Discovery of piperidine-aryl urea-based stearoyl-CoA desaturase 1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2008.06.088

A series of structurally novel stearoyl-CoA desaturase1 (SCD1) inhibitors has been identified via molecular scaffold manipulation. Preliminary structure-activity relationship (SAR) studies led to the discovery of potent, and orally bioavailable piperidine-aryl urea-based SCD1 inhibitors. 4-(2-Chlorophenoxy)-N-[3-(methyl carbamoyl)phenyl]piperidine-1-carboxamide 4c exhibited robust in vivo activity with dose-dependent desaturation index lowering effects.

Full text of DOI:10.1016/j.bmcl.2008.06.088

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4298–4302
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of piperidine-aryl urea-based stearoyl-CoA desaturase 1 inhibitors
,
*
Zhili Xin , Hongyu Zhao, Michael D. Serby, Bo Liu, Mei Liu, Bruce G. Szczepankiewicz, Lissa T. J. Nelson,
Harriet T. Smith, Tom S. Suhar, Rich S. Janis, Ning Cao, Heidi S. Camp, Christine A. Collins, Hing L. Sham,
Teresa K. Surowy, Gang Liu
Abbott Laboratories, Global Pharmaceutical Research and Development, 100 Abbott Road, Abbott Park, IL 60064, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of structurally novel stearoyl-CoA desaturase1 (SCD1) inhibitors has been identified via molec-
ular scaffold manipulation. Preliminary structure–activity relationship (SAR) studies led to the discovery
of potent, and orally bioavailable piperidine-aryl urea-based SCD1 inhibitors. 4-(2-Chlorophenoxy)-N-[3-
(methyl carbamoyl)phenyl]piperidine-1-carboxamide 4c exhibited robust in vivo activity with dose-
dependent desaturation index lowering effects.
Received 8 June 2008
Revised 23 June 2008
Accepted 25 June 2008
Available online 28 June 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
SCD1 inhibitors
Desaturation index
The incidence of obesity in industrial societies has increased
dramatically over the past 30 years. Serious consequences of this
trend include a concurrent rise in the number of individuals with
type 2 diabetes mellitus, a projected decrease in the average life-
span of individuals in Western societies, and increasing pressure
on national health care systems to manage the complications
resulting from obesity.1 Although obesity is clearly linked to
chronic over-nutrition, many people find it difficult to achieve
long-term weight loss through diet alone. Pharmaceutical agents
that could safely promote weight loss and allow individuals to
maintain an ideal body weight would offer an important option
to those struggling with obesity.
Stearoyl-CoA desaturase (SCD) is a microsomal enzyme that
catalyzes the rate-limiting step in the biosynthesis of monounsat-
urated fatty acids from saturated fatty acids, in conjunction with
cytochrome b5 reductase, cytochrome b5, and the cofactors
NADH.2–4 The preferred substrates for SCD are palmitoyl(C16:0)-
CoA and stearoyl (C18:0)-CoA, which are converted to palmitoleoyl
(C16:1)-CoA and oleoyl (C18:1)-CoA, respectively. The products,
palmitoleic and oleic acids are major components of cell mem-
brane phospholids, circulating triglycerides, and cholesterol esters.
Four mouse SCD (SCD1, SCD2, SCD3, and SCD4)5 and two human
SCD genes6,7 have been characterized. Human SCD1 shows 85%
homology to the murine SCD1. SCD1 is abundantly expressed in
liver and adipose tissue and is tightly regulated by dietary and
hormonal factors including glucose, insulin, cholesterol and poly-
unsaturated fatty acids.8,9 There is ample evidence indicating that
SCD1 plays an important role in lipid metabolism10 and body
weight control.11 Higher SCD1 activity in humans has been corre-
lated with elevated plasma triglyceride levels.12 SCD1 deficiency
in mice, either naturally deficient Asebia mice13 or laboratory-cre-
ated SCD1 knockout mice (SCD1À/À),14 has been shown to reduce
body adiposity, increase insulin sensitivity, and impart resistance
to diet-induced obesity.15 Despite the fact that SCD1À/À mice con-
sume more food than normal mice, they clearly show a leaner phe-
notype. The SCD1À/À mice also have lower levels of hepatic
cholesterol esters and triglycerides.16 Inhibition of SCD1 activity
via antisense oligonucleotide knockdown of gene expression in
diet induced obese (DIO) mice resulted in reduced adiposity, im-
proved hepatic steatosis and increased energy expenditure.17
These observations make SCD1 a potential therapeutic target for
the treatment of obesity and diabetes.
Recently, a number of patent applications from Xenon Pharma-
ceuticals18,19 and Merck Frosst20 have been published, covering a
few series of small molecules that modulate SCD1 activity and reg-
ulate plasma lipid levels. The SAR studies of SCD1 inhibition based
on a pyridazine carboxamide template have been described by our
co-workers from Abbott Laboratories.21,22 Here, we present the
discovery of a different class of SCD1 inhibitors with good in vitro
potency and in vivo activities.
The nicotinamides (Fig. 1) represent one class of SCD1 inhibitors
disclosed by investigators at Xenon. We synthesized compound 1a
(Fig. 1), and determined an IC50 of 0.4 lM vs murine liver micro-
somal SCD1. In the course of searching for SCD1 inhibitors with a
new scaffold, we decided to replace the central aminopyridine of
* Corresponding author. Tel.: +1 617 914 1110; fax: +1 617 679 3635.
E-mail address: zhili.xin@biogenidec.com (Z. Xin).
Present address: Biogen Idec, 14 Cambridge Center, Cambridge, MA 02142-1453,
USA.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.06.088

Z. Xin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4298–4302
4299
O
O
aniline 6l was prepared from 3-nitrobenzoylchloride via a cycliza-
tion23 and subsequent reduction. Compounds that were further
derivatized through the amide modification were prepared from
an acid core 8, which was obtained by addition of 4-(2-chlorophen-
oxy)piperidine to commercially available ethyl 3-isocyanatobenzo-
ate followed by hydrolysis of the ester. Coupling of acid 8 and
requisite amine mediated by TBTU in DMF with Hunig’s base
provided the desired amide 4n–q.
N
N
R2 NH
N
R1
1
O
O
O
HN
O
N
N
CF3
N
O
NH
N
NH
1a IC50 = 0.4 μM (mSCD1)
4a IC50 = 0.4 μM (mSCD1)
For the characterization of SCD1 inhibitors, both mouse SCD1
and human SCD1 enzymatic activities have been measured. As a
source of human SCD1 activity, recombinant human SCD1 and
accessory protein cytochrome b5 and cytochrome b5 reductase
were cloned and expressed using baculovirus/insect cell express
systems. Structure–activity relationship studies were carried out
and the results are summarized in Table 1. In general, the potency
of inhibitors using the human recombinant sources of enzymes
(hSCD1) was lower than using mouse SCD1 (mSCD1), which
may reflect the difference between human SCD1 and mouse
SCD1. However, the rank order of IC50 was about the same in both
assays. We will discuss our SAR primarily based on mSCD1 data,
since in vivo activity of our SCD1 inhibitor was evaluated in
mouse model.
The optimization began with an examination of substitution on
phenoxy ring. With the ortho-substituted analogues, the IC50s stea-
dily decreased from H (4a, 370 nM) and F (4b, 98 nM) to bulkier
halogen groups, such as Cl and Br (4c and 4d, <4 nM). Consistent
with the SAR trend observed for the pyridazine series,21 increased
lipophilicity on the phenoxy ring, especially on ortho-position, cor-
relates with improved inhibitory activity. As can be observed,
introduction of 2-methyl group resulted in an inhibitor (4e,
17 nM) with >20-fold improvement in potency. The impact was
less pronounced with relatively more hydrophilic methoxy ana-
logue (4f, 81 nM). Meta-substitution was also well tolerated as
exemplified with compound 4g (20 nM), although not as optimal
as ortho-substituted analogue 4c (<4 nM). To explore any addi-
tional lipophilic interaction, we introduced a fluoride at the 4, 5
or 6-position on the basis of 4c. As shown in Table 1, 2,4-di-substi-
tuted analogue 4j was able to maintain most of the potency
observed with 4c, whereas 2,6-di-substitution surrendered all the
gain generated from 2-mono-substitution (4h, 330 nM vs 4a,
370 nM). The co-presence of F at 5-position was found to be bene-
ficial as 2,5-analogue 4i exhibited about twofold potency improve-
ment in human SCD1 (4i, hSCD1 IC50 = 18 nM vs 4c, hSCD1
IC50 = 37 nM).
O
O
O
NH
O
O
O
N
N
CF3
L
N
N
CF3
NH
NH
NH
3a meta-, IC50 = 0.7 μM(mSCD1)
3b para-, IC50 > 10 μM(mSCD1)
2
L: linker
Figure 1. Rational design of novel piperidine-aryl urea-based stearoyl-CoA desat-
urase 1 (SCD1) inhibitors
1a with a urea group. This modification allowed the maximum
conservation of the polarity and geometry of the aminopyridine
in 1a yet led to a new chemotype. Although trans-olefin appears
to be a rational linkage to hold the rest of molecule in place, 2 is
obviously not a suitable synthetic target due to its instability. We
thus introduced a benzene ring next to the urea. Both meta and
para substituted derivatives (3a, 3b) have been constructed to
probe the favorite orientation. 3a, with meta-methylamide,
provided a very promising IC50 against mSCD1 (0.7 lM), while
para-substituted analog 3b failed to demonstrate any potency in
the same assay. We quickly found that piperazine benzamide can
be successfully replaced by piperidine ether without losing any
potency (4a, IC50 = 0.4 lM). Compound 4a features some advanta-
geous characteristics as our lead compound. It carries several open
sites that can be readily modified to build SAR; the piperidine-aryl
urea-based scaffold has not been exploited extensively, and its
analogs might have improved pharmacokinetic profiles.
The synthesis of newly designed SCD1 inhibitors is straightfor-
ward and is outlined in Scheme 1. Mitsunobu reaction was
followed by Boc-deprotection with HCl/dioxane to produce 4-phe-
noxypiperidine 5. Compound 4a–m was synthesized through a
two-step, one-pot reaction. Thus, readily available aniline 6 was
transformed to isocyanate 7 in the presence of triphosgene. Treat-
ment of intermediate 7 in situ with appropriate 4-phenoxypiperi-
dine 5 proceeded smoothly to afford urea 4a–m. In the case of 4l,
O
O
HN
O
N
O
f
a
b
N
OH
e
R
R
O
R
O
5
O
N
O
NH2
N C O
NH
R'
R'
R'
d
4a-m
6
7
NH2
NO2
NO2
c
N
N
Cl
O
O
O
6l
N
N
O
O
N
O
Cl
N
O
Cl
N
C O
f, g
HO
h
NH
NH
EtO
HN
R"
O
4n-q
8
O
O
Scheme 1. Reagents and conditions: (a) phenols, Ph3P, DEAD, THF, rt; (b) 4 N HCl in dioxane, rt; (c) acetamide oxime, Et3N, CH3CN, microwave 150 °C, 15 min; (d) SnCl2Á2H2O,
ethanol, reflux, 1 h; (e) triphosgene, diisopropyethylamine, THF, rt, 5 min; (f) 4-phenoxypiperidine, THF, rt, 1 h; (g) 2 N NaOH, THF, MeOH, rt, overnight; (h) corresponding
amines, TBTU, diisopropylethylamine, DMF, rt.

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Z. Xin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4298–4302
Table 1
SAR summary of SCD-1 inhibitors 4a–q
Compound
Structure
mSCD1 IC50
(l
M)a
hSCD1 IC50
4.0 1.1
(l
M)a
O
HN
O
N
O
4a
0.37 0.25
NH
O
HN
O
N
O
F
4b
0.098 0.047
0.68 0.23
NH
O
HN
O
N
N
N
N
O
O
O
O
Cl
Br
4c
4d
4e
4f
<0.004
0.037 0.017
0.030 0.013
0.12 0.01
1.9 0.2
NH
O
HN
O
<0.004
NH
O
HN
O
0.017 0.013
0.081 0.039
0.020
NH
O
HN
O
OMe
NH
O
HN
O
N
O
4g
0.27 0.04
NH
Cl
O
HN
O
N
N
O
Cl
4h
4i
0.33 0.11
9.7 0.3
NH
F
O
HN
O
O
F
Cl
<0.004
0.018 0.011
NH
O
HN
O
N
O
Cl
F
4j
0.006 0.000
0.058 0.037
NH
O
N
O
Cl
O
4k
4l
0.59 0.13
7.5 1.1
NH
N
O
N
O
N
0.008 0.002
0.11 0.03
N
Cl

Z. Xin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4298–4302
4301
Table 1 (continued)
Compound
Structure
mSCD1 IC50
(l
M)a
hSCD1 IC50 (l
M)a
NH
N
O
N
N
O
Cl
4m
4n
4o
4p
0.010 0.006
0.010 0.00
0.008 0.002
0.81 0.18
>10
0.36 0.10
O
H2N
O
N
O
Cl
Cl
0.059 0.012
0.15 0.09
7.1 2.9
>10
NH
O
HN
O
N
O
NH
O
HN
HN
O
N
O
Cl
NH
O
O
4q
N
O
Cl
NH
a
Values are geometric means of at least two experiments, standard error is given in parentheses.
In general, this series of SCD1 inhibitors features favorable
pharmacokinetic profiles in rodents, characterized by modest vol-
ume of distribution and high oral bioavailability in mice (4c,
CLp = 0.4 L/h/kg; Vss = 0.4 L/kg; F = 92%).
0.6 lM). Fine-tuning of amide derivatives indicated that only pri-
mary amide or small group of secondary amide such as ethylamide
was favorable with comparable IC50 to 4c. Bulky group was detri-
mental to the activity as 4q showed no inhibition at 10 lM.
Based on the encouraging results associated with compound 4c,
we next investigated the replacement of amide group with a het-
erocyclic moiety to further improve SCD1 inhibitory activity. This
modification yielded a couple of analogues with good retention
of IC50 (4l, 8 nM; 4m, 10 nM), although they offered no potency
advantage over 4c. The presence of a functional group on the aryl
3-position seems to be important to possess high potency, as un-
substituted analogue showed dramatic loss of activity (4k,
Since SCD1 activity depends on cytochrome b5 and cytochrome
b5 reductase, we established a selectivity assay to exclude the pos-
sibility that compounds identified as SCD1 inhibitors may actually
inhibit the co-enzyme. The lack of inhibition above the concentra-
tion of 10 lM supports the direct SCD inhibition by our urea-based
chemotype, represented by compound 4c.
We next investigated the selectivity profiles of our potent inhib-
itors. Excellent selectivity over kinases was routinely achieved. 4c
Liver Desaturation index
Plasma Desaturation Index
25.00
45.00
obob vehicle
obob vehicle
40.00
30 mpk 4b
30 mpk 4b
20.00
10 mpk 4c
35.00
10 mpk 4c
lean vehicle
15.00
lean vehicle
30.00
25.00
20.00
15.00
10.00
5.00
10.00
5.00
0.00
0.00
DI 16:1/16/0
DI 18:1n9/18:0
DI 16:1/16/0
DI 18:1n9/18:0
Figure 2. Liver and plasma triacylglycerol desaturation index lowering effect with the treatment of SCD1 inhibitors 4b and 4c in ob/ob mice.

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Z. Xin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4298–4302
was also tested in a 3H-Dofetilide binding assay and showed no sig-
nificant hERG channel blockade activity (IC50 > 100 M).
References and notes
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SCD1 inhibitors 4b and 4c were evaluated in a 5-day efficacy
study using ob/ob mice. A desaturation index, calculated as the
ratio of 16:0/16:1n7 or 18:0/18:1n9, was used as in vivo bio-
marker for activity. The lipid classes examined include choles-
terol ester, diacylglycerol, free fatty acid, free cholesterol, total
phospholipids, and triacylglycerol. 4b (30 mpk bid) and 4c (10
mpk bid) consistently reduced desaturation indices of all these
lipid categories to lean level, or even lower. Figure 2 showed
the desaturation index (18:0/18:1n9) lowering effect with the
treatment of SCD1 inhibitors 4b and 4c. A dose dependent tri-
glyceride desaturation index reduction by 4c was also observed
in ob/ob mice (data not shown). These observations demon-
strated a clear correlation between in vitro activity and in vivo
desaturation index.
In conclusion, we have discovered a series of highly potent and
selective SCD1 inhibitors with excellent pharmacokinetic profiles
based on de novo design. Representative SCD1 inhibitors from this
class demonstrated in vivo efficacy with dose-dependent desatura-
tion index lowering effect. The pharmacology data from chronic
studies will be reported in due time.
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We thank the R4EK staff for pharmacokinetic studies, the R46Y
protein expression/purification group for providing insect cells
co-expressing human SCD1, human cytochrome b5 and human
cytochrome b5 reductase.
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Supplementary data
Experimental procedures for the synthesis and spectral charac-
terization of reported compounds 4a–q in Table 1, the detailed pro-
tocols of mouse SCD1 and human SCD1 assays can be found in the
online version. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.bmcl.2008.06.088.
22. Zhao, H.; Serby, M. D.; Smith, H. T.; Cao, N.; Suhar, T. S.; Surowy, T. K.; Camp, H.
S.; Collins, C. A.; Sham, H.; Liu, G. Bioorg. Med. Chem. Lett. 2007, 17, 3388.
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