Discovery of functionally selective 7,8,9,10-tetrahydro-7,10-ethano-1,2,4- triazolo[3,4-a]phthalazines as GABAA receptor agonists at the α3 subunit

Article abstract of DOI:10.1021/jm040883v

We have previously identified the 7,8,9,10-tetrahydro-7,10-ethano-1,2,4- triazolo[3,4-a]phthalazine (1) as a potent partial agonist for the 0.3 receptor subtype with 5-fold selectivity in binding affinity over α₁. This paper describes a detailed investigation of the substituents on this core structure at both the 3- and 6-positions. Despite evaluating a wide range of groups, the maximum selectivity that could be achieved in terms of affinity for the α₃ subtype over the α₁ subtype was 12-fold (for 57). Although most analogues showed no selectivity in terms of efficacy, some did show partial agonism at α₁ and antagonism at α₃ (e.g., 25 and 75). However, two analogues tested (93 and 96), both with triazole substituents in the 6-position, showed significantly higher efficacy for the α₃ subtype over the α₁ subtype. This was the first indication that selectivity in efficacy in the required direction could be achieved in this series.

Full text of DOI:10.1021/jm040883v

J. Med. Chem. 2005, 48, 1367-1383
1367
Discovery of Functionally Selective
7,8,9,10-Tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthalazines as GABAA
Receptor Agonists at the r3 Subunit
Michael G. N. Russell,* Robert W. Carling, John R. Atack, Frances A. Bromidge, Susan M. Cook, Peter Hunt,
Catherine Isted, Matt Lucas, Ruth M. McKernan, Andrew Mitchinson, Kevin W. Moore, Robert Narquizian,
Alison J. Macaulay, David Thomas, Sally-Anne Thompson, Keith A. Wafford, and Jose´ L. Castro
Merck Sharp & Dohme Research Laboratories, Neuroscience Research Centre, Terlings Park, Eastwick Road,
Harlow, Essex CM20 2QR, U.K.
Received September 29, 2004
We have previously identified the 7,8,9,10-tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthal-
azine (1) as a potent partial agonist for the R3 receptor subtype with 5-fold selectivity in binding
affinity over R1. This paper describes a detailed investigation of the substituents on this core
structure at both the 3- and 6-positions. Despite evaluating a wide range of groups, the
maximum selectivity that could be achieved in terms of affinity for the R3 subtype over the R1
subtype was 12-fold (for 57). Although most analogues showed no selectivity in terms of efficacy,
some did show partial agonism at R1 and antagonism at R3 (e.g., 25 and 75). However, two
analogues tested (93 and 96), both with triazole substituents in the 6-position, showed
significantly higher efficacy for the R3 subtype over the R1 subtype. This was the first indication
that selectivity in efficacy in the required direction could be achieved in this series.
Chart 1
Introduction
GABA (γ-aminobutyric acid) is the major inhibitory
neurotransmitter in the mammalian central nervous
system, binding to three different receptor types, GABAA,
GABAB, and GABAC. The GABAA receptor is a ligand-
gated chloride ion channel that has a pentameric
structure composed from a family of at least 16 subunits
(R1-6, â1-3, γ1-3, δ, ꢀ, π, and θ).1,2 Although this could
potentially lead to a very large number of permutations,
it seems that relatively few occur in vivo, with the
majority of receptors comprising two R, two â, and one
γ subunits.3 The most likely arrangement of these
subunits in the receptor has recently been determined
by molecular modeling.4 In addition to binding GABA,
each receptor possesses a number of allosteric sites that
bind a variety of ligands, leading to a modulation of the
action of GABA. These include the benzodiazepine (BZ),
barbiturate, neurosteroid, and loreclezole sites.
The BZ binding site is found in GABAA receptors
containing â and γ2 subunits in conjunction with an R1,
R2, R3, or R5 (but not R4 or R6) subunit. In such receptors,
it occurs at the interface of the R and γ2 subunits with
both subunits contributing to the binding.5 BZs such as
diazepam (Chart 1) are positive allosteric modulators
(i.e., agonists) in that they enhance the inhibitory effects
of GABA. They display anxiolytic, anticonvulsant, seda-
tive-hypnotic, anaesthetic, and muscle-relaxant activi-
ties, but they are also associated with side effects such
as amnesia, tolerance, dependence, and alcohol poten-
tiation. Although sedation and myorelaxation are of
clinical utility for treating sleep disorders or premedi-
cation prior to procedures such as endoscopy, in terms
of an anxiolytic they are liabilities. Consequently, there
is a need for a nonsedating anxiolytic.6
It has been found through in situ mRNA hybridiza-
tion, subunit specific quantitative immunoprecipitation
and autoradiography that the R1âγ2 assembly is the
most abundant and is located in most brain regions,
while the R2âγ2 and R3âγ2 assemblies are of medium
abundance and can be found in brain areas where the
R1 subunit is absent or at low levels. The R5âγ2 receptors
are low in abundance in the whole brain but are
expressed to a significant extent in the hippocampus.7
This differential location of GABAA receptor subtypes
within the brain suggests that different subtypes might
* Correspondence to Dr. M. G. N. Russell. Tel: 44 1279 440419.
Fax: 44 1279 440390. E-mail: michael_russell@merck.com.
10.1021/jm040883v CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/04/2005

1368 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
Scheme 1a
a Reagents and conditions: (i) NH2NH2‚H2O, NaOAc‚3H2O, AcOH, H2O, reflux, 16 h; (ii) POCl3, reflux, 14 h; (iii) R1CONHNH2, Et3N,
xylene, reflux, 4 d; (iv) NH2NH2‚H2O, EtOH, reflux, 18 h; (v) R1COCl, Et3N, CHCl3, rt, 4-24 h; (vi) POCl3, reflux, 2-5 h; (vii) (a)
3-thiophenecarboxylic acid, oxalyl chloride, CH2Cl2, DMF, rt, 1 h; (b) 102, Et3N, dioxane, reflux, 3 d; (viii) (a) 2-furoyl chloride, Et3N,
dioxane, rt to reflux, 36 h; (b) xylene, reflux, 5 h; (ix) R2OH, NaH, DMF, rt; (x) 2 N NaOH(aq), dioxane, H2O, reflux, 3 d; (xi) (a) NaH,
DMF, 80 °C, 20-30 min; (b) R2X, rt to 80 °C.
be associated with different physiological effects. BZs
generally bind with equal affinity at R1-, R2-, R3-, and
R5-containing subtypes with little affinity for R4- and
R6-containing subtypes. Apart from BZs, a variety of
other chemical classes bind to the BZ site, but most
show no selectivity for the different subtypes. However,
zolpidem (Chart 1) does possess a degree of subtype
selectivity in that it has about 10-fold binding selectivity
for the R1 subunit over R3, and >100-fold selectivity over
R5 (Table 1). This compound has primarily sedative
effects and thus suggests that the R1 subtype may play
a role in the sedative properties of BZs. Moreover,
zolpidem demonstrates that compounds with selectivity
for discrete GABAA receptor subtypes possess different
pharmacological profiles to BZs.
Recently, it has been shown using R1H101R mutant
mice, in which the R1 subunit is rendered insensitive to
diazepam, that diazepam retains its anxiolytic action
but not its sedative effect, further supporting the notion
that the R1 subtype is involved in sedation but not
anxiety.8,9 This, therefore, implies that the R2, R3, and/
or R5 subtypes are likely to mediate the anxiolytic effects
of BZs. There is evidence in mice lacking the R5 sub-
unit that this subtype is associated with memory and
learning and is not involved in anxiety,10 and it is
hypothesised that the R5 subtype may at least in part
mediate the cognitive deficit seen with diazepam. Fur-
ther mouse lines with R2H101R, R3H126R, and R5H101R
mutations have also been generated in an attempt to
further define the subtypes involved in anxiety and the
other actions of diazepam.11-16 We, therefore, chose to
develop BZ site agonists with selectivity for the R2 and/
or the R3 subtype as anxiolytics with a potential for
reduced side effects.
We have previously identified the 7,8,9,10-tetrahydro-
7,10-ethano-1,2,4-triazolo[3,4-a]phthalazine 1 as a po-
tent partial agonist for the R3 receptor subtype with
5-fold selectivity in binding affinity over R1.17 This paper
describes a detailed investigation of the substituents on
this core structure which, although not leading to
enhanced subtype selective binding affinity, did lead to
the discovery of a functionally selective compound for
the R3 subtype.
Chemistry
The final compounds were all synthesized through the
3-substituted 6-chloro-7,8,9,10-tetrahydro-7,10-ethano-
1,2,4-triazolo[3,4-a]phthalazines (101a-p) (Scheme 1).
These in turn were prepared by reacting 4,5,6,7-tetra-
hydro-4,7-ethano-2-benzofuran-1,3-dione18 with hydra-
zine, and the resulting phthalazine-1,4-dione (99) was
reacted with phosphorus oxychloride to give the 1,4-
dichloro-phthalazine (100). This could then be cyclized
directly with the appropriate acylhydrazide and triethyl-
amine in refluxing xylene to give 101, or a stepwise
procedure could be followed by treating 100 with hy-
drazine to form the mono-hydrazino adduct (102), which
in turn could be cyclized directly with the appropriate
acid chloride and triethylamine in refluxing dioxane (for
101l) or xylene (for 101m). Alternatively, the intermedi-
ate hydrazides (103 and 106) were isolated by treating
102 with the corresponding acid chlorides and triethyl-
amine in chloroform at room temperature and subse-
quently cyclized in phosphorus oxychloride at reflux to
give 101i and 101p, respectively. The acylhydrazide
(105) was prepared by treating the corresponding meth-
yl ester (104) with hydrazine (Scheme 2). The chloro-
imidates (101) were then treated with an alcohol and

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1369
Scheme 2a
Scheme 5a
a Reagents and conditions: (i) (a) BuLi, THF, -78 °C, 1 h; (b)
CO2, -78 °C to room temperature, 2 h; (ii) HCl, MeOH, rt, 16 h;
(iii) NH2NH2‚H2O, MeOH, rt, 1.5 h.
a Reagents and conditions: (i) tetravinyltin, (Ph3P)2PdCl2, LiCl,
DMF, 100 °C, 16 h; (ii) (a) O3, CH2Cl2, -78 °C to room temperature,
16 h; (b) Me2S, -78 °C to room temperature, 1 h; (iii) NaBH4,
MeOH, 0 °C, 1 h.
Scheme 3a
Scheme 6a
a Reagents and conditions: (i) NaBH4, MeOH, rt, 1 h.
Scheme 7a
a Reagents and conditions: (i) t-BuMe2SiCl, imidazole, DMF,
60 °C, 16 h; (ii) Tf2O, i-PrNEt2, CH2Cl2, -10 °C to room temper-
ature, 25 h; (iii) tetraallyltin, (Ph3P)2PdCl2, LiCl, DMF, 80 °C, 12
h; (iv) TBAF, THF, rt, 25 min; (v) H2, Pd/C, EtOAc, 30 psi, 30
min.
Scheme 4a
a Reagents and conditions: (i) m-CPBA, CH2Cl2, 0 °C to room
temperature, 16 h; (ii) (a) Ac2O, 110 °C, 16 h; (b) HCl, MeOH, rt,
16 h.
Scheme 8a
a Reagents and conditions: (i) Me3SiCN, CH2Cl2, rt, 25 min; (ii)
Et2NCOCl, rt, 4 d; (iii) H2, Pd/C, 2 N HCl(aq), 30 psi, 2 h.
sodium hydride to give the required compounds. Alter-
natively, the chloroimidate could be hydrolyzed with
sodium hydroxide to the corresponding amide (131),
which was then treated with an alkyl halide and sodium
hydride to afford the requisite analogues.
Although many of the alcohols were commercially
available or known in the literature, some were novel.
Thus, (3-propylpyridin-2-yl)methanol (111) was pre-
pared by selectively protecting 3-hydroxy-2-(hydroxy-
methyl)pyridine with a TBDMS group, converting the
free hydroxyl to a triflate and performing a Stille
reaction with tetraallyltin to give 109 (Scheme 3). The
silyl group was then removed, and the olefin was
hydrogenated to give the required alcohol (111).
The (3,6-dimethylpyridin-2-yl)methanol (113) was
synthesized from 2,5-dimethylpyridine-1-oxide19 by treat-
ment with trimethylsilyl cyanide, followed by N,N-
diethylcarbamoyl chloride to give the 2-cyanopyridine
(112) (Scheme 4). This was then hydrogenated in
aqueous acid to give the methanol derivative (113).
The (3-alkoxypyridin-2-yl)methanols (114-118, Chart
1) were prepared by reacting 2-(hydroxymethyl)pyri-
dine-3-ol hydrochloride with the appropriate alkyl ha-
lide in the presence of either potassium hydroxide or
potassium carbonate in DMSO or DMF. (6-Methyl-
pyridazin-3-yl)methanol (121) was synthesized from
3-chloro-6-methylpyridazine by a Stille coupling with
a Reagents and conditions: (i) NaBH4, MeOH, 0 °C, 40 min; (ii)
101a, NaH, DMF, rt; (iii) 5 N HCl(aq), 50 °C, 90 min.
tetravinyltin to give the vinylpyridazine (119), which
was treated with ozone to give the carbaldehyde (120),
and then reduced with sodium borohydride to give 121
(Scheme 5).
The (4- and 5-methyl-1,3-thiazol-2-yl)methanols (123
and 125) were prepared by reducing the carbaldehydes
(12220 and 12421) with sodium borohydride (Scheme 6).
The (5-methyl-1,3-thiazol-4-yl)methanol (127) was syn-
thesized by treating 4,5-dimethylthiazole with 3-chloro-
peroxybenzoic acid to form the N-oxide (126), which was
then reacted with acetic anhydride and subjected to an
acid-catalyzed rearrangement to give the alcohol (127)
(Scheme 7). The (5-methyl-1,2,4-oxadiazol-3-yl)methanol
(128, Chart 1) was prepared from the THP-protected
hydroxyacetamide oxime22 by reacting with ethyl ace-
tate and sodium hydride, followed by removal of the
THP group.
The (imidazol-2-yl)methanol was reacted with chloro-
imidate (101a) as its [2-(trimethylsilyl)ethoxy]methyl

1370 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
Scheme 9a
cyanuric acid in chloroform at reflux. Thus, 132-134
and 138-142 (Chart 1) were all prepared in this
manner. The preparation of (2-chloromethyl)pyrimidine
(137) also used this chemistry in the final step, although
in this case the 2-methylpyrimidine (136) had to be
synthesized from 2-bromopyrimidine by reaction with
dimethyl malonate and sodium hydride to form the
malonate (135), followed by double decarboxylation
under Krapcho conditions (Scheme 9). 5-(Chloromethyl)-
3-methyl-1,2,4-oxadiazole (143, Chart 1) was prepared
by reacting acetamide oxime with chloroacetyl chloride
and sodium hydride.
The analogues with a carbon instead of an oxygen as
the first linkage atom in the side chain were all
prepared from an initial reaction of the chloride (101a)
with copper(I) cyanide to form mainly the cyanide (144)
together with a small amount of the carboxamide (145)
(Scheme 10). The cyanide (144) was hydrolyzed with
sodium hydroxide to the carboxylic acid, which was then
treated with thionyl chloride and ethanol to give the
ethyl ester (146). This was then reduced with sodium
borohydride and calcium chloride to the hydroxymethyl
derivative (147), which was subjected to a Mitsunobu
a Reagents and conditions: (i) NaH, CH2(CO2Me)2, dioxane,
reflux, 16 h; (ii) NaCl, DMSO, H2O, 160 °C, 16 h; (iii) trichloro-
isocyanuric acid, CHCl3, reflux, 9 h.
(SEM)-protected derivative (129), which was obtained
from the carbaldehyde23 by reduction with sodium
borohydride (Scheme 8). After coupling the SEM group
was removed with hydrochloric acid to give 77. The
4-methylimidazol-2-yl analogue (79) was prepared in the
same way from the mixture of SEM-protected imid-
azoles (130a and 130b).
Some of the alkyl chlorides used to react with amide
(131) also had to be prepared. In compounds where a
chloromethyl substituent was in a position adjacent to
a nitrogen atom in an aromatic heterocycle, these could
generally be made from the corresponding methyl
substituted analogue by treating with trichloroiso-
Scheme 10a
a Reagents and conditions: (i) CuCN, NMP, 200 °C, 36 h; (ii) H2, Pd/C, EtOH, CHCl3, 50 psi, 22 h; (iii) 2-bromopyridine, 160 °C, 6 h;
(iv) (a) 4 N NaOH(aq), EtOH, reflux, 5 h; (b) 5 M HCl(aq); (c) SOCl2, EtOH, reflux, 5 h; (v) NaBH4, CaCl2, EtOH, -10 °C to room temperature,
30 min; (vi) 2-hydroxypyridine, Ph3P, DEAD, THF, rt, 3 h; (vii) concd HCl, 100-120 °C, 46 h; (viii) (a) SOCl2, 50-60 °C, 20 h; (b)
2-aminopyridine, Et3N, THF, rt, 3.5 h.

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1371
Scheme 11a
a Reagents and conditions: (i) BrCH2CO2Me, NaH, DMF; (ii) KOH, MeOH, H2O, rt, 3 d; (iii) (a) N,N′-carbonyldiimidazole, DMF, rt, 2
h; (b) BnNHMe, rt, 24 h.
Table 1. Binding Affinities of 3-Substituted 6-(Pyridin-2-ylmethoxy)-7,8,9,10-tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthalazines
at Cloned Human GABAA Receptor Subtypes
Ki (nM)a
compd
R
R1â3γ2
R2â3γ2
R3â3γ2
33 ( 3
R5â3γ2
diazepam
13 ( 1
6.6 ( 0.5
103 ( 17
720 ( 110
26 ( 2
11 ( 1
>3333
zolpidem
27 ( 1
246 ( 18
850 ( 120
13 ( 2
CL218,872
66 ( 0
460 ( 10
1.2 ( 0.1
170 ( 20
6.0 ( 0.2
4.2 ( 2.7
22 ( 3
1
Ph
71 ( 8
2
2-MeO-Ph
3-MeO-Ph
4-MeO-Ph
2-Me-Ph
>1000
>1000
>1000
3
140 ( 0
230 ( 20
>1000
79 ( 5
29 ( 7
4
74 ( 4
52 ( 4
5
280 ( 30
210 ( 20
120 ( 10
16 ( 6
280 ( 0
140 ( 30
32 ( 10
6.1 ( 0.1
58 ( 25
38 ( 1
6
3-Me-Ph
570 ( 40
310 ( 20
28 ( 7
310 ( 60
260 ( 10
>1000
130 ( 20
270 ( 20
>1000
130 ( 0
>1000
17 ( 1
7
4-Me-Ph
4.7 ( 0.4
0.54 ( 0.03
27 ( 8
8
2-F-Ph
9
4-F-Ph
180 ( 30
54 ( 7
10
11
12
13
14
15
16
3-pyridyl
4-pyridyl
3-thienyl
2.7 ( 0.1
20 ( 0
320 ( 10
52 ( 19
110 ( 10
140 ( 0
24 ( 2
150 ( 40
38 ( 20
53 ( 11
100 ( 10
18 ( 2
4.4 ( 0.9
5.3 ( 1.8
26 ( 1
2-furyl
4-Me-thiazol-2-yl
cyclopropyl
morpholin-4-yl
1.8 ( 0.1
>1000
>1000
>1000
a Inhibition of [3H]Ro15-1788 binding to recombinant hGABAA receptor subtypes stably expressed in L (tk-) cells. Values are the geometric
mean ( SEM for n ) 2-5, expressed to two significant figures. Six to eight concentrations of each test compound incremented in half-log
units were used in the determinations.
reaction with 2-hydroxypyridine in the presence of
triphenylphosphine and diethyl azodicarboxylate to give
the N-alkylated analogue as the major product together
with a low yield of the required O-alkylated product
(49). Other alkylation conditions gave only N-alkylated
product. The cyanide (144) could also be hydrogenated
over palladium on carbon to the aminomethyl derivative
(148), which was then alkylated with 2-bromopyridine
to give 50. Finally, the carboxamide (145) was hydro-
lyzed by concentrated hydrochloric acid to the carboxylic
acid (149), which was then treated with thionyl chloride,
followed by 2-aminopyridine to give the amide (51).
The N-benzyl-N-methylacetamide analogue (67) was
prepared by alkylating the amide (131) with methyl
bromoacetate and then hydrolyzing the ester with
potassium hydroxide to afford the acid (150) (Scheme
11). This was then treated with N,N′-carbonyldiimid-
azole, followed by N-benzylmethylamine to give 67.
Finally, the two propyl-substituted triazoles (95 and 96)
were prepared by alkylation of the unsubstituted tri-
azole (92) with iodopropane and sodium hydride.
Results and Discussion
The binding affinities of compounds were measured
by the inhibition of [3H]Ro15-1788 binding to human
recombinant GABA receptor subtypes stably expressed
in L(tk-) cells containing R1, R2, R3, and R5 subunits in
combination with â3 and γ2.24,25
The efficacy of each compound was measured on the
same combinations of receptor subtypes expressed in
Xenopus oocytes using two-electrode voltage-clamp elec-
trophysiology. A concentration of GABA was used that
elicited a response 20% in amplitude of the maximum
obtainable GABA current (EC20). Modulation of this
current by test compounds was carried out using a
concentration of 100 × Ki of the test compound.26, 27
It can be seen from Table 1 that both methoxy (2-4)
and methyl (5-7) substituents in any position on the

1372 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
Table 2. Binding Affinities of Six-Membered Heteroarylmethoxy Groups in the 6-Position of
7,8,9,10-Tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthalazines at Cloned Human GABAA Receptor Subtypes
Ki (nM)a
compd
R
R1â3γ2
R2â3γ2
R3â3γ2
R5â3γ2
1
2-pyridyl
71 ( 8
26 ( 2
13 ( 2
1.2 ( 0.1
6.5 ( 2.0
4.7 ( 1.0
0.46 ( 0.08
2.0 ( 0.2
1.2 ( 0.3
2.6 ( 0.7
3.1 ( 1.0
0.84 ( 0.17
0.20b
1.0 ( 0.3
0.54 ( 0.01
2.5 ( 0.6
34 ( 8
0.65 ( 0.16
0.36 ( 0.13
0.50 ( 0.08
0.75 ( 0.02
4.2 ( 1.1
7.0 ( 3.5
0.88 ( 0.30
9.2 ( 3.4
0.55 ( 0.03
0.77 ( 0.05
2.1 ( 0.6
1.3 ( 0.1
0.69 ( 0.15
9.5 ( 6.7
3.9 ( 0.9
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
3-pyridyl
150 ( 10
140 ( 0
9.8 ( 0.8
93 ( 2
68 ( 25
82 ( 14
2.0 ( 0.1
19 ( 0
25 ( 0
4-pyridyl
13 ( 1
3-Me-2-pyridyl
4-Me-2-pyridyl
5-Me-2-pyridyl
6-Me-2-pyridyl
3-Pr-2-pyridyl
2.1 ( 0.4
18 ( 1
56 ( 16
160 ( 30
3.5 ( 1.1
27 ( 2
3.4 ( 0.7
11 ( 2
13 ( 2
21 ( 11
270 ( 0
17 ( 3
3.9 ( 0.9
13 ( 1
6.9 ( 0.3
32(3
17 ( 5
15 ( 7
20 ( 5
36 ( 10
9.9 ( 2.9
8.7 ( 1.3
3.4 ( 0.5
4.0 ( 0.0
5.9 ( 1.2
30 ( 12
470 ( 60
9.1 ( 1.0
2.8 ( 0.9
9.8 ( 0.2
5.6 ( 0.2
43 ( 11
100 ( 30
14 ( 4
2.4 ( 0.9
3.6 ( 0.4
0.71 ( 0.5
1.7 ( 0.4
1.7 ( 0.7
7.1 ( 2.7
180 ( 10
2.4 ( 0.4
1.1 ( 0.3
3.9 ( 0.2
2.3 ( 0.7
38 ( 7
3,6-diMe-2-pyridyl
3,5-diMe-2-pyridyl
3,4-diMe-2-pyridyl
3-CN-2-pyridyl
3-MeO2C-2-pyridyl
3-HO-2-pyridyl
3-MeO-2-pyridyl
3-EtO-2-pyridyl
3-methoxyethoxy-2-pyridyl
3-cyclopropyl-methoxy-2-pyridyl
3-cyclobutyloxy-2-pyridyl
3-BnO-2-pyridyl
pyridazin-3-yl
160 ( 60
33 ( 13
87 ( 17
22 ( 4
20 ( 7
8.5 ( 1.1
33 ( 12
3.1 ( 0.4
3.0 ( 2.0
10 ( 1
pyrimidin-2-yl
68 ( 7
pyrimidin-4-yl
8.1 ( 1.0
6.5 ( 4.4
22 ( 1
pyrazin-2-yl
16 ( 6
6-Me-pyridazin-3-yl
6-Cl-pyridazin-3-yl
isoquinolin-1-yl
50 ( 4
73 ( 9
42 ( 16
7.5 ( 0.3
200 ( 10
34 ( 5
23 ( 5
29 ( 5
4.5 ( 2.3
77 ( 16
26 ( 12
quinolin-2-yl
quinoxalin-2-yl
480 ( 0
82 ( 22
a See corresponding footnote in Table 1. b Value for n ) 1 determination.
3-phenyl ring of compound 1 resulted in a reduction in
the affinity of the compounds at all receptor subtypes.
Table 5 shows the efficacy values measured on some of
the higher affinity analogues. It can be seen that the
efficacy at the R3 subtype for 3, 4, and 7 is essentially
the same as 1 (33-43%), although the efficacy at R1
shows more variability (9-51%), with both para-
substituted compounds (4 and 7) showing a little
selectivity for R3 over R1. The efficacies at the R2 and R5
subtypes were also measured for 7 and mirrored those
of 1, being somewhat lower than at the R3 subtype,
which is a general trend in this series. The only
substituent that had similar affinity to 1 was 2-fluoro
(8), but the 4-fluoro analogue (9) had less affinity.
Replacement of the phenyl ring by six- or five-membered
heteroaromatic rings (10-14) once again led to a drop
in affinity. The efficacy of the 3-pyridyl analogue (10)
was much less than for 1 at the R3 subtype. The small
cyclopropyl group gave a compound (15) with similar
affinity to 1, but the larger morpholinyl substituent (16)
was completely inactive. It can be seen from this set of
compounds that there was only modest selectivity in the
binding affinities between the different subtypes. The
affinity for the R5 subtype was between 2- and 14-fold
higher than for the R3 subtype, while the best selectivity
for the R3 subtype over the R1 subtype was obtained with
the 4-methyl analogue (7), which was only 10-fold
selective. The binding selectivity of the R3 subtype over
the R2 subtype was even smaller, varying between 1-
and 4-fold. In summary, substitution at the 3-position
had an equivalent effect on affinity at all subtypes with
the general trend of affinity (i.e. higher at R5 than at
R1, R2, and R3 and modest or negligible selectivity for
R2 and R3 over R1) and efficacy (partial agonism with
little or no selectivity) being maintained.
Table 2 shows the effect on the binding affinities
produced by changes at the 6-position to the 2-pyridyl
group, retaining a six-membered heteroaromatic or
benzo-fused heteroaromatic ring and a 3-phenyl sub-
stituent. Thus, moving the N atom around the ring to
give the 3- and 4-pyridyl analogues (17 and 18) led to
similar affinities at the R3 subtype compared to 1, but
the efficacies of these two analogues at the R3 subtype
were somewhat lower than for 1 (20% and 17% cf. 38%).
Methylation of the 2-pyridyl group had little effect on
affinity for 20, 21, and 22 except the 3-methyl substitu-
ent (19), which resulted in a 6- to 7-fold increase in
affinity at the R1 and R3 subtypes. However, 19 had
much lower efficacy at the R3 subtype than the other
three methyl analogues. The 3-propyl derivative (23),
however, had the same affinity at the R3 subtype as the
3-methyl analogue (19), although less selectivity over
the R1 subtype, but much increased efficacy at the R3
subtype. An increase in efficacy corresponding to in-
creased size of the alkyl group at this position is a
general trend and can be seen for later compounds as
well. An additional methyl group in 19 at the 5-position
(25) led to another 3-fold rise in affinity at the R1 and

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1373
Table 3. Binding Affinities of Other 6-Substituted-3-phenyl-7,8,9,10-tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthalazines at
Cloned Human GABAA Receptor Subtypes
Ki (nM)a
compd
R
R1â3γ2
>500
R2â3γ2
>500
R3â3γ2
>500
R5â3γ2
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
3-pyridyloxy
>500
2-pyridylethoxy
480 ( 20
75 ( 7
270 ( 10
190 ( 10
390 ( 0
230 ( 40
>1000
290 ( 30
>1000
200 ( 20
240 ( 30
550 ( 90
120 ( 10
>1000
170 ( 0
>1000
44 ( 0
6-Me-2-pyridylpropoxy
1- ( 2-pyridyl)ethoxy
2-pyridyloxymethyl
2-pyridylaminomethyl
2-pyridyl-NHCO
30 ( 3
>1000
64 ( 20
58 ( 1
440 ( 20
>1000
>1000
>1000
>1000
40 ( 19
110 ( 20
2.6 ( 1.3
7.8 ( 4.6
9.4 ( 1.6
11 ( 2
PhCH2O
2-CN-PhCH2O
190 ( 30
>1000
83 ( 18
180 ( 70
110 ( 10
110 ( 32
76 ( 7
53 ( 22
66 ( 28
70 ( 22
43 ( 7
3-CN-PhCH2O
4-CN-PhCH2O
310 ( 20
490 ( 120
520 ( 80
190 ( 50
96 ( 13
>500
3-HOCH2-PhCH2O
4-HOCH2-PhCH2O
3-Me2NCH2-PhCH2O
4-MeSO-PhCH2O
44 ( 3
11 ( 2
64 ( 11
41 ( 5
24 ( 8
4.5 ( 0.1
7.6 ( 1.3
>500
31 ( 1
4-CF3O-PhCH2O
>500
>500
3,4-methylenedioxy-PhCH2O
1-Me-piperidin-2-ylmethoxy
1-Me-piperidin-3-ylmethoxy
5-oxo-2-pyrrolidinemethoxy
Me2NCOCH2O
>500
>1000
750 ( 40
730 ( 170
220 ( 50
230 ( 20
21 ( 1
650 ( 200
71 ( 37
150 ( 0
>1000
>500
>500
>500
>1000
>1000
>1000
260 ( 40
480 ( 140
160 ( 40
160 ( 40
72 ( 10
310 ( 60
34 ( 9
460 ( 240
260 ( 10
89 ( 20
50 ( 8
100 ( 10
59 ( 2
10 ( 3
1-pyrrolidine-COCH2O
BnMeNCOCH2O
9.0 ( 2.7
7.4 ( 0.7
42 ( 13
8.5 ( 1.0
41 ( 19
88 ( 23
41 ( 10
170 ( 10
19 ( 8
57 ( 5
>1000
Hydroxypropoxy
Hydroxybutoxy
trans-4-HOCH2-cyclohexylmethoxy
cis-4-HOCH2-cyclohexylmethoxy
77 ( 1
>1000
a See corresponding footnote in Table 1.
R3 subtypes, making this compound the most active in
this series, although an antagonist at the R3 subtype.
Extra methyl groups at the 4- and 6-positions (26 and
24) made little difference to the affinity or the R3 efficacy
of 19.
of 40 at R3 was lower than for 36. Of the benzo-fused
analogues, the 2-quinoline (43) had significantly lower
affinity, the quinoxaline (44) had 5- to 9-fold lower
affinity across all subtypes than the corresponding non-
benzo-fused pyrazine (39), but the 1-isoquinoline (42)
had slightly higher affinity than 1. However, 42 had low
efficacy at R3 and much higher efficacy at R1.
Other more drastic changes at the 6-position were
now explored (Table 3). Removing the methylene group
from the linkage between the pyridine and the triazolo-
phthalazine core led to a dramatic loss of affinity for
45, while extending the linkage by one (46) or two (47)
carbon atoms gave a significant fall in affinity compared
to 1 and 22, respectively (15- and 12-fold at R3). An
R-methyl group in the linkage (48) also lost over 40-
fold in affinity at the R3 subunit compared to 1, while
reversing the carbon and oxygen atoms in the linkage
(49) led to a 9-fold reduction over 1 in affinity at R3. If
the oxygen in 49 was replaced by a nitrogen atom (50),
affinity was lost completely, while an amide linkage (51)
was 13-fold lower in affinity than 1 at R3.
A range of other substituents at the 3-position of the
2-pyridine ring was then explored. Thus, a cyano
substituent (27) had similar affinity and efficacy to 19,
a methyl carboxylate group (28) had slightly lower
affinity and slightly higher efficacy, and a hydroxyl
substituent (29) had greatly reduced affinity. However,
alkylation of this hydroxyl substituent with small
groups (30-33) recovered all of the affinity, although
this tailed off with larger groups such as cyclobutyloxy
(34) and benzyloxy (35). The efficacy at R3 ranged from
a very low partial agonist in the case of methoxy (30)
to full agonism in the case of methoxyethoxy (32),
cyclopropyloxy (33), and benzyloxy (35), with ethoxy (31)
being halfway between these extremes. However, there
was still no significant selectivity over R1 in terms of
either affinity or efficacy.
Addition of another N atom in the heteroaromatic ring
gave similar affinity to 1 in the case of pyridazine (36),
slightly lower affinity for the 2-pyrimidine (37), and
higher affinity for the 4-pyrimidine (38) and pyrazine
(39). However, 38 and 39 both have lower efficacy than
1 at the R3 subtype, although 36 has slightly higher
efficacy but no selectivity over the R1 subtype. Adding
a substituent to the 6-position of 36 such as methyl (40)
or chloro (41) did not improve affinity, and the efficacy
If the pyridyl group of 1 was replaced by a phenyl
ring (52), affinity was lost completely, although substi-
tution of this phenyl ring by a cyano group in the ortho-,
meta-, or para-position (53-55) gave compounds with
only 4 to 6-fold lower affinity than 1 at R3, with the
meta-analogue (54) showing partial agonism at both the
R1 and R3 subtypes. A hydroxymethyl substituent at
either the meta- or para-position (56, 57) gave similar
affinities at R3 to the cyano analogues with 11 to 12-

1374 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
Table 4. Binding Affinities of Five-Membered Heteroarylmethoxy Groups in the 6-Position of
7,8,9,10-Tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthalazines at Cloned Human GABAA Receptor Subtypes
Ki (nM)a
compd
R
R1â3γ2
R2â3γ2
R3â3γ2
R5â3γ2
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
2-furyl
>500
>500
>500
>500
2-thienyl
3-thienyl
pyrazol-1-yl
>500
>500
>500
>500
>500
>500
43 ( 6
>500
19 ( 1
>500
130 ( 20
23 ( 1
2.7 ( 0.2
0.26 ( 0.01
0.87 ( 0.05
0.45 ( 0.01
0.90 ( 0.18
0.29 ( 0.06
0.21 ( 0.06
2.7 ( 0.4
3.6 ( 0.8
1.2 ( 0.2
2.9 ( 0.8
2.0 ( 0.3
0.77 ( 0.15
23 ( 1
3,5-diMe-pyrazol-1-yl
imidazol-2-yl
7.5 ( 2.5
18 ( 8
2.3 ( 0.2
6.7 ( 1.6
4.3 ( 0.1
7.8 ( 1.8
1.0 ( 0.1
2.0 ( 0.4
18 ( 7
53 ( 1
19 ( 4
1-Me-imidazol-2-yl
4-Me-imidazol-2-yl
1-Et-imidazol-2-yl
1-Bn-imidazol-2-yl
5-Me-isoxazol-3-yl
thiazol-2-yl
7.1 ( 0.1
15 ( 4
85 ( 16
3.3 ( 0.1
0.81 ( 0.07
80 ( 28
100 ( 20
68 ( 4
2.3 ( 0.1
1.7 ( 0.0
35 ( 0
35 ( 1
21 ( 1
19 ( 5
thiazol-4-yl
10 ( 5
4-Me-thiazol-2-yl
5-Me-thiazol-2-yl
5-Me-thiazol-4-yl
benzothiazol-2-yl
3-Me-isothiazol-5-yl
3-Me-1,2,4-oxadiazol-5-yl
5-Me-1,2,4-oxadiazol-3-yl
1,2,4-triazol-3-yl
140 ( 50
100 ( 30
35 ( 4
40 ( 21
28 ( 14
21 ( 2
30 ( 7
24 ( 6
12 ( 5
>1000
>1000
250 ( 60
99 ( 3
210 ( 0
290 ( 20
140 ( 10
43 ( 2
130 ( 20
250 ( 10
110 ( 20
25 ( 3
11 ( 2
51 ( 8
12 ( 0
66 ( 6
16 ( 3
19 ( 5
2.8 ( 1.0
2.1 ( 0.5
0.39 ( 0.10
9.0 ( 0.8
0.19 ( 0.01
4.4 ( 0.0
6.5 ( 0.8
1-Me-1,2,4-triazol-3-yl
2-Me-1,2,4-triazol-3-yl
1-Pr-1,2,4-triazol-3-yl
2-Pr-1,2,4-triazol-3-yl
1-Me-tetrazol-5-yl
2-Me-tetrazol-5-yl
31 ( 4
11 ( 1
16 ( 2
5.2 ( 0.0
50 ( 1
2.5 ( 0.1
59 ( 11
57 ( 11
8.0 ( 0.0
2.8 ( 0.7
40 ( 6
78 ( 17
0.90 ( 0.02
78 ( 1
1.4 ( 0.1
21 ( 1
37 ( 1
60 ( 5
a See corresponding footnote in Table 1.
fold selectivity over R1. A 3-(dimethylamino)methyl (58)
and a 4-methyl sulfoxide (59) group also gave similar
affinities at R3 but reduced selectivity. However, 58 was
a partial inverse agonist at the R3 subunit. The 4-tri-
fluoromethoxy (60) and 3,4-methylenedioxy (61) ana-
logues were much lower in affinity.
Moving on to some nonaromatic substituents at the
6-position of the triazolophthalazines, it was found that
saturation of the pyridine ring of 1 to piperidines (62,
63) led to much reduced affinity, while a pyrrolidinone
(64) was also some 20-fold lower in affinity than 1 at
R3. When amides were put in the position of the pyridine
with various substituents on the nitrogen atom (65-
67), affinities were reduced by 3- to 7-fold compared to
1. Finally, simple hydroxyalkoxy substituents (68-71)
could have reasonable affinities with the optimum being
the hydroxybutoxy analogue (69), which had an affinity
of the same order as 1 at R3, but lower efficacy. There
was a significant difference in affinity between the
trans- and cis-4-(hydroxymethyl)cyclohexylmethoxy iso-
mers (70 and 71).
We then turned our attention to five-membered
heteroaromatic rings (Table 4). The furan and thiophene
analogues (72-74) had little affinity. However, the
1-pyrazole (75) had similar affinity to 1, which could
be increased further by 3,5-dimethyl substitution (76).
Although 76 was 10-fold selective in binding over R1,
both 75 and 76 had significantly higher efficacy at R1
than at R3. Indeed, 75 was a high partial agonist at R1
with zero efficacy at R3. The unsubstituted imidazole
(77) had similar affinity to 1, as did 78 and 79, in which
the imidazole was substituted with a methyl group in
either the 1- or 4-position. However, the 1-ethyl ana-
logue (80) had significantly higher affinity at the R3
subtype, while the 1-benzyl derivative (81) was not
much different. As expected, 81 had significantly higher
efficacy than 77-80, but in all compounds tested, the
efficacy at the R1 subunit was similar to that at the R3
subtype.
The isoxazole (82) had similar affinity to 1, as did the
two unsubstituted thiazoles (83 and 84). The efficacies
of 84 at R1 and R3 were the same but for 83 the efficacy
at R1 was significantly higher than at R3. Substitution
of the 2-thiazole (83) with methyl at either the 4- or
5-position (85 and 86) made little difference to the
affinity, and the 5-methyl analogue (87) of the 4-thiazole
had similar affinity to 84 itself. The benzo-fused deriva-
tive (88) had much lower affinity and the isothiazole
(89) had 8-fold lower affinity at the R3 subtype than 1.
The two oxadiazoles (90 and 91) possessed 4- to 5-fold
lower affinity than 1. The unsubstituted triazole (92)
had similar affinity to 1, and substituting in the
1-position with a methyl group (93) retained this, while
a larger propyl group (95) resulted in a fall in affinity.
On the other hand, a 2-methyl substituent (94) afforded
nearly a 7-fold increase in affinity over 92 at the R3
subtype, while a propyl group in this position (96) now
gave a further 2-fold increase in affinity. The tetrazoles
(97 and 98) both had similar or lower affinity than 1.
The interesting feature of the triazoles 93 and 96,

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1375
Table 5. Efficacies of
7,8,9,10-Tetrahydro-7,10-ethano-1,2,4-triazolo[3,4-a]phthalazines
at Cloned Human GABAA Receptor Subtypes
efficacy (%)a
compd
R1â3γ2
R2â3γ2
R3â3γ2
R5â3γ2
diazepam 103 ( 14 ( 8) 138 ( 11 (6) 118 ( 28 (6) 106 ( 3 (5)
1
51 ( 13 (5)
51 ( 7 (4)
14 ( 1 (4)
9 ( 2 (4)
36 ( 5 (4)
51 ( 1 (4)
38 ( 3 (4)
17 ( 4 (4)
41 ( 7 (4)
100 ( 18 (6)
53 ( 12 (4)
62 ( 10 (8)
-
23 ( 4 (4)
38 ( 7 (5)
43 ( 8 (5)
33 ( 5 (4)
40 ( 8 (6)
9 ( 7 (6)
20 ( 3 (5)
17 ( 4 (5)
7 ( 3 (6)
18 ( 7 (3)
3
-
-
4
7
-
-
14 ( 5 (4)
6 ( 2 (4)
31 ( 5 (3)
10
17
18
19
20
21
22
23
24
25
26
27
28
30
31
32
33
35
36
38
39
40
42
54
58
69
75
76
77
78
79
80
81
83
84
92
93
94
95
96
-
-
-
-
-
-
-
33 ( 9 (5)
74 ( 16 (5)
44 ( 9 (5)
52 ( 7 (4)
12 ( 1 (5)
-2 ( 2 (5)
17 ( 4 (6)
17 ( 5 (6)
29 ( 4 (4)
8 ( 3 (5)
-
-
-
36 ( 6 (5)
15 ( 3 (4)
-
-
-
-
-
-
-
-
-
-
-
34 ( 7 (4)
-
-
-
-
-
-
-
-
-
66 ( 9 (4)
77 ( 11 (4)
175 ( 26 (5)
178 ( 24 (4)
64 ( 11 (5)
-
-
46 ( 8 (5)
97 ( 21 (5)
Figure 1. The above image shows a three-dimensional graph
with the selective triazoles 93 and 96 illustrated as crosses.
The points are shaded and sized with respect to their selective
efficacy over R1 with the darker/larger points being the more
selective. The axes of the graph are the selective efficacy value
for the R3 subtype over R1 (A3-A1), the calculated polar
surface area (PSA), and the calculated pKa of the molecules
(ACD_PKA) using the ACDLabs desktop software version 6.0.
-
-
139 ( 22 (5) 50 ( 7 (3)
-
132 ( 9 (4)
-
35 ( 5 (4)
57 ( 11 (5) 39 ( 3 (3)
-
14 ( 3 (4)
27 ( 5 (4)
31 ( 1 (4)
14 ( 4 (6)
38 ( 8 (5)
-
-
-
-
-
-
-
45 ( 9 (5)
23 ( 7 (7)
-
-
-
-
23 ( 7 (3)
-
-16 ( 2 (4) -25 ( 2 (3)
-
-
20 ( 6 (6)
0 ( 6 (5)
7 ( 2 (4)
-
-
76 ( 8 (6)
31 ( 4 (4)
35 ( 7 (6)
24 ( 1 (4)
-
-
-
1 ( 6 (3)
-
29 ( 8 (6)
24 ( 6 (5)
28 ( 7 (5)
23 ( 6 (5)
100 ( 18 (6)
27 ( 7 (5)
33 ( 7 (5)
49 ( 10 (5)
88 ( 6 (4)
22 ( 6 (5)
83 ( 6 (4)
78 ( 16 (5)
-
-
-
-
-
26 ( 4 (4)
73 ( 8 (7)
84 ( 17 (5)
33 ( 3 (4)
-
-
-
-
-
-
-
-
-
-
-
26 ( 9 (7)
-
16 ( 2 (5)
26 ( 7 (2)
-
-
-
-
-
-
-
41 ( 5 (4)
a Modulation of the current in response to GABA at hGABAA
Figure 2. An image of the BZ binding site created from a
homology model derived from the published crystal structure
of the snail nACh binding protein with diazepam represented
in ball-and-stick mode while the protein backbone is repre-
sented by a ribbon.
receptors expressed in Xenopus oocytes. Data represents percent-
age increase (or decrease) of the EC20 GABA concentration in the
presence of a maximal concentration (∼100 × Ki) of the test
compound as measured by two electrode voltage-clamp electro-
physiology. Values are the mean ( SEM of at least three
independent determinations (with the actual number shown in
brackets).
of the compounds with the next most selectively effica-
cious compound being 81 (circled) which lies distant
from the triazoles and has too much agonism at the R1
subtype. The closest compound to the triazoles in terms
of PSA and ACD_pKa is compound 32 which does have
limited selective efficacy (a difference of 20%) but again
has too much agonism at the R1 subtype. Hence accept-
able selective efficacy was produced by compounds with
a PSA >85 and with a calculated pKa of between 2 and
3.
If one considers the environment of the benzodi-
azepine binding site then these relationships have more
meaning. Figure 2 shows an image of the binding site
created from a homology model derived from the pub-
lished crystal structure of the snail nACh binding
protein.29 The lighter ribbon on the left of the image
corresponds to the R subunit and one can see that one
however, was that, unlike any of the other substituents
at the 6-position, they showed significantly higher
efficacy at the R3 subtype compared to the R1 subtype.
Indeed, 93 was almost a full agonist at R3 but only a
very weak partial agonist at R1. In addition, it also
showed selectivity over the R2 subunit.
To determine what, if anything, distinguished the
selective triazole derivatives from other nonselective
analogues, the common molecular properties were cal-
culated for all compounds on which efficacy had been
measured at both the R1 and R3 subtypes. It was found
that when the polar surface area (PSA) (calculated using
the 2D methodology derived by Ertl et al.28) and pKa
(calculated by ACD) were considered, one can see in
Figure 1 that the triazoles lie apart from the remainder

1376 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
obtained from commercial sources and used as received unless
otherwise indicated.
side of the benzodiazepine binding site is created by a
â-sheet and loop domain. This part of the protein chain
extends all the way to the putative membrane spanning
domain and while some of this loop region is conserved,
there are interesting differences between the various R
subunits. It has been shown that mutating the R1
subunit in this region by changing Gly201 to Glu (the
corresponding residue found in the R3 subunit) has an
effect on the efficacy of CL218,872 (Chart 1) as well
as its affinity.30,31 The more conservative change of
Val203 to Ile also has been shown to affect affinity.32
There are other residues within this region which are
different between the R subtypes, e.g., Ile202Thr (in R2),
Gln204Arg (in R3), and Ser205Thr (in R5), all of which
have some change in polarity and may therefore be
affected by the changes in the polar nature of the
ligands. Further work on mutating the other residues
within this region may give a more detailed picture of
the requirements for selective efficacy as well as affinity
between all the subtypes.
In summary, these data clearly show that, despite a
wide variety of substituents at both the 3- and 6-posi-
tions of the central 7,8,9,10-tetrahydro-7,10-ethano-
1,2,4-triazolo[3,4-a]phthalazine core, it was not possible
to achieve greater than 12-fold binding selectivity (seen
for 57). In retrospect, this is possibly not surprising since
it has been hypothesised that it is the γ subunit, which
is constant between all four subtypes, that makes the
major contribution to the BZ site binding energy.33
Moreover, while compounds such as zolpidem and the
triazolopyridazine CL218,872 (Chart 1) have selectivity
in favor of the R1 subtype over the R2 and R3 subtypes
(Table 1), attributable to a single amino acid (R1G201/
R3E225),30 this is no better than our compounds in the
reverse direction (i.e., R2/R3 over R1 binding selectivity).
Most analogues in the current work showed no selectiv-
ity in terms of efficacy, although some did show partial
agonism at R1 and antagonism at R3 (e.g., 25 and 75).
Only two of the analogues tested (93 and 96) showed
significantly higher efficacy for the R3 subtype over the
R1 subtype. This was the first indication that we could
obtain functional selectivity in efficacy in the required
direction in this series and led us to focus on 1,2,4-
triazoles in subsequent work, which will be the subject
of further communications.
2,3,5,6,7,8-Hexahydro-5,8-ethanophthalazine-1,4-di-
one (99) and 1,4-dichloro-5,6,7,8-tetrahydro-5,8-ethano-
phthalazine (100) have been described by Street et al.27
6-Chloro-3-phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazine (101a) and 3-phenyl-6-(pyri-
din-2-ylmethoxy)-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazine (1) have been described by Carling
et al.17
6-Chloro-3-(2-methoxyphenyl)-7,8,9,10-tetrahydro-7,10-
ethano[1,2,4]triazolo[3,4-a]phthalazine (101b). A suspen-
sion of 100 (2.5 g, 10.9 mmol) in xylene (50 mL) with
2-methoxybenzoic hydrazide (2.01 g, 12.1 mmol) and triethyl-
amine (1.68 mL, 12.1 mmol) was heated under reflux for 4
days. The solvent was evaporated, and the residue was purified
by chromatography (silica gel, 0-40% EtOAc/CH2Cl2) to give
1.5 g (40%) of 101b as a solid: 1H NMR (250 MHz, DMSO-d6)
δ 1.41 (4H, m), 1.92 (4H, m), 3.43 (1H, s), 3.78 (3H, s), 3.82
(1H, s), 7.15 (1H, t, J ) 7.5 Hz), 7.28 (1H, d, J ) 8.4 Hz), 7.51
(1H, dd, J ) 7.5 and 1.7 Hz), 7.62 (1H, td, J ) 8.4 and 1.7
Hz); MS (ES+) m/z 341/343 [M + H]+.
Compounds 101c-h,j,k,o were prepared from 100 by a
method similar to that described for 101b using the corre-
sponding commercially available hydrazides.
1-Chloro-4-hydrazino-5,6,7,8-tetrahydro-5,8-ethano-
phthalazine (102) has been described by Street et al.27
N′-(4-Chloro-5,6,7,8-tetrahydro-5,8-ethanophthalazin-
1-yl)-4-fluorobenzohydrazide (103). To a solution of 102
(2.003 g, 8.91 mmol) in chloroform (40 mL) under nitrogen was
added triethylamine (1.24 mL, 8.90 mmol), and then dropwise
4-fluorobenzoyl chloride (1.07 mmol, 8.95 mmol), causing a
solid to start precipitating. The mixture was stirred at room
temperature for 4 h and then filtered. The collected solid was
washed twice with chloroform and then with diethyl ether and
dried under vacuum at 50 °C to afford 2.295 g (74%) of 103 as
a white solid: 1H NMR (250 MHz, CDCl3) δ 1.37 (4H, m), 1.85
(4H, m), 3.23 (1H, s), 3.43 (1H, s), 6.97 (2H, t, J ) 8.6 Hz),
7.60 (1H, br s), 7.89 (2H, dd, J ) 8.8 and 5.3 Hz), 10.90 (1H,
br s); MS (ES) m/z 347/349 [M + H]+.
6-Chloro-3-(4-fluorophenyl)-7,8,9,10-tetrahydro-7,10-
ethano[1,2,4]triazolo[3,4-a]phthalazine (101i). A solution
of 103 (1.0014 g, 2.89 mmol) in phosphorus oxychloride (7 mL)
was heated at reflux for 5 h. The solvent was evaporated and
ice-cold water (20 mL) was added to the residue. The aqueous
layer was neutralized to pH 7 with saturated aqueous sodium
hydrogen carbonate (6 mL), and the resulting solid was
collected by filtration, washed twice with water and then with
hexane, and dried under vacuum at 50 °C. This was purified
by flash chromatography (silica gel, 10% EtOAc/CH2Cl2) to give
0.5743 g (61%) of 101i as a white solid: 1H NMR (360 MHz,
CDCl3) δ 1.50 (4H, m), 1.98 (4H, m), 3.57 (1H, s), 4.06 (1H, s),
7.25 (2H, t, J ) 8.7 Hz), 8.50 (2H, dd); MS (ES+) m/z 329/331
[M + H]+.
Experimental Section
6-Chloro-3-(3-thienyl)-7,8,9,10-tetrahydro-7,10-ethano-
[1,2,4]triazolo[3,4-a]phthalazine (101l). To a solution of
3-thiophenecarboxylic acid (0.8 g, 6.25 mmol) in dichloro-
methane (30 mL) was added oxalyl chloride (0.645 mL, 7.39
mmol), followed by DMF (3 drops). The mixture was stirred
at room temperature for 1 h and then concentrated. Dichloro-
methane was added to the residue and evaporated twice. This
was then dissolved in dioxane (50 mL) with 102 (1.7 g, 5.7
mmol) and triethylamine (0.866 mL, 6.21 mmol). The mixture
was stirred at room temperature for 15 min and then heated
at reflux for 3 days. The solvent was evaporated, and the
residue was purified by flash chromatography (silica gel, 0-2%
MeOH/CH2Cl2) and recrystallized from EtOAc to afford 1.2 g
(50%) of 101l: 1H NMR (360 MHz, CDCl3) δ 1.49 (4H, m), 1.97
(4H, m), 3.57 (1H, s), 4.05 (1H, s), 7.49 (1H, dd, J ) 5.1 and
3.0 Hz), 8.10 (1H, dd, J ) 5.1 and 1.2 Hz), 8.60 (1H, m).
6-Chloro-3-(2-furyl)-7,8,9,10-tetrahydro-7,10-ethano-
[1,2,4]triazolo[3,4-a]phthalazine (101m). To a solution of
102 (1.0 g, 4.4 mmol) and triethylamine (0.68 mL, 4.9 mmol)
in dioxane (20 mL) was added portionwise 2-furoyl chloride
General Methods. Melting points were obtained on a
Reichert Thermovar hot stage and are uncorrected. Proton
NMR spectra were obtained using either a Bruker AM360 or
a Bruker AC250 spectrometer. Mass spectra were recorded on
a Quattro operating in an electrospray (ES) mode. (Note that
only the strongest peaks from the mass spectra are reported
below.) Elemental analysis for carbon, hydrogen, and nitrogen
were performed by Butterworth Laboratories Ltd. Unless
otherwise stated, high performance liquid chromatography
(HPLC) analysis was performed on a Hewlett-Packard HP1090
instrument using a Hichrom S5 ODS2 23 cm column, eluting
with acetonitrile/water (containing 0.2% triethylamine and
made to pH 3.5 with orthophosphoric acid). Analytical thin-
layer chromatography (TLC) was conducted on precoated silica
gel 60 F254 plates (Merck). Visualization of the plates was
accomplished by using UV light and/or iodine and/or aqueous
potassium permanganate solution. Chromatography was con-
ducted on silica gel 60, 220-440 mesh (Fluka), under low
pressure. Solutions were evaporated on a Bu¨chi rotary evapo-
rator under reduced pressure. All starting materials were

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1377
(0.44 mL, 4.4 mmol), and the mixture was stirred at room
temperature for 30 min and then heated at reflux for 36 h.
The solvent was replaced by xylene, and the mixture was
heated at reflux for a further 5 h. The solvent was evaporated,
and the residue was triturated with ethyl acetate to afford 1.07
g (82%) of 101m as a solid: MS (ES+) m/z 301 [M + H]+.
Methyl 4-methyl-1,3-thiazole-2-carboxylate (104). To a
solution of 4-methylthiazole (5 g, 50.4 mmol) in anhydrous
THF (200 mL) at -78 °C was added n-butyllithium (1.6 M
solution in hexane; 34.65 mL, 55.4 mmol) dropwise. The
solution was stirred at -78 °C for 1 h, at which point solid
carbon dioxide was passed through the solution for 20 min at
-78 °C. The solution was then allowed to warm to room
temperature over 2 h, and the precipitate was collected by
filtration, dissolved in methanol (200 mL), and added to
methanolic hydrogen chloride (200 mL). The solution was
stirred at room temperature overnight. The solvent was
evaporated, and diethyl ether was added to the residue. The
resultant solid was collected by filtration to yield 2.2 g (28%)
of 104 as a white solid: 1H NMR (250 MHz, DMSO-d6) δ 2.44
(3H, s), 3.89 (3H, s), 7.74 (1H, s); MS (ES+) m/z 158 [M + H]+.
was recrystallized from ethyl acetate-petroleum ether to give
0.410 g (67%) of 2 as a white solid: mp 208-210 °C; 1H NMR
(360 MHz, CDCl3) δ 1.49 (4H, m), 1.92 (4H, m), 3.54 (1H, s),
3.80 (3H, s), 3.99 (1H, s), 5.40 (2H, s), 7.05-7.11 (2H, m), 7.24
1H, m), 7.40 (1H, d, J ) 7.9 Hz), 7.51 (1H, td, J ) 7.6 and 1.8
Hz), 7.57 (1H, dd, J ) 7.5 and 1.8 Hz), 7.69 (1H, dt, J ) 7.7
and 1.8 Hz), 8.59 (1H, m); MS (ES+) m/z 414 [M + H]+. Anal.
[C24H23N5O2] C, H, N.
Compounds 3-16 were prepared in a similar manner from
the corresponding chlorides 101c-101p.
Compounds 17-26, 30-35, 40, 46, 52, 58, 59, 62-64, 68,
76, 78, 80-87, 89, and 91-94 were prepared using a method
similar to that described for 2 from 101a and the corresponding
alcohol. Where the alcohol was not commercially available,
their preparations are described below.
(3-Methylpyridin-2-yl)methanol, used to make 19, was
prepared in similar way to that described by Iqbal et al.34 (4-
Methylpyridin-2-yl)methanol, used to make 20, has been
prepared by Ku¨hler et al.35 (5-Methylpyridin-2-yl)methanol
used to make 21, has been prepared by Appel et al.36
2-({[tert-Butyl(dimethyl)silyl]oxy}methyl)pyridin-3-
ol (107). To 3-hydroxy-2-(hydroxymethyl)pyridine hydrochlo-
ride (15.0 g, 93 mmol) in DMF (500 mL) were added imidazole
(19.0 g, 0.28 mol) and tert-butyldimethylsilyl chloride (16.8 g,
0.11 mol) with stirring at room temperature. The mixture was
then stirred at 60 °C under nitrogen overnight. The solvent
was evaporated, and the crude product was partitioned
between water (200 mL) and dichloromethane (200 mL). The
aqueous phase was washed with more dichloromethane (2 ×
200 mL), and then the combined organic layers were washed
with water (200 mL) and with saturated sodium chloride
solution (200 mL), dried (MgSO4), and evaporated. The re-
sidual material was purified by flash chromatography (silica
gel, 5-20% EtOAc/hexane, yielding 8.5 g (38%) of 107 as a
colorless solid: 1H NMR (250 MHz, CDCl3) δ 0.17 (6H, s), 0.94
(9H, s), 5.08 (2H, s), 7.07-7.18 (2H, m), 8.03 (1H, dd, J ) 4.4
and 1.6 Hz), 8.66 (1H, br s); MS (ES+) m/z 240 [M + H]+.
2-({[tert-Butyl(dimethyl)silyl]oxy}methyl)pyridin-3-
yl Trifluoromethanesulfonate (108). To 107 (11.5 g, 48.2
mmol) in dichloromethane (200 mL) was added N,N-diiso-
propylethylamine (8.38 mL, 6.22 g, 48 mmol) dropwise with
stirring. The mixture was then cooled to -10 °C (salt-ice bath),
and trifluoromethanesulfonic anhydride (8.09 mL, 13.6 g, 48
mmol) was added dropwise with stirring. The solution was
stirred at -10 °C for 1 h and then was allowed to warm to
room temperature and stirred under nitrogen for 24 h. The
solution was washed with water (3 × 200 mL), and then the
combined aqueous layers were extracted with dichloromethane
(200 mL). The combined organic layers were dried (MgSO4)
and evaporated. The residual brown oil was purified by flash
chromatography (silica gel, 5-10% EtOAc/hexane, yielding
15.1 g (84%) of 108 as a pale yellow oil: 1H NMR (250 MHz,
CDCl3) δ 0.11 (6H, s), 0.90 (9H, s), 4.92 (2H, s), 7.32-7.38 (1H,
m), 7.63 (1H, dd, J ) 8.4, 1.3 Hz), 8.49 (1H, m); MS (ES+) m/z
372 [M + H]+.
3-Allyl-2-({[tert-butyl(dimethyl)silyl]oxy}methyl)-
pyridine (109). To 108 (5.00 g, 13.5 mmol) in DMF (100 mL)
were added tetraallyltin (6.47 mL, 7.63 g, 27 mmol) and
lithium chloride (1.17 g, 28 mmol), and the mixture was
degassed by bubbling nitrogen through for 15 min. Bis-
(triphenylphosphine)palladium(II) chloride (949 mg, 1.35 mmol)
was added, and the mixture was degassed as before and then
was heated at 80 °C under nitrogen for 12 h. The mixture was
filtered to remove inorganics, and then the filtrate was diluted
with water (200 mL) and washed with hexane (3 × 200 mL).
The combined organic layers were washed with water (200 mL)
and then with saturated sodium chloride solution (200 mL),
dried (MgSO4), and evaporated to give a yellow oil. This was
purified by flash chromatography (silica gel, 5-20% EtOAc/
hexane) to yield 2.79 g (79%) of 109 as a colorless oil: 1H NMR
(250 MHz, CDCl3) δ 0.07 (6H, s), 0.89 (9H, s), 3.57 (2H, d, J )
6.5 Hz), 4.84 (2H, s), 5.00-5.14 (2H, m), 5.88-5.04 (1H, m),
7.15-7.20 (1H, m), 7.51 (1H, dd, J ) 7.7 and 1.6 Hz), 8.39
(1H, dd, J ) 4.8 and 1.7 Hz); MS (ES+) m/z 264 [M + H]+.
4-Methyl-1,3-thiazole-2-carbohydrazide (105). To a so-
lution of 104 (2.1 g, 13.4 mmol) in methanol (20 mL) was added
hydrazine hydrate (3.2 mL, 65.8 mmol) dropwise over 30 min.
The mixture was stirred for 1.5 h and the precipitate collected
by filtration and washed with diethyl ether to afford 1.6 g
(76%) of 105 as a white solid: 1H NMR (250 MHz, DMSO-d6)
δ 2.64 (3H, s), 4.82 (2H, bs), 7.79 (1H, s), 10.25 (1H, bs); MS
(ES+) m/z 158 [M + H]+.
6-Chloro-3-(4-methyl-1,3-thiazol-2-yl)-7,8,9,10-tetrahy-
dro-7,10-ethano[1,2,4]triazolo[3,4-a]phthalazine (101n).
This was prepared in 17% yield using a method similar to that
described for 101b but using 105 instead of 2-methoxybenzoic
hydrazide and triethylamine hydrochloride instead of tri-
ethylamine: 1H NMR (250 MHz, DMSO-d6) δ 1.41 (4H, m),
1.94 (4H, m), 2.54 (3H, s), 3.48 (1H, s), 3.85 (1H, s), 7.66 (1H,
s); MS (ES+) m/z 332/334 [M + H]+.
N′-(4-Chloro-5,6,7,8-tetrahydro-5,8-ethanophthalazin-
1-yl)morpholine-4-carbohydrazide (106). To a solution of
102 (1.024 g, 4.56 mmol) in chloroform (20 mL) under nitrogen
was added triethylamine (0.635 mL, 4.56 mmol), followed by
freshly distilled 4-morpholinecarbonyl chloride (0.532 mL, 4.56
mmol) and the mixture was stirred at room temperature for
24 h. The solvent was evaporated, and the residue was purified
by flash chromatography (silica gel, 4% MeOH/CH2Cl2) to give
1.265 g (82%) of 107 as an off-white solid: 1H NMR (360 MHz,
CDCl3) δ 1.38 (4H, m), 1.85 (4H, m), 3.16 (1H, s), 3.40 (1H, s),
3.53 (4H, t, J ) 5.2 Hz), 3.71 (4H, t, J ) 5.1 Hz), 6.85 (1H, br
s), 8.53 (1H, br s); MS (ES) m/z 338/340 [M + H]+.
6-Chloro-3-morpholin-4-yl-7,8,9,10-tetrahydro-7,10-
ethano[1,2,4]triazolo[3,4-a]phthalazine (101p). A solution
of 106 (0.4021 g, 1.19 mmol) in phosphorus oxychloride (5 mL)
under nitrogen was heated at reflux for 2 h. The solvent was
evaporated, and a little water and dichloromethane were added
to the residue. The aqueous layer was neutralized to pH 8 with
saturated aqueous sodium hydrogen carbonate (21 mL), and
the mixture was extracted with dichloromethane (3 × 50 mL).
The combined extracts were washed with saturated aqueous
NaCl solution (30 mL), dried (Na2SO4), and evaporated. The
residue was purified by flash chromatography (silica gel, 2%
MeOH/CH2Cl2) to give 0.2426 g (64%) of 101p as a yellow
solid: 1H NMR (250 MHz, CDCl3) δ 1.44 (4H, m), 1.92 (4H,
m), 3.48 (1H, s), 3.67 (4H, t, J ) 4.9 Hz), 3.94 (5H, m); MS
(ES+) m/z 320/322 [M + H]+.
3-(2-Methoxyphenyl)-6-(pyridin-2-ylmethoxy)-7,8,9,10-
tetrahydro-7,10-ethano[1,2,4]triazolo[3,4-a]phthal-
azine (2). To a solution of 2-pyridylcarbinol (0.199 mL, 2.06
mmol) in DMF (25 mL) was added sodium hydride (60%
dispersion in oil, 80 mg, 2.00 mmol), and the reaction mixture
was stirred at room temperature for 15 min. After this time,
101b (0.50 g, 1.47 mmol) was added and the reaction mixture
was stirred at room temperature for 75 min. Water was added
until the solution became cloudy, and after stirring for a
further 45 min, a solid was collected by filtration. This solid

1378 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
(3-Allylpyridin-2-yl)methanol (110). A solution of 109
(2.50 g, 9.51 mmol) in 1 M tetrabutylammonium fluoride
solution in THF (25 mL) was stirred at room temperature for
25 min. The solvent was removed in vacuo, and the residue
was taken up in water (50 mL). The resulting solution was
washed with dichloromethane (3 × 50 mL). The combined
organic layers were washed with saturated sodium chloride
solution (50 mL), dried (MgSO4), and evaporated. The residual
yellow oil was purified by flash chromatography (silica gel, 50%
EtOAc/isohexane), yielding 1.10 g (77%) of 110 as a colorless
oil: 1H NMR (250 MHz, CDCl3) δ 3.30 (2H, d, J ) 6.3 Hz),
4.73 (2H, s), 4.99-5.17 (2H, m), 5.81-5.97 (1H, m), 7.18-7.23
(1H, m), 7.51 (1H, dd, J ) 7.6 and 1.5 Hz), 8.45 (1H, dd, J )
4.9 and 1.5 Hz); MS (ES+) m/z 150 [M + H]+.
(3-Propylpyridin-2-yl)methanol (111). A solution of 110
(400 mg, 2.68 mmol) in ethyl acetate (10 mL) was hydro-
genated over 10% palladium on carbon (40 mg) at 30 psi on a
Parr apparatus for 30 min. The catalyst was separated by
filtration, and the filtrate was evaporated, yielding 371 mg
(92%) of 111 as a pale yellow oil: 1H NMR (250 MHz, CDCl3)
δ 0.98 (3H, t, J ) 7.3 Hz), 1.55-1.70 (2H, m), 2.49 (2H, t, J )
7.7 Hz), 4.74 (2H, s), 7.16-7.21 (1H, m), 7.49 (1H, dd, J ) 7.6
and 0.9 Hz), 8.41 (1H, d, J ) 4.0 Hz); MS (ES+) m/z 152 [M +
H]+. This was used to prepare 23.
3,6-Dimethylpyridine-2-carbonitrile (112). To 2,5-di-
methylpyridine 1-oxide16 (12.5 g, 0.102 mol) in dichloromethane
(180 mL) was added trimethylsilyl cyanide (14.3 mL, 10.6 g,
0.107 mol) with stirring at room temperature. The mixture
was stirred at room temperature under nitrogen for 25 min,
N,N-diethylcarbamoyl chloride (13.6 mL, 14.6 g, 0.107 mol)
was added, and the solution was stirred as before for 4 days.
Aqueous potassium carbonate (400 mL of 10% solution) was
added, and the mixture was stirred vigorously for 15 min. The
aqueous phase was separated and washed with dichloro-
methane (3 × 200 mL). The combined organic layers were
washed with more 10% potassium carbonate solution (200 mL)
and then with saturated sodium chloride solution (200 mL),
dried (Na2SO4), and evaporated. The residual brown oil was
purified by flash chromatography (silica gel, 5-20% EtOAc/
hexane) yielding 9.72 g (72%) of 112 as a colorless low melting
point solid: 1H NMR (250 MHz, CDCl3) δ 2.52 (3H, s), 2.56
(3H, s), 7.28 (1H, d, J ) 8.0 Hz), 7.56 (1H, d, J ) 8.0 Hz); MS
(ES+) m/z 133 [M + H]+.
(3,6-Dimethylpyridin-2-yl)methanol (113). A solution of
112 (1.15 g, 8.71 mmol) in 2 N hydrochloric acid (20 mL) was
hydrogenated at 30 psi over 10% palladium on carbon (200
mg) for 2 h. The catalyst was removed by filtration, and the
filtrate was basified by the addition of saturated sodium
hydrogen carbonate solution. The resulting mixture was
washed with ethyl acetate (3 × 50 mL), and then the combined
organic layers were dried (MgSO4) and evaporated, yielding
0.68 g (57%) of 113 as a yellow oil: 1H NMR (250 MHz, CDCl3)
δ 2.16 (3H, s), 2.52 (3H, s), 4.64 (2H, s), 6.98 (1H, d, J ) 7.6
Hz), 7.35 (1H, d, J ) 7.6 Hz); MS (ES+) m/z 138 [M + H]+.
This was used to prepare 24.
chloride solution (100 mL), dried (MgSO4), and evaporated to
give 2.40 g (43%) of 114 as a dark brown solid: 1H NMR (250
MHz, CDCl3) δ 0.35 (2H, m), 0.65 (2H, m), 1.26 (1H, m), 3.85
(2H, d, J ) 6.8 Hz), 4.33 (1H, br s), 4.77 (2H, s), 7.13 (2H, m),
8.13 (1H, m); MS (ES+) m/z 180 [M + H]+. This was used to
prepare 33.
The (3-alkoxypyridin-2-yl)methanols 115-117 were pre-
pared by the same procedure as that described for 114
employing the corresponding alkyl halide and used to synthe-
size 30-32, respectively.
[3-(Cyclobutyloxy)pyridin-2-yl]methanol (118). 3-Hy-
droxy-2-hydroxymethylpyridine hydrochloride (1.57 g, 9.73
mmol), cyclobutyl bromide (5.00 g, 37.0 mmol), and potassium
carbonate (8.09 g, 58.5 mmol) were stirred together in DMF
(20 mL) at 50 °C for 24 h. Water (40 mL) was added, and the
resulting mixture was acidified by the addition of 5 N
hydrochloric acid and was then washed with dichloromethane
(3 × 100 mL). The aqueous phase was basified with 4 N sodium
hydroxide solution and washed with more dichloromethane (3
× 100 mL). The combined organic layers from the second
extraction were washed with water (100 mL), dried (MgSO4),
and evaporated. The residual pale brown solid was recrystal-
lized from hexane, yielding 443 mg (25%) of 118 as a tan
colored solid: 1H NMR (250 MHz, CDCl3) δ 1.62-1.96 (2H,
m), 2.10-2.25 (2H, m), 2.40-2.52 (2H, m), 4.31 (1H, br s),
4.60-4.71 (1H, m), 4.74 (2H, s), 6.97 (1H, dd, J ) 8.2 and 1.2
Hz), 7.14 (1H, dd, J ) 8.2 and 4.8 Hz), 8.13 (1H, dd, J ) 4.8
and 1.1 Hz); MS (ES+) m/z 180 [M + H]+. This was used to
prepare 34.
[3-(Benzyloxy)pyridin-2-yl]methanol used to prepare 35 has
been synthesized by Takeda et al.38 {3-[(Dimethylamino)-
methyl]phenyl}methanol used to make 58 has been prepared
by Brown and Ife.39 [4-(Methylsulfinyl)phenyl]methanol used
to make 59 has been prepared by Samanen and Brandeis.40
3-Methyl-6-vinylpyridazine (119). A solution of 3-chloro-
6-methyl pyridazine (20 g, 156 mmol), tetravinyltin (50 mL,
264 mmol), and lithium chloride (13.2 g, 311 mmol) in DMF
(250 mL) was degassed with nitrogen for 10 min. The flask
was then evacuated and refilled with nitrogen before adding
dichlorobis(triphenylphosphine)palladium(II) (11.0 g, 15.6
mmol). The mixture was heated at 100 °C overnight. The
solvent was evaporated, and water (100 mL) and dichloro-
methane (100 mL) was added to the residue. The mixture was
filtered, and the aqueous layer was extracted further with
dichloromethane (100 mL). The combined organic extracts
were dried (MgSO4) and evaporated. The residue was purified
by flash chromatography (silica gel, 0-5% MeOH/CH2Cl2) to
give 8.37 g (45%) of 119: 1H NMR (360 MHz, CDCl3) δ 2.71
(3H, s), 5.63 (1H, d, J ) 11.1 Hz), 6.71 (1H, d, J ) 17.8 Hz),
7.03 (1H, dd, J ) 17.8 and 11.0 Hz), 7.28 (1H, d, J ) 8.8 Hz),
7.49 (1H, d, J ) 8.7 Hz).
6-Methylpyridazine-3-carbaldehyde (120). A solution of
119 (8.37 g, 69.8 mmol) in dichloromethane (200 mL) cooled
to -78 °C was treated with ozone for 5 h. The mixture was
then allowed to warm to room temperature overnight before
it was recooled to -78 °C and nitrogen bubbled through it for
10 min. Dimethyl sulfide (5 mL) was added and the mixture
left for 1 h and then warmed to room temperature. The
mixture was diluted with water (100 mL) and neutralized with
saturated aqueous NaHCO3. The aqueous layer was further
extracted with dichloromethane (2 × 100 mL), and the
combined organic extracts were dried (MgSO4) and evaporated
to afford 0.50 g (6%) of 120: 1H NMR (250 MHz, CDCl3) δ
2.85 (3H, s), 7.52 (1H, d, J ) 8.5 Hz), 7.94 (1H, d, J ) 8.6 Hz),
10.37 (1H, s); MS (ES+) m/z 123 [M + H]+.
(3,5-Dimethylpyridin-2-yl)methanol was prepared by a simi-
lar procedure to that described by Ku¨hler et al.35 and used to
make 25. (3,4-Dimethylpyridin-2-yl)methanol was prepared by
the method of Katz et al.37 and used to make 26.
[3-(Cyclopropylmethoxy)pyridin-2-yl]methanol (114).
Potassium hydroxide (5.2 g, 0.093 mol) was ground to a powder
under nitrogen, added to DMSO (30 mL) and stirred for 20
min under nitrogen at room temperature. The mixture was
cooled to 0 °C, and 2-(hydroxymethyl)pyridin-3-ol hydrochlo-
ride (5.0 g, 0.031 mol) was added. The slurry was stirred at 0
°C for 1 h before the addition of cyclopropylmethyl bromide
(3.01 mL, 4.2 g, 0.031 mol). The mixture was allowed to warm
to room temperature and stirred under nitrogen overnight.
Water (100 mL) was added, and the resultant solution was
acidified to pH 1 with hydrochloric acid (5 N). The solution
was washed with dichloromethane (3 × 100 mL), basified to
pH 14 with sodium hydroxide solution (4 N), and extracted
with dichloromethane (3 × 100 mL). The organic extracts were
combined, washed with water (100 mL), and saturated sodium
(6-Methylpyridazin-3-yl)methanol (121). To a solution
of 120 (0.50 g, 4.07 mmol) in methanol (10 mL) at 0 °C under
nitrogen was added sodium borohydride (0.05 g, 1.30 mmol),
and the solution was stirred at 0 °C for 1 h. Saturated aqueous
NaCl (5 mL) was added, and the mixture was stirred at room
temperature for 15 min. The methanol was evaporated, and
the aqueous residue was extracted with ethyl acetate (3 × 50
mL). The organic extracts were combined, dried (Na2SO4), and
evaporated to give 370 mg (73%) of 121 as an oil: 1H NMR

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1379
(360 MHz, CDCl3) δ 2.69 (3H, s), 4.94 (2H, s), 7.33 (1H, d, J )
8.6 Hz), 7.41 (1H, d, J ) 8.6 Hz); MS (ES+) m/z 125 [M + H]+.
This was used to prepare 40.
1-Ethyl-2-(hydroxymethyl)imidazole was prepared according
to the procedure of Tasaka et al.41 and used to prepare 80.
1,3-Thiazol-2-ylmethanol has been prepared by Dondoni and
Perrone42 and was used to make 83. 4-Hydroxymethylthiazole
has been prepared by Houssin et al.43 and was used to prepare
84.
(4-Methyl-1,3-thiazol-2-yl)methanol (123). To a solution
of 4-methyl-1,3-thiazole-2-carbaldehyde (122)20 (2.23 g, 0.0175
mmol) in methanol (50 mL) was added sodium borohydride
(0.664 g, 0.0175 mmol). After 1 h, the mixture was evaporated
and the residue was partitioned between dichloromethane and
water. The organic layer was washed with brine, dried
(MgSO4), and evaporated to afford 1.12 g (35%) of 123: 1H
NMR (250 MHz, CDCl3) δ 2.42 (3H, d, J ) 1.1 Hz), 3.74 (1H,
br s), 4.90 (2H, s), 6.84 (1H, q, J ) 1.0 Hz). This was used to
prepare 85.
(5-Methyl-1,3-thiazol-2-yl)methanol (125). This was pre-
pared by the same procedure as that described for 123 but
using 5-methyl-1,3-thiazole-2-carbaldehyde (124).21 Yield
65%: 1H NMR (250 MHz, CDCl3) δ 2.46 (3H, d, J ) 1.0 Hz),
3.70 (1H, br s), 4.85 (2H, s), 7.35 (1H, q, J ) 1.2 Hz). This was
used to prepare 86.
4,5-Dimethyl-1,3-thiazole 3-oxide (126). To a solution of
4,5-dimethylthiazole (20 g, 0.177 mol) in dichloromethane (100
mL) at 0 °C was added slowly a solution of 3-chloroperoxy-
benzoic acid (60 g) in dichloromethane (400 mL), and the
mixture was stirred at room temperature overnight. 4 N
Aqueous NaOH solution (40 mL) was added, and the pH was
adjusted to 8-9. The aqueous layer was extracted several more
times with dichloromethane, and the combined organic ex-
tracts were dried (MgSO4) and evaporated. The residue was
triturated with diethyl ether, and the resulting solid was
collected by filtration to give 4.8 g (21%) of 126: 1H NMR (360
MHz, CDCl3) δ 2.30 (3H, s), 2.39 (3H, s), 8.07 (1H, s).
(5-Methyl-1,3-thiazol-4-yl)methanol (127). Solid 126 (4.8
g) was added in portions to a solution of acetic anhydride (30
mL) at 110 °C. The mixture was then stirred at 110 °C
overnight, and the product was isolated by distillation: bp 115
°C (0.22 mbar). This was dissolved in methanolic HCl (100 mL)
and left to stand overnight. The solvent was evaporated, and
the residue was partitioned between 4 N aqueous NaOH
solution (20 mL) and dichloromethane. The organic layer was
washed with brine, dried (MgSO4), and evaporated to leave
900 mg (19%) of crude 127: 1H NMR (250 MHz, CDCl3) δ 2.48
(3H, s), 3.41 (1H, br s), 4.71 (2H, s), 8.58 (1H, s). This was
used to prepare 87.
1H NMR (360 MHz, CDCl3) δ 2.61 (3H, s), 3.67 (1H, br t), 4.76
(2H, d, J ) 5.0 Hz). This was used to make 91.
1H-1,2,4-Triazol-5-ylmethanol was prepared as described by
Jones and Ainsworth45 and used to make 92. (1-Methyl-1H-
1,2,4-triazol-3-yl)methanol and (1-methyl-1H-1,2,4-triazol-5-
yl)methanol were prepared using the conditions described by
Itoh and Okonogi46 and used to make 93 and 94, respectively.
3-Phenyl-6-(1H-pyrazol-1-ylmethoxy)-7,8,9,10-tetrahy-
dro-7,10-ethano[1,2,4]triazolo[3,4-a]phthalazine (75). This
compound was prepared using the procedure described for 2
using 1-(hydroxymethyl)pyrazole47 and adding 101a at the
same time as the sodium hydride in order to yield the correct
product. Yield 64%: mp 196 °C (EtOAc-hexane); 1H NMR (360
MHz, DMSO-d6) δ 1.47 (4H, m), 1.99 (4H, m), 3.38 (1H, s),
3.87 (1H, s), 6.51 (1H, m), 6.62 (2H, s), 7.73 (4H, m), 8.18 (1H,
m), 8.60 (2H, m); MS (ES+) m/z 373 [M + H]+. Anal.
[C21H20N6O] C, H, N.
6-(1H-Imidazol-2-ylmethoxy)-3-phenyl-7,8,9,10-tetrahy-
dro-7,10-ethano[1,2,4]triazolo[3,4-a]phthalazine (77). This
was prepared as for 2 using (1-{[2-(trimethylsilyl)ethoxy]-
methyl}-1H-imidazol-2-yl)methanol (129),27 but followed by an
additional step in which the product was stirred at 50 °C in 5
N hydrochloric acid for 90 min before evaporation and recrys-
tallization from ethyl acetate/methanol. Yield 58%: mp 219
°C (dec) (EtOAc-MeOH); 1H NMR (360 MHz, DMSO-d6) δ 1.42
(4H, m), 1.91 (4H, m), 3.51 (1H, s), 3.78 (1H, s), 5.84 (2H, s),
7.59 (3H, m), 7.76 (2H, s), 8.23 (2H, m); MS (ES+) m/z 373 [M
+ H]+. Anal. [C21H20N6O‚2HCl‚0.7H2O] C, H, N.
(4-Methyl-1-{[2-(trimethylsilyl)ethoxy]methyl}-1H-imid-
azol-2-yl)methanol (130a) and (5-Methyl-1-{[2-(trimeth-
ylsilyl)ethoxy]methyl}-1H-imidazol-2-yl)methanol (130b).
This mixture of compounds was prepared in an analogous
manner to 129 from 4- and 5-methyl-1-{[2-(trimethylsilyl)-
ethoxy]methyl}-1H-imidazole-2-carbaldehyde.23 Yield 87%: 1H
NMR (250 MHz, CDCl3) δ 0.00 (9H, s), 0.91 (2H, m), 2.18 and
2.25 (3H, two s), 3.53 (2H, m), 4.66 and 4.68 (2H, two s), 5.30
and 5.33 (2H, two s), 6.65 and 6.69 (1H, two s); MS (ES+) m/z
243 [M + H]+.
6-[(4-Methyl-1H-imidazol-2-yl)methoxy]-3-phenyl-
7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo[3,4-a]-
phthalazine (79). This compound was prepared using the
procedure described for 77 using 130a/130b. Yield 34%: mp
1
220 °C (dec) (EtOH-EtOAc); H NMR (360 MHz, DMSO-d6)
δ 1.43 (4H, m), 1.91 (4H, m), 2.29 (3H, s), 3.50 (1H, s), 3.77
(1H, s), 5.80 (2H, s), 7.43 (1H, s), 7.59 (3H, m), 8.28 (2H, m);
MS (ES+) m/z 387 [M + H]+. Anal. [C22H22N6O‚2HCl‚1.8H2O‚
0.2C4H8O2] C, H, N.
3-Phenyl-6-(pyridin-3-yloxy)-7,8,9,10-tetrahydro-7,10-
ethano[1,2,4]triazolo[3,4-a]phthalazine (45). This com-
pound was prepared as part of a rapid analogue library using
the following methodology. To 3-hydroxypyridine (50 mg, 0.526
mmol) in a test tube with a ground glass joint sealed with a
septum under nitrogen was added a solution of 101a (50 mg,
0.161 mmol) in DMF (1.5 mL), followed by lithium bis-
(trimethylsilyl)amide (1 M solution in hexanes, 0.50 mL, 0.50
mmol). The reaction was stirred at room temperature for 18
h. The mixture was poured into water (10 mL), and the
precipitate formed was isolated by filtration and dried in a
vacuum oven at 80 °C to yield 20 mg (34%) of 45: MS (ES+)
m/z 370 [M + H]+; HPLC >99% (RT 3.68 min, 50% acetonitrile/
pH 3.5 phosphate buffer).
(3-Methylisothiazol-5-yl)methanol has been prepared by
Layton and Lunt44 and was used to make 89.
(5-Methyl-1,2,4-oxadiazol-3-yl)methanol (128). To a so-
lution of N′-hydroxy-2-(tetrahydro-2H-pyran-2-yloxy)ethan-
imidamide22 (7.0 g, 0.040 mol) in THF (100 mL) with 3 Å
molecular sieves (20 g) was added sodium hydride (60%
dispersion in oil, 3.2 g, 0.080 mol), and the mixture was heated
at 50 °C for 1 h. Ethyl acetate (3.9 mL, 0.040 mol) was added,
and the mixture was stirred for a further 2 h. After cooling,
the mixture was partitioned between water (100 mL) and
dichloromethane (200 mL). The aqueous layer was extracted
further with dichloromethane, and the combined organic
extracts were washed with brine, dried (MgSO4), and evapo-
rated. The residue was dissolved in methanol (300 mL), and
pyridinium p-toluenesulfonate (1.2 g, 4.8 mmol) was added.
The mixture was stirred at room-temperature overnight and
then evaporated. The residue was dissolved in dichloromethane,
washed with water, dried (MgSO4), and evaporated. This was
redissolved in methanol, treated with p-toluenesulfonic acid
(50 mg, 0.26 mmol), and stirred overnight at room tempera-
ture. The solvent was evaporated, and the residue was
partitioned between dichloromethane and saturated aqueous
NaHCO3 solution. The organic layer was dried (MgSO4) and
evaporated. The residue was purified by flash chromatography
(silica gel, 0-2% MeOH/CH2Cl2) to give 520 mg (11%) of 128:
Compounds 47, 56, 57, 60, 61, 69, 72-74 were prepared by
the same method as described for 45.
(trans- and cis-4-{[(3-Phenyl-7,8,9,10-tetrahydro-7,10-
ethano[1,2,4]triazolo[3,4-a]phthalazin-6-yl)oxy]methyl}-
cyclohexyl)methanol (70 and 71). These compounds were
prepared as for 45 using a mixture of cis- and trans-1,4-
cyclohexanedimethanol to give a 67% yield of 70 and 71 as an
82:18 mixture, which was separated by preparative HPLC on
a Pirkle-type dinitrobenzyl-D-phenylglycine chiral stationary
phase column (250 × 10 mm i.d.) eluting at 6 mL/min with
2% MeOH/chlorobutane.
70: MS (ES+) m/z 419 [M + H]+, HPLC >99.5% (tR 12.68
min, using a Pirkle-type dinitrobenzyl-D-phenylglycine chiral

1380 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
stationary phase column, a flow rate of 1.5 mL/min, and
eluting with 2% MeOH/chlorobutane).
2-Methylpyrimidine (136). A mixture of 135 (14.0 g, 66.6
mmol), sodium chloride (17.1 g, 293 mmol), and water (5.24
mL) were heated together in DMSO (50 mL) at 160 °C
overnight. The solution was allowed to cool and the inorganic
material filtered off. The filtrate was distilled at atmospheric
pressure, and the fraction boiling between 95 and 112 °C was
collected. The distillate was redistilled at atmospheric pres-
sure, collecting the fraction boiling between 97 and 99 °C to
give 1.41 g (17%) of 136 and dimethyl sulfide as a 2:1 mixture.
This material was used in the next step without further
71: MS (ES+) m/z 419 [M + H]+, HPLC >99.5% (tR 11.06
min, using a Pirkle-type dinitrobenzyl-D-phenylglycine chiral
stationary phase column, a flow rate of 1.5 mL/min, and
eluting with 2% MeOH/chlorobutane).
3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo-
[3,4-a]phthalazin-6-ol (131). To a solution of 101a (3.0 g,
9.6 mmol) in 10% aqueous 1,4-dioxane (100 mL) was added 2
N sodium hydroxide solution (24 mL, 48 mmol), and the
reaction mixture was heated under reflux for 3 days. The
organic solvent was removed by rotary evaporation, and the
residue was partitioned between water (250 mL) and diethyl
ether (250 mL). The aqueous layer was separated, washed
twice more with diethyl ether (100 mL), and then treated with
5 N aqueous hydrochloric acid until a pH of 2 was attained.
The solid which precipitated out of solution was collected by
filtration to give 2.7 g (96%) of 131 as a white solid: mp ∼
300 °C (dec); 1H NMR (250 MHz, CDCl3) δ 1.35 (4H, m), 2.00
(4H, m), 3.49 (1H, s), 3.84 (1H, s), 7.71 (3H, m), 8.54 (2H, d, J
) 7.8 Hz); MS (ES+) m/z 293 [M + H]+.
2-(Chloromethyl)nicotinonitrile (132). To 2-methyl-
nicotinonitrile20 (2.0 g, 16.9 mmol) in chloroform (30 mL) at
reflux was added trichloroisocyanuric acid (1.57 g, 6.75 mmol)
in portions, and the mixture was heated at reflux overnight.
After cooling, the mixture was filtered, and the filtrate was
diluted with dichloromethane, washed with sodium hydroxide
solution and then brine, dried (MgSO4), and evaporated to give
1.5 g of impure 132, which by NMR contained ∼19% starting
material and 7% dichlorinated product: 1H NMR (360 MHz,
CDCl3) δ 4.85 (2H, s), 7.43 (1H, dd, J ) 7.9 and 4.9 Hz), 8.02
(1H, dd, J ) 7.9 and 1.7 Hz), 8.81 (1H, dd, J ) 4.9 and 1.7
Hz).
1
purification. H NMR (250 MHz, CDCl3) δ 2.70 (3H, s), 7.13
(1H, t, J ) 4.9 Hz), 8.66 (2H, d, J ) 4.9 Hz); MS (ES+) m/z 95
[M + H]+.
2-(Chloromethyl)pyrimidine (137). This was prepared as
for 132 from impure 136 (0.57 g) to give 0.11 g of 137 as a
pale orange/brown oil, which by NMR contained ∼16% starting
material: 1H NMR (250 MHz, CDCl3) δ 4.77 (2H, s), 7.27 (1H,
t, J ) 4.9 Hz), 8.79 (2H, d, J ) 4.9 Hz); MS (ES+) m/z 129 [M
+ H]+. This was used to prepare 37.
2-Chloromethylquinoxaline and 2-(1-chloroethyl)pyridine
were prepared as described by Jeromin et al.49 and used to
prepare 44 and 48, respectively.
5-(Chloromethyl)-3-methyl-1,2,4-oxadiazole (143). To a
solution of acetamide oxime (1 g, 0.0135 mol) in dichloro-
methane (30 mL) was added triethylamine (2.06 mL, 0.015
mol) and the mixture was cooled to 0 °C. Chloroacetyl chloride
(1.18 mL, 0.015 mol) was added dropwise over 5 min. The
reaction was stirred at 0 °C for 10 min and then at room
temperature for 1 h. The reaction was diluted with dichloro-
methane (40 mL) and washed with water (2 × 30 mL) and
then brine (30 mL). The organic layer was dried (MgSO4),
filtered, and evaporated to yield the crude 143. This was used
to prepare 90.
2-{[(3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazin-6-yl)oxy]methyl}nicotino-
nitrile (27). To a stirred solution of 131 (0.3 g, 1.0 mmol) in
DMF (20 mL) was added sodium hydride (60% dispersion in
oil, 49 mg, 1.2 mmol), and the mixture was heated at 80 °C
for 30 min before the above impure 132 (0.35 g) was added.
After 1 h at 80 °C, water was added until the solution turned
cloudy, and the resulting solid was collected by filtration.
Recrystallization from MeOH-EtOAc afforded 140 mg (33%)
of 27 as a solid: mp 278 °C; 1H NMR (360 MHz, CDCl3) δ 1.51
(4H, m), 1.92 (4H, m), 3.60 (1H, s), 3.98 (1H, s), 5.78 (2H, s),
7.42 (1H, dd, J ) 7.8 and 4.9 Hz), 7.47-7.54 (3H, m), 8.04
(1H, dd, J ) 7.9 and 1.6 Hz), 8.37 (2H, d, J ) 7.0 Hz), 8.81
(1H, dd, J ) 4.9 and 1.6 Hz); MS (ES+) m/z 409 [M + H]+.
Anal. [C24H20N6O] C, H, N.
5-(Chloromethyl)-1-methyl-1H-tetrazole and 5-(chloromethyl)-
2-methyl-2H-tetrazole were prepared as described by Moder-
hack50 and used to prepare 97 and 98, respectively.
3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo-
[3,4-a]phthalazine-6-carbonitrile (144) and 3-Phenyl-
7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo[3,4-a]-
phthalazine-6-carboxamide (145). A mixture of 101a (1.003
g, 3.23 mmol) and copper(I) cyanide (0.522 g, 5.83 mmol) in
anhydrous 1-methyl-2-pyrrolidinone (3.2 mL) under nitrogen
was heated at 200 °C for 36 h. After cooling, the mixture was
partitioned between aqueous ammonia solution (50 mL) and
dichloromethane (50 mL). The aqueous layer was further
extracted with dichloromethane (3 × 50 mL). The organic
extracts were combined, dried (MgSO4), and evaporated. The
residue was purified by flash chromatography (silica gel, 1-3%
MeOH/CH2Cl2 and then 15% EtOAc/CH2Cl2) to afford 0.643 g
(66%) of 144 as a yellow solid: 1H NMR (360 MHz, CDCl3) δ
1.53 (4H, m), 2.04 (4H, m), 3.59 (1H, s), 4.11 (1H, s), 7.53-
7.62 (3H, m), 8.47 (2H, d).
Compounds 28, 36-39, 41-44, 48, 53-55, 66, 88, 90, 97, and
98 were prepared in essentially the same way to that described
for 27 from 131 and the corresponding halide. Where the
halide was not commercially available, their preparations are
described below.
From the first column 0.151 g (15%) of 145 was also isolated,
which was triturated in boiling chloroform to leave a cream
solid: 1H NMR (250 MHz, DMSO-d6) δ 1.39 (4H, m), 1.93 (4H,
m), 3.65 (1H, s), 3.82 (1H, s), 7.57-7.66 (3H, m), 8.10 (1H, s),
8.34 (1H, s), 8.44 (2H, d).
Chlorides 133, 134, 138-141, and 14248 were prepared from
the corresponding methyl analogues in the same way as that
described for 132 and used to prepare 28, 36, 38, 39, 41, 42,
and 88, respectively.
Dimethyl Pyrimidin-2-ylmalonate (135). To dimethyl
malonate (41.6 g, 0.315 mol) in 1,4-dioxane (900 mL) was
added sodium hydride (60% dispersion in mineral oil; 18.9 g,
0.473 mol) portionwise. To the resultant gel was added
2-bromopyrimidine (50.0 g, 0.314 mol) in 1,4-dioxane (200 mL)
dropwise. The mixture was stirred at room temperature for 1
h and then at reflux overnight. To the cooled solution was
added water (400 mL), and 5 N hydrochloric acid until the
pH was ∼ 1. The solution was washed with ethyl acetate (2 ×
400 mL), the organic layers combined, washed with saturated
sodium hydrogen carbonate solution (400 mL) and saturated
sodium chloride solution (400 mL), dried (MgSO4), and evapo-
rated. The residue was purified by flash chromatography (silica
gel, 0-20% EtOAc/CH2Cl2) to yield 24.1 g (37%) of 135 as a
yellow-orange oil: 1H NMR (250 MHz, CDCl3) δ 3.83 (6H, s),
Ethyl 3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazine-6-carboxylate (146). To a solu-
tion of 144 (327 mg, 1.09 mmol) in ethanol (62 mL) was added
4 N aqueous sodium hydroxide solution (2.75 mL, 11.0 mmol),
and the solution was heated at reflux for 5 h. After cooling,
the mixture was acidified with 5 M hydrochloric acid to pH
<2 and then evaporated. The solid was azeotroped with
ethanol twice. To the residue was added more ethanol, and
the mixture was cooled under nitrogen to 5 °C before thionyl
chloride (0.813 mL, 11.1 mmol) was added dropwise over 5
min. The mixture was then heated at reflux for 2 h. After
cooling, the solvent was evaporated, and the residue was
partitioned between water (30 mL) and dichloromethane (30
mL), making the pH of the aqueous layer 7 with a few drops
of saturated sodium hydrogen carbonate solution. The aqueous
layer was further extracted with dichloromethane (2 × 20 mL),
and the organic extracts were combined, dried (MgSO4), and
5.16 (1H, s), 7.28 (1H, t, J ) 5.0 Hz), 8.87 (2H, d, J ) 5.0 Hz);
MS (ES+) m/z 211 [M + H]
.
+

GABAA Receptor Agonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1381
evaporated to afford 353 mg (93%) of 146 as a pale yellow
solid: 1H NMR (250 MHz, CDCl3) δ 1.46-1.52 (7H, m), 1.98
(4H, m), 3.82 (1H, s), 4.10 (1H, s), 4.53 (2H, q, J ) 7.1 Hz),
7.54-7.57 (3H, m), 8.41 (2H, dd, J ) 8.1 and 1.6 Hz); MS (ES+)
m/z 349 [M + H]+.
to give 0.151 g (72%) of 149 as a pale brown solid: 1H NMR
(250 MHz, DMSO-d6) δ 1.41 (4H, m), 1.93 (4H, m), 3.77 (1H,
s), 3.84 (1H, s), 7.58-7.67 (3H, m), 8.42 (2H, d).
3-Phenyl-N-pyridin-2-yl-7,8,9,10-tetrahydro-7,10-ethano-
[1,2,4]triazolo[3,4-a]phthalazine-6-carboxamide (51). A
mixture of 149 (0.1748 g, 0.546 mmol) in thionyl chloride (3
mL) was stirred at 50-60 °C for 20 h. The excess thionyl
chloride was removed in vacuo, and the residue was azeotroped
with toluene (10 mL). To the residue was added anhydrous
THF (10 mL), followed by triethylamine (84 µL, 0.601 mmol),
and then dropwise, over 6 min, a solution of 2-aminopyridine
(56.4 mg, 0.599 mmol) in anhydrous THF (5 mL), while
stirring. The mixture was stirred at room temperature under
nitrogen for 3.5 h and then evaporated. The residue was
partitioned between dichloromethane (25 mL) and water (25
mL) brought to pH 10 with saturated aqueous Na2CO3 solu-
tion. The aqueous layer was further extracted with dichloro-
methane (3 × 25 mL), and the combined extracts were dried
(MgSO4) and evaporated. The residue was purified by flash
chromatography (silica gel, 2% MeOH/CH2Cl2, and then
alumina, 15% EtOAc/CH2Cl2) to afford 104.3 mg (48%) of 51
as a white solid: mp 270-275 °C (CH2Cl2-EtOAc-hexane);
1H NMR (360 MHz, CDCl3) δ 1.54 (4H, m), 2.00 (4H, m), 4.11
(1H, s), 4.42 (1H, s), 7.13 (1H, t, J ) 5.9 Hz), 7.53-7.64 (3H,
m), 7.80 (1H, t, J ) 8.8 Hz), 8.36 (2H, d, J ) 7.5 Hz), 8.43
(2H, d, J ) 7.0 Hz), 9.51 (1H, s); MS (ES+) m/z 397 [M + H]+.
Anal. [C23H20N6O‚0.1H2O] C, H, N.
[(3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazin-6-yl)oxy]acetic Acid (150). 107
(2.50 g, 8.56 mmol) was alkylated with methyl bromoacetate
using the procedure described for the preparation of 27 to give
2.98 g (96%) of crude methyl [(3-phenyl-7,8,9,10-tetrahydro-
7,10-ethano[1,2,4]triazolo[3,4-a]phthalazin-6-yl)oxy]acetate,
which was used without further purification.
To the crude intermediate (2.50 g, 6.87 mmol) in methanol
(40 mL) was added a solution of potassium hydroxide (900 mg,
16.0 mmol) in water (15 mL). The resulting yellow solution
was stirred at room temperature for 3 days. The methanol was
evaporated, and the remaining aqueous phase was washed
with ethyl acetate (3 × 30 mL) and acidified (pH 6) by the
addition of 5 N hydrochloric acid, precipitating a solid. This
was separated by filtration, washed with water, and dried, to
yield 1.78 g (74%) of 150 as a white solid: 1H NMR (360 MHz,
DMSO-d6) δ 1.32-1.45 (4H, m), 1.85-1.99 (4H, m), 3.43 (1H,
s), 3.75 (1H, s), 4.98 (2H, s), 7.49-7.58 (3H, m), 8.33-8.35 (2H,
m); MS (ES+) m/z 351 [M + H]+.
(3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo-
[3,4-a]phthalazin-6-yl)methanol (147). A solution of 146
(701 mg, 2.01 mmol) in ethanol (10 mL) was added to a solution
of anhydrous calcium chloride (90 mg, 0.81 mmol). The
resulting solution was cooled to -10 °C and sodium boro-
hydride (170 mg, 4.49 mmol) in ethanol (10 mL) was slowly
added. The mixture was then allowed to stand at room
temperature for 30 min. The solvent was evaporated, and the
residue was diluted with 1 N aqueous HCl. The resulting solid
was collected by filtration and washed several times with
water to give 0.499 g (81%) of 147 as a white solid: 1H NMR
(250 MHz, CDCl3) δ 1.71 (4H, m), 1.96 (4H, m), 3.35 (1H, s),
4.02 (1H, s), 4.98 (2H, s), 7.57-7.66 (3H, m), 8.41 (2H, dd, J )
8.1 and 1.6 Hz); MS (ES+) m/z 307 [M + H]+.
3-Phenyl-6-[(pyridin-2-yloxy)methyl]-7,8,9,10-tetrahy-
dro-7,10-ethano[1,2,4]triazolo[3,4-a]phthalazine (49). To
a solution of 147 (150 mg, 0.48 mmol), triphenylphosphine (180
mg, 0.72 mmol), and 2-hydroxypyridine (60 mg, 0.63 mmol)
in THF (3.5 mL) was slowly added diethyl azodicarboxylate
(0.120 mL, 0.75 mmol) at room temperature. The mixture was
stirred at room temperature for 3 h. Water was then added,
and the mixture was extracted with dichloromethane. The
extracts were washed with water and brine, dried (MgSO4),
and evaporated. The residue was purified by flash chroma-
tography (silica gel, 5% MeOH/CH2Cl2, and then alumina, 20%
EtOAc/CH2Cl2) and then preparative TLC (5% MeOH/CH2Cl2)
to give 21.6 mg (9%) of 49, which was further purified by
preparative HPLC on S5 ODS 2 (250 × 4.6 mm) column,
eluting with 70% MeCN/H2O containing 0.1% TFA: HPLC
>99.5% (tR, 10 min, 70% MeCN/H2O containing 0.1% TFA).
[(3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]tri-
azolo[3,4-a]phthalazin-6-yl)methyl]amine (148). A mix-
ture of 144 (0.4974 g, 1.65 mmol) and palladium on activated
charcoal (10%, 0.2516 g) in ethanol (100 mL) and chloroform
(2 mL) was hydrogenated on a Parr apparatus at 50 psi for 22
h. The catalyst was removed by filtration and washed well with
ethanol. The combined filtrates were evaporated in vacuo, and
the residue was partitioned between 1 N NaOH solution (30
mL) and dichloromethane (100 mL). The aqueous layer was
extracted further with dichloromethane (100 mL), and the
combined extracts were dried (Na2SO4) and evaporated. The
residue was purified by flash chromatography (silica gel, 3%
MeOH/CH2Cl2) to give 0.3236 g (64%) of 148 as a pale yellow
solid: 1H NMR (360 MHz, CDCl3) δ 1.47 (4H, m), 1.95 (4H,
m), 3.35 (1H, s), 4.02 (1H, s), 4.20 (2H, s), 7.46-7.57 (3H, m),
8.50 (2H, d).
N-[(3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazin-6-yl)methyl]pyridin-2-amine
(50). A solution of 148 (0.1504 g, 0.492 mmol) and 2-bromo-
pyridine (3.0 mL) was heated at 160 °C under nitrogen for 6
h. After cooling, the solvent was evaporated and the residue
was purified by flash chromatography (silica gel, 2-5% MeOH/
CH2Cl2) to yield 0.1909 g (100%) of 50 as a yellow solid: mp
165-170 °C (CH2Cl2-EtOAc-hexane); 1H NMR (360 MHz,
CDCl3) δ 1.47 (4H, m), 1.95 (4H, m), 3.45 (1H, s), 4.03 (1H, s),
4.93 (2H, d, J ) 5.5 Hz), 5.23 (1H, m), 6.58 (1H, d, J ) 8.3
Hz), 6.66 (1H, t, J ) 5.5 Hz), 7.46-7.53 (4H, m), 8.15 (1H, d),
8.38 (2H, d, J ) 8.0 Hz); MS (ES+) m/z 383 [M + H]+. Anal.
[C23H22N6‚0.06C4H8O2] C, H, N.
N-Benzyl-N-methyl-2-[(3-phenyl-7,8,9,10-tetrahydro-
7,10-ethano[1,2,4]triazolo[3,4-a]phthalazin-6-yl)oxy]-
acetamide (67). To 150 (300 mg, 0.86 mmol) in DMF (10 mL)
was added N,N′-carbonyldiimidazole (153 mg, 0.945 mmol)
with stirring, and the resulting mixture was stirred at room
temperature under nitrogen for 2 h. N-Benzylmethylamine
(0.111 mL, 104 mg, 0.86 mmol) was added, and the mixture
was stirred as before for 24 h. Water (40 mL) was added,
precipitating a hygroscopic solid which was separated by
filtration and purified by flash chromatography (silica gel, 10%
MeOH/CH2Cl2). The resulting solid was recrystallized from
ethyl acetate/hexane, yielding 151 mg (39%) of 67 as a white
1
solid: mp 168.3-169.3 °C; H NMR (360 MHz, DMSO-d6) δ
1.30-1.58 (4H, m), 1.78-1.99 (4H, m), 3.04 and 3.03 (3H, 2
singlets, rotamers), 3.45 and 3.59 (1H, 2 singlets, rotamers),
3.94 and 3.98 (1H, 2 singlets, rotamers), 4.60 and 4.62 (2H,
two singlets, rotamers), 5.13 and 5.17 (2H, 2 singlets, rotam-
ers), 7.16-7.3 (5H, m), 7.36-7.52 (3H, m), 8.30-8.39 (2H, m);
MS (ES+) m/z 454 [M + H]+. Anal. [C27H27N5O2] C, H, N.
3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo-
[3,4-a]phthalazine-6-carboxylic Acid (149). A solution of
145 (0.21 g, 0.66 mmol) in concentrated hydrochloric acid (5
mL) was stirred at 100-120 °C for 46 h. After cooling, the
mixture was diluted with water (20 mL) and dichloromethane
(20 mL) and then filtered. The solid was washed with water
then dichloromethane and dried at 60 °C under vacuum. The
combined filtrates were extracted with dichloromethane (12
× 50 mL), and the combined extracts were dried (MgSO4) and
evaporated. This was combined with the solid obtained above
2-{[(3-Phenyl-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazin-6-yl)oxy]methyl}pyridin-3-ol
(29). A solution of 33 (51.6 mg, 0.11 mmol) in methanol (2.5
mL) with concentrated hydrochloric acid (2.5 mL) was stirred
at reflux for 9 h. A solid precipitated from solution upon cooling
to room temperature. The solid was separated by filtration and
recrystallized from methanol/ethyl acetate to yield 23.0 mg
(43%) of 29 as a colorless solid. Dihydrochloride salt: mp 220
°C (dec); 1H NMR (360 MHz, DMSO-d6) δ 1.37-1.49 (4H, m),

1382 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Russell et al.
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Rudolph, U. Molecular and Neuronal Substrate for the Selective
Attenuation of Anxiety. Science 2000, 290, 131-134.
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Molecular Targets for the Myorelaxant Action of Diazepam. Mol.
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1.80-1.99 (4H, m), 3.49 (1H, s), 3.799 (1H, s), 5.80 (2H, s),
7.54-7.62 (3H, m), 7.78 (1H, dd, J ) 8.5 and 5.4 Hz), 8.11
(1H, d, J ) 8.5 Hz), 8.26-8.31 (3H, m), 12.25 (1H, br s); MS
(ES+) m/z 400 [M + H]+. Anal. [C23H21N5O2‚2HCl‚1.3H2O] C,
H, N.
3-Phenyl-6-[(1-propyl-1H-1,2,4-triazol-3-yl)methoxy]-
7,8,9,10-tetrahydro-7,10-ethano[1,2,4]triazolo[3,4-a]-
phthalazine (95) and 3-Phenyl-6-[(1-propyl-1H-1,2,4-tri-
azol-5-yl)methoxy]-7,8,9,10-tetrahydro-7,10-ethano[1,2,4]-
triazolo[3,4-a]phthalazine (96). To a stirred mixture of
sodium hydride (60% dispersion in oil, 22.1 mg, 0.553 mmol)
and iodopropane (0.0553 mL, 0.567 mmol) in anhydrous DMF
(2 mL) under nitrogen, at 0 °C, was added dropwise, over 8
min, a solution of 92 (0.1767 g, 0.473 mmol) in anhydrous DMF
(7 mL). The mixture was then stirred for 1.5 h and allowed to
warm slowly to 12 °C. More sodium hydride (60% dispersion
in oil, 4.4 mg, 0.110 mmol) was added, and the mixture was
stirred for another 1 h. Water (40 mL) was added, and the
mixture was stirred for a few minutes. The mixture was
filtered, a little saturated aqueous NaCl solution was added
to the filtrate, and this was extracted with ethyl acetate (2 ×
50 mL). The combined organic extracts were dried (MgSO4)
and evaporated. The residue was purified by flash chroma-
tography (silica gel, 0-3% MeOH/EtOAc) to afford 75.8 mg
(39%) of 96 and 106.9 mg (54%) of 95 as white solids:
95: mp 203-205 °C (CH2Cl2-EtOAc-hexane); 1H NMR
(360 MHz, CDCl3) δ 0.95 (3H, t, J ) 7.4 Hz), 1.46 (4H, m),
1.82-1.99 (6H, m), 3.51 (1H, s), 3.96 (1H, s), 4.14 (2H, t, J )
7.1 Hz), 5.54 (2H, s), 7.45-7.56 (3H, m), 8.08 (1H, s), 8.52 (2H,
d); MS (ES+) m/z 416 [M + H]+. Anal. [C23H25N7O‚0.4H2O] C,
H, N.
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96: mp 166-181 °C (CH2Cl2-EtOAc-hexane); 1H NMR
(360 MHz, CDCl3) δ 0.94 (3H, t, J ) 7.4 Hz), 1.39 (2H, m),
1.51 (2H, m), 1.86-1.97 (6H, m), 3.41 (1H, s), 4.01 (1H, s), 4.17
(2H, t, J ) 7.1 Hz), 5.61 (2H, s), 7.48-7.58 (3H, m), 7.97 (1H,
s), 8.44 (2H, d, J ) 6.8 Hz); MS (ES+) m/z 416 [M + H]+. Anal.
[C23H25N7O‚0.23C6H14] C, H, N.
Biological Methods. Radioligand Binding Studies.
This procedure has been fully described by Chambers et al.25
Electrophysiology. Voltage Clamp in Xenopus laevis
Oocytes. This procedure has been described by Street et al.27
Acknowledgment. We thank Christophe Derrien
for the preparative HPLC purifications.
Supporting Information Available: Yields, melting
points, and spectral data for all final compounds and inter-
mediates not included above. This material is available free
of charge via the Internet at http://pubs.acs.org.
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