Synthetic approaches to 1,8-naphthyridine-2,5-dione compounds

Article abstract of DOI:10.1016/j.tetlet.2010.11.063

A novel, efficient route for the synthesis of 1,8-naphthyridine-2,5-dione compounds is reported. The synthetic scheme allows for diversification at the 4-position of the core, and it was utilized to develop a series of inhibitors for MEK kinase.

Full text of DOI:10.1016/j.tetlet.2010.11.063

Tetrahedron Letters 52 (2011) 477–479
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthetic approaches to 1,8-naphthyridine-2,5-dione compounds
⇑
Toufike Kanouni, Qing Dong, Benjamin Abelovski, Michael B. Wallace
Department of Medicinal Chemistry, Takeda San Diego, 10275 Science Center Drive, San Diego, CA 92121, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel, efficient route for the synthesis of 1,8-naphthyridine-2,5-dione compounds is reported. The syn-
thetic scheme allows for diversification at the 4-position of the core, and it was utilized to develop a ser-
ies of inhibitors for MEK kinase.
Received 25 October 2010
Revised 9 November 2010
Accepted 11 November 2010
Available online 18 November 2010
Ó 2010 Elsevier Ltd. All rights reserved.
There has been considerable interest recently in targeting the
inhibition of MEK (Mitogen-Activated Protein Kinase) kinases as
a potential strategy to control cell growth and to provide a treat-
ment for various cancers.1 Several MEK inhibitors are currently
being evaluated in clinical trials for oncology indications.2 During
the course of our recent medicinal chemistry efforts toward devel-
oping inhibitors of MEK, we became interested in designs built
upon a 1,8-naphthyridine-2,5-dione ring system (Fig. 1). Although
there have been a few reported syntheses of similar naphthyridin-
edione systems,3 the published procedures we evaluated arrived at
the naphthyridinedione through a 1,8-naphthyridine-4(1H)-one
intermediate, producing the dione either by hydrolysis of a chloro
or amino substituent or by demethylation of a methoxy group.
These approaches did not meet our needs for synthetic versatility
or for our specific requirements to incorporate aniline substituents
at the 4-position of the core. Therefore, we have developed a new
synthetic route in order to access the 1,8-naphthyridine-2,5-dione
core.
The synthesis of the naphthyridinedione ring system is outlined
in Scheme 1. The bis-thioether 1 was obtained in 43% yield from
the reaction of diethyl 3-oxopentanedioate with carbon disulfide
in the presence of potassium carbonate, followed by quenching
with methyl iodide.4 Reaction of intermediate 1 with an amine
led to methanethiol bis-displacement. When this displacement
was carried out with controlled addition at low temperature, any
cyclization of the mono-amine intermediate prior to the displace-
ment of the second sulfide was minimized. For synthetic simplic-
ity, it is preferable in this reaction scheme that R and R1 be
equivalent; otherwise the bis-thiol displacement reaction and sub-
sequent cyclization can lead to a mixture of aminopyridone prod-
ucts. As part of our SAR studies, the displacement reactions were
carried out with either methylamine or ethylenediamine. The
intermediate of the displacement reaction was then heated in eth-
anol, which allowed for cyclization to the pyridone compounds
2a,b.
Selective chlorination of the 4-hydroxyaminopyridones 2a,b
with phosphorous oxychloride gave compounds 3a,b in 81–87%
yield. The hydrolysis of esters 3a,b under basic conditions pro-
ceeded with a subsequent decarboxylation, yielding the amino-
pyridones 4a,b. The carboxylic acid intermediates were detected
over the course of the reaction, but decarboxylation was too rapid
for isolation of these compounds to be practical.
From the aminopyridones 4a,b,
a Gould–Jacobs reaction
sequence was utilized to construct the naphthyridinedione ring
system.5 Condensation of compounds 4a,b with dimethyl meth-
oxymethylenemalonate afforded the malonate compounds 5a,b,
which were cyclized to the naphthyridinediones 6a,b by heating
in polyphosphoric acid (PPA). The use of thermal methods6 or other
strong acids7 for the cyclization step proved to be less effective. Fi-
nally, acidic hydrolysis of the esters 6a,b gave the carboxylic acid
compounds 7a,b.
Table 1
Selected naphthyridinedione chloride displacement reactions
R3
R4
H
O
O
N
N
O
O
Cl
N
R3
R4
O
O
O
4
5
3
N
O
6
7
N
N
O
8 - 11
N
H
N
H
O
6a
2
8
1
Entry
R3R4NH
Temp (°C)
Time (h)
Yield (%)
8
9
10
11
Pyrrolidine
23
50
50
50
2
24
21
27
84
97
89
92
Figure 1. General structure of the 1,8-naphthyridine-2,5-dione core.
Diethylamine
Butylamine
Benzylamine
⇑
Corresponding author. Tel.: +1 858 731 3598; fax: +1 858 550 0526.
E-mail address: michael.wallace@takedasd.com (M.B. Wallace).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.11.063

478
T. Kanouni et al. / Tetrahedron Letters 52 (2011) 477–479
O
S
O
S
O
O
OH
O
Cl
O
O
O
c
a
b
O
O
O
O
O
O
HN
R
N
O
HN
R
N
R1
O
R1
1
2a
R = R1 = Me
2b R and R1 = -CH2CH2-
3a-b
Cl
Cl
N
O
Cl
O
Cl
O
O
g
d
O
O
f
HO
O
e
O
O
N
R
HN
R
N
R1
O
N
N
R
O
N
R
N
R1
O
R1
R1
O
7a R = R1 = Me
7b
5a-b
6a-b
4a-b
R and R1 = -CH2CH2-
Scheme 1. Synthesis of the naphthyridinedione ring system. Reagents and conditions: (a) 1—CS2, K2CO3, DMSO; 2—MeI (43%); (b) MeNH2 or H2NCH2CH2NH2, EtOH (46% for
2a, 86% for 2b); (c) POCl3, dimethylaniline (81–87%); (d) LiOH (69–75%); (e) dimethyl methoxymethylenemalonate, o-dichlorobenzene or bromobenzene, 150–170 °C
(55–61%); (f) PPA, 110 °C (67–72%); (g) H2SO4, H2O/HOAc (65–85%).
Displacement at the 4-position occurred readily with primary
F
I
or secondary amines (Table 1). The reaction of the intermediate es-
ter 6a with pyrrolidine occurred at ambient temperature within
2 h. Reactions with primary amines (benzylamine, butylamine) oc-
curred slowly at room temperature, but proceeded to completion
within 30 h when heated at 50 °C.
O
Cl
O
O
HN
O
HO
a
HO
N
R
N
R1
O
N
R
12a-b
N
R1
O
Derivitization of the naphthyridinedione intermediates 6a and
7a to make inhibitors of MEK kinase is shown in Scheme 2. At the
4-position, we sought to install a 2-fluoro-4-iodoaniline moiety, a
previously described recognition motif for the MEK allosteric site.8
The chloride displacement reactions with anilines, however, proved
to be less facile than with primary and secondary amines. Direct
displacement of the 4-position chloride of 7a,b with 2-fluoro-
4-iodoaniline under basic conditions gave 12a,b in an optimized
yield of 26%. These were then decarboxylated using the cyanide
mediated conditions of Reuman et al.9 to give compounds 13a,b.
A higher yield (76%) for the displacement step was obtained for
the reaction of 6a with 2-fluoro-4-nitroaniline using palladium
chemistry under Buchwald–Hartwig amination conditions.10 The
nitro group was reduced with zinc and converted into the iodide
using Sandmeyer reaction conditions. Chlorination of 14a with
N-chlorosuccinimide occurred selectively at the 3-position to give
compound 15a.
7a R = R1 = Me
7b R and R1 = -CH2CH2-
F
I
O
HN
b
N
R
N
R1
O
13a-b
F
I
O
N
Cl
N
O
N
HN
O
O
c
O
O
N
O
O
6a
14a
Several of the compounds synthesized were active against
MEK1 kinase, and the biological activities11 of selected compounds
(13a–15a, 13b) are shown in Table 2. These analogs showed
sub-micromolar activity against MEK in both enzymatic and cellu-
lar assays. In summary, we have established a new synthetic route
F
I
O
N
HN
d
O
Cl
O
N
O
Table 2
Selected MEK inhibition data for naphthyridinedione compounds
15a
Scheme 2. Synthesis of naphthyridinedione compounds as MEK kinase inhibitors.
Reagents and conditions: (a) 2-fluoro-4-iodoaniline, LiN(SiMe3)2, HMPA, THF (26%);
(b) NaCN, DMF, 150 °C (69–72%); (c) 1—2-fluoro-4-nitroaniline, Pd2(dba)3, Xant-
phos, Cs2CO3, dioxane, 110 °C (76%); 2—Zn, HOAc/MeOH (64%); 3—NaNO2, CuI, I2,
HOAc/H2O (42%); (d) NCS, DCM (44%).
F
I
O
HN
R2
R5
O
toward the synthesis of the 1,8-naphthyridine-2,5-dione system
that allows for a high degree of diversity at the 4- and 6-positions
of the core.
N
R
N
R1
Compd
R, R1
R2
R5
MEK1
Colo205
IC50 (nM)
EC50 (nM)
Acknowledgements
14a
15a
13a
13b
Me
Me
Me
–CH2CH2–
CO2Me
CO2Me
H
H
Cl
H
H
120
29
140
39
230
90
440
190
The authors thank Lihong Shi, Petro Halkowycz, and Shawn M.
O’Connell for providing in vitro assay data. We also thank Haihong
Wu for providing analytical chemistry support.
H

T. Kanouni et al. / Tetrahedron Letters 52 (2011) 477–479
479
Bridges, A.; Kaufman, M.; Tecle, H.; Gowan, R.; Sebolt-Leopold, J.; Leopold, W.;
Merriman, R.; Przybranowski, S.; Valik, H.; Chen, J.; Ohren, J.; Pavlovsky, A.;
Whithead, C.; Ahang, E. Bioorg. Med. Chem. Lett. 2008, 18, 6171; (c) Spicer, J. A.;
Rewcastle, G. W.; Kaufman, M. D.; Black, S. L.; Plummer, M. S.; Denny, W. A.;
Quin, J.; Shahripour, A. B.; Barrett, S. D.; Whitehead, C. E.; Milbank, J. B. J.;
Ohren, J. F.; Gowan, R. C.; Omer, C.; Camp, H. S.; Esmaeil, N.; Moore, K.; Sebolt-
Leopold, J. S.; Pryzbranowski, S.; Merriman, R. L.; Ortwine, D. F.; Warmus, J. S.;
Flamme, C. M.; Pavlovsky, A. G.; Tecle, H. J. Med. Chem. 2007, 50, 5090.
9. Reuman, M.; Eissenstat, M. A.; Weaver, J. D. Tetrahedron Lett. 1994, 35, 8303.
10. (a) Surry, D. S.; Buchwald, S. L. Angew. Chem., Int. Ed. 2008, 47, 6338; (b)
Ohshita, K.; Ishiyama, H.; Oyanagi, K.; Nakata, H.; Kobayashi, J. Bioorg. Med.
Chem. 2007, 15, 3235.
11. (a) MEK1 enzyme assay: inhibition of compounds relative to MEK1 were
determined using a cascade assay method in 384 well format under the
following reaction conditions: test compounds serial diluted in DMSO were
diluted into assay buffer (50 mM HEPES pH 7.3, 10 mM NaCl, 10 mM MgCl2,
0.01% Brij35, 1 mM DTT) and added into ERK1, fluorescent labeled ERK1
substrate: IPTTPITTYFFFK-5FAM-COOH, and the reaction was initiated with
Supplementary data
Supplementary data (chemistry experimental procedures and
compound characterization) associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.2010.11.063.
References and notes
1. (a) Wang, D.; Boerner, S. A.; Winkler, J. D.; LoRusso, P. M. Biochem. Biophys. Acta
2007, 1773, 1248; (b) Montagut, C.; Settleman, J. Cancer Lett. 2009, 283, 125.
2. (a) Wallace, E. M.; Lyssikatos, J. P.; Yeh, T.; Winkler, J. D.; Koch, K. Curr. Top. Med.
Chem. 2005, 5, 215; (b) Rosen, L. S.; Galatin, P.; Fehling, J. M.; Laux, I.; Dinolfo,
M.; Frye, J.; Laird, D.; Sikic, B. I. ASCO Annual Meeting Abstract 14585, 2008.; (c)
Iverson, C.; Larson, G.; Lai, C.; Yeh, L.-T.; Dadson, C.; Weingarten, P.; Appleby, T.;
Vo, T.; Maderna, A.; Vernier, J.-M.; Hamatake, R.; Miner, J. N.; Quart, B. Cancer
Res. 2009, 69, 6839; (d) Tai, Y.-T.; Kim, K.; Li, X.-F.; Fulciniti, M.; Song, W.;
Nahar, S.; Burger, P.; Rumizen, M. J.; Podar, K.; Chauhan, D.; Hideshima, T.;
Schlossman, R. L.; Munshi, N. C.; Richardson, P.; Clark, A.; Ogden, J.; Andreas, G.;
Rastelli, L.; Anderson, K. C. ASH Annual Meeting and Exposition Abstract 3848,
2009.; (e) Wallace, E. M.; Lyssikatos, J.; Blake, J. F.; Marlow, A.; Greschuk, J.;
Yeh, T. C.; Callejo, M.; Marsh, V.; Poch, G.; Otten, J.; Hingorani, G.; Winski, S. L.;
Anderson, D. A.; Lee, P.; Winkler, J.; Koch, K.; Davies, B. R.; Jones, D. C.; Logie, A.;
Curtis, N. J.; Chresta, C. M.; Smith, P. D.; Robinson, D. T. AACR Abstract 3696,
2009.; (f) Lee, L.; Niu, H.; Rueger, R.; Igawa, Y.; Deutsch, J.; Ishii, N.; Mu, S.;
Sakamoto, Y.; Busse-Reid, R.; Gimmi, C.; Goelzer, P.; Schepper, S. D.; Yoshimura,
Y.; Barrett, J.; Ishikawa, Y.; Weissgerber, G.; Peck, R. Clin. Cancer Res. 2009, 15,
7368.
1 nM MEK1 and 400 lM ATP or 10 lM ATP. Reaction product was determined
quantitatively by fluorescent polarization using progressive IMAP beads from
Molecular Devices. Inhibition constants (IC50) were calculated using standard
mathematical models. An ERK1 assay was also conducted to rule out that
inhibition was due to ERK1 in the cascade assay. Since all compounds tested
showed almost identical IC50 when assayed at 400
lM or 10 lM ATP, only IC50
results assayed at 400 M ATP were listed. Based on KmATP for MEK1 at 20 lM
l
determined using direct assay method (not shown), no potency shift when
compounds were assayed at 10 Â Km and 0.5 Â Km ATP concentration indicated
compounds were not ATP competitive inhibitors. (b) Colo205 EC50s were
generated using a cellular colorimetric MTS assay which measures newly
produced NADH. Briefly, human cancer cell lines were seeded between 3000
and 10,000 cells per 96 well and incubated for 16 h in a humidified 5% CO2
atmosphere incubator at 37 °C. Cells were then incubated with an 11 point
dilution of test compound in duplicate for 72 h and subsequently assayed for
NADH levels via the CellTiter 96-AQueousÒ kit (Promega) which utilizes a MTS
tetrazolium salt conversion. The resulting colorimetric reaction was read on a
spectrophotometer (Molecular Devices) at OD 490 nm and EC50 values of
compound concentration versus total NADH levels were calculated in Activity
Base (IDBS). It is important to note the Colo205 cell lines posses the
BRAF(V600E) mutation making them reliant upon MEK signaling for survival.
All compounds listed were also tested against the PC3 cell line whose survival
is independent of MEK signaling and served as a control for MEK inhibitory
selectivity. The EC50s generated for all compounds listed were at a minimum
50-fold higher in the PC3 cell line. Compounds from this series did not inhibit
3. (a) Remuzon, P.; Bouzard, D.; Di Cesare, P.; Essiz, M.; Jacquet, J. P.; Kiechel, J. R.;
Ledoussal, B.; Kessler, R. E.; Fung-Tomc, J. J. Med. Chem. 1991, 34, 29; (b) Suzuki,
N.; Tanaka, Y.; Dohmori, R. Chem. Pharm. Bull. 1980, 28, 235; (c) Vaillancourt, V.
A.; Thorarensen, A. U.S. Patent Application US 2002//0019413, 2002.
4. For similar approaches, see: (a) Bright, G. M.; Welch, W. M. U.S. Patent
US5,968,944. (b) Aoki, I.; Kuragano, T.; Nobuyuki, O.; Okada, Y. U.S. Patent
US4,872,901.
5. Gould, R. G.; Jacobs, W. A. J. Am. Chem. Soc. 1939, 61, 2890.
6. Lappin, G. R. J. Am. Chem. Soc. 1948, 70, 3348.
7. (a) Zewge, D.; Chen, D.-Y.; Deer, C.; Dormer, P. G.; Hughes, D. L. J. Org. Chem.
2007, 72, 4276; (b) Agui, H.; Mitani, T.; Nakashita, M.; Nakagome, T. J.
Heterocycl. Chem. 1971, 8, 357.
8. (a) Barrett, S. D.; Bridges, A. J.; Flamme, C. M.; Kaufam, M.; Doherty, A. M.;
Kennedy, R. M.; Marston, D.; Howard, W. A.; Smith, Y.; Warmus, J. S.; Tecle, H.;
Dudley, D. T.; Saltiel, A. R.; Fergus, J. H.; Delaney, A. M.; Lepage, S.; Leopold, W.
R.; Przybranowski, S. A.; Sebolt-Leopold, J.; Van Becelaere, K. Bioorg. Med. Chem.
Lett. 2008, 18, 6501; (b) Warmus, J. S.; Flamme, C.; Zhang, L. Y.; Barrrett, S.;
other kinases tested with inhibitor concentrations up to 10
Abl1, AKT3, c-RAF, CamK1 , CDK2/cyclinA, cMet, cSRC, EGFR, GSK3b, IR, JAK3,
P38 , PDGFRb, PDK1, PKC , PLK3, Syk, Tie2).
lM (Kinase Panel:
D
a
a