Synthetic studies on selective type 4 phosphodiesterase (PDE 4) inhibitors. 1. Structure-activity relationships and pharmacological evaluation of 1,8-naphthyridin-2(1H)-one derivatives.

Article abstract of DOI:10.1248/cpb.50.1050

In order to develop novel and orally active phosphodiesterase (PDE) 4 inhibitors, random screening was performed using our chemical library to find YM-10335 possessing the 1,8-naphthyridin-2(1H)-one skeleton which is a completely different structure from rolipram. In this report, the syntheses and structure-activity relationships of the YM-10335 derivatives were described. Some compounds showed selective inhibitory activities for PDE 4 derived from human peripheral blood cells and no effect on the other PDE types (1, 2, 3, 5). The inhibition of the tumor necrosis factor-alpha (TNF-alpha) release in vitro and the carrageenan-induced pleurisy in rats were also described.

Full text of DOI:10.1248/cpb.50.1050

1050
Chem. Pharm. Bull. 50(8) 1050—1059 (2002)
Vol. 50, No. 8
Synthetic Studies on Selective Type 4 Phosphodiesterase (PDE 4)
Inhibitors. 1. Structure–Activity Relationships and Pharmacological
Evaluation of 1,8-Naphthyridin-2(1H)-one Derivatives
Kazuhisa TAKAYAMA, ,a Masahiro IWATA,a Hiroyuki HISAMICHI,a Yoshinori OKAMOTO,a
*
b
Motonori AOKI,a and Akira NIWA
a Institute for Drug Discovery Reserch, Yamanouchi Pharmaceutical Co., Ltd.; 21 Miyukigaoka, Tsukuba, Ibaraki
305–8585, Japan: and b Institute for Drug Development Research, Yamanouchi Pharmaceutical Co., Ltd.; 3–17–1 Hasune,
Itabashi-ku, Tokyo 174–8612, Japan. Received February 27, 2002; accepted May 28, 2002
In order to develop novel and orally active phosphodiesterase (PDE) 4 inhibitors, random screening was
performed using our chemical library to find YM-10335 possessing the 1,8-naphthyridin-2(1H)-one skeleton
which is a completely different structure from rolipram. In this report, the syntheses and structure–activity rela-
tionships of the YM-10335 derivatives were described. Some compounds showed selective inhibitory activities for
PDE 4 derived from human peripheral blood cells and no effect on the other PDE types (1, 2, 3, 5). The inhibi-
tion of the tumor necrosis factor-alpha (TNF-a) release in vitro and the carrageenan-induced pleurisy in rats
were also described.
Key words 1,8-naphthyridin-2(1H)-one; phosphodiesterase 4 inhibitor; rolipram; YM-10335
Asthma is a respiratory disease symptomatically character-
In order to remove these drawbacks, the creation of a novel
ized by repeated stridor and paroxysm due to airway contrac- class of PDE 4 inhibitors structurally different form rolipram
tion. The number of patients with this disease is gradually in- would be necessary. Therefore, random screening was per-
creasing, especially in the industrial countries. Although a formed using our chemical library, and YM-1033513) was
number of drugs have been used for the treatment of asthma, found to possess a structure completely different from
a new type of anti-asthmatic drug is strongly desirable due to rolipram. Unfortunately, YM-10335 has some problems such
the unsatisfactory effectiveness as well as adverse effects of as a weak activity, moderate selectivity (PDE 2 vs. 4) and
existing drugs. Since asthma is believed to be a chronic in- poor membrane permeability. To improve these biological
flammatory disease based on recent studies in pathophysiol- profiles of YM-10335, several modification of YM-10355
ogy, a drug, which can inhibit the inflammatory process, may were performed. As a consequence, several compounds with
offer a new therapeutic approach for curing for asthma pa- good in vitro as well as in vivo activities have been found and
tients. Therefore, compounds possessing inhibitory activities are going further extensive pharmacological evaluations.
for both airway contraction and airway inflammation may be- Herein, the syntheses, structure–activity relationships, and
come a novel therapeutic agent for asthma.
biological activities of a series of 1,8-naphthyridin-2(1H)-
It is known that phosphodiesterase (PDE) can regulate one derivatives are described.
some cell functions through the hydrolysis of cAMP.1) Within
Synthesis A procedure for the preparation of YM-10335
the phosphodiesterases, as at least ten subclasses,2—4) PDE 4 and the 5,7-disubstituted 1,8-naphthyridine derivatives have
has recently attracted much attention due not only to their been reported.13) In order to optimize the yields and to pro-
roles in airway contraction and airway inflammation proved vide new compounds, the synthetic route was modified
by rolipram,5—8) an authentic PDE 4 inhibitor, but also their (Chart 1).
locations in the airway smooth muscles and infiltrated
The 7-substituted derivatives without 5-substituents were
synthesized by the methods shown in Chart 2. The 3-cyano
cells.9—11)
So far, several PDE 4 inhibitors mainly derived from or 3-carboxyl-2-chloropyridine derivatives were treated with
rolipram have been developed and some of them were proved the corresponding Grignard reagents, substituted by amines,
to be effective for the treatment of asthma.12) However, ad- acetylated, followed by aldol condensation and dehydration
verse effects such as emesis and poor pharmacological pro- that produced the naphthyridine compounds (7). In the case
files have made them difficult to undergo further clinical de- of the 4-(2-chlorophenyl)- and 4-(3-bromophenyl)-deriva-
velopment.
tives, no desired compound was obtained by the Grignard re-
Chart 1
To whom correspondence should be addressed. e-mail: takaya_k@yamanouchi.co.jp
© 2002 Pharmaceutical Society of Japan

August 2002
1051
Chart 2
Chart 3
action. Therefore, another synthetic route for compound 6
Although the naphthyridine-2-one derivative without a 1-
was adopted as shown in Chart 3. Namely, the corresponding substituent (14) was not able to be synthesized by the above
benzonitriles were converted to benzoylacetonitrile 8, hy- methods, we prepared it as shown in Chart 5. The 3-position
drolyzed by polyphosphoric acid (PPA), and cyclized using of 2-pivaroylaminopyridine (11)14) was lithiated by n-butyl-
acetal to give pyridone 9. Compound 9 was tosylated and lithium, then benzoylated using N-methoxy-N-methylbenz-
substituted by amines similar to the chlorides (5) in Chart 2.
amide to give the benzoylpyridine derivative (12). Compound
The 7-ethyl (7o, p) or 7-propyl (7q) derivatives were af- 12 was treated with the lithium enolate of tert-butyl acetate
forded by the further alkylation of the 7-methyl derivative and subsequently cyclized to 4-phenyl-1,8-naphthyridine-2-
(Chart 4).
one (14).

1052
Vol. 50, No. 8
Chart 4
Chart 5
Chart 6
Chart 7
As shown in Chart 6, the carbonyl group at the 2-position investigated. As shown in Table 1, removal of all the methyl
of 4a was converted to the thiocarbonyl group using phos- groups or two methyl groups at the 5- and 7-positions of
phorus pentasulfide to give 15, and the double bond at the YM-10335 showed no inhibitory activity (14, 7a). Com-
3,4-position of 4a was reduced by the platinum dioxide-cat- pound 7j with methyl groups at both of the 1- and 7-posi-
alyzed hydrogenation to afford 16.
tions on the naphthyridine ring was found to show increased
The quinolone derivative (19) was synthesized using the inhibitory activity. Moreover, the 5-substituent should be un-
methods of Chart 7. Ethylaniline was treated with 1 under necessary for inhibition since the activity of 7j was better
basic conditions and cyclized to the quinolone 18, which was than that of YM-10335. To ascertain this expectation, re-
alkylated to obtain compound 19.
placement of the 5-methyl group in 4b with an ethyl group
(4c) was performed. The inhibitory activity of 4c was de-
creased, therefore, the 1,7-substituted 1,8-naphthyridine de-
Results and Discussion
In order to assess the structure–activity relationships, the rivatives are favorable to show PDE 4 inhibitory activity. Be-
compounds synthesized above were evaluated for their in cause of the steric interaction of the 5-substituent with the
vitro inhibitory activity against human leukocyte PDE 4.
benzene ring at the 4-position, the 5-substituted 1,8-naph-
At first, the effect of each methyl group in YM-10335 was thyridine derivatives are unable to adopt a conformation ap-

August 2002
1053
Table 1. Inhibitory Effect of 1,8-Naphthyridine Derivatives on Human Table 3. Inhibitory Effect of 4-Substituted 1,8-Naphthyridine Derivatives
PDE 4 (1, 5, and 7 Position) on Human PDE 4
IC50 (nM)a)
Enzyme
IC50 (nM)a)
Enzyme
Compound
R1
R2
R3
Compound
R
Rolipram
YM-10335
820
220
12
23
350
7b
7c
7d
7m
7e
7f
7g
7h
7i
H
3-Chloro
4-Chloro
2-Chloro
3-Fluoro
5.9
1.1
35
8.4
9.5
2.8
26
130
1.2
1.2
Methyl
Ethyl
Methyl
Methyl
Ethyl
Ethyl
H
Methyl
Methyl
Methyl
Ethyl
H
4a
4b
4c
7a
7j
Methyl
Methyl
Methyl
Methyl
H
Ͼ3000
90
Ͼ3000
3-Methyl
3-Methoxy
3-Trifluoromethyl
3-Nitro
Methyl
H
H
H
14
a) Data of in vitro experiment are expressed as mean from two separate experiments,
and the individual experiment was performed in triplicate. The method of measurement
is described in Experimental.
7n
3-Bromo
a) Data of in vitro experiment are expressed as mean from two separate experiments,
and the individual experiment was performed in triplicate. The method of measurement
is described in Experimental.
Table 2. Inhibitory Effect of 1-Substituted 1,8-Naphthyridine Derivatives
on Human PDE 4
Table 4. Inhibitory Effect of 7-Substituted 1,8-Naphthyridine Derivatives
on Human PDE 4
IC50 (nM)a)
Enzyme
Compound
R
IC50 (nM)a)
Enzyme
Compound
R
7j
Methyl
Ethyl
n-Propyl
iso-Propyl
90
5.9
24
68
7b
7k
7l
7c
7p
7q
Methyl
Ethyl
n-Propyl
1.1
0.61
58
a) Data of in vitro experiment are expressed as mean from two separate experiments,
and the individual experiment was performed in triplicate. The method of measurement
is described in Experimental.
a) Data of in vitro experiment are expressed as mean from two separate experiments,
and the individual experiment was performed in triplicate. The method of measurement
is described in Experimental.
propriate for PDE 4 inhibition.
Because it was found that the 1,7-disubstituted derivatives
are favorable for showing activity, each substituent was mod-
ified. As shown in Table 2, replacement of the of the 1-
methyl group in 7j with an ethyl group (7b) increased the in-
hibitory activity up to the nanomolar level, however replace-
ment with the n- and i-propyl groups only provided a moder-
ate increase (7k, 7l). As for the 1-substituents, the ethyl
group is crucial for PDE 4 inhibition and very sensitive for
modification.
Replacement of the 7-methyl group in 7c with an ethyl
group (7p) slightly increased the inhibitory activity, whereas
replacement with a n-propyl group (7q) resulted in signifi-
cantly reduced the activity (Table 4). In the case of the 7-sub-
stituent, a small alkyl group such as a methyl or ethyl is fa-
vorable.
at the ortho (7m) or para (7d) position slightly reduced the
activity. Various meta substituents were introduced, and the
bromo- (7n), methyl- (7f), and nitro- (7i) derivatives showed
potent activities, while the fluoro- (7e) and methoxy- (7g) de-
rivatives showed slightly reduced activities. Based on these
results, there was no significant difference between the elec-
tron-donating and electron-withdrawing groups. It is unclear
why the trifluoromethyl group (7h) showed low activity.
Among the halogen substituents, the fluorine derivative (7e)
showed low activity compared with the other halogen groups,
therefore, an unfavorable interaction seems to be present be-
tween the PDE 4 enzyme and fluorine atom.
Finally, the effects of the nitrogen atom at the 8-position
and the pyridone moiety of the 1,8-naphthyridine ring system
on the PDE 4 inhibitory activity were examined. As shown in
Table 5, replacement of the carbonyl group in compound 4a
with the thiocarbonyl group (15) slightly reduced the activity.
This slight difference is caused by the hydrogen bonding ac-
ceptor ability based on the difference in the bond length and
electron-withdrawing activity between the carbonyl and thio-
Secondly, the effect of the substituent on the benzene ring
at the 4-position of the naphthyridine on the PDE 4 in-
hibitory activity was examined (Table 3). The introduction of
a chlorine atom at the meta position (7c) increased the po-
tency over 7b by almost 5—6 fold, whereas, its introduction

1054
Vol. 50, No. 8
carbonyl groups. Reduction of the double bond in the pyri- favorable. Another experiment is needed for this clarifica-
done moiety (16) dramatically reduced the potency. Although tion.
it is assumed that the existence of p electron should be nec-
These facts described above suggested that three factors
essary, it is the main reason of this result that appropriate affected the PDE 4 inhibitory activity in this series. First, the
spatial positioning of the phenyl group at 4-position relative appropriate size of the substituents such as the methyl and
to 1,8-naphthyridine ring system is essential for PDE 4 inhi- ethyl groups at the 1- and 7-positions on the 1,8-naph-
bition. Exchanging the nitrogen atom of 7o for a carbon atom thyridin-2-one structure is necessary for inhibitory activity.
(19) resulted in the loss of potency. Since the basicity of this Second, the benzene ring at the 4-position of the naphthyri-
nitrogen atom is not so high, this might occur due to the dif- dine has the appropriate position and direction. And third, the
ference as a hydrogen bonding acceptor. It is also possible to nitrogen atom at the 8-position and carbonyl moiety of the
consider that the repulsion between the newly generated hy- 1,8-naphthyridine ring system function as an acceptor of the
drogen at the 8-position and the 1-substituents would be un- hydrogen bonding against the PDE 4 enzyme.
The pharmacophore model of many PDE 4 inhibitors was
reported by Crespo and co-workers,15) in which PDE 4 in-
hibitors related to the nitraquazone structure possess three
Table 5. Inhibitory Effect of Modified 1,8-Naphthyridine Ring Derivatives
on Human PDE 4
hydrogen bond acceptors and three aromatic regions. How-
IC50 (nM)a)
Compound
Structure
ever, our 1,8-naphthyridine derivatives possess two hydrogen
bond acceptors and two aromatic regions. From these points
of view, the 1,8-naphthyridine compounds were novel types
of PDE 4 inhibitors.
Six compounds showing potent PDE 4 inhibitory activities,
as well as YM-10335, rolipram, and CDP-840, were evalu-
ated for their PDE isozyme selectivities and lipopolysac-
charide (LPS)-induced tumor necrosis factor-alpha (TNF-a)
release in vitro (Table 6). All compounds showed good selec-
tivities of more than 500 times for PDE 4 against other PDE
isozymes. In the test of the TNF-a release, they showed good
inhibitory activities except for 7b.
Enzyme
12
4a
15
16
57
Furthermore, five compounds (7c, f, n, o, p), possessing
IC50 values less than 100 nM in the test of the TNF-a release,
were tested in the carrageenan-induced pleurisy model for
evaluation of their ability to inhibit cell infiltration and oral
effectiveness (Table 7). Three compounds (7c, n, p) showed
1600
Table 7. In Vivo Activities of 1,8-Naphthyridine Derivatives
Inhibition of carrageenan-induced pleurisy in rats (p.o.)
7o
19
1.8
No.
ED30 (mg/kg)a)
7c
7f
7n
7o
7p
15
Ͼ30
11
Ͼ30
15
220
a) Data of in vitro experiment are expressed as mean from two separate experiments,
and the individual experiment was performed in triplicate. The method of measurement
is described in Experimental.
a) Data of in vivo experiments showed mean of 6 animals in one group. The method
of measurement is described in Experimental.
Table 6. In Vitro Activities of 1,8-Naphthyridine Derivatives
PDE 4
PDEs inhibition IC50 (mM)a)
TNF-a
No.
inhibition
inhibition
IC50 (nM)a)
1
2
3
5
IC50 (nM)a)
YM-10335
220
5.9
1.1
2.8
1.2
1.8
0.61
820
19
70.9
7.93
245
Ͼ10
Ͼ10
Ͼ3
Ͼ3
Ͼ10
Ͼ3
Ͼ100
Ͼ100
Ͼ100
41
7b
7c
7f
7n
7o
Ͼ10
Ͼ10
0.57
Ͼ3
Ͼ10
Ͼ3
Ͼ10
Ͼ10
Ͼ3
Ͼ3
Ͼ10
Ͼ3
1.6
1.0
0.90
0.55
0.91
0.48
22
33
62
20
76
19
7p
Rolipram
CDP-840
Ͼ100
Ͼ30
Ͼ100
Ͼ30
Ͼ100
Ͼ30
Ͼ100
Ͼ30
a) Data of in vitro experiment are expressed as mean from two separate experiments, and the individual experiment was performed in triplicate. The method of measurement is
described in Experimental.

August 2002
1055
Fig. 1
in general procedure A.
inhibitory activities and their ED30 values were 15, 11, and
15 mg/kg, respectively, whereas 7f and 7o showed no oral ac-
tivity.
7-Ethyl-1,5-dimethyl-4-phenyl-1,8-naphthyridin-2(1H)-one (4b): 92%
yield; mp 88—88.5 °C (diisopropyl ether–hexane). 1H-NMR (CDCl3) d:
1.35 (3H, t, Jϭ7.0 Hz), 1.83 (3H, s), 2.84 (2H, q, Jϭ7.3 Hz), 3.90 (3H, s),
6.55 (1H, s), 6.76 (1H, s), 7.22—7.30 (2H, m), 7.40—7.45 (3H, m). MS m/z:
In conclusion, a novel class of PDE 4 inhibitors, YM-
10335, was found by chemical file screening and structural 278 (Mϩ). Anal. Calcd for C18H18N2O: C, 77.67; H, 6.52; N, 10.06. Found:
C, 77.67; H, 6.54; N, 10.05.
modification of YM-10335 led us to discover highly potent
and selective compounds. These YM-10335 derivatives also
showed potent inhibitory activities of the in vitro TNF-a re-
5,7-Diethyl-1-methyl-4-phenyl-1,8-naphthyridin-2(1H)-one (4c): 69% yield;
mp 68—69 °C (diisopropyl ether–hexane). 1H-NMR (CDCl3) d: 0.86 (3H, t,
Jϭ7.3 Hz), 1.37 (3H, t, Jϭ7.3 Hz), 2.18 (2H, q, Jϭ7.3 Hz), 2.86 (2H, q,
lease and in vivo carrageenan-induced pleurisy model. Fur-
ther modification and pharmacological evaluations are now
in progress.
Jϭ7.3 Hz), 3.90 (3H, s), 6.52 (1H, s), 6.85 (1H, s), 7.30—7.35 (2H, m),
7.38—7.45 (3H, m). MS m/z: 292 (Mϩ). Anal. Calcd for C19H20N2O: C,
78.05; H, 6.89; N, 9.58. Found: C, 78.17; H, 6.98; N, 9.62.
General Procedure B. Grignard Reaction with 2-Chloro-6-methylni-
cotinic Acid 2-Chloro-3-(3-fluorobenzoyl)-6-methylpyridine (5e): To a
Experimental
Chemistry Melting points were determined on a Yanaco micro-melting stirred solution of 3-bromochlorobenzene (46 g, 262 mmol) in anhydrous
apparatus and are uncorrected. Proton magnetic resonance (1H-NMR) spec- tetrahydrofuran (400 ml) was slowly added magnesium turnings (6.3 g,
tra were obtained in CDCl3 or dimethylsulfoxide-d6 (DMSO-d6) using a
262 mmol). After the exothermal reaction was completed, the reaction mix-
JEOL JNM-EX90, JNM-EX400, JNM-GX500 or JNM-A500 spectrometer. ture was cooled to Ϫ20 °C, and 2-chloro-6-methylnicotinic acid (21.1 g,
Chemical shifts are recorded in parts per million (d), downfield relative to 122 mmol) was added all at one time. The reaction mixture was stirred
tetramethylsilane as the internal standard. Mass spectra (MS) were recorded overnight at room temperature, diluted with saturated ammonium chloride
on a JEOL JMS-DX300 or a Hitachi M-80 mass spectrometer. Elemental aqueous solution, and extracted by ethyl acetate. The organic layer was
analyses were carried out on Yanaco MT-3 or MT-5 CHN analyzer and a washed with brine, dried over anhydrous magnesium sulfate, filtered, and
Yokogawa IC 7000S Ion Chromatoanalyzer. Chromatographic separations concentrated. The residue was chromatographed on silica gel using chloro-
1
were performed using a silica gel column (Wakogel C-200). Analytical thin- form as an eluent to provide 5 h (11.0 g, 36%) as a colorless oil. H-NMR
layer chromatography (TLC) was carried out on precoated glass plates (CDCl3) d: 2.64 (3H, s), 7.24 (1H, d, Jϭ7.6 Hz), 7.28—7.36 (1H, m),
(Merck Kieselgel 60F254).
7.42—7.56 (3H, m), 7.66 (1H, d, Jϭ7.6 Hz). MS m/z: 249 (Mϩ).
6-Amino-1-ethyl-4-phenyl-2(1H)-pyridone (3b): Ethyl 4-cyano-3-phenyl-
The following compounds were obtained in the same manner as described
3-butenoate13) (2, 29.0 g, 0.13 mol) and 28% ethylamine–methanol solution in general procedure B.
(41 g) were added to a methanol solution (120 ml) of sodium (4.1 g, 0.17
mol), and the mixture was stirred for 20 h at room temperature. The reaction (1H, dd, Jϭ7.8, 4.9 Hz), 7.50 (2H, t, Jϭ7.8 Hz), 7.66 (1H, t, Jϭ7.8 Hz), 7.75
3-Benzoyl-2-chloropyridine (5a): 55% yield; 1H-NMR (CDCl3) d: 7.39
solution was poured onto ice water and extracted with chloroform. The or-
ganic layer was dried over anhydrous magnesium sulfate, filtered, and con- 2.0 Hz). MS m/z: 217 (Mϩ).
centrated. The residue was washed with diethyl ether–diisopropyl ether to
3-Benzoyl-2-chloro-6-methylpyridine (5b): 57% yield; H-NMR (CDCl3)
(1H, dd, Jϭ7.8, 2.0 Hz), 7.81 (1H, dd, Jϭ8.3, 1.5 Hz), 8.55 (1H, dd, Jϭ4.9,
1
provide 3b (16.5 g, 57%) as a gray solid. 1H-NMR (DMSO-d6) d: 1.15 (3H, d: 2.63 (3H, s), 7.22 (1H, d, Jϭ7.6 Hz), 7.46—7.50 (2H, m), 7.60—7.66
t, Jϭ7.0 Hz), 4.00 (2H, q, Jϭ7.0 Hz), 5.68 (1H, d, Jϭ2.1 Hz), 5.74 (1H, d,
(2H, m), 7.79—7.82 (2H, m). FAB-MS m/z: 232 [MϩH]ϩ.
Jϭ2.1 Hz), 6.58 (2H, s), 7.35—7.60 (5H, m). MS m/z: 214 (Mϩ).
2-Chloro-3-(3-chlorobenzoyl)-6-methylpyridine (5c): 44% yield; 1H-
General Procedure A 1-Ethyl-5,7-dimethyl-4-phenyl-1,8-naphthyridin- NMR (CDCl3) d: 2.64 (3H, s), 7.24 (1H, d, Jϭ7.3 Hz), 7.43 (1H, t,
2(1H)-one (4a): A mixture of diphosphorus pentoxide (10.7 g) and phos- Jϭ7.9 Hz), 7.60 (1H, m), 7.65 (2H, m), 7.78 (1H, s). FAB-MS m/z: 266
phoric acid (5 ml) was stirred at 140 °C until it became transparent. 3b [MϩH]ϩ.
(2.14 g, 10 mmol) and acetylacetone (1.1 ml, 10 mmol) were then added to
this solution, and the mixture was stirred at 140 °C for 3 h. The reaction so- NMR (CDCl3) d: 2.63 (3H, s), 7.24 (1H, d, Jϭ7.6 Hz), 7.46 (2H, d,
lution was poured onto ice water, made alkaline by adding a 1 N sodium hy-
Jϭ8.8 Hz), 7.65 (1H, d, Jϭ7.6 Hz), 7.75 (2H, d, Jϭ8.8 Hz). FAB-MS m/z:
droxide aqueous solution and then extracted with ethyl acetate. After drying 266 [MϩH]ϩ.
2-Chloro-3-(4-chlorobenzoyl)-6-methylpyridine (5d): 37% yield; 1H-
the organic layer with anhydrous magnesium sulfate, the magnesium sulfate
2-Chloro-3-(3-methylbenzoyl)-6-methylpyridine (5f): 56% yield; 1H-
was removed by filtration and the filtrate was concentrated under reduced NMR (CDCl3) d: 2.40 (3H, s), 2.63 (3H, s), 7.22 (1H, t, Jϭ7.3 Hz), 7.43
pressure. The residue was purified by silica gel column chromatography (1H, d, Jϭ7.3 Hz), 7.57 (1H, d, Jϭ7.3 Hz), 7.60—7.65 (2H, m). MS m/z:
(toluene–ethyl acetate) to give 4a (2.10 g, 76%). Recrystallization from di- 245 (Mϩ).
isopropyl ether–hexane provided an analytical sample as colorless minute
prisms, mp 113—114 °C. 1H-NMR (CDCl3) d: 1.37 (3H, t, Jϭ7.0 Hz), 1.81 NMR (CDCl3) d: 2.63 (3H, s), 3.86 (3H, s), 7.15—7.19 (1H, m), 7.22 (1H,
(3H, s), 2.56 (3H, s), 4.66 (1H, q, Jϭ7.0 Hz), 6.53 (1H, s), 6.75 (1H, s),
d, Jϭ7.4 Hz), 7.26—7.29 (1H, m), 7.36 (1H, t, Jϭ7.9 Hz), 7.40—7.43 (1H,
7.25—7.30 (2H, m), 7.41—7.43 (3H, m). MS m/z: 278 (Mϩ). Anal. Calcd m), 7.64 (1H, d, Jϭ7.4 Hz). FAB-MS m/z: 262 [MϩH]ϩ.
2-Chloro-3-(3-methoxybenzoyl)-6-methylpyridine (5g): 46% yield; 1H-
for C18H18N2O: C, 77.67; H, 6.52; N, 10.06. Found: C, 77.93; H, 6.54; N,
9.93.
The following compounds were obtained in the same manner as described Jϭ7.8 Hz), 7.69 (1H, d, Jϭ7.8 Hz), 7.88 (1H, d, Jϭ7.8 Hz), 7.96 (1H, d,
2-Chloro-6-methyl-3-(3-trifluoromethylbenzoyl)pyridine (5h): 34% yield;
1H-NMR (CDCl3) d: 2.65 (3H, s), 7.27 (1H, d, Jϭ7.8 Hz), 7.64 (1H, t,

1056
Vol. 50, No. 8
Jϭ7.8 Hz), 8.08 (1H, s). FAB-MS m/z: 300 [MϩH]ϩ.
umn chromatography hexane–ethyl acetate as the eluent and the resulting
solid was washed with chloroform/hexane to provide 8a (23.6 g, 36%) as a
colorless solid. 1H-NMR (CDCl3) d: 4.15 (2H, s), 7.38—7.54 (3H, m), 7.64
(1H, dd, Jϭ7.8, 1.4 Hz). MS m/z: 179 (Mϩ).
2-Chloro-6-methyl-3-(3-nitrobenzoyl)pyridine (5i) 5b (3.00 g, 12.9
mmol) dissolved in concentrated sulfuric acid (40 ml) was cooled to below
5 °C, then fuming nitric acid (1.0 ml) was slowly added dropwise, followed
by stirring for 30 min. The reaction solution was poured into ice-water, neu-
tralized with a sodium hydroxide aqueous solution and then extracted with
ethyl acetate. The organic layer was washed with brine and dried over anhy-
drous magnesium sulfate. After removing the magnesium sulfate by filtra-
tion, the solvent was evaporated under reduced pressure and the resulting
residue was washed with ethyl acetate–diisopropyl ether to give 5i (1.81 g,
The following compound was obtained in the same manner as described
in general procedure D.
3-(3-Bromophenyl)-3-oxopropanenitrile (8b): 75% yield; 1H-NMR
(CDCl3) d: 4.06 (2H, s), 7.42 (1H, t, Jϭ7.8 Hz), 7.77—7.87 (2H, m), 8.06
(1H, t, Jϭ1.8 Hz). MS m/z: 223, 225 (Mϩ).
General Procedure E 3-(2-Chlorobenzoyl)-6-methyl-2-pyridone (9a):
A mixture of 8a (20.0 g, 111 mmol) and 75% diphosphorus pentoxide
(100 ml) was stirred at 100 °C for 2 h. The reaction solution was poured onto
ice water and extracted with ethyl acetate. The organic layer was washed
with saturated sodium bicarbonate aqueous solution and dried over anhy-
drous magnesium sulfate. The magnesium sulfate was removed by filtration
and the filtrate was concentrated under reduced pressure. The residue was
dissolved in ethanol (250 ml) and mixed with 1,1-dimethoxy-3-butanone
(20 ml, 151 mmol) and sodium ethoxide (9.0 g, 132 mmol). The mixture was
stirred overnight under reflux. The reaction mixture was poured onto ice-
water and extracted with chloroform. The organic layer was washed with
brine and dried over anhydrous magnesium sulfate. After removing the mag-
nesium sulfate by filtration, the solvent was evaporated under reduced pres-
sure and the resulting residue was washed with ether to give 9a (24.2 g,
84%) as a solid. 1H-NMR (DMSO-d6) d: 2.27 (3H, s), 6.21 (1H, d,
Jϭ7.4 Hz), 7.31—7.54 (4H, m), 7.92 (1H, d, Jϭ7.4 Hz), 12.11 (1H, br s).
FAB-MS m/z: 248 [MϩH]ϩ.
1
51%) as a solid. H-NMR (CDCl3) d: 2.67 (3H, s), 7.30 (1H, d, Jϭ7.6 Hz),
7.72 (1H, t, Jϭ7.6 Hz), 8.15 (1H, m), 8.48 (2H, m), 8.60 (1H, m). MS m/z:
276 (Mϩ).
General Procedure C. Substitution by Alkylamines 2-Ethylamino-3-
(3-fluorobenzoyl)-6-methylpyridine (6e): A mixture of 5i (5.0 g, 20 mmol)
and a 70% ethylamine aqueous solution (15 ml) was stirred for 4 h at 100 °C
in a sealed tube. The reaction mixture was cooled to room temperature and
diluted with ethyl acetate. The organic layer was subsequently washed with
water and brine, dried over anhydrous magnesium sulfate, filtered, and con-
centrated. The residue was chromatographed on silica gel using
hexane–ethyl acetate as the eluent to provide 6e (4.35 g, 84%) as a yellow
oil. 1H-NMR (CDCl3) d: 1.31 (3H, t, Jϭ7.3 Hz), 2.44 (3H, s), 3.64 (2H, m),
6.33 (1H, d, Jϭ8.1 Hz), 7.17—7.27 (2H, m), 7.31 (1H, dt, Jϭ7.3, 1.3 Hz),
7.42 (1H, dt, Jϭ8.1, 5.5 Hz), 7.57 (1H, d, Jϭ8.1 Hz), 8.84 (1H, br s). FAB-
MS m/z: 259 [MϩH]ϩ.
The following compounds were obtained in the same manner as described
in general procedure B.
3-Benzoyl-2-methylaminopyridine (6a): 89% yield; H-NMR (CDCl3) d:
3.14 (3H, d, Jϭ4.9 Hz), 6.49 (1H, dd, Jϭ7.8, 4.9 Hz), 7.45—7.60 (5H, m),
7.73 (1H, dd, Jϭ7.8, 2.0 Hz), 8.35 (1H, dd, Jϭ4.9, 2.0 Hz), 8.75 (1H, br s).
MS m/z: 212 (Mϩ).
The following compounds were obtained in the same manner as described
in general procedure E.
1
3-(3-Bromobenzoyl)-6-methyl-2-pyridone (9b): 79% yield; 1H-NMR
(DMSO-d6) d: 2.28 (3H, s), 6.21 (1H, d, Jϭ7.6 Hz), 7.44 (1H, t, Jϭ8.4 Hz),
7.68 (1H, d, Jϭ7.2 Hz), 7.74 (1H, d, Jϭ7.6 Hz), 7.76—7.82 (2H, m), 12.16
(1H, br s). FAB-MS m/z: 292, 294 [MϩH]ϩ.
3-Benzoyl-2-ethylamino-6-methylpyridine (6b): Without purification.
3-(3-Chlorobenzoyl)-2-ethylamino-6-methylpyridine (6c): 56% yield; H-
3-Benzoyl-6-methyl-2-pyridone (9c): 57% yield; 1H-NMR (DMSO-d6) d:
2.27 (3H, s), 6.17 (1H, d, Jϭ6.8 Hz), 7.47 (2H, t, Jϭ7.9 Hz), 7.59 (1H, t,
Jϭ7.4 Hz), 7.64 (1H, d, Jϭ6.8 Hz), 7.71 (2H, d, Jϭ7.4 Hz), 12.1 (1H, br s).
MS m/z: 213 (Mϩ).
1
NMR (CDCl3) d: 1.31 (3H, t, Jϭ7.0 Hz), 2.44 (3H, s), 3.64 (2H, m), 6.33
(1H, d, Jϭ7.9 Hz), 7.35—7.60 (5H, m), 8.84 (1H, br s). MS m/z: 274 (Mϩ).
3-(4-Chlorobenzoyl)-2-ethylamino-6-methylpyridine (6d): 92% yield; 1H-
NMR (CDCl3) d: 1.31 (3H, t, Jϭ7.3 Hz), 2.44 (3H, s), 3.63 (2H, m), 6.32
(1H, d, Jϭ8.1 Hz), 7.42 (2H, d, Jϭ8.3 Hz), 7.50 (2H, d, Jϭ8.3 Hz), 7.55
(1H, d, Jϭ8.1 Hz), 8.81 (1H, br s). FAB-MS m/z: 275 [MϩH]ϩ.
General Procedure
Methylbenzenesulfonate (10a):
F
3-(2-Chlorobenzoyl)-6-methyl-2-pyridyl 4-
mixture of 9a (20.0 g, 80 mmol),
A
dichloroethane (250 ml), p-toluenesulfonyl chloride (16.8 g, 88 mmol), tri-
ethylamine (12.2 ml, 88 mmol), and 4-dimethylaminopyridine (980 mg,
8 mmol) was stirred for 2 h at room temperature. The reaction mixture was
subsequently washed with water, 1 N hydrochloric acid, and saturated sodium
bicarbonate aqueous solution. The organic layer was dried over anhydrous
magnesium sulfate, filtered, and concentrated. The residue was chro-
matographed on silica gel using hexane–ethyl acetate as the eluent to pro-
1
2-Ethylamino-3-(3-methylbenzoyl)-6-methylpyridine (6f): 83% yield; H-
NMR (CDCl3) d: 1.31 (3H, t, Jϭ7.3 Hz), 2.40 (3H, s), 2.43 (3H, s), 3.63
(2H, m), 6.31 (1H, d, Jϭ7.9 Hz), 7.32 (3H, s), 7.36 (1H, s), 7.61 (1H, d,
Jϭ7.9 Hz), 8.85 (1H, br s). MS m/z: 254 (Mϩ).
2-Ethylamino-3-(3-methoxybenzoyl)-6-methylpyridine (6g): 83% yield;
1H-NMR (CDCl3) d: 1.31 (3H, t, Jϭ7.4 Hz), 2.43 (3H, s), 3.64 (2H, m),
3.84 (3H, s), 6.32 (1H, d, Jϭ8.1 Hz), 7.02—7.12 (3H, m), 7.34 (1H, t,
Jϭ7.8 Hz), 7.63 (1H, d, Jϭ8.1 Hz), 8.85 (1H, br s). FAB-MS m/z: 271
[MϩH]ϩ.
1
vide 10a (30.9 g, 96%) as a syrup. H-NMR (CDCl3) d: 2.44 (3H, s), 2.49
(3H, s), 7.16 (1H, d, Jϭ7.8 Hz), 7.26—7.42 (5H, m), 7.46 (1H, dd, Jϭ7.5,
1.6 Hz), 7.78 (2H, d, Jϭ7.3 Hz), 8.04 (1H, d, Jϭ7.8 Hz). FAB-MS m/z: 402
[MϩH]ϩ.
2-Ethylamino-3-(3-trifluoromethylbenzoyl)-6-methylpyridine (6h): 86%
1
The following compounds were obtained in the same manner as described
in general procedure F.
yield; H-NMR (CDCl3) d: 1.32 (3H, t, Jϭ7.4 Hz), 2.45 (3H, s), 3.66 (2H,
m), 6.34 (1H, d, Jϭ8.3 Hz), 7.51 (1H, d, Jϭ8.3 Hz), 7.59 (1H, t, Jϭ7.9 Hz),
7.72 (1H, d, Jϭ7.9 Hz), 7.76 (1H, d, Jϭ7.9 Hz), 8.87 (1H, br s). MS m/z:
308 (Mϩ).
3-(3-Bromobenzoyl)-6-methyl-2-pyridyl 4-Methylbenzenesulfonate (10b):
89% yield; 1H-NMR (CDCl3) d: 2.44 (3H, s), 2.56 (3H, s), 7.19 (1H, d,
Jϭ8.0 Hz), 7.25—7.34 (3H, m), 7.62 (1H, d, Jϭ8.0 Hz), 7.68 (1H, d,
Jϭ8.4 Hz), 7.74 (2H, d, Jϭ8.4 Hz), 7.81—7.84 (2H, m). FAB-MS m/z: 446,
448 [MϩH]ϩ.
3-Benzoyl-6-methyl-2-pyridyl 4-Methylbenzenesulfonate (10c): Quantita-
tive yield; 1H-NMR (CDCl3) d: 2.41 (3H, s), 2.54 (3H, s), 7.17 (1H, d,
Jϭ7.8 Hz), 7.24 (2H, d, Jϭ8.3 Hz), 7.45 (2H, t, Jϭ7.8 Hz), 7.59 (1H, t,
Jϭ7.3 Hz), 7.72—7.76 (2H, m), 7.80 (1H, d, Jϭ7.8 Hz). FAB-MS m/z: 368
[MϩH]ϩ.
2-Ethylamino-6-methyl-3-(3-nitrobenzoyl)pyridine (6i): 56% yield; 1H-
NMR (CDCl3) d: 1.32 (3H, t, Jϭ7.4 Hz), 2.46 (3H, s), 3.63—3.70 (2H, m),
6.35 (1H, d, Jϭ8.0 Hz), 7.49 (1H, d, Jϭ8.0 Hz), 7.66 (1H, t, Jϭ8.0 Hz), 7.87
(1H, dt, Jϭ8.0, 1.3 Hz), 8.35—8.40 (2H, m), 8.88 (1H, br s). MS m/z: 285
(Mϩ).
General Procedure D 3-(2-Chlorophenyl)-3-oxopropanenitrile (8a): A
solution of 2-chlorobenzonitrile (50.0 g, 363 mmol), acetonitrile (21.0 ml,
402 mmol) and tert-butanol (4.0 ml, 42 mmol) in tetrahydrofuran (200 ml)
was added dropwise to a mixture of sodium hydride/60% oil dispersion
(16.0 g, 400 mmol) and tetrahydrofuran (200 ml), and the mixture was stirred
at 40 °C for 8 h. The reaction mixture was poured onto ice water and ex-
tracted with ethyl acetate. The organic layer was washed with brine and
dried over anhydrous magnesium sulfate. The magnesium sulfate was re-
moved by filtration and the filtrate was concentrated under reduced pressure.
The residue was then dissolved in chloroform (350 ml) and then 3 N hy-
drochloric acid (300 ml) was added. The mixture was stirred at room tem-
perature for 4 h and organic layer was separated. The aqueous layer was ex-
tracted with chloroform and the chloroform layer was combined. The or-
ganic layer was washed with brine and dried over anhydrous magnesium sul-
fate. Magnesium sulfate was removed by filtration and the filtrate was con-
centrated under reduced pressure. The residue was purified by silica gel col-
General Procedure G. Substitution by Alkylamines 3-(2-Chloroben-
zoyl)-2-ethylamino-6-methylpyridine (6m):
A mixture of 10a (8.0 g,
20 mmol), 70% ethylamine aqueous solution (10 ml), and toluene (30 ml)
was stirred for 1.5 h at 100 °C in a sealed tube. The reaction mixture was
cooled to room temperature, diluted with ethyl acetate, and washed well
with water. The organic layer was dried over anhydrous magnesium sulfate,
filtered, and concentrated. The residue was chromatographed on silica gel
using hexane–ethyl acetate as the eluent to provide 6m (5.36 g, 98%) as a
1
yellow oil. H-NMR (CDCl3) d: 1.33 (3H, t, Jϭ7.3 Hz), 2.42 (3H, s), 3.66
(2H, m), 6.28 (1H, d, Jϭ8.3 Hz), 7.24—7.46 (4H, m), 9.02 (1H, br s). FAB-
MS m/z: 275 [MϩH]ϩ.
The following compounds were obtained in the same manner as described
in general procedure G.

August 2002
1057
3-Benzoyl-6-methyl-2-methylaminopyridine (6j): 84% yield; 1H-NMR
(CDCl3) d: 2.46 (3H, s), 3.14 (3H, d, Jϭ4.9 Hz), 6.33 (1H, d, Jϭ7.9 Hz),
7.42—7.56 (5H, m), 7.61 (1H, d, Jϭ7.9 Hz), 8.85 (1H, br s). FAB-MS m/z:
227 [MϩH]ϩ.
1-Ethyl-4-(3-methoxyphenyl)-7-methyl-1,8-naphthyridin-2(1H)-one (7g):
84% yield; mp 116—117 °C (ethyl acetate–diisopropyl ether). 1H-NMR
(CDCl3) d: 1.38 (3H, t, Jϭ7.0 Hz), 2.64 (3H, s), 3.85 (3H, s), 4.65 (2H, q,
Jϭ7.0 Hz), 6.66 (1H, s), 6.91—7.04 (4H, m), 7.40 (1H, t, Jϭ7.8 Hz), 7.77
(1H, d, Jϭ8.3 Hz). FAB-MS m/z: 295 [MϩH]ϩ. Anal. Calcd for
C18H18N2O2: C, 73.45; H, 6.16; N, 9.52. Found: C, 73.48; H, 6.19; N, 9.51.
1-Ethyl-7-methyl-4-(3-trifluoromethylphenyl)-1,8-naphthyridin-2(1H)-
one (7h): 86% yield; mp 136—137 °C (ethyl acetate–diisopropyl ether). 1H-
NMR (CDCl3) d: 1.38 (3H, t, Jϭ7.1 Hz), 2.65 (3H, s), 4.66 (2H, q,
Jϭ7.1 Hz), 6.67 (1H, s), 6.99 (1H, d, Jϭ8.3 Hz), 7.58—7.69 (4H, m), 7.76
(1H, d, Jϭ7.8 Hz). FAB-MS m/z: 333 [MϩH]ϩ. Anal. Calcd for
C18H15N2OF3: C, 65.06; H, 4.55; N, 8.43; F, 17.15. Found: C, 65.12; H, 4.39;
N, 8.45; F, 17.22.
1-Ethyl-7-methyl-4-(3-nitrophenyl)-1,8-naphthyridin-2(1H)-one (7i): mp
184—189 °C (ethyl acetate–diisopropyl ether). 1H-NMR (CDCl3) d: 1.39
(3H, t, Jϭ7.0 Hz), 2.66 (3H, s), 4.66 (1H, q, Jϭ7.0 Hz), 6.69 (1H, s), 7.01
(1H, d, Jϭ8.0 Hz), 7.60 (1H, d, Jϭ8.0 Hz), 7.69—7.77 (2H, m), 8.28—8.31
(1H, m), 8.36 (1H, dt, Jϭ7.3, 2.0 Hz). FAB-MS m/z: 310 [MϩH]ϩ. Anal.
Calcd for C17H15N3O3: C, 66.01; H, 4.89; N, 13.58. Found: C, 66.22; H,
4.70; N, 13.57.
3-Benzoyl-6-methyl-2-propylaminopyridine (6k): 93% yield; 1H-NMR
(CDCl3) d: 1.04 (3H, t, Jϭ7.3 Hz), 1.72 (2H, m), 2.43 (3H, s), 3.58 (2H, m),
6.31 (1H, d, Jϭ8.1 Hz), 7.42—7.56 (5H, m), 7.61 (1H, d, Jϭ8.1 Hz), 8.95
(1H, br s). FAB-MS m/z: 255 [MϩH]ϩ.
3-Benzoyl-2-isopropylamino-6-methylpyridine (6l): 52% yield; 1H-NMR
(CDCl3) d: 1.31 (6H, d, Jϭ6.4 Hz), 2.43 (3H, s), 4.51 (1H, m), 6.30 (1H, d,
Jϭ8.1 Hz), 7.41—7.56 (5H, m), 7.60 (1H, d, Jϭ8.1 Hz), 8.83 (1H, br d,
Jϭ6.3 Hz). FAB-MS m/z: 255 [MϩH]ϩ.
3-(3-Bromobenzoyl)-2-ethylamino-6-methylpyridine (6n): 59% yield; 1H-
NMR (CDCl3) d: 1.31 (3H, t, Jϭ7.3 Hz), 2.44 (3H, s), 3.64 (2H, m), 6.33
(1H, d, Jϭ7.9 Hz), 7.32 (1H, t, Jϭ7.9 Hz), 7.45 (1H, d, Jϭ7.3 Hz), 7.55 (1H,
d, Jϭ7.9 Hz), 7.63 (1H, dd, Jϭ7.9, 1.2 Hz), (1H, s), 7.68 (1H, s), 8.83 (1H,
br s). FAB-MS m/z: 319, 321 [MϩH]ϩ.
General Procedure H. Acetylation and Cyclization 1-Ethyl-4-(3-fluo-
rophenyl)-7-methyl-1,8-naphthyridin-2(1H)-one (7e): To a solution of 6e
(2.25 g, 8.7 mmol) in dichloroethane (30 ml) was added acetyl chloride
(1.25 ml, 17.6 mmol) and 4-dimethylaminopyridine (1.17 g, 9.6 mmol), and
the solution was stirred under reflux for 1 h. The reaction mixture was al-
lowed to cool to room temperature and subsequently washed with water, 1 N
hydrochloric acid, and saturated sodium bicarbonate aqueous solution. The
organic layer was dried over anhydrous magnesium sulfate, filtered, and con-
centrated to provide the crude N-[3-(3-fluorobenzoyl)-6-methyl-2-pyridyl]-
N-ethylacetamide. To the N-[3-(3-fluorobenzoyl)-6-methyl-2-pyridyl]-N-eth-
ylacetamide was added ethanol (30 ml) and sodium ethoxide (220 mg,) and
stirred under reflux for 30 min. The reaction mixture was allowed to cool to
room temperature and diluted with chloroform. The organic layer was subse-
quently washed with 1 N hydrochloric acid, and saturated sodium bicarbonate
aqueous solution, dried over anhydrous magnesium sulfate, filtered, and con-
centrated. The residue was chromatographed on silica gel using hexane–
ethyl acetate as the eluent to provide 7e (1.18 g, 95%). Recrystallization
from ethyl acetate–diisopropyl ether provided an analytical sample as color-
less minute prisms, mp 106—107 °C. 1H-NMR (CDCl3) d: 1.38 (3H, t,
Jϭ7.0 Hz), 2.64 (3H, s), 4.65 (2H, q, Jϭ7.0 Hz), 6.65 (1H, s), 6.98 (1H, d,
Jϭ7.8 Hz), 7.09—7.21 (3H, m), 7.47 (1H, m), 7.70 (1H, d, Jϭ7.8 Hz). FAB-
MS m/z: 283 [MϩH]ϩ. Anal. Calcd for C17H15N2OF: C, 72.33; H, 5.36; N,
9.92; F, 6.73. Found: C, 72.36; H, 5.39; N, 9.90; F, 6.71.
1,7-Dimethyl-4-phenyl-1,8-naphthyridin-2(1H)-one (7j): 89% yield; mp
117—119 °C (ethyl acetate–diisopropyl ether). 1H-NMR (CDCl3) d: 2.65
(3H, s), 3.89 (3H, s), 6.68 (1H, s), 6.97 (1H, d, Jϭ8.3 Hz), 7.38—7.42 (2H,
m), 7.47—7.53 (3H, m), 7.74 (1H, d, Jϭ8.3 Hz). FAB-MS m/z: 251
[MϩH]ϩ. Anal. Calcd for C16H14N2O: C, 76.78; H, 5.64; N, 11.19. Found:
C, 77.00; H, 5.67; N, 11.11.
7-Methyl-4-phenyl-1-propyl-1,8-naphthyridin-2(1H)-one (7k): 89% yield;
1
mp 92—93 °C (isopropyl ether–hexane). H-NMR (CDCl3) d: 1.04 (3H, t,
Jϭ7.3 Hz), 1.83 (2H, m), 2.63 (3H, s), 4.54 (2H, t, Jϭ7.6 Hz), 6.65 (1H, s),
6.95 (1H, d, Jϭ7.8 Hz), 7.38—7.42 (2H, m), 7.46—7.53 (3H, m), 7.73 (1H,
d, Jϭ7.8 Hz). FAB-MS m/z: 279 [MϩH]ϩ. Anal. Calcd for C18H18N2O: C,
77.67; H, 6.52; N, 10.06. Found: C, 77.77; H, 6.51; N, 9.99.
1-Isopropyl-7-methyl-4-phenyl-1,8-naphthyridin-2(1H)-one (7l): 66% yield;
1
mp 137—139 °C (isopropyl ether–hexane). H-NMR (CDCl3) d: 1.69 (6H,
d, Jϭ6.8 Hz), 2.62 (3H, s), 6.60 (1H, s), 6.93 (1H, d, Jϭ8.3 Hz), 7.37—7.41
(2H, m), 7.46—7.52 (3H, m), 7.71 (1H, d, Jϭ8.3 Hz). FAB-MS m/z: 279
[MϩH]ϩ. Anal. Calcd for C18H18N2O: C, 77.67; H, 6.52; N, 10.06. Found:
C, 77.68; H, 6.67; N, 10.14.
4-(2-Chlorophenyl)-1-ethyl-7-methyl-1,8-naphthyridin-2(1H)-one (7m):
81% yield; mp 122—123 °C (ethyl acetate–diisopropyl ether). 1H-NMR
(CDCl3) d: 1.40 (3H, t, Jϭ7.1 Hz), 2.63 (3H, s), 4.66 (2H, m), 6.62 (1H, s),
6.94 (1H, d, Jϭ7.8 Hz), 7.26—7.46 (4H, m), 7.53 (1H, dd, Jϭ7.4, 1.5 Hz).
FAB-MS m/z: 299 [MϩH]ϩ. Anal. Calcd for C17H15N2OCl: C, 68.34; H,
5.06; N, 9.38; Cl, 11.87. Found: C, 68.31; H, 5.03; N, 9.54; Cl, 11.87.
4-(3-Bromophenyl)-1-ethyl-7-methyl-1,8-naphthyridin-2(1H)-one (7n):
The following compounds were obtained in the same manner as described
in general procedure H.
1-Methyl-4-phenyl-1,8-naphthyridin-2(1H)-one (7a): 72% yield; mp
133—135 °C (diisopropyl ether). 1H-NMR (CDCl3) d: 3.90 (3H, s), 6.75
(1H, s), 7.13 (1H, dd, Jϭ7.8, 4.7 Hz), 7.38—7.47 (2H, m), 7.49—7.53 (3H,
m), 7.88 (1H, dd, Jϭ7.8, 1.5 Hz), 8.62 (1H, dd, Jϭ4.7, 1.5 Hz). MS m/z: 236
(Mϩ). Anal. Calcd for C15H12N2O: C, 76.25; H, 5.12; N, 11.86. Found: C,
76.26; H, 5.23; N, 11.85.
1-Ethyl-7-methyl-4-phenyl-1,8-naphthyridin-2(1H)-one (7b): 56% yield;
mp 105—107 °C (isopropyl ether–hexane). 1H-NMR (CDCl3) d: 1.38 (3H, t,
Jϭ7.0 Hz), 2.64 (3H, s), 4.65 (2H, q, Jϭ7.0 Hz), 5.30 (1H, q, Jϭ6.7 Hz),
6.65 (1H, s), 6.96 (1H, d, Jϭ7.9 Hz), 7.38—7.42 (2H, m), 7.46—7.52 (3H,
m), 7.73 (1H, d, Jϭ7.9 Hz). FAB-MS m/z: 265 [MϩH]ϩ. Anal. Calcd for
C17H16N2O: C, 77.25; H, 6.10; N, 10.60. Found: C, 77.53; H, 6.20; N, 10.57.
1
79% yield; mp 134—135 °C (ethyl acetate). H-NMR (CDCl3) d: 1.37 (3H,
t, Jϭ7.0 Hz), 2.64 (3H, s), 4.64 (2H, q, Jϭ7.0 Hz), 6.63 (1H, s), 6.98 (1H, d,
Jϭ7.9 Hz), 7.33 (1H, d, Jϭ7.3 Hz), 7.38 (1H, t, Jϭ7.3 Hz), 7.55 (1H, s),
7.62 (1H, d, Jϭ7.3 Hz), 7.67 (1H, d, Jϭ7.9 Hz). FAB-MS m/z: 343, 345
[MϩϩH]ϩ. Anal. Calcd for C17H15N2OBr: C, 59.49; H, 4.41; N, 8.16; Br,
23.28. Found: C, 59.62; H, 4.46; N, 8.10; Br, 23.04.
General Procedure I. Alkylation of 7-Methyl Group 4-(3-Chloro-
phenyl)-1,7-diethyl-1,8-naphthyridin-2(1H)-one (7p): In an atmosphere of
argon, a 1.6 M n-butyllithium hexane solution (1.3 ml, 2.1 mmol) was added
dropwise to a tetrahydrofuran solution (5 ml) of diisopropylamine (203 mg,
2 mmol) which had been cooled at Ϫ78 °C. After the addition was complete,
this solution was warmed to ϫ30 °C, then cooled to Ϫ78 °C and 7c (597 mg,
2 mmol) was slowly added dropwise and the solution was stirred for 15 min
at the same temperature. Methyl iodide (1.3 ml, 2.1 mmol) was slowly added
dropwise at Ϫ78 °C and the solution was stirred for 30 min at same tempera-
ture. The reaction solution was mixed with water and extracted with ethyl
acetate. The organic layer was dried over anhydrous magnesium sulfate.
After removing the magnesium sulfate, the solvent was evaporated under re-
duced pressure. The residue was purified by silica gel column chromatogra-
phy (hexane–ethyl acetate) and further recrystallized from hexane to give 7p
(161 mg, 26%) as colorless crystals. mp 74—75 °C. 1H-NMR (CDCl3) d:
1.35—1.40 (6H, m), 2.91 (2H, q, Jϭ7.5 Hz), 4.66 (2H, q, Jϭ7.1 Hz), 6.61
(1H, s), 6.99 (1H, d, Jϭ8.2 Hz), 7.28 (1H, d, Jϭ6.7 Hz), 7.40—7.50
(3H, m), 7.70 (1H, d, Jϭ8.2 Hz). MS m/z: 312 (Mϩ). Anal. Calcd for
C18H17N2OCl: C, 69.12; H, 5.48; N, 8.96; Cl, 11.33. Found: C, 69.19; H,
5.42; N, 8.92; Cl, 11.68.
4-(3-Chlorophenyl)-1-ethyl-7-methyl-1,8-naphthyridin-2(1H)-one
(7c):
1
39% yield; mp 112—113 °C (diisopropyl ether–hexane). H-NMR (CDCl3)
d: 1.37 (3H, t, Jϭ7.1 Hz), 2.64 (3H, s), 4.65 (2H, q, Jϭ7.1 Hz), 6.64 (1H, s),
6.98 (1H, d, Jϭ7.9 Hz), 7.28 (1H, m), 7.40—7.50 (3H, m), 7.67 (1H, d,
Jϭ7.9 Hz). MS m/z: 298 (Mϩ). Anal. Calcd for C17H15N2OCl: C, 68.34; H,
5.06; N, 9.38; Cl, 11.87. Found: C, 68.14; H, 5.03; N, 9.36; Cl, 11.95.
4-(4-Chlorophenyl)-1-ethyl-7-methyl-1,8-naphthyridin-2(1H)-one (7d):
92% yield; mp 133—135 °C (ethyl acetate–diisopropyl ether). 1H-NMR
(CDCl3) d: 1.37 (3H, t, Jϭ6.9 Hz), 2.64 (3H, s), 4.65 (1H, q, Jϭ6.9 Hz),
6.63 (1H, s), 6.97 (1H, d, Jϭ8.0 Hz), 7.34 (2H, d, Jϭ8.3 Hz), 7.48 (1H, d,
Jϭ8.3 Hz), 7.68 (1H, d, Jϭ8.0 Hz). FAB-MS m/z: 299 [MϩH]ϩ. Anal.
Calcd for C17H15N2OCl: C, 68.34; H, 5.06; N, 9.38; Cl, 11.87. Found: C,
68.41; H, 5.04; N, 9.35; Cl, 11.99.
1-Ethyl-7-methyl-4-(3-methylphenyl)-1,8-naphthyridin-2(1H)-one (7f):
79% yield; mp 89—91 °C (hexane). 1H-NMR (CDCl3) d: 1.37 (3H, t,
Jϭ7.1 Hz), 2.43 (3H, s), 2.63 (3H, s), 4.65 (2H, q, Jϭ7.1 Hz), 6.64 (1H, s),
6.96 (1H, d, Jϭ8.2 Hz), 7.18—7.21 (2H, m), 7.28 (1H, d, Jϭ7.9 Hz), 7.38
(1H, t, Jϭ7.6 Hz), 7.74 (1H, d, Jϭ8.2 Hz). MS m/z: 278 (Mϩ). Anal. Calcd
for C18H18N2O: C, 77.67; H, 6.52; N, 10.06. Found: C, 77.75; H, 6.50; N,
9.98.
The following compounds were obtained in the same manner as described
in general procedure I.
4-(3-Chlorophenyl)-1-ethyl-7-propyl-1,8-naphthyridin-2(1H)-one (7q):

1058
Vol. 50, No. 8
37% yield; mp 80—81 °C (hexane). 1H-NMR (CDCl3) d: 1.01 (3H, t,
Jϭ7.3 Hz), 1.38 (3H, t, Jϭ7.0 Hz), 2.85 (2H, m), 2.85 (2H, t, Jϭ7.6 Hz),
4.66 (2H, q, Jϭ7.0 Hz), 6.64 (1H, s), 6.97 (1H, d, Jϭ8.2 Hz), 7.28 (1H, d,
Jϭ7.3 Hz), 7.40—7.50 (3H, m), 7.69 (1H, d, Jϭ8.2 Hz). FAB-MS m/z: 327
[MϩH]ϩ. Anal. Calcd for C19H19N2OCl: C, 69.83; H, 5.86; N, 8.57; Cl,
10.85. Found: C, 69.69; H, 5.91; N, 8.49; Cl, 11.06.
4-Phenyl-1,8-naphthyridin-2(1H)-one (14) A mixture of 13 (2.09 g,
5.25 mmol), 3 N hydrochloric acid (10 ml), and dioxane (10 ml) was stirred
under reflux for 3 d. The reaction mixture was allowed to cool to room tem-
perature, mixed with water, and the aqueous layer was neutralized with a sat-
urated sodium bicarbonate aqueous solution. The resulting precipitate was
filtered, washed with water, and recrystallized from acetonitrile to give 14
(600 mg, 51%) as colorless needles. mp 200Ͻ(sblimated) °C. 1H-NMR
(CDCl3) d: 6.72 (1H, s), 7.17 (1H, dd, Jϭ7.9, 4.9 Hz), 7.44—7.45 (2H, m),
7.50—7.56 (3H, m), 7.90 (1H, dd, Jϭ7.9, 1.2 Hz), 8.71 (1H, dd, Jϭ4.9,
1.2 Hz), 11.56 (1H, br s). MS m/z: 222 (Mϩ). Anal. Calcd for C14H10N2O: C,
75.66; H, 4.54; N, 12.60. Found: C, 75.68; H, 4.65; N, 12.70.
N-3-Ethylphenyl 3-Phenyl-3-oxopropanamide (17) A mixture of 3-
ethylaniline (5.00 g, 41 mmol), ethyl 3-phenyl-3-oxopropanate (9.50 g, 49
mmol), and pyridine (2 drops) in xylene (30 ml) was stirred under reflux for
72 h. The reaction mixture was concentrated under reduced pressure and di-
luted with 1 N hydrochloric acid. The aqueous layer was extracted with chlo-
roform and the organic layer was washed with brine, and dried over anhy-
drous sodium sulfate. After removing the sodium sulfate, the solvent was
evaporated under reduced pressure. The residue was purified by silica gel
column chromatography (hexane–ethyl acetate) to give 17 (2.85 g, 26%) as a
syrup. 1H-NMR (CDCl3) d: 1.23 (3H, t, Jϭ7.5 Hz), 2.64 (2H, q, Jϭ7.5 Hz),
4.11 (2H, s), 6.97 (1H, d, Jϭ8.0 Hz), 7.20—7.30 (2H, m), 7.41 (2H, s), 7.52
(2H, t, Jϭ7.3 Hz), 7.64 (1H, t, Jϭ6.7 Hz), 8.04 (2H, d, Jϭ7.9 Hz), 9.19 (1H,
s). FAB-MS m/z: 268 [MϩH]ϩ.
1,7-Diethyl-4-phenyl-1,8-naphthyridin-2(1H)-one (7o): 36% yield; mp
1
85—86 °C (isopropyl ether–hexane). H-NMR (CDCl3) d: 1.35—1.41 (6H,
m), 2.90 (2H, q, Jϭ7.3 Hz), 4.67 (2H, q, Jϭ7.3 Hz), 6.66 (1H, s), 6.96 (1H,
d, Jϭ7.9 Hz), 7.38—7.42 (2H, m), 7.46—7.52 (3H, m), 7.75 (1H, d,
Jϭ7.9 Hz). MS m/z: 278 (Mϩ). Anal. Calcd for C18H18N2O: C, 77.67; H,
6.52; N, 10.06. Found: C, 77.60; H, 6.50; N, 9.98.
1-Ethyl-5,7-dimethyl-4-phenyl-1,8-naphthyridin-2(1H)-thione (15)
Diphosphorous pentasulfide (1.55 g, 6.96 mmol) was added to a solution of
4a (1.02 g, 3.67 mmol) in dichloromethane (30 ml), and the mixture was
stirred under reflux for 3 d. The reaction mixture was allowed to cool to
room temperature, mixed with a saturated sodium bicarbonate aqueous solu-
tion and then extracted with chloroform. The organic layer was washed with
brine and dried over anhydrous sodium sulfate. After removing the sodium
sulfate, the solvent was evaporated under reduced pressure. The residue was
purified by silica gel column chromatography (hexane–benzene then ben-
zene) and further recrystallized from diisopropyl ether to give 15 (388 mg,
36%) as yellow crystals. mp 148—149 °C. 1H-NMR (CDCl3) d: 1.46 (3H, t,
Jϭ6.7 Hz), 1.86 (3H, s), 2.61 (3H, s), 5.30 (1H, q, Jϭ6.7 Hz), 6.87 (1H, s),
7.25—7.27 (2H, m), 7.41—7.42 (3H, m), 7.49 (1H, s). MS m/z: 294 (Mϩ).
Anal. Calcd for C18H18N2S: C, 73.43; H, 6.16; N, 9.51; S, 10.89. Found: C,
73.52; H, 6.16; N, 9.46; S, 11.16.
7-Ethyl-4-phenylquinolin-2(1H)-one (18) A mixture of diphosphorus
pentoxide (15 g) and phosphoric acid (15 ml) was stirred at 100 °C for
15 min. Then, 17 (2.83 g, 10 mmol) was added to this solution, and the mix-
ture was stirred at 100 °C for 1 h. The reaction solution was poured onto ice
water, the resulting precipitate was collected and dissolved in chloroform.
The organic layer was subsequently washed with a 1 N sodium hydroxide
aqueous solution and brine. After drying the organic layer with anhydrous
sodium sulfate, the sodium sulfate was removed by filtration and the filtrate
was concentrated under reduced pressure. The residue was purified by silica
gel column chromatography (chloroform–ethyl acetate) to give 18 (2.35 g,
1-Ethyl-3,4-dihydro-5,7-dimethyl-4-phenyl-1,8-naphthyridin-2(1H)-
one (16) A solution of 4a (1.02 g, 3.67 mmol) in acetic acid (15 ml) was
hydrogenated over 10% platinum dioxide (130 mg) at atmospheric pressure.
When the reaction was judged complete by TLC analysis, the catalyst was
filtered off. The filtrate was mixed with a 1 N sodium hydroxide aqueous so-
lution and extracted with chloroform. The organic layer was washed with
brine and dried over anhydrous sodium sulfate. After removing the sodium
sulfate, the solvent was evaporated under reduced pressure. The residue was
purified by silica gel column chromatography (benzene then benzene–ethyl
acetate) and further recrystallized from hexane to give 16 (100 mg, 10%) as
1
89%) as a syrup. H-NMR (CDCl3) d: 1.29 (3H, t, Jϭ7.3 Hz), 2.76 (2H, q,
Jϭ7.3 Hz), 6.55 (1H, s), 7.02 (1H, dd, Jϭ8.5, 1.2 Hz), 7.31 (1H, s), 7.40—
7.55 (6H, m), 12.36 (1H, s). MS m/z: 249 (Mϩ).
1
crystals. mp 66—71 °C. H-NMR (CDCl3) d: 1.18 (3H, t, Jϭ6.4 Hz), 2.12
1,7-Diethyl-4-phenylquinolin-2(1H)-one (19) To
a solution of 18
(3H, s), 2.47 (3H, d, Jϭ1.2 Hz), 2.90 (1H, d, Jϭ15.9 Hz), 2.98—3.02 (1H,
m), 4.12—4.19 (1H, m), 4.26 (1H, d, Jϭ6.7 Hz), 4.29—4.36 (1H, m), 6.69
(1H, s), 6.97 (2H, d, Jϭ7.3 Hz), 7.16—7.26 (3H, m). MS m/z: 280 (Mϩ).
Anal. Calcd for C18H20N2O: C, 77.11; H, 7.19; N, 9.99. Found: C, 77.03; H,
7.32; N, 9.73.
(2.30 g, 9 mmol) in dimethylformamide (100 ml) was added a sodium hy-
dride/60% oil dispersion (450 mg, 112 mmol) and the mixture was stirred at
80 °C for 30 min. To the reaction mixture was added ethyl iodide (2.90 g,
19 mmol) and then it was stirred for 1 h. The mixture was concentrated and
diluted with water, and then extracted with chloroform. The organic layer
was washed with brine and dried over anhydrous sodium sulfate. The
sodium sulfate was removed by filtration and the filtrate was concentrated
under reduced pressure. The residue was purified by silica gel column chro-
matography (hexane–ethyl acetate) to give 19, (983 mg, 38%) as a syrup.
1H-NMR (CDCl3) d: 1.32 (3H, t, Jϭ7.3 Hz), 1.42 (3H, t, Jϭ7.3 Hz), 2.80
(2H, q, Jϭ7.3 Hz), 4.43 (2H, q, Jϭ7.3 Hz), 6.61 (1H, s), 7.26 (1H, s), 7.01
(1H, d, Jϭ7.9 Hz), 7.39—7.53 (6H, m). MS m/z: 276 (MϩϪ1).
3-Benzoyl-2-pivaroylaminopyridine (12) In an atmosphere of argon, a
1.69 M n-butyllithium hexane solution (43 ml, 73 mmol) was added dropwise
to a tetrahydrofuran solution (60 ml) of 2-pivaroylaminopyridine (11, 61.1 g,
34 mmol) which was cooled at Ϫ78 °C. After the addition was complete, this
solution was warmed to 0 °C and stirred for 2.5 h. Then, N-methoxy-N-
methylbenzamide (6.25 g, 38 mmol) was slowly added dropwise at Ϫ78 °C,
the solution was warmed to room temperature and stirred for 2 h. The reac-
tion solution was poured into water and extracted with ethyl acetate. The or-
ganic layer was dried over anhydrous magnesium sulfate. After removing the
magnesium sulfate, the solvent was evaporated under reduced pressure. The
residue was purified by silica gel column chromatography (chloroform then
chloroform–ethyl acetate) and further washed with diisopropyl ether to give
12 (5.70 g, 59%) as a solid. 1H-NMR (CDCl3) d: 1.23 (9H, s), 7.14 (1H, dd,
Jϭ7.8, 4.9 Hz), 7.48 (2H, t, Jϭ7.8 Hz), 7.58 (1H, t, Jϭ7.8 Hz), 7.72 (2H, d,
Jϭ7.8 Hz), 7.91 (1H, dd, Jϭ7.8, 2.0 Hz), 8.61 (1H, dd, Jϭ4.9, 2.0 Hz), 9.83
(1H, br). MS m/z: 282 (Mϩ).
tert-Butyl 3-(2-Pivaroylaminopyridin-3-yl)-3-hydroxy-3-phenylpro-
panate (13) In an atmosphere of argon, a 1.69 M n-butyllithium hexane so-
lution (53 ml, 90 mmol) was added dropwise to an ether solution (150 ml) of
diisopropylamine (9.61 g, 95 mmol) which was cooled at Ϫ78 °C. After
15 min of stirring, an ether solution (20 ml) of tert-butyl acetate (10.5 g,
90.5 mmol) was slowly added dropwise. After 30 min of stirring, a tetrahy-
drofuran solution (20 ml) of 12 (12.0 g, 42.6 mmol) was added dropwise.
After 30 min of stirring, the reaction mixture was warmed to room tempera-
ture and stirred for 5 h. The reaction solution was poured into water and ex-
tracted with chloroform. The organic layer was dried over anhydrous magne-
sium sulfate. After removing the magnesium sulfate, the resulting filtrate
was concentrated under reduced pressure to give 13 (16.9 g, 100%) as an oil.
1H-NMR (CDCl3) d: 1.02 (9H, s), 2.91 (1H, d, Jϭ16.6 Hz), 6.19 (1H, s),
7.03 (1H, dd, Jϭ7.8, 4.9 Hz), 7.23—7.56 (5H, m), 7.55 (1H, dd, Jϭ7.8,
1.5 Hz), 8.51—8.52 (1H, m), 9.68 (1H, br). FAB-MS m/z: 222 [MϩH]ϩ.
Authentic Materials Rolipram16) and CDP84017) were prepared in our
laboratory according to the reported methods.
Pharmacology
PDE Inhibitory Activity. Isolation of Human Peripheral Leukocytes
The leukocytes were isolated from the peripheral blood of healthy human
volunteers. Physiological saline supplemented with 3% dextran was added to
heparinized human peripheral blood, and the mixture was incubated for
40 min at 37 °C to precipitate the erythrocytes. The supernatant after precipi-
tation of the erythrocytes was recovered and washed once with PBS, and the
pellet, which contained leukocytes, was resuspended in a buffer (pH 7.4)
containing sodium chloride (140 mM), potassium chloride (5 mM), glucose
(5 mM) and HEPES (10 mM).
Isolation of Human Peripheral Blood Mononuclear Cells (PBMC)
The suspended leukocytes were overlaid on a solution for density gradient
centrifugation use Ficoll® solution, and then centrifuged at room tempera-
ture for 40 min at 450 g, thereby separating the mononuclear cells and gran-
ulocytes. The mononuclear cell fraction was washed once and resuspended
in RPMI with 10% FBS.
Purification of PDE Isozyme PDE2, PDE3, PDE4, and PDE5 were
prepared from human peripheral leukocytes, and PDE1 was prepared from
rat ventricles. All the enzymes were partially purified by Q Sepharose Fast
Flow (Pharmacia Biotech, Sweden) with 0.05 to 1.25 M sodium acetate gra-
dients from the 100000ϫg supernatants. The following protease inhibitors

August 2002
1059
were maintained throughout: phenyl-methyl-sulfonyl-fluoride (50 mM), pep-
statin A (5 mM), leupeptin (40 mM), aprotinin (20 mM) and benzamidine
(2 mM). The characterization of each PDE isozyme was recognized as fol-
lows: PDE1, Ca2ϩ/calmodulin-activated; PDE2, cGMP-activated; PDE3,
cGMP-inhibited; PDE4, cAMP-specific and inhibited by rolipram; PDE5,
cGMP-specific.
Determination of Inhibitory Effect for PDE A predetermined amount
and concentration of each test compound was incubated at 30 °C for 10 min
in a reaction mixture (pH 8.0) containing Tris–HCl (40 mM), magnesium
chloride (5 mM), 2-mercaptoethanol (4 mM), cAMP (1 mM), 3H-cAMP
(10 nM) and a PDE stock solution. The mixture was placed in boiled water
for 1 min, cooled in an ice bath, mixed with 1 unit of 5Ј-nucleotidase and
then incubated at 30 °C for 10 min. The reaction was stopped by the addition
of 1 ml of methanol. The solution was passed through a Dowex 1-X8 (BIO-
RAD, U.S.A.) column to adsorb any unhydrolyzed material, and then the ra-
dioactivity in the elution was measured. The evaluation of each compound
was carried out using an IC50 value, this being the concentration achieving
50% inhibition.
Data Analysis Concentrations or doses causing 50% or 30% inhibition
were determined by nonlinear curve fitting using a statistical software, SAS
system (SAS Institute Inc., Cary, U.S.A.).
Acknowledgements We thank the members of the Pharmacology Labo-
ratories for performing the pharmacological experiments. We also thank the
members of the Analysis & Metabolism Laboratories for performing the ele-
mental analysis and for measuring the NMR and mass spectra.
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