A-ring modifications on the triazafluorenone core structure and their mGluR1 antagonist properties

Article abstract of DOI:10.1016/j.bmcl.2010.03.004

A-ring modifications on the triazafluorenone core structure were investigated. Five membered heterocycles such as pyrazoles and isothiazoles are not tolerated. It has been found that the pyrimidine nucleus was very well tolerated on the left hand side. Am

Full text of DOI:10.1016/j.bmcl.2010.03.004

Bioorganic & Medicinal Chemistry Letters 20 (2010) 2474–2477
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
A-ring modifications on the triazafluorenone core structure
and their mGluR1 antagonist properties
a
a
a
a
b
T. K. Sasikumar a, , Li Qiang , Duane A. Burnett , William J. Greenlee , Cheng Li , Mariagrazia Grilli ,
*
Rosalia Bertorelli b, Gianluca Lozza b, Angelo Reggiani b
a Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
b Schering-Plough Research Institute, San Raffaele Science Park, Via Olgettina, 58, 20132 Milan, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
A-ring modifications on the triazafluorenone core structure were investigated. Five membered heterocy-
cles such as pyrazoles and isothiazoles are not tolerated. It has been found that the pyrimidine nucleus
was very well tolerated on the left hand side. Amino pyrimidine compounds 24 and 27 showed accept-
able PK profile with significant brain penetration. Compound 9 served as a versatile intermediate for a
number of chemical transformations.
Received 3 February 2010
Revised 26 February 2010
Accepted 1 March 2010
Available online 10 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
mGluR1 antagonist
Neuropathic pain
The metabotropic glutamate receptors (mGluRs) perform a vari-
ety of functions in the central and peripheral nervous systems.
They are members of the G-protein coupled receptors and form a
family of eight subtypes (mGlu1 to mGlu8) and are assigned to
three groups. Group I mGluRs (mGluR1 and mGluR5) are widely
studied and are involved in the central sensitization of pain and
other neurological disorders.1–6 There have been remarkable ad-
vances in the development of small molecules that inhibits
mGluR1 activity which are useful for the treatment of neuropathic
or chronic pain models in rodents. Some of the very recent exam-
ples from literature (1–4) are given below in Figure 1.7–11
does not have the left hand side ring system.11 Earlier in this pro-
gram we found that a simple primary amino group is very well tol-
HO
N
N
N
N
N
N
O
N
OMe
S
O
HN
2
1
H2NO2S
Compound 1, originated from the public domain, was identified
as a potent mGluR1 antagonist from our high throughput screening
assay. We as well as others have extensively studied the N-aro-
matic substitution pattern on the C-ring as well as the amino sub-
stitutions on the A-ring of triazafluorenone (Fig. 1). It has been
N
N
HN
N
O
N
N
N
N
O
demonstrated that
a large number of amino substitutions
O
N
Cl
(NR1R2) and a variety of aromatic rings (Ar) are tolerated in the tri-
cyclic framework.7,8 A thorough literature survey indicated that
the A-ring modifications such as reduction/enlargement of the
existing ring are unknown. Thus we decided to modify the left
hand side, keeping the thienopyrimidone part as an invariable
(structure 5) as shown in Figure 2. Additionally we planned to open
up the A-ring and strategically position the basic nitrogens in the
molecule. Compound 4 is a close example from the literature that
3
4
Figure 1. Representative mGluR1 antagonists.
NR1R2
R
N
N
A
N
C
5/6
N
N
Ar
Ar
B
S
S
O
O
5
* Corresponding author. Tel.: +1 908 740 4373; fax: +1 908 740 7164.
E-mail addresses: sasikumartk@ yahoo.com, thavalakulamgar.sasikumar@
merck.com (T.K. Sasikumar).
Figure 2. General SAR plans.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.03.004

T. K. Sasikumar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2474–2477
2475
erated in the triazafluorenone core structure,8 thus we decided to
9
prepare compounds with free primary amino group on the left
hand side of the newly designed structure. A convenient starting
material (6) was available for this strategy. Compound 6 was con-
verted to the amide 7 and cyclized to the thienopyrimidone 8 in
good yields. The methyl sulfide moiety was oxidized to the methyl
sulfone by use of hydrogen peroxide and this intermediate 9 served
as a versatile intermediate for various transformations. Compound
9 was treated with amines such as pyrrolidine and imidazole to
furnish compounds 10 and 11. Compound 11 was treated with
hydroxylamine to get compound 12 as shown in Scheme 1. Ami-
doxime 12 (mixture of cis and trans) may have all the requisite
functionalities to bind to the receptor. These compounds were
tested in the human mGluR1 assay12 and found to be inactive
(compounds 10, 11 and 12: h-mGluR1 IC50 >1000 nM).
a
b
NH2
NH2
N
N
N
HN
N
S
N
N
S
S
O
O
14
13
c
N
N
N
N
N
S
O
13a
Next we turned our attention to the introduction of a five mem-
bered ring in place of the pyridine nucleus as shown in Scheme 2.
As can be seen from Figure 1, pyrazole moiety was well tolerated
in a related system (compound 4 in which the thiophene ring is ab-
sent). Compound 9 was treated with hydrazine to afford the
aminopyrrazole structure 13. Aminoisothiazole compound 14
was prepared according to the literature procedure.13 Methyl sul-
fone compound 9 was treated with NaSH and the resulting thiol
derivative was cyclized with chloramine (prepared from NaOCl
and NH4OH)14 to generate compound 14. Unfortunately these
modifications also generated compounds with only micromolar
activity. One compound showed a human IC50 of 670 nM (per-
methylated compound 13a). All attempts to prepare an amino oxa-
thiazole A-ring analog were unsuccessful.
To break up the extended planar aromatic system, we next tar-
geted the saturated A-ring of the tricyclic system. Methyl triflate
activation of compound 1515 followed by varying equivalents of
NaBH4 afforded compounds 16, 18 and 19 in good yields as illus-
trated in Scheme 3. Oxime analog 17 was also prepared. Any efforts
to reduce the oxime functionality to amine were unsuccessful. All
Scheme 2. Reagents and conditions: (a) NH2NH2ÁH2O, MeOH, 70 °C, 98%; (b) NaSH
in DMF/H2O, then Cl–NH2, see text; (c) NaH, MeI.
O
O
R
N
N
N
a
N
N
N
N
N
S
S
O
O
15
16
b,c
b
NOH
N
N
N
N
S
S
O
O
17
18
, R = H
19, R = OH
Scheme 3. Reagents and conditions: (a) MeOTf, then NaBH4 (1 equiv) 60%; (b)
NaBH4, THF; (c) NH2OHÁHCl, DMF.
compounds showed only micromolar activity in the mGluR1 assay.
Similar results were obtained with compounds 20 and 21, which
were prepared from intermediate 9 by treatment with diamines
as shown in Scheme 4.
N
S
N
S
NH2
NH2
a
H
N
O
Since all our attempts to introduce five or seven membered A-
ring system gave only micromolar active compounds, we turned
our focus to six membered ring systems. Compound 9 was treated
with urea and thiourea to form compound 22 and 23, respectively.
The methyl sulfone also can be reacted with guanidine and substi-
tuted guanidines to form diamino pyrimidines as shown in Scheme
5. Compound 22 showed no activity in the mGluR1 assay, but com-
pound 23 has shown excellent mGluR1 activity. This compound
has a human IC50 of 3.1 nM which is more than 300-fold more po-
tent than the hydroxyl analog 22. Similar results were obtained for
the amino compound 24 with an IC50 of 2.1 nM. Slightly bigger
S
S
S
O
O
7
6
b
N
S
N
S
c
N
N
N
N
S
O
O
O
O
9
8
e
d
N
N
N
N
N
N
N
N
S
N
S
O
O
9
10
11
a
b
f
NH2
S
HO
NH2
S
NH2
N
N
N
N
N
N
N
N
N
N
N
N
N
O
S
H
H
O
O
12
20
21
Scheme 1. Reagents and conditions: (a) p-toluidine, Me3Al, Tol, rt, 98%; (b)
(EtO)3CH, 72%; (c) H2O2, HOAc, 73%; (d) pyrrolidine, DMF, 60%; (e) imidazole, DMF,
100 °C, 84%; (f) NH2OHÁHCl, K2CO3, EtOH, 80 °C, 50%.
Scheme 4. Reagents and conditions: (a) ethylene diamine, DMF, 100 °C, 58%; (b)
1,2-diaminocyclohexane, DMF, 100 °C, 60%.

2476
T. K. Sasikumar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2474–2477
The methyl pyrimidine compound 27 showed an excellent
NH2
S
NH2
N
N
inhibitory activity that encouraged us to study the SAR in detail,
keeping the left hand side constant and varying the C-ring aro-
matic groups. Readily available compound 6 was treated with
H2O2 to produce methylsulfone 30 which was then cyclized with
acetamidine to form aminopyrimidine compound 31 in good
yields. Compound 31 was treated with DMF–DMA to form inter-
mediate 32 in quantitative yield. Heating a solution of compound
32 with appropriate aromatic amine in presence of acetic acid
yielded the final compound in good yields (Scheme 7). As shown
in Table 2, a variety of aromatic groups are tolerated at this posi-
tion. For example, simple phenyl ring (33) showed an IC50 of
16 nM. Methoxy (34) and fluoro (35) derivatives showed slightly
less activity (188 and 68 nM, respectively) where as the chloro
derivative (36) showed excellent potency of 11 nM.
We have shown that the amino pyrimidine structures are po-
tent in the mGluR1 assay and having achieved a desirable level
of potency, we focused our attention on the pharmacokinetic prop-
erties of these molecules. The PK profile of representative examples
are shown in Table 3. Compounds 24 and 27 showed reasonable rat
AUC and the former compound exhibited a brain concentration of
100 ng/g @ 6 h. All mGluR1 active compounds were exquisitely
selective over mGluR5.
N
N
N
N
HO
HS
b
N
N
S
O
O
23
22
a
9
c
d
NH2
S
NH2
N
N
N
N
N
N
HN
R
H2N
N
N
S
O
O
24
25; R = Me
26;
R = Pyrrolidine
Scheme 5. Reagents and conditions: (a) urea, DMF, 80 °C, 72%; (b) thiourea, DMF,
100 °C, 49%; (c) guanidineÁHCl, DMF, 100 °C, 80%; (d) R-guanidineÁHCl, DMF, 100 °C.
groups such as methylamino or pyrrolidine are not tolerated as
shown in Table 1.
Since small functional moieties such as –SH and –NH2 are very
well tolerated in the A-ring, we investigated more functional
groups at that position. Compounds 27–29 were synthesized by
the reaction of compound 9 with different amidines under basic
conditions (Scheme 6). Methyl and cyclopropyl analogs 27
(IC50 = 27 nM) and 29 (IC50 = 326 nM) were tolerated, however tri-
fluoromethyl analog 28 did not showed any mGluR1 activity. This
difference in potency might be explained by electron withdrawing
effect of the trifluoromethyl group.
In summary, we have tried to modify the A-ring of triazafluor-
enone lead structure and found that 2-alkyl or 2-amino pyrimi-
NH2
S
N
S
NH2
NH2
b
N
a
6
O
O
N
S
O
O
O
O
30
31
Table 1
c
mGluR1 binding properties for compounds 1, 22–29
NH2
N
N
N
NH2
S
N
N
N
R
N
N
N
d
N
N
Me
S
N
O
O
N
R
N
22-29
S
O
O
a
Compd
R
h-mGluR1 IC50 (nM)
h-mGluR5 IC50 (nM)
32
27, 33-36
1
22
23
24
25
26
27
28
29
9.5
>1000
3.1
>3000
>3000
>3000
>3000
>3000
>3000
>3000
>3000
>3000
–OH
–SH
–NH2
–NHMe
–Pyrrolyl
–CH3
Scheme 7. Reagents and conditions: (a) H2O2, HOAc; (b) acetamidamideÁHCl, TEA,
DMSO, 100 °C, 58% (two steps); (c) DMF–DMA, DMF, 100 °C; (d) amine, HOAc,
160 °C.
2.1
>1000
>1000
27
>1000
326
–CF3
–Cyclopropyl
Table 2
mGluR1 binding properties for compounds 27, 33–36
a
NH2
An average of at least three measurements performed on human mGlu1/5
receptors. The standard error was 10%, and variability was less than twofold from
assay to assay.
N
N
N
N
R
S
O
27, 33-36
NH2
S
N
S
N
N
a
N
Compd
R
h-mGluR1 IC50 (nM)
h-mGluR5 IC50 (nM)
a
N
N
R
27
33
34
35
36
–CH3
–H
–OMe
–F
27
16
188
68
>3000
>3000
>3000
>3000
>3000
N
S
O
O
O
O
27; R = CH3
28; R= CF3
29; R = Cp
9
–Cl
11
a
An average of at least three measurements performed on human mGlu1/5
receptors. The standard error was 10%, and variability was less than twofold from
assay to assay.
Scheme 6. Reagents and conditions: (a) alkyl imidamide, DMF, TEA, 100 °C (50–
70%).

T. K. Sasikumar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2474–2477
2477
Table 3
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5. Kunishima, N.; Shimada, Y.; Tsuji, Y.; Sato, T.; Yamamoto, M.; Kumasaka, T.;
Nakanishi, S.; Jingami, H.; Morikawa, K. Nature 2000, 407, 971.
6. Constantino, G.; Macchiarulo, A.; Pellicciari, R. Bioorg. Med. Chem. 2001, 9, 847.
7. Zheng, G. Z.; Bhatia, P.; Daanen, J.; Kolasa, T.; Patel, M.; Latshaw, S.; Kouhen, O.
F. E.; Chang, R.; Uchic, M. E.; Miller, L.; Nakane, M.; Lehto, S. G.; Honore, M. P.;
Moreland, R. B.; Brioni, J. D.; Stewart, A. O. J. Med. Chem. 2005, 48, 7374.
8. Our efforts in the modification of tricyclic structure is being published in the
following patents, WO 2006/002051 and US 2006/167029. Also see: Wu, W.-L.;
Burnett, D. A.; Domalski, D.; Greenlee, W. J.; Li, C.; Bertorelli, R.; Fredduzzi, S.;
Lozza, G.; Veltri, A.; Reggiani, A. J. Med. Chem. 2007, 50, 5550 (Biology materials
and methods were described in this Letter).
9. Owen, D. R.; Dodd, P. G.; Gayton, S.; Greener, B. S.; Harbottle, G. W.; Mantell, S.
J.; Maw, G. N.; Osborne, S. A.; Rees, H.; Ringer, T. J.; Rodriguez-Lens, M.; Smith,
G. F. Bioorg. Med. Chem. Lett. 2007, 17, 486.
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P.; Betts, A. M.; Monhemius, R.; Prime, R. L. Bioorg. Med. Chem. Lett. 2009, 19,
2190.
PK profile of selected compounds
NH2
S
N
N
N
R
N
O
Parameters
R = NH2 (24)
R = CH3 (27)
Human mGluR1 IC50 (nM)
Rat mGluR1 Ki (nM)
Human mGluR5 IC50 (nM)
Efflux substrate
2.1
9.3
27
115.2
>3000
No
2112
29
>3000
No
965
100
0.9
Rat PK, (10 mg/kg), AUC (ng h/mL)16
Brain concn @ 6 h (ng/g)
Brain/plasma
0.2
11. Wang, X.; Kolasa, T.; El Kouhen, O. F.; Chovan, L. E.; Black-Shaefer, C. L.;
Wagenaar, F. L.; Garton, J. A.; Moreland, R. B.; Honore, P.; Lau, Y. Y.; Dandliker,
P. J.; Brioni, J. D.; Stewart, A. O. Bioorg. Med. Chem. Lett. 2007, 17, 4303.
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Hodgson, R. A.; Sherry, X. L.; Nicolussi, E.; Pond, A. J.; Parker, E. M.; Hunter, J. C.;
Higgins, G. A.; Reggiani, A.; Bertorelli, R. Psychopharmacology 2005, 179, 207.
13. Khalil, Z. H.; Yanni, A. S.; Gaber, A. M.; Abdel-Mohsen, S. A. Phosphorus, Sulfur
Silicon Relat. Elem. 2000, 162, 65.
dines are very well tolerated. A highly versatile intermediate 9 has
been used to probe the SAR of the A-ring of these tricyclics. Com-
plementary C-ring changes have also been explored. A very com-
prehensive SAR study on the pyrimidine core will be published
elsewhere.
14. Wang, Y.; Guziec, F. S. J. Org. Chem. 2001, 66, 8293.
15. Sasikumar, T. K.; Qiang, L.; Burnett, D. A.; Greenlee, W. J.; Li, C.; Heimark, L.;
Pramanik, B.; Grilli, M.; Bertorelli, R.; Lozza, G.; Reggiani, A. Bioorg. Med. Chem.
Lett. 2009, 19, 3199.
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References and notes
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