2
J. Med. Chem. 2007, 50, 2-5
Letters
To manage the inherent risk involved with developing a
kinase inhibitor for a chronic indication, a high premium was
placed on identifying ROCK1 inhibitors that were not only
potent, but also highly selective over other protein kinases (initial
goal: >100-fold). An internal screening effort led to the
discovery of the aminofurazan (oxadiazole), azabenzimidazole
1, a potent inhibitor of ROCK1 (IC50 ) 19 nM).4 Although 1
had good kinase selectivity (IC50 >10 000 nM, >500-fold, over
a range of 30 diverse protein kinases), several kinases were
inhibited with submicromolar activity (Table 1). Inhibition of
RSK1 and p70S6K5 was nearly equipotent with ROCK1
inhibition; in addition, 1 has been reported to be a very potent
(3 nM) inhibitor of MSK1.6 Modest selectivity (ranging from
10- to 30-fold) was also observed against CDK2 and GSK3â.7
Discovery of Aminofurazan-azabenzimidazoles as
Inhibitors of Rho-Kinase with High Kinase
Selectivity and Antihypertensive Activity
Robert A. Stavenger,*,† Haifeng Cui,† Sarah E. Dowdell,†
Robert G. Franz,† Dimitri E. Gaitanopoulos,†
Krista B. Goodman,† Mark A. Hilfiker,† Robert L. Ivy,†
Jack D. Leber,† Joseph P. Marino, Jr.,† Hye-Ja Oh,†
Andrew Q. Viet,† Weiwei Xu,† Guosen Ye,† Daohua Zhang,†
Yongdong Zhao,† Larry J. Jolivette,‡ Martha S. Head,§
Simon F. Semus,§ Patricia A. Elkins,§
Robert B. Kirkpatrick,| Edward Dul,| Sanjay S. Khandekar,|
Tracey Yi,| David K. Jung, Lois L. Wright,#
Gary K. Smith,# David J. Behm,X Christopher P. Doe,4
Ross Bentley,4 Zunxuan X. Chen,X Erding Hu,X and
Dennis Lee†
Departments of Medicinal Chemistry, InVestigatiVe Biology,
Vascular Biology, and Drug Metabolism and Pharmacokinetics,
CVU CEDD, Department of Computation and Structural Sciences,
and Department of Gene Expression and Protein Biochemistry,
GlaxoSmithKline, 709 Swedeland Road, King of Prussia,
Two general syntheses of these analogs are outlined in
Scheme 1. The original route, which provided compounds 6a-d
and 6f, starts with oxidation of 4-chloro-3-nitropyridine (1) to
provide 4-chloro-3-nitro-2-pyridone.8 This intermediate was then
treated with POCl3 to provide 2,4-dichloro-5-nitropyridine (3).
The 4-chloride was then preferentially displaced by ethyl-
amine at room temperature, followed by displacement of the
6-chloride. Although the second displacement could be achieved
by anion formation with NaH, followed by heating in DMF, a
milder and more generally useful method involved heating the
chloride and nucleophile in the presence of K2CO3 in CH3CN.
Hydrogenation of the nitro group, followed by amide coupling
with cyanoacetic acid and cyclo-dehydration provided the
cyanomethyl-azabenzimidazoles 5. Transformation of the cyano-
methyl group to the aminofurazan was then accomplished by
preparation of the R-cyano oxime with sodium nitrite and
aqueous acid, followed by a two-step sequence involving
addition of hydroxylamine and closure to 6a-e by heating in
Et3N/THF. Deprotection of 6e with sulfuric acid provided the
free aniline 6f; amide coupling to 6f then provided inhibitors
6g-n.
A more efficient method for preparing analogs at the
6-position (6o-p) was then developed utilizing CuI-promoted
couplings9 to the late-stage C6-bromide 10, Scheme 2. This
bromide was prepared similarly to the analogs above starting
from 2,4-dibromo-5-nitropyridine (8).
During the course of initial SAR studies around the azaben-
zimidazole core, we quickly found that substitution on the
6-position was tolerated and could provide improved kinase
selectivity. Addition of a methoxy group on the 6-position (6a)
led to a 4-fold improvement in potency against ROCK1 and an
increase in selectivity with respect to most other kinases (Table
1). The incorporation of an unsubstituted phenoxy group
provided compound 6b, although less potent than 6a, and
increased selectivity over CDK2 and GSK3â.
PennsylVania 19406, and Department of Assay DeVelopment and
Compound Profiling and High-Throughput Chemistry,
GlaxoSmithKline, Research Triangle Park, North Carolina 27709
ReceiVed July 24, 2006
Abstract: The discovery, proposed binding mode, and optimization
of a novel class of Rho-kinase inhibitors are presented. Appropriate
substitution on the 6-position of the azabenzimidazole core provided
subnanomolar enzyme potency in vitro while dramatically improving
selectivity over a panel of other kinases. Pharmacokinetic data was
obtained for the most potent and selective examples and one (6n) has
been shown to lower blood pressure in a rat model of hypertension.
Despite many available treatments, hypertension remains a
prevalent problem. In fact, some 30% of hypertensive patients
are unable to reach their blood pressure goals. Thus, a new anti-
hypertensive treatment, which acts on a broader patient popula-
tion, would be an important addition to existing treatments.
A number of vasoconstrictive agents, including angiotensin
II, endothelin-1, and urotensin-II, exert their effect through
RhoA and the downstream kinase Rho-kinase (ROCK1).1
Because of its central role in the control of smooth muscle
contraction, inhibition of ROCK1 could lead to a more broadly
efficacious anti-hypertensive agent.2 ROCK1 inhibitors have
been shown to relax vascular smooth muscle and lower blood
pressure in several animal models of hypertension.3 Therefore,
we began an effort to identify potent ROCK1 inhibitors with
pharmacokinetic profiles consistent with once daily oral dosing.
* To whom correspondence should be addressed. Phone: 610-270-5098.
Fax: 610-270-4490. E-mail: robert.a.stavenger@gsk.com.
† Department of Medicinal Chemistry.
‡ Department of Drug Metabolism and Pharmacokinetics.
§ Department of Computation of Structural Sciences.
| Department of Gene Expression and Protein Biochemistry.
Department of High-Throughput Chemistry.
# Department of Assay Development and Compound Profiling.
X Department of Vascular Biology.
Substitution on the phenoxy substituent revealed that the
3-acetamide 6c provided a >10-fold boost in ROCK1 potency
4 Department of Investigative and Cardiac Biology.
10.1021/jm060873p CCC: $37.00 © 2007 American Chemical Society
Published on Web 12/15/2006