p38 inhibitors: Piperidine- and 4-aminopiperidine-substituted naphthyridinones, quinolinones, and dihydroquinazolinones

Article abstract of DOI:10.1016/S0960-894X(02)00990-3

We have synthesized a series of C7-piperidine- and 4-aminopiperidine-substituted naphthyridinones, quinolinones, and dihydroquinazolinones that are highly potent inhibitors of both p38 MAP kinase activity and TNF-α release. The 4-aminopentamethylpiperidin

Full text of DOI:10.1016/S0960-894X(02)00990-3

Bioorganic & Medicinal Chemistry Letters 13 (2003) 467–470
p38 Inhibitors: Piperidine- and 4-Aminopiperidine-Substituted
Naphthyridinones, Quinolinones, and Dihydroquinazolinones
Julianne A. Hunt,a,* Florida Kallashi,a Rowena D. Ruzek,a Peter J. Sinclair,a Ida Ita,a
Sherrie X. McCormick,a James V. Pivnichny,a Cornelis E. C. A. Hop,b Sanjeev Kumar,b
Zhen Wang,b Stephen J. O’Keefe,c Edward A. O’Neill,c Gene Porter,c
James E. Thompson,c Andrea Woods,c Dennis M. Zallerc and James B. Dohertya
aDepartment of Medicinal Chemistry, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
bDepartment of Drug Metabolism, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
cDepartment of Inflammation and Rheumatology, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
Received 3 September 2002; accepted 15 October 2002
Abstract—We have synthesized a series of C7-piperidine- and 4-aminopiperidine-substituted naphthyridinones, quinolinones, and
dihydroquinazolinones that are highly potent inhibitors of both p38 MAP kinase activity and TNF-a release. The 4-aminopenta-
methylpiperidine naphthyridinone 5, which was designed to block metabolism at major ‘hot spots’, combined excellent inhibitory
potency with good oral bioavailability in the rat.
# 2002 Elsevier Science Ltd. All rights reserved.
The p38 MAP kinase regulates the release from leuko-
cytes of IL-1 and TNF-a, two cytokines that are asso-
ciated with the progression of rheumatoid arthritis
(RA). Inhibitors of p38 activity are known to suppress
the release of these cytokines, and thus could be valu-
able in the treatment of RA.1 We have previously
this compound pointed to metabolism at the C4
benzylic position alpha to the urea moiety (Fig. 1).
Thus, we decided to synthesize the analogous dihy-
droquinolinone 2, in which the urea was replaced by an
amide; and the quinolinone 3 and 1,6-naphthyridinone
4, each with an sp2 center at C4.
described
a series of piperidine-substituted dihy-
droquinazolinones (e.g., 1) that are potent and selective
inhibitors of p38 activity and TNF-a release; unfortu-
nately, these compounds showed poor pharmacokinetic
properties.2 We have therefore developed a related ser-
ies of piperidine-substituted quinolinones (e.g., 3) and
naphthyridinones (e.g., 4 and 5) with improved phar-
macokinetic properties. Of these compounds, the 4-
amino-pentamethylpiperidine naphthyridinone 5 proved
to be a potent inhibitor of p38 activity and TNF-a release
with good oral bioavailability (F%=44) in the rat.
Isopropyl piperidine-substituted dihydro quinazolinone
1 is an excellent inhibitor of p38 activity and TNF-a
release;3 however, this compound showed low oral
bioavailability and high clearance in both rat and rhesus
monkey (Table 1). Identification of the metabolites of
*Corresponding author. Tel.: +1-732-59-0463; fax: +1-732-594-9473;
e-mail: julianne_hunt@merck.com
Figure 1. Inhibitors of p38 activity.
0960-894X/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00990-3

468
J. A. Hunt et al. / Bioorg. Med. Chem. Lett. 13 (2003) 467–470
Table 2. Comparison of analogous 4-aminopiperidine-substituted
naphthyridinones (5 and 6) and dihydroquinazolinones (7)
Table 1. Isopropyl piperidines
Compd p38 IC50 (nM) TNF-a IC50 (nM) F (%) Clp (mL/min/kg)
Compd
p38a
TNF-a nAUCiv
Clp
t1/2 F (%)
1
2
3
4
0.6
0.8
0.2
1.3
5.6
24
5.5
4.9
16
10
17
32
84
70
39
51
IC50 (nM) IC50 (nM) (mM h) (mL/min/kg) (h)
6a
7a
6b
7b
6c
7c
6d
7d
5
0.2
0.5
1.1
1.6
0.4
0.4
0.8
3.7
1.1
18
36
51
31
24
20
10
200
13
0.82
3.38
2.78
38
9.4
11
2.6
2.7
8.5
5.9
As shown in Table 1, dihydroquinolinone 2 was a less
potent inhibitor of TNF-a release than the lead 1, and
showed no clear advantage in pharmacokinetic proper-
ties. However, both quinolinone 3 and 1,6-naphthyr-
idinone 4, while maintaining similar potency to 1,
showed significantly lower clearance in the rat, and in
the case of 4, a 2-fold increase in rat oral bioavailability.
This improvement in pharmacokinetic parameters
encouraged us to further investigate the 1,6-naphthyr-
idinone scaffold for p38 inhibitors.
3.4 44
Table 3. Pharmacokinetics of pentamethylpiperidine naphthyr-
idinone 5 in three animal species
Species nAUCiv
(mM h)
Clp (mL/
min/kg)
Vdss
(L/kg)
t1/2
(h)
nAUCpo
(mM h)
F (%)
Rat
Rhesus
Dog
2.78
0.64
0.68
11
46
45
3.2
19.5
19.8
3.4
5.0
3.7
1.2
0.08
0.04
44
13
5
Because of both synthetic accessibility (see below) and
promising biological activity, we focused on the synth-
esis and structure–activity relationships of a family of
C7-aminopyridines, represented by the generic structure
6 (Fig. 2). In light of our previous work with other p38
inhibitor scaffolds,1b,2 we were not surprised to discover
that piperidine substituents at C7 are potency-enhan-
cing. A representative group of 4-aminopiperidine-sub-
aminopiperidine- substituted naphthyridinones. Stabi-
lizing the C4 benzylic position with an sp2 center mark-
edly
lowered
clearance
and
improved
oral
bioavailability in the naphthyridinones as compared to
the analogous dihydroquinazolinones (Table 1). Meta-
bolite identification for dihydroquinazolinone 1 pointed
to further metabolism at the C7 piperidine ring. We
reasoned that blocking metabolism at both C4 and the
two positions alpha to the piperidine nitrogen would
further improve the pharmacokinetics of these com-
pounds. Analysis of the pharmacokinetic properties of
three naphthyridinones shown in Table 2, 6c, 6d, and 5,
corroborates this hypothesis.
stituted naphthyridinones
6 are paired with the
analogous dihydroquinazolinones 7 in Figure 2 and
Table 2. These 4-aminopiperidines are all excellent
inhibitors of p38 activity, and in all cases, the naph-
thyridinones are as potent as, or more potent than, the
analogous dihydroquinazolinones.
Having shown that the naphthyridinones equalled or
surpassed the dihydroquinazolinones as inhibitors of
p38 activity and TNF-a release, we turned next to an
examination of the pharmacokinetic properties of the 4-
Our initial attempt at an a,a0-stabilized piperidine, tro-
pine amine 6c (conformational constraints on the tro-
pine ring system prevent imine formation), showed
clearance similar to that of the isopropyl piperidines,
and had poor oral bioavailability, most likely because of
metabolism at the tropine N-methyl. In contrast,
a,a,a0,a0-tetramethylpiperidine 6d had low clearance, a
reasonable half-life, and good intravenous bioavail-
ability, but this compound had disappointingly poor
oral bioavailability. Fortunately, methylation of the free
piperidine to provide 5 resulted in a compound with low
clearance, a respectable half-life, and good oral bioa-
vailability in the rat.
The pharmacokinetics of compound 5 were next studied
in the rhesus monkey and the dog. As shown in Table 3,
the promising pharmacokinetic properties seen in the
rat did not translate to the monkey or dog: Clearance
was much higher and bioavailability much lower in the
latter two species.
Metabolite identification for naphthyridinone 5 eluci-
dated the key pathways for metabolic degradation of
this compound. Primarily, the piperidine N-methyl was
demethylated in all species (leading to compound 6d).
Oxidation followed by phase II conjugation at the
Figure 2. 4-Aminopiperidine-substituted naphthyridinones (5 and 6)
and dihydroquinazolinones (7).

J. A. Hunt et al. / Bioorg. Med. Chem. Lett. 13 (2003) 467–470
469
2-chlorophenyl ring constituted a second significant
metabolic pathway. Interestingly, a third major path-
way involved rearrangement of the tetramethyl-
piperidine substituent to a ring-contracted pyrrolidine
analogue. Because tetramethylpiperidine N-oxide
(TEMPO) is known to be a stabilized radical, it is likely
that the pyrrolidine metabolite arises via oxidation of
the piperidine nitrogen followed by rearrangement of a
radical intermediate.
tetrahydropyridine 14, reduction of the tetra-
hydropyridine double bond,4 BOCdeprotection, and
reductive alkylation with acetone.
The naphthyridinone core 19 was synthesized from
pyridine 175 (Fig. 5) via elaboration to the methyl pro-
pionate, aluminum-mediated amidation to form 18, and
Ullmann cyclization to the corresponding dihy-
dronaphthyridinone.
Oxidation
of
the
dihy-
dronaphthyridinone via benzylic bromination followed
by DBU-promoted elimination6 provided 7-bromo-
naphthyridinone 19, which was elaborated to the iso-
propyl piperidine 4 as described above for compounds 2
and 3.4 The C7-amino-substituted naphthyridinones of
structure class 6 (see Fig. 2) were prepared by heating
compound 19 with the appropriate amine (neat or as a
DMSO solution, 130 ꢀC) to effect nucleophilic substitu-
tion of the C7-bromine of 19.7
Synthesis
Preparation of the dihydroquinolinone core of 2 (Fig. 3)
followed the outline of the dihydroquinazolinone
synthesis described previously.2 Benzylic bromination of
2,6-dibromo-4-methoxytoluene 8 followed by alkylation
with t-butyl acetate and acidolysis of the resulting t-
butyl propionate provided the corresponding propionic
acid. Amidation of this acid (via the acid bromide) with
2,6-dichloroaniline provided amide 9, which cyclized to
dihydroquinolinone 10 under standard Ullmann cou-
pling conditions.2 Suzuki coupling with 2-chloro-4-
fluorophenylboronic acid provided the required dihy-
droquinolinone core 12, poised for elaboration at the
C7 position. Oxidation of 10 via benzylic bromination
followed by spontaneous elimination provided quinoli-
none 11, which was elaborated via Suzuki coupling with
2-chlorophenylboronic acid to provide the analogous
quinolinone core 13.
Finally,
quinazolinones of structure class 7 were prepared via a
the
C7-amino-substituted
dihydro-
modification of our original dihydroquinazolinone
Installment of the C7 isopropyl piperidine followed the
same route for both the dihydroquinolinone core 12 and
the quinolinone core 13 (Fig. 4). Conversion of the C7-
methoxy to the corresponding hydroxy compound was
achieved with BBr3, and the hydroxy moiety was acti-
vated as the triflate. Elaboration to isopropyl piper-
idines 2 and 3 proceeded by Stille coupling with N-BOC
Figure 4. Synthesis of C7 isopropyl piperidines 2 and 3.
Figure 5. Synthesis of the naphthyridinone core 19 and isopropyl
piperidine 4.
Figure 3. Synthesis of the dihydroquinolinone and quinolinone cores.

470
J. A. Hunt et al. / Bioorg. Med. Chem. Lett. 13 (2003) 467–470
demethylation at the piperidine N-methyl, radical-medi-
ated rearrangement of the piperidine ring, and oxidation
followed by conjugation of the 2-chlorophenyl ring,
allowed us to design compounds which would not suffer
from the metabolic fate of naphthyridinone 5. We will
describe the synthesis and biological properties of these
compounds in a subsequent publication.8
Acknowledgements
The authors gratefully acknowledge Dr. S. R. Natar-
ajan for providing intermediate 17.
References and Notes
1. (a) Liverton, N. J.; Butcher, J. W.; Claiborne, D. A.; Libby,
B. E.; Nguyen, K. T.; Pitzenberger, S. M.; Selnick, H. G.;
Smith, G. R.; Tebben, A.; Vacca, J. P.; Varga, S. L.; Agarwal,
L.; Dancheck, K.; Forsyth, A. J.; Fletcher, D. S.; Frantz, B.;
Hanlon, W. A.; Harper, C. F.; Hofsess, S. J.; Kostura, M.;
Lin, J.; Luell, S.; O’Neill, E. A.; Orevillo, C. J.; Pang, M.;
Parsons, J.; Rolando, A.; Sahly, Y.; Visco, D. M.; O’Keefe,
S. J. J. Med. Chem. 1999, 42, 2180, and references therein. (b)
Natarajan, S. R.; Wisnoski; D. D.; Singh; S. B.; Stelmach; J.
E.; O’Neill; E. A.; Schwartz; C. D.; Thompson; C. M.; Fitz-
gerald; C. E.; O’Keefe; S. J.; Kumar; S.; Hop; C. E. C. A.;
Zaller; D. M.; Schmatz; D. M.; Doherty; J. B. Bioorg. Med.
Chem. Lett. In press, and references therein.
2. Stelmach; J. E.; Liu; L.; Patel; S. B.; Pivnichny; J. V.; Sca-
pin; G.; Singh; S.; Hop; C. E. C. A.; Wang; Z.; Strauss; J. R.;
Cameron; P. M.; Nichols; E. A.; O’Keefe; S. J.; O’Neill; E. A.;
Schmatz; D. M.; Schwartz; C. D.; Thompson; C. M.; Zaller;
D. M.; Doherty; J. B. Bioorg. Med. Chem. Lett. In press.
3. For assay details, see ref 1b.
4. For both quinolinone 3 and naphthyridinone 4, the C7 tet-
rahydropyridine double bond was reduced selectively (<4 h
for 4, and <2 h for 3) in the presence of the C3–C4 double
bond by monitoring of the reaction progression.
5. Pyridine 17 was prepared from 2-chloro-3-methyl-5-nitro-
pyridine (Hawkins, G. F.; Roe, A. J. Org. Chem. 1949, 14,
328) via the following four steps: (1) 2-Cl-phenylboronic acid,
Cs2CO3, Pd(PPh3)4. (2) RaNi. (3) Br2, HCl. (4) t-BuONO.
Synthetic details will be provided: S. R. Natarajan et al.,
manuscript in preparation.
Figure 6. Synthesis of dihydroquinazolinones 7.
synthesis.2 As shown in Figure 6, benzylic bromination of
2,6-dibromo-4-nitrotoluene 20 followed by reaction with
4-methoxybenzylamine provided a PMB-protected amine,
which was treated with 2,6-dichloroisocyanate to give urea
21. Ullmann cyclization was followed by Suzuki coupling
with 2-chlorophenyl boronic acid, and the resulting 7-
nitrodihydroquinazolinone 22 was then reduced to the
corresponding 7-amino analogue. This amine was
reductively alkylated with the appropriate ketones and
then deprotected to provide compounds 7a–c.7
We have synthesized a series of C7-piperidine- and 4-
aminopiperidine-substituted naphthyridinones, quinoli-
nones, and dihydroquinazolinones that are highly
potent inhibitors of both p38 MAP kinase activity and
TNF-a release. The quinolinone and naphthyridinone
inhibitors showed markedly improved pharmacokinetic
properties over the lead compound 1 because of the
stabilization of a metabolic ‘hot spot’ at the C4 benzylic
position in the dihydroquinazolinone core.
6. The benzyl bromide was stable to flash chromatography,
however, the oxidation-elimination was performed in one pot.
7. Isopropyl piperidines 6b and 7b were prepared from 6a and
7a, respectively, by reductive alkylation with acetone.
8. Bao; J.; Hunt; J. A.; Miao; S.; Rupprecht; K. M.; Stelmach;
J. E.; Liu; L.; Ruzek; R. D.; Sinclair; P. J.; Pivnichny; J. V.;
Hop; C. E. C. A.; Kumar; S.; Zaller; D. M.; Shoop; W. L.;
O’Neill; E. A.; O’Keefe; S. J.; Thompson; C. M.; Doherty, J.
B. In preparation.
Naphthyridinone 5, in which both the C4 benzylic
position and the positions alpha to the piperidine nitro-
gen were blocked, had a particularly promising phar-
macokinetic profile in the rat. Disappointingly, this
promise was not fulfilled in other animal species. How-
ever, analysis of the metabolites of 5, which pointed to