3,4-Dihydronaphthalen-1(2H)-ones: Novel ligands for the benzodiazepine site of α5-containing GABAA receptors

Article abstract of DOI:10.1016/j.bmcl.2004.03.054

A series of substituted 3,4-dihydronaphthalen-1(2H)-ones with high binding affinity for the benzodiazepine site of GABA_A receptors containing the α5-subunit has been identified. These compounds have consistently higher binding affinity for the GABA_A α5 receptor subtype over the other benzodiazepine-sensitive GABA_A receptor subtypes (α1, α2 and α3). Compounds with a range of efficacies for the benzodiazepine site of α5-containing GABA_A receptors were identified, including the α5 inverse agonist 3,3-dimethyl-8-methylthio-5- (pyridin-2-yl)-3,4-dihydronaphthalen-1(2H)-one 22 and the α5 agonist 8-ethylthio-3-methyl-5-(1-oxidopyridin-2-yl)-3,4-dihydronaphthalen-1(2H)-one 19.

Full text of DOI:10.1016/j.bmcl.2004.03.054

Bioorganic & Medicinal Chemistry Letters 14 (2004) 2871–2875
3
,4-Dihydronaphthalen-1(2H)-ones: novel ligands for the
benzodiazepine site of a5-containing GABA receptors
A
*
Helen J. Szekeres, John R. Atack, Mark S. Chambers, Susan M. Cook,
Alison J. Macaulay, Gopalan V. Pillai andAngus M. MacLeod
Merck, Sharp & Dohme Research Laboratories, The Neuroscience Research Centre, Terlings Park, Eastwick Road, Harlow,
Essex CM20 2QR, UK
Received15 January 2004; revised12 March 2004; accepted15 March 2004
Abstract—A series of substituted 3,4-dihydronaphthalen-1(2H)-ones with high binding affinity for the benzodiazepine site of
GABA
GABA
A
receptors containing the a5-subunit has been identified. These compounds have consistently higher binding affinity for the
a5 receptor subtype over the other benzodiazepine-sensitive GABA receptor subtypes (a1, a2 and a3). Compounds with a
receptors were identified, including the a5 inverse agonist
,3-dimethyl-8-methylthio-5-(pyridin-2-yl)-3,4-dihydronaphthalen-1(2H)-one 22 andthe a5 agonist 8-ethylthio-3-methyl-5-(1-
A
A
range of efficacies for the benzodiazepine site of a5-containing GABA
3
A
oxidopyridin-2-yl)-3,4-dihydronaphthalen-1(2H)-one 19.
Ó 2004 Elsevier Ltd. All rights reserved.
c-Aminobutyric acid(GABA) is the major inhibitory
neurotransmitter in the central nervous system. GABAA
receptors are GABA-gatedchlori de ion channels, com-
posedof pentameric assemblies of members of the
GABA
site (andwhich comprise around75% of all GABA
A
receptor subtypes, which possess a BZ binding
A
4
receptor subtypes present in the brain) contain b and
c2-subunits in conjunction with either an a1, a2, a3 or
4
GABA receptor gene family (a1-6, b1-3, c1-3, d, e, h
a5-subunit. Receptors containing the a5-subunit
account for approximately 5% of the total GABAA
A
1;2
and p) with the majority of GABAA receptors com-
prising of a, b and c-subunits arrangedin a 2:2:1 stoi-
chiometry. The binding of GABA to its receptor can be
receptor population in the brain, however, in the hip-
pocampus they constitute approximately 20% of all
3
5
modulated by simultaneous binding of chemical entities
to allosteric sites on the ion channel complex. One of the
most studied of these allosteric sites is the benzodiaze-
pine (BZ) binding site due to the clinical efficacy of BZ
GABA receptors. The hippocampus is a region of the
A
brain closely associatedwith learning andmemory
processes indicating that there may be a link between
GABAA receptors containing the a5-subunit andthese
â
6;7
ligands such as diazepam (Valium ), as anxiolytics,
processes.
We sought to identify selective inverse
receptors containing
an a5-subunit, as potential cognition enhancers, which
anticonvulsants andhypnotics. Basedupon their mod-
ulatory effects on GABA-induced GABAA receptor
activation, BZ ligands are categorised as either: agonists
agonists at the BZ site of GABA
A
8
9
may lack the anxiogenic or convulsant (or procon-
vulsant)
GABA
10
(
antagonists (which bindto GABA receptors but have
which increase the affinity of GABA for the receptor),
side effects observed with nonselective
full inverse agonists, such as the b-carboline
A
A
no intrinsic efficacy) or inverse agonists (which decrease
the affinity of GABA for the receptor), spanning the
efficacy spectrum from full agonist through partial
agonist, antagonist, partial inverse agonist to full inverse
agonist. Currently, all clinically effective BZ ligands are
classifiedas full agonists at the BZ bin di ng site.
methyl 6,7-dimethoxy-4-ethyl-b-carboline-3-carboxylate
(DMCM; 1, Fig. 1).
One of the leadstructures on the GABA A a5 pro-
gramme, identified using a directed screening approach,
was 6,6-dimethyl-3-methylthio-1-(1H-pyrazol-5-yl)-6,7-
dihydro-2-benzothiophen-4(5H)-one 2, a high affinity
GABA
A
a5 receptor ligand( K
i
: 5.2 nM) with 4–13-fold
a1, a2 and a3
receptor subtypes. Structure–activity relationships in
binding selectivity over the GABA
A
11
*
0
Corresponding author. Tel.: +44-1279-440417; fax: +44-1279-4403-
0; e-mail: mark_chambers@merck.com
9
this thiophene series have been reportedby Chambers
960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.03.054

2872
H. J. Szekeres et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2871–2875
O
O
SR
S
SMe
S
CO
2
Me
O
OH
Br
O
OH
O
O
NMe
2
MeO
MeO
N
R
1
a
b
N
H
NH
N
Het
N
S
N
S
c
1
(DMCM)
2
3
5
Figure 1.
O
1
2
et al. As well as investigating the thiophenes we sought
to identify alternative core skeletons based on this novel
lead. In particular, the thiophene moiety was replaced
with a phenyl ring to give a series of 3,4-di-
hydronaphthalen-1(2H)-ones 3. This manuscript
describes the syntheses of these a-tetralones, andtheir
O
SCH
2
Het
O
S
NMe
2
d
N
S
N
S
1
5-17
14
affinity andefficacy at the BZ site of GABA
A
receptors
containing an a5-subunit (hereafter referredto as the
a5-subtype). To investigate the effect of varying the
heterocycle at the C5 position of the tetralone core,
the bromophenyl intermediate 8 was utilisedas shown in
Scheme 2. Synthesis of the C8-heteroarylmethylthio derivatives 15–17.
Reagents and conditions: (a) 2-tributylstannyl-1,3-thiazole, 1,4-diox-
TM
ane, Pd(PPh
PhNMe
3
)
4
,
reflux; (b) Me
2
NCSCl, DABCO
, DMF; (c)
2
2
, reflux; (d) KOH, MeOH, reflux then HetCH Cl, 25 °C.
13
Scheme 1. 5-Bromo-8-methoxy-3-methyl-3,4-dihydro-
14
naphthalen-1(2H)-one (4) was de-methylated using
boron tribromide to give the phenol 5, which was
then convertedto the O-arylthiocarbamate 6 using
O
SMe
O
SO
2
Me
O-
O
SEt
15
a
standard chemistry. The O-arylthiocarbamate 6 was
then subjectedto the thermal Newman–Kwart rear-
rangement to affordthe S-arylthiocarbamate 7, which
was readily hydrolysed and subsequently alkylated in
situ with ethyl (or methyl) iodide to give bromide 8.
Finally, the Stille cross-coupling procedure was used to
introduce the heterocycle. As shown in Scheme 2, the
b
O-
+
N
N
N+
13
18
19
c
16
17
C8-heteroarylmethylthio analogues (15, 16 and 17 )
were synthesisedin an efficient manner from the
S-arylthiocarbamate 14, in which a preferredC5-het-
erocycle such as thiazole was incorporatedearly in the
synthesis. The pyridine-N-oxide 19 was obtainedfrom
O
S
S
O
S
S
d
O-
N+
N
1
3 in two steps as shown in Scheme 3. Treatment of 13
2
0
21
with an excess of m-CPBA afforded the methanesulfon-
yl-pyridine-N-oxide 18, which was reactedwith so di um
Scheme 3. Synthesis of the pyridine-N-oxide 19 andthe C8-thienylthio
derivative 21. Reagents andcon idt ions: (a) m-CPBA (3.0 equiv),
DCM, 1,4-dioxane; (b) NaSEt, THF; (c) thiophene-2-thiol, NaH,
THF; (d) PPh
, 200 °C.
3
S
O
OMe
Br
O
OH
Br
O
O
NMe
2
a
b
ethanethiolate to afford 19. Similarly, reaction of 18
with sodium thiophene-2-thiolate produced the thienyl-
Br
3
thio analogue 20, which was then reduced with PPh to
4
5
6
give the desired pyridine 21. The C3-gem-dimethyl
derivative 22 andthe C3-unsubstitutedtetralone 23 were
obtainedusing similar chemistry to that shown in
Scheme 1, starting from 5-bromo-3,3-dimethyl-8-meth-
c
O
13
oxy-3,4-dihydronaphthalen-1(2H)-one or 5-bromo-8-
methoxy-3,4-dihydronaphthalen-1(2H)-one, respectiv-
O
SR
O
SR
Br
O
S
NMe2
e
d
18
ely.
Het
Br
Within the series, compounds that demonstrated good
19
9
-13
8
7
a5 binding affinity were testedin an in vitro efficacy
R = Et, Me
assay using human GABA
A
a5 receptors. The efficacy at
GABAA a5 receptors was determined by one of two
Scheme 1. Synthesis of the C5-heterocyclic analogues 9–13. Reagents
12
TM
different methods as described by Chambers et al. The
efficacy of those compounds shown in Table 1 were
determined using a two-electrode voltage clamp
andcon di tions: (a) BBr
DMF; (c) PhNMe , reflux; (d) KOH, MeOH, reflux then EtI or MeI,
5 °C; (e) Het-SnBu , 1,4-dioxane, Pd(PPh , reflux.
3
, DCM, 0 °C; (b) Me
2
NCSCl, DABCO
,
2
2
3
3
)
4

H. J. Szekeres et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2871–2875
2873
Table 1. GABA
A
receptor subtype affinity of a-tetralones with efficacy measuredin Xenopus oocytes
O
SR
Het
a
b
CompoundR
Het
K
i
(nM) human GABA
A
axb3c2 receptors
a2 a3
13 ± 5
a5 Selectivity
Oocyte Efficacy
a5 (%)
a5
a1
DMCM
CDZ
––
––
––
––
2.2 ± 1.0
368 ± 66
10 ± 1
605 ± 136
7.5 ± 1.2
3–6
––
)34 ± 5
+134 ± 13
c
392 ± 73
471 ± 164
9
Et
Et
N
1.9 ± 0.8
25 ± 6
13 ± 7
15 ± 2
7–13
5–9
+2 ± 2
+2 ± 1
2.1
1.8, 2.4)
11
(9, 13)
19
(19, 19)
13
(12, 14)
10
N
(
N
1
.0
1.0, 1.0)
5.4
(4.8, 6.0)
15
(15, 15)
12
(12, 12)
1
1
1
2
Et
Et
5–15
6–14
)8 ± 4
N
S
O
N
(
2
.6
2.6, 2.6)
37
(35, 39)
38
(37, 39)
16
(12, 20)
+5 ± 2
N
(
1
3
1
Me
7.5
(
63
(59, 67)
63
(58, 71)
42
(36, 48)
6–8
)5 ± 2
6.3, 8.7)
2
N
0.5 ± 0.3
2.3 ± 0.5
5.4 ± 0.3
4.5 ± 0.4
5–11
+50 ± 17
S
a
3
Inhibition of [ H]Ro 15-1788 binding to recombinant human GABA
A
i
receptor subtypes. K values are the mean ± SEM of at least three independent
determinations. Where no SEM value is given the value is the mean of two independent determinations and the values of each determination are
given in parentheses.
b
c
Efficacy is determined as the percentage modulation of the submaximal (EC20) response to GABA. Values given are the mean ± SEM of at least
three individual cells from the a5b3c2 human receptor subtype transiently expressedin Xenopus laevis oocytes.
Value is the mean ± SEM of four individual cells using CDZ ¼ 10 lM.
recording from Xenopus laevis oocytes, transiently
20;21
the ethylthio derivatives 9–12, showedthat all four
compounds have low intrinsic efficacy ()8% to +5%)
and, given that the full agonist CDZ and the full inverse
agonist DMCM have efficacies of +134% and )34%,
respectively, tetralones 9–12 are regarded as antagonists
at the a5-subtype. Replacement of the ethylthio group in
expressing the GABA
A
a5b3c2 receptor subtype.
The efficacy is measuredas the percentage mo du lation
of the submaximal (EC ) response to GABA using a
20
drug concentration equivalent to 100ꢀ the K
i
value,
which wouldbe anticipatedto give a maximal response.
The efficacy values shown in Tables 2 and3 were
9 with methylthio (13; K ða5Þ: 7.5 nM) has a slightly
i
2
2
determined using a whole cell patch clamp recording
ꢁ
detrimental effect on a5 affinity but no significant effect
on efficacy. However, introducing a thienylthio group at
the C8-position afforded the subnanomolar a5-subtype
from mouse fibroblast L(tk ) cells, stably expressing the
19
human GABAA a5b3c2 receptor. The efficacy is
measuredas the percentage maximum modulation of the
current relative to a submaximal (EC20) GABA
response. Positive values represent a potentiation of the
GABA-induced current (agonism) whereas negative
values represent an attenuation (inverse agonism). All
compounds were compared relative to the full inverse
ligand 21 (K
efficacy: +50%) at the BZ site on the GABA
i
: 0.5 nM), which is a partial agonist (oocyte
A
a5
receptor. Table 2 shows the binding and efficacy data for
a selectednumber of C8-heteroarylmethylthio de riva-
tives (15–17) andthe C5-pyri di ne- N-oxide 19. It should
be notedthat for these analogues du e to the availability
23
agonist DMCM and the full agonist chlordiazepoxide
CDZ).
of the stably transfectedclonedcell line the GABA
ꢁ
a5
efficacy was recorded using L(tk ) cells. The hetero-
A
24
(
arylmethylthio derivatives 15–17 retain high binding
Table 1 shows the binding and efficacy data for a
selectednumber of analogues in which the heterocycle is
varied at C5. As is clearly indicated, various five- and
six-memberedheterocycles can be toleratedat this
position with a5 binding selectivity in the range of 5–15-
fold. Measurement of the efficacy in X. laevis oocytes of
affinity at a5-containing receptors (K : 1.0–3.2 nM) and
i
for the two triazole analogues (16 and 17) a modest
increase in a5-subtype binding selectivity was obtained,
comparedto the ethylthio analogue 11. Whilst all three
heteroarylmethylthio derivatives have very similar a5
binding affinity, their in vitro efficacy is significantly

2874
H. J. Szekeres et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2871–2875
ꢁ
Table 2. GABA
A
receptor subtype affinity of a-tetralones with efficacy measuredin L(tk ) cells
O
SR
Het
a
ꢁ
b
CompoundR
Het
K
i
(nM) human GABA
A
axb3c2 receptors
a3
a5 Selectivity
L(tk ) Efficacy
a5 (%)
a5
a1
a2
DMCM
CDZ
––
––
––
––
2.2 ± 1.0
368 ± 66
10 ± 1
605 ± 136
13 ± 5
392 ± 73
7.5 ± 1.2
471 ± 164
3–6
––
)57 ± 1
+99 ± 3
c
N
S
1
5
N
3.2 ± 0.1
1.0 ± 0.2
40 ± 1
38 ± 4
34 ± 5
20 ± 5
35 ± 7
16 ± 3
10–13
+57 ± 7
N
S
S
OMe
N
1
1
6
7
N
N
16–38
14–35
+29 ± 3
+6 ± 4
N
N
N
Me
2.6
(2.5, 2.7)
92
(87, 97)
57
(52, 62)
36
(30, 42)
N
S
H
N
O-
N+
19
Et
25 ± 6
>300
271 ± 58
286 ± 27
>11
+80 ± 9
a
b
c
3
Inhibition of [ H]Ro 15-1788 binding to recombinant human GABA
A
i
receptor subtypes. K values are the mean ± SEM of at least three independent
determinations. Where no SEM value is given the value is the mean of two independent determinations and the values of each determination are
given in parentheses.
Efficacy is determined as the percentage maximum modulation of the current relative to a submaximal (EC20) GABA response. Values are the mean
maximum modulation ± SEM from at least three individual fitted concentration–response curves produced in the a5b3c2 human receptor subtype
stably expressedin mouse fibroblast L(tk ) cells.
Value is the mean ± SEM from 27 cells produced using CDZ ¼ 3 lM.
ꢁ
A
Table 3. GABA receptor subtype affinity andefficacy of C3 mo di fied a-tetralones
O
SR
R
1
R2
N
a
ꢁ
b
CompoundR
R
1
R
2
K
i
(nM) human GABA
A
axb3c2 receptors
a2 a3
13 ± 5
a5 Selectivity L(tk ) Efficacy
a5 (%)
a5
a1
DMCM
CDZ
––
––
––
––
––
2.2 ± 1.0
368 ± 66
7.5
10 ± 1
605 ± 136
63
7.5 ± 1.2
471 ± 164
42
3–6
––
)57 ± 1
c
––
H
392 ± 73
63
+99 ± 3
+2 ± 1
13
Me
Me
6–8
(
6.3, 8.7)
19 ± 7
(59, 67)
229 ± 16
>300
(58, 71)
60 ± 10
>300
(36, 48)
59 ± 6
>300
2
2
3
Me
Et
Me
H
Me
H
3–12
>3
)32 ± 3
––
2
103 ± 24
a
b
c
3
A i
Inhibition of [ H]Ro 15-1788 binding to recombinant human GABA receptor subtypes. K values are the mean ± SEM of at least three independent
determinations. Where no SEM value is given the value is the mean of two independent determinations and the values of each determination are
given in parentheses.
Efficacy is determined as the percentage maximum modulation of the current relative to a submaximal (EC20) GABA response. Values are the mean
maximum modulation ± SEM from at least three individual fitted concentration–response curves produced in the a5b3c2 human receptor subtype
stably expressedin mouse fibroblast L(tk ) cells.
Value is the mean ± SEM from 27 cells produced using CDZ ¼ 3 lM.
ꢁ
different; whereas the 1,2,3-triazole 17 is an antagonist at
ꢁ
crease in a5 affinity anda large increase in efficacy, to
affordwhat is essentially a full agonist (L(tk ) efficacy:
ꢁ
the a5-subtype (L(tk ) efficacy: +6%) the N-methylated-
1,2,4-triazole 16 andthe 5-methoxy-1,2,4-thia di azole 15
ꢁ
are both partial agonists (L(tk ) efficacy: +29% and
+80%) at the a5-subtype. Table 3 shows the effect of
methyl substitution at the C3-position. Comparison of
+
57%, respectively). N-Oxidation of 9 to produce 19
ða5Þ: 25 nM) results in an order of magnitude de-
the C3-methyl andC3-unsubstitute de dr ivatives
9
(
K
i
(K ða5Þ: 103 nM), respectively,
i
ða5Þ: 1.9 nM) and 23 (K
i

H. J. Szekeres et al. / Bioorg. Med. Chem. Lett. 14 (2004) 2871–2875
2875
clearly demonstrates that a C3-substituent is crucial for
high a5-subtype binding affinity, with the unsubstituted
analogue exhibiting 50-foldlower a5 affinity. The
introduction of a second methyl substituent at C3 does
not improve affinity (cf. thiomethyl analogues 13
5. Sur, C.; Quirk, K.; Dewar, D.; Atack, J. R.; McKernan,
R. M. Mol. Pharmacol. 1998, 54, 928–933.
6
7
. Collinson, N.; Kuenzi, F. M.; Jarolimek, W.; Maubach,
K. A.; Cothliff, R.; Sur, C.; Smith, A.; Otu, F. M.; Howell,
O.; Atack, J. R.; McKernan, R. M.; Seabrook, G. R.;
Dawson, G. R.; Whiting, P. J.; Rosahl, T. W. J. Neurosci.
(
a profoundeffect on the GABA
K ða5Þ: 7.5 nM) and 22 (K ða5Þ: 19 nM) but it does have
i
i
2
002, 22, 5572–5580.
A
a5 efficacy––convert-
ing an antagonist (13, L(tk ) efficacy: +2%) into an
. Crestani, F.; Keist, R.; Fritschy, J.-M.; Benke, D.; Vogt,
K.; Prut, L.; Bluthmann, H.; Mohler, H.; Rudolph, U.
Proc. Natl. Am. Sci. 2002, 99, 8980–8985.
ꢁ
ꢁ
inverse agonist (22, L(tk ) efficacy: )32%). Throughout
the course of the programme a variety of C3-gem-di-
methyl derivatives were synthesised but they had unac-
8. Dorow, R.; Horowski, R.; Paschelke, G.; Amin, M.;
Braestrup, C. Lancet 1983, 2, 98–99.
9
1
. Petersen, E. N. Eur. J. Pharmacol. 1983, 94, 117–124.
0. Little, H. J.; Nutt, D. J.; Taylor, S. C. Br. J. Pharmacol.
984, 83, 951–958.
ceptably low a5-subtype affinity (i.e., K > 10 nM) and,
i
as a consequence, were not pursuedany further. It
shouldbe notedthat for all those compoun sd that
possess a single C3 methyl group the data given in the
tables are for the racemic mixture. However, the pyridyl
derivative 9 has been resolvedinto its ini dv iud al
enantiomers using chiral HPLC. The data obtained for
these enantiomers showedthat whilst there was an order
of magnitude difference in their a5-subtype binding
1
1
1. Chambers, M. S.; Atack, J. R.; Bromidge, F. A.; Brough-
ton, H. B.; Cook, S.; Dawson, G. R.; Hobbs, S. C.;
Maubach, K. A.; Reeve, A. J.; Seabrook, G. R.; Wafford,
K.; MacLeod, A. M. J. Med. Chem. 2002, 45, 1176–1179.
2. Chambers, M. S.; Atack, J. R.; Broughton, H. B.;
Collinson, N.; Cook, S.; Dawson, G. R.; Hobbs, S. C.;
Marshall, G.; Maubach, K. A.; Pillai, G. V.; Reeve, A. J.;
MacLeod, A. M. J. Med. Chem. 2003, 46, 2227–2240.
3. Bryant, H. J.; Chambers, M. S.; Hobbs, S. C. U.S. Patent
1
affinity (K
i
values 0.5 and10 nM) there was no signifi-
ꢁ
1
1
1
1
cant efficacy difference (L(tk ) efficacy: +6% and+18%).
6
,156,761, 2000.
4. Nishiyama, T.; Kameoka, H. Chem. Express 1991, 6,
09–113.
5. Sebok, P.; Timar, T.; Eszenyi, T.; Patonay, T. Synthesis
994, 837–840.
6. For the synthesis of 15, 5-chloro-3-chloromethyl-1,2,4-
thiadiazole was the alkylating agent used in step (d) of
Scheme 2. During the reaction, methoxide displaced the
chloride on the thiadiazole.
From the selectedanalogues shown in the tables it is
clear that relatively minor structural changes at different
positions on the tetralone core couldpro du ce a signifi-
1
1
cant effect on GABA
A
a5 efficacy. However, it was
foundthat these structure–efficacy observations were
not consistent across the series, andas a consequence a
robust structure–efficacy relationship was not estab-
lished.
17. Compound 17 was synthesisedfrom the SEM-protected
triazole analogue using 5-chloromethyl-1-{[2-(trimethyl-
silyl)ethoxy]methyl}-1H-1,2,3-triazole as the alkylating
agent in step (d) of Scheme 2. The SEM group was
removedby reaction with 2 N HCl in ethanol at reflux.
In summary, a series of 3,4-dihydronaphthalen-1(2H)-
ones has been identified as a novel class of ligands at
the BZ site of GABAA receptors, with higher binding
affinity for receptors containing the a5-subunit com-
paredto the a1, a2 and a3-containing subtypes. Within
the series compounds with a range of efficacies were
identified, from the a5-subtype agonist 19 through
partial agonists andantagonists to the a5-subtype
inverse agonist 22.
1
8. Chatterjee, A.; Hazra, B. G. Tetrahedron 1980, 36, 2513–
519.
2
1
9. Hadingham, K. L.; Wingrove, P.; Le Bourdelles, B.;
Palmer, K. J.; Ragan, C. I.; Whiting, P. J. Mol. Pharma-
col. 1993, 43, 970–975.
20. Casula, M. A.; Bromidge, F. A.; Pillai, G. V.; Wingrove,
P. B.; Martin, K.; Maubach, K.; Seabrook, G. R.;
Whiting, P. J.; Hadingham, K. L. J. Neurochem. 2001,
7
7, 445–451.
2
1. Hadingham, K. L.; Garret, E. M.; Wafford, K. A.; Bain,
C.; Heavens, R. P.; Sirinathsinghji, D. J. S.; Whiting, P. J.
Mol. Pharmacol. 1996, 49, 253–259.
References and notes
1
. Barnard, E. A.; Skolnick, P.; Olsen, R. W.; Mohler, H.;
Sieghart, W.; Biggio, G.; Braestrup, C.; Bateson, A. N.;
Langer, S. Z. Pharmacol. Rev. 1999, 50, 291–313.
. Bonnert, T. P.; McKernan, R. M.; Farrar, S.; Le Bourd-
elles, B.; Heavens, R. P.; Smith, D. W.; Hewson, L.;
Rigby, M. R.; Sirinathsinghji, D. J. S.; Brown, N.;
Wafford, K. A.; Whiting, P. J. Proc. Natl. Acad. Sci.
U.S.A. 1999, 96, 9891–9896.
22. Horne, A. L.; Hadingham, K. L.; Macaulay, A. J.;
Whiting, P.; Kemp, J. A. Br. J. Pharmacol. 1992, 107,
732–737.
2
23. Lui, R.; Zhang, P.; McKernan, R. M.; Wafford, K.; Cook,
J. M. Med. Chem. Res. 1995, 5, 700–709.
ꢁ
24. Since efficacy recordings using L(tk ) cells provided full
concentration–response curves this methodof efficacy
measurement was preferredto that obtainedusing
oocytes. It shouldbe notedthat obtaining concentra-
tion–response curves in oocytes is a problematic process,
3
. Farrar, S. J.; Whiting, P. J.; Bonnert, T. P.; McKernan,
R. M. J. Biol. Chem. 1999, 274, 10100–10104.
4
. McKernan, R. M.; Whiting, P. J. Trends Neurosci. 1996,
9, 139–143.
due to the rapid de-sensitisation of the GABA receptor at
A
relatively high concentrations.
1