Synthesis and SAR study of novel tricyclic pyrazoles as potent phosphodiesterase 10A inhibitors

Article abstract of DOI:10.1016/j.ejmech.2014.07.020

Novel pyrazolo[5,1-f][1,6]naphthyridines, pyrazolo[5,1-a][2,6] naphthyridines, pyrazolo[5,1-a][2,7]naphthyridines and pyrazolo[5,1-a] isoquinolines phenylimidazole/benzimidazole ethylene-linked were designed and synthesized for PDE10A interaction. An AgOTf and proline-cocatalyzed multicomponent methodology based on use of o-alkynylaldehydes, tosylhydrazide and ketones was developed and proved to be a convenient route for assembly of most of the novel tricyclic pyrazoles synthesized. Pyrazolo[5,1-f][1,6] naphthyridine 43 and 59, pyrazolo[5,1-a][2,6]naphthyridine 66, and pyrazolo[5,1-a][2,7]naphthyridine 42 showed the highest affinity for PDE10A enzyme (IC₅₀ = 40, 42, 40, 55 nM, respectively).

Full text of DOI:10.1016/j.ejmech.2014.07.020

European Journal of Medicinal Chemistry 84 (2014) 181e193
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and SAR study of novel tricyclic pyrazoles as potent
phosphodiesterase 10A inhibitors
,
Antonio Dore a, Battistina Asproni a *, Alessia Scampuddu a, Gerard Aime Pinna a,
Claus Tornby Christoffersen b, Morten Langgård c, Jan Kehler c
a
ꢀ
Dipartimento di Chimica e Farmacia, Universita di Sassari, Via F. Muroni 23/A, 07100 Sassari, Italy
b H. Lundbeck A/S, Department of Molecular Pharmacology, 9 Ottiliavej, DK-2500 Valby, Denmark
c H. Lundbeck A/S, Discovery Chemistry and DMPK, 9 Ottiliavej, DK-2500 Valby, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel pyrazolo[5,1-f][1,6]naphthyridines, pyrazolo[5,1-a][2,6]naphthyridines, pyrazolo[5,1-a][2,7]naph-
thyridines and pyrazolo[5,1-a]isoquinolines phenylimidazole/benzimidazole ethylene-linked were
designed and synthesized for PDE10A interaction. An AgOTf and proline-cocatalyzed multicomponent
methodology based on use of o-alkynylaldehydes, tosylhydrazide and ketones was developed and proved
to be a convenient route for assembly of most of the novel tricyclic pyrazoles synthesized. Pyrazolo[5,1-f]
[1,6]naphthyridine 43 and 59, pyrazolo[5,1-a][2,6]naphthyridine 66, and pyrazolo[5,1-a][2,7]naphthyr-
idine 42 showed the highest affinity for PDE10A enzyme (IC50 ¼ 40, 42, 40, 55 nM, respectively).
© 2014 Elsevier Masson SAS. All rights reserved.
Received 9 September 2013
Received in revised form
17 June 2014
Accepted 6 July 2014
Available online 7 July 2014
Keywords:
Tricyclic pyrazoles
PDE10A inhibition
Structureeactivity relationships
1. Introduction
treatment of central nervous system disorders associated to
dysfunction in the basal ganglia circuit like e.g. Parkinson's disease,
Phosphodiesterases (PDEs) are a class of key enzymes in cellular
signalling pathways. They are bimetallic hydrolases that degrade
the intracellular second messengers cyclic adenosine mono-
phosphate (cAMP) and cyclic guanosine monophosphate (cGMP) by
catalytic hydrolysis of the 30-50 phosphodiester bond, forming the
inactive 50-monophosphates AMP and GMP, respectively. Thereby,
they play a crucial role in regulation of the intracellular levels of
these ubiquitous second messengers. PDEs are a superfamily of
enzymes encoded by 21 genes and consist of 11 families (PDE1-
PDE11) with over 60 isoforms based on structural and functional
properties. They can be classified by the substrate specificity: the
cAMP-specific PDEs, including PDE4, PDE7, and PDE8; the cGMP-
selective enzymes PDE5, PDE6 and PDE9; the dual-substrate
PDEs, PDE1, PDE2, PDE3, PDE10 and PDE11 [1,2].
Huntington's disease, schizophrenia, addiction and obsessive
compulsive disorder [6].
During the last decade, an increasing number of pharmaceutical
companies were involved in identifying a huge diversity of chem-
ical scaffolds and molecular architectures for PDE10A interaction
and to evaluate their therapeutic potential [7]. In this context, Pfizer
has been a leading company having disclosed the natural alkaloid
papaverine as the first relatively selective PDE10A inhibitor, eval-
uating its in vivo activity in animal models predictive of antipsy-
chotic activity [8] and presented the first highly selective PDE10A
inhibitor clinical candidate, namely MP-10 (PF-2545920), for the
treatment of schizophrenia (Fig.1) [9]. Preclinical data generated by
the investigation of MP-10 [10] and its close N-trifluoroethyl
analogue TP-10 [11] (Fig. 1) indicated that a PDE10A inhibitor
exhibited antipsychotic activity in several animal models, spanning
from positive, cognitive and negative symptoms of schizophrenia.
Nevertheless, in spite of the strong preclinical evidences for anti-
psychotic activity of PDE10A inhibitors, the development of PF-
2545920 as clinical candidate for the treatment of schizophrenia
was recently halted following the observation that the efficacy of
MP-10 in acute exacerbation of schizophrenia was not significantly
different from placebo [12]. On the other hand, several emerging
preclinical data indicated the potential of PDE10A inhibitors for
PDE10A is a relatively newly identified phosphodiesterase [3]
and among the 11 PDE families, it has the most restricted distri-
bution, with mRNA being highly expressed in human brain [4]. In
the brain, the enzyme is predominantly expressed in medium spiny
neurons of the striatum [5], making it an intriguing target for the
* Corresponding author.
E-mail address: asproni@uniss.it (B. Asproni).
http://dx.doi.org/10.1016/j.ejmech.2014.07.020
0223-5234/© 2014 Elsevier Masson SAS. All rights reserved.

182
A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
Fig. 1. PDE10A inhibitors Papaverine, MP-10, TP-10, 1,2,4-triazolo[1,5-c]quinazoline I, pyrazolo[1,5-c]quinazoline II and the novel pyrazolonaphthyridines 1, 2, 3 and pyr-
azoloisoquinoline 4.
treatment of patients with Huntington's disease. Recent reports
described the activity of TP-10 in reducing striatal and cortical cell
loss in different animal models of Huntington's disease [13].
MP-10 and TP-10 are representative terms of a series of
pyrazolyl-phenoxymethyl-quinolines [9] endowed with sub-
nanomolar PDE10A affinity and excellent selectivity (>3000-fold)
versus other PDEs [11]. X-ray data of the complex formed between
MP-10 and the catalytic domain of PDE10A [9] revealed a binding
mode which does not involve the conserved glutamine residue, but
an alternative interaction involving a hydrogen bond between the
quinoline nitrogen and a tyrosine residue at the “selectivity pocket”
which is in proximity to the catalytic site of the PDE10A enzyme.
Occupation of this pocket by the ligand has been reported to pro-
vide nearly complete selectivity versus other PDEs [7f].
In a recent disclosure [14] we have developed a series of phe-
nylimidazole-pyrazolo[1,5-c]quinazolines exemplified by com-
pound II, Fig. 1, as potent PDE10A inhibitors (IC50 y 12e400 nM),
endowed with high selectivity against the other PDE isoforms

A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
183
Table 1
(IC50 > 10000 nM). The reported research was based on design
considerations derived from an X-ray analyses of the benzimid-
azole-triazolo[1,5-c]quinazoline I bound to the catalytic domain of
PDE10A [15]. Our structureeactivity relationship (SAR) in-
vestigations prompted us to assume that the planar pyr-
azoloquinazoline ring system might occupy the hydrophobic clamp
of the PDE10A catalytic domain. The ethylene group could act as a
linker reaching into the well defined selectivity pocket, where the
phenylimidazole nitrogen is involved in a hydrogen bond interac-
tion with the tyrosine residue. The concomitant intervention of
above mentioned binding interactions presumably contribute to
the high potency and especially the selectivity of the investigated
phenylimidazole-pyrazolo[1,5-c]quinazolines.
As part of our ongoing efforts to generate SARs around II, we
envisioned that bioisosteric modification of the pyrazoloquinazo-
line core might offer new templates that could provide better in-
teractions with the PDE10A enzyme. Thus, four different tricyclic
scaffolds including pyrazolo[5,1-f][1,6]naphthyridine 1, pyrazolo
[5,1-a][2,6]naphthyridine 2, pyrazolo[5,1-a][2,7]naphthyridine 3
and pyrazolo[5,1-a]isoquinoline 4 have been designed (Fig. 1). We
planned also to make use of the phenylimidazole/benzimidazole
fragments as useful hydrogen bond acceptors for the selectivity
pocket, and evaluate the effect of different substituents such as CH3,
COOC2H5, CF3, CH2OCH3, at the pyrazole portion of the tricyclic
system.
Structure and PDE10A potency for pyrazolonaphthyridines and pyrazoloisoquino-
lines compounds.
Entry
1
Compound
PDE10A IC50a (nM)
40
2
3
170
220
4
1300
In this paper we report the synthesis and the biological evalu-
ation of novel tricyclic pyrazoles whose structures are reported in
Table 1.
2. Results and discussion
2.1. Chemistry
5
6
190
The chemistry employed to prepare the pyrazolonaphthyr-
idines- and pyrazoloisoquinoline-based compounds (Fig. 1 and
Table 1) is outlined in Schemes 1e4.
Schemes 1 and 2 depict the synthetic routes used to synthesize
most of the title compounds presented in this paper, and consist
firstly in the preparation of methoxymethyl-based tricyclic pyr-
azoles 18e22 (Scheme 1), whose functionalization reactions
(Scheme 2) provided the desired pyrazolonaphthyridines- and
pyrazoloisoquinoline-based molecules.
42
The synthetic procedure developed to assemble the pyr-
azolonaphthyridine and pyrazoloisoquinoline cores (Scheme 1)
make use of a multicomponent methodology (step c) which is
based on a “dual-activation concept” of the electrophiles and nu-
cleophiles, through one-pot combination of metal and organo-
catalysis. One-pot combination of AgOTf and proline catalysis was
applied successfully by Wu et al. for the synthesis of 1,2-
dihydroisoquinoline derivatives in multicomponent reactions,
starting from appropriate o-alkynylbenzaldehydes, amines, and
ketones [16]. More recently, Wu et al. described the unexpected
formation of the substituted pyrazolo[5,1-a]isoquinoline core by
AgOTf-catalyzed tandem reactions of o-alkynylbenzylidene-tosyl-
hydrazones with alkynes or silyl enolates in the presence of a base
[17,18].
7
40
55
8
9
480
Taking into account these results, we reasoned that the pyr-
azolonaphthyridine and pyrazoloisoquinoline products 18e22
(Scheme 1) could be synthesized by one-pot combination of AgOTf
and proline catalysis by reacting the tosylhydrazones 14e17 and
appropriate ketones, followed by treatment with a base. The syn-
thetic sequence commenced with o-haloaldehydes 6e9 which
were allowed to react with methyl propargyl ether under the
conventional Sonogashira conditions to give the corresponding o-
alkynylaldehydes 10e13. The o-Br-aldehydes 6, 7 and 9 were
10
900
(continued on next page)

184
A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
Table 1 (continued )
more methine carbon. The structure of novel tricyclic pyrazoles was
a
also confirmed with an alternative six-steps synthetic approach
applied for the preparation of pyrazolo[5,1-f][1,6]naphthyridine 18
as representative term of the series (vide infra and Supplementary
data, Scheme 5).
Entry
Compound
PDE10A IC50 (nM)
11
1000
Methoxymethyl-based tricyclic pyrazoles 18, 19, 21 and 22
(Scheme 2) were converted into the corresponding alcohols 23e26
by treatment with BBr3. SOCl2 chlorination of 23e26 afforded the
chloromethyl-based tricyclic pyrazole intermediates 27e30 which
were reacted with triphenylphosphine to give the phosphonium
salts 31e34, whereas the alcohols 23 and 26 were converted in high
yields into the corresponding aldehydes 35 and 36 using Dess-
Martin periodinane (DMP). Wittig reaction between the phospho-
nium salts 32, 33 and 1-methyl-4-phenyl-1H-imidazole-2-
carbaldehyde and between the phosphonium salts 31e34 and 1-
methyl-1H-benzo[d]imidazole-2-carbaldehyde afforded alkenes
37, 38 and 45e48, respectively. Wittig reaction between the alde-
hydes 35, 36 and ((1-methyl-4-phenyl-1H-imidazol-2-yl)methyl)
triphenylphosphonium chloride furnished alkenes 39 and 40,
respectively. All alkenes were isolated in general with high yields as
E/Z mixtures. Final reduction of alkenes with PTSH allowed to
obtain the title compounds 41e44 and 49e52 in satisfactory yields.
Alternatively, Scheme 3 depicts a further application of above
mentioned multicomponent methodology starting from the o-
alkynylaldehyde intermediate 56 which incorporates in its struc-
ture the necessary ethyl-phenylimidazole portion. Compound 56
was reacted in situ with PTSH to give the corresponding tosylhy-
drazone in the presence of AgOTf and DL-proline, which after
sequential treatment with ethyl pyruvate or trifluoroacetone and
Na2CO3 afforded target compounds 41 and 57 in high yields,
respectively. Compound 56 was synthesized from 2-(but-3-yn-1-
yl)-1-methyl-4-phenyl-1H-imidazole (55) which was submitted
to Sonogashira reaction with 2-bromonicotinaldehyde (6) to give
the desired o-alkynylaldehyde 56 in good yields. This two-step
straight synthetic approach used for the synthesis of 41 and 57
make use of the alkyne 55, synthesized starting from 4-pentynoic
acid (53), which after sequential treatment with Cs2CO3 and 2-
bromoacetophenone formed the keto-ester 53′. The addition of
NH4OAc to a xylene solution of 53′ at reflux, afforded in high yield
the phenylimidazole 54. Alkylation of 54 with CH3I in the presence
of NaH gave the desired alkyne 55.
12
50
a
IC50 values are means of at least two experiments, and a typical standard de-
viation was 30%.
commercially available, whereas the o-I-aldehyde 8 was obtained
by making use of a trans-halogenation reaction by reacting 4-
chloronicotinaldehyde (5) with NaI in the presence of acetyl chlo-
ride [19]. Compounds 10e13 were condensed in situ with p-tolue-
nesulfonyl hydrazide (PTSH) at room temperature in ethanol and in
the presence of AgOTf (10 mol %), DL-proline (10 mol %) to give
tosylhydrazones 14e17 (not isolated), which were converted into
the desired tricyclic pyrazoles 18e22 by sequential treatment with
acetone or ethyl pyruvate, heating the reaction mixture by micro-
wave irradiation to 50e60 ꢀC, and finally with Na2CO3 at room
temperature. The formation of 18e22 can be explained by the
initial formation of 1,2-dihydroisoquinoline intermediate 14′-17′
[16] which undergoes intramolecular dehydrative condensation
with the sulfonohydrazide portion of the molecule to afford the
tricyclic intermediate 1400-1700. Base mediated elimination of the
tosyl group and aromatization afford the desired tricyclic com-
pounds 18e22. The use of pure tosylhydrazones did not improve
the reaction yields, and therefore isolation and purification of these
intermediates was omitted.
All tricyclic pyrazoles were characterized using 1H, 13C-APT
NMR, and mass spectrometry. The 1H NMR spectra of 18e22
revealed the presence of two distinct singlet peaks (1H) at dH 6.85,
7.31 (18), 7.55, 7.63 (19), 6.95, 7.13 (20), 6.95, 7.03 (21), 6.82, 7.05
(22), indicating HeC1/HeC6 for 18, 19, 20, 22 and HeC10/HeC5 for
21 [14,17]. The 13C-APT NMR spectra revealed the presence of at
least 10 carbons, five quaternary carbons and five methine carbons,
indicating the above described di-substituted pyrazolonaphthyr-
idine or pyrazoloisoquinoline skeleton with the last one with one
Reduction of the ester function of 41 with NaBH4 afforded the
alcohol 58 which was methylated to compound 59.
Looking at the yields (30e75%) of tricyclic pyrazoles obtained by
the multicomponent reaction described in Schemes 1 and 3, the
H
O
N
N
Z
Z
Z
N
S
O
O
O
a
b
c (1)
O
Y
Y
Y
Cl
X
Halo
X
X
O
O
5
6: X = N; Y,Z = CH; Halo = Br
7: X,Z = CH; Y = N; Halo = Br
8: X,Y = CH; Z = N; Halo = I
9: X,Y,Z = CH; Halo = Br
10: X = N; Y,Z = CH
11: X,Z = CH; Y = N
12: X,Y = CH; Z = N
13: X,Y,Z = CH
14: X = N; Y,Z = CH
15: X,Z = CH; Y = N
16: X,Y = CH; Z = N
17: X,Y,Z = CH
O
R
R
R
X
H
H
N
N
N
N
Ts
Z
N
Ts
O
c (2)
c (3)
Z
N
Z
Y
Y
O
Y
O
X
X
14'-17'
14"-17"
18: X = N; Y,Z = CH; R = CH3
(75%)
19: X = N; Y,Z = CH; R = COOEt (70%)
20: X,Z = CH; Y = N; R = CH3
21: X,Y = CH; Z = N; R = CH3
22: X,Y,Z = CH; R = CH3
(9%)
(58%)
(30%)
Scheme 1. Reagents and conditions: (a) NaI, AcCl, dry MeCN, 0 ꢀC / r.t., 1 h; (b) methyl propargyl ether, Pd(PPh3)2Cl2, CuI, Et3N, dry DMF, r.t., 1 h; (c) (1) PTSH, AgOTf, DL-Proline, dry
EtOH, r.t., 20 min; (2) acetone (for 18, 20e22) or ethyl pyruvate (for 19), MW, 50e60 ꢀC, 30 min; (3) Na2CO3, r.t., 12 h.

A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
185
R
N
R
N
Y
N
Y
N
b
c
Cl
PPh3Cl
R
N
R
N
X
X
27: X = N; Y = CH; R = CH3
28: X = N; Y = CH; R = COOEt
29: X = CH; Y = N; R = CH3
30: X,Y = CH; R = CH3
31: X = N; Y = CH; R = CH3
32: X = N; Y = CH; R = COOEt
33: X = CH; Y = N; R = CH3
34: X,Y = CH; R = CH3
Y
N
Y
N
a
O
OH
R
X
X
18: X = N; Y = CH; R = CH3
19: X = N; Y = CH; R = COOEt
21: X = CH; Y = N; R = CH3
22: X,Y = CH; R = CH3
23: X = N; Y = CH; R = CH3
24: X = N; Y = CH; R = COOEt
25: X = CH; Y = N; R = CH3
26: X,Y = CH; R = CH3
N
Y
N
d
O
X
35: X = N; Y = CH; R = CH3
36: X,Y = CH; R = CH3
R
N
R
N
e
32, 33
Y
N
Y
N
g
N
N
X
X
f
35, 36
N
N
37: X = N; Y = CH; R = COOEt
38: X = CH; Y = N; R = CH3
39: X = N; Y = CH; R = CH3
40: X,Y = CH; R = CH3
41: X = N; Y = CH; R = COOEt
42: X = CH; Y = N; R = CH3
43: X = N; Y = CH; R = CH3
44: X,Y = CH; R = CH3
R
R
N
N
N
N
Y
Y
h
g
31-34
N
N
X
X
N
N
45: X = N; Y = CH; R = CH3
46: X = N; Y = CH; R = COOEt
47: X = CH; Y = N; R = CH3
48: X,Y = CH; R = CH3
49: X = N; Y = CH; R = CH3
50: X = N; Y = CH; R = COOEt
51: X = CH; Y = N; R = CH3
52: X,Y = CH; R = CH3
Scheme 2. Reagents and conditions: (a) BBr3 (1 M in DCM), dry DCM, 0 ꢀC /r.t., N2, 1.5 h; (b) SOCl2, dry DCM, 0 ꢀC / r.t., 12 h; (c) PPh3, MeCN, reflux, 12 h; (d) DMP, dry DCE, N2, r.t.,
12 h; (e) NaH (60% in mineral oil), 1-methyl-4-phenyl-1H-imidazole- 2-carbaldehyde, dry DMF, 0 ꢀC / r.t., 5 h; (f) NaH (60% in mineral oil), ((1-methyl-4-phenyl-1H-imidazol-2- yl)
methyl)triphenylphosphonium chloride, dry DMF, 0 ꢀC / r.t., 5 h; (g) PTSH, dry DMF, N2, 120 ꢀC, 4e6 h; (h) NaH (60% in mineral oil), 1-methyl-1H-benzo[d]imidazole-2-
carbaldehyde, dry DMF, 0 ꢀC / r.t., 5 h.
reaction works well both with acetone, ethyl pyruvate, and tri-
fluoroacetone, and appear to be a general methodology for the as-
sembly of pyrazolo[5,1-f][1,6]naphthyridines 18, 19, 41, 57 (70e75%
yield), pyrazolo[5,1-a][2,7]naphthyridine 21 (58% yield), and pyr-
azolo[5,1-a]isoquinoline 22 (30% yield), even if the last one was
obtained with lower yields. Nevertheless, this methodology was
found to be not convenient with o-alkynylaldehyde 11 (Scheme 1),
since the pyrazolo[5,1-a][2,6]naphthyridine-based compound 20
was obtained only in poor yields (9% yield). This finding prompted us
to explore an alternative synthetic route for pyrazolo[5,1-a][2,6]
naphthyridine tricyclic ring system that is depicted in Scheme 4 for
the synthesis of final compound 66. The key step involves the final
heterocyclization of the ketoxime 65 into the pyrazolo[5,1-a][2,6]
naphthyridine 66 via catalytic rearrangement of the azirine inter-
mediate 65′ [20]. The synthetic sequence started with 3-
bromoisonicotinaldehyde (7), which was submitted to Sonogashira
reaction with alkyne 55 to afford the o-alkynylaldehyde 60 that in
turn was converted into the aldoxime 61 by a conventional proce-
dure. Treatment of 61 with K2CO3 in ethanol at room temperature
afforded the 2,6-naphthyridine-2-oxide 62 in high yield [21]. Com-
pound 62 gave satisfactory 1H NMR data, and the dH values of the 2,6-
naphthyridine 2-oxide system is in agreement with literature data
[21]. POCl3 chlorination of 62 gave the 1-chloro-2,6-naphthyridine
63 which upon palladium-catalyzed cross-coupling reaction with
isopropenyl acetate in the presence of tributyl(methoxy)stannane,
2-dicyclohexylphosphino-20-(N,N-dimethylamino)biphenyl (Dave-
Phos) [22] furnished in almost quantitative yield the
a-2,6-
naphthyridine acetone-based derivative 64. Treatment of 64 with
hydroxylamine gave the desired ketoxime 65 which treated with
trifluoroacetic anhydride (TFAA) and Et3N to give the azirine inter-
mediate 65′ (step f1) [20]. Final rearrangement was achieved by
heating the azirine intermediate (not isolated) in the presence of
FeCl2 to give the desired final compound 66 in 8% of yield.
This procedure works well with 2-(3-methoxyprop-1-yn-yl)nic-
otinaldehyde (10) which was submitted to the above described
sequence reactions to give the corresponding ketoxime which was
converted into the pyrazolo[5,1-f][1,6]naphthyridine 18 in 41% of
yield (Scheme 5, Supplementary data).
2.2. Inhibition of PDE10A activity and SAR study
The ability of pyrazolonaphthyridine and pyrazoloisoquinoline
derivatives to inhibit the PDE10A mediated hydrolysis of cAMP was
measured using 3H-labelled cAMP in an yttrium silicate SPA bead
assay making use of the fact that cAMP has low affinity for yttrium
silicate SPA beads, whereas hydrolyzed 50-AMP has high affinity for

186
A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
OH
O
O
a
N
N
b
c
O
O
HN
54
N
53
53'
55
CF3
N
N
d
O
e
N
N
N
N
N
56
57 (75%)
N
e
COOEt
N
CH2OH
CH2OCH3
N
N
N
N
N
f
c
N
N
N
N
N
N
N
N
N
41 (71%)
58
59
Scheme 3. Reagents and conditions: (a) (1) Cs2CO3, EtOH/H2O 1:1, r.t., 1 h; (2) 2-bromoacetophenone, dry DMF, r.t., 15 min; (b) NH4OAc, xylene, reflux, 12 h; (c) NaH (60% in mineral
oil), dry THF, 0 ꢀC, 30 min, then MeI, 0 ꢀC to r.t., 12 h; (d) 2-bromonicotinaldehyde (6), Pd(PPh3)2Cl2, CuI, Et3N, dry DMF, MW, 50 ꢀC, 20 min; (e) (1) PTSH, AgOTf, DL-Proline, dry EtOH,
r.t., 20 min; (2) ethyl pyruvate (for 41) or 1,1,1-trifluoroacetone (for 57), MW, 50e60 ꢀC, 30 min; (3) Na2CO3, r.t., 12 h; (f) NaBH4, EtOH, reflux, 12 h.
OH
O
O
O
N
N
a
b
c
N
N
N
N
N
Br
N
N
N
7
60
61
62
N
N
OH
Cl
OH
N
N
N
N
d
e
b
N
N
N
N
N
N
N
N
N
63
64
65
N
N
N
N
f (1)
f (2)
N
N
N
N
N
N
65'
66
Scheme 4. Reagents and conditions: (a) 2-(but-3-yn-1-yl)-1-methyl-4-phenyl-1H-imidazole (55), Pd(PPh3)2Cl2, CuI, Et3N, dry DMF, MW, 70 ꢀC, 2 h; (b) NH2OH,HCl, AcONa,3H2O,
EtOH, r.t., 4 h; (c) dry K2CO3, dry EtOH, r.t., 6 h; (d) POCl3, MeCN, reflux, 2 h; (e) isopropenyl acetate, DavePhos, nBu3SnOMe, Pd2(dba)3, dry toluene, N2, 100 ꢀC, 12 h; (f) (1) TFAA,
Et3N, dry DME, N2, 0 ꢀC / r.t.; (2) FeCl2, 75 ꢀC, 12 h.
yttrium silicate SPA beads [14,15]. The potency in inhibiting PDE10A
was calculated and the IC50 values are shown in Table 1. For com-
parison, the IC50 value of the lead compound 2-methyl-5-(2-(1-
methyl-4-phenyl-1H-imidazol-2-yl)ethyl)pyrazolo[1,5-c]quinazo-
line (II) has been reported. Compound 43 (Entry 1), incorporating
the pyrazolo[5,1-f][1,6]naphthyridine core, exhibited high potency
in inhibiting PDE10A activity, with an IC50 value very similar to that
of the reference compound II (Entry 12), indicating that the shifting
of nitrogen from the central ring to the side one does not signifi-
cantly influence the affinity for the enzyme. The replacement of the
phenylimidazole motif in 43 with the benzimidazole to give com-
pound 49 (Entry 2) weakened the affinity about 4-fold. Interest-
ingly, the trend of the phenylimidazole being slightly more potent
than the corresponding benzimidazole appear to be a constant in
all tested compounds (see 43 versus 49, 41 versus 50, 42 versus 51
and 44 versus 52). The carboxyethyl analogues 41 and 50 exhibited
5- and 7-fold decreased affinity when compared to compounds 43
and 49, respectively. A similar trend was observed with the tri-
fluoromethyl analogue 57 (Entry 5) which exhibited 5-fold
decreased affinity with respect to 43. Considering that the methyl
and trifluoromethyl groups are comparable in size, the observed
decreased affinity in 57 could be speculated to be influenced by the
electron-withdrawing properties of the CF3 group. To further
investigate the interaction mode of compounds 43 and 57 in the
catalytic domain of PDE10A, molecular docking study was per-
formed using the Glide XP protocol [23]. The receptor docking site
was generated from the PDE10A X-ray structure in complex with
the close analogue triazoloquinazoline ligand I, which was ob-
tained from the Protein Data Bank (PDB code 2Y0J). As showed in
Fig. 2, the docking study of 43 and 57 in the PDE10A catalytic

A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
187
domain suggests that the pyrazole nitrogen of tricyclic system in-
teracts with the conserved glutamine residue through hydrogen-
bond interaction, and the strength of the H-bond might be weak-
ened by an electron-withdrawing group. This result seems to be
consistent with the binding mode depicted from the X-ray struc-
ture of triazoloquinazoline I bound to PDE10A catalytic site [14,15],
where the triazolo N-3 nitrogen interact with the glutamine res-
idue of PDE10A through hydrogen-bond interaction. However,
although a similar argument could be made to explain the weaker
affinity of the carboxyethyl analogue 41, the docking study suggest
an alternative binding mode (Fig. 2, C), where the N-7 of the pyr-
azolo[5,1-f][1,6]naphthyridine interacts with the conserved gluta-
mine residue of PDE10A. The unfavourable effect was not exerted
by the methoxymethyl group in compound 59 (Entry 6), which was
equipotent with 43 in inhibiting the PDE10A. Compounds 66, and
42 (Entry 7 and 8), incorporating the pyrazolo[5,1-a][2,6]naph-
thyridine and pyrazolo[5,1-a][2,7]naphthyridine core respectively,
showed PDE10A potency almost similar to that of 43. In contrast,
compound 44 (Entry 10), incorporating the pyrazolo[5,1-a]iso-
quinoline core, displayed marked decrease of potency with respect
to the aza-analogues 43, 66 and 42, highlighting the same versa-
tility of all pyrazolonaphthyridines to inhibit the PDE10A enzyme
activity with a potency lying in a similar range.
The new compounds were all screened in a panel of nine other
PDEs representing members from the other PDE families and data
are shown in Table 2 [14,15]. It can be noted, that all compounds
demonstrated a high selectivity towards PDE1C, PDE2A, PDE3A,
PDE4D6, PDE5A, PDE7B, PDE8A, PDE9 and PDE11, as might also
have been expected based upon an assumption of a binding mode,
where the phenylimidazole and the benzimidazole are occupying
the selectivity pocket.
For five of the compounds the in vitro permeability using MDCK-
MDR1 cells [24] was assessed showing that the new compounds
possessed a range of permeabilities, ranging from low passive
permeability (44: PAPP-A-B ¼ 3.1; 52: PAPP-A-B ¼ 1.1; 57: PAPP-A-
B ¼ 3.1) to medium passive permeability (66: PAPP-A-B ¼ 11.7; 59:
PAPP-A-B ¼ 17.8 e comparable to MP-10) and importantly, none of
them appeared to be pgp-substrates PAPP-A-B(PAPP-A-B/PAPP-B-
A-ratio < 0.62).
proline-cocatalyzed multicomponent methodologybased onuse ofo-
alkynylaldehydes, PTSH and ketones was developed and proved to be
a convenient route for assembly of most of the novel tricyclic pyr-
azoles synthesized. Our in vitro studies highlighted the same ability of
all pyrazolonaphthyridines to affect PDE10A activity with a potency in
the near nM range, close to that of the lead compound II. Within the
series, a clear trend of thephenylimidazole better than benzimidazole
and methyl, methoxymethyl better than trifluoromethyl, carbox-
yethyl was observed. All compounds were profiled for PDE isoform
selectivity and showed high selectivity for PDE10A. Even if the aim to
obtain new templates for PDE10A interaction was achieved, the high
microsomal intrinsic clearance of most of the novel compounds
presented in this paper hampered their further development.
4. Experimental section
4.1. Chemistry: general procedures
€
Melting points were obtained on a Kofler melting point appa-
ratus and are uncorrected. 1H NMR spectra were taken on a Varian
Unity 200 NMR spectrometer with 1H being observed at 200 MHz.
13C NMR spectra were taken on a Bruker 400 Avance III NanoBay
spectrometer with 13C being observed at 100.6 MHz. Chemical
shifts for 1H and 13C NMR spectra were reported in
d (ppm)
downfield from tetramethylsilane, and coupling constants (J) were
expressed in Hertz. Multiplicities are recorded as s (singlet), br s
(broad singlet), d (doublet), t (triplet), dd (doublet of doublets), m
(multiplet). Atmospheric Pressure Ionization Electrospray (API-ES)
mass spectra were obtained on an Agilent 1100 series LC/MSD
spectrometer. Elemental analyses were performed with a Per-
kineElmer 2400 analyzer, and results were within 0.40% of the
calculated values. Microwave experiments were carried out by a
Biotage Iniziator-8-microwave system (max pressure 20 bar, IR
temperature sensor). TLC was performed on Merck silica gel 60 TLC
plates F254 and visualized using UV. Flash chromatography (FC)
was performed using Merck silica gel 60 (230e400 mesh ASTM).
The o-haloaldehydes 5e7 and 9 were purchased by Livchem
GmbH. 1-Methyl-1H-benzo[d]imidazole-2-carbaldehyde and 4-
pentynoic acid (53) were purchased by Lancaster. 1-Methyl-4-
phenyl-1H-imidazole-2-carbaldehyde [25] was obtained accord-
ing to reported procedure.
For six of the compounds (41e43 and 49e51) the respective
metabolic stability was assessed by measuring the intrinsic clear-
ance in human and rat liver microsomes (HLM Cl, int and RLM Cl,
int) and all of the compounds appeared to possess high clearance in
both species (>14 L/min in HLM and >170 L/min in RLM).
4.1.1. Synthesis of 4-iodonicotinaldehyde (8)
NaI (20 eq, 56 mmol) was added under nitrogen atmosphere to a
solution of 4-chloronicotinaldehyde (5) (1 eq, 2.80 mmol) in dry
MeCN (40 mL), the whole cooled to 0 ꢀC, and acetyl chloride (3 eq,
8.40 mmol) was then added. The resulting reaction mixture was
maintained at room temperature for about 1 h and then quenched
with ice and neutralized with saturated aqueous NaHCO3 solution.
The crude product was extracted with DCM. The combined organic
layers were washed with saturated aqueous Na2S2O3 solution,
3. Conclusions
In summary, a new series of pyrazolo[5,1-f][1,6]naphthyridines,
pyrazolo[5,1-a][2,6]naphthyridines, pyrazolo[5,1-a][2,7]naphthyr-
idines and pyrazolo[5,1-a]isoquinolines phenylimidazole/benzimid-
azole ethylene-linked were designed and synthesized. An AgOTf and
Fig. 2. Proposed binding mode of pyrazolo[5,1-f][1,6]naphthyridines 43 (A), 57 (B), and 41 (C) in the PDE10A catalytic site.

188
A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
Table 2
Selectivity of final compounds towards PDE isoforms.
Entry (Compd.)
% Inhibition @ 10 mM
PDE1C
PDE2A
PDE3A
PDE4D
PDE5A
PDE7B
PDE8A
PDE9A
PDE10A
PDE11A
1 (43)
2 (49)
3 (41)
4 (50)
5 (57)
6 (59)
7 (66)
8 (42)
9 (51)
10 (44)
11 (52)
15
28
28
55
44
20
13
69
17
20
54
14
8
5
16
13
1
28
51
49
13
30
20
15
38
23
45
24
44
58
68
25
15
12
11
35
67
13
38
33
38
59
15
39
22a
20
18
27
ꢁ4
17
41
47
53
41
ꢁ3
13
11
16
13
46
ꢁ6
31
29
37
25
46
17
36
5
102a
93a
88a
73a
101
106
102
100a
79a
72
34
43
7
10
25a
70a
37a
7
21
20
ꢁ2
8
15
12
53
15
NDb
10
ꢁ20
27
ꢁ3
7
24
11
10
1
ꢁ1
13a
12a
ꢁ7
77
a
% inhibition @ 2 mM.
b
ND is not determined.
water, brine, dried over Na2SO4, and evaporated to afford 8 as
yellow solid (g 0.489, 75%) used in the following step with no
further purification. Rf 0.47 (petroleum ether/AcOEt 6:4); mp
163e165 ꢀC; 1H NMR (CDCl3) 10.09 (s, 1H), 8.90 (s, 1H), 8.34 (d,
J ¼ 4.8 Hz, 1H), 7.92 (d, J ¼ 4.8 Hz, 1H). API-ES m/z: [MþH]þ calcd for
C6H5INO: 233.9, found 233.7.
4.1.3. General procedure II. Synthesis of methoxymethyl-based
tricyclic pyrazoles (18e22)
A
mixture of the appropriate o-alkynylaldehyde (1 eq,
1.88 mmol), PTSH (1.05 eq, 1.97 mmol), AgOTf (0.1 eq, 0.19 mmol),
DL-Proline (0.1 eq, 0.19 mmol), in dry ethanol (15 mL) was stirred at
room temperature for 20 min. The appropriate ketone (10 eq,
18.80 mmol) was added, and the whole heated by microwave
irradiation to 60 ꢀC for 30 min. The reaction mixture was cooled to
room temperature; Na2CO3 (6 eq, 11.28 mmol) was added and the
mixture stirred at room temperature for 12 h. The solvent was
evaporated to afford a crude residue which was purified by FC
(petroleum ether/AcOEt 3:7).
4.1.2. General procedure I. Synthesis of o-alkynylaldehydes (10e13)
A mixture of the appropriate o-haloaldehyde (1 eq, 2.60 mmol),
methyl propargyl ether (1.2 eq, 3.12 mmol), Pd(PPh3)2Cl2 (0.04 eq,
0.10 mmol), CuI (0.075 eq, 0.19 mmol), Et3N (1.5 eq, 3.90 mmol), in
dry DMF (12 mL), was stirred under nitrogen atmosphere, at room
temperature for 1 h. The mixture was quenched with H2O and the
product was extracted with Et2O. The combined organic layers
were washed with water, brine, dried over Na2SO4, and evaporated.
The crude product was purified by FC (petroleum ether/AcOEt 6:4).
4.1.3.1. 5-(Methoxymethyl)-2-methylpyrazolo[5,1-f][1,6]naphthyr-
idine (18). Synthesized from the o-alkynylaldehyde 10 and acetone
as ketone. Pale yellow solid (0.320 g, 75%); Rf 0.53 (petroleum
ether/AcOEt 3:7); mp 134e135 ꢀC; 1H NMR (CDCl3) 8.82 (dd,
Jm ¼ 1.6 Hz, Jo ¼ 4.8 Hz, 1H), 8.30 (d, J ¼ 8.0 Hz, 1H), 7.44 (dd,
J ¼ 4.8 Hz, 8.0 Hz, 1H), 7.31 (s, 1H), 6.85 (s, 1H), 4.99 (s, 2H), 3.62 (s,
3H), 2.55 (s, 3H); 13C NMR (CDCl3) 151.5, 150.4, 146.2, 139.1, 138.8,
131.2, 121.5, 119.0, 109.4, 98.6, 69.0, 59.4, 14.2; API-ES m/z: [MþH]þ
calcd for C13H14N3O: 228.1, found: 227.9.
4.1.2.1. 2-(3-Methoxyprop-1-yn-yl)nicotinaldehyde
(10).
Synthesized from the o-bromoaldehyde 6. Cream solid (0.414 g,
91%); Rf 0.23 (petroleum ether/AcOEt 6:4); mp 53e55 ꢀC; 1H NMR
(CDCl3) 10.53 (s, 1H), 8.78 (dd, Jm ¼ 1.8 Hz, Jo ¼ 4.8 Hz, 1H), 8.18 (dd,
Jm ¼ 1.8 Hz, Jo ¼ 8.0 Hz, 1H), 7.41 (dd, J ¼ 4.8 Hz, 8.0 Hz, 1H), 4.42 (s,
2H), 3.48 (s, 3H). API-ES m/z: [MþH]þ calcd for C10H10NO2: 176.1,
found: 176.0.
4.1.3.2. Ethyl 5-(methoxymethyl)pyrazolo[5,1-f][1,6]naphthyridine-2-
carboxylate (19). Synthesized from the o-alkynylaldehyde 10 and
ethyl pyruvate as ketone. Grey solid (0.375 g, 70%); Rf 0.61 (petro-
leum ether/AcOEt 2:8); mp 130e132 ꢀC; 1H NMR (CDCl3) 8.93 (dd,
Jm ¼ 1.6 Hz, Jo ¼ 4.4 Hz, 1H), 8.41 (d, J ¼ 7.6 Hz, 1H), 7.63 (s, 1H), 7.55
(s, 1H), 7.53e7.49 (m, 1H), 5.10 (s, 2H), 4.51 (q, J ¼ 7.0 Hz, 2H), 3.66
(s, 3H), 1.47 (t, J ¼ 7.0 Hz, 3H); 13C NMR (CDCl3) 162.5, 151.1, 146.0,
145.2, 139.8, 138.9, 131.4, 122.2, 119.5, 112.5, 101.8, 68.6, 61.5, 59.6,
14.4; API-ES m/z: [MþH]þ calcd for C15H16N3O3: 286.1, found:
286.0.
4.1.2.2. 3-(3-Methoxyprop-1-yn-1-yl)isonicotinaldehyde
(11).
Synthesized from the o-bromoaldehyde 7. Cream solid (0.373 g,
82%); Rf 0.24 (petroleum ether/AcOEt 6:4); mp 56e57 ꢀC; 1H NMR
(CDCl3) 10.51 (s, 1H), 8.90 (s, 1H), 8.74 (d, J ¼ 5.0 Hz, 1H), 7.70 (d,
J ¼ 5.0 Hz, 1H), 4.42 (s, 2H), 3.49 (s, 3H). API-ES m/z: [MþH]þ calcd
for C10H10NO2: 176.1, found: 176.0.
4.1.3.3. 5-(Methoxymethyl)-2-methylpyrazolo[5,1-a][2,6]naphthyr-
idine (20). Synthesized from the o-alkynylaldehyde 11 and acetone
as ketone. Pale yellow solid (0.038 g, 9%); Rf 0.55 (petroleum ether/
AcOEt 3:7); mp 104e106 ꢀC; 1H NMR (CDCl3) 9.05 (s, 1H), 8.63 (d,
J ¼ 5.6 Hz, 1H), 7.83 (d, J ¼ 5.4 Hz, 1H), 7.13 (s, 1H), 6.95 (s, 1H), 4.98
(s, 2H), 3.64 (s, 3H), 2.56 (s, 3H); 13C NMR (CDCl3) 151.3, 149.8, 145.7,
137.5, 137.0, 127.9, 123.8, 116.5, 105.3, 99.5, 69.0, 59.4, 14.1; API-ES
m/z: [MþH]þ calcd for C13H14N3O: 228.1, found: 227.9.
4.1.2.3. 4-(3-Methoxyprop-1-yn-yl)nicotinaldehyde
(12).
Synthesized from the o-iodoaldehyde 8. Yellow solid (0.291 g, 64%);
Rf 0.34 (petroleum ether/AcOEt 6:4); mp 58e60 ꢀC; 1H NMR (CDCl3)
10.51 (s, 1H), 9.10 (s, 1H), 8.76 (d, J ¼ 5.2 Hz, 1H), 7.44 (d, J ¼ 5.2 Hz,
1H), 4.42 (s, 2H), 3.49 (s, 3H). API-ES m/z: [MþH]þ calcd for
C
10H10NO2: 176.1, found: 176.0.
4.1.2.4. 2-(3-Methoxyprop-1-yn-1-yl)benzaldehyde
(13)
[26].
Synthesized from the o-bromoaldehyde 9. Obtained heating the
reaction mixture using microwave irradiation to 70 ꢀC for 2 h. The
crude product was purified by FC (petroleum ether/AcOEt 8:2).
Yellow oil (0.411 g, 91%). Rf 0.61 (petroleum ether/AcOEt 8:2).
4.1.3.4. 6-(Methoxymethyl)-9-methylpyrazolo[5,1-a][2,7]naphthyr-
idine (21). Synthesized from the o-alkynylaldehyde 12 and
acetone as ketone. Obtained by using 0.2 eq of AgOTf. White
solid (0.247 g, 58%); Rf 0.53 (petroleum ether/AcOEt 3:7); mp

A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
189
112e113 ꢀC; 1H NMR (CDCl3) 9.40 (s, 1H) 8.64 (d, J ¼ 5.6 Hz, 1H),
4.1.6. General procedure V. Synthesis of triphenylphosphonium
chlorides (31e34)
7.55 (d, J ¼ 5.6 Hz, 1H), 7.03 (s, 1H), 6.95 (s, 1H), 4.99 (s, 2H), 3.65 (s,
3H), 2.56 (s, 3H); 13C NMR (CDCl3) 151.9, 146.6, 146.5, 140.0, 137.8,
133.7, 119.9, 118.9, 105.3, 97.7, 68.9, 59.5, 14.1; API-ES m/z: [MþH]þ
calcd for C13H14N3O: 228.1, found: 228.0.
A mixture of the appropriate chloride (1 eq, 0.80 mmol), PPh3
(1.5 eq, 1.2 mmol), in dry MeCN (9 mL) was refluxed for 12 h. The
solvent was evaporated and the residue was triturated with Et2O,
the solid filtered to give the desired triphenylphosphonium chlo-
ride in almost quantitative yields as white solid, which was used in
the following step with no further purification.
4.1.3.5. 5-(Methoxymethyl)-2-methylpyrazolo[5,1-a]isoquinoline
(22). Synthesized from the o-alkynylaldehyde 13 and acetone as
ketone. The crude product was purified by FC (petroleum ether/
AcOEt 8:2). Pale yellow solid (0.127 g, 30%); Rf 0.56 (petroleum
ether/AcOEt 8:2); mp 63e65 ꢀC; 1H NMR (CDCl3) 8.07e8.02 (m,
1H), 7.74e7.70 (m, 1H), 7.54e7.50 (m, 2H), 7.05 (s, 1H), 6.82 (s, 1H),
4.98 (s, 2H), 3.63 (s, 3H), 2.55 (s, 3H); 13C NMR (CDCl3) 150.7, 139.7,
134.9, 128.9, 127.7, 127.0, 126.9, 123.5, 123.4, 108.0, 97.4, 69.2, 59.3,
14.2; API-ES m/z: [MþH]þ calcd for C14H15N2O: 227.1, found: 226.9.
4.1.7. Synthesis of ((1-methyl-4-phenyl-1H-imidazol-2-yl)methyl)
triphenylphosphonium chloride
Step 1.
A mixture of 1-methyl-4-phenyl-1H-imidazole-2-
carbaldehyde [25] (1 eq, 2.70 mmol), NaBH4 (3 eq, 8.10 mmol) in
dry MeOH (34 mL) was stirred at room temperature for 4 h. The
solvent was evaporated and the residue was solubilized in AcOEt.
The organic solution was washed with water, brine, dried over
Na2SO4, and evaporated to give (1-methyl-4-phenyl-1H-imidazol-
2-yl)methanol as white solid (0.510 g, 100%). 1H NMR (CDCl3)
7.62e7.75 (m, 2H), 7.18e7.39 (m, 3H), 6.95 (s, 1H), 4.71 (s, 2H), 3.52
(s, 3H). Step 2. (1-methyl-4-phenyl-1H-imidazol-2-yl)methanol (1
eq, 2.71 mmol) was converted into the titled phosphonium salt
following the above described General procedures IV and V.
4.1.4. General procedure III. Synthesis of hydroxymethyl-based
tricyclic pyrazoles (23e26)
To a cooled solution (0 ꢀC) of the appropriate methyl ether (1 eq,
1.76 mmol) in dry DCM (24 mL), under nitrogen atmosphere, BBr3
(1 M in DCM, 3 eq, 5.28 mmol) was added and the mixture warmed
to room temperature and stirred for 1.5 h. The whole was cooled to
0
ꢀC and treated with saturated aqueous NaHCO3 solution (7 mL);
4.1.8. General procedure VI. Synthesis of carbaldehyde-based
tricyclic pyrazoles (35, 36)
the aqueous phase was extracted with DCM. The combined organic
layer was washed with water, brine, dried over Na2SO4, and evap-
orated. The crude product was purified by FC (petroleum ether/
AcOEt 3:7 / AcOEt).
To a solution of the appropriate alcohol (1 eq, 0.90 mmol) in dry
DCE (22 mL), under nitrogen atmosphere, DMP (1.1 eq, 0.99 mmol)
was added and the whole stirred at room temperature for 12 h.
Saturated aqueous NaHCO3 solution (18 mL) was added and the
aqueous phase extracted with Et2O. The combined organic layer
was washed with water, brine, dried over Na2SO4, and evaporated.
The crude product was used in the following step with no further
purification.
4.1.4.1. (2-Methylpyrazolo[5,1-f][1,6]naphthyridin-5-yl)methanol
(23). Synthesized from the methyl ether 18. White solid (0.303 g,
81%); mp 188e189 ꢀC; 1H NMR (CDCl3) 8.85 (d, J ¼ 4.4 Hz, 1H), 8.33
(d, J ¼ 8.0 Hz, 1H), 7.45 (dd, J ¼ 4.4 Hz, 8.0 Hz, 1H), 7.19 (s, 1H), 6.86
(s, 1H), 5.08 (s, 2H), 2.55 (s, 3H); API-ES m/z: [MþH]þ calcd for
C
12H12N3O: 214.1, found: 213.9.
4.1.8.1. 2-Methylpyrazolo[5,1-f][1,6]naphthyridin-5-carbaldehyde
(35). Synthesized from the alcohol 23. Pale yellow solid (0.157 g,
83%); mp 182e183 ꢀC; 1H NMR (CDCl3) 10.90 (s, 1H), 8.93 (dd,
Jm ¼ 1.6 Hz, Jo ¼ 4.6 Hz, 1H), 8.35 (d, J ¼ 8.2 Hz, 1H), 7.83 (s, 1H), 7.56
(dd, J ¼ 4.4 Hz, 8.2 Hz, 1H), 6.92 (s, 1H), 2.60 (s, 3H); API-ES m/z:
[MþH]þ calcd for C12H10N3O: 212.0, found: 211.9.
4.1.4.2. Ethyl 5-(hydroxymethyl)pyrazolo[5,1-f][1,6]naphthyridine-2-
carboxylate (24). Synthesized from the methyl ether 19. White
solid (0.300 g, 63%); mp 183 ꢀC dec.; 1H NMR (CDCl3) 9.0e8.85 (m,
1H), 8.42 (d, J ¼ 7.6 Hz, 1H), 7.62 (s, 1H), 7.60e7.48 (m, 1H), 7.46 (s,
1H), 5.19 (s, 2H), 4.50 (q, J ¼ 7.2 Hz, 2H), 1.47 (t, J ¼ 7.2 Hz, 3H). API-
ES m/z: [MþH]þ calcd for C14H14N3O3: 272.1, found: 272.0.
4.1.8.2. 2-Methylpyrazolo[5,1-a]isoquinoline-5-carbaldehyde
(36).
Synthesized from the alcohol 26. Pale yellow solid (0.185 g, 98%);
mp 163e164 ꢀC; 1H NMR (CDCl3) 10.86 (s, 1H), 8.06 (d, J ¼ 7.8 Hz,
1H), 7.85 (d, J ¼ 7.8 Hz, 1H), 7.60 (m, 3H), 6.86 (s, 1H), 2.58 (s, 3H);
API-ES m/z: [MþH]þ calcd for C13H11N2O: 211.1, found: 211.0.
4.1.4.3. (9-Methylpyrazolo[5,1-a][2,7]naphthyridin-6-yl)methanol
(25). Synthesized from the methyl ether 21. White solid (0.168 g,
45%); mp 189e191 ꢀC dec.; 1H NMR (CDCl3) 9.39 (s, 1H), 8.65 (d,
J ¼ 5.2 Hz, 1H), 7.53 (d, J ¼ 5.6 Hz, 1H), 6.94 (s, 1H); 6.88 (s, 1H), 5.06
(s, 2H), 2.56 (s, 3H); API-ES m/z: [MþH]þ calcd for C12H12N3O: 214.1,
found: 214.0.
4.1.9. General procedure VII. Synthesis of alkenes (37e40, 45e48)
To a suspension of 60% NaH in mineral oil (2 eq, 1.42 mmol) in
dry DMF (4e6 mL) cooled to ꢁ5 ꢀC, the appropriate phosphonium
salt (1 eq, 0.71 mmol) was portionwise added, and the resulting
solution stirred for 30 min at the same temperature. The appro-
priate aldehyde (1 eq, 0.71 mmol) was portionwise added, and the
resulting mixture stirred at room temperature for 5 h. The whole
was quenched with H2O, and the crude product extracted with
AcOEt. The combined organic layer was washed with water, brine,
dried over Na2SO4, and evaporated to afford a crude residue puri-
fied by FC (petroleum ether/AcOEt 3:7).
4.1.4.4. (2-Methylpyrazolo[5,1-a]isoquinolin-5-yl)methanol
(26).
Synthesized from the methyl ether 22. White solid (0.238 g, 64%);
mp 157e158 ꢀC; 1H NMR (CDCl3) 8.04 (m, 1H), 7.62 (m, 1H), 7.55 (m,
2H), 7.09 (s, 1H), 6.85 (s, 1H), 4.97 (s, 2H), 2.58 (s, 3H); API-ES m/z:
[MþH]þ calcd for C13H13N2O: 213.1, found: 213.0.
4.1.5. General procedure IV. Synthesis of chloromethyl-based
tricyclic pyrazoles (27e30)
To a cooled (0 ꢀC) solution of the appropriate alcohol (1 eq,
0.80 mmol) in dry DCM (5 ml), SOCl2 (10 eq, 8.0 mmol) was added
and the whole stirred at room temperature for 12 h. The solution
was evaporated to afford a crude product which was used in the
following step with no further purification.
4.1.9.1. Ethyl 5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)vinyl)pyr-
azolo[5,1-f][1,6]naphthyridine-2-carboxylate (37). Synthesized from
the phosphonium salt 32 and 1-methyl-4-phenyl-1H-imidazole-2-
carbaldehyde. Yellow solid (0.189 g, 63%); API-ES m/z: [MþH]þ
calcd for C25H22N5O2: 424.2, found: 424.0.

190
A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
4.1.9.2. 9-Methyl-6-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)vinyl)
pyrazolo[5,1-a][2,7]naphthyridine (38). Synthesized from the
phosphonium salt 33 and 1-methyl-4-phenyl-1H-imidazole-2-
carbaldehyde. Yellow solid (0.259 g, 100%); API-ES m/z: [MþH]þ
calcd for C23H20N5: 366.2, found: 366.0.
114.7, 101.9, 61.4, 33.1, 30.7, 24.7, 14.4; API-ES m/z: [MþH]þ calcd for
C25H24N5O2: 426.2, found: 426.0. Anal. (C25H23N5O2) C, H, N.
4.1.10.2. 9-Methyl-6-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)ethyl)
pyrazolo[5,1-a][2,7]naphthyridine (42). Synthesized from the
alkene 38. White solid (0.073 g, 57%); Rf 0.6 (CHCl3/CH3OH 95:5);
mp 163e165 ꢀC; 1H NMR (CDCl3) 9.37 (s, 1H), 8.60 (d, J ¼ 5.0 Hz,
1H), 7.75 (d, J ¼ 7.0 Hz, 2H), 7.46 (d, J ¼ 5.0 Hz, 1H), 7.37 (t, J ¼ 7.4 Hz,
2H), 7.22 (t, J ¼ 7.2 Hz, 1H), 7.06 (s, 1H), 6.96 (s, 1H), 6.79 (s, 1H),
4.1.9.3. 2-Methyl-5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)vinyl)
pyrazolo[5,1-f][1,6]naphthyridine (39). Synthesized from ((1-
methyl-4-phenyl-1H-imidazol-2-yl)methyl)triphenylphospho-
nium chloride and the aldehyde 35. Yellow solid (0.168 g, 65%); API-
ES m/z: [MþH]þ calcd for C23H20N5: 366.2, found: 366.0.
3.63e3.59 (m, 2H), 3.57 (s, 3H), 3.39e3.32 (m, 2H), 2.58 (s, 3H); 13
C
NMR (CDCl3) 151.6, 147.6, 146.6, 142.2, 140.3, 137.8, 134.3, 133.9,
128.6, 126.5, 124.7, 119.6, 118.9, 116.5, 107.8, 97.8, 32.7, 31.0, 24.6,
14.2; API-ES m/z: [MþH]þ calcd for C23H22N5: 368.2, found: 368.0.
Anal. (C23H21N5) C, H, N.
4.1.9.4. 2-Methyl-5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)vinyl)
pyrazolo[5,1-a]isoquinoline (40). Synthesized from ((1-methyl-4-
phenyl-1H-imidazol-2-yl)methyl)triphenylphosphonium chloride
and the aldehyde 36. Purified by FC (petroleum ether/AcOEt 7:3).
Yellow solid (0.144 g, 56%); API-ES m/z: [MþH]þ calcd for C24H21N4:
365.2, found: 365.0.
4.1.10.3. 2-Methyl-5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)ethyl)
pyrazolo[5,1-f][1,6]naphthyridine (43). Synthesized from the alkene
39. White solid (0.079 g, 62%); Rf 0.29 (petroleum ether/AcOEt 2:8);
mp 148e150 ꢀC; 1H NMR (CDCl3) 8.79 (dd, Jm ¼ 1.8 Hz, Jo ¼ 4.8 Hz,
1H), 8.27 (dd, Jm ¼ 1.8 Hz, Jo ¼ 8.1 Hz, 1H), 7.74 (d, J ¼ 7.2 Hz, 2H),
7.40e7.33 (m, 3H), 7.23 (t, J ¼ 7.2 Hz, 1H), 7.08 (s, 1H), 7.06 (s, 1H),
6.85 (s, 1H), 3.62 (s, 3H), 3.60e3.55 (m, 2H), 3.36e3.30 (m, 2H), 2.55
(s, 3H); 13C NMR (CDCl3) 151.3, 150.4, 147.6, 146.3,141.6, 140.3, 138.7,
134.4, 131.1, 128.5, 126.5, 124.8, 121.3, 118.9, 116.5, 110.9, 98.8, 32.7,
30.7, 24.6, 14.2; API-ES m/z: [MþH]þ calcd for C23H22N5: 368.2,
found: 368.1. Anal. (C23H21N5) C, H, N.
4.1.9.5. 2-Methyl-5-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)vinyl)
pyrazolo[5,1-f][1,6]naphthyridine (45). Synthesized from the phos-
phonium salt 31 and 1-methyl-1H-benzo[d]imidazole-2-
carbaldehyde. Yellow solid (0.238 g, 99%); API-ES m/z: [MþH]þ
calcd for C21H18N5: 340.1, found: 340.0.
4.1.9.6. Ethyl
5-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)vinyl)pyr-
azolo[5,1-f][1,6]naphthyridine-2-carboxylate (46). Synthesized from
the phosphonium salt 32 and 1-methyl-1H-benzo[d]imidazole-2-
carbaldehyde. Yellow solid (0.211 g, 75%); API-ES m/z: [MþH]þ
calcd for C23H20N5O2: 398.1, found: 398.0.
4.1.10.4. 2-Methyl-5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)ethyl)
pyrazolo[5,1-a]isoquinoline (44). Synthesized from the alkene 40.
Purified by FC (petroleum ether/AcOEt 6:4); white solid (0.103 g,
81%); Rf 0.57 (petroleum ether/AcOEt 2:8); mp 123e125 ꢀC; 1H
NMR (CDCl3) 8.06e7.98 (m, 1H), 7.76 (dd, Jm ¼ 1.2 Hz, Jo ¼ 7.4 Hz,
2H), 7.67e7.58 (m, 1H), 7.55e7.44 (m, 2H), 7.41e7.33 (m, 2H),
7.29e7.18 (m, 1H), 7.05 (s, 1H), 6.83 (s, 1H), 6.81 (s, 1H), 3.62e3.47
(m, 2H), 3.55 (s, 3H), 3.42e3.30 (m, 2H), 2.56 (s, 3H); 13C NMR
(CDCl3) 150.4, 148.1, 140.0, 139.6, 137.2, 134.3, 129.2, 128.6, 127.7,
126.7, 126.5, 124.8, 123.4, 123.4, 116.4, 109.9, 97.4, 32.7, 31.0, 24.7,
14.2; API-ES m/z: [MþH]þ calcd for C24H23N4: 367.2, found: 367.0.
Anal. (C24H22N4) C, H, N.
4.1.9.7. 9-Methyl-6-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)vinyl)
pyrazolo[5,1-a][2,7]naphthyridine (47). Synthesized from the
phosphonium salt 33 and 1-methyl-1H-benzo[d]imidazole-2-
carbaldehyde. Yellow solid (0.240 g, 100%); API-ES m/z: [MþH]þ
calcd for C21H18N5: 340.1, found: 340.0.
4.1.9.8. 2-Methyl-5-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)vinyl)
pyrazolo[5,1-a]isoquinoline (48). Synthesized from the phospho-
nium salt 34 and 1-methyl-1H-benzo[d]imidazole-2-carbaldehyde.
Purified by FC (petroleum ether/AcOEt 7:3). Yellow solid (0.230 g,
96%); API-ES m/z: [MþH]þ calcd for C22H19N4: 339.1, found: 339.0.
4.1.10.5. 2-Methyl-5-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)ethyl)
pyrazolo[5,1-f][1,6]naphthyridine (49). Synthesized from the alkene
45. White solid (0.085 g, 71%); Rf 0.27 (petroleum ether/AcOEt 3:7);
mp 188e190 ꢀC; 1H NMR (CDCl3) 8.81 (dd, Jm ¼ 1.6 Hz, Jo ¼ 4.6 Hz,
1H), 8.31 (dd, Jm ¼ 1.8 Hz, Jo ¼ 8.2 Hz, 1H), 7.77e7.73 (m, 1H), 7.41
(dd, J ¼ 4.6 Hz, 8.2 Hz, 1H), 7.31e7.23 (m, 3H), 7.12 (s, 1H), 6.88 (s,
1H), 3.81 (s, 3H), 3.76e3.67 (m, 2H), 3.59e3.49 (m, 2H), 2.55 (s, 3H);
13C NMR (CDCl3) 154.0, 151.3, 150.4, 146.3, 142.7, 141.4, 138.7, 135.9,
131.1, 122.2, 122.0, 121.4, 119.3, 119.0, 111.0, 109.0, 98.8, 30.2, 29.7,
25.4, 14.2; API-ES m/z: [MþH]þ calcd for C21H20N5: 342.2, found:
342.1. Anal. (C21H19N5) C, H, N.
4.1.10. General procedure VIII. Synthesis of final compounds
(41e44, 49e52)
A mixture of the appropriate alkene (1 eq, 0.35 mmol), PTSH (3
eq, 1.05 mmol), in dry DMF (6 mL) was heated at 120 ꢀC for 4 h
under nitrogen atmosphere. PTSH (1.5 eq, 0.53 mmol) was further
added and the whole heated for 2 h. The mixture was cooled to
room temperature, quenched with H2O and basified with saturated
aqueous NaHCO3 solution. The crude product was extracted with
AcOEt; the combined organic layer was washed with water, brine,
dried over Na2SO4, and evaporated to afford a crude residue which
was purified by FC (petroleum ether/AcOEt 3:7 / AcOEt).
4.1.10.6. Ethyl 5-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)ethyl)pyr-
azolo[5,1-f][1,6]naphthyridine-2-carboxylate (50). Synthesized from
the alkene 46. Purified by FC (CHCl3/MeOH 9.5:0.5); white solid
(0.092 g, 66%); Rf 0.31 (petroleum ether/AcOEt 3:7); mp
135e137 ꢀC; 1H NMR (CDCl3): 8.91e8.89 (m, 1H), 8.41 (d, J ¼ 7.8 Hz,
1H), 7.73e7.71 (m, 1H), 7.64 (s, 1H), 7.56e7.47 (m, 1H), 7.38 (s, 1H),
7.35e7.26 (m, 3H), 4.50 (q, J ¼ 7.2 Hz, 2H), 3.97 (s, 3H), 3.80e3.76
(m, 2H), 3.67e3.65 (m, 2H), 1.48 (t, J ¼ 7.2 Hz, 3H); 13C NMR (CDCl3)
162.5, 153.6, 151.2, 146.0, 144.9, 142.0, 141.4, 138.8, 135.7, 131.4,
122.5, 122.2, 122.1, 119.6, 119.0, 114.8, 109.3, 101.9, 61.4, 30.3, 30.0,
25.2, 14.4; API-ES m/z: [MþH]þ calcd for C23H22N5O2: 400.2, found:
400.0. Anal. (C23H21N5O2) C, H, N.
4.1.10.1. Ethyl 5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)ethyl)pyr-
azolo[5,1-f][1,6]naphthyridine-2-carboxylate (41). Synthesized from
the alkene 37. Purified by FC (CHCl3/MeOH 9.5:0.5); white solid
(0.077 g, 52%); Rf 0.57 (CHCl3/CH3OH 95:5); mp 172e174 ꢀC; 1H
NMR (CDCl3) 8.91e8.89 (m, 1H), 8.40 (d, J ¼ 8.0 Hz, 1H), 7.75 (d,
J ¼ 6.8 Hz, 2H), 7.64 (s, 1H), 7.51 (dd, J ¼ 4.6 Hz, 8.0 Hz, 1H),
7.41e7.36 (m, 3H), 7.29e7.19 (m, 1H), 7.13 (s, 1H), 4.49 (q, J ¼ 7.0 Hz,
2H), 3.83 (s, 3H), 3.75e3.55 (m, 2H), 3.50e3.25 (m, 2H), 1.47 (t,
J ¼ 7.0 Hz, 3H); 13C NMR (CDCl3) 162.6, 151.2, 147.4, 146.1, 144.9,
141.8, 140.3, 138.9, 134.4, 131.3, 128.5,126.5,124.8, 122.1, 119.6,116.7,

A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
191
4.1.10.7. 9-Methyl-6-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)ethyl)
pyrazolo[5,1-a][2,7]naphthyridine (51). Synthesized from the
alkene 47. White solid (0.046 g, 39%); Rf 0.54 (CHCl3/CH3OH 95:5);
mp 170e171 ꢀC; 1H NMR (CDCl3) 9.36 (s,1H), 8.59 (d, J ¼ 4.8 Hz,1H),
7.74e7.65 (m, 1H), 7.45 (d, J ¼ 4.8 Hz, 1H), 7.35e7.20 (m, 3H), 6.95 (s,
1H), 6.79 (s, 1H), 3.74 (s, 3H), 3.74e3.67 (m, 2H), 3.56e3.48 (m, 2H),
2.56 (s, 3H); 13C NMR (CDCl3) 153.9, 151.7, 146.7, 146.6, 142.6, 141.9,
137.8, 135.9, 133.8, 122.2, 122.0, 119.6, 119.2, 118.9, 109.1, 107.8, 97.8,
30.5, 29.7, 25.4,14.2; API-ES m/z: [MþH]þ calcd for C21H20N5: 342.2,
found: 342.0. Anal. (C21H19N5) C, H, N.
following the general synthetic procedure I, heating the reaction
mixture using microwave irradiation at 50 ꢀC for 20 min. Purified
by FC (petroleum ether/AcOEt 4:6 / AcOEt); yellow solid (0.243 g,
60%); Rf 0.13 (petroleum ether/AcOEt 4:6); mp 98e100 ꢀC; 1H NMR
(CDCl3): 10.45 (s, 1H), 8.74 (dd, Jm ¼ 1.2 Hz, Jo ¼ 4.4 Hz, 1H), 8.14 (dd,
Jm ¼ 1.2 Hz, Jo ¼ 8.0 Hz, 1H), 7.74 (d, J ¼ 7.2 Hz, 2H), 7.50e7.32 (m,
3H), 7.27e7.21 (m, 1H), 7.10 (s, 1H), 3.68 (s, 3H), 3.10 (s, 4H); 13C
NMR (CDCl3) 191.1, 154.3, 146.5, 146.2, 140.3, 134.7, 134.2, 131.9,
128.5, 126.6, 124.8, 124.7, 123.1, 116.7, 96.7, 32.9, 25.7, 18.8; API-ES
m/z: [MþH]þ calcd for C20H18N3O: 316.1, found: 316.0.
4.1.10.8. 2-Methyl-5-(2-(1-methyl-1H-benzo[d]imidazol-2-yl)ethyl)
pyrazolo[5,1-a]isoquinoline (52). Synthesized from the alkene 48.
Purified by FC (petroleum ether/AcOEt 6:4); white solid (0.092 g,
77%); Rf 0.42 (petroleum ether/AcOEt 4:6); mp 120e122 ꢀC; 1H
NMR (CDCl3) 8.06e7.96 (m, 1H), 7.80e7.74 (m, 1H), 7.66e7.57 (m,
1H), 7.55e7.43 (m, 2H), 7.33e7.19 (m, 3H), 6.82 (s, 1H), 6.81 (s, 1H),
4.1.13. Synthesis of final compounds (41 and 57)
4.1.13.1. Ethyl 5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)ethyl)pyr-
azolo[5,1-f][1,6]naphthyridine-2-carboxylate (41). Synthesized from
56 (1 eq, 0.97 mmol) and ethyl pyruvate following the general
procedure II (0.292 g, 71%).
3.73 (s, 3H), 3.68e3.59 (m, 2H), 3.58e3.46 (m, 2H), 2.55 (s, 3H); 13
C
4.1.13.2. 5-(2-(1-Methyl-4-phenyl-1H-imidazol-2-yl)ethyl)-2-(tri-
fluoromethyl)pyrazolo[5,1-f][1,6]naphthyridine (57).
NMR (CDCl3) 154.4, 150.5, 142.7, 139.7, 137.1, 135.9, 129.1, 127.7,
126.7, 123.4, 122.1, 121.9, 119.2, 109.9, 109.1, 97.4, 30.5, 29.7, 25.6,
14.2; API-ES m/z: [MþH]þ calcd for C22H21N4: 341.2, found: 341.0.
Anal. (C22H20N4) C, H, N.
Synthesized from 56 (1 eq, 0.97 mmol) and 1,1,1-trifluoroacetone,
following the general procedure II. Purified by FC (AcOEt / AcOEt/
MeOH 9:1); white solid (0.301 g, 75%); Rf 0.38 (petroleum ether/
AcOEt 2:8); mp 159e161 ꢀC; 1H NMR (CDCl3) 8.93 (dd, Jm ¼ 1.6 Hz,
Jo ¼ 4.6 Hz, 1H), 8.39 (dd, Jm ¼ 1.6 Hz and 8.0 Hz, 1H), 7.74 (d,
J ¼ 7.2 Hz, 2H), 7.52 (dd, J ¼ 4.6 Hz, 8.0 Hz, 1H), 7.36 (t, J ¼ 7.4 Hz,
2H), 7.35 (s, 1H), 7.27e7.21 (m, 2H), 7.11 (s, 1H), 3.76 (s, 3H),
3.71e3.62 (m, 2H), 3.39e3.31 (m, 2H). 13C NMR (CDCl3) 151.5, 147.2,
146.1,144.5,144.1,143.7,143.4,141.6, 140.2,138.9,134.2,131.3, 128.5,
126.5,124.7,122.2,119.1,116.7,114.7, 97.5, 32.8, 30.5, 24.6; API-ES m/
z: : [MþH]þ calcd for C23H19F3N5: 422.1, found: 422.0. Anal.
(C23H18F3N5) C, H, N.
4.1.11. Synthesis of 2-(but-3-yn-1-yl)-1-methyl-4-phenyl-1H-
imidazole (55)
Scheme 3, Step a. Cs2CO3 (0.5 eq, 5.10 mmol) was added to a
solution of 4-pentynoic acid (53) (1 eq, 10.20 mmol) in EtOH/H2O
1:1 (20 mL), and the whole stirred at room temperature for 1 h. The
solvent was evaporated and the crude residue solubilized in dry
DMF (12.5 mL);
a solution of 2-bromoacetophenone (1 eq,
10.20 mmol) in dry DMF (6.5 mL) was dropwise added and the
whole stirred at room temperature for 15 min. The solvent was
evaporated, the residue taken up with AcOEt and the inorganic salt
was filtered off. The filtrate was dried over Na2SO4, and the solvent
evaporated to afford a yellow oily residue. Step b. The oily residue
was solubilized in xylene (50 mL). NH4OAc (15 eq, 153.00 mmol)
was added and the resulting solution refluxed for 12 h using a
DeaneStark trap. The solution was cooled to room temperature,
washed with H2O and the organic phase evaporated to give a res-
idue which was taken up with AcOEt. The organic phase was
washed with saturated aqueous NaHCO3 solution, brine, dried with
Na2SO4 and evaporated to give 2-(but-3-yn-1-yl)-4-phenyl-1H-
imidazole (54) as crude residue purified by FC (petroleum ether/
AcOEt 6:4). Orange solid (1.960 g, 98%); Rf 0.10 (petroleum ether/
AcOEt 6:4); mp 53e55 ꢀC; 1H NMR (CDCl3) 7.67 (d, J ¼ 7.4 Hz, 2H),
7.40e7.23 (m, 4H), 3.02 (t, J ¼ 6.8 Hz, 2H), 2.63 (dt, J ¼ 2.4, 6.8 Hz,
2H), 2.12 (t, J ¼ 2.4 Hz, 1H). Step c. 60% NaH in mineral oil (1.5 eq,
15.00 mmol) was added to a cooled solution (0 ꢀC) of 54 (1 eq,
9.98 mmol) in dry THF (50 mL), and the whole stirred at the same
temperature for 30 min. MeI (1.1 eq, 11.00 mmol) was dropwise
added and the resulting solution warmed to room temperature and
stirred for 12 h. The solution was washed with H2O, brine, dried
with Na2SO4 and evaporated to give 55 as crude residue purified by
FC (petroleum ether/AcOEt 1:1). Orange oil (1.572 g, 75%); Rf 0.59
(petroleum ether/AcOEt 4:6); 1H NMR (CDCl3): 7.72 (d, J ¼ 7.4 Hz,
2H), 7.39e7.20 (m, 3H), 7.07 (s, 1H), 3.65 (s, 3H), 2.97 (t, J ¼ 7.6 Hz,
2H), 2.70 (dt, J ¼ 2.4, 7.6 Hz, 2H), 2.00 (t, J ¼ 2.4 Hz, 1H). 13C NMR
(CDCl3) 147.1, 140.2, 134.3, 128.5, 126.5, 124.7, 116.5, 83.3, 69.2, 32.9,
26.1, 17.9; API-ES m/z: [MþH]þ calcd for C14H15N2: 211.1, found:
211.0.
4.1.14. Synthesis of final compound 2-(methoxymethyl)-5-(2-(1-
methyl-4-phenyl-1H-imidazol-2-yl)ethyl)pyrazolo[5,1-f][1,6]
naphthyridine (59)
Scheme 3, Step f. NaBH4 (2.2 eq, 0.88 mmol) was added to a
solution of 41 (1 eq, 0.40 mmol) in dry EtOH (4 mL), and the whole
refluxed for 12 h. The solvent was evaporated to give (5-(2-(1-
methyl-4-phenyl-1H-imidazol-2-yl)ethyl)pyrazolo[5,1-f][1,6]naph-
thyridin-2-yl)methanol (58) as crude residue purified by FC (CHCl3/
MeOH 9.5:0.5). White solid (0.093 g, 61%); Rf 0,28 (CHCl3/CH3OH
95:5); 1H NMR (CDCl3) 8.77 (dd, Jm ¼ 1.6 Hz, Jo ¼ 4.6 Hz,1H), 8.24 (d,
J ¼ 8.4 Hz,1H), 7.73 (d, J ¼ 7.0 Hz, 2H), 7.39e7.17 (m, 5H), 7.05 (s,1H),
4.96 (s, 2H), 3.59 (s, 3H), 3.53e3.49 (m, 2H), 3.31e3.23 (m, 2H), 2.87
(br s, 1H). Step c. Compound 58 (1 eq, 0.20 mmol) was converted
into 59 following the procedure used for the synthesis of 55
(Scheme 3, Step c). Purified by FC (CHCl3/MeOH 9.5:0.5). Yellow
solid (0.046 g, 58%); Rf 0.53 (CHCl3/CH3OH 9.5:0.5); mp
133e134 ꢀC; 1H NMR (CDCl3) 8.84 (d, J ¼ 4.4 Hz, 1H), 8.35 (d,
J ¼ 7.8 Hz, 1H), 7.75 (d, J ¼ 8.0 Hz, 2H), 7.48e7.40 (m, 1H), 7.36 (t,
J ¼ 8.0 Hz, 2H), 7.30e7.20 (m, 1H), 7.17 (s, 1H), 7.13 (s, 1H), 7.10 (s,
1H), 4.74 (s, 2H), 3.70e3.55 (m, 2H), 3.66 (s, 3H), 3.50 (s, 3H),
3.40e3.25 (m, 2H); 13C NMR (CDCl3) 152.0, 150.6, 147.5, 146.2, 141.7,
140.1, 138.9, 134.1, 131.2, 128.6, 126.6, 124.8, 121.6, 119.2, 116.6, 112.0,
98.3, 68.7, 58.6, 32.8, 30.5, 24.6; API-ES m/z: [MþH]þ calcd for
C24H24N5O 398.2, found: 398.0. Anal. (C24H23N5O) C, H, N.
4.1.15. Synthesis of 3-(4-(1-methyl-4-phenyl-1H-imidazol-2-yl)
but-1-yn-1-yl)isonicotinaldehyde (60)
Synthesized from 3-bromoisonicotinaldehyde (7) (1 eq,
1.39 mmol) and the alkyne 55, following the general synthetic
procedure I, heating the reaction mixture using microwave irradi-
ation at 70 ꢀC for 2 h. Purified by FC (petroleum ether/AcOEt 4/6).
Yellow solid (0.346 g, 79%); Rf 0.22 (petroleum ether/AcOEt 4:6);
mp 118e119 ꢀC; 1H NMR (CDCl3) 10.42 (s, 1H), 8.81 (s, 1H), 8.67 (d,
4.1.12. Synthesis of 2-(4-(1-methyl-4-phenyl-1H-imidazol-2-yl)
but-1-yn-1-yl)nicotinaldehyde (56)
Synthesized from 2-bromonicotinaldehyde (6) (1 eq, 1.29 mmol)
and 2-(but-3-yn-1-yl)-1-methyl-4-phenyl-1H-imidazole (55),

192
A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
J ¼ 5 Hz, 1H), 7.74 (d, J ¼ 7.8 Hz, 2H), 7.64 (d, J ¼ 5 Hz, 1H), 7.36 (t,
J ¼ 7.4 Hz, 2H), 7.25e7.21 (m, 1H), 7.11 (s, 1H), 3.68 (s, 3H), 3.08 (s,
4H); 13C NMR (CDCl3) 191.0, 154.8, 149.0, 146.5, 140.8, 140.4, 134.2,
128.6,126.6,124.7, 121.7,119.0,116.6, 99.5, 74.4, 32.9, 25.8,18.9; API-
ES m/z: [MþH]þ calcd for C20H18N3O: 316.1, found: 316.0.
(s, 1H), 3.61 (s, 3H), 3.30e3.12 (m, 4H), 2.26 (s, 3H). API-ES m/z:
[MþH]þ calcd for C23H23N4O 371.2, found 371.0.
4.1.20. Synthesis of 1-(3-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)
ethyl)-2,6-naphthyridin-1-yl)propan-2-one oxime (65)
Synthesized from 64 (1 eq, 0.97 mmol) following the procedure
used for the synthesis of 61. Purified by FC (CHCl3/MeOH 9.5:0.5).
Yellow solid (0.321 g, 86%); Rf 0.33 (petroleum ether/AcOEt 1:9);
mp 84e86 ꢀC; 1H NMR (CDCl3) 9.17 (s, 1H), 8.56 (d, J ¼ 5.8 Hz, 1H),
7.90 (d, J ¼ 6 Hz, 1H), 7.72 (d, J ¼ 7.4 Hz, 2H), 7.51 (s, 1H), 7.35 (t,
J ¼ 8 Hz, 2H), 7.24e7.02 (m,1H), 7.00 (s,1H), 4.18 (s, 2H), 3.51 (s, 3H),
3.45e3.38 (m, 2H), 3.30e3.22 (m, 2H), 1.95 (s, 3H). API-ES m/z:
[MþH]þ calcd for C23H24N5O 386.2, found: 386.0.
4.1.16. Synthesis of 3-(4-(1-methyl-4-phenyl-1H-imidazol-2-yl)
but-1-yn-1-yl)isonicotinaldehyde oxime (61)
A mixture of 60 (1 eq, 4.12 mmol), NH2OH$HCl (1.5 eq,
6.18 mmol) and AcONa$H2O (1.5 eq, 6.18 mmol) in EtOH (24 mL)
was stirred at room temperature for 4 h. The solvent was evapo-
rated and the residue was extracted with Et2O. The organic phase
was dried with Na2SO4 and evaporated to give a crude residue used
without purification. Yellow solid (0.816 g, 60%); Rf 0.45 (petroleum
ether/AcOEt 3:7); mp 145e147 ꢀC; 1H NMR (CDCl3) 8.58 (s,1H), 8.47
(s, 1H), 8.39 (d, J ¼ 5.2 Hz, 1H), 7.76e7.68 (m, 2H), 7.65 (d, J ¼ 5.2 Hz,
1H), 7.39e7.22 (m, 3H), 7.11 (s, 1H); 3.70 (s, 3H), 3.15e3.11 (m, 2H),
3.00e2.95 (m, 2H); API-ES m/z: [MþH]þ calcd for C20H19N4O: 331.1,
found: 331.0.
4.1.21. Synthesis of 2-methyl-5-(2-(1-methyl-4-phenyl-1H-
imidazol-2-yl)ethyl)pyrazolo[5,1-a][2,6]naphthyridine (66)
To a cooled solution (0 ꢀC) of 65 (1.0 eq, 0.8 mmol) in dry DME
(5 mL) was added TFAA (1 eq, 0.80 mmol) and the mixture stirred
for 10 min. Et3N (3.1 eq, 2.4 mmol) was added dropwise over
15 min, and then the whole was warmed to room temperature and
stirred for 0.5 h. FeCl2 (0.05 eq, 0.039 mmol) was added and the
mixture heated to 75 ꢀC for 12 h. The mixture was poured into
water, basified with a saturated aqueous K2CO3 solution and
extracted with AcOEt. The organic phase was dried under Na2SO4
and evaporated to afford a crude residue purified by FC (petroleum
ether/AcOEt 4:6). White solid (0.023 g, 8%). Rf 0.30 (petroleum
ether/AcOEt 2:8); mp 99e100ꢀ C; 1H NMR (CDCl3) 9.00 (s, 1H), 8.63
(d, J ¼ 5.4 Hz, 1H), 7.81 (d, J ¼ 5.4, 1H), 7.74 (d, J ¼ 7.6 Hz, 2H), 7.37 (t,
J ¼ 7.6 Hz, 2H), 7.27e7.22 (m, 1H), 7.06 (s, 1H), 6.96 (s, 1H), 6.91 (s,
1H), 3.62e3.51 (m, 5H), 3.38e3.31 (m, 2H), 2.58 (s, 3H). 13C NMR
(CDCl3) 151.0, 149.7, 147.6, 145.6, 140.3, 139.7, 137.0, 134.4, 128.6,
128.0, 126.5, 124.7, 123.8, 116.5, 116.2, 107.8, 99.6, 32.7, 30.8, 24.6,
14.2; API-ES m/z: [MþH]þ calcd for C23H22N5: 368.2, found: 368.0.
Anal. (C23H21N5) C, H, N.
4.1.17. Synthesis of 3-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)
ethyl)-2,6-naphthyridine 2-oxide (62)
A mixture of 61 (1 eq, 1.82 mmol) and dry K2CO3 (1.5 eq,
2.73 mmol) in dry EtOH (36 mL) was stirred at room temperature
for 6 h. The solvent was evaporated and the residue extracted with
DCM. The organic phase was dried with Na2SO4 and evaporated to
give a crude residue used in the following step with no further
purification. Yellow solid (0.558 g, 93%); Rf 0.0 (petroleum ether/
AcOEt 4:6); mp 194e196 ꢀC; 1H NMR (CDCl3) 9.16 (s, 1H), 8.80 (s,
1H), 8.60 (d, J ¼ 5.8 Hz, 1H), 7.96 (s, 1H), 7.73 (d, J ¼ 7.2 Hz, 2H), 7.47
(d, J ¼ 5.8 Hz, 1H), 7.40e7.22 (m, 3H), 7.07 (s, 1H), 3.65 (s, 3H), 3.53
(t, J ¼ 7 Hz, 2H), 3.26 (t, J ¼ 7 Hz, 2H); API-ES m/z: [MþH]þ calcd for
C
20H19N4O: 331.1, found: 331.0.
4.1.18. Synthesis of 1-chloro-3-(2-(1-methyl-4-phenyl-1H-
imidazol-2-yl)ethyl)-2,6-naphthyridine (63)
4.2. Biology experimental
POCl3 (5 eq, 15 mmol) was added to a solution of 62 (1 eq,
3.0 mmol) in dry MeCN (20 mL) and the whole refluxed for 2 h. The
solution was evaporated, the residue taken up with ice, the
resulting solution basified with conc. NH4OH and extracted with
DCM. The organic phase was dried with Na2SO4 and evaporated to
give 63 as crude residue purified by FC (petroleum ether/AcOEt
3:7). White solid (0.396 g, 40%); Rf 0.24 (petroleum ether/AcOEt
3:7); mp 171e172 ꢀC; 1H NMR (CDCl3) 9.25 (s, 1H), 8.74 (d,
J ¼ 5.8 Hz, 1H), 8.02 (d, J ¼ 5.8 Hz, 1H), 7.73 (d, J ¼ 7 Hz, 2H), 7.66 (s,
1H), 7.36 (t, J ¼ 7 Hz, 2H), 7.25e7.21 (m,1H), 7.03 (s,1H), 3.58 (s, 3H),
3.49 (t, J ¼ 7.6 Hz, 2H), 3.25 (t, J ¼ 7.6 Hz, 2H); 13C NMR (CDCl3)
155.5, 151.7, 150.3, 147.5, 145.4, 140.1, 134.4, 132.6, 128.5, 128.0,
126.5, 124.7, 117.8, 117.7, 116.3, 35.8, 32.8, 26.2; API-ES m/z: [MþH]þ
calcd for C20H18ClN4: 349.1, found: 349.0.
4.2.1. PDE10A enzyme
PDE10A can be prepared in different cell types, for example,
insect cells or Escherichia coli. Catalytically active PDE10A was ob-
tained as follows: human PDE10A (amino acids 14e779 from the
sequence with accession number NP_006652) was amplified from
total human brain total RNA by standard RT-PCR and cloned into
the BamH1 and Not1 sites of the pFastBac-HTb (Invitrogen).
Expression in Sf9 cells using the Bac-to-Bac® Baculovirus Expres-
sion System (Gibco). Sf9 cells were grown at 27 ꢀC in Sf-900 II
serum free medium containing 50 units/ml penicillin and 50 mg/ml
streptomycin and were infected with 1 ml of virus for 25 ml of
media. At 72 h, cells were harvested and disrupted in lysis buffer
(50 mM Tris8.0 þ 1 mM MgCl2 þ PI þ 0.5%triton) for 15 min on ice
and then centrifuged at 20,000g for 20 min PDE10A was partially
purified on Q sepharose and the most active fractions were pooled.
4.1.19. Synthesis of 1-(3-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)
ethyl)-2,6-naphthyridin-1-yl)prop-1-en-2-ol (64)
4.2.2. PDE10A inhibition assay
A solution of 63 (1 eq, 1.15 mmol) in dry toluene (5 mL) was
deoxygenated with bubbling N2. Isopropenyl acetate (1.5 eq,
1.73 mmol) was added to the reaction mixture, followed by the
addition of DavePhos (0.1 eq, 0.11 mmol) and then tribu-
tyl(methoxy)stannane (1.5 eq, 1.72 mmol) and tris(dibenzylide-
neacetone)dipalladium (0) (0.01 eq, 0.01 mmol). The solution was
heated to 100ꢀ C and stirred for 12 h. The solution was evaporated
and the residue purified by FC (CHCl3/MeOH 9.5:0.5). Orange solid
(0.384 g, 96%); Rf 0.46 (CHCl3/CH3OH 95:5); mp 73e75 ꢀC; 1H NMR
(CDCl3) 15.45 (br s, 1H), 8.86 (s, 1H), 8.56 (d, J ¼ 6.0 Hz, 1H),
7.74e7.73 (m, 3H), 7.39e7.21 (m, 3H), 7.07 (s, 1H), 6.62 (s, 1H), 6.06
A PDE10A assay was performed as follows: the assay was per-
formed in 60 mL samples containing a fixed amount of the relevant
PDE enzyme (sufficient to convert 20e25% of the cyclic nucleotide
substrate), a buffer (50 mM HEPES 7.6; 10 mM MgCl2; 0.02%
Tween20), 0.1 mg/ml BSA, 225 pCi of 3H-labelled cyclic nucleotide
substrate, tritium labelled cAMP to a final concentration of 5 nM
and varying amounts of inhibitors. Reactions were initiated by
addition of the cyclic nucleotide substrate, and reactions were
allowed to proceed for 1 h at room temperature before being
terminated through mixing with 15
mL 8 mg/ml yttrium silicate SPA
beads (Amersham). The beads were allowed to settle for 1 h in the

A. Dore et al. / European Journal of Medicinal Chemistry 84 (2014) 181e193
193
A.W. Schmidt, C.J. Schmidt, J.A. Suiciak, S. Liras, Discovery of a novel class of
phosphodiesterase 10A inhibitors and identification of clinical candidate 2-[4-
(1-methyl-4-pyridin-4-yl-1H-pyrazol-3-yl)-phenoxymethyl]-quinoline (PF-
2545920) for the treatment of schizophrenia, J. Med. Chem. 52 (2009)
5188e5196.
dark before the plates were counted in a Wallac 1450 Microbeta
counter. The measured signals were converted to activity relative to
an uninhibited control (100%) and IC50 values were calculated using
the Xlfit extension to EXCEL.
[10] S.M. Grauer, V.L. Pulito, R.L. Navarra, M.P. Kelly, C. Kelley, R. Graf, B. Langen,
S. Logue, J. Brennan, L. Jiang, E. Charych, U. Egerland, F. Liu, K.L. Marquis,
M. Malamas, T. Hage, T.A. Comery, N.J. Brandon, Phosphodiesterase 10A in-
hibitor activity in preclinical models of the positive, cognitive, and negative
symptoms of schizophrenia, J. Pharmacol. Exp. Ther. 331 (2009) 574e590.
[11] C.J. Schmidt, D.S. Chapin, J. Cianfrogna, M.L. Corman, M. Hajos, J.F. Harms,
W.E. Hoffman, L.A. Lebel, S.A. McCarthy, F.R. Nelson, C. Proulx-LaFrance,
M.J. Majchrzak, A.D. Ramirez, K. Schmidt, P.A. Seymour, J.A. Siuciak,
F.D. Tingley III, R.D. Williams, P.R. Verhoest, F.S. Menniti, Preclinical charac-
terization of selective phosphodiesterase 10A inhibitors: a new therapeutic
approach to the treatment of schizophrenia, J. Pharmacol. Exp. Ther. 325
(2008) 681e690.
Acknowledgements
Financial support from the Regione Autonoma della Sardegna
(CRP-26417) is acknowledged.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.ejmech.2014.07.020.
[12] N. DeMartinis, A. Banerjee, V. Kumar, S. Boyer, C. Schmidt, S. Arroyo, Results of
a phase 2A proof-of-concept trial with a PDE10A inhibitor in the treatment of
acute exacerbation of schizophrenia, in: Abstracts of the 3rd Biennial
Schizophrenia International Research Conference, Schizophrenia Research,
136, 2012. Suppl. 1 S262 poster 212.
References
ꢀ
[13] For implications in Huntington's disease see: a) C. Giampa, S. Patassini,
[1] M. Conti, J. Beavo, Biochemistry and physiology of cyclic nucleotide phos-
phodiesterases: essential components in cyclic nucleotide signalling, Annu.
Rev. Biochem 76 (2007) 481e511.
[2] J.A. Beavo, S.H. Francis, M.D. Houslay, Cyclic Nucleotide Phosphodiesterases in
Health and Disease, Crc Press, 2006.
A. Borreca, D. Laurenti, F. Marullo, G. Bernardi, F.S. Menniti, F.R. Fusco, Phos-
phodiesterase 10 inhibition reduces striatal excitotoxicity in the quinolinic
acid model of Huntington's disease, Neurobiol. Dis. 34 (2009) 450e456;
ꢀ
b) C. Giampa, D. Laurenti, S. Anzilotti, G. Bernardi, F.S. Menniti, F.R. Fusco,
Inhibition of the striatal specific phosphodiesterase PDE10A ameliorates
striatal and cortical pathology in R6/2 mouse model of Huntington's disease,
PLoS ONE 5 (2010) e13417;
[3] a) S.H. Soderling, S.J. Bayuga, J.A. Beavo, Isolation and characterization of a
dual-substrate phosphodiesterase gene family: PDE10A, Proc. Natl. Acad. Sci.
U.S.A. 96 (1999) 7071e7076;
c) R.J. Kleiman, L.H. Kimmel, S.E. Bove, T.A. Lanz, J.F. Harms, A. Romegialli,
K.S. Miller, A. Willis, S. des Etages, M. Kuhn, C.J. Schmidt, Chronic suppression
of phosphodiesterase 10A alters striatal expression of genes responsible for
neurotransmitter synthesis, neurotransmission, and signaling pathways
implicated in Huntington's disease, J. Pharmacol. Exper. Ther. 336 (2011)
64e76.
b) K. Fujishige, J. Kotera, H. Michibata, K. Yuasa, S. Takebayashi, K. Okumura,
K. Omori, Cloning and characterization of a novel human phosphodiesterase
that hydrolyzes both cAMP and cGMP (PDE10A), J. Biol. Chem. 274 (1999)
18438e18445;
c) K. Loughney, P.B. Snyder, L. Huher, G.J. Rosman, K. Ferguson, V.A. Florio,
Isolation and characterization of PDE10A, a novel human 3', 5'-cyclic nucle-
otide phosphodiesterase, Gene 234 (1999) 109e117.
[14] B. Asproni, G. Murineddu, A. Pau, G.A. Pinna, M. Langgård, C.T. Christoffersen,
J. Nielsen, J. Kehler, Synthesis and SAR study of new phenylimidazole-pyr-
azolo[1,5-c]quinazolines as potent phosphodiesterase 10A inhibitors, Bioorg.
Med. Chem. 19 (2011) 642e649.
[4] V. Lakics, E.H. Karran, F.G. Boess, Quantitative comparison of phosphodies-
terase mRNA distribution in human brain and peripheral tissues, Neuro-
pharmacology 59 (2010) 367e374.
[5] a) T.F. Seeger, B. Bartlett, T.M. Coskran, J.S. Culp, L.C. James, D.L. Krull,
J. Lanfear, A.M. Ryan, C.J. Schmidt, C.A. Strick, A.H. Varghese, R.D. Williams,
P.G. Wylie, F.S. Menniti, Immunohistochemical localization of PDE10A in the
rat brain, Brain Res. 985 (2003) 113e126;
ꢁ
[15] J. Kehler, A. Ritzen, M. Langgård, S.L. Petersen, M.M. Farah, C. Bundgaard,
C.T. Christoffersen, J. Nielsen, J.P. Kilburn, Triazoloquinazolines as a novel class
of phosphodiesterase 10A (PDE10A) inhibitors, Bioorg. Med. Chem. Lett. 21
(2011) 3738e3742.
[16] Q. Ding, J. Wu, Lewis acid- and organocatalyst-cocatalyzed multicomponent
reactions of 2-alkynylbenzaldehydes, amines, and ketones, Org. Lett. 9 (2007)
4959e4962.
[17] Z. Chen, X. Yang, J. Wu, AgOTf-catalyzed tandem reaction of N'-(2-
alkynylbenzylidene)hydrazide with alkyne, Chem. Commun. 23 (2009)
3469e3471.
[18] X. Yu, Z. Chen, X. Yang, J. Wu, Tandem reactions of N'-(2-alkynylbenzylidene)
hydrazides with silyl enolates: a facile route to H-pyrazolo[5,1-a]isoquino-
lines, J. Comb. Chem. 12 (2010) 374e378.
[19] A.C. Bissember, M.G. Banwell, Microwave-assisted trans-halogenation re-
actions of various chloro-, bromo-, trifluoromethanesulfonyloxy- and
nonafluorobutanesulfonyloxy-substituted quinolines, isoquinolines, and pyr-
idines leading to the corresponding iodinated heterocycles, J. Org. Chem. 74
(2009) 4893e4895.
b) T.M. Coskran, D. Morton, F.S. Menniti, W.O. Adamowicz, R.J. Kleiman,
A.M. Ryan, C.A. Strick, C.J. Schmidt, D.T. Stephenson, Immunohistochemical
localization of phosphodiesterase 10A in multiple mammalian species,
J. Histochem. Cytochem. 54 (2006) 1205e1213;
c) Z. Xie, W.O. Adamowicz, W.D. Eldred, A.B. Jakowski, R.J. Kleiman,
D.G. Morton, D.T. Stephenson, C.A. Strick, R.D. Williams, F.S. Menniti, Cellular
and subcellular localization of PDE10A, a striatum-enriched phosphodies-
terase, Neuroscience 139 (2006) 597e607.
[6] F.S. Menniti, W.S. Faraci, C.J. Schmidt, Phosphodiesterases in the CNS: targets
for drug development, Nat. Rev. Drug. Discov. 5 (2006) 660e670.
ꢁ
[7] a) J. Kehler, A. Ritzen, D.R. Greve, The potential therapeutic use of phospho-
diesterase 10 inhibitors, Expert Opin. Ther. Patents 17 (2007) 147e158;
b) F.S. Menniti, T.A. Chappie, J.M. Humphrey, C.J. Schmidt, Phosphodiesterases
10A inhibitors:
a novel approach to the treatment of the symptoms of
[20] Glaxosmithkline, Fitzgerald RN, Jung DK, Eaddy JF, Process for the preparation
of chemical compounds, US20030212275A1 Novemb., 13 (2003).
[21] A. Numata, Y. Kondo, T. Sakamoto, General synthetic method for naphthyr-
schizophrenia, Curr. Opin. Invest. Drugs 8 (2007) 54e59;
c) T. Chappie, J. Humphrey, F. Menniti, C. Schmidt, PDE10A inhibitors: an
assessment of the current CNS drug discovery landscape, Curr. Opin. Drug.
Discov. Devel. 12 (2009) 458e467;
d) J. Kehler, J.P. Kilburn, Patented PDE10A inhibitors: novel compounds since
2007, Expert Opin. Ther. Patents 19 (2009) 1715e1725;
e) J. Kehler, J. Nielsen, PDE10A inhibitors: novel therapeutic drugs for
schizophrenia, Curr. Pharm. Des. 17 (2011) 137e150;
f) T.A. Chappie, C.J. Helal, X. Hou, Current landscape of phosphodiesterase 10A
(PDE10A) inhibition, J. Med. Chem. 55 (2012) 7299e7331;
g) N. Hoefgen, C. Grunwald, B. Langen, Targeting PDE10A in schizophrenia,
Drugs Future 37 (2012) 577e589;
h) J. Kehler, Phosphodiesterase 10A inhibitors: a 2009-2012 patent update,
Expert Opin. Ther. Patents 23 (2013) 31e45;
i) B. Asproni, A. Dore, G. Murineddu, G.A. Pinna, Chemistry of tricyclic-based
heterocycles as useful scaffolds for phosphodiesterase 10A ligands, Mini-
Rev. Org. Chem. 10 (2013) 123e140.
idines and their N-oxides containing isoquinolinic nitrogen, Synthesis
(1999) 306e311.
2
[22] P. Liu, T.J. Lanza Jr., J.P. Jewell, C.P. Jones, W.K. Hagmann, L.S. Lin, A highly
active catalyst system for the heteroarylation of acetone, Tetrahedron Lett. 44
(2003) 8869e8871.
€
[23] Glide, Version 5.7, Schrodinger, LLC, New York, NY, 2011.
[24] R. Risgaard, A. Ettrup, T. Balle, A. Dyssegaard, H.D. Hansen, S. Lehel, J. Madsen,
H. Pedersen, A. Püschl, L. Badolo, B.B. -Andersen, G.M. Knudsen, J.L. Kristensen,
Radiolabelling and PET brain imaging of the
a₁-adrenoceptor antagonist Lu
AE43936, Nucl. Med. Biol. 40 (2013) 135e140.
[25] S.F. Poon, D.J. St Jean Jr., P.E. Harrington, C. Henley III, J. Davis, S. Morony,
F.D. Lott, J.D. Reagan, J.Y.-L. Lu, Y. Yang, C. Fotsch, Discovery and optimization
of substituted 1-(1-phenyl-1H-pyrazol-3-yl)methanamines as potent and
efficacious type II calcimimetics, J. Med. Chem. 52 (2009) 6535e6538.
[26] T. Godet, C. Vaxelaire, C. Michel, A. Milet, P. Belmont, Silver versus gold
catalysis in tandem reactions of carbonyl functions onto alkynes: a versatile
access to furoquinoline and pyranoquinoline cores, Chem. Eur. J. 13 (2007)
5632e5641.
[8] J.A. Siuciak, D.S. Chapin, J.F. Harms, L.A. Lebel, S.A. McCarthy, L. Chambers,
A. Shrikhande, S. Wong, F.S. Menniti, C.J. Schmidt, Inhibition of the striatum-
enriched phosphodiesterase PDE10A: a novel approach to the treatment of
psychosis, Neuropharmacology 51 (2006) 386e396.
[9] P.R. Verhoest, D.S. Chapin, M. Corman, K. Fonseca, J.F. Harms, X. Hou, E.S. Marr,
F.S. Menniti, F. Nelson, R. O'Connor, J. Pandit, C. Proulx-LaFrance,