C-5 Substituted heteroaryl 3-pyridinecarbonitriles as PKCθ inhibitors: Part I

Article abstract of DOI:10.1016/j.bmcl.2009.07.109

We earlier reported that 3-pyridinecarbonitriiles with a 4-methylindolyl-5-amino group at C-4 and a phenyl group at C-5 were inhibitors of PKCθ. Keeping the group at C-4 of the pyridine core constant, we varied the water solubilizing group on the phenyl r

Full text of DOI:10.1016/j.bmcl.2009.07.109

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5423–5425
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
C-5 Substituted heteroaryl 3-pyridinecarbonitriles as PKCh inhibitors: Part I
a
a
a
a
b
b
Joan Subrath a, , Daniel Wang , Biqi Wu , Chuansheng Niu , Diane H. Boschelli , Julie Lee , Xiaoke Yang ,
*
Agnes Brennan b, Divya Chaudhary b
a Wyeth Research, Chemical Sciences, 401 N. Middletown Road, Pearl River, NY 10965, United States
b Wyeth Research, Inflammation, 200 Cambridge Park Drive, Cambridge, MA 02140, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
We earlier reported that 3-pyridinecarbonitriiles with a 4-methylindolyl-5-amino group at C-4 and a
phenyl group at C-5 were inhibitors of PKCh. Keeping the group at C-4 of the pyridine core constant,
we varied the water solubilizing group on the phenyl ring at C-5 and then replaced the C-5 phenyl ring
with several monocyclic heteroaryl rings, including furan, thiophene and pyridine. Analog 6e with a 4-
methylindol-5-ylamino group at C-4 and a 5-[(4-methylpiperazin-1-yl)methyl]-2-furyl group C-5 had
an IC50 value of 4.5 nM for the inhibition of PKCh.
Received 8 June 2009
Revised 22 July 2009
Accepted 23 July 2009
Available online 26 July 2009
Keywords:
PKCh
Ó 2009 Elsevier Ltd. All rights reserved.
Pyridinecarbonitrile
The members of the protein kinase C (PKC) family of serine
threonine kinases are subdivided into three classes based on the
activation requirements of their N-terminal regulatory domains.1,2
The conventional or classical isoforms require both calcium and
diacylglycerol (DAG), the novel isoforms require only DAG and
the atypical isoforms require neither. The PKC inhibitors currently
in clinical development target either the conventional isoforms or
both the conventional and novel isoforms.3
(IC50 = 7.4 nM) as a more potent inhibitor of PKCh.15,16 In efforts
to optimize this series, we kept the C-4 group of 1b, and varied
the water solubilizing group on the phenyl ring at C-5.
NH
NH
O
O
O
N
HN
N
HN
N
N
CN
CN
PKCh, a novel isoform, is primarily expressed on T cells and
plays a key role in various signaling pathways of the immune re-
sponse.4–6 PKCh activates T cell cytokine production, specifically
that of IL-2, which regulates T cell proliferation. Mice engineered
to have a deficiency in PKCh have a diminished development of
several inflammatory diseases including asthma, multiple sclero-
sis, arthritis, inflammatory bowel disease, and transplant rejection,
making this kinase a desirable target for therapeutic intervention.
The PKC isoforms have a strong structural similarity in their C-
terminal catalytic domains, with PKCd having the closest homology
to PKCh.7 The ATP binding sites of these two kinases differ by only
one amino acid. In contrast to PKCh, mice where the gene for PKCd
was deleted or ‘knocked out’ developed autoimmune disease as a
result of B cell hyperproliferation and an accompanying overpro-
duction of inflammatory cytokines.8,9 PKCd is therefore often used
as a counter assay where the desired target is PKCh.
1a
1b
The analogs in Table 1 were prepared as shown in Scheme 1. Su-
zuki coupling of 216 and the corresponding formylphenylboronic
acid followed by reductive amination of the aldehyde gave 4a,
4b, and 4d–4g. Commercially available 2-[(dimethylamino)-
methyl]phenylboronic acid was subjected to a Suzuki coupling
reaction with 2 to provide 4c. As depicted in Table 1, since the para
and meta isomers (4a and 4b) exhibited greater potency against
PKCh than the ortho isomer (4c), additional optimization by vary-
ing the amine was only done on the para and meta isomers.
The N-methylpiperazine and morpholine analogs 4d–4g were
prepared by reductive amination of 3a and 3b as shown in Scheme
1. The analogs with an N-methylpiperazine group (4d and 4e)
(Table 1) exhibited increased PKCh inhibition compared to those
with a dimethylamine (4a and 4b) or a morpholine substituent (4f
and 4g). Therefore, the N-methylpiperazine group was retained for
further study.
There are only a few reports in the literature of efforts to iden-
tify a selective inhibitor of PKCh.10–16 We earlier reported that opti-
mization of the group at C-4 and of the substituents on the C-5
phenyl ring of 1a14 (IC50 = 70 nM) led to the identification of 1b
Replacement of the C-5 phenyl ring with various heteroaryl
rings was carried out as depicted in Scheme 2. Intermediate 2
was subjected to Suzuki coupling with various formylheteroaryl
boronic acids to give 5a–5e. The aldehydes, 5a–5e, then underwent
reductive amination with N-methylpiperazine to provide 6a–6e.
* Corresponding author. Tel.: +1 845 602 8142; fax: +1 845 602 5561.
E-mail address: subratj@wyeth.com (J. Subrath).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.109

5424
J. Subrath et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5423–5425
Table 1
PKCh and PKCd inhibitory activity of C-5 phenyl and heteroaryl analogs
NH
HN
N
R'RN
Ring
CN
18
18
Compound number
NRR0
Ring
PKCh IC50
PKCd IC50
d/h
(nM)
(nM)
4a
4b
4c
4d
4e
4f
4g
6a
6b
6c
6d
6e
6f
NMe2
NMe2
NMe2
N-Methylpiperazine
N-Methylpiperazine
Morpholine
1,4-Phenyl
1,3-Phenyl
1,2-Phenyl
1,4-Phenyl
1,3-Phenyl
1,4-Phenyl
1,3-Phenyl
3,6-Pyridine
3,5-Pyridine
2,5-Thiophene
3,5-Thiophene
2,5-Furan
8.4
6.9
200
5.0
3.0
9.0
23
58
25
2400
25
22
6.9
3.6
12
5.0
7.3
7.8
3.7
6.6
NA18
8.2
2.0
10
70
84
Morpholine
N-Methylpiperazine
N-Methylpiperazine
N-Methylpiperazine
N-Methylpiperazine
N-Methylpiperazine
N-Methylpiperazine
38
250
NT18
50
9.7
45
190
6.1
4.9
4.5
12
3,5-Furan
36
3.0
N
NH
R
NH
NH
NH
NH
NH
OHC
N
N
b
R'
OHC
Het
a
HN
N
HN
N
HN
N
a
HN
HN
HN
b
CN
CN
Het
I
CN
CN
I
CN
CN
N
N
2
N
4a, b, d-g
3a: para- isomer
2
6a-6e
5a-5e
3b: meta- isomer
a: Het = 3,6-pyridine
b: Het = 3,5-pyridine
c: Het = 2,5-thiophene
d: Het = 3,5-thiophene
e: Het = 2,5-furan
NH
NH
HN
N
HN
c
Scheme 2. Reagents and conditions: (a) 1.5–2 equiv formylheteroarylboronic ester
or acid, 0.05 equiv Pd(PPh3)4, DME, satd aq NaHCO3, reflux, 4 h, overnight; (b) for
6a,b,e: 4–5 equiv N-methylpiperazine, 4–5 equiv NaBH(OAc)3, THF, room temper-
ature, overnight; for 6c: 1.1 equiv N-methylpiperazine, 1.3 equiv NaBH3CN,
1.2 equiv HOAc, EtOH, room temperature, 7 h; for 6d: 3.2 equiv N-methylpipera-
zine, 5 equiv NaBH(OAc)3, cat HOAc, CH2Cl2, NMP, room temperature, overnight.
CN
I
CN
N
N
2
4c
Scheme 1. Reagents and conditions: (a) for 3a: 1.2 equiv 4-CHO-Ph-B(OH)2,
0.05 equiv Pd(PPh3)4, DME, satd aq NaHCO3, 95 °C, overnight; for 3b: 1.2 equiv 3-
CHO-Ph-B(OH)2, 0.05 equiv Pd(PPh3)4, DME, satd aq NaHCO3, 95 °C, overnight; (b)
10 equiv RR0NH, 5 equiv NaBH(OAc)3, THF, room temperature, overnight; (c)
1.2 equiv 2-(CH2NMe2)-Ph-B(OH)2, 0.05 equiv Pd(Ph3P)4, DME, satd aq NaHCO3,
100 °C, overnight.
NH
N
1
2
O
HN
N
O
a
b
N
3
O
CHO
CN
5
N
4
Br
Br
N
As depicted in Scheme 3, 4-bromo-2-furaldehyde was subjected
to reductive amination with N-methylpiperazine followed by
treatment with n-butyl lithium and triisopropyl borate to give
the furanylboronic ester. The ester was then coupled with 2 under
Suzuki conditions to give 6f.
Selectivity for PKCh over PKCd with 6a–f varied from 2- to 10-
fold, as shown in Table 1. When compared to the phenyl analogs,
4a and 4b, loss of potency was observed with the C-5 pyridine ana-
logs, 6a and 6b, while the thiophene and furan analogs 6c–6f re-
tained the potency. Overall 6e exhibited the highest potency for
the inhibition of PKCh as well as the best selectivity over PKCd.
Therefore, the 2,5-furan ring of 6e was retained for further
optimization.
6f
Scheme 3. Reagents and conditions: (a) 5 equiv N-methylpiperazine, 5 equiv
NaBH(OAc)3, 2 equiv HOAc, CH2Cl2, room temperature, overnight; (b) (1) 2.5 equiv
triisopropyl borate, 2.7 equiv n-BuLi, THF, ꢀ78 °C 3 h, room temperature 1 h; (2)
0.5 equiv 2, 0.05 equiv Pd(dppf)2Cl2ꢁCH2Cl2, DME, satd aq Na2CO3, 85 °C, 1.5 h.
compound, replacement with a piperidine, pyrrolidine or a diethyl-
amino group (7c–e) led to decreased inhibition of PKCh (Table 2).
Interestingly, addition of a 4-dimethylamino group to the piperi-
dine ring of 7c, namely 7f, provided increased activity against both
PKC isoforms; however the selectivity against PKCd dropped. Var-
iation of the methyl group on 6e with either an isopropyl or a
cyclopentyl group, 7g and 7h, also resulted in slightly increased
potency against both PKC isoforms with decreased selectivity
against PKCd.
Compounds 7a–h were prepared via reductive amination of 5e
with the corresponding amine (Scheme 4). While replacement of
the N-methylpiperazine group of 6e with a morpholine (7a) or thi-
omorpholine (7b) group retained much of the activity of the parent

J. Subrath et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5423–5425
5425
R
N
Compound 6e exhibited acceptable permeability (3.20 ꢂ
NH
NH
a
10ꢀ7 cm/s as measured in a PAMPA assay) and good solubility at
R'
OHC
pH 7.4 (>100 lg/mL). However, it had very poor stability in mouse,
O
HN
O
HN
N
rat, and human liver microsomes (half lives of less than 10 min).
Our continuing optimization of this series of 3-pyridinecarbo-
nitriles is described in the subsequent Letter.17 Replacement of
the heteroaryl ring at C-5 with a bicyclic heteroaryl ring resulted
in improved potency against PKCh, improved selectivity over PKCd
and improved metabolic stability.
CN
CN
N
5e
7a-h
Scheme 4. Reagents and conditions: (a) 10 equiv RR0NH, 5 equiv NaBH(OAc)3, THF,
room temperature, overnight.
Acknowledgments
Table 2
We thank the Wyeth Chemical Technology department for
compound characterization and the pharmaceutical profiling re-
sults, the Wyeth Screening Sciences department for the kinase
selectivity results, the Wyeth Discovery Synthetic Chemistry and
Chemical Development departments for the preparation of multi-
gram batches of both 2 and 5-amino-4-methylindole and Dr. Tarek
Mansour for his support.
PKCh and PKCd inhibitory activity of 6e analogs
NH
R'RN
HN
N
CN
O
18
18
Compound
number
NRR0
PKCh IC50
(nM)
PKCd IC50
(nM)
d/h
References and notes
6e
7a
7b
7c
7d
7e
7f
N-Methylpiperazine
Morpholine
Thiomorpholine
Piperidine
Pyrrolidine
N,N-Diethylamine
4-Dimethylaminopiperidine
N-Isopropylpiperazine
N-Cyclopentylpiperazine
4.5
7.8
7.5
41
35
42
1.3
2.4
3.5
45
86
94
390
300
190
8.2
14
10
11
13
9.5
8.6
4.5
6.3
5.8
5.1
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