Discovery of tetrahydropyridopyrimidine phosphodiesterase 10A inhibitors for the treatment of schizophrenia

Article abstract of DOI:10.1016/j.bmcl.2012.07.072

We describe the discovery of potent and orally bioavailable tetrahydropyridopyrimidine inhibitors of phosphodiesterase 10A by systematic optimization of a novel HTS lead. Lead compound THPP-1 exhibits nanomolar potencies, excellent pharmacokinetic propert

Full text of DOI:10.1016/j.bmcl.2012.07.072

Bioorganic & Medicinal Chemistry Letters 22 (2012) 5903–5908
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of tetrahydropyridopyrimidine phosphodiesterase 10A inhibitors
for the treatment of schizophrenia
Izzat T. Raheem a, , Michael J. Breslin a, Christine Fandozzi c, Joy Fuerst e, Nicole Hill e, Sarah Huszar b,
⇑
Monika Kandebo g, Somang H. Kim c, Bennett Ma c, Georgia McGaughey d, John J. Renger g,
John D. Schreier a, Sujata Sharma f, Sean Smith g, Jason Uslaner b, Youwei Yan f, Paul J. Coleman a,
Christopher D. Cox a
a Discovery Chemistry, Merck Research Laboratories, West Point, PA 19486, United States
b In Vivo Pharmacology, Merck Research Laboratories, West Point, PA 19486, United States
c Pharmacokinetics, Pharmacodynamics, and Drug Metabolism, Merck Research Laboratories, West Point, PA 19486, United States
d Chemistry Modeling and Informatics, Merck Research Laboratories, West Point, PA 19486, United States
e Basic Pharmaceutical Sciences, Merck Research Laboratories, West Point, PA 19486, United States
f Structural Chemistry, Merck Research Laboratories, West Point, PA 19486, United States
g Neurosymptomatics, Merck Research Laboratories, West Point, PA 19486, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
We describe the discovery of potent and orally bioavailable tetrahydropyridopyrimidine inhibitors of
phosphodiesterase 10A by systematic optimization of a novel HTS lead. Lead compound THPP-1 exhibits
nanomolar potencies, excellent pharmacokinetic properties, and a clean off-target profile. It displays
in vivo target engagement as measured by increased rat striatal cGMP levels upon oral dosing. It shows
dose-dependent efficacy in a key pharmacodynamic assay predictive of antipsychotic activity, the psy-
chostimulant-induced rat hyperlocomotion assay. Further, THPP-1 displays significantly fewer preclini-
cal adverse events in assays measuring prolactin secretion, catalepsy, and weight gain, in contrast to the
typical and atypical antipsychotics haloperidol and olanzapine.
Received 17 May 2012
Revised 16 July 2012
Accepted 20 July 2012
Available online 27 July 2012
Keywords:
Phosphodiesterase 10A inhibitor
Schizophrenia
Hyperlocomotion assay
Conditioned avoidance response assay
Tetrahydropyridopyrimidine
Ó 2012 Elsevier Ltd. All rights reserved.
Schizophrenia is a chronic and debilitating mental disorder
affecting close to 1% of the world population. With disease onset
typically occurring in the early-to-mid 20s and with no known
cure, patients require life-long treatment or institutionalization,
compounding the disease burden on the individual, their families,
and society.1 Schizophrenia is marked by three key symptom
domains. The well-known positive symptoms include the halluci-
nations and delusions that typify the disease. The less understood
negative symptoms include anhedonia and withdrawal from soci-
ety. Cognitive impairment also accompanies the disease, and is of-
ten predictive of the functional outcome. A large number of
marketed therapeutics exists for the treatment of schizophrenia
in the form of the typical antipsychotics (haloperidol, fluphen-
azine) and atypical antipsychotics (clozapine, olanzapine). How-
ever, not only do the vast majority of these drugs treat only the
positive symptoms of the disease, but they suffer from a high rate
of discontinuation due to a lack of both efficacy and tolerability.1b–h
The wide array of adverse events that accompany treatment with
typical and atypical antipsychotics include significant weight
gain, the onset of diabetes, tardive dyskinesia, dystonia, akatheisa,
increased prolactin release, and cardiac events. To this end, im-
proved treatment for schizophrenia continues to represent an
unmet medical need.
The phosphodiesterases (PDEs) are a superfamily of 11 enzymes
encoded by 21 genes.2 The PDEs catalyze the hydrolytic degrada-
tion of cyclic guanosine monophosphate (cGMP) and cyclic adeno-
sine monophosphate (cAMP), thereby playing a critical role in
regulating the circulating levels of these important and ubiquitous
second messengers. Over the past decades, efforts toward elucidat-
ing the physiological roles of these enzymes have resulted in the
identification of numerous PDE inhibitors, both selective and non-
selective, that have subsequently led to the identification of poten-
tial therapeutic opportunities.
PDE10A, first identified in 1999,3 is a dual phosphodiesterase
that hydrolyzes both cGMP (Km = 3 lM) and cAMP (Km = 0.05 lM).
It is expressed nearly exclusively in the medium spiny neurons of
⇑
Corresponding author.
E-mail address: izzat_raheem@merck.com (I.T. Raheem).
the mammalian striatum.4 The striatum is involved in both motor
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.07.072

5904
I. T. Raheem et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5903–5908
and cognitive function through the integration of signalling from
the midbrain dopaminergic pathway and cortical glutamatergic
pathway, and abnormal striatal output is implicated in the patho-
physiology of schizophrenia.5 It has therefore been hypothesized
that PDE10A inhibition in the striatum will result in increased sec-
ond messenger signaling and striatal output, restoring the behav-
ioral inhibition that is impaired in schizophrenic patients.3e
Preclinical studies further support the antipsychotic potential of
PDE10 inhibition.6 Recent publications report that PDE10A inhibi-
tors are efficacious in a number of assays predictive of antipsy-
chotic activity, including the psychostimulant-induced rat
hyperlocomotion assay (LMA), as well as the conditioned avoid-
ance response assay (CAR) and pre-pulse inhibition assay (PPI).7
Further, PDE10A inhibitors have been shown to improve perfor-
mance in models of cognition, including executive function and
episodic memory.8 Additionally, they display fewer preclinical ad-
verse events (AEs) relative to marketed typical and atypical anti-
psychotics. Together, these data suggest that PDE10A inhibitors
have the potential to affect not only positive symptoms, but cogni-
tive dysfunction as well.
Following a successful high throughput screening campaign, our
laboratory was drawn to compounds in the tetrahydropyridopyrimidne
class (THPP), as exemplified by THPP-2 (Table 1, entry 1).9 Early
synthetic efforts to access compounds in this class followed a 5-step
sequence described in a previous publication from our laboratory.10
While suboptimal, the overall synthesis was high-yielding and
modular, facilitating rapid generation of SAR in the series.
Beginning with THPP-2, we carried out systematic optimization
of the R1 and R2 positions of the core, with the initial goal of
improving compound potency while maintaining overall physical
properties. As highlighted in Table 1, no improvement in potency
was realized with this effort, as flat SAR existed for all-carbon aro-
matic, heteroaromatic, amine, and aliphatic substituents (Table 1,
entries 2–7). At R2, urea, carbamate, amido, and sulfonyl function-
alities were tolerated, but provided no improvements in compound
potency (Table 1, entries 8–15). Moreover, compounds bearing
amino substitution at the R3 position were typically substrates of
both rat and human P-glycoprotein (P-gp) with BA/AB ratios of
>3.5. To this end, we turned our attention to the R3 position, and
were gratified to discover that replacement of the R3 amino group
with alkoxy substitution not only ameliorated P-gp susceptibility,
but also, for the first time, provided marked improvements in com-
pound potency (Table 1 entries 16–20), particularly with the
installation of an isopropoxy group. Unfortunately, the change to
this functionality came at the expense of overall compound solu-
bility.11 In order to address this issue, we looked to introduce basic
nitrogen functionality in the periphery of the molecule. Installation
of a tertiary amine at R3 in the form of an N-methyl piperidine (Ta-
ble 1, Entry 21), provided potent compounds with improved over-
all physical properties. However, this structural change resulted in
high plasma clearance (Cl = >100 mL/min/kg) and P-gp susceptibil-
ity (BA/AB ratio = 22.1) in rats. Ultimately, our strategy proved
fruitful as transposition of this basic nitrogen from a tertiary amine
at R3 to an aromatic amine at R2 led to the identification of THPP-3
(Table 1, entry 22), an important benchmark molecule that facili-
tated assay validation for the program.
While holding constant the R3 alkoxy group, we carried out a
second round of optimization of the R1 heterocycle of the THPP
core. We discovered that functionalization ortho to the pyridyl
nitrogen had a dramatic effect on compound potency (Table 2,
R4), with halogenation providing a consistent potency improve-
ment ranging from 2- to 10-fold. However, compounds bearing
halo-substituted pyridines suffered from lower aqueous solubili-
ties than compounds bearing unsubsituted pyridines (<10
lM vs.
>75 M at pH 7), possibly due to a loss in compound basicity.
l
Table 1
Initial optimization and SAR of the THPP framework
N
R3
N
CH3
O
N
N
R2
N
H
N
N
N
N
R1
N
THPP-2 (HTS)
PDE10 Ki = 94 nM
Entry
R1
R2
R3
PDE10 Ki (nM)
1 (THPP-2)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
4-Pyridyl
3-Pyridyl
2-Pyridyl
C6H5
3-Br-C6H4
CH3
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NH(4-pyr)
C(O)NH(4-OCH3C6H4)
C(O)NH(3-FC6H4)
C(O)Ot-Bu
C(O)NHt-Bu
C(O)(4-ClC6H4)
C(O)i-Bu
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
N(CH3)CH2CH2(2-pyr)
OCH3
94
121
864
500
991
4340
512
117
122
156
186
223
522
868
843
422
135
98
N(CH3)2
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
4-Pyridyl
3-Pyridyl
3-Pyridyl
3-Pyridyl
3-Pyridyl
SO2CH3
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NHC6H5
C(O)NH(3-EtC6H4)
C(O)NH(4-CH3-3-pyr)
17
18
19
20
OCH2CH2OCH3
Oi-Pr
OCH3
Oi-Pr
O-(4-N-Methylpiperidine)
Oi-Pr
93
17
14
7.9
21
22 (THPP-3)

I. T. Raheem et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5903–5908
5905
Table 2
H3CO
O
N
O
Optimization of pyridine substitution
N
N
N
N
O
N
O
R5
Cl
N
N
N
N
H
THPP-1
PDE 10Ki = 1.0 nM
B-A/A-B (h,r): 0.6, 0.8 (Papp= 32x10-6 cm/s)
pH 7 solubility = 20 μM
R4
N
Entry
R4
R5
PDE10 Ki (nM)
cGMP: (+)at 10 mpk PO
LMA: (+) at 3 mpk PO
1 (THPP-3)
H
CH3
F
4-CH3-3-pyr
4-CH3-3-pyr
4-CH3-3-pyr
4-CH3-3-pyr
4-CH3-3-pyr
4-CH3-3-pyr
7.9
8.0
3.0
0.6
63
2
3
4
5
6
7
Figure 2. Structure and profile of THPP-1.
Cl
OH
CF3
Cl
247
1.0
THPP-4 was shortened from six steps and 6% overall yield to two
steps and 45% overall yield requiring no silica gel purification.
While no replacement for the potency-enhancing chloropyri-
dine was identified, significant structural variation was tolerated
at both R2 and R3, and we continued to interrogate these regions
of the THPP core in a more synthetically streamlined manner.
Our efforts culminated in the identification of THPP-1 ( Fig. 2),
which bears a moderately basic imidazopyridine amide at R2 and
a methoxyethyl ether linkage at R3. These functionalities provided
moderate solubility and improved potency over THPP-4 while
maintaining a similar overall profile. THPP-1 is a 1-nM inhibitor
of PDE10A. It is not a P-gp substrate and has high passive perme-
ability. It is not a significant reversible or time-dependent inhibitor
of CYP enzymes and does not activate the pregnane-X receptor at
drug concentrations tested, indicating a low potential to be a per-
petrator of DDIs via CYP inhibition or induction. Additionally,
THPP-1 has a good PDE selectivity profile, with >1000-fold selec-
tivity over most PDEs except for PDE5A, PDE6A, and PDE11A (Table
3).
N-CH3-4-Pyrazole
Re-investigation of the R2 portion of the core served to amelio-
rate some of concerns around the aqueous solubilities of our com-
pounds. To this end, an improvement was realized by changing the
urea linker to an amide, thereby eliminating a hydrogen bond
donor, and installing a more basic heterocycle at R2; THPP-4 con-
tains an imidazole amide (Fig. 1). While compound potency was
slightly compromised relative to the corresponding pyridyl urea
analog (Table 2, entry 4), THPP-4 had higher solubility, bore excel-
lent PK, and provided in vivo efficacy in the LMA assay upon oral
administration.
The LMA assay is a well-established model for antipsychotic
activity that measures the ability of compounds to attenuate the
psychomotor activating response produced by psychostimulants,
such as MK-801; all currently marketed antipsychotics are effica-
cious in this assay.7 THPP-4 displayed dose-dependent efficacy in
the rat LMA assay, with full attenuation achieved following an oral
The synthesis of THPP-1 (Scheme 1) harnessed a slightly mod-
ified version of the previously described 3CC reaction. 1-Tert-butyl
3-ethyl 4-oxopiperidine-1,3-dicarboxylate undergoes facile 3CC
with 6-chloropyridine-3-carboximidamide hydrochloride and 2-
bromoethyl methyl ether. Boc removal with HCl followed by amide
dose of 4.5 mg/kg PO ([THPP-4]t=2h,plasma = 3.0 l
M).12 Additionally,
unlike previous amido compounds bearing a chloropyridine, the
higher pKa of the imidazole allowed THPP-4 to be isolated as a sta-
ble hydrochloride salt providing excellent dose proportionality in
in vivo studies.
13
coupling provides THPP-1 in 3 steps and 36% overall yield.
With an advanced promising series identified in the THPPs, we
sought to improve their overall synthesis by employing THPP-4 as
a model system. While the initial synthetic route was robust and
versatile, typically providing products in overall yields ranging
from 5–25%, we were attracted to the possibility of employing a
more convergent synthesis that harnessed the nucleophilic charac-
ter of an intermediate pyrimidinone oxygen. The optimization of
this chemistry is detailed in an earlier publication,10 and provided
a general three-component coupling (3CC) methodology amenable
to the synthesis of THPP-4. With this advance, the synthesis of
THPP-1 bears an excellent PK profile across preclinical species
(Table 4), with moderate clearances (3.8–7.7 mL/min/kg) and
half-lives (1.4–7.7 h), and good oral bioavailability (31–79%).
THPP-1 also has a favorable preclinical safety profile. THPP-1
was negative in a 5-strain Ames assay up to 5000 lg per plate, pro-
duced no significant hits in an 117-assay PanLabs off-target panel,
and had no observable QTc prolongation in an in vivo cardiovascu-
lar dog model with an anticipated margin of up to a 50-fold.14
The in vivo profile of THPP-1 revealed robust dose-dependent
activity in our primary efficacy and target engagement assays.
O
O
N
Table 3
Selectivity of THPP-1 for PDE10A compared to other human PDE families
N
N
CH3
N
N
PDE
PDE10A Ki (nM)
Selectivity
PDE1A
PDE2A
PDE3A
PDE4A
PDE5A
PDE6A
PDE7A
PDE8A
PDE9A
PDE11A
>50000
1200
3300
5900
116
>1000Â
>1000Â
>1000Â
>1000Â
116Â
Cl
N
THPP-4
PDE 10 Ki = 4.5 nM
pH 7 solubility = 69
Rat PK: Cl= 2.4 mL/min/kg
Dog PK: Cl= 0.94 mL/min/kg
LMA: (+) at 4.5 mpk PO
μM
44
44Â
11200
>50000
>50000
298
>1000Â
>1000Â
>1000Â
300Â
Figure 1. Structure and profile of THPP-4.

5906
I. T. Raheem et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5903–5908
H3CO
1. CH3OCH2CH2Br
O
N
O
O
NH
K2CO3, DMF
60 °C
•HCl
NH2
N
NH
OEt
+
2. HCl (g)
(43%, 2 steps)
N
Boc
Cl
N
Cl
N
O
H3CO
O
N
O
HO
N
N
N
N
N
N
EDC, HOBt
TEA, DMF
(84%)
Cl
N
THPP-1
Scheme 1. Synthesis of THPP-1.
Table 4
measured in a NOR assay, with effects comparable to those of
donepezil.12
Preclinical PK profile of THPP-1
Species
Cl (mL/min/kg)
t1/2 (h)
F (%)
THPP-1 showed negligible activity in our AE assays. It did not
significantly influence circulating prolactin levels nor induce
catalepsy following oral dosing up to 50 mg/kg PO (Fig. 3c and
d), compared to a clinically relevant dose of haloperidol (1.5 mg/
kg). Notably, chronic dosing (7 days) of THPP-1 to rats significantly
decreased body weight gain, total body fat, and lean body mass
compared to the positive control olanzapine (Fig. 4a–c). This AE
profile is significantly distinguished from those of both typical
and atypical antipsychotics, suggesting the potential for improved
patient compliance.
The PDE10A active site possesses a number of regions critical for
inhibitor binding and potency.15 Among these are a H-bond interac-
tion with Q726 and a pi-stacking interaction (hydrophobic clamp)
with F729. In addition, studies with selective PDE10A inhibitors
such as MP-10 (PF-02545920) suggest that the formation of a
Rat
Dog
Monkey
6.0
3.8
7.7
1.4
7.2
1.4
47
79
31
THPP-1 displayed full attenuation of hyperlocomotion at 3 mg/kg
PO ([THPP-1]t=2h,plasma = 730 nM) in the rat LMA assay (Fig. 3a) as
well as increased striatal cGMP at doses >10 mg/kg PO (>150%
relative to vehicle, Figure 3b), an in vivo marker for target engage-
ment. THPP-1 displayed similar dose-dependent efficacy in the
CAR assay (data not shown), another well-established preclinical
model for antipsychotic activity.12 Additionally, it displayed an
increase in cognitive function when dosed up to 1 mg/kg PO, as
Figure 3. (a) Effect of THPP-1 administration on the attenuation of MK-801-induced rat hyperlocomotion. Asterisks indicate significantly greater activity compared to vehicle
(Veh) only (⁄p <0.05, ⁄⁄p <0.01). Alpha indicates significantly less activity compared to animals receiving MK-801. (b) Effect of THPP-1 administration on cGMP concentration
in the rat striatum 2 h after administration compared to Veh injected control. (c) Circulating prolactin levels in rat upon oral administration of THPP-1 (control = haloperidol;
1.5 mg/kg). (d) Assessment of rat catalepsy by fore-limb retraction (paw test) upon oral administration of THPP-1 (control = haloperidol; 1.5 mg/kg).

I. T. Raheem et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5903–5908
5907
a
Change in Body Fat
(after 7 days dosing)
b
Change in Body Weight
(after 7 days dosing)
6
4
14
12
10
8
*
*
2
α
6
α
4
0
2
-2
0
Veh
Olz
3
10
Veh
Olz
3
10
THPP-1 (mg/kg)
THPP-1 (mg/kg)
c
Change in Lean Body Mass
(after 7 days dosing)
10
8
*
6
4
2
0
Veh
Olz
3
10
THPP-1 (mg/kg)
Figure 4. (a) Influence of THPP-1 and olanzapine (Olz; 4 mg/kg) on weight gain, (b) body fat, and (c) lean body mass following 7 days of dosing. Asterisks indicate significantly
greater than vehicle (Veh) and alpha indicates significantly less than Veh, n = 12/group.
Figure 5. Computational model of THPP-1 docked in the PDE10A active site.
H-bond with non-conserved Y693 in the so-called ‘selectivity pock-
et’ of the active site is crucial for selectivity across the PDE fami-
lies.6b Indeed, MP-10 displays exquisite PDE10A selectivity of
>5000-fold over all other PDEs.
well with the corresponding X-ray crystal stucture (data not
shown). The suboptimal PDE5A, PDE6A, and PDE11A selectivities
of THPP-1 (Table 3) are explained by a lack of interaction with
Y693 in the PDE10A ‘selectivity pocket.’
A computationally docked model of THPP-1 bound in the active
site of PDE10A is shown in Figure 5, and the two conserved inter-
actions described above are highlighted.16 This model agrees very
In summary, we have described the discovery of a novel tetra-
hydropyridopyrimidine PDE10A inhibitor for the treatment of the
positive symptoms of schizophrenia. THPP-1 was identified

5908
I. T. Raheem et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5903–5908
8. (a) Grauer, S. M.; Pulito, V. L.; Navarra, R. L.; Kelly, M. P.; Kelley, C.; Graf, R.;
Langen, B.; Logue, S.; Brennan, J.; Jiang, L.; Charych, E.; Egerland, U.; Liu, F.;
Marquis, K. L.; Malamas, M.; Hage, T.; Comery, T. A.; Brandon, N. J. J. Pharmacol.
Exp. Ther. 2009, 331, 574; (b) Rodefer, J. S.; Murphy, E. R.; Baxter, M. G. Eur. J.
Neurosci. 2005, 21, 1070.
9. All reported apparent inhibition constants (Ki) were determined as described
by: Mosser, S. D.; Gaul, S. L.; Bednar, B.; Koblan, K. S.; Bednar, R. A. J. Assoc.
Laboratory Automation 2003, 8, 54.
through systematic optimization of a proprietary HTS lead, aided
by the development of novel facilitating methodology that assem-
bles the full structural framework in a single 3CC transformation.
THPP-1 is potent, selective, and possesses a highly favorable PK
profile across preclinical species. It is efficacious in two models
of antipsychotic activity (LMA, CAR) and possesses a promising
AE profile, significantly distinguishing it and other PDE10A inhibi-
tors from currently marketed antipsychotics. THPP-1 is positioned
for further advancement as a leading compound and additional
progress will be detailed in due course.
10. Raheem, I. T.; Schreier, J. D.; Breslin, M. J. Tetrahedron Lett. 2011, 52, 3849.
11. For the purposes of optimization of compound physical properties, aqueous
solubilities at pH 7 <10
lM were deemed poor, >10
lM and <75 lM were
deemed moderate, and >75
lM were deemed good.
12. Smith, S. M.; Uslaner, J. M.; Cox, C. D.; Huszar, S. L.; Cannon, C. E.; Vardigan, J.
D.; Eddins, D.; Toolan, D. M.; Kandebo, M.; Yao, L.; Raheem, I. T.; Schreier, J. D.;
Breslin, M. J.; Coleman, P. J.; Renger, J. J. Neuropharmacology 2012, [Epub ahead
of print].
Acknowledgments
13. Experimental procedure for the synthesis of THPP-1: 2-(6-chloropyridin-3-yl)-
4-(2-methoxyethoxy)-5,6,7,8-tetrahydropyrido[4,3-]pyrimidine. A mixture of 1-
tert-butyl 3-ethyl 4-oxopiperidine-1,3-dicarboxylate (5.1 g, 18.80 mmol), 6-
chloropyridine-3-carboximidamide hydrochloride (5.95 g, 26.3 mmol) and
K2CO3 (5.72 g, 41.4 mmol) was diluted with dimethylformamide (75 mL) and
treated with 2-bromoethyl methyl ether (4.42 mL, 47.0 mmol) with stirring.
The mixture was heated to 65 °C. After 2 h, the mixture was treated with
additional 2-bromoethyl methyl ether (4.42 ml, 47.0 mmol) and K2CO3 (5.72 g,
41.4 mmol) and heated for an additional 4 h. The mixture was diluted with
EtOAc (150 mL), and washed with water (150 mL) and brine (150 mL). The
organic phase was dried over Na2SO4, filtered, and concentrated in vacuo. The
resulting residue was dissolved in EtOAc (100 mL) and treated with HCl gas
until the solvent was saturated. The mixture stirred at room temperature for
30 min, treated again with HCl gas, and then stirred for an additional 30 min.
The mixture was concentrated to dryness and the amine HCl salt was dissolved
in water (50 mL). The solution was washed with ethyl acetate (2 Â 200 mL)
and then basified with aqueous 4 N NaOH. The aqueous phase was extracted
with 4:1 CHCl3:isopropanol (2 Â 200 mL). The combined organic phases were
concentrated in vacuo, and the residue dissolved in CH2Cl2 (300 mL), dried over
Na2SO4, filtered, and concentrated in vacuo. The resulting residue was purified
by gradient elution on silica gel (0–100% [9% methanol in CH2Cl2] in CH2Cl3) to
provide the title compound as a white solid (2.6 g, 43%, 2 steps). 1H NMR
(500 MHz, CDCl3): d 9.35 (1H, d, J = 2.34 Hz), 8.61 (1H, dd, J = 8.30, 2.41 Hz),
7.40 (1H, d, J = 8.32 Hz), 4.66 (2 H, t, J = 4.71 Hz), 3.96 (3H, s), 3.80 (2H, t,
J = 4.71 Hz), 3.45 (2H, d, J = 0.74 Hz), 3.22 (2H, t, J = 5.85 Hz), 2.88 (2H, t,
J = 5.86 Hz); LRMS [M+H]: 321.3 found, 321.7 required. [2-(6-chloropyridin-3-
yl)-4-(2-methoxyethoxy)-7,8-dihydropyrido[4,3-d]pyrimidin-6(5H)-
The authors thank the Merck West Point NMR and Mass Spec-
trometry facilities for assistance in characterizing the compounds
presented in this manuscript.
References and notes
1. (a) van Os, J.; Kapur, S. Lancet 2009, 374, 635; (b) Tsutsumi, C.; Uchida, H.;
Suzuki, T.; Watanabe, K.; Takeuchi, H.; Nakajima, S.; Kimura, Y.; Tsutsumi, Y.;
Ishii, K.; Imasaka, Y.; Kapur, S. Schizophr. Res. 2011, 130, 40; (c) Ray, W. A.;
Chung, C. P.; Murray, K. T.; Hall, K.; Stein, C. M. N. Engl. J. Med. 2009, 360, 225;
(d) Uchida, H.; Mamo, D. C.; Mulsant, B. H.; Pollock, B. G.; Kapur, S. J. Clin.
Psychiatry 2009, 70, 397; (e) Green, M. F.; Nuechterlein, K. H.; Gold, J. M.; Barch,
D. M.; Cohen, J.; Essock, S.; Fenton, W. S.; Frese, F.; Goldberg, T. E.; Heaton, R. K.;
Keefe, R. S.; Kern, R. S.; Kraemer, H.; Stover, E.; Weinberger, D. R.; Zalcman, S.;
Marder, S. R. Biol. Psychiatry 2004, 56, 301; (f) Keefe, R. S.; Bilder, R. M.; Davis, S.
M.; Harvey, P. D.; Palmer, B. W.; Gold, J. M.; Meltzer, H. Y.; Green, M. F.;
Capuano, G.; Stroup, T. S.; McEvoy, J. P.; Swartz, M. S.; Rosenheck, R. A.; Perkins,
D. O.; Davis, C. E.; Hsiao, J. K.; Lieberman, J. A. Arch. Gen. Psychiatry 2007, 64,
633; (g) Kern, R. S.; Green, M. F.; Nuechterlein, K. H.; Deng, B. H. Schizophr. Res.
2004, 72, 11.
2. (a) Jeon, Y. H.; Heo, Y. S.; Kim, C. M.; Hyun, Y. L.; Lee, T. G.; Ro, S.; Cho, J. M. Cell.
Mol. Life Sci. 2005, 62, 1198; (b) Manallack, D. T.; Hughes, R. A.; Thompson, P. E.
J. Med. Chem. 2005, 48, 3449; (c) Grootendorst, D. C.; Klaus, R. F. Curr. Opin.
Allergy Clin. Immunol. 2002, 2, 61; (d) Barnes, P. J. Nat. Rev. Drug Discov. 2002, 1,
437; (e) Travadi, J. N.; Patole, S. K. Pediatr. Pulmonol. 2003, 36, 457; (f) Marko,
D.; Pahlke, G.; Merz, K.-H.; Eisenbrand, G. Chem. Res. Toxicol. 2000, 13, 944; (g)
Ghofrani, H. A.; Osterloh, I. H.; Grimminger, F. Nat. Rev. Drug Discov. 2006, 5,
689; (i) Kass, D. A.; Champion, H. C.; Beavo, J. A. Circ. Res. 2007, 101, 1084; (j)
Menniti, F. S.; Faraci, W. S.; Schmidt, C. J. Nat. Rev. Drug Discov. 2006, 5, 660; (k)
Rotella, D. P. Nat. Rev. Drug Discov. 2002, 1, 674.
3. (a) Soderling, S. H.; Bayuga, S. J.; Beavo, J. A. Proc. Natl. Acad. Sci. U.S.A. 1999, 96,
7071; (b) Fujishige, K.; Kotera, J.; Michibata, H.; Yuasa, K.; Takebayashi, S.;
Okumura, K.; Omori, K. J. Biol. Chem. 1999, 274, 18438; (c) Loughney, K.; Snyder,
P. B.; Uher, L.; Rosman, G. J.; Ferguson, K.; Florio, V. A. Gene 1999, 234, 109; (d)
Bender, A. T.; Beavo, J. A. Pharmacol. Rev. 2006, 58, 488; (e) Menniti, F. S.;
Chappie, T. A.; Humphrey, J. M.; Schmidt, C. J. Curr. Opin. Investig. Drugs 2007, 8,
54.
4. (a) Seeger, T. F.; Bartlett, B.; Coskran, T. M.; Culp, J. S.; James, L. C.; Krull, D. L.;
Lanfear, J.; Ryan, A. M.; Schmidt, C. J.; Strick, C. A.; Varghese, A. H.; Williams, R.
D.; Wylie, P. G.; Menniti, F. S. Brain Res. 2003, 985, 113; (b) Coskran, T. M.;
Morton, D.; Menniti, F. S.; Adamowicz, W. O.; Kleiman, R. J.; Ryan, A. M.; Strick,
C. A.; Schmidt, C. J.; Stephenson, D. T. J. Histochem. Cytochem. 2006, 54, 1205; (c)
Xie, Z.; Adamowicz, W. O.; Eldred, W. D.; Jakowski, A. B.; Kleiman, R. J.; Morton,
D. G.; Stephenson, D. T.; Strick, C. A.; Williams, R. D.; Menniti, F. S. Neuroscience
2006, 139, 597.
yl](imidazo[1,5-a]pyridin-1-yl)methanone (THPP-1).
A
solution of 2-(6-
chloropyridin-3-yl)-4-(2-methoxyethoxy)-5,6,7,8-tetrahydropyrido-[4,3-
d]pyrimidine (2.0 g, 6.23 mmol), imidazo[1,5-a]pyridine-1-carboxylic acid
(1.1 g, 6.86 mmol), EDC (1.32 g, 6.86 mmol), and HOBt (0.9 g, 5.92 mmol) in
dimethylformamide (31 mL) was treated with triethylamine (2.61 mL,
18.7 mmol) at room temperature. The mixture was heated to 60 °C for
40 min. The mixture was diluted with EtOAc (100 mL) and washed with sat.
aq. NaHCO3 (100 mL), water (100 mL), and brine (100 mL). The organic phase
was dried over Na2SO4, filtered, and concentrated in vacuo. The resulting
material was purified by gradient elution on silica gel (0–45% [10% methanol in
CH2Cl2] in CH2Cl2) to provide THPP-1 as a light yellow solid (2.66 g, 84%). 1H
NMR (500 MHz, CDCl3): d 9.36 (1H, s), 8.62 (1H, d, J = 8.41 Hz), 8.28 (1H, d,
J = 9.27 Hz), 8.09 (1H, s), 8.03 (1H, d, J = 6.99 Hz), 7.40 (1H, d, J = 8.35 Hz), 7.04
(1H, t, J = 7.85 Hz), 6.77 (1H, t, J = 6.75 Hz), 5.8–4.0 (4H, bm), 4.69 (2H, t,
J = 4.68 Hz), 3.83 (2H, t, J = 4.62 Hz), 3.47 (3H, s), 3.14 (2H, s); 13C NMR
(125 MHz, CDCl3): d 165.88, 163.93, 158.71, 152.95, 149.83, 138.05, 134.73,
132.23, 126.14, 124.89, 123.85, 123.23, 122.47, 120.71, 114.30, 113.21, 70.51,
65.92, 59.25, 44.4–41.8 (1C, br s), 41.8–39.0 (1C, br s), 33.2–31.2 (1C, br s).
HRMS [M+H]: 465.1426 found, 465.1436 required.
14. THPP-1 was administered intravenously during
periods at 13, 29, and 42 mg/kg in DMSO (10 mL/30 min) to evaluate the
effects of the test article on cardiovascular function in anesthetized,
3 sequential 30-minute
5. (a) Perez-Costas, E.; Melender-Rerro, M.; Roberts, R. C. J. Neurochem. 2010, 113,
287; (b) Simpson, E. H.; Kellendonk, C.; Kandel, E. Neuron 2010, 65, 585; (c)
Baumeister, A. A.; Francis, J. L. J. Hist. Neurosci. 2002, 11, 265; (d) Delay, J.;
Deniker, P.; Harl, J. M. Ann. Med. Psychol. 1952, 110, 112; (e) DeLong, M. R.;
Wichmann, T. Arch. Neurol. 2007, 64, 20.
6. (a) Chappie, T. A.; Humphrey, J. M.; Allen, M. P.; Estep, K. G.; Fox, C. B.; Lebel, L.
A.; Liras, S.; Marr, E. S.; Menniti, F. S.; Pandit, J.; Schmidt, C. J.; Tu, M.; Williams,
R. D.; Yang, F. V. J. Med. Chem. 2007, 50, 182; (b) Verhoest, P. R.; Chapin, D. S.;
Corman, M.; Fonseca, K.; Harms, J. F.; Hou, X.; Marr, E. S.; Menniti, F. S.; Nelson,
F.; O’Connor, R.; Pandit, J.; Proulx-LaFrance, C.; Schmidt, A. W.; Schmidt, C. J.;
Suiciak, J. A.; Liras, S. J. Med. Chem. 2009, 52, 5188; (c) Hoefgen, N.; Stange, H.;
Schindler, R.; Lankau, H.-J.; Grunwald, C.; Langen, B.; Egerland, U.; Tremmel, P.;
Pangalos, M. N.; Marquis, K. L.; Hage, T.; Harrison, B. L.; Malamas, M. S.;
Brandon, N. J.; Kronbach, T. J. Med. Chem. 2010, 53, 4399.
3
vagotomized dogs. Heart rate (HR), mean blood pressure (MBP) and
electrocardiographic parameters (PR, QRS and QTcB intervals; QTcB-heart rate
correction using Bazett’s method) were monitored and blood samples were
collected for plasma drug concentration analysis. The cardiovascular effects of
the vehicle alone (30 mL/90 min) were evaluated in a separate set of 3 dogs, for
time-matched comparison with the respective doses of THPP-1.
15. Wang, H.; Liu, Y.; Hou, J.; Zheng, M.; Robinson, H.; Ke, H. Proc. Natl. Acad. Sci.
U.S.A. 2007, 104, 5782.
16. Using the 3UI7 (Yang, S.-H., et al., Bioorg. Med. Chem. Lett. 2012, 22, 235.) PDB
structure, the THPP-1 structure was docked into the active site using Glide SP
(Schrodinger, LLC, Glide, version 9.1, Schrödinger, Inc., New York, NY, 2009)
with default options. The grid was computed and a hydrogen bond to the
invariant Gln726 was defined. Poses were examined and the depicted structure
in Figure 5 was within the top 5 poses retrieved.
7. (a) Wanderberg, M. L.; Kapur, S.; Soliman, A.; Jones, C.; Vaccarino, F.
Psychopharmacology 2000, 150, 422; (b) Wadenberg, M. L.; Soliman, A.;
VanderSpek, S. C.; Kapur, S. Neuropsychopharmacology 2001, 25, 633.