3-Phenyl-6-(2-pyridyl)methyloxy-1,2,4-triazolo[3,4-a]phthalazines and Analogues: High-Affinity γ-Aminobutyric Acid-A Benzodiazepine Receptor Ligands with α2, α3, and α5-Subtype Binding Selectivity over α1

Article abstract of DOI:10.1021/jm031020p

Studies with our screening lead 5 and the literature compound 6 led to the identification of 6-benzyloxy-3-(4-methoxy)phenyl-1,2,4-triazolo[3,4-a]phthalazine 8 as a ligand with binding selectivity for the γ-aminobutyric acid-A (GABA-A) α3- and α5-containing receptor subtypes over the GABA-A α1 subtype (K_i: α2 = 850 nM, α3 = 170 nM, α5 = 72 nM, α1 = 1400 nM). Early optimization studies identified the close analogue 10 (K_i: α2 = 16 nM, α3 = 41 nM, α5 = 38 nM, α1 = 280 nM) as a suitable lead for further study. High-affinity ligands were identified by replacing the 6-benzyloxy group of compound 10 with 2-pyridylmethoxy (compound 29), but binding selectivity was not enhanced (K _i: α2 = 1.7 nM, α3 = 0.71 nM, α5 = 0.33 nM, α1 = 2.7 nM). Furthermore, on evaluation in xenopus oocytes, 29 was discovered to be a weak to moderate inverse agonist at all four receptor subtypes α1, -7%; α2, -5%; α3, -16%; α5, -5%). Replacement of the 3-phenyl group of 29 with alternatives led to reduced affinity, and smaller 3-substituents led to reduced efficacy. Methyl substitution of the benzo-fused ring of 29 at the 7-, 8-, and 10-positions resulted in increased efficacy although selectivity was abolished. Increased efficacy and retention of selectivity for α3 over α1 was achieved with the 7,8,9,10-tetrahydro-(7,10-ethano)-phthalazine 62. Compound 62 is currently one of the most binding selective GABA-A α3-benzodiazepine-site partial agonists known, and although its selectivity is limited, its good pharmacokinetic profile in the rat (33% oral bioavailability after a 3 mg/kg dose, reaching a peak plasma concentration of 179 ng/mL; half-life of 1 h) made it a useful pharmacological tool to explore the effect of a GABA-A α2/α3 agonist in vivo.

Full text of DOI:10.1021/jm031020p

J . Med. Chem. 2004, 47, 1807-1822
1807
3-P h en yl-6-(2-p yr id yl)m eth yloxy-1,2,4-tr ia zolo[3,4-a ]p h th a la zin es a n d
An a logu es: High -Affin ity γ-Am in obu tyr ic Acid -A Ben zod ia zep in e Recep tor
Liga n d s w ith r2, r3, a n d r5-Su btyp e Bin d in g Selectivity over r1
Robert W. Carling,* Kevin W. Moore,* Leslie J . Street, Deborah Wild, Catherine Isted, Paul D. Leeson,
Steven Thomas, Desmond O’Connor, Ruth M. McKernan, Katherine Quirk, Susan M. Cook, J ohn R. Atack,
Keith A. Wafford, Sally A. Thompson, Gerard R. Dawson, Pushpinder Ferris, and J ose´ L. Castro
Departments of Medicinal Chemistry, Biochemistry, and Pharmacology, The Neuroscience Research Centre, Merck Sharp and
Dohme Research Laboratories, Terlings Park, Eastwick Road, Harlow, Essex CM20 2QR, U.K.
Received September 4, 2003
Studies with our screening lead 5 and the literature compound 6 led to the identification of
6-benzyloxy-3-(4-methoxy)phenyl-1,2,4-triazolo[3,4-a]phthalazine 8 as a ligand with binding
selectivity for the γ-aminobutyric acid-A (GABA-A) R3- and R5-containing receptor subtypes
over the GABA-A R1 subtype (Ki: R2 ) 850 nM, R3 ) 170 nM, R5 ) 72 nM, R1 ) 1400 nM).
Early optimization studies identified the close analogue 10 (Ki: R2 ) 16 nM, R3 ) 41 nM, R5
) 38 nM, R1 ) 280 nM) as a suitable lead for further study. High-affinity ligands were identified
by replacing the 6-benzyloxy group of compound 10 with 2-pyridylmethoxy (compound 29),
but binding selectivity was not enhanced (Ki: R2 ) 1.7 nM, R3 ) 0.71 nM, R5 ) 0.33 nM, R1
) 2.7 nM). Furthermore, on evaluation in xenopus oocytes,22 29 was discovered to be a weak
to moderate inverse agonist at all four receptor subtypes (R1, -7%; R2, -5%; R3, -16%; R5,
-5%). Replacement of the 3-phenyl group of 29 with alternatives led to reduced affinity, and
smaller 3-substituents led to reduced efficacy. Methyl substitution of the benzo-fused ring of
29 at the 7-, 8-, and 10-positions resulted in increased efficacy although selectivity was abolished.
Increased efficacy and retention of selectivity for R3 over R1 was achieved with the 7,8,9,10-
tetrahydro-(7,10-ethano)-phthalazine 62. Compound 62 is currently one of the most binding
selective GABA-A R3-benzodiazepine-site partial agonists known, and although its selectivity
is limited, its good pharmacokinetic profile in the rat (33% oral bioavailability after a 3 mg/kg
dose, reaching a peak plasma concentration of 179 ng/mL; half-life of 1 h) made it a useful
pharmacological tool to explore the effect of a GABA-A R2/R3 agonist in vivo.
In tr od u ction
anesthetics, loreclezole, avermectins, and benzodiaz-
epines that all modulate opening of the channel through
different mechanisms of action.8 Of these, the benzodi-
azepine (BZ) site is the best characterized because of
its role in mediating the clinical effects of anxiolytics
such as diazepam (1, Table 1). Ligands at the BZ
binding site of GABA-A receptors fall into three func-
tional classes categorized by their effect on the ion
current elicited by the endogenous neurotransmitter
GABA: Agonists (positive allosteric modulators) give an
increased ion flux, resulting in a greater inhibitory effect
on the postsynaptic neurone, while inverse agonists
(negative allosteric modulators) cause a decrease in the
ion flux in response to GABA. A continuum of ligand
activities is possible, including antagonists (neutral
allosteric modulators) that have no effect on the ion
channel response to GABA but will competitively dis-
place other BZ site ligands from the receptor. It has been
shown that the benzodiazepine binding site occurs at
the interface of the R and γ subunit of the GABA-A
receptor, with the pharmacology of the benzodiazepine
site being determined by the particular R and γ subunits
present.8 It has also been shown that the major benzo-
diazepine-sensitive GABA-A receptor subtypes in brain
are R1â2/3γ2, R2â3γ2, R3â3γ2, and R5â3γ2.6 Currently,
only a limited number of GABA-A subtype selective
ligands have been reported. Zolpidem7 (2, Table 1) and
GABA (γ-aminobutyric acid) is the major inhibitory
neurotransmitter in the brain.1 There are three phar-
macological classes of GABA receptors, GABA-A, GABA-
B, and GABA-C, of which GABA-A2 and GABA-C3 are
ligand-gated chloride ion channels and GABA-B is
G-protein-linked. It has recently been proposed that
GABA-C receptors could be classified as a subset of
GABA-A receptors on the basis of similarities in mo-
lecular biology.3 In any event, GABA-A receptors con-
stitute the largest population of inhibitory neurotrans-
mitter receptors.4 The purification, cloning, and sequenc-
ing of the GABA-A receptor have led to the identification
of 19 subunits from within 8 families of structurally
related subunits (R1-R6, â1-â3, γ1-γ3, δ, ꢀ, π, F1-3,
and θ).5 Expression of recombinant receptors shows that
at least one R, one â, and one γ (or δ) subunit are
required to form a pentameric, functional GABA-gated
chloride ion channel,5,6 with several recent studies
suggesting a subunit stoichiometry of two R, two â, and
one γ subunit.7 As well as a neurotransmitter (GABA)
binding site, GABA-A receptors also have multiple
allosteric modulatory sites for barbiturates, steroid
* To whom correspondence should be addressed. For R.W.C.: phone,
(+1279) 440000; fax, (+1279) 440187; e-mail, robert_carling@merck.com.
For K.W.M.: phone, (+1279) 440000; fax, (+1279) 440187; e-mail,
kevin moore@merck.com.
10.1021/jm031020p CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/02/2004

1808 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
Ta ble 1. Reference Compounds: Affinities at Cloned Human
Ta ble 2. Lead Compounds and Early Optimization Studies
GABA-A Receptorsa
Affinities at Cloned Human GABA-A Receptorsa
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analyss results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
the mean.
CL-218,8729 (3, Table 1) have 10- to 20-fold selectivity
for R1- over R3-containing subunits, and Cook has
reported some â-carboline derivatives with similar bind-
ing selectivity.10 The benzodiazepine 4 (Table 1) has
been reported to have greater than 50-fold selectivity
for R5- over R1-, R2-, and R3-containing subunits.11
There is a recent report of some pyrazoloquinolin-3-one
GABA-A ligands with minimal binding selectivity for
R2-containing subunits over the R3 subtype,12 and a
series of 7,8,9,10-tetrahydroimidazo[1,2-c]pyrido[3,4-e]-
pyrimidin-5(6H)-ones have been reported to be function-
ally selective GABA-A R2/R3 ligands.13 We have recently
published work from our own laboratories highlighting
functionally selective GABA-A R2/314,15 and R5 ligands.16
Currently used anxiolytic benzodiazepines such as
diazepam (1) are nonselective, high-efficacy agonists,
and these compounds show sedative,17 muscle-relax-
ant,18 and amnesic19 properties. Zolpidem (2) is a high-
efficacy agonist that has selectivity for the R1 subtype
(the major subtype of GABA-A receptors in the central
nervous system),6 and it is particularly sedative in
animal tests and in man.20 This suggests that com-
pounds with selectivity for the R2 subtype and/or R3
subtype may retain the desirable anxiolytic activity of
unselective benzodiazepines but possess an improved
side effect profile. Further evidence for the role of R1-
containing receptors in sedation has been provided
recently by the Mohler group who bred transgenic mice
where the R1 subunit was rendered BZ-insensitive.21 On
treatment with diazepam, these animals were not
sedated or amnesic, but anxiolytic, anticonvulsant, and
myorelaxant effects were still apparent. On the basis
of this rationale, we began a medicinal chemistry pro-
gram with the aim of identifying subtype-selective
GABA-A R2/R3 benzodiazepine-site ligands/agonists. In
this paper, we describe the identification of the 1,2,4-
triazolo[3,4-a]phthalazine 10 as a lead compound and
optimization studies that were carried out on this com-
pound aimed at improving affinity, selectivity, and
efficacy at GABA-A R2- and R3-containing receptors in
particular.
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analysis results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
the mean.
Biology
Compounds were routinely tested for their ability to
displace [3H]Ro15-1788 from different R-subunit-con-
taining (R1â2γ3, R2â3γ2, R3 â3γ2, or R5 â3γ2) human
recombinant GABA-A receptors, stably expressed in
L(tk) cells.22 The binding data for all compounds are the
mean of at least three independent determinations, and
the errors of the mean are within 2-fold of the mean.
Efficacies of a number of compounds were determined
at a maximal concentration of test ligand (100 × Ki)
using the EC20 concentration of GABA. Two electrode-
voltage-clamp techniques were used on R1â3γ2, R2â3γ2,
R3â3γ2, or R5â3γ2 receptors expressed in Xenopus
oocytes.23
Lea d Id en tifica tion
Our strategy began with the screening of literature
compounds, known to be benzodiazepine site GABA-A
ligands, and the Merck sample collection for GABA-A
R2/R3 subtype selective leads. The 2,3-dihydrophthala-
zine-1,4-dione 524 (Table 2) was identified as a weakly
active R2/R3 binding selective compound, but initial
optimization studies involving independent deletion and
replacement of hydrogen-bonding and hydrophobic groups
gave only inactive compounds. We were intrigued by the
similarity of 5 to the known GABA-A ligand 6 (Table
2), which has been reported to show some dissociation
of anxiolysis and sedation,25 and thus, we identified the
molecule 7 as one potential target along with other
hybrid molecules. Compound 7 was prepared from the
hydrazine 6326 by acylation with 4-methoxybenzoyl
chloride, subsequent cyclization in refluxing DMF to

Phthalazines and Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1809
Sch em e 1a
F igu r e 2. Nuclear Overhauser effects observed between the
benzyl protons and the ortho protons of 3-aryl ring.
F igu r e 3. Nuclear Overhauser effects observed between the
methyl protons and the proton at the 7-position as well as the
ortho protons of the 3-aryl ring.
a
Reagents: (i) 4-methoxybenzoyl chloride, Et3N, 1,4-dioxan,
room temp; (ii) DMF, reflux; (iii) NaH, DMF, PhCH2Br, 100 °C.
seen in both molecules. The structures of compounds 7
and 8 were assigned on the basis of the 6-methoxy-3-
phenyl analogue 9 being the major regioisomer formed
on reaction of the 1,2,4-triazolo[3,4-a]phthalazine 65
with iodomethane under analogous conditions (Scheme
2). Nuclear Overhauser effects were observed between
the 6-methoxy protons and the 7-proton of 9 as well as
the 3-(o-phenyl) protons (Figure 3; see Experimental
Section for full details). The 3-phenyl analogue of the
lead compound 8 was prepared by an analogous route
to give compound 10 (Scheme 2). This change resulted
in both a moderately improved affinity (Ki(10): R3 )
41 nM) and retention of selectivity. A rapid and unam-
biguous synthetic route for the preparation of 10 (and
close analogues) was also developed (Scheme 3). This
involved direct reaction of benzoic hydrazide with 3,6-
dichlorophthalazine 6627-29 to give 6-chloro-3-phenyl-
triazolophthalazine 67, which on reaction with the
alkoxide of benzyl alcohol gave 10. This unambiguous
synthesis of 10 provided conclusive evidence for the
original regiochemical assignments of compounds 7, 8,
and 10.
F igu r e 1. Nuclear Overhauser effects observed between the
benzyl protons and the ortho protons of 3-aryl ring.
form a 1,2,4-triazolo[3,4-a]phthalazine (64), and finally
treatment with benzyl bromide after deprotonation with
sodium hydride (Scheme 1). Compound 7, whose regio-
chemistry was assigned by NOE studies (see below), was
isolated as a minor product from the reaction and was
found to be inactive in the binding assay. Serendipi-
tously, the major product of the alkylation reaction, the
O-benzylated derivative 8, was found to have good
affinity at the R3 and R5 receptors (for Ki(8), R3 ) 170
nM and R5 ) 72 nM) with some selectivity over R1 (for
Ki(8), R1 ) 1400 nM). Direct NOE studies did not aid
the assignment of the regioisomers 7 (Figure 1) and 8
(Figure 2) because enhancements between the ortho
protons of the 3-aryl ring and the benzylic protons were
Sch em e 2a
a
Reagents: (i) benzoyl chloride, Et3N, 1,4-dioxan, room temp; (ii) DMF, reflux; (iii) NaH, DMF, PhCH2Br, 100 °C; (iv) NaH, DMF,
CH3I; (v) NaH, DMF, RCH2Br or RCH2Cl.

1810 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
Sch em e 3a
a
Reagents: (i) PhCONHNH2, Et3N, dioxan, reflux; (ii) ROH, NaH, DMF; (iii) R1CONHNH2, Et3N, xylene, reflux; (iv) R1COCl, Et3N,
dioxan, reflux.
Sch em e 4a
a
Reagents: (i) PhCH2SH, NaH, DMF, 80 °C; (ii) PhCH2NH(R1), 120 °C.
Ch em istr y
case of the 9-methyl (57) and 8-methyl (58) isomers,
chromatographic separation was carried out on the final
compounds (Scheme 6) and regiochemical assignments
were largely carried out through the observation of an
NOE between the methylene protons and the 7-H
singlet of 58 (see Experimental Section for more details).
The benzo-fused ring of 10 was also replaced with a
cyclohexyl group to give 60 and a 2,2,2-bridged ring
system to give 62 using chemistry similar to that
outlined in Scheme 5, starting from the appropriate
commercially available 3,6-dichloropthalazine. In the
case of the cycloheptyl compound 61, the synthesis was
carried out starting from 1-cycloheptene-1,2-dicarboxylic
anhydride.30
Compounds 11-62 were prepared for optimization
studies based on the lead compound 10. Reaction of a
range of alkyl halides with the sodium anion of com-
pound 65 gave a number of 6-alkoxy analogues (Scheme
2). An alternative procedure for the formation of 6-alkoxy
derivatives was to react the chloroimidate 67 with the
sodium salt of an appropriate alcohol (Scheme 3).
Alternatives to the phenyl group at the 3-position of the
1,2,4-triazolo[3,4-a]phthalazines were introduced by
reaction of the known hydrazine 69 with an appropriate
acid chloride under the conditions of Tarzia et al.25 or
by reaction of 3,6-dichlorophthalazine 66 with an ap-
propriate acyl hydrazide in refluxing xylene to give
intermediates 68 (Scheme 3). Treatment of compounds
68 with the appropriate alkoxide gave analogues 43-
55. The thioether 15 was prepared by reaction of 67 with
the sodium salt of benzyl mercaptan, while the amidines
16 and 17 were made by heating 67 with a large excess
of the appropriate amine (Scheme 4).
A number of changes were made to the benzo-fused
ring of the phthalazine core of 10 including methyl
substitution to give compounds 56-59 (Schemes 5 and
6). These compounds were made using the meth-
ylphthalic anhydrides 70 or 75 as starting materials
with key intermediates being the dichlorophthalazines
72 and 77, respectively. In the synthesis of 56 and 59,
the separation of the 7- and 10-methyl regioisomers was
carried out after the penultimate step by chromatogra-
phy of the chlorotriazolophthalazines 73 and 74 (Scheme
5). The regiochemistries of 56 and 59 were ultimately
assigned by the observation of an NOE between the
methyl protons and the methylene protons of 59. In the
Resu lts a n d Discu ssion
Replacement of the 6-benzyloxy group of the lead
compound 10 with methoxy to give 9 resulted in
decreased affinity at R3 and loss of selectivity over other
GABA-A receptor subtypes (Table 2). Saturation of the
6-substituent (11) or deletion of the methylene spacer
(12) resulted in the abolition of binding affinity at all
receptor subtypes (Table 3). Homologation of the 6-ben-
zyloxy group (13 and 14) was better tolerated, but
affinity at the R3 receptor was still reduced by an order
of magnitude. Replacement of the 6-ether linkage with
either thioether (15) or amino (16 and 17) was also not
well tolerated. The data in Table 3 indicate that an
imidate group with one methylene linker to a phenyl
ring (10) is optimal for affinity at R2, R3, and R5 and
for selectivity over R1.
Limited exploration of aromatic substitution on the
aryl ring of the 6-benzyloxy group of 10 was carried out

Phthalazines and Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1811
Sch em e 5a
a
Reagents: (i) NH2NH2‚H2O, AcOH, NaOAc, reflux; (ii) POCl3, reflux; (iii) PhCONHNH2, Et3N, xylene, reflux; (iv) chromatography;
(v) ROH, NaH, DMF.
Sch em e 6a
a
Reagents: (i) NH2NH2‚H2O, AcOH, NaOAc, reflux; (ii) POCl3, reflux; (iii) PhCONHNH2, Et3N, xylene, reflux; (iv) ROH, NaH, DMF;
(v) chromatography.
(Table 4). Substitution with chlorine (18-20) and meth-
oxy (21 and 23) generally led to significantly reduced
affinity; however the m-methoxy analogue 22 retained
affinity and selectivity for R3 over R1.
The effect of replacing the aryl ring of the 6-benzyloxy
group of the lead compound 10 with heterocycles was
next explored (Table 5). With the exception of the
3-furan 28, all the thiophene and furan analogues (25-
27) had significantly reduced affinity at R3-containing
receptors. Significantly improved binding affinity was
obtained with the 2-pyridylmethyloxy compound 29,
which has subnanomolar affinity at the R5 the R3
subtypes and has some selectivity over R1 receptors. The
pyridazine 32, the pyrimidine 33, the pyrazine 34, and
the N-methylimidazole 35 are also high-affinity ligands,
but all have only minimal selectivity for other R recep-
tors over R1-containing receptors. The piperidine 36 and
the homologated pyridine 37 both lose significant af-

1812 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
Ta ble 3. Effect of Saturation, Chain Length, and Heteroatom
Replacement at the 6-Position of Compound 9: Affinities at
Cloned Human GABA-A Receptorsa
Ta ble 4. Effect of Aromatic Substitution on the Benzyl Group
at the 6-Position of Compound 9: Affinities at Cloned Human
GABA-A Receptorsa
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
mass spectra and gave satisfactory elemental analyss results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
the mean.
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analysis results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
the mean.
finity relative to the pyridine 29. The data in Table 5
indicate that significantly improved binding affinity at
all GABA-A receptor subtypes can be achieved by
replacing the phenyl ring of the 6-benzyloxy group of
the lead compound 10 with heterocycles containing
nitrogens with H-bond-accepting potential, thus sug-
gesting an H-bond-donating interaction from the recep-
tor to that portion of the molecule.
but methylation elsewhere on the 2-pyridylmethyloxy
system is detrimental.
Replacement of the 3-phenyl group of 29 with alter-
natives and the effect on affinity (Table 7) and efficacy
were explored. The 3-methyl analogue 43 lost ap-
proximately 2 orders of magnitude in affinity at all
GABA-A receptor subtypes and has significant inverse
agonism at R3 (-38%). Homologation of 43 (compounds
44-46) had no significant effect on R2, R3, or R5 affinity,
but selectivity over R1 was reduced and the isopropyl
derivative 46 is an inverse agonist at R3 (-21%). The
3-tert-butyl compound 47 is essentially inactive, indicat-
ing steric intolerance at that position of the molecule.
The alkene 48 is approximately 10-fold lower in affinity
and is clearly lower in efficacy (-31% at R3) than the
lead compound 29, while the 3-benzyl compound 49 is
only weakly active at R1, R2, and R3 but has good
affinity at R5-containing receptors, suggesting greater
bulk tolerance for binding to the R5 receptor. The
3-cyclopropyl derivative 50 has very good affinity at R3
and R5 with good selectivity over R1, and it is an inverse
agonist (-20% at R1, -26% at R3). The 6-methylpyridyl
analogue of 50 (51) retains very good affinity, is 10-fold
selective for R3 over R1, and shows less inverse agonism
(-15% at R1, -13% at R3). Compound 51 is a weak
partial agonist at R5 (26%) with 35-fold selectivity for
R5 over R1-containing receptors and is thus one of the
most selective R5 ligands yet reported. Replacing the
3-cyclopropyl group of 50 with cyclobutyl (52) results
in reduced affinity and negligible selectivity. Introduc-
tion of a dimethylaminomethylene group to the 3-posi-
tion (53) gives poor affinity, but interestingly very high
Following the identification of the 2-pyridyl analogue
29 as a high-affinity but weakly selective R3 ligand, the
efficacy of the compound was measured at R1â3γ2,
R2â3γ2, R3â3γ2, and R5â3γ2 receptors expressed in
Xenopus oocytes.22 At all four receptor subtypes, the
ligand was found to be a weak to moderate inverse
agonist (R1, -7%; R2, -5%; R3, -16%; R5, -5%). Methyl
substitution around the 2-pyridine ring was explored
in order to determine the effect on selectivity and
efficacy (Table 6). The 6-methylpyridine 38 has binding
affinity at R3-containing receptors comparable to that
of compound 29 but also shows a degree of binding
selectivity over R1- and R2-containing receptors. Com-
pound 38 was found to be a weak partial inverse
agonist/antagonist at R1 (+1%), R2 (-4%), and R3 (-8%)
and a weak partial agonist at R5 (+11%). The 5-methyl
(39) and 4-methyl analogues (40) both show reduced
affinity at R3 receptors. The 3-methylpyridine derivative
41 is a high-affinity GABA-A ligand but is unselective.
The effect of methylation at the benzylic position of 29
to give 42 was to significantly reduce affinity, but
efficacy at R1 (+36%) and R3 (+25%) was increased to
give a partial agonist. The results in Table 6 show that
methyl substitution at the 6-position or the 3-position
of the pyridine ring is well tolerated in terms of affinity,

Phthalazines and Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1813
Ta ble 5. Effect of Replacing the Benzyl Group at the
6-Position of Compound 9 with Heterocycles: Affinities at
Cloned Human GABA-A Receptorsa
Ta ble 6. Effect of Methylation of the 6-Pyridylmethyloxy
Portion of 11: Affinities and Efficacies at Cloned Human
GABA-A Receptorsa
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analysis results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
the mean.
increased substantially (R1, +65%; R3, +27%). The
7-methyl analogue (59) is 50-fold lower in R3 affinity
than the lead compound 29 and efficacy is markedly
higher (R1, +43%; R3, +39%), but the compound shows
no binding selectivity. The data in Table 8 support the
hypothesis that appropriately placed hydrophobic groups
can raise efficacy but the partial agonists identified (58
and 59) have lost R3/R1 binding selectivity.
As an alternative approach toward increasing hydro-
phobicity around the benzo-fused ring of 29, we con-
structed the 7,8,9,10-tetrahydrophthalazine 60, and this
compound retained high binding affinity and selectivity
and also showed a small increase in efficacy (R1, +16%;
R3, +17%) relative to the lead compound (Table 9). The
seven-membered-ring homologue 61 shows significant
loss of affinity and selectivity for R3 but has increased
efficacy (R1, +30%; R3, +30%). In an effort to increase
efficacy further, we synthesized the 7,8,9,10-tetrahydro-
(7,10-ethano)-phthalazine 62. Although the compound
lost more than 10-fold binding affinity, selectivity was
retained and efficacy was increased to significant levels
(R1, +51%; R3, +38%). In terms of relative binding
affinity, 62 is one of the most selective GABA-A R2/R3-
benzodiazepine-site agonist/partial agonists known, and
although its selectivity is limited, its good pharmaco-
kinetic profile in the rat (33% oral bioavailability after
a 3 mg/kg dose reaching a peak plasma concentration
of 179 ng/mL; half-life 1h) made it a useful pharmaco-
logical tool to explore the effect of a GABA-A R2/R3-
agonist in vivo. Compound 62 showed a statistically
significant anxiolytic effect in the rat elevated plus
maze33 (at a dose of 30 mg/kg in 0.5% aqueous methyl
cellulose [po] (n ) 15)). Moreover, an in vivo radioligand
([3H]Ro15-1788) binding assay9 carried out on some of
the test animals (n ) 8) showed 62 to exhibit selective
occupancy for benzodiazepine receptors in rat spinal
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analysis results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
d
the mean. Not determined.
inverse agonism is observed (-65% at R1 and -65% at
R3). Para substitution (54 and 55) of the 3-phenyl ring
of the lead compound 29 results in slightly lower R3
affinity. The results in Table 7 are consistent with there
being a size-limited binding pocket adjacent to the
3-position of the triazolopthalazines, with unsubstituted
phenyl being the best group identified for affinity. The
results also indicate that reduced hydrophobicity at the
3-position generally leads to lower efficacy.
The conversion of GABA-A inverse agonists and
antagonists to partial agonists, within structural series,
has been accomplished with the introduction of ap-
propriate local hydrophobicity to molecules.31,32 With
this precedent in mind, we next explored substitution
of the benzo-fused ring of the lead compound 29 (Table
8). Introduction of methyl to the 10-position (56) results
in a high-affinity ligand with moderately increased
efficacy at R3 (+19%), while 9-methyl substitution (57)
causes the complete abolition of activity. 8-Methylation
(58) gives a high-affinity compound, but efficacy is

1814 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
Ta ble 7. Replacement of the 3-Phenyl Group: Affinities and
Ta ble 8. Methylation of Benzo-Fused Ring: Affinities and
Efficacies at Cloned Human GABA-A Receptorsa
Efficacies at Cloned Human GABA-A Receptorsa
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analysis results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
d
the mean. % changes in electrophysiological response at
a
maximal concentration of test compound (100Ki) in the presence
of GABA (EC20 ofconcentrated GABA) are the mean values of at
least four independent determinations. e Not determined.
number of the analogues prepared show binding selec-
tivity for the R3, R2, and R5 subtypes over the R1
subtype. Generally, the compounds show binding selec-
tivity in the order R5 > R3 > R2 > R1. Overall, our
attempts to optimize the triazolophthalazines for
GABA-A subtype binding selectivity have met with
limited success. At best, only 10-fold selectivity for R3
over R1 binding has been obtained (the 3-cyclopropyl
analogue 51), and this is consistent with the fact that
the most selective R1 ligands currently known, zolpidem
(2) and CL-218,872 (3), are themselves only 10- to 20-
fold selective over R3.9 It is possible to get greater (35-
fold) R5/R1 binding selectivity, as evidenced by com-
pound 51 again, where selectivity comparable to that
of the literature compound 411 (Table 1) is achieved. The
fact that only limited binding selectivity is achievable
suggests it is probable that the γ2 subunit, which is a
constant between the different receptor subtypes, is the
major determinant of benzodiazepine site binding af-
finity (since it has been shown that the benzodiazepine
binding site occurs at the interface of the R and γ
subunits of the GABA-A receptor).8
a
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3,
b
or 5). All compounds were characterized by proton NMR and
mass spectra and gave satisfactory elemental analysis results.
c Binding data are the mean values of at least three independent
determinations, and the errors of the mean are within 2-fold of
the mean.
cord (R2- or R3-containing tissue, 43% receptor oc-
cupancy) over benzodiazepine receptors in rat cerebel-
lum (R1-containing tissue, 4% receptor occupancy).
These data suggest that R2/R3 subtype selective agon-
ists are anxiolytic and support other recent evidence
indicating this.14,15
Changes in efficacy at all the subtypes have been
achieved. Reducing the size of the 3-substituent of 29
results in reduced efficacy, and increasing hydrophobic-
ity around the benzo-fused ring of compound 29 in-
creased efficacy. The optimal R3 binding selective
agonist identified from this work was the 7,8,9,10-
tetrahydro-(7,10-ethano)-phthalazine 62. Although the
compound lost more than 10-fold binding affinity rela-
tive to 29, selectivity was retained and efficacy was
increased to significant levels (R1, +51%; R3, +38%).
Compound 62 showed a statistically significant anxi-
Con clu sion s
We have identified 3-phenyl-6-(2-pyridyl)methyloxy-
1,2,4-triazolo[3,4-a]phthalazines as a class of GABA-A
receptor ligands with binding affinities in the low
nanomolar to subnanomolar range. The large improve-
ment in binding affinity on replacing the 6-benzyloxy
group of 10 with 2-pyridylmethyloxy to give 29 suggests
an important hydrogen-bond-donating interaction from
the receptor adjacent to that portion of the molecule. A

Phthalazines and Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1815
Ta ble 9. Saturation and Homologation of the Benzo-Fused Ring Affinities and Efficacies at Cloned Human GABA-A Receptorsa
a
b
Recombinant human GABA-A receptors Rxâ3γ2 (x ) 1, 2, 3, or 5). All compounds were characterized by proton NMR and mass
spectra and gave satisfactory elemental analysis results. c Binding data are the mean values of at least three independent determinations,
and the errors of the mean are within 2-fold of the mean. % changes in electrophysiological response at a maximal concentration of test
d
compound (100Ki) in the presence of GABA (EC20 of concentrated GABA) are the mean values of at least four independent determinations.
olytic effect in the rat elevated plus maze31 (at a dose
(1.29 mL, 1.1 mol equiv) was added in one portion. After 1 h,
the reaction mixture was allowed to cool and the solvent was
removed by rotary evaporation. The residue was heated with
water (100 mL), and a solid was collected by filtration. This
of 30 mg/kg in 0.5% aqueous methyl cellulose [po] (n )
15)). These data suggest that R2/R3 subtype selective
agonists are anxiolytic and support other recent evi-
solid was recrystallized from methanol, and pure compound 8
dence indicating this.14,15
1
was collected by filtration: 2.2 g (59%), mp 216 °C. H NMR
(360 MHz, DMSO) δ 3.87 (3 H, s), 5.65 (2 H, s), 7.17 (2 H, d,
J ) 8.6 Hz), 7.47 (3 H, m), 7.61 (2 H, d, J ) 8.4 Hz), 7.91 (1 H,
m), 8.07 (1 H, m), 8.23 (1 H, m), 8.32 (2 H, d, J ) 8.4 Hz), 8.53
(1 H, m). Irradiation of the benzylic protons at δ 5.65 produced
nuclear Overhauser effects to δ 8.32 (the ortho protons on the
3-aryl ring) and δ 7.61 (the ortho protons on the 6-benzyl ring).
MS (ES+) m/e 383 [MH]+.
The mother liquors from the recrystallization, which gave
pure 8, were concentrated in vacuo and the residue obtained
was purified by chromatography on silica gel using 0-40%
ethyl acetate in dichloromethane as eluent to give crude 7,
which was recrystallized from diethyl ether and collected by
filtration to give pure 7: 0.045 g (1%), mp 156 °C. 1H NMR
(360 MHz, DMSO) δ 3.85 (3 H, s), 5.23 (2 H, s), 6.56 (2 H, d,
J ) 6.6 Hz), 7.04 (2 H, dd, J ) 8.8 and 2.1 Hz), 7.09-7.17 (3
H, m), 7.48 (2 H, dd, J ) 8.8 and 2.1 Hz), 7.86 (1 H, dd, J )
7.8 and 1.2 Hz, 7.99 (1 H, dd, J ) 7.8 and 1.2 Hz, 8.33 (2 H,
m). Irradiation of the benzylic protons at δ 5.23 also produced
nuclear Overhauser effects to δ 7.48 (the ortho protons on the
3-aryl ring) and δ 6.56 (the ortho protons on the 6-benzyl ring).
MS (ES+) m/e 383 [MH]+.
Exp er im en ta l Section
Gen er a l Meth od s. 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 instrument operating in an electrospray (ES) mode
or on a VB70-250 instrument operating in the electron impact
(EI) or chemical ionization (CI) mode as indicated. (Note that
only the strongest peaks from the mass spectra are reported
below.) Elemental analyses for carbon, hydrogen, and nitrogen
were performed by Butterworth Laboratories Ltd. 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 conducted on silica gel 60, 220-440 mesh (Fluka), under
low pressure. Solutions were evaporated on a Bu¨chi rotary
evaporator under reduced pressure. All starting materials were
obtained from commercial sources and used as received unless
otherwise indicated.
5-Ben zyl-3-(4-m et h oxy)p h en yl-1,2,4-t r ia zolo[3,4-a ]-
p h t h a la zin -6-on e (7) a n d 6-Ben zyloxy-3-(4-m et h oxy)-
p h en yl-1,2,4-t r ia zolo[3,4-a ]p h t h a la zin e (8). 4-Hydrazi-
nophthalazin-1-one (63, 3 g, 0.17 mol) was suspended in dioxan
(45 mL) with triethylamine (2.6 mL, 1.1 mol equiv), and
4-methoxybenzoyl chloride (3.2 g, 1.1 mol equiv) in dioxan (10
mL) was added dropwise over 10 min at room temperature.
The reaction mixture was stirred at room temperature for 30
min, and then the dioxan was removed by rotary evaporation.
The residue was dissolved in DMF (50 mL), and the mixture
was then heated under reflux for 4 h, after which time water
was added dropwise until the solution became cloudy. After
the mixture was allowed to cool, a solid was collected by
filtration, washed with water, and vacuum-dried (64, 2.85 g).
1H NMR (360 MHz, DMSO) δ 3.87 (3 H, s), 7.15 (2 H, d, J )
8.9 Hz), 7.89 (1 H, t, J ) 7.7 Hz), 8.06 (1 H, t, J ) 7.3 Hz),
8.21 (1 H, d J ) 8.3 Hz), 8.34 (2 H, d, J ) 8.9 Hz), 8.46 (1 H,
d, J ) 8.0 Hz), 12.97 (1H, br s). This solid (64, 2.8 g, 0.0098
mol) was dissolved in DMF (80 mL), and sodium hydride (0.432
g of a 60% dispersion in oil, 1.1 mol equiv) was added in
portions. When the addition was complete, the reaction
mixture was heated at 100 °C for 15 min and benzyl bromide
6-Meth oxy-3-ph en yl-1,2,4-tr iazolo[3,4-a ]ph th alazin e (9).
4-Hydrazinophthalazin-1-one (63, 4.5 g, 0.0256 mol) was
suspended in dioxan (50 mL) with triethylamine (3.92 mL, 1.1
mol equiv), and benzoyl chloride (3.27 mL, 1.1 mol equiv) in
dioxan (20 mL) was added dropwise over 10 min at room
temperature. The reaction mixture was stirred at room tem-
perature for 15 min and then heated at reflux temperature
for 2 h. The dioxan was then removed by rotary evaporation,
and the residue was dissolved in DMF (50 mL). The mixture
was then heated under reflux for 4 h, after which time water
was added dropwise until the solution became cloudy. After
the solution was allowed to cool, a solid was collected by
filtration, washed with water, and vacuum-dried (65, 0.54 g,
1
37%). H NMR (360 MHz, DMSO) δ 7.53-7.62 (3 H, m), 7.90
(1 H, t, J ) 7.7 Hz), 8.05 (1 H, t, J ) 7.3 Hz), 8.22 (1 H, d, J
) 8.3 Hz), 8.39-8.41 (2 H, m), 8.50 (1 H, d, J ) 8.0 Hz), 13.02
(1H, br s). This solid (65, 0.262 g, 0.001 mol) was dissolved in
DMF (30 mL), and sodium hydride (0.044 g of a 60% dispersion
in oil, 1.1 mol equiv) was added in portions. When the addition
was complete, the reaction mixture was heated at 80 °C for
15 min and allowed to cool to room temperature and then
methyl iodide (0.069 mL, 1.1 mol equiv) was added in one

1816 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
portion. After 4 h, the solvent was removed by rotary evapora-
tion. The residue was heated with water (50 mL), and a solid
was collected by filtration. This solid was recrystallized from
methanol, and pure compound 9 was collected by filtration:
0.07 g (25%), mp 230 °C. 1H NMR (360 MHz, DMSO) δ 4.20 (3
H, s), 7.54-7.64 (3 H, m), 7.90 (1 H, m), 8.05 (1 H, m), 8.19 (1
H, d, J ) 8.0 Hz), 8.42 (2 H, d, J ) 7.2 Hz), 8.51 (1 H, d, J )
8.0 Hz). Irradiation of the methyl protons at δ 4.20 produced
nuclear Overhauser effects to δ 8.42 (the ortho protons on the
3-aryl ring) and δ 8.19 (the proton at the 7-position of the
triazolophthalazine ring. MS (ES+) m/e 277 [MH]+.
6-P h en oxy-3-p h en yl-1,2,4-t r ia zolo[3,4-a ]p h t h a la zin e
(12). This compound was prepared using method B part 2 for
the formation of 10 using phenol instead of benzyl alcohol: mp
189-199 °C. 1H NMR (360 MHz, DMSO) δ 7.34-7.58 (8 H,
m), 8.08-8.15 (4 H, m), 8.44 (1 H, d, J ) 8.1 Hz), 8.61 (1 H, d,
J ) 8.1 Hz). MS (ES+) m/e 339 [MH]+.
6-P h en yleth yloxy-3-ph en yl-1,2,4-tr iazolo[3,4-a ]ph th ala-
zin e (13). This compound was prepared using method A for
the formation of 10 using phenethylbromide instead of benzyl
1
bromide: mp 160-161 °C. H NMR (360 MHz, DMSO) δ 3.22
(2 H, t, J ) 6.6 Hz), 4.75 (2 H, t, J ) 6.6 Hz), 7.26 (1 H, m),
7.34 (2 H, t, J ) 7.7 Hz), 7.42 (2 H, d, J ) 7.1 Hz), 7.60 (3 H,
m), 8.04 (1 H, t, J ) 7.7 Hz), 8.04 (1 H, t, J ) 6.4 Hz), 8.12 (1
H, d, J ) 7.8 Hz), 8.14 (2 H,d, J ) 7.8 Hz), 8.38 (1 H, d, J )
6.6 Hz). MS (ES+) m/e 367 [MH]+.
6-Be n zyloxy-3-p h e n yl-1,2,4-t r ia zolo[3,4-a ]p h t h a la -
zin e (10). Meth od A. Compound 65 (0.262 g, 0.001 mol) was
dissolved in DMF (30 mL), and sodium hydride (0.044 g of a
60% dispersion in oil, 1.1 mol equiv) was added in portions.
When the addition was complete, the reaction mixture was
heated at 80 °C for 15 min and then benzyl bromide (0.131
mL, 1.1 mol equiv) was added in one portion. After 1 h the
solvent was removed by rotary evaporation, the residue was
heated with water (50 mL), and a solid was collected by
filtration. This solid was recrystallized from methanol, and
pure compound 10 was collected by filtration: 0.19 g (54%),
6-P h en ylpr opyloxy-3-ph en yl-1,2,4-tr iazolo[3,4-a ]ph th al-
a zin e (14). This compound was prepared using method A for
the formation of 10 using 1-bromo-3-phenylpropane instead
1
of benzyl bromide: mp 162 °C. H NMR (360 MHz, DMSO) δ
2.26 (2H, m), 2.87 (2 H, t, J ) 6.7 Hz), 4.52 (2 H, t, J ) 6.7
Hz), 7.19 (1 H, m), 7.30 (4 H, m), 7.56 (3 H, m), 7.88 (1 H, t, J
) 6.5 Hz), 8.04 (1 H, t, J ) 6.5 Hz), 8.13 (1 H, d, J ) 7.9 Hz),
8.36 (2 H,d, J ) 7.8 Hz), 8.48 (1 H, d, J ) 6.6 Hz). MS (ES+)
m/e 381 [MH]+.
1
mp 211 °C. H NMR (360 MHz, DMSO) δ 5.65 (2 H, s), 7.40-
6-P h en ylm et h ylt h io-3-p h en yl-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (15). This compound was prepared using method
B part 2 for the formation of 10 using benzylthiol instead of
7.52 (3 H, m), 7.55-7.70 (5 H, m), 7.93 (1 H, m), 8.08 (1 H,
m), 8.25 (1 H, d, J ) 8.3 Hz), 8.35 (2 H, d, J ) 7.8 Hz), 8.53 (1
H, m). Irradiation of the benzylic protons at δ 5.65 only
produced nuclear Overhauser effects to δ 8.35 (the ortho
protons on the 3-aryl ring) and δ 7.61 (the ortho protons on
the 6-benzyl ring, hidden beneath the multiplet between δ 7.55
and δ 7.70). MS (ES+) m/e 353 [MH]+.
1
benzyl alcohol: mp 219-220 °C. H NMR (360 MHz, CDCl3)
δ 5.58 (2 H, s), 7.30-7.33 (3 H, m), 7.44-7.52 (5 H, m), 7.76
(1 H, dt, J ) 1.0 and 7.1 Hz), 8.01 (1 H, t, J ) 7.2 Hz), 8.10 (1
H, d, J ) 8.2 Hz), 8.34-8.35 (2 H, m), 8.72 (1 H, d, J ) 8.0
Hz). MS (ES+) m/e 369 [MH]+.
NOE studies did not aid the regiochemical assignment of
10 because only enhancements between the benzylic protons
and the ortho protons of the 3-aryl ring were observed. The
assignment was carried out on the basis of the nuclear
Overhauser effectss seen in compound 9 and an unambiguous
synthesis as described below in method B.
6-P h en ylm et h yla m in o-3-p h en yl-1,2,4-t r ia zolo[3,4-a ]-
p h t h a la zin e (16). 6-Chloro-3-phenyl-1,2,4-triazolo[3,4-a]-
phthalazine (67, 0.5 g, 0.018 mol) was added to benzylamine
(10 mL), and the mixture was heated at 120 °C for 8 h. After
the mixture was allowed to cool, water (200 mL) was added
and the aqueous layer was washed with ether (1 × 30 mL).
On standing, the aqueous layer became cloudy and a solid was
collected by filtration. This solid was recrystallized from a
mixture of dichloromethane and methanol to give pure 16: mp
Meth od B, P a r t 1. To a solution of 1,4-dichlorophthalazine
(66, 2 g, 0.01 mol) in dioxan (50 mL) was added triethylamine
(1.53 mL, 1.1 mol equiv) and benzoic hydrazide (1.5 g, 1.1 mol
equiv). This mixture was heated at reflux for 60 h under
nitrogen. After cooling, the reaction mixture was concentrated
under vacuum and the solid obtained was partitioned between
dichloromethane (2 × 100 mL) and water (1 × 50 mL). The
organic layer was dried (Mg SO4), filtered, and concentrated
in vacuo to leave a solid that was triturated with diethyl ether,
collected by filtration, and dried under vacuum to yield
6-chloro-3-phenyl-1,2,4-triazolo[3,4-a]phthalazine (67): 2.6 g
(92%), mp 176 °C (dec). 1H NMR (250 MHz, DMSO) δ 7.60
(3H, m), 8.00 (1H, t, J ) 8.4 Hz), 8.19 (1H, t, J ) 8.4 Hz), 8.31
(3H,m), 8.61 (1H, d, J ) 6.3 Hz). MS m/e 280 [MH]+.
1
293-294 °C. H NMR (360 MHz, DMSO) δ 5.72 (2 H, d, J )
5.4 Hz), 7.26-7.48 (9 H, m), 7.77 (1 H, t, J ) 7.7 Hz), 7.88 (1
H, t, J ) 7.7 Hz), 8.28-8.30 (3H, m), 8.64 (1 H, d, J ) 7.8 Hz).
MS (ES+) m/e 352 [MH]+.
6-(N-Met h yl)p h en ylm et h yla m in o-3-p h en yl-1,2,4-t r ia -
zolo[3,4-a ]p h th a la zin e (17). This compound was prepared
in the same way as compound 16 but using N-methylbenzyl-
amine instead of benzylamine: mp 176-177 °C. 1H NMR (360
MHz, DMSO) δ 3.03 (3 H, s), 5.72 (2 H, s), 7.30-7.58 (8 H,
m), 7.7 (1 H, t, J ) 7.7 Hz), 8.00 (1 H, t, J ) 7.7 Hz), 8.22 (1H,
dd, J ) 1.0 and 7.8 Hz), 8.33 (2 H, dd, J ) 1.0 and 8.5 Hz),
8.58 (1 H, d, J ) 7.8 Hz). MS (ES+) m/e 366 [MH]+.
Meth od B, P a r t 2. To a solution of benzyl alcohol (0.22 mL)
in DMF (10 mL) at room temperature was added sodium
hydride (0.086 g of a 60% dispersion in oil, 1.2 mol equiv), and
the reaction mixture was stirred at room temperature for 15
min. After this time, 67 (0.5 g, 0.0018 mol) was added and the
reaction mixture was heated at 70 °C for 3 h. Water was added
until the solution became cloudy. After the solution was cooled
to room temperature, a solid was collected by filtration and
washed several times in the sinter funnel with water. Recrys-
tallization from methanol gave pure 10, 0.32 g (50%), identical
in all respects to the product obtained from method A.
6-(2-Ch lor op h en yl)m eth yloxy-3-p h en yl-1,2,4-tr ia zolo-
[3,4-a ]p h th a la zin e (18). This compound was prepared using
method A for the formation of 10 using 2-chlorobenzyl bromide
instead of benzyl bromide: mp 246-247 °C. 1H NMR (360
MHz, DMSO) δ 5.72 (2 H, s), 7.32-7.35 (2 H, m), 7.48-7.57
(5H, m), 7.78 (1 H, t, J ) 7.7 Hz), 7.96 (1 H, t, J ) 7.7 Hz),
8.26 (1 H, d, J ) 7.9 Hz), 8.24 (2H, d, J ) 7.8 Hz), 8.71 (1 H,
d, J ) 7.9 Hz). MS (ES+) m/e 387 [MH]+.
6-(3-Ch lor op h en yl)m eth yloxy-3-p h en yl-1,2,4-tr ia zolo-
[3,4-a ]p h th a la zin e (19). This compound was prepared using
method A for the formation of 10 using 3-chlorobenzyl bromide
instead of benzyl bromide: mp 228-229 °C. 1H NMR (360
MHz, DMSO) δ 5.66 (2 H, s), 7.46-7.57 (2 H, m), 7.59-7.64
(4 H, m), 7.71 (1 H, s), 7.93 (1 H, t, J ) 7.2 Hz), 8.07 (1 H, t,
J ) 7.2 Hz), 8.26 (1 H, d, J ) 7.9 Hz), 8.35 (2H, d, J ) 7.8 Hz),
8.69 (1 H, d, J ) 7.9 Hz). MS (ES+) m/e 387 [MH]+.
6-Cycloh exylm eth yloxy-3-p h en yl-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (11). This compound was prepared using method
A for the formation of 10 using cyclohexylmethylbromide
instead of benzyl bromide: mp 180-181 °C. 1H NMR (360
MHz, CDCl3) δ 1.19-1.38 (5 H, m), 1.74-2.02 (6H, m), 4.36
(2 H, d, J ) 6.2 Hz), 7.48-7.57 (3 H, m), 7.77 (1 H, t, J ) 7.2
Hz), 7.90 (1 H, t, J ) 7.2 Hz), 8.20 (1 H, d, J ) 7.8 Hz), 8.46
(2 H, d, J ) 7.8 Hz), 8.65 (1 H, d, J ) 7.8 Hz). MS (ES+) m/e
359 [MH]+.
6-(4-Ch lor op h en yl)m eth yloxy-3-p h en yl-1,2,4-tr ia zolo-
[3,4-a ]p h th a la zin e (20). This compound was prepared using
method A for the formation of 10 using 4-chlorobenzyl bromide
instead of benzyl bromide: mp 204-205 °C. 1H NMR (360
MHz, DMSO) δ 5.64 (2 H, s), 7.51-7.66 (7 H, m), 7.92 (1 H, t,

Phthalazines and Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1817
J ) 7.2 Hz), 8.08 (1 H, t, J ) 7.2 Hz), 8.25 (1 H, d, J ) 7.9
Hz), 8.35 (2H, d, J ) 7.8 Hz), 8.59 (1 H, d, J ) 7.9 Hz). MS
(ES+) m/e 387 [MH]+.
instead of benzyl alcohol: mp 177-178 °C. 1H NMR (360 MHz,
CDCl3) δ 5.73 (2H, s), 7.29 (1H, m), 7.47-7.59 (4 H, m), 7.75-
7.82 (2 H, m), 7.94 (1 H, m), 8.32-8.37 (3 H, m), 8.88-8.91 (2
H, m); m/e 354 [MH]+.
6-(2-Meth oxyph en yl)m eth yloxy-3-ph en yl-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (21). This compound was prepared using
method B part 2 for the formation of 10 using 2-methoxybenzyl
alcohol instead of benzyl alcohol: mp 209-210 °C. 1H NMR
(360 MHz, CDCl3) δ 3.88 (3 H, s), 5.65 (2 H, s), 6.97-7.03 (2
H, m), 7.37 (1 H, t, J ) 7.7H), 7.48-7.56 (4 H, m), 7.74 (1 H,
t, J ) 7.2 Hz), 7.92 (1 H, t, J ) 7.2 Hz), 8.22 (1 H, d, J ) 7.9
Hz), 8.45 (2 H, d, J ) 7.8 Hz), 8.68 (1 H, d, J ) 7.9 Hz). MS
(ES+) m/e 383 [MH]+.
6-(3-Meth oxyph en yl)m eth yloxy-3-ph en yl-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (22). This compound was prepared using
method B part 2 for the formation of 10 using 3-methoxybenzyl
alcohol instead of benzyl alcohol: mp 190-191 °C. 1H NMR
(360 MHz, CDCl3) δ 3.80 (3 H, s), 5.57 (2 H, s), 6.92 (1 H, dd,
J ) 5.6 and 2.2 Hz), 7.08-7.13 (2 H, m), 7.35 (1 H, t, J ) 7.8
Hz), 7.50-7.57 (3 H, m), 7.78 (1 H, t, J ) 7.2 Hz), 7.94 (1 H,
t, J ) 7.2 Hz), 8.24 (1 H, d, J ) 7.9 Hz), 8.39 (2 H, d, J ) 7.8
Hz), 8.68 (1 H, d, J ) 7.9 Hz). MS (ES+) m/e 383 [MH]+.
6-(4-Meth oxyph en yl)m eth yloxy-3-ph en yl-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (23). This compound was prepared using
method B part 2 for the formation of 10 using 4-methoxybenzyl
alcohol instead of benzyl alcohol: mp 166-167 °C. 1H NMR
(360 MHz, CDCl3) δ 3.83 (3 H, s), 5.53 (2 H, s), 6.94 (1 H, dd,
J ) 6.6 and 2.9 Hz), 7.45-7.59 (5 H, m), 7.74 (1 H, t, J ) 7.8
Hz), 7.89 (1 H, t, J ) 7.8 Hz), 7.94 (1 H, t, J ) 7.5 Hz), 8.20 (1
H, d, J ) 7.8 Hz), 8.39 (2 H, d, J ) 6.7 Hz), 8.68 (1 H, d, J )
7.9 Hz). MS (ES+) m/e 383 [MH]+.
3-P h en yl-6-(3-p yr id yl)m eth yloxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (30). This compound was prepared using method
A for the formation of 10 using 3-picolyl chloride hydrochloride
instead of benzyl bromide: mp 182-183 °C. 1H NMR (360
MHz, CDCl3) δ 5.55 (2 H, s), 7.30-7.33 (1 H, m), 7.45-7.52 (3
H, m), 7.70-8.12 (3 H, m), 8.13 (1 H, d, J ) 8.0 Hz), 8.2-8.29
(2 H, m), 8.64 (2 H, m), 8.78 (1 H s). MS (ES+) m/e 354 [MH]+.
3-P h en yl-6-(4-p yr id yl)m eth yloxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (31). This compound was prepared using method
A for the formation of 10 using 4-picolyl chloride hydrochloride
instead of benzyl bromide: mp 229-230 °C. 1H NMR (360
MHz, CDCl3) δ 5.62 (2 H, s), 7.45-7.53 (5 H, m), 7.81-7.96 (2
H, m), 8.26-8.29 (3 H, m), 8.70 (3 H, m). MS (ES+) m/e 354
[MH]+.
3-P h en yl-6-(3-p yr ida zin yl)m eth yloxy-1,2,4-tr ia zolo[3,4-
a ]p h th a la zin e (32). A solution of 3-methylpyridazine (3 g,
0.32 mol) in chloroform (100 mL) was heated to reflux, and
solid trichloroisocyanuric acid (3.11 g, 0.42 mol equiv) was
carefully added over 1 h. The solution was refluxed for a
further 2 h. Once the reaction mixture had cooled to room
temperature, it was filtered through Hyflo and washed with
1 N sodium hydroxide. The organic layer was dried (MgSO4),
filtered, and concentrated in vacuo to give 3-chloromethylpy-
ridazine (3.6 g). 1H NMR (250 MHz, CDCl3) δ 4.90 (2 H, s),
7.48-7.60 (1 H, m), 7.76 (1 H, dd, J ) 2.3 and 12.2 Hz), 9.21
(1 H, m).
6-(3-Cya n op h en yl)m et h yloxy-3-p h en yl-1,2,4-t r ia zolo-
[3,4-a ]p h th a la zin e (24). This compound was prepared using
method A for the formation of 10 using 3-cyanobenzyl bromide
instead of benzyl bromide: mp 226-228 °C. 1H NMR (360
MHz, DMSO) δ 5.72 (2 H, s), 7.57-7.70 (4 H, m), 7.86-8.12
(5 H, m), 8.33 (3 H, t, J ) 7.2 Hz), 8.58 (1 H, d, J ) 7.9 Hz).
MS (ES+) m/e 378 [MH]+.
3-P h en yl-6-(2-t h en yl)m et h yloxy-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (25). This compound was prepared using method
B part 2 for the formation of 10 using 2-thiophene methanol
instead of benzyl alcohol: mp 229-231 °C. 1H NMR (360 MHz,
CDCl3) δ 5.65 (2 H, s), 7.04-7.06 (1 H, m), 7.27 (1 H, d, J )
1.2 Hz), 7.53 (1 H, dd, J ) 1.2 and 5.2 Hz), 7.51-7.59 (3H, m),
7.76 (1 H, t, J ) 7.6 Hz), 7.91 (1 H, t, J ) 7.4 Hz), 8.19 (1 H,
d, J ) 8.1 Hz), 8.46 (2 H, d, J ) 6.8 Hz), 8.68 (1 H, d, J ) 7.9
Hz). MS (ES+) m/e 359 [MH]+.
This compound was prepared using method A for the
formation of 10 using 3-chloromethylpyridazine (as described
above) instead of benzyl bromide: mp 187-189 °C. H NMR
1
(360 MHz, DMSO) δ 5.74 (2 H, s), 7.52-7.54 (3 H, m), 7.82-
7.96 (1 H, m), 7.99 (1 H, t, J ) 7.2 Hz), 8.11-8.15 (3 H, m),
8.41 (1 H, d, J ) 7.8 Hz), 8.58 (1 H, d, J ) 7.8 Hz), 8.86 (1 H,
d, J ) 5.2 Hz), 9.25 (1 H, d, J ) 1.3 Hz). (ES+) m/e 355 [MH]+.
3-P h en yl-6-(4-p yr im id in yl)m et h yloxy-1,2,4-t r ia zolo-
[3,4-a ]p h th a la zin e (33). This compound was prepared using
the method described above for the formation of 32 using
4-methylpyrimidine instead of 3-methylpyridazine: mp 199-
201 °C. 1H NMR (360 MHz, DMSO) δ 5.74 (2 H, s), 7.53-7.55
(3 H, m), 7.83 (1 H, d, J ) 5.3 Hz), 8.00 (1 H, t, J ) 7.3 Hz),
8.13-8.16 (3 H, m), 8.40 (1 H, d, J ) 7.8 Hz), 8.58 (1 H, d, J
) 7.8 Hz), 8.87 (1 H, d, J ) 5.2 Hz), 9.25 (1 H, d, J ) 1.3 Hz).
MS (ES+) m/e 355 [MH]+.
3-P h en yl-6-(3-t h en yl)m et h yloxy-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (26). This compound was prepared using method
B part 2 for the formation of 10 using 3-thiophene methanol
instead of benzyl alcohol: mp 216-217 °C. 1H NMR (360 MHz,
CDCl3) δ 5.61 (2 H, s), 7.25 (1 H, d, J ) 1.2 Hz), 7.38-7.40 (1
H, m), 7.47-7.57 (4H, m), 7.76 (1 H, t, J ) 7.6 Hz), 7.91 (1 H,
t, J ) 7.4 Hz), 8.22 (1 H, d, J ) 8.1 Hz), 8.44 (2 H, d, J ) 6.8
Hz), 8.69 (1 H, d, J ) 7.9 Hz). MS (ES+) m/e 359 [MH]+.
6-(2-F u r yl)m et h yloxy-3-p h en yl-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (27). This compound was prepared using method
B part 2 for the formation of 10 using 2-furfuryl alcohol instead
of benzyl alcohol: mp 213-215 °C. 1H NMR (360 MHz, CDCl3)
δ 5.57 (2 H, s), 6.43 (1 H, dd, J ) 1.9 and 3.3 Hz), 6.57 (1 H,
d, J ) 3.1 Hz), 7.50-7.59 (4 H, m), 7.70 (1 H, t, J ) 7.8 Hz),
7.90 (1 H, t, J ) 7.8 Hz), 8.20 (1 H, d, J ) 7.8 Hz), 8.40 (2 H,
d, J ) 6.7 Hz), 8.65 (1 H, d, J ) 7.9 Hz). MS (ES+) m/e 343
[MH]+.
6-(3-F u r yl)m et h yloxy-3-p h en yl-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (28). This compound was prepared using method
B part 2 for the formation of 10 using 3-furfuryl alcohol instead
of benzyl alcohol: mp 210-211 °C. 1H NMR (360 MHz, CDCl3)
δ 5.49 (2 H, s), 6.58 (1 H, d, J ) 1.1 Hz), 7.46-7.57 (5 H, m),
7.77 (1 H, t, J ) 7.8H), 7.92 (1 H, t, J ) 7.8 Hz), 8.18 (1 H, d,
J ) 7.8 Hz), 8.45 (2 H, d, J ) 6.7 Hz), 8.70 (1 H, d, J ) 7.9
Hz). MS (ES+) m/e 343 [MH]+.
3-P h en yl-6-(2-p yr a zin yl)m et h yloxy-1,2,4-t r ia zolo[3,4-
a ]p h th a la zin e (34). This compound was prepared using the
method above for the formation of 32 using 2-methylpyrazine
instead of 3-methylpyridazine: mp 163-165 °C. 1H NMR (360
MHz, DMSO) δ 5.79 (2 H, s), 7.56-7.59 (3 H, m), 7.96 (1 H, t,
J ) 7.2 Hz), 8.10 (1 H, t, J ) 7.3 Hz), 8.22-8.25 (2 H, m), 8.34
(1 H, d, J ) 7.8 Hz), 8.58 (1 H, d, J ) 7.8 Hz), 8.70 (2 H, dd,
J ) 10.2 and 1.3 Hz), 8.99 (1 H, d, J ) 1.3 Hz). MS (ES+) m/e
355 [MH]+.
3-P h en yl-6-(2-(1-m eth yl)im id a zoyl)m eth yloxy-1,2,4-tr i-
a zolo[3,4-a ]p h th a la zin e (35). This compound was prepared
using method B part 2 described above for the formation of
10 using 1-methyl-2-imidazoylmethanol instead of benzyl
1
alcohol: mp 240 °C. H NMR (360 MHz, DMSO) δ 3.79 (3 H,
s), 5.69 (2 H, s), 6.97 (1 H, s), 7.30 (1 H, s), 7.58-7.67 (3 H,
m), 7.90 (1 H, t, J ) 7.2 Hz), 8.10 (1 H, t, J ) 7.2 Hz), 8.18 (1
H, d, J ) 7.9 Hz), 8.46-8.58 (3 H, m). MS (ES+) m/e 357 [MH]+.
3-P h en yl-6-(4-p ip er id yl)m eth yloxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e Bish yd r och or id e (36). This compound was
prepared using method B part 2 for the formation of 10 using
4-hydroxymethyl-N-tert-butyloyxcarbonylpiperidine (0.499 mg)
instead of benzyl alcohol. The crude product was dissolved in
methanol (50 mL), and a 10% solution of hydrogen chloride in
methanol (20 mL) was added. The reaction mixture was stirred
for 18 h at room temperature, the solvent was removed under
vacuum, and the crude product was purified by recrystalliza-
tion from a mixture of ethyl acetate and methanol to yield
compound 36: mp 287-289 °C. 1H NMR (360 MHz, D2O) δ
3-P h en yl-6-(2-p yr id yl)m eth yloxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (29). This compound was prepared using method
B part 2 for the formation of 9 but using 2-pyridyl carbinol

1818 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
1.41 (2 H, m), 1.81 (2 H, m), 2.95 (2H, m), 3.44 (3H, m), 4.78
(2 H, s), 7.14-7.56 (9 H, m). MS (ES+) m/e 360 [MH]+.
3-P h en yl-6-(2-p yr id yl)et h yloxy-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (37). This compound was prepared using method
A for the formation of 10 using 2-chloroethylpyridine instead
of benzyl bromide: mp 171-173 °C. 1H NMR (360 MHz,
CDCl3) δ 3.45 (2H, t, J ) 6.4 Hz), 4.90 (2 H, t, J ) 6.4 Hz),
7.16-7.20 (1H, m), 7.32 (1 H, d, J ) 7.8 Hz), 7.49-7.59 (3 H,
m), 7.63-7.75 (2H, m), 7.89 (1H, t, J ) 8.2 Hz), 8.07 (1 H, d,
J ) 8.0 Hz), 8.44-8.62 (4H, m). MS (ES+) m/e 368 [MH]+.
3-P h en yl-6-(6-m eth ylpyr id-2-yl)m eth yloxy-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (38). This compound was prepared using
method B part 2 for the formation of 10 using 6-methyl-2-
pyridylmethanol (prepared by the method of Katsuhiro et al.)34
instead of benzyl alcohol: mp 186-187 °C. 1H NMR (360 MHz,
DMSO) δ 2.34 (3 H, s), 5.66 (2 H, s), 7.53-7.58 (4 H, m), 7.68
(1 H, d, J ) 8.0 Hz), 7.93 (1 H, t, J ) 7.7 Hz), 8.07 (1 H, t, J
) 7.7 Hz), 8.25-8.30 (3 H, m), 8.46 (1 H, s), 8.59 (1H, d, J )
7.7 Hz). MS (ES+) m/e 368 [MH]+.
3-P h en yl-6-(5-m eth ylpyr id-2-yl)m eth yloxy-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (39). This compound was prepared using
method B part 2 for the formation of 10 using 5-methyl-2-
pyridylmethanol34 instead of benzyl alcohol: mp 213 °C (dec).
1H NMR (360 MHz, DMSO) δ 2.52 (3 H, s), 5.65 (2 H, s), 7.25
(1 H, d, J ) 7.7 Hz), 7.47-7.58 (4 H, m), 7.78 (1 H, t, J ) 7.7
Hz), 7.94 (1 H, t, J ) 7.7 Hz), 8.28 (1 H, t, J ) 7.7 Hz), 8.30-
8.33 (3 H, m), 8.58 (1H, d, J ) 7.7 Hz). MS (ES+) m/e 368
[MH]+.
3-P h en yl-6-(4-m eth ylpyr id-2-yl)m eth yloxy-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (40). This compound was prepared using
method B part 2 for the formation of 10 using 4-methyl-2-
pyridylmethanol34 instead of benzyl alcohol: mp 199-201 °C.
1H NMR (360 MHz, DMSO) δ 2.34 (3 H, s), 5.66 (2 H, s), 7.21
(1 H, d, J ) 7.7 Hz), 7.52-7.60 (4 H, m), 7.96 (1 H, t, J ) 7.7
Hz), 8.06 (1 H, t, J ) 7.7 Hz), 8.26-8.29 (3 H, m), 8.48 (1H, d,
J ) 5.2 Hz), 8.58 (1 H, d, J ) 7.8). MS (ES+) m/e 368 [MH]+.
3-P h en yl-6-(3-m eth ylpyr id-2-yl)m eth yloxy-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (41). This compound was prepared using
method B part 2 for the formation of 10 using 3-methyl-2-
pyridylmethanol34 instead of benzyl alcohol: mp 210 °C (dec).
1H NMR (360 MHz, DMSO) δ 2.44 (3 H, s), 5.76 (2 H, s), 7.31-
7.34 (1 H, m), 7.55-7.58 (3 H, m), 7.92 (1 H, d, J ) 7.7HZ),
7.94 (1 H, t, J ) 7.7 Hz), 8.23 (1 H, t, J ) 7.7 Hz), 8.25-8.28
(3 H, m), 8.30 (1H, m), 8.58 (1 H, d, J ) 7.8). MS (ES+) m/e
368 [MH]+.
CDCl3) δ 1.52 (3H, t, J ) 7.5 Hz), 3.22 (2H, q, J ) 7.5 and 15
Hz), 7.79-8.00 (2H, m), 8.28 (1H, dd, J ) 0.5 and 8.0 Hz),
8.65 (1H, dd, J ) 0.5 and 8.0 Hz).
To a solution of 2-pyridylcarbinol (0.27 mL) in DMF (20 mL)
at room temperature was added sodium hydride (0.112 g of a
60% dispersion in oil, 1.3 mol equiv), and the reaction mixture
was stirred at room temperature for 20 min. After this time,
6-chloro-3-ethyl-1,2,4-triazolo[3,4-a]phthalazine from above
(0.5 g, 0.0021 mol) was added and the reaction mixture was
stirred for 14 h at room temperature. The reaction mixture
was concentrated under vacuum, and the solid obtained was
partitioned between dichloromethane (150 mL) and water (3
× 100 mL). The organic layer was washed with brine, dried
(Mg SO4), filtered, and concentrated in vacuo to yield a solid
that was recrystallized from a mixture of ethyl acetate and
hexane to give pure 44: 0.142 g (22%), mp 157-158 °C. 1H
NMR (360 MHz, CDCl3) δ 1.41 (3H, t, J ) 7.5 Hz), 3.11 (2H,
q, J ) 7.5 and 15 Hz), 5.69 (2H, s), 7.28-7.33 (1H, m), 7.52
(1H,d, J ) 11.2 Hz), 7.75-7.94 (3H, m), 8.29 (1H, dd, J ) 0.5
and 8.0 Hz), 8.60-8.7 (2H, m). MS (ES+) m/e 306 [MH]+.
3-P r op yl-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (45). This compound was prepared using the
method above for the formation of 44 using butyryl chloride
1
instead of propionyl chloride: mp 138-139 °C. H NMR (360
MHz, CDCl3) δ 1.01 (3H, t, J ) 7.4 Hz), 1.84 (2H,m), 3.07 (2H,
t, J ) 7.4 Hz), 5.69 (2H, s), 7.28-7.32 (1H, m), 7.57 (1H,d, J
) 11.2 Hz), 7.73-7.80 (2H, m), 7.80-7.92 (1H, m), 8.27 (1H,
d, J ) 8.0 Hz), 8.62 (H, d, J ) 8.0 Hz), 8.65 (1H, d, J ) 4.0
Hz). MS (ES+) m/e 320 [MH]+.
3-Isop r op yl-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia zolo[3,4-
a ]p h th a la zin e (46). This compound was prepared using the
method above for the formation of 44 using isobutyryl chloride
1
instead of propionyl chloride: mp 149-150 °C. H NMR (360
MHz, CDCl3) δ 1.47 (6H, d, J ) 7.0 Hz), 3.07 (1H, q, J ) 7.0
and 14.0 Hz), 5.69 (2H, s), 7.27-7.31 (1H, m), 7.56 (1H, d, J )
7.8 Hz), 7.73-7.79 (2H, m), 7.80-7.92 (1H, m), 8.26 (1H, d, J
) 8.0 Hz), 8.62 (1H, d, J ) 8.0 Hz), 8.65 (1H, d, J ) 3.6 Hz).
MS (ES+) m/e 320 [MH]+.
3-ter t-Bu tyl-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia zolo[3,4-
a ]p h th a la zin e (47). This compound was prepared using the
method above for the formation of 44 using pivaloyl chloride
1
instead of propionyl chloride: mp 155-157 °C. H NMR (360
MHz, CDCl3) δ 1.55 (9H, s), 5.68 (2H, s), 7.29-7.31 (1H, m),
7.55 (1H, d, J ) 7.9 Hz), 7.75-7.78 (2H, m), 7.89 (1H, t, J )
7.3 Hz), 8.24 (1H, d, J ) 8.0 Hz), 8.6-8.70 (2H, m). MS (ES+)
m/e 334 [MH]+.
3-P h en yl-6-(1-(2-p yr id yl)eth yl)oxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (42). This compound was prepared using method
A for the formation of 10 using 1-chloroethylpyridine instead
3-Eth en yl-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (48). This compound was prepared using the
method above for the formation of 44 using acryloyl chloride
1
of benzyl bromide: mp 220-221 °C. H NMR (360 MHz, D6-
MSO) δ 1.81 (3H, d, J ) 6.6 Hz), 6.15 (1 H, q, J ) 6.6 Hz),
7.31-7.35 (1H, m), 7.52-7.61 (4 H, m), 7.80 (1 H, t, J ) 1.7
Hz), 7.97 (1 H, t, J ) 1.7 Hz), 8.07-8.09 (3H, m), 8.38 (1 H, d,
J ) 7.9 Hz), 8.52 (1H, d, J ) 7.9 Hz), 8.60 (1H, m). MS (ES+)
m/e 368 [MH]+.
1
instead of propionyl chloride: mp 156-157 °C. H NMR (360
MHz, CDCl3) δ 5.68 (2H, s), 5.75 (1H, dd, J ) 1.9 and 16.8
Hz), 6.70 (1H, dd, J ) 2.0 and 25.8 Hz), 7.02-7.14 (1H, m),
7.25-7.30 (1H, m), 7.58 (1H, d, J ) 7.9 Hz), 7.78 (2H, t, J )
8.5 Hz), 7.96 (1H, t, J ) 7.3 Hz), 8.24 (1H, d, J ) 11.0 Hz),
8.62-8.72 (2H, m). MS (ES+) m/e 304 [MH]+.
6-(2-P yr id ylm eth yl)oxy-3-m eth yl-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (43). This compound was prepared using the
method above for the formation of 9 using acetyl chloride in
place of benzoyl chloride and 2-picolyl chloride instead of
methyl iodide: mp 165-166 °C. 1H NMR (360 MHz, CDCl3) δ
2.71 (3H, s), 5.70 (2 H, s), 7.28-7.32 (1H, m), 7.59 (1H, d, J )
7.9 Hz), 7.79-7.93 (3H, m), 8.27 (1 H, d, J ) 7.9 Hz), 8.61
(1H, d, J ) 7.9 Hz), 8.64 (1H, m). MS (ES+) m/e 292 [MH]+.
3-E t h yl-6-(2-p yr id ylm et h yl)oxy-1,2,4-t r ia zolo[3,4-a ]-
p h th a la zin e (44). 4-Hydrazino-1-chlorophthalazine (69, 2 g,
0.087 mol) was suspended in dioxan (200 mL) with triethyl-
amine (1.46 mL, 1.2 mol equiv), and propionyl chloride (0.91
mL, 1.2 mol equiv) was added. The reaction mixture was
stirred at room temperature for 2 h and then heated under
reflux for 14 h. After cooling, the reaction mixture was
concentrated under vacuum and the solid obtained was
partitioned between dichloromethane (200 mL) and water (2
× 200 mL). The organic layer was dried (Mg SO4), filtered,
and concentrated in vacuo to yield 6-chloro-3-ethyl-1,2,4-
3-Ben zyl-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia zolo[3,4-a ]-
p h th a la zin e (49). This compound was prepared using the
method above for the formation of 44 using phenylacetyl
chloride instead of propionyl chloride: mp 170-171 °C. 1H
NMR (360 MHz, CDCl3) δ 4.47 (2H,s), 5.63 (2H, s), 7.17-7.31
(4H, m), 7.36 (2H, d, J ) 7.2 Hz), 7.47 (1H, d, J ) 7.8 Hz),
7.70-7.74 (2H, m), 7.91 (1H, t, J ) 8.1 Hz), 8.25 (1H, d, J )
11.0 Hz), 8.61 (1H, d, J ) 7.9 Hz), 8.64 (1H, m). MS (ES+) m/e
368 [MH]+.
3-Cyclop r op yl-6-(2-p yr id ylm et h yl)oxy-1,2,4-t r ia zolo-
[3,4-a ]p h th a la zin e (50). This compound was prepared using
the method above for the formation of 44 using cyclopropan-
ecarbonyl chloride instead of propionyl chloride: mp 157-158
°C. 1H NMR (360 MHz, CDCl3) δ 1.09-1.16 (2H, m), 1.31-
1.37 (2H, m), 2.34-2.44 (1H, m), 5.70 (2H, s), 7.28-7.33 (1H,
m), 7.58 (1H, d, J ) 7.9 Hz), 7.74-7.79 (3H, m), 8.25 (1H, d,
J ) 11.1 Hz), 8.58 (1H, d, J ) 11.1 Hz), 8.65 (1H, m). MS (ES+)
m/e 318 [MH]+.
1
triazolo[3,4-a]phthalazine: 1.88 g (94%). H NMR (250 MHz,

Phthalazines and Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1819
3-Cyclop r op yl-6-(2-(6-m eth ylp yr id yl)m eth yl)oxy-1,2,4-
tr ia zolo[3,4-a ]p h th a la zin e (51). This compound was pre-
pared using the method above for the formation of 44 using
cyclopropanecarbonyl chloride instead of propionyl chloride
and 6-methyl-2-pyridinemethanol in place of 2-pyridylcar-
To a solution of 1,4-dichloro-5-methylphthalazine (72, 5.5
g, 0.026 mol) in xylene (100 mL) was added triethylamine (4.36
mL, 1.2 mol equiv) and benzoic hydrazide (3.85 g, 1.1 mol
equiv). This mixture was heated at reflux for 24 h under
nitrogen. After cooling, the reaction mixture was concentrated
under vacuum and the solid obtained was partitioned between
dichloromethane (2 × 100 mL) and water (1 × 50 mL). The
organic layer was dried (MgSO4), filtered, and concentrated
in vacuo to leave a solid that was purified by silica gel column
chromatography using 0.5-3% methanol in DCM as eluent
to yield both 6-chloro-3-phenyl-7-methyl-1,2,4-triazolo[3,4-a]-
phthalazine (74, high Rf product) and 6-chloro-3-phenyl-10-
methyl-1,2,4-triazolo[3,4-a]phthalazine (73, low Rf product) in
a ratio of 3:1. 73: 1H NMR (250 MHz, DMSO) δ 2.98 (3H,s),
7.59-7.68 (3H, m), 7.82 (1H, d, J ) 7.6 Hz), 7.98 (1H, t, J )
7.6 Hz), 8.27-8.31 (2H, m), 8.51 (1H, d, J ) 7.5 Hz). 74: 1H
NMR (250 MHz, DMSO) δ 3.05 (3H,s), 7.57-7.67 (3H, m),
7.85-8.06 (2H, m), 8.28 (1H, d, J ) 7.5 Hz), 8.27-8.28 (3H,
m).
1
binol: mp 134-136 °C. H NMR (360 MHz, DMSO) δ 1.22-
1.25 (4H, m), 2.50-2.52 (1H, m), 2.74 (3H, s), 5.90 (2H, s), 7.72
(1H, d, J ) 7.8 Hz), 7.96-8.10 (2H, m), 8.12 (1H, t, J ) 6.8
Hz), 8.27-8.37 (2H, m), 8.5 (1H, d, J ) 11.1 Hz). MS (ES+)
m/e 332 [MH]+.
3-Cyclobu tyl-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia zolo[3,4-
a ]p h th a la zin e (52). This compound was prepared using the
method above for the formation of 44 using cyclobutanecar-
bonyl chloride instead of propionyl chloride: mp 170-171 °C.
1H NMR (360 MHz, CDCl3) δ 2.08-2.23 (2H, m), 2.41-2.49
(2H, m), 2.59-2.70 (2H, M), 4.39-4.08 (1H, m), 5.69 (2H, s),
7.28-7.31 (1H, m), 7.56 (1H, d, J ) 7.8 Hz), 7.7-7.79 (3H,
m), 8.26 (1H, d, J ) 7.8 Hz), 8.62-8.70 (2H, m). MS (ES+) m/e
332 [MH]+.
To a solution of 2-hydroxymethylpyridine (0.158 mL, 0.0016
mol) in DMF (20 mL) at room temperature was added sodium
hydride (0.066 g of a 60% dispersion in oil, 0.0016 mol), and
the reaction mixture was stirred at room temperature for 15
min. After this time, 73 (0.4 g, 0.0014 mol) was added and the
reaction mixture was stirred at room temperature for 18 h.
The reaction mixture was concentrated under vacuum, and
the solid obtained was partitioned between dichloromethane
(2 × 100 mL) and water (1 × 50 mL). The organic layer was
dried (MgSO4), filtered, and concentrated in vacuo to leave a
solid that was recrystallized from a mixture of ethyl acetate
and dichloromethane to give pure 56: 0.101 g, (21%), mp 197-
3-Dim eth yla m in om eth yl-6-(2-p yr id ylm eth yl)oxy-1,2,4-
tr ia zolo[3,4-a ]p h th a la zin e (53). This compound was pre-
pared using method B for the formation of 10 using N,N-
dimethylglycine hydrazide hydrochloride instead of benzoic
hydrazide and 2-pyridylcarbinol instead of benzyl alcohol: mp
1
122-124 °C. H NMR (360 MHz, CDCl3) δ 2.39 (6H, s), 4.02
(2H, s), 5.71 (2H, s), 7.28-7.32 (1H, m), 7.59 (1H, d, J ) 7.8
Hz), 7.78 (2H, dt, J ) 1.0 and 7.9 Hz), 7.90 (1H, t, J ) 8.2
Hz), 8.28 (1H, d, J ) 7.8 Hz), 8.65-8.72 (2H, m). MS (ES+)
m/e 335 [MH]+.
3-(4-F lu or op h en yl)-6-(2-p yr id ylm et h yl)oxy-1,2,4-t r ia -
zolo[3,4-a ]p h th a la zin e (54). This compound was prepared
using the method above for the formation of 44 using 4-fluo-
robenzoyl chloride instead of propionyl chloride: mp 186-187
°C. 1H NMR (250 MHz, DMSO) δ 5.69 (2H, s), 7.38-7.45 (3H,
m), 7.70 (1H,d, J ) 7.8 Hz), 7.90-7.97 (2H, m), 8.09 (1H, dt,
J ) 1.0 and 7.8 Hz), 8.28-8.34 (3H, m), 8.57 (H, d, J ) 7.9
Hz), 8.64 (1H, d, J ) 4.0 Hz). MS (ES+) m/e 372 [MH]+.
1
198 °C. H NMR (360 MHz, DMSO) δ 2.48 (3 H, s), 5.66 (2 H,
s), 7.37-7.40 (1H, m), 7.54-7.56 (3 H, m), 7.66 (1H, d, J )
7.8 Hz), 7.73 (1H, d, J ) 7.8 Hz), 7.86-7.94 (2H, m), 8.24 (2
H, dd, J ) 1.6 and 8.0 Hz), 8.42 (1H, d, J ) 8.0 Hz), 8.70 (1H,
m). MS (ES+) m/e 368 [MH]+.
3-P h en yl-6-(2-pyr idylm eth yl)oxy-7-m eth yl-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (59). To a solution of 2-hydroxymethylpy-
ridine (0.197 mL, 0.002 mol) in DMF (30 mL) at room
temperature was added sodium hydride (0.082 g of a 60%
dispersion in oil, 0.002 mol), and the reaction mixture was
stirred at room temperature for 15 min. After this time, 74
(0.5 g, 0.0017 mol) was added and the reaction mixture was
stirred at room temperature for 18 h, after which time TLC
showed 80% conversion. More sodium hydride (0.016 g of a
60% dispersion in oil, 0.0004 mol) was added, and the reaction
mixture was stirred for a further 3 h. The reaction mixture
was concentrated under vacuum, and the solid obtained was
partitioned between dichloromethane (2 × 100 mL) and water
(1 × 50 mL). The organic layer was dried (MgSO4), filtered,
and concentrated in vacuo to leave a solid. Recrystallization
from a mixture of ethyl acetate and dichloromethane gave pure
59: 0.165 g (45%), mp 169-171 °C. 1H NMR (360 MHz,
DMSO) δ 3.01 (3 H, s), 5.66 (2 H, s), 7.37-7.39 (1H, m), 7.53-
7.56 (3H, m), 7.66 (1H, d, J ) 7.8 Hz), 7.76-7.89 (3H, m), 8.13
(1H, d, J ) 7.8 Hz), 8.21-8.24 (2H, m), 8.64 (1H, m).
Irradiation of the benzylic protons at δ 5.66 produced a nuclear
Overhauser effect to δ 3.01 (methyl group). MS (ES+) m/e 368
[MH]+.
3-(4-Meth ylp h en yl)-6-(2-p yr id ylm eth yl)oxy-1,2,4-tr ia -
zolo[3,4-a ]p h th a la zin e (55). This compound was prepared
using method B for the formation of 10 using 4-toluic hydrazide
hydrochloride instead of benzoic hydrazide and 2-pyridyl-
1
carbinol instead of benzyl alcohol: mp 224-225 °C. H NMR
(250 MHz, DMSO) δ 2.45 (3H,s), 5.72 (2H, s), 7.29-7.34 (3H,
m), 7.57 (1H, d, J ) 7.8 Hz), 7.75-7.81 (2H, m), 7.91-7.93
(1H, m), 8.22-8.31 (3H, m), 8.68-8.71 (2H, m). MS (ES+) m/e
372 [MH]+.
3-P h en yl-6-(2-p yr id ylm eth yl)oxy-10-m eth yl-1,2,4-tr ia -
zolo[3,4-a ]p h th a la zin e (56). To a solution of 3-methylphthal-
ic anhydride (70, 15 g, 0.093 mol) in aqueous acetic acid (300
mL of 40%) was added hydrazine hydrate (5.4 mL, 0.11 mol)
and sodium acetate (15.1 g, 0.11 mol), and the reaction mixture
was heated at reflux for 18 h. When the mixture was cooled,
the resultant solid was collected by filtration and dried, and
NMR analysis showed this to be a mixture of product and
starting material. This material was redissolved in aqueous
acetic acid (500 mL of 40%) with hydrazine hydrate (3.6 mL,
0.072 mol) and sodium acetate (10 g, 0.072mol), and the
reaction mixture was heated under reflux for a further 72 h.
When the mixture was cooled, the solid was collected by
filtration to yield 5-methylphthalazinedione (71, 5.6 g). 1H
NMR (250 MHz, DMSO) δ 2.81 (3H, s), 7.61 (1H, dd, J ) 6.3
and 1.0 Hz), 7.37 (1H, t, J ) 7.5 Hz), 7.88 (1H, dd, J ) 7.5
and 1.0 Hz), 11.4 (2H, bs). MS (ES+) m/e 177 [MH]+.
A solution of 5-methylphthalazinedione (71, 5.5 g) in
phosphorus oxychloride (200 mL) was refluxed for 18 h, cooled,
and evaporated to dryness. The resulting material was dis-
solved in DCM (150 mL) and cold water (200 mL). Solid sodium
hydrogen carbonate was added carefully until pH 11 was
attained, the aqueous layer was extracted with DCM (2 × 100
mL), and then the combined organic layers were washed with
brine. The organic layer was dried (MgSO4), filtered, and
concentrated in vacuo to yield 1,4-dichloro-5-methylphthala-
zine (72, 5.5 g). 1H NMR (250 MHz, DMSO) δ 3.10 (3H,s),
8.04-8.13 (2H, m), 8.13-8.26 (1H, m).
3-P h en yl-6-(2-pyr idylm eth yl)oxy-9-m eth yl-1,2,4-tr iazolo-
[3,4-a ]p h th a la zin e (57) a n d 3-P h en yl-6-(2-p yr id ylm eth -
yl)oxy-8-m eth yl-1,2,4-tr ia zolo[3,4-a ]p h th a la zin e (58). To
a solution of 4-methylphthalic anhydride (75, 30 g, 0.19 mol)
in aqueous acetic acid (400 mL of 40%) was added hydrazine
hydrate (10.8 mL, 0.22 mol) and sodium acetate (30.2 g, 0.22
mol). The reaction mixture was heated under reflux for 18 h.
When the mixture was cooled, the resultant solid was collected
by filtration and dried to yield 6-methylphthalazinedione (76,
1
32 g). H NMR (250 MHz, DMSO) δ 2.51 (3H,s), 7.70 (1H, dd,
J ) 1.4 and 8.2 Hz), 7.87 (1H, d, J ) 1.4 Hz), 7.98 (1H, dd, J
) 1.4 and 8.1 Hz), 11.47 (2H,bs). MS (ES+) m/e 177 [MH]+.
A solution of 6-methylphthalazinedione (76, 28 g) in phos-
phorus oxychloride (500 mL) was refluxed for 18 h, cooled, and
evaporated to dryness. The resulting material was dissolved

1820 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Carling et al.
in DCM (200 mL) and cold water (300 mL), and solid sodium
hydrogen carbonate was added carefully until pH 11 was
achieved. The aqueous layer was extracted with DCM (2 ×
200), and the combined organic layers were washed with brine.
The organic layer was dried (MgSO4), filtered, and concen-
trated in vacuo to yield 1,4-dichloro-6-methylphthalizine (77,
29 g). 1H NMR (250 MHz, DMSO) δ 2.60 (3H, s), 8.07-8.16
(2H, m), 8.24 (1H, d, J ) 8.3 Hz).
To a solution of 1,4-dichloro-5-methylphthalazine (77, 15 g,
0.07 mol) in xylene (200 mL) was added triethylamine (11.8
mL, 1.2 mol equiv) and benzoic hydrazide (10.5 g, 1.1 mol
equiv). The reaction mixture was heated under reflux for 48
h under nitrogen. After cooling, the reaction mixture was
concentrated under vacuum and the solid obtained was
partitioned between dichloromethane (2 × 100 mL) and water
(1 × 50 mL). The organic layer was dried (MgSO4), filtered,
and concentrated in vacuo to leave a solid that was shown to
be a 3:2 mixture of two regioisomers by NMR: chloro-3-phenyl-
9-methyl-1,2,4-triazolo[3,4-a]phthalazine (78) and 6-chloro-3-
phenyl-8-methyl-1,2,4-triazolo[3,4-a]phthalazine (79). The two
isomers were inseparable and were thus used in the next step
as a mixture. NMR data for mixture: 1H NMR (250 MHz,
DMSO) δ 2.59 (3H, s, minor isomer), 2.63 (3H, s, major isomer),
7.58-8.30 (8H, m).
To a solution of 2-hydroxymethylpyridine (0.990 mL, 0.01
mol) in DMF (30 mL) at room temperature was added sodium
hydride (0.326 g of a 60% dispersion in oil, 0.082 mol), and
the reaction mixture was stirred at room temperature for 15
min. After this time the mixture of chloro-3-phenyl-9-methyl-
1,2,4-triazolo[3,4-a]phthalazine (78) and 6-chloro-3-phenyl-8-
methyl-1,2,4-triazolo[3,4-a]phthalazine (79, 2.0 g, 0.068 mol)
was added and the reaction mixture was stirred at room
temperature for 18 h. The reaction mixture was concentrated
under vacuum, and the solid obtained was partitioned between
dichloromethane (3 × 200 mL) and water (1 × 50 mL). The
organic layer was dried (MgSO4), filtered, and concentrated
in vacuo to leave a solid. The two products were separated by
column chromatography using 3% methanol in dichloromethane
as eluent, and the required products were individually recrys-
tallized from a mixture of ethyl acetate and dichloromethane
to give 3-phenyl-6-(2-pyridylmethyl)oxy-9-methyl-1,2,4-tria-
zolo[3,4-a]phthalazine (57, 0.275 g, high Rf product) and
3-phenyl-6-(2-pyridylmethyl)oxy-8-methyl-1,2,4-triazolo[3,4-a]-
phthalazine (58, 0.16 g, low Rf product). 57: mp 190-191 °C.
1H NMR (360 MHz, DMSO) δ 2.60 (3 H, s), 5.67 (2 H, s), 7.37-
7.41 (1H, m), 7.53-7.56 (3H, m), 7.70 (2H, m), 7.86 (1H, t, J
) 6.0), 8.18 (1H, d, J ) 8.2 Hz), 8.26 (2H, m), 8.32 (1H, s),
8.68 (1H, d, J ) 6.0 Hz). Irradiation of the benzylic protons at
δ 5.67 did not produce an NOE to the singlet at δ 8.32. MS
(ES+) m/e 368 [MH]+. 58: mp 202-204 °C. 1H NMR (360 MHz,
DMSO) δ 2.57 (3 H, s), 5.70 (2 H, s), 7.37-7.41 (1H, m), 7.53-
7.58 (3H, m), 7.68 (1H, d, J ) 7.8 Hz), 7.86-7.91 (2H, m), 8.10
(1H, s), 8.22-8.24 (2H, m), 8.40 (1H, d, J ) 8.1 Hz), 8.67 (1H,
d, J ) 6.0 Hz). Irradiation of the benzylic protons at δ 5.70
produced a nuclear Overhauser effect to the singlet at δ 8.10.
MS (ES+) m/e 368 [MH]+.
temperature for 15 min. After this time 6-chloro-3-phenyl-
7,8,9,10-tetrahydro-1,2,4-triazolo[3,4-a]phthalazine (0.55 g,
0,002 mol) was added and the reaction mixture was stirred
for 14 h. Water was added until the solution became cloudy,
and the solid that precipitated was collected by filtration and
recrystallized from ethyl acetate to give pure 60 (0.2 g, 29%):
1
mp 194 °C. H NMR (360 MHz, CDCl3) δ 1.94 (4 H, m), 2.74
(2 H, m), 3.14 (2 H, m), 5.56 (2 H, s), 7.27 (1 H, m), 7.47 (4 H,
m), 7.73 (1 H, m), 8.36 (2 H, d, J ) 6.6 Hz), 8.66 (1 H, m). MS
(ES+) m/e 358 [MH]+.
3-P h en yl-6-(2-p yr id yl)m et h yloxy-(7,8-p en t a n o)-1,2,4-
tr ia zolo[3,4-a ]p yr id a zin e (61). 1-Cycloheptene-1,2-dicar-
boxylic anhydride29 (5.6 g, 0.034 mol) and sodium acetate (5.5
g, 0.040 mol, 1.2 mol equiv) were dissolved in 60% acetic acid
(150 mL), and hydrazine hydrate (1.97 mL, 0.040 mol, 1.2 mol
equiv) was added. The reaction mixture was heated under
reflux for 16 h, allowed to cool to room temperature, and
diluted with water (200 mL). The solid that precipitated was
collected by filtration, washed several times with water, and
dried under vacuum to give 2,3,6,7,8,9-hexahydro-5H-cyclo-
hepta[d]pyridazine-1,4-dione: 0.88 g (15%). 1H NMR (250
MHz, CDCl3) δ 1.47-1.78 (6 H, m), 2.49-2.67 (4 H, m), 10.8
(1 H, br s), 11.74 (1 H, br, s). MS (ES+) m/e 181 [MH]+. This
product (0.87 g, 0.0048 mol) was dissolved in phosphorus
oxychloride (100 mL), and the mixture was heated under reflux
for 14 h. The reaction mixture was concentrated under
vacuum, azeotroped with toluene (2 × 50 mL), then dissolved
in dichloromethane (30 mL), washed with saturated NaHCO3
solution, dried (MgSO4), filtered, and concentrated under
vacuum to give 1,4-dichloro-6,7,8,9-tetrahydro-5H-cyclohepta-
[d]pyridazine: 0.63 g (60%). 1H NMR (250 MHz, CDCl3) δ
1.48-1.98 (6 H, m), 2.59 (2 H, m), 3.08 (2 H, m). MS (ES+)
m/e 216 [MH]+. This product (0.63 g, 0.0029 mol) and benzoic
hydrazide (0.44 g, 0.000 319 mol, 1.1 mol equiv) were dissolved
in xylene (30 mL) with triethylamine (0.44 mL, 1.1 mol equiv)
and heated under reflux for 60 h. The solvent was removed
under vacuum and the residue was purified by chromatogra-
phy on silica gel using 0-20% ethyl acetate in dichloromethane
as eluent to give a crude product. Trituration with hot ethyl
acetate and filtration gave purified product in the filtrate,
which was further purified by recrystallization from dichlo-
romethane to give 6-chloro-3-phenyl-(7,8-pentano)-1,2,4-tria-
zolo[3,4-a]pyridazine: 0.25 g (29%). 1H NMR (360 MHz, CDCl3)
δ 1.64-2.04 (6 H, m), 3.14 (2 H, m), 3.45 (2 H, m), 7.56 (3 H,
m), 8.44 (2 H, m). MS (ES+) m/e 299 [MH]+. 2-Pyridylcarbinol
(0.078 mL, 0.001 13 mol, 1.4 mol equiv) was dissolved in DMF
(20 mL), sodium hydride (0.045 g of a 60% dispersion in oil,
1.4 mol equiv) was added, and the reaction mixture was stirred
at room temperature for 10 min. After this time 6-chloro-3-
phenyl-(7,8-pentano)-1,2,4-triazolo[3,4-a]pyridazine (0.24 g,
0.000 81 mol) was added and the reaction mixture was stirred
for 14 h. Water was added until the solution became cloudy,
and the solid that precipitated was collected by filtration and
purified by chromatography on silica gel using 0-3% methanol
in dichloromethane as eluent. The crude solid was recrystal-
lized from ethyl acetate to give pure 61 (0.076 g, 25%): mp
3-P h en yl-6-(2-p yr id yl)m eth yloxy-7,8,9,10-tetr a h yd r o-
1,2,4-tr ia zolo[3,4-a ]p h th a la zin e (60). To a solution of 3,6-
dichloro-7,8,9,10-tetrahydrophthalazine28 (7 g, 0.0345 mol) in
dioxan (100 mL) was added triethylamine (5.2 mL, 1.1 mol
equiv) and benzoic hydrazide (5.16 g, 1.1 mol equiv). This
mixture was heated at reflux for 18 h under nitrogen, after
which time there was little reaction. After cooling, the reaction
mixture was concentrated under vacuum and the residue
obtained was heated neat at 150 °C for 30 min. After the
mixture was cooled, the solid obtained was recrystallized from
ethanol/ethyl acetate and collected by filtration to yield 6-
chloro-3-phenyl-7,8,9,10-tetrahydro-1,2,4-triazolo[3,4-a]phthal-
1
208 °C. H NMR (360 MHz, CDCl3) δ 1.71 (2H, m), 1.81 (2H,
m), 1.99 (2H, m), 3.01 (2H, m), 3.38 (2H, m), 5.58 (2 H, s),
7.28 (1 H, m), 7.48 (4 H, m), 7.76 (1 H, m), 8.37 (2 H, d, J )
7.8 Hz), 8.67 (1 H, m). MS (ES+) m/e 372 [MH]+.
3-P h en yl-6-(2-p yr id yl)m eth yloxy-7,8,9,10-tetr a h yd r o-
(7,10-eth a n o)-1,2,4-tr ia zolo[3,4-a ]p h th a la zin e (62). 3,6-
Dichloro-4,5-diazatricyclo[6.2.2.2,7]dodeca-2(7),3,5-triene29 (2.5
g, 0.011 mol) was suspended in xylene (50 mL) with benzoic
hydrazide (1.65 g, 1.1 mol equiv) and triethylamine (1.68 mL,
1.1 mol equiv), and the reaction mixture was heated under
reflux for 6 days. The solvent was removed under high vacuum
and the residue was purified by chromatography on silica gel
using 0-50% ethyl acetate in dichloromethane as eluent
followed by recrystallization from ethyl acetate/hexane to give
6-chloro-3-phenyl-7,8,9,10-tetrahydro-(7,10-ethano)-1,2,4-tria-
zolo[3,4-a]phthalazine: 1.3 g (38%), mp 186-188 °C. 1H NMR
(250 MHz, CDCl3) δ 1.43-1.59 (4 H, m), 1.91-2.05 (4 H, m),
1
azine (3.2 g, 33%). H NMR (250 MHz, CDCl3) δ 1.94-1.98 (4
H, m), 2.76-2.80 (2 H, m), 3.20-3.25 (2 H, m), 7.47-7.60 (3
H, m), 8.44 (2 H, d, J ) 8.0 Hz). 2-Pyridylcarbinol (0.23 mL,
0.0024 mol, 1.2 mol equiv) was dissolved in DMF (20 mL),
sodium hydride (0.096 g of a 60% dispersion in oil, 1.2 mol
equiv) was added, and the reaction mixture was stirred at room

Phthalazines and Analogues
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3.57 (1 H, s), 4.07 (1 H, s), 7.58 (3 H, m), 8.58 (2 H, dd, J ) 7.8
and 1.5 Hz). MS (ES+) m/e 311 [MH]+. Anal. found: C, 65.56;
H, 4.83; N, 17.74. C17H15ClN4 requires C, 65.70; H, 4.87; N,
18.03%.
To a solution of 2-pyridylcarbinol (0.263 mL, 0.0024 mol) in
DMF (20 mL) was added sodium hydride (0.113 g of a 60%
dispersion in oil, 1.75 mol equiv), and the reaction mixture
was stirred at room temperature for 15 min. After this time
6-chloro-3-phenyl-7,8,9,10-tetrahydro-(7,10-ethano)-1,2,4-tria-
zolo[3,4-a]phthalazine (0.5 g, 0.0016 mol) was added and the
reaction mixture was stirred at room temperature for 1 h.
Water was added until the solution became cloudy. After the
solution was stirred for a further 15 min, a solid was collected
by filtration. This solid was recrystallized from ethyl acetate
to give pure 62: 0.112 g (18%), mp 196-198 °C. 1H NMR (360
MHz, CDCl3) δ 1.45 (4 H, m), 1.95 (4 H, m), 3.58 (1 H, s), 4.00
(1 H, s), 7.26 (1H, m), 5.48 (2 H, s), 7.44-7.53 (4 H, m), 7.77
(1 H, m), 8.40 (2 H, dd, J ) 7.8 and 1.5 Hz), 8.68 (1 H, m). MS
(ES+) m/e 384 [MH]+.
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