Discovery of potent, selective, and orally bioavailable pyridone-based dipeptidyl peptidase-4 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2005.11.052

anti-Substituted β-methylphenylalanine derived amides have been shown to be potent DPP-IV inhibitors exhibiting excellent selectivity over both DPP8 and DPP9. The optimized compound exhibited good pharmacokinetic profiles in three preclinical species.

Full text of DOI:10.1016/j.bmcl.2005.11.052

Bioorganic & Medicinal Chemistry Letters 16 (2006) 1346–1349
Discovery of potent, selective, and orally bioavailable
pyridone-based dipeptidyl peptidase-4 inhibitors
Jinyou Xu,a,* Lan Wei,a Robert Mathvink,a Scott D. Edmondson,a Anthony Mastracchio,a
George J. Eiermann,c Huaibing He,a Joseph F. Leone,a Barbara Leiting,b
Kathryn A. Lyons,a Frank Marsilio,b Reshma A. Patel,b Aleksandr Petrov,c
Joseph K. Wu,b Nancy A. Thornberryb and Ann E. Webera
aDepartment of Medicinal Chemistry, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
bDepartment of Metabolic Disorders, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
cDepartment of Pharmacology, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
Received 11 October 2005; revised 14 November 2005; accepted 14 November 2005
Available online 5 December 2005
Abstract—anti-Substituted b-methylphenylalanine derived amides have been shown to be potent DPP-IV inhibitors exhibiting excel-
lent selectivity over both DPP8 and DPP9. The optimized compound exhibited good pharmacokinetic profiles in three preclinical
species.
Ó 2005 Elsevier Ltd. All rights reserved.
O
Glucagon-like peptide-1 (GLP-1) and glucose-depen-
dent insulinotropic polypeptide (GIP) are incretin hor-
mones that are released from the gut during meals and
serve as enhancers of glucose-stimulated insulin release
from pancreatic b cells.1 Chronic infusion of GLP-1 to
patients with type 2 diabetes resulted in significant
decreases in both blood glucose and hemoglobin A1c lev-
els;2 however, GLP-1 as well as GIP is rapidly degraded
in plasma by the serine protease dipeptidyl peptidase 4
(DPP-4). Inhibition of DPP-4 increases the levels of
endogenous intact circulating GLP-1 and GIP. Conse-
quently, inhibition of DPP-4 is rapidly emerging as a
novel therapeutic approach to the treatment of type 2
diabetes.3
F
F
F
N
NH2
O
NH2
N
N
F
N
N
F
1
CF3
sitagliptin
IC50(DPP-IV) = 18 nM
IC50(DPP-IV) = 64 nM
O
O
N
O
N
N
NH2
O
NH2
HN
N
F
H
F
3
O
2
IC50(DPP-IV) = 25 nM
IC50(DPP-IV) = 3 nM
Figure 1. Lead DPP-4 inhibitors.
Earlier reports from our laboratories described a series
of (R)-b-homophenylalanine-based dipeptidyl pepti-
dase-4 inhibitors lacking an electrophile.4 Our efforts
in that area culminated in the discovery of sitagliptin,
which is currently in the phase III clinical trials.5 In an
effort to discover a structurally diverse back-up com-
pound to sitagliptin, we designed and executed the initial
SAR studies of a novel series of anti-substituted biaryl
b-methylphenylalanine-based dipeptidyl peptidase-4
inhibitors.6 While lipophilic compounds in this series
such as 1 (Fig. 1) exhibited good oral bioavailability in
rats, they usually had poor selectivity over off-target en-
zymes such as quiescent cell proline dipeptidase (QPP)
and hERG.7 Incorporation of an acidic heterocycle at
the 30-position on the pendant phenyl group in 1 in-
creased potency against DPP-4 as well as selectivity over
QPP and hERG. However, incorporation of the polar
functionality was detrimental to pharmacokinetic prop-
Keyword: DPP-4 inhibitors.
*
Corresponding author. Tel.: +1 732 594 2217; e-mail: Jinyou_ Xu@
merck.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.11.052

J. Xu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1346–1349
1347
erties as evidenced by the extremely poor oral bioavail-
ability of 5-oxo-1,2,4-oxadiazole 2.6 These preliminary
results suggest that there is a fine balance among lipo-
philicity, selectivity, and oral bioavailability.
Inhibitors were tested for their selectivity profiles against
a variety of DPP-4 homologs and proline-specific en-
zymes including quiescent cell proline dipeptidase
(QPP/DPP-II), prolyl endopeptidase (PEP), amino pep-
tidase P (APP), prolidase, DPP8, and DPP9. Since sig-
nificant off-target activity was only observed with QPP
(<10,000 nM), QPP data are presented for comparison.9
Safety studies using a dual DPP8/DPP9 selective inhibi-
tor suggest that inhibition of DPP8 and/or DPP9 may be
associated with toxicity in preclinical species.10 Thus,
DPP8 and DPP9 data are also included for safety
reasons.
Replacement of the b-methyl group in 1 with a polar
substituent such as dimethylamide improved the poten-
cy, selectivity, and pharmacokinetic profile of this prom-
ising new series of DPP-4 inhibitors. However, these
compounds still suffered from poor selectivity over
hERG and a large serum shift.8 During the course of
our investigation, we discovered pyridone 3, which
exhibited a promising selectivity and pharmacokinetic
profile. The work described here summarizes our initial
efforts at optimizing the potency, selectivity, and oral
bioavailability of this novel series of pyridone-based
DPP-4 inhibitors. The optimized compound (9) exhibit-
ed good pharmacokinetic profiles in three preclinical
species.
With the goal of finding analogs of pyridone 3 with in-
creased potency and selectivity, initially we looked at the
effect of substitution on the pyridone nitrogen in 3. Ta-
ble 1 summarizes the DPP-4 inhibitory properties of
these a-aminoacid pyrrolidides. Unfortunately, substitu-
tion on the nitrogen was not tolerated as the potency de-
creased as the size of R increased. While N-methyl
pyridone 9 was slightly less potent than the unsubstitut-
ed analog 3, it showed improved PK properties and
selectivity over ion channels (see below). Thus, further
SAR studies were conducted on this lead.
The b-methylphenylalanine-based DPP-4 inhibitors
were prepared from the known aryl bromide 4 (Scheme
1).6 The route began with a Suzuki coupling reaction of
aryl bromide 4 with 4-methoxy-3-pyridinylboronic acid
to give biaryl compound 5. Demethylation of 5 with pyr-
idine hydrochloride followed by selective N-methylation
and deprotection of the tert-butylcarbamate thus pro-
vided pyridone 9. Alternatively, the aryl bromide 4
could be first converted to boronate 7, which was subse-
quently coupled to various aryl bromides as illustrated
by the synthesis of pyridone 15.
To further increase the potency and selectivity over
QPP, we next looked at substitution on the pendant
pyridone group in lead 9. The results are summarized
in Table 2. Substitution on the heteroaryl ring usually
had little effect or was detrimental to activity. Interest-
ingly, introduction of a bulky substituent at 6-position
usually improved the selectivity over QPP. Especially
noteworthy was compound 22 which exhibited excellent
selectivity over QPP.
MeO
a
N
Br
NHBOC
b
NHBOC
N
O
The effect of changing the right-hand side amide in this
series was next explored. In general, consistent with
what we observed in the related a-amino acid series,
only small changes were tolerated at the P1-site (Table
3).8,11 While 4- and 5-membered rings were well tolerat-
ed, a substantial drop in potency against DPP-4 was ob-
served with the 6-membered ring compound 30.
F
N
O
F
5
4
6
H
N
O
O
N
c, d
TFA-
+
NHBOC
NH3
N
O
N
F
F
O
9
Table 1. Effect of substitution on the pyridone nitrogen
O
O
Br
e
f
B
NHBOC
O
NHBOC
N
N
+
N
O
R
O
NH3
TFA-
F
F
N
O
F
4
7
O
N
F
O
N
F
g
TFA-
+
NHBOC
NH3
Compound
R
H
IC50 (lM)
N
O
N
DPP-IV
QPP
DPP8
DPP9
F
F
O
3
9
0.025
0.034
0.074
0.117
0.090
0.092
0.229
5.0
8.0
6.1
3.9
5.9
2.5
2.1
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
8
15
Me
Et
10
11
12
13
14
Scheme 1. Reagents and conditions: (a) ArB(OH)2, toluene, EtOH,
2 N Na2CO3, Pd(dppf)2Cl2, 90 °C; (b) PyHCl, 190 °C; (c) Cs2CO3,
MeI, DMF; (d) TFA/CH2Cl2, 1 h; (e) bis(pinacolato)diboron,
Pd(dppf)2Cl2, KOAc, DMF, 80 °C; (f) ArBr, toluene, EtOH, 2 N
Na2CO3, Pd(dppf)2Cl2, 90 °C; (g) TFA/CH2Cl2, 1 h.
cPr-CH2
CH2CO2Et
CF2CO2Et
4-FPh

1348
J. Xu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1346–1349
Table 2. Inhibitory properties of selected DPP-4 inhibitors
Table 4. Pharmacokinetic properties of selected DPP-4 inhibitors in
the rat (1/2 mpk iv/po) and hERG binding
O
Compound
Clp
(mL/min/kg)
t1/2
F
hERG IC50
(lM)
N
(h)
(%)
2
+
Me
O
NH3
TFA-
N
3
9
35.8
7.7
1.9
1.4
1.1
2.6
10
34
61
3
8.3
>100
>100
>100
F
6
R
15
22
11.2
68.1
Compound
R
H
IC50 (lM)
DPP-IV QPP
DPP8 DPP9
Table 5. Pharmacokinetic properties of compound 9 in the dog and
rhesus monkey (1/2 mpk iv/po)
9
15
16
17
18
19
20
21
22
23
24
25
0.034
0.029
0.32
8.0 >100 >100
2-F
2-Me
14
>100
>100
>100
>100
6.2 >100
9.0 >100
O
2-Me, 5-Br
5-F
5-Br
0.57
N
+
0.049
0.069
0.061
0.052
0.038
0.067
0.037
7.1
41.3 >100
M e
O
NH
3
-
7.4 >100
5.5 >100
>100
>100
>100
>100
>100
>100
59
N
TFA
F
6-F
6-Me
15
>100
24
>100
>100
>100
6-CH2OH
6-OMe
5-Cl, 6-F
Species
Clp (mL/min/kg)
t1/2 (h)
F (%)
4.5 >100
8.5 >100
5-F, 6-NHCO2Et 0.12
Dog
Rhesus
4.7
6.7
3.8
3.9
95
50
oral bioavailability. The most potent compound in this
series, 3, had demonstrable ion channel binding (hERG
binding Ki = 8300 nM). Pyridone 9 exhibited excellent
selectivity over ion channel binding and good oral bio-
availability in rat. Consequently, 9 was chosen for fur-
ther evaluation (Table 5). We were pleased to find that
9 showed excellent oral bioavailability in dogs and mon-
keys (95% and 51%, respectively). An oral glucose toler-
ance test (OGTT) was used to assess the ability of 9 to
improve glucose tolerance in mice. In lean animals, 9
was orally administered 1 h prior to dextrose challenge
and reduced blood glucose excursion in a dosage-depen-
dent manner from 1 mg/kg (33% reduction) to 10 mg/kg
(56% reduction).
Table 3. Effect of changing the right-hand side amide
O
X
+
Me
O
NH3
N
Compound
X
IC50 (lM)
DPP-IV QPP
DPP8 DPP9
N
N
9
26
27
28
29
30
0.034
0.026
0.048
0.026
0.031
1.1
8.0
>100
>100
>100
>100
>100
>100
>100
F
F
In summary, we have discovered a novel series of potent
and selective DPP-4 inhibitors. The optimized com-
pound 9 exhibited good pharmacokinetic profiles in
three preclinical species. In vitro and in vivo metabolism
studies revealed that N-demethylation occurred, leading
to the formation of the initial lead compound 3, which
had unacceptable hERG binding. Replacement of the
N-methyl pyridone with a less metabolically labile group
and improving the potency of 9 will be the focus of fu-
ture work in this series. These results will be reported
in due course.
0.55 >100
F
3.9
>100
N
N
N
N
0.81 >100
S
16
>100
>100
F
1.1
F
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