antagonists: Surprising effect of a nitro group in 2-position

Article abstract of DOI:10.1016/j.bmcl.2015.10.076

Benzo[7]annulen-7-amines 7 without further polar substituents have been reported as conformationally restricted Ro 25-6981 analogs and show unexpectedly high GluN2B affinity. Herein the corresponding 2-NO₂ derivatives 8 were synthesized and pharmacologically evaluated. NO₂ derivatives 8 show 5- to 10-fold higher GluN2B affinity than the unsubstituted ligands 7. Docking studies of ligands 7c and 8c reveal an important contribution of the 2-NO₂-substituent in determining the binding pose and modulating the GluN2B affinity.

Full text of DOI:10.1016/j.bmcl.2015.10.076

Bioorganic & Medicinal Chemistry Letters 25 (2015) 5748–5751
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Benzo[7]annulene-based GluN2B selective NMDA receptor
antagonists: Surprising effect of a nitro group in 2-position
Sandeep Gawaskar a,b,c, Dirk Schepmann a, Alessandro Bonifazi d, Dina Robaa e, Wolfgang Sippl e,
Bernhard Wünsch a,c,
⇑
a Institut für Pharmazeutische und Medizinische Chemie der Universität Münster, Corrensstraße 48, 48149 Münster, Germany
b NRW Graduate School of Chemistry, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
c Cells-in-Motion Cluster of Excellence (EXC 1003—CiM), Westfälische Wilhelms-Universität Münster, Germany
d Scuola di Scienze del Farmaco e dei Prodotti della Salute, Università di Camerino, Via S. Agostino, 1, 62032 Camerino, Italy
e Institut für Pharmazeutische und Medizinische Chemie der Martin-Luther-Universität Halle-Wittenberg, Wolfgang-Langenbeck-Straße 4, 06120 Halle (Saale), Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Benzo[7]annulen-7-amines 7 without further polar substituents have been reported as conformationally
restricted Ro 25-6981 analogs and show unexpectedly high GluN2B affinity. Herein the corresponding
2-NO2 derivatives 8 were synthesized and pharmacologically evaluated. NO2 derivatives 8 show 5- to
10-fold higher GluN2B affinity than the unsubstituted ligands 7. Docking studies of ligands 7c and 8c
reveal an important contribution of the 2-NO2-substituent in determining the binding pose and
modulating the GluN2B affinity.
Received 22 September 2015
Revised 23 October 2015
Accepted 25 October 2015
Available online 31 October 2015
Keywords:
NMDA receptor
Ó 2015 Elsevier Ltd. All rights reserved.
GluN2B antagonists
2-Nitrobenzo[7]annulen-7-amines
Structure affinity relationships
Selectivity
Conformational restriction
Docking studies
The neurodegenerative disorder Alzheimer’s disease (AD) is
affecting 21–35 million people worldwide.1 Current treatment
options for AD are limited to managing symptoms. Among the
Excess of (S)-glutamate leads to overactivation of the NMDA
receptor and an increased influx of Ca2+ ions into the neuronal cell,
which is associated with damage of neuronal cells up to cell death.
This self-reinforcing phenomenon is termed excitotoxicity. Loss of
neuronal cells due to excitotoxicity is involved in the progression
of neurodegenerative disorders like AD,9 but also in many
other disorders like stroke,10 cerebral ischemia,11 depression12
and epilepsy.13
available therapies the weak N-methyl-D-aspartate (NMDA) recep-
tor channel blocker memamtine has been approved for the treat-
ment of mild to severe AD.2
The NMDA receptor belongs to the family of ionotropic
glutamate receptors.3–5 This ligand-gated ion channel plays an
important role in synaptic plasticity, memory and learning. The
NMDA receptor consists of four subunits, which are classified
as GluN1a-h (8 splice variants), GluN2A-D (4 subunits) and
Since different NMDA receptor subunits show different
expression in various regions of the central nervous system
(CNS), subunit selective NMDA antagonists address NMDA recep-
tors only in some regions of the CNS resulting in improved side
effect profiles. In particular, NMDA antagonists interacting
selectively with the GluN2B subunit display neuroprotective
effects through negative allosteric modulation of the ion channel
opening state.14
GluN3A-B (2 subunits).
A functional heterotetrameric NMDA
receptor is generally composed of two GluN1 and two GluN2
subunits.6 Activation of the NMDA receptor requires the binding
of two agonists at their respective orthosteric binding sites,
glycine at the GluN1 subunit and (S)-glutamate at the GluN2
subunit, along with the removal of the Mg+ blockade. These
events allow the penetration of Ca2+ and Na+ cations into the
neuronal cell.7,8
Ifenprodil (1)15 was the first compound discovered to bind with
high affinity at a specific binding site at the GluN2B subunit
(Fig. 1). In spite of its high GluN2B affinity (IC50 = 13.3 nM),16 the
further development of ifenprodil was discontinued due to lack
of selectivity (affinity toward 5-HT1A, 5-HT2, a1
, r1 and r2 recep-
⇑
Corresponding author. Tel.: +49 251 8333311; fax: +49 251 8332144.
E-mail address: wuensch@uni-muenster.de (B. Wünsch).
tors)17,18 and low bioavailability.19 However, ifenprodil inspired
http://dx.doi.org/10.1016/j.bmcl.2015.10.076
0960-894X/Ó 2015 Elsevier Ltd. All rights reserved.

S. Gawaskar et al. / Bioorg. Med. Chem. Lett. 25 (2015) 5748–5751
(a)
5749
OH
OH
O
O
O
N
N
O2N
CH3
CH3
HO
9
HO
HO
NO2
R1
10
11
ifenprodil (1)
Ro 25-6981 (2)
(b)
8
OH
OH
OH
a
b
c
d
CH2Ph
NHR1
N
N
(CH2)2Ph
(CH2)3Ph
(CH2)4Ph
F
O2N
CH3
Cl
8a-d
traxoprodil (3)
eliprodil (4)
Scheme 1. Synthesis of 2-nitrobenzo[7]annulen-7-amines 8a–d. Reagents and
reaction conditions: (a) HNO3/H2SO4 1:1, À15 °C, dropwise addition of 9, 25 min at
À15 °C, 59% (10). (b) H2N(CH2)nPh (1–2 equiv), NaBH(OAc)3 (1.6–2.1 equiv), CH2Cl2,
2–12 h, 77% (8a), 98% (8b), 57% (8c), 58% (8d).
Figure 1. Potent GluN2B selective NMDA receptor antagonists.
the development of novel GluN2B selective NMDA receptor antag-
onists, like Ro 25-6981 (2),20 traxoprodil (3) and eliprodil (4).21
In 2011, the structures of a dimer of the amino terminal
domains (ATD) of the GluN1b and GluN2B subunits together with
affinity and docking studies of benzo[7]annulen-7-amines
bearing a NO2 moiety in 2-position.
8
The synthesis of the core benzo[7]annulen-7-one 9 started with
double Knoevenagel condensation of phthalaldehyde with
1
and 2
were reported.22 Crystallization of the tetrameric
a
dimethyl 3-oxoglutarate (Scheme 1). Catalytic hydrogenation of
the resulting product followed by hydrolysis and decarboxylation
led to the ketone 9.26
((GluN1b)2/(GluN2B)2) full-length NMDA receptor in complex with
allosteric antagonists 1 and 2 succeeded in 2014.23,24 Both types of
crystal structures reveal binding of the allosteric antagonists at the
interface of GluN1b and GluN2B subunits. The phenolic OH group
forms an H-bond interaction with the carboxylate moiety of
Glu236 (GluN2B), while the protonated amino moiety and the
benzylic OH group form H-bonds with the O- and N-atoms of the
carbamoyl moiety of Gln110 (GluN2B). Furthermore, the phenylpi-
peridine part of ifenprodil occupies a hydrophobic pocket formed
by the residues of Tyr109 and Ala75 of the GluN1b subunit as well
as Phe114, Ile111, and Ile82 of the GluN2B subunit. According to
the crystal structures, the recognition of ifenprodil and similar
ligands at the ifenprodil binding site is mediated predominantly
through lipophilic interactions.22
In a previous study, novel benzo[7]annulen-7-amines 5 and 6
designed as conformationally restricted analogs of Ro 25-6981
(2) were identified as GluN2B selective NMDA antagonists
(Fig. 2). Unexpectedly, compound 6 lacking the benzylic OH moiety
showed slightly increased GluN2B affinity compared to the alcohol
5.25 This observation was pursued with the unsubstituted benzo[7]
annulen-7-amines 7, which preserved high GluN2B affinity as well
(e.g. 7c (R1 = (CH2)3Ph): Ki = 16 nM, see Table 1).26
The nitration of the ketone 9 required substantial optimization.
Temperatures >0 °C and nitration with 100% HNO3 at À35 °C led to
decomposition of 9. A 1:1 mixture of HNO3 and H2SO4 was suitable
for nitration of 9. (Scheme 1) The formation of the two regioiso-
mers 10 and 11 was dependent on the temperature of the reaction
mixture. Reaction times >60 min led to either low yields or decom-
position. Finally, a reaction temperature of À15 °C and dropwise
addition of the ketone 9 provided the nitrated compounds 10
and 11 in a ratio of 73:27 (determined by 1H NMR spectroscopy).
Recrystallization of the mixture of regioisomers 10 and 11 with
tert-butyl methyl ether (TBME) resulted in a yield of 59% of the
2-nitro compound 10.
The purified nitroketone 10 was used to introduce various
amino moieties at 7-position. For this purpose, the ketone 10
was reacted with homologous phenylalkylamines in the presence
of NaBH(OAc)3 to afford the secondary amines 8a–d in yields
ranging from 57% to 98% (Scheme 1). Since the phenylpropylami-
nes 5–7 show high GluN2B affinity, the 3-phenylpropyl moiety of
8c represents the preferred N-substituent. In order to investigate
the effect of the alkyl spacer length, the longer 4-phenylbutyl
(8d) and shorter 2-phenylethyl (8b) and benzyl (8a) derivatives
were also included into the study.
Since we have shown that a proton (7c: Ki = 16 nM) and an elec-
tron donating methoxy group (6: Ki = 10 nM) in the benzo[7]annu-
len-7-amine system result in high GluN2B affinity, we became
interested in the effects of an electron withdrawing substituent
on GluN2B affinity. In order to test this effect, introduction of a
NO2 moiety as prototypical electron withdrawing group was
envisaged (Fig. 2). Thus, herein we report the synthesis, GluN2B
The GluN2B affinity of the synthesized ligands was determined
in a radioligand binding assay developed previously in our group.16
In brief, membrane preparations were obtained from L(tk-) cells
stably transfected with a vector containing the genetic information
X
HO
CH3
N
NH
2
H3CO
HO
5:
X = OH
Ro 25-6981 (2)
6: X = H
NHR1
NHR1
2
O2N
H
8
7
Figure 2. Development of 2-nitrobenzo[7]annulen-7-amines 8.

5750
S. Gawaskar et al. / Bioorg. Med. Chem. Lett. 25 (2015) 5748–5751
Table 1
Table 1 displays the affinity of benzo[7]annulenamines 7 and 8
to the PCP binding site of the NMDA receptor as well as to r1 and
r2 receptors. At a test compound concentration of 1 lM, neither
Receptor affinities of the benzo[7]annulenamines 8 with NO2 moiety compared with
the affinities of the corresponding lead compounds 7 without NO2 moiety and some
reference compounds
the unsubstituted compounds 7 nor the nitro derivatives 8 were
able to compete with the radioligand [3H](+)-MK-801 indicating
high selectivity over the PCP binding site.
NHR1
NHR1
O2N
H
The NO2 derivatives 8 show two-digit nanomolar affinities
8
7
toward both r1 and r2 receptors. The
r affinities of 8 are consid-
erably higher than the affinities of the unsubstituted derivatives 7
indicating a strong contribution of the NO2 moiety to the interac-
tions with r1 and r2 receptors. However, the NO2 derivatives 8
are still selective for GluN2B containing NMDA receptors over both
r1 and r2 receptors, due to their very high GluN2B affinity. The
most potent GluN2B ligand 8c (Ki = 1.6 nM) is 11-fold and 7-fold
selective for GluN2B-containing NMDA receptors over r1 and r2
receptors, respectively. Interestingly, reduction of the phenyl-
propyl to the phenylethyl side chain in 7b and 8b leads to
increased selectivity over r2 receptors, while maintaining high
Compd
R1
Ki SEM [nM] (n = 3)
GluN2B
PCP
r1
r2
7a26
7b26
7c26
7d26
8a
8b
8c
8d
CH2Ph
57 5.7
20 7.4
16 3.5
17 1.5
7.6 0.7
3.3 1.0
1.6 0.9
3.8 2.1
10 0.7
13 2.0
—
16%
0%
0%
107
22 6.7
150
203
198
(CH2)2Ph
(CH2)3Ph
(CH2)4Ph
CH2Ph
(CH2)2Ph
(CH2)3Ph
(CH2)4Ph
27 12
55 7.4
16 2.0
44 25
11 3.9
11 5.2
98 34
—
2%
6%
8%
3%
3%
—
216
21 5.8
20 5.1
18 5.0
24 0.9
125 24
—
Ifenprodil (1)
Eliprodil (4)
Dexoxadrol
Haloperidol
Di-o-tolylguanidine
GluN2B affinity (GluN2B/r2 = 10 (7b) and 13 (8b)).
—
In order to understand the high GluN2B affinity of the NO2
derivatives 8, the most potent GluN2B ligand 8c and its unsubsti-
tuted analog 7c were docked into the Ro 25-6981 binding site of
the NMDA receptor. The binding poses of the ligands 7c and 8c
are displayed in Figure 3A and B, respectively. The docking studies
reveal that both ligands 7c and 8c form the same central H-bond
between the protonated amino moiety and the carbonyl O-atom
of Gln110 (GluN2B subunit) as ifenprodil. The phenylpropyl resi-
due rests in the hydrophobic pocket formed by lipophilic amino
acid residues such as Phe114 (GluN2B), Pro78 (GluN2B) and
Tyr109 (GluN1b). The phenylpiperidine part of ifenprodil occupies
the same lipophilic pocket in the crystal structure.
32 7.4
—
—
—
—
—
—
6.3 1.6
89 29
78 2.3
57 18
Note: For compounds with low affinity only the inhibition of the radioligand
binding (in%) at a test compound concentration of 1 M is given.
l
of GluN1a and GluN2B subunits.27 After induction of the produc-
tion of the NMDA receptor subunits by addition of dexamethasone,
the cells were grown, harvested, worked-up and the membrane
preparations were standardized. [3H]-labeled ifenprodil ([3H]1)
was employed as radioligand.
The GluN2B affinity of benzo[7]annulenamines without NO2
moiety (7) and with NO2 moiety in 2-position (8) is summarized
in Table 1. The Ki(GluN2B) values of the secondary amines 8 with
a 2-NO2 group are lower than 10 nM, indicating a higher GluN2B
affinity than the reference compound ifenprodil (Ki = 10 nM).
Compared to the unsubstituted benzo[7]annulenamines 7, the
GluN2B affinity of the NO2 derivatives 8 is 5 to 10-fold higher.
The unsubstituted amines 7 show a strong dependence of the
GluN2B affinity on the length of the amino substituent.26
Whereas the benzylamine 7a with the shortest side chain
displays the lowest GluN2B affinity (Ki = 57 nM), the phenyl-
propylamine 7c has the highest GluN2B affinity (Ki = 16 nM).
The same trend is observed for the NO2 derivatives 8, but at a
considerably higher level of affinity: the lowest affinity was found
for the benzylamine 8a (Ki = 7.6 nM), the highest affinity for the
phenylpropylamine 8c (Ki = 1.6 nM). The same trend within both
series of ligands supports the hypothesis that a distance of four
bond lengths (three CH2 moieties) between the amino moiety
and the terminal phenyl ring is optimal for this type of GluN2B
ligands.
In the crystal structure the phenolic OH group of ifenprodil
forms an H-bond with carboxylate of Glu236 (GluN2B). The miss-
ing substituent at 2-position of 7c precludes the formation of this
H-bond interaction with Glu236. The lack of this anchoring sub-
stituent led in addition to the depicted binding pose to inverted
binding poses, i.e., binding poses with the benzo[7]annulene sys-
tem occupying the above mentioned lipophilic binding pocket.
The energetically most favored pose is depicted in Figure 3A. The
comparable GluN2B affinity of 7c (Ki = 16 nM) with ifenprodil
(Ki = 10 nM) suggests that the lipophilic nature of ligand 7c is able
to compensate the loss of enthalpic contribution to binding.
An additional H-bond interaction with the phenolic OH group of
ifenprodil and a bound H2O molecule is found in the X-ray crystal
structure of the dimeric receptor containing ifenprodil. The dock-
ing studies of the 2-NO2 derivative 8c led also to polar interactions
between this H2O molecule and the 2-NO2 moiety (Fig. 3B). This
H2O molecule is bound to the receptor by a network of H-bonds
with the backbone amino acids Leu205 (GluN2B), Met207
(GluN2B) and Tyr175 (GluN2B). It is assumed that the polar inter-
actions between the NO2 moiety and the bound H2O molecule in
the receptor binding pocket are responsible for the high GluN2B
affinity of the NO2 derivatives 8 compared to the unsubstituted
derivative 7. Additionally, the NO2 group anchors the ligand 8c in
a particular pose as shown in Figure 3B and leads to a preferential
orientation over an inverted pose, in contrast to the observation for
7c.
The lead compounds 1–3 contain an OH moiety at the benzene
ring, which increases the electron density of the benzene ring and
is able to act as H-bond donor. Since the NO2 moiety represents an
electron withdrawing substituent, which can only function as H-
bond acceptor, the high GluN2B affinity of the NO2 derivatives 8
was completely unexpected.
In order to learn more about the selectivity, the affinity of the
2-nitro derivatives 8 at the PCP binding site of the NMDA receptor
In conclusion, conformational restriction of the potent GluN2B
ligand Ro 25-6981 and removal of the polar OH moieties led to
and at
was considered, since it represents an alternative binding site at
the NMDA receptor.28–30 The affinity toward the
receptors was
r1 and r2 receptors were determined. The PCP binding site
the unsubstituted benzo[7]annulen-7-amines
7 with GluN2B
affinities in the range 16–57 nM. This result showed that the polar
substituents of Ro 25-6981 are not essential for strong interaction
with GluN2B containing NMDA receptors. Introduction of an addi-
tional NO2 moiety in 2-position of the benzo[7]annulene scaffold
increased, however, the GluN2B affinity 5- to 10-fold compared
with the unsubstituted derivatives 7. The phenylpropylamines 7c
r
recorded, since ifenprodil interacts also with r1 and r2
receptors.31–33 In the radioligand binding assays the radioligands
[3H](+)-MK-801 (PCP binding), [3H](+)-pentazocine ( 1) and [3H]
r
di-tolylguanidine (r2), were used.

S. Gawaskar et al. / Bioorg. Med. Chem. Lett. 25 (2015) 5748–5751
5751
Figure 3. Comparison of the docking poses of unsubstituted ligand 7c (A) and NO2 derivative 8c (B) in the ifenprodil binding site. Docking was performed using GOLD; images
generated by PyMOL.
2. Esposito, Z.; Belli, L.; Toniolo, S.; Sancesario, G.; Bianconi, C.; Martorana, A. CNS
Neurosci. Ther. 2013, 19, 549.
ligands, respectively. The very high affinity of the NO2 derivatives
3. Kennedy, M. B. Science 2000, 290, 750.
(Ki = 16 nM) and 8c (Ki = 1.6 nM) represent the most potent
was unexpected, because the electron withdrawing NO2 moiety
represents an H-bond acceptor in contrast to the electron donating
OH moiety present in the lead compounds 1–3. Docking studies of
the phenylpropylamines 7c and 8c revealed an important H-bond
interaction between the protonated central amino moiety of 7c
and 8c and the carbamoyl moiety of Gln110. The same interaction
was found for ifenprodil and Ro 25-6981 in the crystal structure
indicating that this interaction is crucial for tight binding of
benzo[7]annulen-7-amines 7 and 8. Due to a missing anchoring
group at the aromatic system, the unsubstituted benzo[7]annu-
len-7-amine 7c can adopt two binding modes within the binding
site. The additional NO2 moiety of 8c is able to form H-bonds with
a H2O molecule bound in the ifenprodil binding site of the receptor.
These interactions lead to an exact orientation of the NO2 deriva-
tive 8c in the binding pocket and possibly to its high binding affin-
ity. Even though introduction of the NO2 group led to high GluN2B
affinity, additional substituents at 2-position will be explored, due
to the inherent metabolic instability associated with the NO2
moiety.
4. Bräuner-Osborne, H.; Egebjerg, J.; Nielsen, E. O.; Madsen, U.; Krogsgaard-
Larsen, P. J. Med. Chem. 2000, 43, 2609.
5. Stark, H.; Reichert, U.; Graßmann, S. Pharm. Unserer Zeit 2000, 2, 228.
6. Paoletti, P. Eur. J. Neurosci. 2011, 33, 1351.
7. Neyton, J.; Paoletti, P. J. Neurosci. 2006, 26, 1331.
8. Cull-Candy, Stuart; Brickley, S.; Farrant, M. Curr. Opin. Neurobiol. 2001, 11, 327.
9. Wessell, R. H.; Ahmed, S. M.; Menniti, F. S.; Dunbar, G. L.; Chase, T. N.; Oh, J. D.
Neuropharmacology 2004, 47, 184.
10. Liu, Y.; Wong, T. P.; Aarts, M.; Rooyakkers, A.; Liu, L.; Lai, T. W.; Wu, D. C.; Lu, J.;
Tymianski, M.; Craig, A. M.; Wang, Y. T. J. Neurosci. 2007, 27, 2846.
11. Di, X.; Bullock, R.; Watson, J.; Fatouros, P.; Chenard, B.; White, F.; Corwin, F.
Stroke 1997, 28, 2244.
12. Mony, L.; Kew, J. N. C.; Gunthorpe, M. J.; Paoletti, P. Br. J. Pharmacol. 2009, 157,
1301.
13. Lodge, D., Danysz, W., Parsons, C. G., Eds.; FP Graham Publishing Co.: Johnson
City, TN, 2002.
14. Williams, K. Curr. Drug Targets 2001, 2, 285.
15. Reynolds, I. J.; Miller, R. J. Mol. Pharmacol. 1989, 36, 758.
16. Schepmann, D.; Frehland, B.; Lehmkuhl, K.; Tewes, B.; Wünsch, B. J. Pharm.
Biomed. Anal. 2010, 53, 603.
17. Chenard, B. L.; Bordner, J.; Butler, T. W.; Chambers, L. K.; Collins, M. A.; De
Costa, D. L.; Ducat, M. F.; Dumont, M. L.; Fox, C. B. J. Med. Chem. 1995, 38, 3138.
18. Chenard, B. L.; Shalaby, I. A.; Koe, B. K.; Ronau, R. T.; Butler, T. W.; Prochniak, M.
A.; Schmidt, A. W.; Fox, C. B. J. Med. Chem. 1991, 34, 3085.
19. Falck, E.; Begrow, F.; Verspohl, E.; Wünsch, B. J. Pharm. Biomed. Anal. 2014, 88,
96.
20. Fischer, G.; Mutel, V.; Trube, G.; Malherbe, P.; Kew, J. N.; Mohacsi, E.; Heitz, M.
P.; Kemp, J. A. J. Pharmacol. Exp. Ther. 1997, 283, 1285.
Acknowledgements
21. Layton, M. E.; Kelly, M. J.; Rodzinak, K. J. Curr. Top. Med. Chem. 2006, 6, 697.
22. Karakas, E.; Simorowski, N.; Furukawa, H. Nature 2011, 475, 249.
23. Karakas, E.; Furukawa, H. Science 2014, 344, 992.
24. Lee, C.-H.; Lü, W.; Michel, J. C.; Goehring, A.; Du, J.; Song, X.; Gouaux, E. Nature
2014, 511, 191.
25. Benner, A.; Bonifazi, A.; Shirataki, C.; Temme, L.; Schepmann, D.; Quaglia, W.;
Shoji, O.; Watanabe, Y.; Daniliuc, C.; Wünsch, B. ChemMedChem 2014, 9, 741.
26. Gawaskar, S.; Schepmann, D.; Bonifazi, A.; Wünsch, B. Bioorg. Med. Chem. 2014,
22, 6638.
The authors also thank the NRW Graduate School of Chemistry
for a PhD scholarship to S.G., which was funded by the Government
of the State of Nordrhein-Westfalen and the Westfälische Wil-
helms-Universität Münster. Moreover, we are grateful to Cells-in-
Motion (CiM) Cluster of Excellence for funding a postdoc position
for S.G.
27. Steinmetz, R. D.; Fava, E.; Nicotera, P.; Steinhilber, D. J. Neurosci. Methods 2002,
113, 99.
28. Banerjee, A.; Schepmann, D.; Köhler, J.; Würthwein, E. U.; Wünsch, B. Bioorg.
Med. Chem. 2010, 18, 7855.
29. Köhler, J.; Bergander, K.; Fabian, J.; Schepmann, D.; Wünsch, B. J. Med. Chem.
2012, 55, 8953.
30. Wirt, U.; Schepmann, D.; Wünsch, B. Eur. J. Org. Chem. 2007, 2007, 462.
31. Meyer, C.; Neue, B.; Schepmann, D.; Yanagisawa, S.; Yamaguchi, J.; Würthwein,
E.-U.; Itami, K.; Wünsch, B. Bioorg. Med. Chem. 1844, 2013, 21.
32. Miyata, K.; Schepmann, D.; Wünsch, B. Eur. J. Med. Chem. 2014, 83, 709.
33. Hasebein, P.; Frehland, B.; Lehmkuhl, K.; Fröhlich, R.; Schepmann, D.; Wünsch,
B. Org. Biomol. Chem. 2014, 12, 5407.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2015.10.
076.
References and notes
1. Meek, P. D.; McKeithan, E. K.; Schumock, G. T. Pharmacotherapy 1998, 18, 68.