Synthesis and evaluation of 1-arylsulfonyl-3-piperazinone derivatives as factor Xa inhibitors IV. A series of new derivatives containing a spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4′-piperidin]-5-one skeleton

Article abstract of DOI:10.1248/cpb.52.406

In the course of development of factor Xa (FXa) inhibitor in an investigation involving the synthesis of 1-arylsulfonyl-3-piperazinone derivatives, we found new compounds containing a unique spiro skeleton. Among such compounds, (-)-7-[(6-chloro-2-naphtha

Full text of DOI:10.1248/cpb.52.406

406
Chem. Pharm. Bull. 52(4) 406—412 (2004)
Vol. 52, No. 4
Synthesis and Evaluation of 1-Arylsulfonyl-3-piperazinone Derivatives as
Factor Xa Inhibitors1—3) IV. A Series of New Derivatives Containing a
Spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-one Skeleton
Hidemitsu NISHIDA,* Takafumi MUKAIHIRA, Fumihiko SAITOH, Kousuke HARADA, Miyuki FUKUI,
Tomokazu MATSUSUE, Atsushi OKAMOTO, Yoshitaka HOSAKA, Miwa MATSUMOTO, Ikuya SHIROMIZU,
Shuhei OHNISHI, and Hidenori MOCHIZUKI
Discovery Research Center, Mochida Pharmaceutical Co., Ltd.; 722 Jimba-aza-uenohara, Gotemba, Shizuoka 412–8524,
Japan. Received November 5, 2003; accepted February 2, 2004
In the course of development of factor Xa (FXa) inhibitor in an investigation involving the synthesis of 1-
arylsulfonyl-3-piperazinone derivatives, we found new compounds containing a unique spiro skeleton. Among
such compounds, (؊)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxymethyl)-1؅-(4-pyridinyl)-
spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-one (28, M55529) had activity more favorable than those
of previously reported compounds. The inhibitory activity of M55529 for FXa is IC50؍2 nM, with high selectivity
for FXa over thrombin and trypsin.
Key words factor Xa inhibitor; N,O-spiro acetal; M55529; structure–activity relationship; intramolecular cyclization
Factor Xa (FXa), a trypsin-like serine protease, holds the
In more recent investigations, fixation of the conformation
central position that links the intrinsic and extrinsic mecha- of testing compounds is believed to affect the strength of in-
nisms in the blood coagulation cascade. FXa is known to ac- teraction between such compounds and the target enzyme.
tivate prothrombin to thrombin. Thrombin has several pro- Accordingly, in the next stage of investigation our interest
coagulant functions that include the activation of platelets, was focused on the synthesis of compounds containing a
feedback activation of other coagulation factors, and conver- rigid structure in the central part of the compound (2, 3), and
sion of fibrinogen to insoluble fibrin clots.4—8) Comparison of on comparison of the inhibitory activities of the compounds
hirudin9—13) (a thrombin inhibitor) and tick anticoagulant thus synthesized for FXa with those of previously reported
peptide14—20) (a FXa inhibitor) suggests that inhibition of compounds. A molecule with a spiro structure in between the
FXa may result in less bleeding risk, leading to a more favor- piperidine moiety and piperazine moiety was therefore de-
able safety/efficacy ratio.21—24)
signed as the next candidate for further development of FXa
Direct inhibition to FXa has therefore emerged as an at- inhibitor. The present paper concerns the synthesis of
tractive strategy for the discovery of novel antithrombotic a series of compounds 4 with a spiro[5H-oxazolo[3,2-
agents.25—31) In preceding papers,1,2) we reported the synthe- a]pyrazine-2(3H),4Ј-piperidin]-5-one skeleton, together with
sis and evaluation of compounds in a series of 1-arylsul- the FXa inhibitory activities of these new compounds.
fonyl-3-piperazinone derivatives, of which M55113 (1) 4-
[(6-chloro-2-naphthalenyl)sulfonyl]-1-[[1-(4-pyridinyl)-4- Chemistry
piperidinyl]methyl]-2-piperazinone, M55196 (2) 4-[(6-
First, acyclic precursor 9 was prepared as shown in Chart
chloro-2-naphthalenyl)sulfonyl]-1-[[4-hydroxy-1-(4- 1. Sulfonylamidation of glycine ethyl ester hydrochloride (5)
pyridinyl)-4-piperidinyl]methyl]-2-piperazinone and M55551 with 6-chloro-2-naphthalenesulfonyl chloride (6) under tradi-
(3) (R)-4-[(6-chloro-2-naphthalenyl)sulfonyl]-6-oxo-1-[[1- tional conditions yielded the corresponding naphthalenesul-
(4-pyridinyl)-4-piperidinyl]methyl]-2-piperazinecarboxylic fonylamide 7. When 7 was treated with 1-acetoxy-3-
acid were found to be potent inhibitors of FXa (IC50ϭ60 nM, chloroacetone (8) in DMF in the presence of potassium car-
31 nM, 6 nM, respectively) with high selectivity for FXa over bonate, 9 was obtained in good yield as expected.
trypsin and thrombin.
When 4-(aminomethyl)-1-benzyl-4-piperidinol (10) was
allowed to react with acyclic precursor 9 under acidic condi-
tions, a product 11 containing a spiro N,O-acetal structure on
the piperazinone ring was obtained, as expected.
The reaction pathway of the formation of the spiro skele-
ton from 9 and 10 is illustrated in Chart 2. In the first step, a
Schiff base was formed by dehydration between a carbonyl
group in 9 and a primary amino group in 10. Subsequent nu-
cleophilic addition of a hydroxyl group to an azomethine
Spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4-piperidin]-5-one derivatives
4
To whom correspondence should be addressed. e-mail: hnishida@mochida.co.jp
© 2004 Pharmaceutical Society of Japan

April 2004
407
Chart 1. Synthesis of Acyclic Precursor 9
Chart 2. The Reaction Mechanism of the Spiro Skeleton
Chart 3. Synthesis of Compounds 13, 14 and 16
bond (CϭN) followed by intramolecular amide formation
gave rise to the spiro skeleton.
1H- and 13C-NMR spectral data for the product are consis-
tent with the proposed spiro structure, as shown in Fig. 1. In
addition, the results of high-resolution MS are in good agree-
ment with the structure.
As shown in Chart 3, conversions of the spiro compound
11 to various derivatives were carried out. When compound
12 prepared by the deprotection of 11 with 1-chloroethyl
chloroformate in 1,2-dichloroethane and with 1 N NaOH in
MeOH was treated with 4-chloropyridine, the desired com-
pound 13 was obtained. Then, compound 13 was methylated
with dimethyl sulfate in the presence of a phase-transfer
catalyst (benzyltriethylammonium chloride) to obtain the
methyl ether 14. Compound 13 was treated with phthalimide
by Mitsunobu reaction32) and with hydrazine to obtain the
Fig. 1. Assignment of NMR Data
corresponding amino compound 16.
Synthesis of compounds 21 and 22 was achieved as shown
in Chart 4. Compound 17, prepared by the reaction of the
key intermediate 11 with benzyl chloroformate in the pres-

408
Vol. 52, No. 4
Chart 4. Synthesis of Compounds 21 and 22
Table 1. Comparison of FXa Inhibitory Activity of Spiro Skeleton and Piperazinone Derivative
Spiro skeleton
Piperazinone derivative2)
Compd. No. IC50 (nM)
R
Compd. No.
IC50 (nM)
–CH2OH
–CH2OMe
–CH2NH2
–CO2Et
13
14
16
21
22
5
5
2
5
3
23
24
25
26
27
12
31
12
30
10
ϩ
–CO2ϪNH4
ence of 1,8-bis(N,N-dimethylamino)naphthalene and with 1 N spiro structure synthesized in the present investigation were
NaOH in MeOH, was oxidized with Ca(OCl)2 in the pres- measured using the same method as described in the preced-
ence of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl ben- ing paper.1)
zoate in CH2Cl2 to obtain carboxylic acid 18 in good yield.
Compared with the activities of previously tested piperazi-
The ethyl ester 19 was followed by esterification of 18 with none type compounds, those of new compounds were higher
EtOH in traditional conditions, and compound 20 was af- for all the derivatives containing the corresponding substitu-
forded by deprotection of the 19. Desired compound 21 was tion.
obtained by coupling reaction of compound 20 with 4-
As listed in Table 1, the inhibitory activities (IC50) of new
chloropyridine hydrochloride under basic conditions. When compounds varied from twice to six times those of piperazi-
compound 21 was treated with 1 N NaOH, the corresponding none (prototype) compounds. It is conceivable that the rigid-
carboxylic acid 22 was obtained. The spectral data for all of ity of structures in the linker moiety of the testing com-
these products are in good agreement with the proposed pounds is important for exhibition of FXa inhibitory activity.
structures.
An N,O-spiro acetal skeleton fixes the conformation of the
Throughout the chemical modifications described above, new compounds, and their shape may be more suitable for
the spiro structure is fairly stable, although the skeleton has inhibition of FXa. On the other hand, the conformation of
an N,O-acetal linkage.
prototype compounds is relatively loose.
In addition to the above, little effect on activity was ob-
served by introducing a functional group to the new com-
Results and Discussion
The FXa inhibitory activities of new compounds with a pounds (IC50 2—5 nM), while some effects on activity were

April 2004
409
Table 2. Selectivity of M55529 for FXa over Other Serine Protease
thrombin (Sigma Co., 0.09 U/ml) and S-2238 (Chromogenix AB, 0.2 mM);
human trypsin (Athens Research and Technology, Inc., 15 ng/ml) and S-
2222 (Chromogenix AB, 0.4 mM). To calculate the inhibitory activity of the
test compound, the initial reaction velocity was compared with the value for
a control containing no test compound. The inhibitory activity of a test com-
pound was expressed as IC50.
Ethyl N-[(6-Chloro-2-naphthalenyl)sulfonyl]glycinate (7) Ethyl glyci-
nate hydrochloride (5) (9.88 g, 70.7 mmol) was suspended in CH2Cl2
(500 ml). Et3N (20.2 ml, 144.9 mmol) and 6-chloro-2-naphthalenesulfonyl
chloride (6) (17.6 g, 67.4 mmol) were added to the suspension under cooling
with ice. After stirring at room temperature for 1 h, the mixture was adjusted
to pH 2 by addition of 1 N HCl, and the reaction mixture was extracted with
CH2Cl2. The organic layer was washed with brine and dried over dry
Na2SO4. The solvent was distilled off under reduced pressure. After washing
the resulting crystals in hexane, the crystals were collected by filtration and
air-dried to give compound 7 (22.4 g, quant.) as pale yellow crystal, mp
93—94 °C.
M55529
IC50 (nM)
Selectivity (Enzyme/FXa)
FXa
Thrombin
APC
Trypsin
Plasmin
t-PA
2
—
Ͼ10000
Ͼ10000
Ͼ10000
Ͼ10000
1900
Ͼ5000
Ͼ5000
Ͼ5000
Ͼ5000
950
HR-MS m/z: Calcd for C14H1435ClNO4S: 327.0332. Found : 327.0325. 1H-
NMR (300 MHz, CDCl3) d: 8.43—7.57 (6H, m, naphthyl), 5.22—5.15 (1H,
m, NH), 4.01 (2H, q, Jϭ7.1 Hz, CO2CH2CH3), 3.82 (2H, d, Jϭ5.3 Hz,
Urokinase
Ͼ10000
Ͼ5000
CH2CO2CH2CH3), 1.11 (3H, t, Jϭ7.1 Hz, CH2CO2CH2CH3). IR (film) cmϪ1
:
1745, 1330, 1159, 1120, 1079, 696.
Ethyl N-(3-Acetyloxy-2-oxopropyl)-N-[(6-chloro-2-naphthalenyl)sul-
fonyl]glycinate (9) To DMF (25 ml) solution of compound 7 (2.50 g,
7.63 mmol) were added K2CO3 (1.58 g, 11.4 mmol) and NaI (1.14 g,
7.63 mmol), and a solution of 1-acetoxy-3-chloroacetone (8) (1.72 g,
observed for the corresponding derivatives of prototype com-
pounds (IC50 10—30 nM).
Based on these data, the steric shape of the molecule is
concluded to more strongly affect FXa inhibition than the hy- 11.4 mmol) in DMF (7 ml) was added dropwise at room temperature. The
reaction mixture was stirred at room temperature for 1.5 h, and the mixture
was extracted with Et2O. The organic layer was washed with brine and dried
over dry Na2SO4. The solvent was distilled off under reduced pressure. The
resulting residue was crystallized in Et2O, and the crystals were collected by
drogen bond-forming ability of the functional group intro-
duced.
At the final stage of the present investigation, comparison
was made of stereoisomers including a substitution at the 8-
position of the new skeletons for inhibitory activity. It is
known that compounds with polar substitution undergo little
absorption in the body, and that ester substitution will tend to
induce hydrolysis in the body. Compound 14 was therefore
considered likely to exhibit the best absorption in the body,
as a candidate for development.
The activities of stereoisomers (28, 29) of compound 14
obtained by optical resolution with liquid column chroma-
tography were measured. (Ϫ)-Isomer 28 (IC50ϭ2 nM) had
stronger activity than (ϩ)-isomer 29 (IC50ϭ129 nM).
Though we are investigating absolute configuration of the
compound 28 and 29, it has not resolved yet.
Compound 28 (M55529) exhibited clear selectivity for
FXa over related serine protease, and was 5000-fold more se-
lective for FXa than for thrombin, as shown in Table 2.
The above results suggest that M55529 is promising as
FXa inhibitor. Crystallization of a complex of M55529 with
FXa has already been successfully performed in our labora-
tory, and the results of X-ray crystallographic analysis will
be published in the near future.
filtration and air-dried to obtain the compound 9 (2.72 g, 81%) as pale yel-
low crystal, mp 75—76 °C.
HR-MS m/z: Calcd for C19H2035ClNO7S: 441.0649. Found: 441.0600. 1H-
NMR (300 MHz, CDCl3) d: 8.42—7.52 (6H, m, naphthyl), 4.84 (2H, s,
CH2COCH2OCOCH3), 4.31 (2H, s, CH2COCH2OCOCH3), 4.15 (2H, s,
CH2CO2CH2CH3), 4.06 (2H, q, Jϭ7.1 Hz, CH2CO2CH2CH3), 2.16 (3H, s,
OCOCH3), 1.17 (3H, t, Jϭ7.1 Hz, CH2CO2CH2CH3). IR (film) cmϪ1: 1743,
1461, 1340, 1234, 1159, 586.
8a-[(Acetyloxy)methyl]-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahy-
dro-1؅-benzyl-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-
one (11) To a solution of compound 9 (1.6 g, 3.62 mmol) and 4-
(aminomethyl)-1-benzyl-4-piperidinol (10) (800 mg, 3.62 mmol) in PhMe
(200 ml) was added p-toluenesulfonic acid monohydrate (34.0 mg,
0.18 mmol), and the mixture was refluxed for 1 h by using a Dean-Stark ap-
paratus. The reaction mixture was allowed to cool, and the solvent was dis-
tilled off under reduced pressure. The resulting residue was purified by silica
gel column chromatography (eluent: EtOAc) to give the compound 11
(1.08 g, 50%) as ivory crystal, mp 84—86 °C.
HR-MS m/z: Calcd for C30H3235ClN3O6S: 597.1700. Found: 597.1650. 1H-
NMR (300 MHz, CDCl3) d: 8.36—7.19 (11H, m, naphthyl and phenyl), 4.41
(1H, d, Jϭ11.5 Hz, CH2OCOCH3), 4.38 (1H, d, Jϭ11.7 Hz, C8-H), 4.33
(1H, d, Jϭ16.7 Hz, C6-H), 4.23 (1H, d, Jϭ11.7 Hz, C3-H), 4.17 (1H, d,
Jϭ11.5 Hz, CH2OCOCH3), 3.46 (2H, s, CH2Ph), 3.33 (1H, d, Jϭ16.7 Hz,
C6-H), 3.08 (1H, d, Jϭ11.7 Hz, C3-H), 2.62—2.21 (4H, m, C2Ј,6Ј-H of piperi-
dine), 2.32 (1H, d, Jϭ11.7 Hz, C8-H), 2.11 (3H, s, OCOCH3), 1.93—1.34
(4H, m, C3Ј,5Ј-H of piperidine). 13C-NMR (75 MHz, CDCl3) d: 170.05
(CH2OCOCH3), 162.74 (C5), 138.09—123.47 (16C, naphthyl and phenyl),
90.21 (C8a), 81.57 (C2), 64.65 (CH2OCOCH3), 62.73 (CH2Ph), 51.54
(C3), 50.37 (C2Ј,6Ј of piperidine), 50.16 (C8), 49.89 (C2Ј,6Ј of piperidine),
47.86 (C6), 36.69 (C3Ј,5Ј of piperidine), 36.07 (C3Ј,5Ј of piperidine), 20.83
(CH2OCOCH3). IR (film) cmϪ1: 1749, 1673, 1224, 1168, 698.
Experimental
Melting points (mp) were determined by using METTLER FP82 hotstage
melting point apparatus and were uncorrected. Nuclear magnetic resonance
(NMR) spectra were taken with JEOL JNM-EX270 FT-NMR or JEOL JNM-
LA300 in CDCl3, dimethyl sulfoxide-d6 (DMSO-d6) or CD3OD using
tetramethylsilane as the internal reference. High-resolution mass spectra
(HR-MS) were obtained using JEOL JMS-GCMATE. Infrared absorption
spectra (IR) were run using HORIBA FT-720 FT-IR. High performance liq-
uid chromatographies (HPLC) were conducted by using Shimadzu LC-10A.
Optical rotations were measured with JASCO DIP-1000 digital polarimeter.
Measurement of Factor Xa, Thrombin and Trypsin Inhibition En-
zyme solution was mixed with a test compound dissolved at various concen-
trations in dimethyl sulfoxide (DMSO). Synthetic substrate was added and
incubated in a 20 mM Tris–HCl buffer (pH 7.5) containing 0.13 M NaCl at
37 °C. The absorbance at 405 nm was measured continuously. Enzyme and
substrate were used as follows: human factor Xa (Enzyme Research Labora-
tories, Inc., 0.019 U/ml) and S-2222 (Chromogenix AB, 0.4 mM); human
7-[(6-Chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(hydroxymethyl)-
spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-one (12) To
a
solution of compound 11 (1.0 g, 1.67 mmol) in ClCH2CH2Cl (10 ml) were
added 1-chloroethyl chloroformate (0.46 ml, 4.18 mmol) and 1,8-bis(N,N-di-
methylamino)naphthalene (72 mg, 0.34 mmol), and the mixture was heated
under reflux for 30 min. The reaction mixture was allowed to cool, and the
solvent was distilled off under reduced pressure. To the residue was added
MeOH (10 ml), and the mixture was heated under reflux for 30 min. The re-
action mixture was allowed to cool, and the solvent was distilled off under
reduced pressure. To a solution of the residue in MeOH (14 ml) was added
1 N NaOH (4 ml) and the mixture was stirred for 1 h at room temperature.
The solvent was distilled off under reduced pressure. To the residue, water

410
Vol. 52, No. 4
H), 4.28 (1H, d, Jϭ11.9 Hz, C3-H), 4.19 (1H, d, Jϭ14.5 Hz, CH2-phthalim-
ide), 4.09 (1H, d, Jϭ14.5 Hz, CH2-phthalimide), 3.44—3.16 (4H, m, C2Ј,6Ј-H
of piperidine), 3.44 (1H, d, Jϭ16.7 Hz, C6-H), 3.04 (1H, d, Jϭ11.9 Hz, C3-
H), 2.41 (1H, d, Jϭ11.7 Hz, C8-H), 1.89—1.40 (4H, m, C3Ј,5Ј-H of piperi-
dine). IR (film) cmϪ1: 1747, 1673, 1417, 1349, 1224, 1168, 698.
8a-(Aminomethyl)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-
1؅-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-
one (16) To a suspension of compound 15 (2.45 g, 3.66 mmol) in EtOH
(50 ml) was added hydrazine monohydrate (0.37 ml, 7.47 mmol) and the
mixture was heated under reflux for 16 h. The reaction mixture was concen-
trated under reduced pressure and the resulting residue was purified by silica
gel column chromatography (eluents: CH2Cl2 : MeOHϭ4 : 1) to give the
compound 16 (1.43 g, 72%) as colorless oil.
(20 ml) was added and extracted with CH2Cl2. The organic layer was washed
with brine and dried over dry Na2SO4. The solvent was distilled off under
reduced pressure. The resulting residue was purified by silica gel column
chromatography (eluents: CH2Cl2 : MeOHϭ10 : 1) to give compound 12
(626 mg, 81%) as pale yellow powder, mp 165—166 °C.
1H-NMR (300 MHz, CD3OD) d: 8.52—7.61 (6H, m, naphthyl), 4.27 (1H,
d, Jϭ11.9 Hz, C8-H), 4.23 (1H, d, Jϭ16.9 Hz, C6-H), 4.16 (1H, d,
Jϭ11.8 Hz, C3-H), 3.78—3.68 (2H, m, CH2OH), 3.48 (1H, d, Jϭ16.9 Hz,
C6-H), 3.28 (1H, d, Jϭ11.8 Hz, C3-H), 3.23—2.83 (4H, m, C2Ј,6Ј-H of piperi-
dine), 2.58 (1H, d, Jϭ11.9 Hz, C8-H), 2.06—1.35 (4H, m, C3Ј,5Ј-H of piperi-
dine). IR (film) cmϪ1: 1662, 1455, 1348, 1166, 1078, 700.
7-[(6-Chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(hydroxymethyl)-
1؅-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-
one (13) To a suspension of compound 12 (11.3 g, 24 mmol) and 4-
chloropyridine hydrochloride (5.4 g, 36 mmol) in EtOH (210 ml) were added
iPr2NEt (21.0 ml, 120 mmol), and the mixture was stirred in a sealed tube at
140—150 °C for 15 h. The reaction mixture was allowed to cool and concen-
trated. The resulting residue was purified by silica gel column chromatogra-
phy (ChromatorexNHTM, eluents: CH2Cl2 : MeOHϭ19 : 1) to give the com-
pound 13 (6.4 g, 49%) as pale yellow powder, mp 141—143 °C.
1H-NMR (270 MHz, CDCl3) d: 8.39—6.58 (10H, m, naphthyl and
pyridinyl), 4.53 (1H, d, Jϭ11.9 Hz, C8-H), 4.38 (1H, d, Jϭ16.8 Hz, C6-H),
4.26 (1H, d, Jϭ11.9 Hz, C3-H), 3.55—3.22 (4H, m, C2Ј,6Ј-H of piperidine),
3.37 (1H, d, Jϭ16.8 Hz, C6-H), 3.18 (1H, d, Jϭ13.5 Hz, CH2NH2), 3.17 (1H,
d, Jϭ11.9 Hz, C3-H), 2.89 (1H, d, Jϭ13.5 Hz, CH2NH2), 2.24 (1H, d,
Jϭ11.9 Hz, C8-H), 1.94—1.48 (4H, m, C3Ј,5Ј-H of piperidine). 13C-NMR
(75 MHz,, CDCl3) d: 162.77 (C5), 154.31 (C4 of pyridine), 149.92 (C2,6 of
pyridine), 135.71—123.40 (10C, naphthyl), 108.52 (C3,5 of pyridine), 93.27
(C8a), 80.25 (C2), 51.72 (C3), 48.91 (C8), 48.04 (C6), 46.50 (CH2NH2), 43.62
(C2Ј or C6Ј of piperidine), 43.21 (C2Ј or C6Ј of piperidine), 35.76 (C3Ј or C5Ј
of piperidine), 35.43 (C3Ј or C5Ј of piperidine). IR (KBr) cmϪ1: 3395, 2920,
2360, 1666, 1597, 1348, 1167.
1؅-Benzyloxycarbonyl-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahy-
dro-8a-(hydroxymethyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-
piperidin]-5-one (17) The compound 11 (67.2 g, 112.4 mmol) and 1,8-
bis(N,N-dimethylamino)naphthalene (4.80 g, 22.5 mmol) were dissolved in
ClCH2CH2Cl (670 ml) and benzyl chloroformate (32.1 ml, 224.7 mmol) was
added dropwise to the solution with the reaction temperature maintained at
0 °C. The reaction mixture was stirred at room temperature for 2 h, and sat.
aq. NaHCO3 was added under cooling with ice. The mixture was extracted
with CH2Cl2 and the organic layer was washed with brine and dried over dry
Na2SO4. The solvent was distilled off under reduced pressure. The resulting
residue was dissolved in a mixed solution of MeOH (1.33 l) and CH2Cl2
(1.33 l), and 1 N NaOH (140 ml) was added dropwise to this solution under
cooling with ice. After stirring at room temperature for 30 min, the solvent
was distilled off under reduced pressure. To the residue was added sat. aq.
NH4Cl and the mixture was extracted with CH2Cl2. The organic layer was
washed with brine and dried over dry Na2SO4. The solvent was distilled off
under reduced pressure. The resulting residue was purified by silica gel col-
umn chromatography (eluents: CH2Cl2 : MeOHϭ40 : 1—30 : 1) to give the
compound 17 (67.9 g, quant.) as pale yellow powder, mp 96—98 °C.
1H-NMR (300 MHz, CDCl3) d: 8.37—7.25 (11H, m, naphthyl and
phenyl), 5.10 (2H, s, OCH2Ph), 4.43 (1H, d, Jϭ11.7 Hz, C8-H), 4.38 (1H, d,
Jϭ16.8 Hz, C6-H), 4.23 (1H, d, Jϭ11.9 Hz, C3-H), 3.96—3.24 (6H, m,
CH2OH and C2Ј,6Ј-H of piperidine), 3.36 (1H, d, Jϭ16.8 Hz, C6-H), 3.14
(1H, d, Jϭ11.9 Hz, C3-H), 2.29 (1H, d, Jϭ11.7 Hz, C8-H), 1.89—1.34 (4H,
m, C3Ј,5Ј-H of piperidine). IR (film) cmϪ1: 1697, 1670, 1455, 1419, 1238,
1166, 698.
1؅-Benzyloxycarbonyl-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahy-
dro-5-oxo-spiro[8aH-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidine]-8a-
carboxylic Acid (18) To a solution of compound 17 (68.0 g, 113.4 mmol)
in CH2Cl2 (680 ml) was added 4-benzyloxy-2,2,6,6-tetramethylpiperidine 1-
oxyl (314 mg, 1.14 mmol). 5% aq. NaHCO3 (1.36 l) was added dropwise
with stirring under cooling with ice and bleaching powder (54.0 g,
227 mmol) was added. The mixture was vigorously stirred for 1.5 h under
cooling with ice, adjusted to pH 1 with 1 N HCl and was extracted with
CH2Cl2. The organic layer was washed with water, brine and dried over dry
Na2SO4. The solvent was distilled off under reduced pressure to give the
compound 18 (62.7 g, 90%) as pale yellow powder, mp 182—184 °C.
1H-NMR (300 MHz, CD3OD) d: 8.52—7.25 (11H, m, naphthyl and
phenyl), 5.08 (2H, s, OCH2Ph), 4.64 (1H, d, Jϭ11.3 Hz, C8-H), 4.17 (1H, d,
Jϭ16.6 Hz, C6-H), 4.02 (1H, d, Jϭ11.5 Hz, C3-H), 3.82—3.17 (4H, m,
C2Ј,6Ј-H of piperidine), 3.43 (1H, d, Jϭ16.6 Hz, C6-H), 3.29 (1H, d,
Jϭ11.5 Hz, C3-H), 2.72 (1H, d, Jϭ11.3 Hz, C8-H), 1.87—1.39 (4H, m,
C3Ј,5Ј-H of piperidine). IR (film) cmϪ1: 1656, 1423, 1349, 1240, 1164, 698.
Ethyl 1؅-Benzyloxycarbonyl-7-[(6-chloro-2-naphthalenyl)sulfonyl]-
tetrahydro-5-oxo-spiro[8aH-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperi-
HR-MS m/z: Calcd for C26H2735ClN4O5S: 542.1390. Found: 542.1421. 1H-
NMR (270 MHz, CDCl3) d: 8.38—6.58 (10H, m, naphthyl and pyridinyl),
4.43 (1H, d, Jϭ11.9 Hz, C8-H), 4.32 (1H, d, Jϭ17.0 Hz, C6-H), 4.27 (1H, d,
Jϭ11.6 Hz, C3-H), 3.92 (1H, d, Jϭ11.6 Hz, CH2OH), 3.72 (1H, d,
Jϭ11.6 Hz, CH2OH), 3.54—3.22 (4H, m, C2Ј,6Ј-H of piperidine), 3.40 (1H,
d, Jϭ17.0 Hz, C6-H), 3.19 (1H, d, Jϭ11.6 Hz, C3-H), 2.42 (1H, d,
Jϭ11.9 Hz, C8-H), 2.22—1.48 (4H, m, C3Ј,5Ј-H of piperidine). 13C-NMR
(67.5 MHz, CDCl3) d: 162.96 (C5), 154.28 (C4 of pyridine), 150.02 (C2,6 of
pyridine), 135.72—123.39 (10C, naphthyl), 108.53 (C3,5 of pyridine), 92.51
(C8a), 80.61 (C2), 64.76 (CH2OH), 52.09 (C3), 49.07 (C8), 48.00 (C6), 43.56
(C2Ј or C6Ј of piperidine), 43.14 (C2Ј or C6Ј of piperidine), 35.72 (C3Ј or C5Ј
of piperidine), 35.04 (C3Ј or C5Ј of piperidine). IR (film) cmϪ1: 3300, 1664,
1599, 1348, 1167, 700.
7-[(6-Chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxymethyl)-
1؅-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-
one (14) To a solution of compound 13 (100 mg, 0.18 mmol), benzyltri-
ethylammonium chloride (4.0 mg, 0.018 mmol), and Me2SO4 (0.018 ml,
0.198 mmol) in CH2Cl2 (2 ml) was gradually added 50% NaOH (0.6 ml)
with vigorous stirring under cooling with ice. After stirring the reaction
mixture at room temperature for 2 h, water (5 ml) was added under cooling
with ice, and the mixture was extracted with CH2Cl2. The organic layer was
washed with brine and dried over dry Na2SO4. The solvent was distilled off
under reduced pressure. The resulting residue was purified by silica gel col-
umn chromatography (Chromatorex NHTM, eluents: hexane : EtOAcϭ1 : 4—
1 : 6) to give compound 14 (48.0 mg, 47%) as brown powder, mp 111—
113 °C.
HR-MS m/z: Calcd for C27H2935ClN4O5S: 556.1547, Found: 556.1540. 1H-
NMR (300 MHz, CDCl3) d: 8.38—6.58 (10H, m, naphthyl and pyridinyl),
4.38 (1H, d, Jϭ11.9 Hz, C8-H), 4.35 (1H, d, Jϭ16.8 Hz, C6-H), 4.20 (1H, d,
Jϭ11.3 Hz, C3-H), 3.67 (1H, d, Jϭ10.2 Hz, CH2OMe), 3.62 (1H, d,
Jϭ10.2 Hz, CH2OMe), 3.53—3.22 (4H, m, C2Ј,6Ј-H of piperidine), 3.43 (3H,
s, CH2OMe), 3.35 (1H, d, Jϭ16.8 Hz, C6-H), 3.20 (1H, d, Jϭ11.3 Hz, C3-H),
2.30 (1H, d, Jϭ11.9Hz, C8-H), 2.03—1.45 (4H, m, C3Ј,5Ј-H of piperidine).
13C-NMR (75 MHz, CDCl3) d: 162.75 (C5), 154.23 (C4 of pyridine), 150.33
(C2,6 of pyridine), 135.70—123.46 (10C, naphthyl), 108.54 (C3,5 of pyri-
dine), 92.85 (C8a), 80.67 (C2), 74.88, (CH2OMe) 59.78 (CH2OMe), 52.15
(C3), 49.69 (C8), 47.98 (C6), 43.59 (C2Ј or C6Ј of piperidine), 43.20 (C2Ј or
C6Ј of piperidine), 35.82 (C3Ј or C5Ј of piperidine), 34.81 (C3Ј or C5Ј of
piperidine). IR (film) cmϪ1: 1671, 1594, 1417, 1349, 1168, 1103, 698.
7-[(6-Chloro-2-naphthalenyl)sulfonyl]-8a-[(1,3-dihydro-1,3-dioxo-2H-
isoindol-2-yl)methyl]tetrahydro-1؅-(4-pyridinyl)-spiro[5H-oxazolo[3,2-
a]-pyrazine-2(3H),4؅-piperidin]-5-one (15) To a solution of phthalimide
(4.88 g, 33.1 mmol) and Ph3P (8.69 g, 33.1 mmol) in CH2Cl2 (150 ml) was
added dropwise 40% DEAD solution in PhMe (10.0 ml, 33.1 mmol) under
cooling with ice. Compound 13 (3.0 g, 5.52 mmol) was added and the mix-
ture was stirred overnight at room temperature. After adding sat. aq.
NaHCO3 to the reaction mixture, the reaction mixture was extracted with
CH2Cl2. The organic layer was washed with water and brine and dried over
dry Na2SO4. The solvent was distilled off under reduced pressure and the re-
sulting residue was purified by silica gel column chromatography (eluents:
CH2Cl2 : MeOHϭ19 : 1) to give compound 15 (2.5 g, 68%) as brown pow-
der, mp 84—87 °C.
dine]-8a-carboxylate (19) To
a solution of compound 18 (62.7 g,
0.10 mol) in pyridine (640 ml) was added EtOH (58.4 ml, 1.0 mol). After
gradually adding p-toluene-sulfonyl chloride (97.3 g, 0.51 mol) with stirring
under cooling with ice, the mixture was stirred at room temperature for 4 h.
1H-NMR (300 MHz, CDCl3) d: 8.44—6.51 (14H, m, naphthyl, pyridinyl
and phthaloyl), 4.54 (1H, d, Jϭ11.7 Hz, C8-H), 4.35 (1H, d, Jϭ16.7 Hz, C6-

April 2004
411
Jϭ11.2 Hz, C8-H), 1.97—1.52 (4H, m, C3Ј,5Ј-H of piperidine). 13C-NMR
(75 MHz, CDCl3) d: 173.44 (CO2Ϫ), 163.27 (C5), 155.00 (C4 of pyridine),
147.60 (C2,6 of pyridine), 135.68—123.70 (10C, naphthyl), 107.90 (C3,5 of
pyridine), 91.59 (C8a), 79.82 (C2), 52.11 (C3), 50.53 (C8), 48.46 (C6), 42.73
(C2Ј or C6 Ј of piperidine), 42.64 (C2Ј or C6Ј of piperidine), 35.31 (C3Ј or C5Ј
of piperidine), 33.93 (C3Ј or C5Ј of piperidine). IR (KBr) cmϪ1: 1657, 1628,
1601, 1396, 1348, 1169.
After addition of ice water, the reaction mixture was extracted with EtOAc.
The organic layer was washed with water, 1 N HCl and brine and dried over
dry Na2SO4. The solvent was distilled off under reduced pressure and the re-
sulting residue was purified by silica gel column chromatography (eluents:
hexane : EtOAcϭ3 : 1—2 : 1) to obtain the compound 19 (40.1 g, 61%) as
pale yellow powder, mp 82—84 °C.
1H-NMR (300 MHz, CDCl3) d: 8.36—7.28 (11H, m, naphthyl and
phenyl), 5.10 (2H, s, OCH2Ph), 4.75 (1H, d, Jϭ11.3 Hz, C8-H), 4.32 (1H, d,
Jϭ16.6 Hz, C6-H), 4.12 (2H, q, Jϭ7.1 Hz, CO2CH2CH3), 4.07 (1H, d,
Jϭ11.5 Hz, C3-H), 3.81—3.22 (4H, m, C2Ј,6Ј-H of piperidine), 3.43 (1H, d,
Jϭ16.6 Hz, C6-H), 3.29 (1H, d, Jϭ11.5 Hz, C3-H), 2.45 (1H, d, Jϭ11.3 Hz,
C8-H), 1.75—1.42 (4H, m, C3Ј,5Ј-H of piperidine), 1.34 (3H, t, Jϭ7.1 Hz,
CO2CH2CH3). IR (film) cmϪ1: 1745, 1681, 1419, 1238, 1166, 1079, 698.
Ethyl 7-[(6-Chloro-2-naphthalenyl)sulfonyl]tetrahydro-5-oxo-spiro-
(؊)-7-[(6-Chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-
(methoxymethyl)-1؅-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-
2(3H),4؅-piperidin]-5-one (28) and (؉)-7-[(6-Chloro-2-naphthalenyl)sul-
fonyl]tetrahydro-8a-(methoxymethyl)-1؅-(4-pyridinyl)-spiro[5H-oxa-
zolo[3,2-a]pyrazine-2(3H),4؅-piperidin]-5-one (29) Compound 14 was
optically resolved on HPLC [Waters DeltaPrep 4000 manufactured by Wa-
ters Inc.: Column used, Daicel ChiralcelTM OD manufactured by Daicel
Chemical Industries, Ltd., 2 cmϫ25 cm: eluent: hexane : EtOH : Et2NHϭ
60 : 40 : 1: flow rate, 10 ml/min, detection wavelength, 254 nm] to obtain
(ϩ)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxymethyl)-
1Ј-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4Ј-piperidin]-5-one
(29) as brown powder [retention time: 43.5 min, mp 112—113 °C, [a]D25
ϩ48.8° (cϭ1.247, CHCl3), [a]D33 ϩ91.3° (cϭ1.000, MeOH), Ͼ99% ee],
[8aH-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidine]-8a-carboxylate
(20)
To a solution of the compound 19 (40.0 g, 62.2 mmol) in MeCN (400 ml)
was added TMSI (22.2 ml, 155.8 mmol) under cooling with ice. After stir-
ring the mixture for 45 min under cooling with ice, the reaction mixture was
poured into 1 N HCl under cooling with ice and hexane was added to this
mixture. The mixture was stirred for separation, and the aqueous layer was
washed with hexane followed by addition of CH2Cl2. 2 N NaOH was added
with stirring under cooling with ice and the pH of the mixture was adjusted
to 11. The mixture was extracted with CH2Cl2, and the organic layer was
washed with brine and dried over dry Na2SO4. The solvent was distilled off
under reduced pressure to give compound 20 (29.7 g, 94%) as colorless
powder, mp 252—254 °C.
and
(Ϫ)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxy-
methyl)-1Ј-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4Ј-
piperidin]-5-one (28) as pale yellow powder [retention time: 63.0 min,
mp 111—112 °C, [a]D25 Ϫ48.4° (cϭ1.175, CHCl3), [a]D33 Ϫ90.7° (cϭ1.000,
MeOH), Ͼ99%ee], respectively.
1H-NMR (300 MHz, CDCl3) d: 8.38—7.58 (6H, m, naphthyl), 4.74 (1H,
d, Jϭ11.4 Hz, C8-H), 4.31 (1H, d, Jϭ16.5 Hz, C6-H), 4.38—4.17 (2H, m,
CO2CH2CH3), 4.10 (1H, d, Jϭ11.4 Hz, C3-H), 3.16—2.77 (4H, m, C2Ј,6Ј-H
of piperidine), 3.33 (1H, d, Jϭ16.5 Hz, C6-H), 3.32 (1H, d, Jϭ11.4 Hz, C3-
H), 2.45 (1H, d, Jϭ11.4 Hz, C8-H), 1.90—1.45 (4H, m, C3Ј,5Ј-H of piperi-
dine), 1.34 (3H, t, Jϭ7.1 Hz, CO2CH2CH3). IR (film) cmϪ1: 1749, 1668,
1344, 1162, 1078, 698.
Acknowledgments The authors thank Emeritus Professor Hiroshi Ya-
manaka of Tohoku University for his encouragement and helpful discussions
throughout this study.
References and Notes
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Ethyl 7-[(6-Chloro-2-naphthalenyl)sulfonyl]tetrahydro-5-oxo-1؅-(4-
pyridinyl)-spiro[8aH-oxazolo[3,2-a]pyrazine-2(3H),4؅-piperidine]-8a-
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HR-MS m/z: Calcd for C28H2935ClN4O6S: 584.1496, Found: 584.1532. 1H-
NMR (300 MHz, CDCl3) d: 8.36—6.57 (10H, m, naphthyl and pyridinyl),
4.76 (1H, d, Jϭ11.6 Hz, C8-H), 4.33 (1H, d, Jϭ16.7 Hz, C6-H), 4.30 (2H,
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(1H, d, Jϭ16.7 Hz, C6-H), 2.49 (1H, d, Jϭ11.6 Hz, C8-H), 1.89—1.52 (4H,
m, C3Ј,5Ј-H of piperidine), 1.36 (3H, t, Jϭ7.2 Hz, CO2CH2CH3). 13C-NMR
(75 MHz, CDCl3) d: 168.02 (CO2CH2CH3), 162.04 (C5), 154.08 (C4 of pyri-
dine), 150.37 (C2,6 of pyridine), 135.68—123.48 (10C, naphthyl), 108.53
(C3,5 of pyridine), 90.08 (C8a), 81.75 (C2), 62.96, (CO2CH2CH3), 52.31 (C3),
50.37 (C8), 47.97 (C6), 43.27 (C2Ј or C6Ј of piperidine), 43.20 (C2Ј or C6Ј of
piperidine), 35.69 (C3Ј or C5Ј of piperidine), 34.46 (C3Ј or C5Ј of piperidine),
14.01 (CO2CH2CH3). IR (film) cmϪ1: 1743, 1678, 1595, 1350, 1167, 1080,
870, 696.
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3.89 (1H, d, Jϭ11.4 Hz, C3-H), 3.69—3.22 (4H, m, C2Ј,6Ј-H of piperidine),
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