Synthesis and biological activity of novel 4-phenyl-1,8-naphthyridin-2(1H)- on-3-yl ureas: Potent acyl-CoA:cholesterol acyltransferase inhibitor with improved aqueous solubility

Article abstract of DOI:10.1016/j.bmcl.2005.09.056

4-Aryl-1,8-naphthyridin-2(1H)-on-3-yl urea derivatives with hydrophilic groups were synthesized in order to improve aqueous solubility and pharmacokinetic property. SMP-797 possessing (4-aminophenyl)ureido and 3-(hydroxypropoxyphenyl) moieties showed pote

Full text of DOI:10.1016/j.bmcl.2005.09.056

Bioorganic & Medicinal Chemistry Letters 16 (2006) 44–48
Synthesis and biological activity of novel
4-phenyl-1,8-naphthyridin-2(1H)-on-3-yl ureas: Potent
acyl-CoA:cholesterol acyltransferase inhibitor
with improved aqueous solubility
Hitoshi Ban,* Masami Muraoka, Katsuhisa Ioriya and Naohito Ohashi
Research Division, Sumitomo Pharmaceuticals Co., Ltd 1-98, Kasugadenaka 3-chome, Konohana-ku, Osaka 554-0022, Japan
Received 11 July 2005; revised 8 August 2005; accepted 21 September 2005
Available online 18 October 2005
Abstract—4-Aryl-1,8-naphthyridin-2(1H)-on-3-yl urea derivatives with hydrophilic groups were synthesized in order to improve
aqueous solubility and pharmacokinetic property. SMP-797 possessing (4-aminophenyl)ureido and 3-(hydroxypropoxyphenyl)
moieties showed potent ACAT inhibitory activity and excellent oral efficacy.
Ó 2005 Elsevier Ltd. All rights reserved.
An enzyme acyl-CoA:cholesterol acyltransferase
(ACAT), which catalyzes the intracellular cholesterol
esterification,1 plays important roles in several physio-
logical processes: (1) absorption of dietary and biliary
cholesterol in the intestines2; (2) determination of cho-
lesteryl ester content and the secretion of hepatic very
low density lipoprotein (VLDL)3; (3) accumulation of
cholesteryl esters in macrophage in the arterial wall.4
Inhibition of ACAT, therefore, is expected to reduce
plasma lipid levels by inhibiting intestinal cholesterol
absorption and hepatic VLDL secretion, and to prevent
progression of atherosclerotic lesions by inhibiting the
accumulation of cholesteryl esters in macrophage. For
this reason, ACAT inhibitor is an attractive target for
the treatment of hypercholesterolemia and atherosclero-
sis5 (Fig. 1).
F
H
N
N
F
O
O
O
S
O
N
H
O
CI -1011
CL-277082
OMe
H
N
H
N
4
3
O
N
N
O
SM-32504
Classical ACAT inhibitors6 such as CL-277082,7
which are considered to inhibit absorption of choles-
terol in the intestines, failed in the clinical trials for
their insufficient efficacy on hypercholesterolemia and
atherosclerosis. The main reason should be their low
systemic bioavailabilities expected from their lipophilic
structural features. Therefore, recent interest in the
Figure 1.
development of ACAT inhibitors is switching the tar-
get from the intestinal ACAT to the liver and the
arterial wall ACAT.6 CI-1011, an ACAT inhibitor
currently in clinical trial, has been found to show high
efficacy not only in a variety of cholesterol-fed animal
models but also in noncholesterol-fed animal models
such as a rabbit model fed a casein-rich diet,8 and is
considered to inhibit ACAT in both the intestines
and the liver.
Keywords: SMP-797; AACAT inhibitor; A4-Phenyl-1,8-naphthyridin-
2(1H)-on-3-yl ureas.
*
Corresponding author. Tel.: +8166 466 5227; fax: +8166 466 5287;
e-mail: ban@sumitomopharm.co.jp
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.09.056

H. Ban et al. / Bioorg. Med. Chem. Lett. 16 (2006) 44–48
45
NHTs
NH2
NH2
We previously found a naphthyridinyl urea SM-32504
as a potent inhibitor of ACAT,9 which showed the cho-
lesterol-lowering effect in cholesterol-fed animal models.
Despite the excellent efficacy, however, this compound
showed only poor oral absorption due to low aqueous
solubility; its maximum drug concentration (Cmax) value
in mice was under the lowest detectable concentration
(<0.01 ng/mL) after oral administration at the dosage
of 30 mg/kg. The cholesterol lowering effect of SM-
32504, therefore, may be due to ACAT inhibitory activ-
ity in the intestines and not to ACAT inhibitory activity
in the liver. The results led us to modify SM-32504 and
develop compounds possessing better pharmacokinetic
properties.
2 steps
a
NO2
3a (3-NO2)
1
NO2
2
3b (4-NO2)
d
b
c
NH2
NH2
I
5
NHTr
4a (3-NHTr)
4b (4-NHTr)
e
NH2
NH2
NH2
We considered that the pharmacokinetic properties of
SM-32504 would be improved by increasing its aqueous
solubility, especially solubility under acidic conditions.
Drugs administered orally are absorbed mainly in the
stomach and/or the small intestine; pH values of gastric
juices are 1.4–2.1 (fasting) or 4.3–5.4 (non-fasting); pH
values of small intestinal fluids are 5.0–7.0.10 We report
herein the synthesis, aqueous solubility, and biological
activity of hydrophilic derivatives of SM-32504.
g
f
CO2Me
HO
TBSO
6
7
8
NH2
N
We examined two modifications of SM-32504 to afford
the hydrophilic derivatives: (i) introduction of an amino
group on the 2,6-diisopropylphenyl moiety; (ii) replace-
ment of the 3-methoxy group at the 4-phenyl moiety
with a hydrophilic group. Although a number of ACAT
inhibitors possessing 2,6-diisopropylphenyl moiety were
reported, the effect of amino group on the aromatic moi-
ety has not been examined.
9
Scheme 1. Reagents and conditions: (a) concd H2SO4, 70 °C, 3 h, 96%;
(b) concd HNO3, concd H2SO4, À10 °C, 1 h; 96%; (c) H2, cat. Pd/C,
MeOH, rt, 2–12 h, then TrCl, Et3N, CH2Cl2, rt, overnight; 4a 64% and
4b 44%; (d) HIO3, I2, AcOH–H2SO4–H2O (150:1:4), 80 °C, 5 h, 91%;
(e) CO, cat. Pd(OAc)2, DPPP, Et3N, MeOH, DMF, 80 °C, 4 h, 83%;
(f) LiAlH4, THF, 60 °C, 30 min, 98%; (g) TBSCl, DMAP, Et3N,
CH2Cl2, rt, overnight, 83%.
The synthesis of 2,6-diisopropylanilines 4a, 4b, 8, and 9
required in the present study is shown in Scheme 1.
Deprotection of N-tosyl-4-nitroaniline 2, readily avail-
able from 2,6-diisopropylaniline (1) in two steps, gave
4-nitroaniline 3b according to the known procedures.11
In contrast, it was found that the direct nitration of
aniline 1 with concd HNO3 in concd H2SO4 gave 3-nit-
roaniline 3a.12 Pd/C-catalyzed hydrogenation of 3a and
3b followed by the selective protection of the less hin-
dered amino group with triphenylmethyl group gave 4a
and 4b, respectively. 4-Iodoaniline 5, readily prepared
from 1 by a known iodination method,13 was converted
to 6 by Pd-catalyzed carbonylation in MeOH-DMF.14
Reduction of 6 with LiAlH4 followed by protection
of the hydroxy group gave a silyl ether 8. A pyridine
desilylation of 14d followed by bromination with PBr3.
Ammonium salt 18a was obtained by reaction of 17 with
potassium phthalimide, cleavage of the phthaloyl group,
and treatment with 1 M HCl in ether. Amination of 17
with N,N-diethylamine followed by treatment with
1 M HCl in ether gave 18b.
The ACAT inhibitory activity and solubility of 15a, 15b,
16, 18a, and 18b are shown in Table 1. All compounds
exhibited enhanced aqueous solubility compared to that
of SM-32504, and 15b and 16 showed more potent
ACAT inhibitory activity than SM-32504. However,
16 was not examined further, since gradual degradation
of the urea moiety took place in an aqueous solution at
pH 2.5 at room temperature.
intermediate
literature.15
9
was prepared according to the
We next focused on the synthesis and activity of 15
derivatives possessing hydrophilic substituents on the
4-phenyl group. The syntheses of 22a–c and 26a–c
are summarized in Scheme 3. Treatment of 11 with
BBr3 in CH2Cl2 gave 19, which was treated with
several x-acetoxyalkyl bromides in the presence of
K2CO3 and KI in DMF to afford 20a–c and 23.
The naphthyridine ureas 21a–d were prepared by the
reaction of 20a–c with 4a or 4b in the presence of
DMAP in DMF at room temperature. Deacylation
of 21a–d with NaOMe in MeOH followed by
Syntheses of naphthyridinyl ureas 15a, 15b, 16, 18a, and
18b are shown in Scheme 2. Curtius rearrangement16 of
acid 109 with diphenylphosphoryl azide gave amine 11,17
which was converted to phenyl carbamate 12. Then, 12
was treated with 4a, 4b, 8, and 9 in the presence of
DMAP in DMF and was converted to the correspond-
ing naphthyridinyl ureas 14a–d, respectively. Deprotec-
tion of 14a and 14b was conducted with 10% HCl in
MeOH at room temperature, and 15a and 15b were
obtained. Treatment of 14c with 1 M HCl in ether gave
the corresponding salt 16. 17 was synthesized by the

46
H. Ban et al. / Bioorg. Med. Chem. Lett. 16 (2006) 44–48
OMe
OMe
OMe
H
N
NH2
O
OPh
CO2H
O
a
b
O
O
N
N
N
N
N
N
10
11
12
OMe
Ar =
d
H
N
H
N
c
Ar
NH2 HCl
NHTr
O
O
N
N
15a (3-NH2)
15b (4-NH2)
14a (3-NHTr)
14b (4-NHTr)
13
e
N
HCl
N
14c
16
h, i, e
or
f, g
Br
OTBS
j, e
R
HCl
18a (R=NH2)
14d
17
18b (R=NEt2)
Scheme 2. Reagents and conditions: (a) DPPA, Et3N, DMF, 50 °C, 2 h, then 6 M NaOH, 50 °C, 3 h, 97%; (b) phenyl chloroformate, THF, 50 °C,
5 h, 84%; (c) 4a, 4b, 8, or 9, DMAP, DMF, rt, overnight; 14a, 79%; 14b, 77%; 14c, 64%; 14d, 73%; (d) 10% HCl/MeOH, rt, overnight; 15a, 94%; 15b,
97%; (e) 1 M HCl/ether, AcOEt, rt, 30 min; 16, 80%; 18a, 63%; 18b, 80%; (f) concd HCl, EtOH, rt, 3 h, 89%; (g) PBr3, CH2Cl2, rt, 3 h, 45%
(h) potassium phthalimide, DMF, rt, overnight, 88%; (i) H2NNH2ÆH2O, EtOH, rt, 3 days, 81%; (j) Et2NH, K2CO3, DMF, rt, 1 h, 62%.
Table 1. ACAT inhibitory activity and solubility of 15a, 15b, 16, 18a,
and 18b
797)19, with the propylene group turning out be the most
potent (IC50, 21 nM) with appreciable improvement of
solubility at broad pH range (pH 2.5–7.4). The amino
derivatives 26a–c showed weak activity in spite of their
higher solubility.
Compound
ACAT inhibitory
activitya IC50 (nM)
Solubilityb (mg/mL)
pH 7.4 pH 5.5 pH 2.5
SM-32504
15a
15b
11
14
<0.001
0.001
<0.001
0.005
0.036
0.062
<0.001
0.001
0.001
0.019
0.023
1.0
<0.001
0.70
SMP-797 (22b) exhibited excellent pharmacokinetic
properties in mice (Cmax, 21.3 lg/mL; after oral admin-
istration at the dosage of 30 mg/kg) and rabbits (Cmax,
8.3
5.4
382
680
0.022
>1.0
0.22
16
18a
18b
>1.0
16.0 ng/mL; area under the blood time curve (AU-
C0–24 h), 39.8 ng h/mL after oral administration at the
dosage of 1.0 mg/kg/day for 21 days). The results are
highly contrasted to those of SM-32504, which was
not absorbed orally at all in the same models. SMP-
797 (22b) was then subjected to evaluation with a rab-
bit model fed a casein-rich diet, which was considered
to exhibit the cholesterol-lowering effect due to the
inhibitory of secretion from the liver. Rabbits were
fed a casein-rich diet for 1 week, and then SMP-797
was orally administered at the dosage of 1.0 mg/kg/
day for further 3 weeks with a casein-rich diet. Under
these conditions SMP-797 decreased the serum total
cholesterol level by 53% compared with control. It
was reported that atorvastatin, the HMG-CoA reduc-
tase inhibitor with the most potent cholesterol lowering
effect currently in clinical use, decreased the cholesterol
level by 54% at a dose of 10 mg/kg/day when it was
a ACAT inhibition in vitro measured in rat macrophages. See Ref. 18
for the detailed protocol.
b Solubility in phosphate buffer (5.53% aq citric acid/1.75% aq
Na2HPO4) at rt was determined by HPLC analysis.
detritylation with 10% HCl in MeOH gave 22a–d.
Urea 24 prepared from 23 was coupled with N,N-
diethylamine, pyrrolidine, or piperidine followed by
deprotection with 10% HCl in MeOH, and naphthy-
ridinyl ureas 26a–c, respectively, were obtained.
The activity and aqueous solubility of 22a–d and 26a–c
are summarized in Table 2. All the compounds showed
enhanced solubility compared to SM-32504 and 15b.
Notably, the length of alkylene exhibits some effect on
the activity as indicated by 22a–d and 22b (SMP-

H. Ban et al. / Bioorg. Med. Chem. Lett. 16 (2006) 44–48
47
( ) n
OH
( ) n
OAc
( ) n
OAc
O
O
O
H
N
H
N
H
N
H
N
d
c
NH2
O
b
NH2
NHTr
O
HCl
O
N
N
O
N
N
N
N
O
OH
22a (n=1, 4-NH2)
22b (n=2, 4-NH2)
22c (n=3, 4-NH2)
22d (n=2, 3-NH2)
R
21a (n=1, 4-NHTr)
21b (n=2, 4-NHTr)
21c (n=3, 4-NHTr)
21d (n=2, 3-NHTr)
20a (n=1)
20b (n=2)
20c (n=3)
NH2
O
a
11
Cl
Cl
N
N
O
O
O
19
H
N
H
N
H
N
H
N
g, e
f
NH2
c
NH2
NHTr
2HCl
O
O
N
N
O
N
N
O
N
N
O
24
23
26a (R=NEt2)
N
N
26b (R=
26c (R=
)
)
Scheme 3. Reagents and conditions: (a) BBr3, CH2Cl2, rt, overnight, 95%; (b) BrCH2(CH2)nOAc, K2CO3, KI, DMF, rt, overnight; 20a (n = 1), 75%;
20b (n = 2), 91%; 20c (n = 3), 92%; (c) phenyl chloroformate, THF, rt, overnight, then 4a or 4b, DMAP, DMF, rt, overnight; 21a, 64%; 21b, 72%; 21c,
83%; 21d, 78%; 24, 49%; (d) NaOMe, MeOH, rt to reflux, 8 h to overnight, then 10% HCl/MeOH, rt, overnight; 22a, 72%; 22b, 83%; 22c, 80%; 22d,
85%; (e) 10% HCl/MeOH, rt, overnight; 26a, quant.; 26b, 84%; 26c, 87%; (f) 1-bromo-3-chloropropane, K2CO3, KI, DMF, rt, overnight, 67%;
(g) N,N-diethylamine, pyrrolidine, or piperidine, K2CO3, KI, DMF, 50 °C, 10 h; 25a, 64%; 25b, 73%; 25c, 30%.
Table 2. ACAT inhibitory activity and solubility of 22 and 26
References and notes
Compound
ACAT inhibitory
activitya IC50 (nM)
Solubilityb (mg/mL)
1. (a) Spector, A. A.; Mathur, S. N.; Kaduce, T. L. Prog.
Lipid Res. 1979, 18, 31; (b) Suckling, K. E.; Stange, E. F.
J. Lipid Res. 1985, 26, 647.
2. (a) Field, F. J.; Salome, R. G. Biochim. Biophys. Acta
1982, 712, 557; (b) Heider, J. G.; Pickens, C. E.; Kelly, L.
A. J. Lipid Res. 1983, 24, 1127.
3. (a) Drevon, C. A.; Engelhorn, S. C.; Steinberg, D. J. Lipid
Res. 1980, 21, 1065; (b) Khan, B.; Wilcox, H. G.;
Heimberg, M. Biochem. J. 1989, 258, 807; (c) Cianflone,
K. M.; Yasruel, Z.; Rodriguez, M. A.; Vas, D.; Snider-
man, A. D. J. Lipid Res. 1990, 31, 2045.
4. (a) Brecher, P. I.; Chobanian, A. V. Circ. Res. 1974, 35,
692; (b) Day, A. J.; Proudlock, J. W. Atherosclerosis 1974,
19, 253; (c) Hashimoto, S.; Dayton, S. Atherosclerosis
1977, 28, 447.
pH 7.4 pH 5.5 pH 2.5
<0.001 <0.001 <0.001
SM-32504
15b
11
8.3
<0.001
0.030
0.010
0.005
0.017
0.64
0.001
0.022
22a
22b (SMP-797)
>1000
21
61
0.032 >1.0
0.014 >1.0
22c
22d
26a
26b
26c
0.007
0.019 >1.0
0.68
43
452
427
540
0.69
0.20
0.18
>1.0
>1.0
>1.0
0.13
0.20
a ACAT inhibition in vitro measured in rat macrophages. See Ref. 18
for the detailed protocol.
b Solubility in phosphate buffer (5.53% aq citric acid/1.75% aq
Na2HPO4) at rt was determined by HPLC analysis.
5. Sliskovic, D. R.; White, A. D. Trends Pharmacol. Sci.
1991, 12, 194.
administered to rabbits fed a casein diet for 6 weeks.20
These results suggest that the cholesterol-lowering
effect of SMP-797 at a dose of 1.0 mg/kg/day is almost
the same as with that of atorvastatin at a dose of
10 mg/kg/day.
6. For recent reviews of ACAT inhibitor, see: (a) Picard, J.
A. Curr. Opin. Ther. Pat. 1993, 3, 151; (b) Matsuda, K.
Med. Res. Rev. 1994, 14, 271; (c) Sliskovic, D. R.;
Trivedi, B. K. Curr. Med. Chem. 1994, 1, 204; (d) Roark,
W. H.; Roth, B. D. Exp. Opin. Invest. Drug 1994, 3,
1143.
7. Harris, W. S.; Dujoune, C. A.; von Bergmam, K.; Neal, J.;
Akester, J.; Windsor, S. L.; Greene, D.; Look, Z. Clin.
Pharmacol. Ther. 1990, 48, 189.
8. Lee, H. T.; Sliskovic, D. R.; Picard, J. A.; Roth, B. D.;
Wierenga, W.; Hicks, J. L.; Bousley, R. F.; Hamelehle, K.
L.; Homan, R.; Speyer, C.; Stanfield, R. L.; Krause, B. R.
J. Med. Chem. 1996, 39, 5031.
In summary, we have developed SMP-797 possessing a
potent ACAT inhibitory activity and significantly en-
hanced aqueous solubility under acidic conditions. The
compound is a promising agent for oral treatment of
hypercholesterolemia. The details of pharmacological
and toxicological studies will be discussed in due course.
9. Ohnuma, S.; Ioriya, K.; Muraoka, M.; Ohashi, N. Bioorg.
Med. Chem. Lett. 2004, 14, 1309.
10. Kararli, T. T. Biopharm. Drug Dispos. 1995, 16, 351.
11. Carver, F. J.; Hunter, C. A.; Livingstone, J. D.; McCabe,
J. F.; Seward, E. M. Chem. Eur. J. 2002, 8, 2847.
12. Giumanini, A. G.; Verardo, G.; Polana, M. J. Prakt.
Chem. 1988, 330, 161.
Acknowledgments
We thank Y. Saitou and Y. Konya for evaluation of
pharmacokinetic properties, and Ms. Y. Nakatsuji for
her technical assistance.
13. Merkushev, E. B. Synthesis 1988, 923.

48
H. Ban et al. / Bioorg. Med. Chem. Lett. 16 (2006) 44–48
14. Donald Valentine, Jr.; Tilley, J. W.; LeMahieu, R. A.
J. Org. Chem. 1981, 46, 4614.
15. Pascual, A.; Rindlisbacher, A. Pestic. Sci. 1994, 42, 253.
16. Curtius, T. Chem. Ber. 1902, 35, 3226.
17. Shioiri, T.; Ninomiya, K.; Yamada, S. J. Am. Chem. Soc.
1972, 94, 6203.
(2H, tt, J = 7.3, 7.3 Hz), 1.87 (2H, tt, J = 6.1, 6.1 Hz), 2.95
(2H, tt, J = 7.3, 7.3Hz), 3.54 (2H, t, J = 6.1 Hz), 4.03 (2H,
t, J = 6.1 Hz), 4.50 (2H, t, J = 7.0 Hz), 6.88–6.89 (2H, m),
7.00–7.03 (3H, m), 7.25 (1H, dd, J = 4.6, 7.9 Hz), 7.40
(1H, t, J = 7.9 Hz), 7.60 (1H, dd, J = 1.5, 7.9 Hz), 7.79
(1H, s), 7.87 (1H, s), 8.61 (1H, dd, J = 1.5, 4.6 Hz), 9.88
(2H, br s); Anal. calcd for C34H43N5O4ÆHClÆH2O: C,
63.79; H, 7.24; Cl, 5.54; N, 10.94. Found: C, 63.85; H,
7.21; Cl, 5.74; N, 10.96.
18. Ioriya, K.; Noguchi, T.; Muraoka, M.; Fujita, K.;
Shimizu, H.; Ohashi, N. Pharmacology 2002, 65, 18.
19. Mp 196–197 °C (MeOH). IR (KBr): m 2966, 1636, 1584,
1546 cmÀ1
;
1H NMR (DMSO-d6, 300 MHz), d (ppm)
20. Auerbach, B. J.; Krause, B. R.; Bisgaier, C. L.; Newton,
R. S. Atherosclerosis 1995, 115, 173.
0.85–0.99 (15H, m), 1.41 (2H, qt, J = 7.3, 7.3 Hz), 1.70