Lead optimization of a pyridine-carboxamide series as DGAT-1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2012.12.040

The structure-activity relationship studies of a novel series of carboxylic acid derivatives of pyridine-carboxamides as DGAT-1 inhibitors is described. The optimization of the initial lead compound 6 based on in vitro and in vivo activity led to the disc

Full text of DOI:10.1016/j.bmcl.2012.12.040

Bioorganic & Medicinal Chemistry Letters 23 (2013) 985–988
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Lead optimization of a pyridine-carboxamide series as DGAT-1
inhibitors
a
a
a
a
b
Pauline C. Ting a, , Joe F. Lee , Nicolas Zorn , Hyunjin M. Kim , Robert G. Aslanian , Mingxiang Lin ,
⇑
Michelle Smith c, Scott S. Walker c, John Cook c, Margaret Van Heek c, Jean Lachowicz c
a Department of Chemical Research, Merck Research Laboratories, 126 E. Lincoln Ave., Rahway, NJ 07065, USA
b Department of Drug Metabolism, Merck Research Laboratories, 126 E. Lincoln Ave., Rahway, NJ 07065, USA
c Department of Biological Research, Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The structure–activity relationship studies of a novel series of carboxylic acid derivatives of pyridine-car-
boxamides as DGAT-1 inhibitors is described. The optimization of the initial lead compound 6 based on
in vitro and in vivo activity led to the discovery of key compounds 10j and 17h.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 16 October 2012
Revised 7 December 2012
Accepted 13 December 2012
Available online 21 December 2012
Keywords:
DGAT-1 inhibitor
Inhibition of triacylglycerol synthesis
Treatment for obesity and diabetes
Obesity is a serious health risk that is characterized by an excess
accumulation of triglycerides (TG) and can lead to a number of
additional conditions including type 2 diabetes, atherosclerosis,
hypertension, and cardiovascular disease.1 Dietary TGs are broken
down in the gut to monoacylglycerol and then absorbed in the
small intestines. TGs are then reassembled with the sequential
addition of two acyl chains. The final step of TG synthesis is cata-
lyzed by the enzyme acyl CoA: diacylglycerol acyltransferase
(DGAT) of which there are two forms.2 Although both DGAT-1
and DGAT-2 are transmembrane proteins found in white adipose
tissue, small intestine, liver, and mammary gland, they are from
different gene families with distinctive functions. DGAT-1 knock-
out mice are viable, exhibit resistance to weight gain when fed a
high-fat diet, have increased insulin sensitivity, and have increased
leptin sensitivity.3 In contrast, DGAT-2 has an essential role since
these knockout mice are not viable due to lipopenia and skin
homeostasis abnormalities.4 DGAT-1 is a member of the acyl
CoA: cholesterol acyltransferase (ACAT) gene family and is more
homologous with ACAT-1 and ACAT-2 than with DGAT-2 which
is more closely related to the monoacylglycerol acyl transferase
(MGAT) enzymes.2 With the resistance to weight gain and positive
physiological effects seen in DGAT-1 null mice, an inhibitor of
DGAT-1 may be a useful therapy for obesity.
generation DGAT-1 inhibitors from Japan Tobacco, Pfizer, Bayer,
and Abbott are shown in Figure 1 and have a terminal carboxylic
acid moiety which mimics the fatty acid substrate of DGAT-1.14–17
Beginning with the non-carboxylic acid, oxazole DGAT-1 inhibitors
by Hoffman-LaRoche/Via Pharmaceuticals, our exploratory chem-
istry group began work on developing novel DGAT-1 inhibitors.18
Initial investigations led to the identification of the lead compound
6 with reasonable DGAT-1 inhibitory activity.
SAR optimization of compound 6 began with left hand side ana-
logs which were synthesized according to the route depicted in
Scheme 1.19 Addition of N-BOC-piperazine to 2-chloro-5-nitropyr-
idine 7 gave pyridyl-piperazine 8. Removal of the BOC protecting
group and reaction with 2-fluorophenyl isocyanate provided nitro
intermediate 9. Reduction of the nitro group by hydrogenation and
HATU promoted amide formation produced the target compound
10.
Representative examples of left hand side modifications are
summarized in Table 1. From a large screen of diverse substituents,
we found that the 2-piperidinyl-4-trifluoromethyl-oxazole ring
could be replaced by a bicyclic indole ring in compound 10a with
increased inhibition of the human DGAT-1 enzyme in our in vitro
screening assay.20 The bicyclic benzofuran ring in compound 10b
and benzothiophene ring in compound 10c exhibited further
improvement of DGAT-1 activity. The 3-trifluoromethyl substitu-
ent appeared to be a positive factor since the hydrogen analog
10d displayed lower activity relative to the methyl 10b, fluoro-
methyl 10e, and difluoromethyl 10f analogs. Substitution on the
phenyl ring of the benzofuran was tolerated in analogs 10g–k.
The discovery of a selective DGAT-1 inhibitor has been the
subject of a number of recent reviews and publications.5–13 First
⇑
Corresponding author.
E-mail address: pauline.ting@merck.com (P.C. Ting).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.12.040

986
P. C. Ting et al. / Bioorg. Med. Chem. Lett. 23 (2013) 985–988
Table 1
COOH
COOH
Replacement of oxazole left hand side in 10a–k
H2N
N
N
H2N
N
O
N
O
H
N
N
R
1
2
N
O
Pfizer
Japan Tobacco
O
N
N
F
H
N
N
10a-k
O
O
O
COOH
COOH
Compd.
R
hDGAT-1a IC50 (nM)
513
F
O
N
N
N
H
CF3
S
N
H
H
4
3
N
F
F
Abbott
6
Bayer
N
O
Me
CF
CF
3 H
N
O
3 H
N
10a
10b
190
25
N
N
N
O
N
O
OMe
O
Me
N
N
N
N
F
H
N
Me
N
O
Me
O
5
6
Hoffman-LaRoche / Via
IC50 = 513 nM
IC50 = 38 nM
10c
10d
10e
55
145
60
S
Figure 1. Selected examples of literature inhibitors for DGAT-1.
O
CH2F
O2N
O
CHF2
O2N
a
b, c
N
N
N
Cl
N
10f
10g
10h
10i
10j
40
39
N
BOC
O
7
8
Me
F
H
N
R
O2N
O
d, e
O
Me
N
N
F
N
F
MeO
Me
H
N
H
N
51
N
N
O
Me
10
9
O
O
42
Scheme 1. Reagents and conditions: (a) N-BOC-piperazine, Hunig’s base, DMF,
100 °C, 100%; (b) TFA, CH2Cl2, 100%; (c) 2-fluorophenyl isocyanate, Et3N, THF, reflux,
100%; (d) H2, PtO2, iPrOH, EtOAc, 92%; (e) RCOOH, HATU, Hunig’s base, DMF.
O
Me
Ph
103
O
Me
For the SAR optimization of the right hand side, it was decided
to explore the inclusion of the key carboxylic acid moiety present
in the original DGAT-1 inhibitors from Figure 1. Analogs were con-
structed by the synthetic routes outlined in Schemes 2 and 3. In
Scheme 2, the methylene-oxy linker was introduced by condensa-
tion of 2-chloro-5-nitro-pyridine 7 with 4-hydroxymethyl-piperi-
dine. Activation of alcohol 11 as the mesylate and subsequent
coupling with methyl 3-hydroxybenzoate provided intermediate
12. Standard hydrogenation of the nitro group, HATU promoted
amide formation, and hydrolysis of the ester produced target 13c
and similar analogs. The reverse oxy-methylene linker was
assembled by addition of 4-hydroxy-piperidine to 2-chloro-5-ni-
tro-pyridine 7 (Scheme 3). Subsequent alkylation with methyl 3-
(bromomethyl)benzoate yielded intermediate 15 which was
converted to target 13e by the usual steps.
10k
24
O
Me
Me
a
Assay values are the average of at least two independent determinations.
O2N
O2N
b, c
a
N
N
N
Cl
OH
7
11
H
N
O2N
R
d, e, f
COOMe
O
N
N
N
N
O
O
COOH
13
12
Selected biological data are collated in Table 2. Compounds
which were active in the in vitro assay (IC50 <100 nM) were subse-
quently tested in the in vivo mouse postprandial triglyceride
(PPTG) assay.21 Our first discovery was that introduction of the car-
boxylic acid in the urea analog 13a exhibited an increase in biolog-
ical activity and a significant increase in blood levels. Replacement
of the urea linker by a methylene ether linker (analogs 13b–d)
indicated a preference for the carboxylic acid at the meta position
in 13c. The reverse oxy-methylene linker in 13e displayed slightly
lower biological activity. Substituting the piperidine ring with a
pyrrolidine ring in analogs 13f–g or inserting a methylene linker
to the carboxylic acid in 13h did not improve inhibition of the
DGAT-1 enzyme.
Scheme 2. Reagents and conditions: (a) 4-hydroxymethyl-piperidine, Hunig’s base,
DMF, 100 °C, 100%; (b) CH3SO2Cl, Et3N, CH2Cl2, 0 °C to rt, 100%; (c) methyl 3-
hydroxybenzoate, NaH, DMF, 90 °C, 78%; (d) H2, PtO2, iPrOH, EtOAc, 100%; (e)
RCOOH, HATU, Hunig’s base, DMF; (f) LiOH, H2O, MeOH, THF, reflux.
phenyl ring 16b–c resulted in a decrease in DGAT-1 inhibition.
These analogs were synthesized by the route depicted in Scheme
2 using 2-chloro-5-nitropyrimidine, 1-fluoro-4-nitrobenzene, or
1,2-difluoro-4-nitrobenzene as starting reagents.
With the identified 2-pyridinyl-4-piperidinyl-methoxybenzoic
acid right hand side, reoptimization of the left hand side was sur-
veyed, and key analogs are presented in Table 4. Compound 13c
demonstrated selectivity over hDGAT-2 (IC50 = 1.3
(IC50 = 4.7 M), and hACAT-1 (IC50 = 0.8 M) and revealed no hERG,
PXR, or liver enzyme (2D6, 3A4, and 2C9) inhibition issues.
lM), hACAT-2
The central pyridine ring appeared to be important for biologi-
cal activity (Table 3). Substitution by a pyrimidine ring 16a or
l
l

P. C. Ting et al. / Bioorg. Med. Chem. Lett. 23 (2013) 985–988
987
Table 3
O2N
O2N
Replacement of pyridine ring in 16a–c
b
a
N
N
O
N
Cl
OH
N
7
14
Me
O
O
COOH
H
N
H
N
N
O2N
R
X
O
c, d, e
16a-c
N
N
N
COOMe
COOH
hDGAT-1a IC50 (nM)
O
Compd.
X
O
13e
15
13c
52
240
774
Scheme 3. Reagents and conditions: (a) 4-hydroxy-piperidine HCl, Hunig’s base,
DMF, 100 °C, 97%; (b) methyl 3-(bromomethyl)benzoate, NaH, nBu4NI, THF, reflux,
58%; (c) H2, PtO2, iPrOH, EtOAc, 100%; (d) RCOOH, HATU, Hunig’s base, DMF; (e)
LiOH, H2O, MeOH, THF, reflux.
N
N
16a
16b
N
Table 2
Replacement of phenyl urea piperazine right hand side in 13a–ha
16c
482
F
a
Assay values are the average of at least two independent determinations.
Me
H
N
O
O
N
R
13a-h
Table 4
Replacement of benzofuran left hand side in 17a–ka
Compd.
R
hDGAT-1a
IC50 (nM)
mPPTGb
3 mg/kg
AUC (0–6 h)
M h
10 mg/kg po
H
l
R
N
O
N
N
O
COOH
F
N
N
H
N
17a-k
N
N
10j
103
70
À32%
À51%
0.44
hDGAT-1a
IC50 (nM)
mPPTGb
3 mg/kg
AUC (0–6 h)
10 mg/kg po
lM h
O
O
Compd.
R
COOH
COOH
H
N
13a
7.5
Me
13c
17a
17b
17c
52
33
À64%
À32%
NT
0.23
NT
O
N
N
N
O
O
O
13b
13c
311
52
NT
NT
Me
S
COOH
À64%
0.23
N
N
Me
O
344
194
NT
O
13d
13e
280
125
NT
NT
2.3
Me
S
COOH
COOH
NT
NT
O
N
N
CF3
À47%
O
N
17d
79
À36%
4.1
O
N
Me
13f
152
119
NT
NT
NT
NT
O
COOH
COOH
17e
17f
116
460
À29%
15.0
NT
13g
O
N
N
NT
N
O
O
13h
120
NT
NT
COOH
17g
17h
54
29
À10%
À63%
7.0
NT = not tested.
11.2
a
O
O
Assay values are the average of at least two independent determinations.
n = 8 Mice.
b
17i
392
NT
NT
Substitution of the 5-phenyl-benzofuran 13c with the 5-phenyl-
thiophene 17a showed a slight decrease of in vivo activity. Conver-
sion of the 5-phenyl-benzofuran 13c to the 5-oxazole-benzofuran
O
O
17j
149
41
NT
NT
6.7
17b or 5-thiazole-benzofuran 17c produced
a decrease in
17k
À35%
DGAT-1 activity. Compound 17d which incorporated our original
piperidinyl-oxazole left hand side was not superior to the 5-phe-
nyl-benzofuran moiety. Replacement of the 5-phenyl-benzofuran
13c with the napthalene analog 17e or quinoline analog 17f also
resulted in a decrease in biological activity. While the biphenyl
ether compounds 17g–h both exhibited good in vitro DGAT-1
inhibition and similar rat pharmacokinetic profiles, the meta
substituted analog 17h showed better in vivo activity in the mouse
NT = not tested.
a
Assay values are the average of at least two independent determinations.
b
n = 8 Mice.
PPTG assay. Target compound 17h was selective over hDGAT-2
(IC50 >50 M), hACAT-2 (IC50 >40 M), and hACAT-1 (IC50 = 3 M),
presented no hERG or PXR issues, but did slightly inhibit liver
l
l
l

988
P. C. Ting et al. / Bioorg. Med. Chem. Lett. 23 (2013) 985–988
11. Bali, U.; Barba, O.; Dawson, G.; Gattrell, W. T.; Horswill, J. G.; Pan, D. A.; Procter,
enzymes 3A4 and 2C9 (IC50 = 5 lM). In comparison to the ether
M. J.; Rasamison, C. M.; Sambrook-Smith, C. P.; Taylor-Warne, A.; Wong-Kai-In,
P. Bioorg. Med. Chem. Lett. 2012, 22, 824.
compounds 17g–h, the keto analog 17i and extended ether analog
17j demonstrated reduced activity. The alkylphenyl ether 17k dis-
played lower in vivo activity while retaining reasonable blood
levels.
In conclusion, novel DGAT-1 inhibitors based on a pyridine-car-
boxamide core have been discovered. Systematic SAR investigation
has optimized the original lead compound 6 into compounds 13c
and 17h. Both compounds 13c and 17h exhibit selectivity for
hDGAT-1, lower triglyceride levels at a 3 mg/kg dose in our
in vivo mouse PPTG assay, and exhibit minimal off-target issues.
Additional SAR results will be the subject of future publications.
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