Studies on new platelet aggregation inhibitors 1. Synthesis of 7-nitro-3,4-dihydroquinoline-2(1H)-one derivatives

Article abstract of DOI:10.1248/cpb.49.822

A series of 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)-ones were prepared and tested for platelet aggregation inhibitory effect, cardiotonic activity and chronotropic activity. These compounds appeared to show selective inhibitory activity against platelet aggregation. Among them, 6-(4-ethoxycarbonylpiperidino)-7-nitro-3,4-dihydroquinoline-2(1H)-one (22f) showed the most potent inhibitory activity and high selectivity. A divergent synthetic route to 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)-one derivatives has also been investigated.

Full text of DOI:10.1248/cpb.49.822

822
Chem. Pharm. Bull. 49(7) 822—829 (2001)
Vol. 49, No. 7
Studies on New Platelet Aggregation Inhibitors 1. Synthesis of
7-Nitro-3,4-dihydroquinoline-2(1H)-one Derivatives
Akira IYOBE,* Masahiko UCHIDA, Kouji KAMATA, Yukihiko HOTEI, Hiroshi KUSAMA, and
Hiromu HARADA
Central Research Laboratories, Kissei Pharmaceutical Co., Ltd., 4365–1 Kashiwabara, Hotaka-machi, Minamiazumi-gun,
Nagano 399–8304, Japan. Received December 26, 2000; accepted March 12, 2001
A series of 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)-ones were prepared and tested for
platelet aggregation inhibitory effect, cardiotonic activity and chronotropic activity. These compounds appeared
to show selective inhibitory activity against platelet aggregation. Among them, 6-(4-ethoxycarbonylpiperidino)-7-
nitro-3,4-dihydroquinoline-2(1H)-one (22f) showed the most potent inhibitory activity and high selectivity. A di-
vergent synthetic route to 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)-one derivatives has also
been investigated.
Key words antiplatelet agent; N-nitroso mimic; 7-nitro-3,4-dihydroquinoline-2(1H)-one; divergent synthesis
As platelets play an important role not only in hemostasis Simple N-nitrosation of 6a leading to 8 can be performed by
and thrombosis but also in atherogenesis and arterial spasm,1) the use of isoamyl nitrite in MeOH in 59% yield. Similarly,
efforts have been made to synthesize compounds which are 6b underwent nitration at the 7-position by treatment with
significantly more active than acetylsalicylic acid in inhibit- NaNO2 (1.4 eq, AcOH/trifluoroacetic acid (TFA)ϭ4/1, room
ing platelet aggregation.2) In our previous study of the syn- temperature, for 0.5 h) to give 7 in 43% yield. Although the
thesis of 6-(1-piperazinyl)-7-nitro-3,4-dihydroquinoline- actual reaction mechanism of these nitrations is not clear, it
2(1H)-one derivatives,3) it was found that the crude sample has been known that nitrous acid undergoes disproportiona-
of 2-(4-methylamino)quinazolinyl derivative (1) (Fig. 1) ex- tion to nitric acid and nitric oxide,5) and there have been sev-
hibited good antiplatelet activity. However, further investiga- eral precedents6) involving nitration with nitrous acid.
tion revealed that pure 1 has only weak antiplatelet activity;
The preparation of the N-acetyl analog 10 was carried out
the true active compound is 7-nitro-6-[1-(4-nitrosopiper- by acetylation of 6a (95% yield, Ac2O in pyridine) followed
azinyl)]-3,4-dihydroquinolin-2(1H)-one 2, which was conta- by nitration at the 7-position of 9 (61% yield, 1.1 eq of
minated as an impurity in a screening sample of 1. Com- NaNO3) in TFA. The nitration of 9 can also be effected using
pound 2 had cardiotonic and chronotropic activities (CTA, NaNO2: 64% yield with NaNO2 (1.0 eq) in 1 M hydrochloric
CRA) in addition to antiplatelet activity (see Table 1).
acid; 86% yield with NaNO2 (1.0 eq) in AcOH/TFAϭ4/1. It
In the present study, we focused on the structure of 2 and should be mentioned that, when the above nitration with
intended to separate its antiplatelet activity from its cardio- NaNO2 was carried out in AcOH alone, an inseparable mix-
vascular effects. This paper describes the synthesis of a series ture of 10/the 5-nitro isomerϭ7.5/1 was formed as evidenced
of derivatives of 2 and the details of their structure–activity by 1H-NMR spectroscopy.7) Compound 10 was hydrolyzed to
relationship. In addition, a divergent synthetic route to 6- 11 in 73% yield, and the N-formyl analog 12 was prepared by
cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)- formylation of 11 in 45% yield.
one derivatives has been investigated.
At this stage, biological assay results of these compounds
suggested that the presence of the 7-nitro group is essential
to their inhibitory activity against platelet aggregation (see
Chemistry
The lead compound 2 and its analogs, having an N- the next part of the text). As the 7-nitro group in the 3,4-di-
acylpiperazine ring (10, 12) or morpholine ring (7) at the 6- hydroquinoline-2(1H)-one system was expected to allow nu-
position of 3,4-dihydroquinoline-2(1H)-one, were prepared cleophilic substitution at the 6-position, a plan was made for
as shown in Chart 1. The acetal 4 obtained from commer- a divergent synthetic approach to the analogs, in which a
cially available 5-chloro-2-nitrobenzaldehyde 3 was con- compound having a 7-nitro group as well as a suitable leav-
verted to the 6-piperazinyl (6a) and 6-morpholino (6b) deriv- ing group at the 6-position is to be used as an intermediate.
atives by a series of reactions based on the patent reported by
A synthetic route to the above mentioned intermediate 19
is given in Chart 2. The aldehyde 14, prepared from commer-
Tominaga et al.4)
As the first step in the preparation of 2, we examined the cially available 5-hydroxy-2-nitrobenzaldehyde 13, was sub-
N-nitrosation of 6a under conventional reaction conditions
(NaNO2 (4.0 eq) in 1 M hydrochloric acid, room temperature,
for 4 h). The 1H-NMR spectrum of the sole product from this
reaction however showed, the presence of only two aromatic
protons (d 7.10, 7.30 ppm, both as a singlet). The product
was identified with 2 by NMR, IR (NO2: 1523, 1375,
1348 cmϪ1) and FAB-MS (MϩHϩ: m/z 306) spectra. Com-
pound 2 was also identical to the impurity found in the initial
screening sample of 1. The yield of 2 from 6a was 83%.
Fig. 1
To whom correspondence should be addressed. e-mail: akira_iyobe@pharm.kissei.co.jp
© 2001 Pharmaceutical Society of Japan

July 2001
823
Reagent and conditions: (a) MeOH, p-toluenesulfonic acid, reflux; in the case of XϭNH: (b) 1) piperazine, N,N-dimethylformamide, 80 °C; 2) HCl, iso-PrOH–H2O, reflux; (c) 1)
Ac2O, pyridine; 2) maloic acid, piperidine, reflux; 3) H2, Pd–C, AcOH; 4) cHCl, reflux; (d) NaNO2, 1 M HCl; in the case of XϭO: (b) 1) morpholine, 1,8-diazabicyclo[5,4,0]undec-
7-ene, 100 °C; 2) HCl, Acetone–H2O, 60 °C; (c) 1) malonic acid, pyridine, piperidine, reflux; 2) H2, Pd–C, AcOH, MeOH, 80 °C; (d) NaNO2, AcOH–TFA; (e) isoamyl-ONO,
MeOH; (f) Ac2O, pyridine; (g) NaNO3, TFA; (h) cHCl, 90 °C; (i) HCOOH, 1,3-dicyclohexylcarbodiimide, CHCl3.
Chart 1. Synthesis of 6-Piperazinyl and 6-Morpholino Derivatives 2, 6a, 7, 8, 10—12
Reagent and conditions: (a) MeI, Cs2CO3, DMF; (b) malonic acid, pyridine, piperidine, reflux; (c) H2, Pd–C, AcOH; (d) AcOEt, 70 °C; (e) NaNO2, TFA; (f) AlCl3,
X
NH
, CH3CN, 80 °C.
dichloroethane, reflux; (g) CF3SO2Cl, Et3N, DMF; (h)
Chart 2. Divergent Synthesis of Cyclic Aliphatic Amine Derivatives 22a—g, 23
jected to Knoevenagel condensation with malonic acid to
give 15 in 71% yield. After hydrogenation of the nitro group
in 15, cyclization was effected simply by heating the reaction
mixture at 70 °C for 1 h, which gave 16 in 88% yield.
Nitration at the 7-position of 16 was examined under sev-
eral conditions. When fuming nitric acid (1.0 eq) was used in
combination with an acid anhydride (0 °C, for 20—30 min),
the desired 7-nitro derivative 17 always accompanied a con-
siderable amount of the 7,8-dinitrated product (Ac2O with a
small amount of conc. H2SO4: 17/7,8-dinitrated productϭ1/3;
Fig. 2. Chemical Structures of Cyclic Aliphatic Amines Used for the
(CF3CO)2O: 17/7,8-dinitrated productϭ2/1) together with Preparation of 22a—g, 23
some of the starting material. Use of NaNO3 (1.0 eq) was
also discouraging, either forming a mixture of 17/8-nitro iso- not commercially available, were prepared as shown in Chart
merϭ9/1 in TFA (room temperature, for 3 h) or giving the 8- 3. The aldehyde 26 was obtained from 24 in an overall yield
nitro isomer in AcOH (100 °C, for 1.5 h, 68% yield).8) The of 40%: tert-butoxycarbonylation followed by the Dess–Mar-
best result was obtained again when 16 was reacted with a tin oxidation. Preparation of the nitrile 28 was carried out by
1.0 eq of NaNO2 in TFA (0 °C, for 20 min, 88% yield of 17).
using 27 in an overall yield of 83%: tert-butoxycarbonylation
Compound 19, which was a key intermediate in our new and subsequent dehydration with trifluoroacetic anhydride
synthetic approach, was prepared by demethylation of 17 (TFAA). The methyl ketone 29 was prepared from 28 with
with AlCl3 (97% yield) followed by treatment of the resulting methyl magnesium iodide in 43% yield. The methyl sulfide
product (18) with CF3SO2Cl (79% yield). Nucleophilic sub- 32 was prepared from 30 in an overall yield of 57%: tert-bu-
stitution of 19 with cyclic aliphatic amines (20a—g, 21, see toxycarbonylation, mesylation and finally thiomethylation.
Fig. 2) was carried out in CH3CN at 80 °C. This gave the de- These N-tert-butoxycarbonyl (N-Boc) piperidines (26, 28,
sired analogs (22a—g, 23) in 4—51% yields.
29, 32) were used for the above-mentioned reaction of 19
Some of cyclic aliphatic amines (20d, e, g, 21), which were after treatment with TFA. Also carried out was further de-

824
Vol. 49, No. 7
rivatization of 22a and 23 to the corresponding sulfoxides
When the 7-nitro group was removed from the lead com-
[22h (45% yield), 22j (79% yield)] and sulfones [22i (61% pound 2, the PIA decreased significantly, as can be seen from
yield), 22k (77% yield)] by m-chloroperoxybenzoic acid the data of 8 in Table 1. As N-nitroso compounds are gener-
(mCPBA) oxidation, as shown in Chart 4.
ally known to be mutagenic or carcinogenic,11) 2 was consid-
ered to be fatal for medicinal application. However, as shown
in the cases of 11 and 6a, removal of the N-nitroso group
Pharmacological Activities and Discussions
All 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline- uniformly resulted in the disappearance of the activities, ex-
2(1H)-ones (2, 8, 6a, 10—12, 22a—k) synthesized in this cept the CTA of 11.
study were evaluated for their effect on platelet aggregation
One would anticipate that a certain electron-withdrawing
inhibitory activity (PIA) in rabbit platelet-rich plasma group could act as a mimic of the nitroso group. Compounds
(PRP),9) CTA and CRA on isolated guinea pig atria10) by the 10 and 12 were prepared based on this assumption. Although
procedures described in the Experimental Section. These re- the N-acetyl derivative 10 was devoid of PIA, we thought the
sults are summarized in Tables 1 and 2.
PIA of the N-formyl derivative 12 deserved further investiga-
tion along this line. As can be seen from the data of 7, 22a
and 22b in Table 2, replacement of one nitrogen atom of the
piperazine ring can be done without significant loss of PIA
only by an oxygen atom, which is more electronegative than
carbon and sulfur atoms. This suggested again that the intro-
duction of an electron-withdrawing functionality to this por-
tion could be promising.
While the sulfur-oxidized analogues (22h, i) of 22a gave
rather discouraging results, the carbonyl-introduced analog
22c showed PIA activity comparable to that of 2. An addi-
tional appeal of 22c is in its improved selectivity: the effects
of this compound to CTA and CRA are much weaker than
those of 2.
Compounds having an electron-withdrawing functionality
at the 4-position of the piperidine ring were also prepared.
Among these compounds 22d—g, j, k, the 4-ethoxycarbonyl
derivative 22f was found to have PIA as high as 2 with a
much weaker CTA. It should be mentioned that the PIA of
22f is higher than that of cilostazol,12) which has been ap-
plied clinically to treat thrombosis.
Reagent and conditions: (a) di-tert-butyl dicarbonate (Boc2O), AcOEt, THF; (b)
Dess–Martin, CH2Cl2; (c) Boc2O, CH2Cl2, pyridine, then TFAA; (d) MeMgI, Et2O; (e)
Boc2O, CH2Cl2, dioxane, then methanesulfonyl chloride (MsCl), Et3N, CH2Cl2; (f)
NaSMe, DMF, 80 °C.
Chart 3. Synthesis of 4-Substituted-piperidine Derivatives 26, 28, 29, 32
Reagent and conditions: (a) mCPBA (1 eq), CH2Cl2; (b) mCPBA (2 eq), CH2Cl2.
Chart 4. Synthesis of Sulfoxide and Sulfone Derivatives 22h—k
Table 1. Biological Data for 6-Piperazinyl-3,4-dihydroquinolin-2(1H)-one Derivatives
CTAa)
(EC30, mM)
CRAb)
(EC10, mM)
PIA
(IC50, mM)
Compd.
R1
R2
2
8
NO
NO
NO2
H
Ͻ1c)
2.2
1.3
32
3.5
65
11
6a
10
12
H
H
NO2
H
NO2
NO2
1.6
Ͼ100
3.2
Ͼ100
Ͼ100
Ͼ100
6.1
Ͼ100
Ͼ100
Ͼ100
31
CH3CO
CHO
3.3
a) EC30 values were the dose that produced a 30% increase in the epinephrine response. b) EC10 values were the dose that produced a 10% increase in the basal response.
c) EC30 value was not calculated. Observed CTA 1 mM was a 42% increase of the epinephrine response.

July 2001
825
Table 2. Biological Data for 6-Cyclic Aliphatic Amino-7-nitro-3,4-dihydroquinolin-2(1H)-one Derivatives
CTAa)
CRAb)
PIAc)
(IC50, mM)
Compd.
X
n
(EC30, m
M
)
(EC10, m
M
)
7
22a
22b
O
S
CH2
11
NT
NT
7.3
NT
NT
65
140
Ͼ100c)
22c
22h
22i
C
S
S
1
1
2
4.4
10
NT
12
29
NT
3.6
420
200
22d
22e
22j
22k
22f
22g
CHO
18
NT
NT
27
NT
NT
NT
10
25
Ͼ100d)
240
180
3.4
CH3CO
CH3SO
CH3SO2
COOEt
CN
NT
Ͼ100
25
Ͼ100
32
4.4
Ͼ100
40
a) EC30 values were the dose that produced a 30% increase in the epinephrine response. b) EC10 values were the dose that produced a 10% increase in the basal response.
c) IC50 values not calculated. Observed PIA inhibition activity was 20% at 100 m
M.
d) IC50 values not calculated. Observed PIA was 23% at 100 m
M.
NT means not tested.
tion of 4 (5 g, 21.6 mmol) and anhydrous piperazine (9.3 g, 108 mmol) in
N,N-dimethylformamide (DMF) (30 ml) was stirred at 80 °C for 4 h. The re-
action mixture was evaporated in vacuo, and the concentrate was partitioned
between CH2Cl2 and 1 M NaOH. The organic layer was washed with brine
and concentrated to give a yellow oil. The residue was dissolved in a mixture
Conclusion
The 7-nitro-3,4-dihydroquinolin-2(1H)-one derivatives,
possessing various 6-membered heterocyclic rings at the 6-
position, were synthesized and evaluated for PIA, CTA and
CRA. Functional groups of the 4-position at the piperidine of 2-propanol (35 ml) and concentrated HCl (2.6 ml), and the mixture was
heated under reflux for 1 h with stirring. The reaction mixture was cooled at
0 °C, and the precipitate was collected by filtration, washed with Et2O and
ring in 7-nitro-6-piperidino-3,4-dihydroquinolin-2(1H)-one
have significant influence on both the potency of antiplatelet
activity and the selectivity in antiplatelet, cardiotonic and
dried in vacuo over P2O5 to give 5a (4.3 g, 73%) as a yellow solid. Recrystal-
1
lization was achieved from hexane–CH2Cl2–MeOH. mp 206—208 °C. H-
chronotropic activities. Introduction of an ethoxycarbonyl
group at the 4-position of the piperidine ring significantly en-
hanced the potency and selectivity of platelet aggregation in-
hibition. Further studies are in progress regarding the mecha-
nism of action of this class of compounds based on their in-
hibitory activity against phosphodiesterase.
NMR (dimethyl sulfoxide (DMSO)-d6) d: 3.18—3.28 (m, 4H), 3.70—3.76
(m, 4H), 7.15 (d, Jϭ2.8 Hz, 1H), 7.27 (dd, Jϭ9.3, 2.8 Hz, 1H), 8.11 (d,
Jϭ9.3 Hz, 1H), 9.10—9.35 (br, 2H), 10.33 (s, 1H). IR (KBr) cmϪ1: 2679—
2494, 1693, 1583, 1500, 1325, 1269. FAB-MS m/z: 236 (MϩH)ϩ. Rf 0.30
(CH2Cl2/MeOHϭ5/1). Anal. Calcd for C11H13N3O3·HCl·H2O: C, 45.60; H,
5.57; N, 14.50. Found: C, 45.65; H, 5.38; N, 14.80.
6-(1-Piperazinyl)-3,4-dihydroquinolin-2(1H)-one (6a) A solution of
5a (54.0 g, 199 mmol) and acetic anhydride (19.7 ml, 209 mmol) in pyridine
(500 ml) was stirred at room temperature for 3.5 h. After the addition of mal-
Experimental
Melting points were determined using a Yanagimoto melting point appa- onic acid (114 g, 1.09 mmol) and piperidine (6.9 ml, 70 mmol), the mixture
ratus and are uncorrected. 1H-NMR spectra were measured at 27 °C (internal was heated under reflux for 4 h with stirring. The reaction mixture was evap-
standard, Me4Si) with a Brucker DRX-500 (500 MHz) spectrometer, orated in vacuo and the residue was acidified with concentrated HCl. The
Brucker AMX-400 (400 MHz) spectrometer or a JEOL GX-270 (270 MHz) precipitate was collected by filtration, washed successively with H2O, EtOH
spectrometer. Mass spectra (MS) were taken on a JEOL JMS-SX102A (in and Et2O and dried in vacuo to leave a yellow solid. The residue was hydro-
FAB mode, glycerin, thioglycerin or m-nitrobenzyl alchol as a matrix) spec- genated (1 atm) in the presence of 10% Pd–C (6.5 g) in acetic acid (500 ml)
trometer. IR spectra were recorded with a Nicolet 510 FT-IR spectrometer. at room temperature overnight. The catalyst was removed by filtration, and
Column chromatography was carried out on silica gel (Silica gel 60, Merck). concentrated HCl (210 ml) was added to the filtrate. The mixture was heated
Thin layer chromatography (TLC) was performed on silica gel (precoated under reflux for 3 h with stirring. After evaporation of the solvent, the pre-
silica gel plate F254, layer thickness, 0.25 mm, Merck). Preparative TLC was cipitate was dissolved in H2O and washed with CHCl3. The aqueous solution
performed on silica gel (precoated silica gel plate F254, layer thickness,
was basified with 2 M NaOH and extracted with CHCl3. The organic extract
0.5 mm, Merck) or aminopropylated silica gel (precoated silica gel plate was dried and evaporated to give 6a (33.8 g, 73%) as a white solid. Recrys-
1
F254, layer thickness, 0.25 mm, NH TLC plate, Fuji Silysia Chemical). All tallization was achieved from hexane–CH2Cl2–MeOH. mp 71—73 °C. H-
organic extracts were dried over anhydrous MgSO4, then filtered. The sol- NMR (CDCl3) d: 2.57—2.65 (m, 2H), 2.89—2.97 (m, 2H), 3.00—3.11 (m,
vent was removed with a rotary evaporator under reduced pressure.
8H), 6.67 (d, Jϭ8.9 Hz, 1H), 6.73—6.79 (m, 2H), 7.79 (br s, 1H). IR (KBr)
5-Chloro-2-nitrobenzaldehyde Dimethyl Acetal (4) A solution of 2- cmϪ1: 3255, 1670, 1508, 1375. FAB-MS m/z: 232 (MϩH)ϩ. Rf 0.36
nitro-5-chlorobenzaldehyde 3 (3 g, 16.2 mmol) and p-toluenesulfonic acid (CH2Cl2/MeOH/NH4OHϭ50/10/1). Anal. Calcd for C13H17N3O: C, 67.51;
monohydrate (84 mg, 0.488 mmol) in MeOH (30 ml) was heated under re- H, 7.41; N, 18.17. Found: C, 67.21; H, 7.45; N, 17.88.
flux for 14 h. The reaction mixture was evaporated in vacuo, and the residue
7-Nitro-6-[1-(4-nitrosopiperazinyl)]-3,4-dihydroquinolin-2(1H)-one
was partitioned between Et2O and saturated aqueous NaHCO3. The organic (2) To a solution of 6a (50 mg, 0.216 mmol) in 1 M HCl (0.65 ml), NaNO2
layer was dried and evaporated to give 4 (3.74 g, 100%) as a light yellow oil. (60 mg, 0.869 mmol) was added at 0 °C, and the mixture was stirred for 4 h
1H-NMR (CDCl3) d: 3.42 (s, 6H), 5.92 (s, 1H), 7.55 (dd, Jϭ8.6, 2.2 Hz, at room temperature. The precipitate was collected by filtration and dried in
1H), 7.79 (d, Jϭ2.2 Hz, 1H), 7.81 (d, Jϭ8.6 Hz, 1H). IR (neat) cmϪ1: 1533,
vacuo over P2O5 to give 2 (55 mg, 83%) as a yellow solid. Recrystallization
1363, 1196, 1111, 1070, 1060. FAB-MS m/z: 200 (MϪOCH3)ϩ. High-reso- was achieved from CH2Cl2–Et2O. mp 238—239 °C. 1H-NMR (CDCl3) d:
lution (HR)-FAB-MS m/z: 230.0236 (MϪH)ϩ. Calcd for C9H9ClNO4: 2.64—2.70 (m, 2H), 2.97—3.05 (m, 4H), 3.24 (t, Jϭ5.0 Hz, 2H), 3.98—
230.0220. Rf 0.43 (hexane/AcOEtϭ10/1).
4.03 (m, 2H), 4.43 (t, Jϭ5.0 Hz, 2H), 7.10 (s, 1H), 7.30 (s, 1H), 8.14 (br,
2-Nitro-5-(1-piperazinyl)benzaldehyde Hydrochloride (5a) A solu- 1H). IR (KBr) cmϪ1: 1689, 1523, 1375, 1348. FAB-MS m/z: 306 (MϩH)ϩ.

826
Vol. 49, No. 7
of acetone (40 ml) and 2 M HCl (10 ml) was stirred at 60 °C for 1 h. After
evaporation of the reaction mixture, the concentrate was partitioned between
AcOEt and 2 M NaOH. The organic layer was dried and evaporated to give
5b (740 mg, 88%) as yellow needles. Recrystallization was achieved from
hexane–AcOEt. mp 149—150 °C. 1H-NMR (CDCl3) d: 3.41—3.47 (m, 4H),
3.84—3.90 (m, 4H), 6.97 (dd, Jϭ9.3, 3.0 Hz, 1H), 7.17 (d, Jϭ3.0 Hz, 1H),
8.14 (d, Jϭ9.3 Hz, 1H), 10.53 (s, 1H). IR (KBr) cmϪ1: 1682, 1593, 1574,
1493, 1317, 1234, 1120, 1036. FAB-MS m/z: 237 (MϩH)ϩ. Rf: 0.58
(hexane/AcOEtϭ1/2). Anal. Calcd for C11H12N2O4: C, 55.93; H, 5.12; N,
11.86. Found: C, 56.02; H, 5.08; N, 12.06.
Rf 0.47 (CH2Cl2/MeOHϭ10/1). Anal. Calcd for C13H15N5O4·0.2H2O: C,
50.55; H, 5.02; N, 22.67. Found: C, 50.79; H, 5.03; N, 22.37.
6-[1-(4-Nitrosopiperazinyl)]-3,4-dihydroquinolin-2(1H)-one (8)
A
mixture of 6a (21 mg, 0.091 mmol) and isoamyl nitrite (0.12 ml, 0.91 mmol)
in MeOH (0.12 ml) was stirred for 2 d at room temperature. After evapora-
tion of the solvent, AcOEt was added to the concentrate. The resulting sus-
pension was filtered, and the filtrate was concentrated in vacou and purified
by preparative TLC (aminopropylated silica gel, CH2Cl2/MeOHϭ20/1) to
give 8 (14 mg, 59%) as a white solid. Recrystallization was achieved from
hexane–CH2Cl2. mp 207—208 °C. 1H-NMR (CDCl3) d: 2.59—2.65 (m,
2H), 2.92—2.97 (m, 2H), 3.07—3.11 (m, 2H), 3.33 (t, Jϭ5.2 Hz, 2H), 3.98
(t, Jϭ5.4 Hz, 2H), 4.42 (t, Jϭ5.2 Hz, 2H), 6.69 (d, Jϭ8.3 Hz), 6.76—6.80
(m, 2H), 7.73 (br s, 1H). IR (KBr) cmϪ1: 1674, 1508, 1425, 1383, 1238.
FAB-MS m/z: 260 Mϩ. Rf 0.27 (CH2Cl2/MeOHϭ20/1). Anal. Calcd for
C13H16N4O2: C, 59.99; H, 6.20; N, 21.52. Found: C, 59.96; H, 6.23; N,
21.36.
6-[1-(4-Acetylpiperazinyl)]-3,4-dihydroquinolin-2(1H)-one (9) A so-
lution of 6a (6.0 g, 25.9 mmol) and acetic anhydride (2.58 ml, 27.3 mmol) in
pyridine (30 ml) was stirred at room temperature overnight. After evapora-
tion of the solvent, the residue was partitioned between CHCl3 and saturated
aqueous NaHCO3. The organic layer was washed with saturated aqueous
NH4Cl, dried, evaporated and crystallized from AcOEt to give 9 (6.70 g,
95%) as a white solid. Recrystallization was achieved from hexane–CH2Cl2.
mp 208—210 °C. 1H-NMR (DMSO-d6) d: 2.03 (s, 3H), 2.35—2.43 (m, 2H),
2.76—2.85 (m, 2H), 2.94—3.00 (m, 2H), 3.00—3.06 (m, 2H), 3.51—3.60
(m, 4H), 6.72 (d, Jϭ11 Hz, 1H), 6.77 (d, Jϭ11 Hz, 1H), 6.81 (s, 1H), 9.86
(s, 1H). IR (KBr) cmϪ1: 1672, 1651, 1508, 1421, 1392, 1234. FAB-MS m/z:
273 Mϩ. Rf 0.48 (CH2Cl2/MeOHϭ10/1). Anal. Calcd for
C15H19N3O2·0.1H2O: C, 65.48; H, 7.03; N, 15.27. Found: C, 65.45; H, 6.94;
N, 15.31.
6-Morpholino-3,4-dihydroquinolin-2(1H)-one (6b) To a refluxing so-
lution of 5b (330 mg, 1.40 mmol) and piperidine (0.17 ml, 1.72 mmol) in
pyridine (9 ml), malonic acid (204 mg, 1.96 mmol) was added, and the mix-
ture was heated under reflux for 1 h. After evaporation of the solvent, the
concentrate was acidified with 1 M HCl. The precipitate was collected by fil-
tration, washed successively with H2O and with AcOEt and dried in vacuo
to give a yellow solid. The solid was hydrogenated in the presence of 10%
Pd–C (30 mg) in AcOH (3 ml) and MeOH (30 ml) for 8 h at room tempera-
ture. The catalyst was removed by filtration and the filtrate was concentrated
in vacuo. Silica gel column chromatography (CH2Cl2/MeOHϭ50/1) of the
filtrate gave 6b (144 mg, 44%) as a white solid. Recrystallization was
1
achieved from hexane–CH2Cl2. mp 179—180 °C. H-NMR (DMSO-d6) d:
2.35—2.42 (m, 2H), 2.77—2.84 (m, 2H), 2.96—3.02 (m, 4H), 3.68—3.74
(m, 4H), 6.73 (s, 2H), 3.79 (s, 1H), 9.85 (s, 1H). IR (KBr) cmϪ1: 1662, 1514,
1387, 1238, 1119. FAB-MS m/z: 232 (M)ϩ. Rf: 0.29 (CH2Cl2/MeOHϭ20/1).
Anal. Calcd for C13H16N2O2·0.1H2O: C, 66.70; H, 6.98; N, 11.97. Found: C,
66.73; H, 6.95; N, 11.93.
6-Morpholino-7-nitro-3,4-dihydroquinolin-2(1H)-one (7) To a solu-
tion of 6b (76 mg, 0.327 mmol) in a mixture of AcOH (4 ml) and TFA
(1 ml), NaNO2 (31 mg, 0.449 mmol) was added, and the mixture was stirred
for 0.5 h at room temperature. After evaporation of the solvent, silica gel
column chromatography (AcOEt) of the concentrate gave 7 (39 mg, 43%) as
an orange solid. Recrystallization was achieved from hexane–AcOEt. mp
6-[1-(4-Acetylpiperazinyl)]-7-nitro-3,4-dihydroquinolin-2(1H)-one
(10) To a solution of 9 (2.02 g, 7.39 mmol) in TFA (20 ml), NaNO3 (0.69 g,
8.12 mmol) was added at 0 °C, and the mixture was stirred at room tempera-
ture overnight. The reaction mixture was basified with 40% aqueous KOH
and extracted with CHCl3. The organic layer was washed with brine, dried
and evaporated to give 10 (1.44 g, 61%) as a pale orange solid. Recrystal-
lization was achieved from hexane–CH2Cl2. mp 228—230 °C. 1H-NMR
(DMSO-d6) d: 2.03 (s, 3H), 2.45—2.53 (m, 2H), 2.87—2.91 (m, 2H),
2.91—2.98 (m, 4H), 3.51—3.57 (m, 4H), 7.29 (s, 1H), 7.34 (s, 1H), 10.25
(s, 1H). IR (KBr) cmϪ1: 1690, 1649, 1517, 1500, 1425, 1342. FAB-MS m/z:
319 (MϩH)ϩ. Rf 0.48 (CH2Cl2/MeOHϭ10/1). Anal. Calcd for C15H18N4O4·
0.3H2O: C, 55.65; H, 5.79; N, 17.31. Found: C, 55.54; H, 5.61; N, 17.25.
7-Nitro-6-(1-piperazinyl)-3,4-dihydroquinolin-2(1H)-one (11) A so-
lution of 10 (2.70 g, 8.48 mmol) in concentrated HCl (25 ml) was stirred at
90 °C for 3 h. The reaction mixture was basified with 40% aqueous KOH at
0 °C, and extracted with CHCl3. The organic layer was dried and evaporated
to give 11 (1.67 g, 73%) as an orange solid. Recrystallization was achieved
from CH3CN–MeOH. mp 280—281 °C (dec.). 1H-NMR (DMSO-d6) d:
2.44—2.53 (m, 2H), 2.75—2.88 (m, 6H), 2.91—2.98 (m, 4H), 7.21 (s, 1H),
7.29 (s, 1H), 8.32 (s, 1H), 10.19 (s, 1H). IR (KBr) cmϪ1: 3360, 1724, 1647,
1529, 1321, 1284. FAB-MS m/z: 277 (MϩH)ϩ. HR-FAB-MS m/z 277.1307
(MϩH)ϩ. Calcd for C13H17N4O3: 277.1301. Rf: 0.16 (CH2Cl2/MeOHϭ5/1).
6-[1-(4-Formylpiperazinyl)]-7-nitro-3,4-dihydroquinolin-2(1H)-one
(12) To a stirred solution of 1,3-dicyclohexylcarbodiimide (DCC) (66 mg,
0.32 mmol) in CHCl3 (0.5 ml), formic acid (0.024 ml, 0.64 mmol) in CHCl3
(0.3 ml) was added at 0 °C. After the mixture was stirred for 5 min, a solu-
tion of 11 (43 mg, 0.16 mmol) in pyridine (0.5 ml) was added to the mixture,
and the stirring was continued for another 1 h. The reaction mixture was
evaporated, and AcOEt was added to the concentrate. After filtration of the
resulting suspension, silica gel column chromatography (CHCl3/MeOHϭ
50/1) of the filtrate gave 12 (22 mg, 45%) as an orange solid. Recrystalliza-
tion was achieved from hexane–AcOEt–CH2Cl2. mp 200—202 °C. 1H-NMR
(DMSO-d6) d: 2.40—2.53 (m, 2H), 2.80—3.00 (m, 6H), 3.44—3.54 (m,
1
61—62 °C. H-NMR (CDCl3) d: 2.63—2.70 (m, 2H), 2.98—3.06 (m, 6H),
3.81—3.87 (m, 4H), 7.02 (s, 1H), 7.26 (s, 1H), 7.80 (s, 1H). IR (KBr) cmϪ1
:
1697, 1522, 1329, 1113. FAB-MS m/z: 278 (MϩH)ϩ. Rf: 0.46 (AcOEt).
Anal. Calcd for C13H15N3O4: C, 56.31; H, 5.45; N, 15.15. Found: C, 56.29;
H, 5.50; N, 15.07.
5-Methoxy-2-nitrobenzaldehyde (14) To a stirred suspension of 5-hy-
droxy-2-nitrobenzaldehyde 13 (3 g, 18.0 mmol) and Cs2CO3 (5.86 g,
18.0 mmol) in DMF (20 ml), MeI (1.12 ml, 18.0 mmol) was added dropwise
at 0 °C. The stirring was continued for 3 d at room temperature. The reaction
mixture was partitioned between AcOEt and H2O. Silica gel column chro-
matography (hexane/AcOEtϭ3/1) of the organic layer gave 14 (3.07 g, 94%)
as colorless needles. Recrystallization was achieved from hexane–AcOEt.
1
mp 80—81 °C. H-NMR (CDCl3) d: 3.91 (s, 3H), 7.16 (dd, Jϭ9.1, 2.9 Hz,
1H), 7.34 (d, Jϭ2.9 Hz, 1H), 8.17 (d, Jϭ9.1 Hz, 1H), 10.49 (s, 1H). IR
(KBr) cmϪ1: 2850, 1691, 1583, 1504, 1329. FAB-MS m/z: 182 (MϩH)ϩ. Rf:
0.41 (hexane/AcOEtϭ3/1). Anal. Calcd for C8H7NO4: C, 53.04; H, 3.89; N,
7.73. Found: C, 53.05; H, 3.90; N, 7.80.
5-Methoxy-2-nitrocinnamic Acid (15) A stirred solution of 14 (10 g,
55.2 mmol), malonic acid (28.7 g, 276 mmol) and piperidine (1.36 ml,
13.8 mmol) in pyridine (100 ml) was heated under reflux for 4 h. After evap-
oration of the solvent, the residue was acidified with 1 M HCl. The precipi-
tate was collected by filtration, washed successively with 2-propanol and
then with Et2O and dried in vacuo over P2O5 to give 15 (8.8 g, 71%) as a
white solid. Recrystallization was achieved from hexane–MeOH. mp 183—
184 °C. 1H-NMR (DMSO-d6) d: 3.94 (s, 3H), 6.55 (d, Jϭ15.7 Hz, 1H), 7.17
(dd, Jϭ9.1, 2.7 Hz, 1H), 7.32 (d, Jϭ2.7 Hz, 1H), 7.96 (d, Jϭ15.7 Hz, 1H),
8.12 (d, Jϭ9.1 Hz, 1H), 12.71 (s, 1H). IR (KBr) cmϪ1: 3000—2500, 2833,
1695, 1577, 1506, 1344. FAB-MS m/z: 224 (MϩH)ϩ. Rf: 0.18 (CH2Cl2/
MeOH/NH4OHϭ50/10/1). Anal. Calcd for C10H9NO5: C, 53.82; H, 4.06; N,
6.28. Found: C, 53.70; H, 4.04; N, 6.39.
4H), 7.30 (s, 1H), 7.34 (s, 1H), 8.06 (s, 1H), 10.25 (s, 1H). IR (KBr) cmϪ1
:
6-Methoxy-3,4-dihydroquinolin-2(1H)-one (16)
A solution of 15
1685, 1653, 1516, 1317, 1284, 1228. FAB-MS m/z: 305 (MϩH)ϩ. Rf: 0.58
(CH2Cl2/MeOHϭ10/1). Anal. Calcd for C14H16N4O4·0.3H2O: C, 54.29; H,
5.40; N, 18.09. Found: C, 54.59; H, 5.28; N, 17.80.
(2.58 g, 11.6 mmol) in AcOH (25 ml) was hydrogenated in the presence of
10% Pd–C (260 mg) for 14 h at room temperature. After the mixture was
heated at 70 °C for 1 h, the catalyst was removed by filtration and the filtrate
was evaporated. The residue was partitioned between AcOEt and 1 M NaOH.
The organic layer was evaporated to give 16 (1.82 g, 88%) as colorless nee-
dles. Recrystallization was achieved from hexane–AcOEt. mp 144—146 °C.
1H-NMR (CDCl3) d: 2.59—2.64 (m, 2H), 2.92—2.97 (m, 2H), 3.82 (s, 3H),
5-Morpholino-2-nitrobenzaldehyde (5b) A mixture of 4 (1.0 g, 4.3
mmol), morpholine (0.38 ml, 4.3 mmol) and 1,8-diazabicyclo[5,4,0]undec-7-
ene (DBU) (0.64 ml, 4.3 mmol) was stirred at 100 °C for 4 h. The reaction
mixture was partitioned between AcOEt and H2O. Silica gel column chro-
matography (CHCl3) of the organic layer gave 5-morpholino-2-nitroben-
zaldehyde dimethyl acetal (1.06 g, 87%, Rf: 0.21, hexane/AcOEtϭ3/1) as a
yellow oil. A solution of the dimethyl acetal (1.0 g, 3.54 mmol) in a mixture
6.67 (d, Jϭ8.3 Hz, 1H), 6.70—6.75 (m, 2H), 7.69 (br, 1H). IR (KBr) cmϪ1
:
1662, 1500, 1387, 1242, 1039. FAB-MS m/z: 178 (MϩH)ϩ. Rf: 0.54
(AcOEt). Anal. Calcd for C10H11NO2: C, 67.78; H, 6.26; N, 7.90. Found: C,

July 2001
827
1234. FAB-MS m/z: 276 (MϩH)ϩ. Rf: 0.21 (hexane/AcOEtϭ1/1). Anal.
Calcd for C14H17N3O3: C, 61.08; H, 6.22; N, 15.26. Found: C, 60.93; H,
6.14; N, 15.15.
67.65; H, 6.23; N, 7.96.
6-Methoxy-7-nitro-3,4-dihydroquinolin-2(1H)-one (17) To a stirred
solution of 16 (1.0 g, 5.64 mmol) in TFA (20 ml), NaNO2 (0.389 g,
5.64 mmol) was added portionwise at 0 °C, and the stirring was continued
for 0.5 h at room temperature. The reaction mixture was poured into ice
water. The precipitate was collected by filtration, washed with Et2O and
dried in vacuo over P2O5 to give 17 (1.11 g, 88%) as a light yellow solid. Re-
crystallization was achieved from Et2O–AcOEt–MeOH. mp 238—241 °C.
1H-NMR (DMSO-d6) d: 2.44—2.51 (m, 2H), 2.94—3.01 (m, 2H), 3.88 (s,
3H), 7.28 (s, 1H), 7.38 (s, 1H), 10.17 (s, 1H). IR (KBr) cmϪ1: 1676, 1522,
1346, 1263. FAB-MS m/z: 223 (MϩH)ϩ. Rf: 0.46 (CH2Cl2/MeOHϭ10/1).
Anal. Calcd for C10H10N2O4: C, 54.05; H, 4.54; N, 12.61. Found: C, 53.84;
H, 4.54; N, 12.50.
6-Hydroxy-7-nitro-3,4-dihydroquinolin-2(1H)-one (18) To a solution
of 17 (1.1 g, 4.95 mmol) in 1,2-dichloroethane (20 ml), Aluminum chloride
(AlCl3) (0.79 g, 5.92 mmol) was added portionwise, and the mixture was re-
fluxed for 0.5 h. To this mixture, additional AlCl3 (0.79 g, 5.92 mmol) was
added portionwise. After further stirring for 1 h at the same temperature, the
reaction mixture was evaporated in vacuo. The concentrate was quenched by
adding H2O. The precipitate was collected by filtration, washed with Et2O
and dried in vacuo over P2O5 to give 18 (1.0 g, 97%) as a yellow solid. Re-
crystallization was achieved from CH2Cl2–Et2O–MeOH. mp 235—238 °C.
1H-NMR (DMSO-d6) d: 2.40—2.48 (m, 2H), 2.88—2.95 (m, 2H), 6.99 (s,
1H), 7.41 (s, 1H), 10.15 (s, 1H), 10.55 (s, 1H). IR (KBr) cmϪ1: 1668, 1537,
1387, 1257. FAB-MS m/z: 209 (MϩH)ϩ. Rf: 0.25 (CH2Cl2/MeOHϭ50/1).
Anal. Calcd for C9H8N2O4: C, 51.93; H, 3.87; N, 13.46. Found: C, 51.71; H,
3.92; N, 13.23.
7-Nitro-6-(4-oxopiperidino)-3,4-dihydroquinolin-2(1H)-one
(22c)
The title compound was obtained as an orange solid (4%), starting from 4-
piperidone monohydrate hydrochloride and following the method as de-
scribed for 22a. Recrystallization was achieved from hexane–AcOEt. mp
251—252 °C. 1H-NMR (CDCl3) d: 2.61—2.69 (m, 6H ), 2.98—3.07 (m,
2H), 3.30—3.37 (m, 4H), 7.06 (s, 1H), 7.31 (s, 1H), 8.66 (br, 1H). IR (KBr)
cmϪ1: 1718, 1684, 1533, 1377, 1334, 1281. FAB-MS m/z: 290 (MϩH)ϩ. Rf:
0.31 (AcOEt). Anal. Calcd for C14H15N3O4: C, 58.13; H, 5.23; N, 14.53.
Found: C, 57.97; H, 5.26; N, 14.29.
6-(4-Formylpiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-one (22d)
The title compound was obtained as an orange solid (4%), starting from 26
and following the method as described for 23. Recrystallization was
achieved from hexane–AcOEt. mp 211—212 °C. 1H-NMR (CDCl3) d:
1.83—1.95 (m, 2H), 1.98—2.07 (m, 2H), 2.36—2.46 (m, 1H), 2.63—2.69
(m, 2H), 2.83—2.92 (m, 2H), 2.96—3.03 (m, 2H), 3.17—3.22 (m, 2H), 7.00
(s, 1H), 7.27 (s, 1H), 8.24 (br, 1H), 9.71 (s, 1H). IR (KBr) cmϪ1: 1720,
1664, 1522, 1377, 1323, 1288. FAB-MS m/z: 304 (MϩH)ϩ. Rf: 0.38
(AcOEt). Anal. Calcd for C15H17N3O4·0.3H2O: C, 58.36; H, 5.75; N, 13.61.
Found: C, 58.49; H, 5.62; N, 13.31.
6-(4-Acetylpiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-one (22e)
The title compound was obtained as an orange solid (12%), starting from 29
and following the method as described for 23. Recrystallization was
achieved from hexane–AcOEt. mp 182—183 °C. 1H-NMR (CDCl3) d:
1.80—1.90 (m, 2H), 1.93—2.00 (m, 2H), 2.20 (s, 3H), 2.40—2.48 (m, 1H),
2.62—2.69 (m, 2H), 2.79—2.88 (m, 2H), 2.96—3.03 (m, 2H), 3.22—3.28
(m, 2H), 6.99 (s, 1H), 7.25 (s, 1H), 7.64 (br, 1H). IR (KBr) cmϪ1: 1701,
1676, 1508, 1381, 1317, 1273. FAB-MS m/z: 318 (MϩH)ϩ. Rf: 0.33
(AcOEt). Anal. Calcd for C16H19N3O4·0.3H2O: C, 59.54; H, 6.12; N, 13.02.
Found: C, 59.66; H, 5.82; N, 13.17.
7-Nitro-6-trifluoromethanesulfonyloxy-3,4-dihydroquinolin-2(1H)-
one (19) To a solution of 18 (0.40 g, 1.92 mmol) in DMF (4 ml), Et3N
(0.29 ml, 2.09 mmol) was added at 0 °C. After the mixture was stirred at
0 °C for 5 min, CF3SO2Cl (0.22 ml, 2.09 mmol) was added, and stirring was
continued for 18 h at room temperature. The reaction mixture was parti-
tioned between AcOEt and saturated aqueous NH4Cl. The organic layer was
washed with brine, dried and evaporated. Silica gel column chromatography
(hexane/AcOEtϭ2/1) of the concentrate gave 19 (0.52 g, 79%) as a colorless
powder. Recrystallization was achieved from hexane–AcOEt. mp 187—
6-(4-Ethoxycarbonylpiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-
one (20f) The title compound was obtained as orange plates (46%), start-
ing from ethyl isonipecotate and following the method as described for 22a.
1
Recrystallization was achieved from hexane–AcOEt. mp 173—175 °C. H-
1
188 °C. H-NMR (DMSO-d6) d: 2.51—2.58 (m, 2H), 3.04—3.11 (m, 2H),
NMR (CDCl3) d: 1.28 (t, Jϭ7.1 Hz, 3H), 1.87—2.06 (m, 4H), 2.38—2.48
(m, 1H), 2.61—2.69 (m, 2H), 2.78—2.87 (m, 2H), 2.96—3.03 (m, 2H),
3.17—3.25 (m, 2H), 4.17 (q, Jϭ7.1 Hz, 2H), 6.99 (s, 1H), 7.25 (s, 1H), 7.78
(br, 1H). IR (KBr) cmϪ1: 1736, 1678, 1516, 1375, 1323, 1282. FAB-MS m/z:
348 (MϩH)ϩ. Rf: 0.47 (AcOEt). Anal. Calcd for C17H21N3O5: C, 58.78; H,
6.09; N, 12.10. Found: C, 58.76; H, 6.06; N, 12.09.
7.67 (s, 1H), 7.71 (s, 1H), 10.60 (s, 1H). IR (KBr) cmϪ1: 1685, 1535, 1423,
1346, 1207. FAB-MS m/z: 341 (MϩH)ϩ. Rf: 0.18 (hexane/AcOEtϭ3/1).
Anal. Calcd for C10H7F3N2O6S: C, 35.30; H, 2.07; N, 8.23. Found: C, 35.25;
H, 2.14; N, 8.29.
7-Nitro-6-thiomorpholino-3,4-dihydroquinolin-2(1H)-one (22a)
A
solution of 19 (357 mg, 1.05 mmol) and thiomorpholine (0.53 ml, 5.25
mmol) in CH3CN (10 ml) was stirred at 80 °C for 4 h. The reaction mixture
was concentrated in vacuo. Preparative TLC (silica gel, hexane/AcOEtϭ2/1)
of the residue gave 22a (156 mg, 51%) as an orange solid. Recrystallization
6-(4-Cyanopiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-one (22g)
The title compound was obtained as orange plates (20%), starting from 28
and following the method as described for 23. Recrystallization was
achieved from hexane–AcOEt. mp 241—242 °C. 1H-NMR (CDCl3) d:
1.97—2.13 (m, 4H), 2.63—2.70 (m, 2H), 2.83—2.91 (m, 1H), 2.96—3.05
(m, 4H), 3.13—3.22 (m, 2H), 7.05 (s, 1H), 7.28 (s, 1H), 8.38 (s, 1H). IR
(KBr) cmϪ1: 2237, 1678, 1522, 1373, 1336, 1282. FAB-MS m/z: 301
(MϩH)ϩ. Rf: 0.18 (hexane/AcOEtϭ1/2). Anal. Calcd for C15H16N4O3·
0.3H2O: C, 58.93; H, 5.47; N, 18.33. Found: C, 59.23; H, 5.31; N, 18.04.
1-tert-Butoxycarbonyl-4-(hydroxymethyl)piperidine (25) To a stirred
solution of 4-(hydroxymethyl)piperidine 24 (2.0 g, 19.4 mmol) in a mixture
of AcOEt (20 ml) and tetrahydrofuran (THF) (10 ml), di-tert-butyl dicarbon-
ate (Boc2O) (4.23 g, 19.4 mmol) was added at room temperature. The mix-
ture was stirred for 14 h at room temperature. After evaporation of the sol-
vent, the concentrate was partitioned between AcOEt and saturated aqueous
NH4Cl. The organic layer was washed with brine, dried and evaporated in
vacuo to give 25 (4.17 g, 100%) as a colorless solid. Recrystallization was
1
was achieved from hexane–AcOEt. mp 203—204 °C. H-NMR (CDCl3) d:
2.64—2.72 (m, 2H), 2.76—2.82 (m, 4H), 2.98—3.06 (m, 2H), 3.22—3.28
(m, 4H), 7.02 (s, 1H), 7.28 (s, 1H), 9.00 (br s, 1H). IR (KBr) cmϪ1: 1716,
1522, 1377, 1333, 1281. FAB-MS m/z: 294 (MϩH)ϩ. Rf: 0.25 (hexane/
AcOEtϭ1/2). Anal. Calcd for C13H15N3O3S·0.2H2O: C, 52.58; H, 5.23; N,
14.15. Found: C, 52.76; H, 5.05; N, 14.02.
6-(4-Methylthiopiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-one
(23) A solution of 32 (300 mg, 1.30 mmol) in TFA (5 ml) was stirred at
0 °C for 0.5 h. The mixture was allowed to stand to come to room tempera-
ture, then stirred for 1 h. The reaction mixture was made basic with 2 M
NaOH at 0 °C, extracted with a mixture of CH2Cl2 and MeOH (5 : 1), dried
and evaporated in vacuo to give a yellow oil (163 mg). A solution of the oil
and 19 (70 mg, 0.308 mmol) in CH3CN (2 ml) was stirred at 90 °C for 2 h.
The reaction mixture was concentrated in vacuo. Preparative TLC (silica gel,
hexane/AcOEtϭ1/1) of the residue gave 23 (29 mg, 29%) as orange plates.
1
achieved from hexane–Et2O. mp 73—74 °C. H-NMR (CDCl3) d: 1.46 (s,
9H), 1.10—1.20 (m, 2H), 1.60—1.74 (m, 3H), 2.64—2.77 (m, 2H), 3.47—
3.53 (m, 2H), 4.06—4.20 (m, 2H). IR (KBr) cmϪ1: 3471, 2937, 1674. FAB-
MS m/z: 216 (MϩH)ϩ. Rf: 0.18 (hexane/AcOEtϭ1/1). Anal. Calcd for
C11H21NO3: C, 61.37; H, 9.83; N, 6.51. Found: C, 61.08; H, 10.09; N, 6.63.
1-tert-Butoxycarbonyl-4-formylpiperidine (26) To a solution of 25
(200 mg, 0.929 mmol) in CH2Cl2 (2 ml), Dess–Martin reagent13) (394 mg,
0.929 mmol) was added at room temperature, and the mixture was stirred for
1 h at room temperature. After evaporation of the solvent, the residue was
partitioned between AcOEt and 0.1 M NaOH. The organic layer was dried
and evaporated. Silica gel column chromatography (hexane/AcOEtϭ1/1) of
1
Recrystallization was achieved from hexane–AcOEt. mp 170—172 °C. H-
NMR (CDCl3) d: 1.75—1.87 (m, 2H), 2.02—2.09 (m, 2H), 2.13 (s, 3H),
2.62—2.77 (m, 3H), 2.80—2.89 (m, 2H), 2.96—3.03 (m, 2H), 3.20—3.28
(m, 2H), 6.99 (s, 1H), 7.28 (s, 1H), 8.45 (br s, 1H). IR (KBr) cmϪ1: 1678,
1522, 1379, 1333, 1284. FAB-MS m/z: 322 (MϩH)ϩ. Rf: 0.08 (hexane/
AcOEtϭ1/1). Anal. Calcd for C15H19N3O3S: C, 56.06; H, 5.96; N, 13.07.
Found: C, 55.92; H, 5.93; N, 13.21.
7-Nitro-6-piperidino-3,4-dihydroquinolin-2(1H)-one (22b) The title
compound was obtained as orange plates (27%), starting from piperidine
and following the method as described for 22a. Recrystallization was
1
the concentrate gave 26 (79 mg, 40%) as a colorless oil. H-NMR (CDCl3)
1
achieved from AcOEt. mp 202—203 °C. H-NMR (CDCl3) d: 1.54—1.62
d: 1.46 (s, 9H), 1.50—1.60 (m, 2H), 1.86—1.93 (m, 2H), 2.37—2.47 (m,
1H), 2.88—2.97 (m, 2H), 3.94—4.05 (m, 2H), 9.66 (s, 1H). IR (neat) cmϪ1
:
(m, 2H), 1.68—1.76 (m, 4H), 2.61—2.66 (m, 2H), 2.93—3.02 (m, 6H), 6.98
(s, 1H), 7.23 (s, 1H), 7.44 (br, 1H). IR (KBr) cmϪ1: 1684, 1522, 1379, 1343,
2976, 1728, 1685. FAB(Ϫ)-MS m/z: 212 (MϪH)Ϫ. HR-FAB-MS m/z

828
Vol. 49, No. 7
214.1427 (MϩH)ϩ. Calcd for C11H20NO3: 214.1443. Rf: 0.47 (hexane/
AcOEtϭ1/1).
13.30.
7-Nitro-6-thiomorpholino-3,4-dihydroquinolin-2(1H)-one S,S-Dioxide
(22i) To a solution of 22a (40 mg, 0.136 mmol) in CH2Cl2 (6 ml), mCPBA
(47 mg, 0.272 mmol) was added at 0 °C, and the mixture was stirred for 1 d
at room temperature. The reaction mixture was partitioned between CH2Cl2
and saturated aqueous NaHCO3. The organic layer was washed with brine,
dried and evaporated. Preparative TLC (silica gel, AcOEt) of the residue
gave 22i (27 mg, 61%) as a light yellow solid. Recrystallization was
achieved from hexane–AcOEt. mp 253—254 °C. 1H-NMR (CDCl3) d:
2.65—2.71 (m, 2H), 3.00—3.07 (m, 2H), 3.20—3.26 (m, 4H), 3.50—3.56
(m, 4H), 7.12 (s, 1H), 7.27 (s, 1H), 7.83 (br, 1H). IR (KBr) cmϪ1: 1674,
1522, 1302, 1126. FAB-MS m/z: 326 (MϩH)ϩ. Rf: 0.26 (AcOEt). Anal.
Calcd for C13H15N3O5S·0.3H2O: C, 47.21; H, 4.74; N, 12.70. Found: C,
47.37; H, 4.74; N, 12.95.
6-(4-Methanesulfinylpiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-
one (22j) To a solution of 23 (30 mg, 0.093 mmol) in CH2Cl2 (5 ml),
mCPBA (16 mg, 0.092 mmol) was added at 0 °C, and the mixture was stirred
for 1 h at 0 °C. The reaction mixture was partitioned between CH2Cl2 and
saturated aqueous NaHCO3. The organic layer was washed with brine, dried
and evaporated. Preparative TLC (silica gel, AcOEt then CH2Cl2/MeOHϭ
20/1) of the residue gave 22j (25 mg, 79%) as an orange solid. Recrystalliza-
tion was achieved from hexane–AcOEt. mp 165—166 °C. 1H-NMR (CDCl3)
d: 1.80—2.00 (m, 3H), 2.20—2.28 (m, 1H), 2.59 (s, 3H), 2.61—2.74 (m,
3H), 2.83—2.96 (m, 2H), 2.97—3.05 (m, 2H), 3.31—3.42 (m, 2H), 7.03 (s,
1H), 7.25 (s, 1H), 7.50 (br s, 1H). IR (KBr) cmϪ1: 1697, 1514, 1317, 1282,
1038. FAB-MS m/z: 338 (MϩH)ϩ. Rf: 0.18 (CH2Cl2/MeOHϭ20/1). Anal.
Calcd for C15H19N3O4S·0.1H2O: C, 53.12; H, 5.71; N, 12.39. Found: C,
53.02; H, 5.73; N, 12.53.
6-(4-Methanesulfonylpiperidino)-7-nitro-3,4-dihydroquinolin-2(1H)-
one (22k) To a solution of 23 (20 mg, 0.062 mmol) in CH2Cl2 (4 ml),
mCPBA (23 mg, 0.133 mmol) was added at 0 °C, and the mixture was stirred
for 17 h at room temperature. The reaction mixture was partitioned between
CH2Cl2 and saturated aqueous NaHCO3. The organic layer was washed with
brine, dried and evaporated. Preparative TLC (silica gel, AcOEt) of the
residue gave 22k (17 mg, 77%) as an orange solid. Recrystallization was
achieved from hexane–AcOEt. mp 332—333 °C. 1H-NMR (CDCl3) d:
1.98—2.08 (m, 2H), 2.22—2.29 (m, 2H), 2.63—2.69 (m, 2H), 2.80—2.90
(m, 5H), 2.91—3.04 (m, 3H), 3.38—3.43 (m, 2H), 7.02 (s, 1H), 7.26 (s,
1H), 7.78 (br, 1H). IR (KBr) cmϪ1: 1699, 1520, 1296, 1132. FAB-MS m/z:
354 (MϩH)ϩ. Rf: 0.13 (AcOEt). Anal. Calcd for C15H19N3O5S·0.1H2O: C,
50.72; H, 5.45; N, 11.83. Found: C, 50.81; H, 5.55; N, 11.56.
CTA on Isolated Guinea Pig Atria Male Hartley guinea pigs (300—
450 g) were sacrificed and then the left atria was isolated. CTA was mea-
sured in the isolated left atria, according to Horii et al.10b) The left atria was
stimulated electrically with a square-wave pulse stimulator at a frequency of
1 Hz and a voltage 20% above the threshold (duration: 5 ms). The atrium
was suspended in Krebs–Henselite solution, aerated with 95% O2 and 5%
CO2 at a temperature of 35 °C, and stretched to a resting tension of 0.5 g.
The physiological solution (in mM) consisted of the following: NaCl, 118;
KCl, 4.7; CaCl2, 2.55; MgSO4 1.18; KH2PO4, 1.18; NaHCO3, 24.88; glu-
cose, 11.1. Before the construction of dose–response curves for each test
compound, the cardiotonic response for epinephrine (10Ϫ7 M) was estab-
lished.
The inotropic potency was expressed as the ratio of the response to each
compound to the response to epinephrine (10Ϫ7 M). EC30 values (micro mole
per liter) represent the dose that produces a 30% increase in the epinephrine
response.
CRA on Isolated Guinea Pig Atria Male Hartley guinea pigs (300—
450 g) were sacrificed, then the right and left atria were isolated. CRA was
measured on these isolated right and left atria. The atrium was suspended in
Krebs-Henselite solution in the same condition described above. The
chronotropic potency was expressed as the ratio of the response to each
compound to the basal response. EC10 values (micro mole per liter) repre-
sent the dose that produces a 10% increase in the basal response.
Platelet Aggregation in Rabbit PRP Rabbit (Japanese White) blood
was obtained from the carotid artery in the presence of a 3.8% trisodium cit-
rate aqueous solution (volume ratio 9 : 1), then centrifuged at 1000 rpm for
10 min at room temperature to give PRP. Platelet counts in PRP were deter-
mined using an automated particle counter (model F-800, Toa Medical Elec-
tronics Co., Ltd.). Platelet concentration was adjusted to 8—12ϫ108
platelets/ml with time-matched platelet-poor plasma (PPP), which was ob-
tained from the precipitate fraction of PRP by centrifugation at 3000 rpm for
10 min at room temperature. The test compound or the control solution
(2 ml) was added to the PRP (0.198 ml), then the mixture was incubated at
1-tert-Butoxycarbonyl-4-cyanopiperidine (28) To a stirred solution of
isonipecotamide 27 (5.0 g, 39.0 mmol) in a mixture of pyridine (24 ml) and
CH2Cl2 (30 ml), Boc2O (9.0 g, 41.2 mmol) in CH2Cl2 (30 ml) was added at
room temperature. The mixture was stirred for 40 min at room temperature.
After the addition of TFAA (15 ml), the stirring was continued for 2 h at
room temperature. After evaporation of the solvent, the concentrate was par-
titioned between Et2O and H2O. The organic layer was washed successively
with 10% aqueous citric acid and with brine, dried and evaporated in vacuo
over P2O5 to give 28 (7.37 g, 83%) as colorless prisms. Recrystallization was
1
achieved from hexane–Et2O. mp 45—46 °C. H-NMR (CDCl3) d: 1.46 (s,
9H), 1.74—1.93 (m, 4H), 2.76—2.84 (m, 1H), 3.29—3.39 (m, 2H), 3.61—
3.71 (m, 2H). IR (KBr) cmϪ1: 2975, 2239, 1697. FAB-MS m/z: 211
(MϩH)ϩ. Rf: 0.55 (hexane/AcOEtϭ1/1). Anal. Calcd for C11H18N2O2: C,
62.83; H, 8.63; N, 13.32. Found: C, 62.55; H, 8.72; N, 13.27.
1-tert-Butoxycarbonyl-4-acetopiperidine (29) Iodomethane (5.12 ml,
82.2 mmol) was added dropwise to a stirred suspension of Mg (2.0 g,
82.3 mmol) in Et2O (30 ml) under Ar ambience. A solution of 28 (4.0 g,
19.0 mmol) in THF (50 ml) was added to the prepared MeMgI. After the
mixture was stirred for 11 h at room temperature, the reaction mixture was
quenched by adding saturated aqueous NH4Cl, neutralized by adding dilute
aqueous HCl and extracted with Et2O. The organic layer was washed succes-
sively with 10% aqueous citric acid and brine, then dried and evaporated.
Silica gel column chromatography (CH2Cl2/Et2Oϭ10/1) of the concentrate
1
gave 29 (1.85 g, 43%) as a colorless oil. H-NMR (CDCl3) d: 1.46 (s, 9H),
1.47—1.57 (m, 2H), 1.80—1.87 (m, 2H), 2.16 (s, 3H), 2.40—2.50 (m, 1H),
2.73—2.83 (m, 2H), 4.05—4.16 (m, 2H). IR (neat) cmϪ1: 2976, 1710, 1690.
FAB-MS m/z: 228 (MϩH)ϩ. HR-FAB-MS m/z 228.1605 (MϩH)ϩ. Calcd
for C12H22NO3: 228.1600. Rf: 0.40 (CH2Cl2/Et2Oϭ10/1).
1-tert-Butoxycarbonyl-4-methanesulfonyloxypiperidine (31) To
a
stirred solution of 4-hydroxypiperidine 30 (1.0 g, 9.69 mmol) in a mixture of
CH2Cl2 (10 ml) and 1.4-dioxane (10 ml), Boc2O (2.11 g, 9.67 mmol) was
added at room temperature. The mixture was stirred for 2 h at room tempera-
ture. After evaporation of the solvent, the concentrate was partitioned be-
tween AcOEt and saturated aqueous NH4Cl. The organic layer was washed
with brine, dried and evaporated to give a yellow oil. To a stirred solution of
the oil in CH2Cl2 (10 ml), Et3N (1.41 ml, 10.1 mmol) and methanesulfonyl
chloride (0.75 ml, 9.69 mmol) were added at 0 °C, and stirring was continued
for 13 h at room temperature. The reaction mixture was partitioned between
CH2Cl2 and saturated aqueous NH4Cl. The organic layer was washed succes-
sively with saturated aqueous NaHCO3 and with brine, dried and evaporated
to give 31 (2.59 g, 96%) as colorless plates. Recrystallization was achieved
from hexane–Et2O. mp 67—68 °C. 1H-NMR (CDCl3) d: 1.46 (s, 9H),
1.78—1.85 (m, 2H), 1.93—1.99 (m, 2H), 3.04 (s, 3H), 3.26—3.35 (m, 2H),
3.67—3.74 (m, 2H), 4.85—3.92 (m, 1H). IR (KBr) cmϪ1: 2968, 1689, 1354,
1173. FAB-MS m/z: 280 (MϩH)ϩ. Rf: 0.48 (hexane/AcOEtϭ1/1). Anal.
Calcd for C11H21NO5S: C, 47.30; H, 7.58; N, 5.01. Found: C, 47.14; H, 7.77;
N, 5.27.
1-tert-Butoxycarbonyl-4-methylthiopiperidine (32) To a stirred solu-
tion of 31 (700 mg, 2.51 mmol) in DMF (15 ml), sodium methanethiolate
(237 mg, 3.38 mmol) was added at room temperature. The stirred mixture
was heated at 80 °C for 2 h. The reaction mixture was quenched by adding
saturated aqueous NH4Cl and extracted with AcOEt. The organic layer was
washed with H2O, dried and evaporated. Silica gel column chromatography
1
(CH2Cl2) of the concentrate gave 32 (343 mg, 59%) as a colorless oil. H-
NMR (CDCl3) d: 1.46 (s, 9H), 1.47—1.56 (m, 2H), 1.87—1.97 (m, 2H),
2.10 (s, 3H), 2.65—2.75 (m, 1H), 2.84—2.96 (m, 2H), 3.90—4.10 (m, 2H).
IR (neat) cmϪ1: 2976, 2920, 1695. FAB-MS m/z: 232 (MϩH)ϩ. HR-FAB-
MS m/z 232.1372 (MϩH)ϩ. Calcd for C11H22NO2S: 232.1371. Rf: 0.20
(hexane/AcOEtϭ10/1).
7-Nitro-6-thiomorpholino-3,4-dihydroquinolin-2(1H)-one S-Oxide
(22h) To a solution of 22a (40 mg, 0.136 mmol) in CH2Cl2 (6 ml), mCPBA
(23 mg, 0.133 mmol) was added at 0 °C, and the mixture was stirred at 0 °C
for 2 h. The stirring was continued for 1 d at room temperature. The reaction
mixture was partitioned between CH2Cl2 and saturated aqueous NaHCO3.
The organic layer was washed with brine, dried and evaporated. Preparative
TLC (silica gel, AcOEt then CH2Cl2/MeOHϭ30/1) of the residue gave 22h
(19 mg, 45%) as an orange solid. Recrystallization was achieved from
hexane–AcOEt. mp 280—282 °C. 1H-NMR (CDCl3) d: 2.64—2.71 (m, 2H),
2.90—3.07 (m, 6H), 3.09—3.16 (m, 2H), 3.77—3.85 (m, 2H), 7.18 (s, 1H),
7.35 (s, 1H), 8.98 (br, 1H). IR (KBr) cmϪ1: 1690, 1522, 1327, 1284, 1032.
FAB-MS m/z: 310 (MϩH)ϩ. Rf: 0.28 (CH2Cl2/MeOHϭ20/1). Anal. Calcd
for C13H15N3O4S: C, 50.48; H, 4.89; N, 13.58. Found: C, 50.60; H, 5.06; N,

July 2001
829
37 °C with stirring for 1 min before the addition of ADP (20 ml, final conc.
20 mM). Changes in light transmission caused by platelet clotting were mea-
sured using an aggregometer (platelet aggregation tracer, Nicho Bioscience
Co., Ltd.) until each trace reached a plateau. Platelet aggregation was ex-
pressed as the percentage change in light transmittance, with the difference
of light transmittance between PRP and PPP as 100%. Antiplatelet activity
was expressed as the percent inhibition of the control value.
1978, 1076—1079.
6) a) Trudell M. L., Lifer S. L., Tan Y.-C., England W. B., Cook J. M., J.
Org. Chem., 53, 4185—4190 (1988); b) Avasthi K., Lee, S.-J., Cook J.
M., Heterocycles, 16, 1453—1461 (1981).
1
7) Data for 5-nitro isomer: H-NMR (MeOH-d4) d: 2.12 (s, 3H), 2.54—
2.62 (m, 2H), 2.80—2.96 (m, 6H), 3.56—3.65 (m, 4H), 7.01 (d,
Jϭ9 Hz, 1H), 7.30 (d, Jϭ9 Hz, 1H).
1
8) Data for 7,8-dinitrated product: H-NMR (DMSO-d6) d: 2.54—2.61
References and Notes
(m, 2H), 3.27—3.34 (m, 2H), 3.94 (s, 3H), 7.75 (s, 1H), 9.96 (br s,
1H). Regiochemistry of the 7,8-dinitrated product was confirmed
based on a nuclear Overhauser effect (NOE) experiment: 18% between
6-OMe and H-5; 14% between H-5 and CH2-4.; Data for 8-nitro iso-
mer: 1H-NMR (DMSO-d6) d: 2.53—2.60 (m, 2H), 2.98—3.05 (m,
2H), 3.81 (s, 3H), 7.35 (d, Jϭ3 Hz, 1H), 7.47 (d, Jϭ3 Hz, 1H), 9.69
(br s, 1H).
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