Discovery, synthesis, and structure-activity relations of 3,4-dihydro-1H-spiro(naphthalene-2,2′-piperidin)-1-ones as potassium-competitive acid blockers

Article abstract of DOI:10.1016/j.bmc.2017.05.012

With the aim to discover a gastric antisecretory agent more potent than the existing proton pump inhibitors, novel 3,4-dihydro-1H-spiro(naphthalene-2,2′-piperidin)-1-one derivatives, which could occupy two important lipophilic pockets (described as LP-1 and LP-2) of H⁺,K⁺-ATPase and can strongly bind to the K⁺-binding site, were designed based on a docking model. Among the compounds synthesized, compound 4d showed a strong H⁺,K⁺-ATPase-inhibitory activity and a high stomach concentration in rats, resulting in potent inhibitory action on histamine-stimulated gastric acid secretion in rats. Furthermore, 4d exerted significant inhibitory action on histamine-stimulated gastric-acid secretion in rats with a rapid onset and moderate duration of action after the administration. These findings may lead to a new insight into the drug design of potassium-competitive acid blockers.

Full text of DOI:10.1016/j.bmc.2017.05.012

Accepted Manuscript
Discovery, synthesis, and structure-activity relations of 3,4-dihydro-1H-spi-
ro(naphthalene-2,2'-piperidin)-1-ones as potassium-competitive acid blockers
Toshihiro Imaeda, Koji Ono, Kazuo Nakai, Yasunobu Hori, Jun Matsukawa,
Terufumi Takagi, Yasushi Fujioka, Naoki Tarui, Mitsuyo Kondo, Akio
Imanishi, Nobuhiro Inatomi, Masahiro Kajino, Fumio Itoh, Haruyuki Nishida
PII:
S0968-0896(17)30701-0
DOI:
http://dx.doi.org/10.1016/j.bmc.2017.05.012
BMC 13730
Reference:
To appear in:
Bioorganic & Medicinal Chemistry
Received Date:
Revised Date:
Accepted Date:
1 April 2017
3 May 2017
5 May 2017
Please cite this article as: Imaeda, T., Ono, K., Nakai, K., Hori, Y., Matsukawa, J., Takagi, T., Fujioka, Y., Tarui,
N., Kondo, M., Imanishi, A., Inatomi, N., Kajino, M., Itoh, F., Nishida, H., Discovery, synthesis, and structure-
activity relations of 3,4-dihydro-1H-spiro(naphthalene-2,2'-piperidin)-1-ones as potassium-competitive acid
blockers, Bioorganic & Medicinal Chemistry (2017), doi: http://dx.doi.org/10.1016/j.bmc.2017.05.012
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Discovery, synthesis, and structure-activity relations of
,4-dihydro-1H-spiro(naphthalene-2,2'-piperidin)-1-ones as potassium-competitive acid blockers
3
Toshihiro Imaeda, Koji Ono, Kazuo Nakai, Yasunobu Hori, Jun Matsukawa, Terufumi Takagi, Yasushi
Fujioka, Naoki Tarui, Mitsuyo Kondo, Akio Imanishi, Nobuhiro Inatomi, Masahiro Kajino, Fumio Itoh,
Haruyuki Nishida*
Pharmaceutical Research Division: Takeda Pharmaceutical Company, Ltd., 26-1, Muraokahigashi
2
-chome, Fujisawa, Kanagawa 251-8555, Japan
*
To whom correspondence should be addressed. Phone: +81 466-32-1239. Fax: +81 466-29-4433.
E-mail: haruyuki.nishida@takeda.com
Present address: 2-26-1, Muraokahigashi, Fujisawa, Kanagawa 251-8555, Japan
+
+
Keywords: H ,K -ATPase; potassium-competitive acid blockers; docking analysis;
3
,4-dihydro-1H-spiro[naphthalene-2,2-piperidin]-1-one derivatives; S-enantiomer
Abbreviations: 1,1-bis(diphenylphosphino)ferrocene (dppf),
-dicyclohexylphosphino-2,4,6-triisopropylbiphenyl (Xphos), N,N-dimethylformamide (DMF),
2
gastroesophageal reflux disease (GERD), high-performance liquid chromatography (HPLC), lithium
diisopropylamide (LDA), potassium-competitive acid blockers (P-CABs), proton pump inhibitors (PPIs),
room temperature (rt), structure–activity relationship (SAR), tetrahydrofuran (THF)
Abstract
With the aim to discover a gastric antisecretory agent more potent than the existing proton pump
inhibitors, novel 3,4-dihydro-1H-spiro(naphthalene-2,2-piperidin)-1-one derivatives, which could

+
+
occupy two important lipophilic pockets (described as LP-1 and LP-2) of H ,K -ATPase and can
+
strongly bind to the K -binding site, were designed based on a docking model. Among the compounds
+
+
synthesized, compound 4d showed a strong H ,K -ATPase-inhibitory activity and a high stomach
concentration in rats, resulting in potent inhibitory action on histamine-stimulated gastric acid secretion
in rats. Furthermore, 4d exerted significant inhibitory action on histamine-stimulated gastric-acid
secretion in rats with a rapid onset and moderate duration of action after the administration. These
findings may lead to a new insight into the drug design of potassium-competitive acid blockers.
1
. Introduction
Gastroesophageal reflux disease (GERD) is the most common disorder of the gastrointestinal tract in
the general population and is increasing in prevalence worldwide. There is acid suppression therapy with
proton pump inhibitors (PPIs), which is associated with well-established benefits in the management of
1
GERD and other acid-related disorders. As a new class of acid suppressant, the so called
2
potassium-competitive acid blockers (P-CABs) are expected to have some therapeutic advantages over
PPIs’ shortcoming such as delayed onset of action, the influence of cytochrome P450 (CYP)
3
polymorphism, and insufficient inhibition of nocturnal acid breakthrough. Although PPIs have a unique
mechanism of action based on their chemistry, the P-CABs have a structural specificity for their target,
+
+
+
+
the K -binding region of the H ,K -ATPase where a P-CAB can bind in or near the K binding site and
prevent access of the cation to the site.
In one study on P-CABs, novel pyrrole derivatives showing a great potential as unprecedented gastric
4
antisecretory agents were found, and then TAK-438 (vonoprazan fumarate) was discovered as a drug
5
candidate for the treatment of GERD, peptic ulcer, and other acid-related diseases. Taking advantage of
the research on pharmacology and structure-based drug design (SBDD) studies in pursuit of novel and
potent P-CABs, we continued to explore a new chemotype, for example, having a docking mode

different from that of TAK-438: our SBDD research has been focused on the two lipophilic pockets
+
(
described as LP-1, LP-2 in Figure 2) to be occupied for strong binding to the K -binding site.
+
+
Figure 1. 1: Selected as a hit compound by in-house screening for H ,K -ATPase-inhibitory activities at
pH 6.5. 2: The general structure of 3,4-dihydro-1H-spiro(naphthalene-2,2-piperidin)-1-one derivatives
after modification for P-CAB designed from hit compound 1 based on the docking model. 4b and 4d:
Found as potent P-CABs showing significant in vivo acid suppression in rats.
During the screening of our in-house chemical library,
1
,3-dihydro-5H-spiro(benzo[cd]indole-4,2-piperidin)-5-one derivative 1 was found as a reversible
+
+
H ,K -ATPase inhibitor with a possibility of occupying both LP-1 and LP-2 according to the docking
+
+
analysis. The compound showed inhibition of H ,K -ATPase activity in pig gastric microsomes with
+
+
IC50 of 1600 nM and more than 100-fold lower affinity for Na , K -ATPase in vitro, and then showed an
inhibitory effect on histamine-stimulated acid secretion in anesthetized rats: 71% inhibition at 10 mg/kg
(
intravenous injection). We, in particular, utilized its
-dihydro-1H-spiro(naphthalene-2,2-piperidin)-1-one skeleton as a pharmacophore for activity based on
the docking analysis, which suggested that the pyrrole moiety of 1 may be removed, whereas the
4

benzene moiety must be necessary to occupy one key lipophilic pocket (described as LP-2 in Figure 2).
We also focused on its N-phenethyl side chain, whose benzene moiety should be necessary to occupy
another key lipophilic pocket (LP-1).
Figure 2. Docking analysis of 4b having the S-configuration at position 2 using a homology model of
+
+
2+
the luminal region of H ,K -ATPase, which was constructed from the crystal structure of Ca -ATPase.
Both lipophilic pockets LP-1 and LP-2 were sufficiently occupied by the substituted phenethyl side
chain and 1,3-dihydro-5H-dihydronaphthalene-5-one skeleton, respectively.
We then designed general structure 2, which consists of core bicyclic scaffold AB, piperizine ring C,
and side chain’s ring D with linkage X. The analysis of linkage X, substitutes (R, R’), and absolute
configuration led to compound 4b, which could occupy both lipophilic pockets very well, as a potent
P-CAB with IC50 of 46 nM. We then discovered acetamide derivative 4d having the strongest in vitro
activity (31 nM) with significant inhibition of acid secretion: by 95% at 1 mg/kg (rats, intravenous

injection). Herein, we report the discovery, synthesis, and structure–activity relations of
3
,4-dihydro-1H-spiro(naphthalene-2,2-piperidin)-1-one derivatives.
2
. Chemistry
The key intermediates of 3,4-dihydro-1H-spiro(naphthalene-2,2-piperidin)-1-one derivatives (8a–e)
were synthesized starting from 1-benzoylpiperidine-2-carboxylic acid 5 or 1-tetralone 9 as outlined in
Scheme 1. Nitrile derivative 6 prepared from carboxylic acid 5 in a usual manner was reacted with
6
phenethyl iodides, which were synthesized from alcohols in a usual manner, to obtain alkylated
compounds 7a–d. The cyano group in 7a,b was activated with a Lewis acid to promote intramolecular
cyclization at position 2 on the benzene ring of the phenethyl group, and then the benzoyl group on the
piperizine ring was removed by basic hydrolysis to produce piperidines 8a and 8b, respectively.
3
-Methoxy derivative 7c has two reaction points at the second and sixth position on the benzene ring,
resulting in two products: 8c and 8d. The reaction for 2-methoxy derivative 7d produced such a complex
mixture that the desired product (8e) was not obtained.

Scheme 1
Reagents and
, pyridine, THF, DMF; (c) LDA, R-C -I,
, toluene or CF Ph; (e) 8N NaOH; (f) PhNMe Br-Br
/Pd-C, AcOH, THF; (i) NaH, Br(CH Br, DMF; (j) cHCl.
conditions: (a) ClCO
2
Et, Et
CO H or CF
, AcOH, DMF; (h) H
3
N, aq. NH
3
, THF; (b) POCl
3
6
H
4
THF; (d) AlCl
3
3
or CF
3
2
3
SO
3
Si(CH
3
)
3
3
3
2
,
THF; (g) NaN
2
)
2 4
Stepwise functionalization at position 2 of 1-tetralone 9a,b using trimethylphenylammonium
tribromide and subsequently sodium azide followed by catalytic hydrogen reduction with acetic
anhydride yielded acetylamido derivatives 11a,b via 10a,b. These compounds were alkylated at position
2
with 1,4-dibromobutane, leading to immediate internal cyclization with formation of N-acylpiperidine
7
derivatives 12a,b, and then the acyl group was removed by acid hydrolysis to obtain piperidines 8d and
8
e, respectively. These intermediates (8a–e) were used in the following steps in a free form or as a HCl
salt, which was prepared by a typical method from a free form to store the oily intermediates as a solid
a scheme and spectral data are not shown).
(
Scheme 2

Reagents and
conditions: (a) D-(R)-(–)-mandelic acid, EtOH; (b) aq. NaOH; (c) L-(S)-(+)-mandelic acid, EtOH.
Preparation of both enantiomeric intermediates 14a and 14b is shown in Scheme 2; this procedure was
conducted by optical resolution using D-(R)-(–)- and L-(S)-(+)-mandelic acids from racemate 8d and
following basic hydrolysis. The absolute configuration of 14a as an S-enantiomer was determined by
X-ray analysis of the optical salt 13a (data not shown).
These intermediates 8a–e and 14a,b were converted to N-alkyl or N-acyl derivatives 3a–n, 3r–u, 4a,
and 4f–k as a free form or HCl salt by treatment with alkyl halides or an acyl halide in the presence of
base reagents (Scheme 3). Both enantiomers of 2-methylphenethyl products 4a,b and 4-fluorophenethyl
derivatives 4e,f were obtained from corresponding racemic derivatives 3k and 3s by standard
preparative chiral high-performance liquid chromatography (HPLC). Their absolute configurations were
determined by comparing their retention time during chiral HPLC with the corresponding optical
derivative compounds (4a, 4f), which were synthesized from the corresponding intermediates (14b,a)
using the R or S absolute configuration information.
Scheme 3

Reagents and
conditions: (a) R′-C
6
H
4
-X-Y (Y = Cl, Br, I), iPr
2
NEt, toluene; (b) 4N HCl/EtOAc, Et
2
O; (c) preparative
chiral HPLC.
Further conversion of the methoxy group of 3k into acetylamido (3o), cyano (3p), or phenyl (3q)
groups via a coupling reaction with a trifluorosulfonyloxy derivative (3w), which was obtained from
demethyl derivative 3v, is shown in Scheme 4. The enantiomers of acetamide derivatives 4c and 4d
were separated from racemate 3o by standard preparative chiral HPLC, with estimation of their absolute
configuration by referring to the order of the retention time values during chiral HPLC and the minus or
plus sign of the specific optical rotation for similar methoxy derivatives 4a and 4b and then by
confirming their in vitro activity.

a
Scheme 4
Reagents and conditions: (a) 46% HBr; (b) (CF
Pd(OAc) , Xphos, K CO , DMA; (d) Zn(CN) , Pd
CO , DMA; (f) 4N HCl/EtOAc, Et O; (g) preparative chiral HPLC.
3
SO
2
)
2
O, pyridine; (c) AcNH
2
, PhB(OH)
2
(cat.),
2
2
3
2
2
(dba)
3
, dppf, DMF; (e) PhB(OH)
2
, Pd(OAc) , Xphos,
2
K
2
3
2
Table 1 summarized the optical active derivatives with enantiomeric excess (ee) measured by chiral
HPLC and specific optical rotation in MeOH.

Table 1 A summary of optical active intermediates 14a,b and derivatives 4a–k with enantiomeric excess (ee) measured
by chiral HPLC and specific optical rotation in MeOH.
a
specific optical rotation
20
compd.
R
R’
salt
config. ee (%)
[
α]
D
(MeOH)
HCl
HCl
HCl
HCl
free
free
HCl
HCl
HCl
HCl
HCl
HCl
HCl
S
R
R
S
98.3
99.7
1
4a
4b
MeO
MeO
MeO
MeO
AcNH
AcNH
MeO
MeO
MeO
MeO
MeO
MeO
MeO
H
H
+31.0 (c = 0.500)
–32.7 (c = 0.505)
–69.9 (c = 0.500)
1
b
99.9
99.4
4
a
CH
CH
CH
CH
2
2
2
2
CH
CH
CH
CH
2
2
2
2
(2-Me)Ph
b
c
4
b
(2-Me)Ph
(2-Me)Ph
(2-Me)Ph
+70.4 (c = 0.505)
–62.1 (c = 0.383)
+66.3 (c = 0.500)
d
R
99.9
4
c
d
S
99.4
4
d
b
e
R
S
S
S
S
S
S
99.8
4
e
CH
CH
CH
CH
2
2
2
2
CH
CH
CH
CH
2
(4-F)Ph
2
(4-F)Ph
2
(3-F)Ph
2
(2-F)Ph
NT
96.7
4
f
+41.6 (c = 0.505)
+40.8 (c = 0.250)
+42.6 (c = 0.250)
+63.5 (c = 0.250)
+42.0 (c = 0.250)
e
NT
4
4
g
e
NT
h
e
NT
4
i
CH
CH
CH
2
CH
2
CH
2
CH
2
2
2
(2-OMe)Ph
(3-OMe)Ph
(4-OMe)Ph
e
NT
4
j
e
NT
4
k
+35.9 (c = 0.250)
a
b
c
Calculated from the area in chiral HPLC, whose retention time was compared with that of the racemate. Measured for their free forms.
+68.7 (c = 0.44, MeOH). There was almost no difference between the HCl salt and free form in
specific optical rotation. Estimated based on retention time order, specific optical rotation, and in vitro activity in a comparison with 4a
2
D
0
Its free form was also analyzed: [α]
d
e
and 4b. Not tested.
3
. Results and Discussion
The compounds synthesized were evaluated for their H ,K -ATPase-inhibitory activities at pH 6.5 by
their IC50 values (in vitro); the results of in vitro evaluation are shown in Table 2.
+
+
+
+
Table 2 H ,K -ATPase inhibitory activities at pH 6.5 of spirodihydronaphthalene derivatives 3a–u and
4
a–k.

in vitro
+
+
compd.
R
Y
R'
config.
salt
H ,K -ATP-inhibitory
activity (IC50, nM)
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R/S
R
HCl
HCl
HCl
HCl
HCl
HCl
HCl
free
free
HCl
HCl
HCl
HCl
HCl
free
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
free
free
HCl
HCl
HCl
HCl
HCl
3
3
a
H
CH
CH
CH
2
2
2
CH
2
2
2
H
2-Me
H
1000
290
b
H
CH
CH
3
c
6-OMe
6-OMe
6-OMe
6-OMe
290
3
d
none
H
>10000
>10000
890
3
e
CH
CH
2
2
H
3
f
CH
2
CH
2
H
3
3
g
6-OMe CH
6-OMe
2
CH
2
CH
2
CH
2
H
>10000
>10000
>10000
300
h
COCH
CH CO
CH C(CH
2
H
3
i
6-OMe
2
H
3
j
6-OMe
6-OMe
5-OMe
7-OMe
8-OMe
6-NHAc
6-CN
2
3
)H
H
3
k
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2-Me
2-Me
2-Me
2-Me
2-Me
2-Me
2-Me
2-Cl
4-F
82
3
l
300
3
m
270
3
n
o
p
q
290
3
45
3
3
>10000
>10000
170
6-Ph
3
r
6-OMe
6-OMe
6-OMe
6-OMe
6-OMe
6-OMe
6-NHAc
6-NHAc
6-OMe
6-OMe
6-OMe
6-OMe
6-OMe
3
s
87
3
t
2-Me,4-F
2,4,6-Me
2-Me
2-Me
2-Me
2-Me
4-F
57
3u
4a
4b
140
>10000
46
S
a
R
4
c
>10000
31
a
S
4
d
R
S
S
S
S
4
e
>10000
64
4
f
4-F
4
4
g
3-F
370
h
2-F
160
4
i
2-OMe
83

S
S
HCl
HCl
4
j
6-OMe
6-OMe
CH
CH
2
CH
CH
2
2
3-OMe
4-OMe
1100
1800
4k
2
a
Estimated based on retention time order, specific optical rotation, and in vitro activity in a comparison with 4a and 4b.
First of all, the 1,3-dihydro-5H-benzo[cd]indole-5-one skeleton of 1 was replaced by a
1
,3-dihydro-5H-dihydronaphthalene-5-one skeleton to simplify its chemical structure for SAR analysis
+
+
based on a docking analysis of 1 and the H ,K -ATPase model. The result revealed that such a
conversion maintained the enzymatic inhibitory potency of 1 (1: IC50 = 1600 nM, 3a: IC50 = 1000 nM).
The introduction of a methyl group at position 2 on the benzene ring of the phenethyl side chain (R’) or
a methoxy group at position 6 on the benzene ring of 1,3-dihydro-5H-dihydronaphthalene-5-one (R)
increased the activity (3b: IC50 = 290 nM, 3c: IC50 = 290 nM). On the other hand, the modification of
the ethylene linker (X) between the skeleton and phenyl of the side chain caused a big loss of activity
irrespective of length, type, and other parameters (3d, 3e, 3g–j vs. 3c) except for propylene linkers (3f).
The combination of the methoxy group at the sixth position on the benzene ring of
1
,3-dihydro-5H-dihydronaphthalene-5-one, ethylene linker (X), and a methyl group at position 2 on the
benzene ring of the phenethyl side chain had a synergistic effect on the in vitro inhibitory activity (3k:
IC50 = 82 nM).
As for the optimization of the R moiety of 3k, the shift of the methoxy group at position 6 of 3k to
position 5, 7, or 8 decreased the activity, and the conversion of the methoxy group at position 6 of 3k to
an acetylamide group yielded stronger potency (3o: IC50 = 45 nM) whereas both the cyano group and
phenyl group led to a big loss of activity (3p and 3q: IC50 = >10000 nM). As for the substituent (R) on
the benzene ring of the 1,3-dihydro-5H-dihydronaphthalene-5-one skeleton, introduction of small
substituents at position 6 (except for electron-withdrawing groups, which could directly affect the role of
the carbonyl group in the activity by electronic effects) seems to be the most favorable for a potent
activity. As a matter of fact, the reduction of carbonyl group at position 1 to a hydroxyl group or
methylene caused a big loss of activity (data were not shown); hence, the carbonyl group must play an

important role in the interaction with the enzyme via a water molecule and stabilization of active
conformation although the docking analysis could not explain the reason very well.
On the other hand, regarding the substituent (R’), the conversion of the methyl group at position 2 on
the benzene ring of the phenethyl side chain of 3k into a chloro group at position 2 or a fluoro group at
position 4 also maintained the potency (3r: IC50 = 170 nM, 3s: IC50 = 87 nM). The compounds with
these multiple substituents on the benzene ring of the phenethyl side chain such as 2-methyl-4-fluoro or
2
,4,6-trimethyl derivatives also showed the similar activity (3t: IC50 = 57 nM, 3u: IC50 = 140 nM).
For the purpose of determining the absolute configuration of the eutomer, we synthesized both
enantiomers of the key compounds. As a result, the optical derivatives having the S absolute
configuration at position 2 in the 3,4-dihydro-1H-spiro(naphthalene-2,2-piperidin)-1-one skeleton (4b,
4
3
d, and 4f) had approximately twice stronger inhibitory activities than their racemates did (3k, 3o, and
s), whereas the enantiomers having the R absolute configuration (4a, 4c, and 4e) showed a (complete)
big loss of activity. Therefore, we continued the optimization of substituents (R’) by synthesizing optical
active derivatives having the S absolute configuration. The shift of fluoro group at position 4 on the
benzene ring of phenethyl side chain of 4f to the 3 and 2 positions (4g, 4h) yielded a slight loss of
activity. The conversion of the methyl group at the 2 position on the benzene ring of phenethyl side
chain of 3k into a methoxy group maintained the activity (4i), but the shift of the methoxy group at the
2
 position on the benzene ring to the 3 and 4 positions decreased the potency (4j, 4k). As for the
substituent (R’) on the benzene ring of the phenethyl side chain, introduction of substituents at the 2
position seems to be the most favorable for the activity.
+
+
The docking analysis of compound 4b using a homology model of the luminal region of H ,K -ATPase,
2
+
8
which was constructed from the crystal structure of Ca -ATPase (PDB ID, 1IWO ) by means of
9
SCWRL ver. 2.9, is shown in Figure 2. Both lipophilic pockets LP-1 and LP-2 were sufficiently
occupied by the substituted phenethyl side chain and 1,3-dihydro-5H-dihydronaphthalene-5-one

skeleton, respectively. The docking analysis of both configurations at position 2 also indicated that the
S-configuration can be more favorable than the R-configuration (data not shown).
Some representative compounds were studied regarding their inhibitory effects on histamine-induced
gastric acid secretion in anesthetized rats (Table 3). The in vivo experiment was conducted by
intravenous administration of the compound at 1, 3, or 10 mg/kg, and the total acid output for 3 h after
the histamine injection was compared with that obtained after administration of the vehicle. In addition,
their concentrations were measured in the rat plasma and stomach after intravenous administration at a
dose of 0.2 mg/kg as free compounds.
Table 3 Inhibitory effects of compounds 1, 4b, and 4d on histamine-induced gastric acid secretion in
anesthetized rats (in vivo) and concentrations in rat plasma and stomach after intravenous administration
at a dose of 0.2 mg/kg as free compounds.
a
a
+
+
AUC0–24h AUC0–24h
in vitro H ,K -ATP
in vivo acid secretion
in rats (1 mg/kg, i.v.,
% inhibition)
71 (10 mg/kg, i.v.)
87
compd. (plasma, (stomach, inhibitory activity (IC50,
.
.
ngh/mL)
ngh/g)
nM)
1600
46
1
71
74
68
1171
3035
4
b
d
4
15131
31
95

a
Calculated from the concentration at 10 min, 1 h, 4 h, and 24 h after administration.
Optically active compound 4b, which had more than 30-fold stronger in vitro activity and twofold
higher concentration in the stomach than those of racemic compound 1, showed considerably higher
potency of the in vivo inhibitory activity (87% inhibition at 1 mg/kg) than that of 1 (71% inhibition at
1
1
0 mg/kg). Furthermore, the conversion of the methoxy group at position 6 on the benzene ring of the
,3-dihydro-5H-dihydronaphthalene-5-one skeleton of 4b into an acetylamide group (4d) improved not
only in vitro activity 1.5-fold but also the concentration in the stomach fivefold. As expected, 4d
showed a significantly more potent in vivo inhibitory activity (95% inhibition at 1 mg/kg) than 4b did.
1
1
Figure 3. Effects of intravenous administration of compound 4d (A) and lansoprazole (B) on pH of a
gastric perfusate under conditions of histamine stimulation in anesthetized rats. Intravenous
administration of 4d at 3 mg/kg increased pH to ~6.0 in anesthetized rats with a rapid onset and
moderate duration after the administration.
Intravenous administration of lansoprazole, as a representative PPI, at 3 mg/kg increased pH of the

gastric perfusate to ~4.5 during histamine stimulation in anesthetized rats as reported in our previous
11
paper (Figure 3B ), whereas intravenous administration of 4d at 3 mg/kg increased pH of the gastric
perfusate to ~6.0 as shown in Figure 3A. In addition to the effectiveness at pH elevation in the gastric
perfusate, 4d showed a rapid onset of action and its effect was sustained until 5 h after the administration
(
Figure 3). Although 4d (log D = 3.56) showed not only much lower ligand-lipophilicity efficiency but
also lower potency as compared to TAK-438 did (log D = 0.4, IC50 = 19 nM, 98% inhibition at 1
5
mg/kg) , these findings suggested that our 3,4-dihydro-1H-spiro[naphthalene-2,2-piperidin]-1-one
derivatives could be further optimized as a P-CAB for the treatment of GERD, peptic ulcer, or other
acid-related diseases.
+
+
The docking analysis using a homology model of the luminal region of H ,K -ATPase indicated that any
significant interactions except for lipophilic pockets LP-1 and LP-2 can not be observed (Figure 2).
Therefore, it might be able to find a more excellent P-CAB by introducing polar groups aimed for new
ionic interactions.
4
. Conclusion
We synthesized a series of 3,4-dihydro-1H-spiro[naphthalene-2,2-piperidin]-1-one derivatives and
+
+
evaluated their SAR for inhibitory activities on H ,K -ATPase in vitro. Our results show that the
N-phenethyl side chain is the most suitable for potency; introduction of both substituents into the
benzene ring of 1,3-dihydro-5H-dihydronaphthalene-5-one (R) and into the benzene ring of the
phenethyl side chain (R’) dramatically increased in vitro activity. As shown in a docking model of 4b
+
+
with H ,K -ATPase, 3,4-dihydro-1H-spiro[naphthalene-2,2-piperidin]-1-one derivatives can occupy
both important lipophilic pockets (LP-1 and LP-2) very well and the absolute configuration of
3
,4-dihydro-1H-spiro[naphthalene-2,2-piperidin]-1-one derivatives with the S-enantiomer should be
related to the active conformation. In addition, acetamide derivative 4d showed not only a stronger in

vitro activity but also a much higher concentration in the stomach than enantiomer 4b did, resulting in
potent inhibitory actions on histamine-stimulated gastric acid secretion in rats. Intravenous
administration of 4d at 3 mg/kg increased pH of the gastric perfusate to ~6.0 in anesthetized rats with a
rapid onset and moderate duration after the administration. These findings may lead to a new insight into
the drug design of P-CABs.
5
. Experimental Section
5
.1. General
Melting points (mp) were determined on a Yanagimoto micro melting point apparatus or Buchi melting
1
point apparatus and are uncorrected. Proton nuclear magnetic resonance ( H-NMR) spectra were
recorded on a Varian Mercury-300, a Jeol JNM-AL400 or a Bruker AV-300 M spectrometer. Chemical
shifts were reported in δ value (ppm) with tetramethylsilane as an internal standard. Splitting patterns
are designated as follows: s, singlet; d, doublet; t, triplet; dd, double doublet; br s, broad singlet; m,
multiplet. Coupling constants (J) are reported in hertz (Hz). Elemental analyses (C, H, N) and specific
optical rotation were carried out by Takeda Analytical Research Laboratories, Ltd, and the results were
within 0.4% of theoretical values. Thin-layer chromatography (TLC) analyses were performed with
silica gel 60 F254 plate (Merck Art. 5715), alumina 60 F254 plate (Type E) and NH TLC plates (Fuji
Silysia Chemical Ltd.). Chromatographic separations were performed with Merck Aluminium oxide 90
(
basic, activity III) and NH silica gel (Fuji Silysia Chemical Ltd.).
5
.2.
To a solution of 5 (10.0 g, 42.9 mmol) in THF (90 mL) were added Et
solution of ethyl chloroformate (5.28 g, 47.2 mmol) at –20 to –15 °C. After stirring at –20 to –15 °C for
0 min, 28–30% aqueous NH (20.2 mL, 300 mmol) was added to the mixture. This mixture was stirred
(2RS)-1-Benzoylpiperidine-2-carbonitrile (6)
3
N (6.70 mL, 47.2 mmol) and a
3
3

at rt for 3 h, and then, concentrated under reduced pressure. The residue was partitioned between H O
2
(
30 mL) and EtOAc (100 mL). The separable aqueous layer was extracted with EtOAc (100 mL x 2).
The combined organic layers were dried over MgSO , filtered, concentrated under reduced pressure. The
4
residue was washed with Et O to obtain (2RS)-1-Benzoylpiperidine-2-carboxamide (6.11 g, 61%) as
2
white powder. Furthermore, the recrystallization from n-hexane/EtOAc gave colorless prism: mp 172 °C
1
(
n-hexane/EtOAc); H-NMR (CDCl
3
) δ 1.24–1.97 (5H, m), 2.33 (1H, d, J = 12.9 Hz), 3.07 (1H, dd, J =
1
3.3 Hz), 3.72 (1H, d, J = 12.9 Hz), 5.27 (1H, brs), 5.43 (1H, brs), 6.44 (1H, brs), 7.44 (5H, s); IR (KBr)
-1
cm 3331, 3198, 3061, 2939, 2862, 1691, 1682, 1668, 1653, 1622, 1599, 1578, 1495, 1445, 1435, 1393,
369, 1352, 1313, 1285, 1271, 1238, 1184, 1142, 1099, 1076, 1038, 1007, 926, 907; Anal. Calcd for
: C, 67.22; H, 6.94; N, 12.06. Found: C, 66.76; H, 7.02; N, 12.04.
To a solution of (2RS)-1-Benzoylpiperidine-2-carboxamide (5.90 g, 25.4 mmol) in THF (110 mL) were
added pyridine (3.50 mL, 43.2 mmol) and POCl (3.60 mL, 38.1 mmol) at 0 °C. The mixture was stirred
at rt for 10 h, and then, DMF (100 mL) was added to the mixture. After stirring at rt for 13 h and at
0 °C for 4 h, the reaction was quenched by the addition of 1 N NaOH (100 mL). This mixture was
extracted with EtOAc (100 mL). The separable organic layer was washed with 2 N HCl (100 mL), H
50 mL), brine (50 mL), dried over MgSO , filtered, concentrated under reduced pressure. The residue
1
C
13
H
16
N
2
O
2
3
8
2
O
(
4
was purified by column chromatography (SiO , n-hexane/EtOAc = 1/0–4/1) to obtain 6 (1.86 g, 34%) as
2
1
yellow oil: H-NMR (CDCl
3
) δ 1.33–2.27 (6H, m), 3.12–3.44 (1H, m), 3.88 (1H, brs), 5.79 (1H, brs),
-
1
7
1
9
.36–7.56 (5H, m); IR (KBr) cm 3510, 3061, 3028, 3000, 2943, 2862, 2237, 1651, 1601, 1578, 1493,
464, 1447, 1408, 1371, 1354, 1339, 1319, 1273, 1234, 1177, 1144, 1134, 1103, 1076, 1032, 999, 928,
+
01; LC/MS (ESI) m/z 216 (M+H) .
5
.3.
(2RS)-1-Benzoyl-2-(2-phenylethyl)piperidine-2-carbonitrile (7a)
To a solution of 6 (9.40 g, 43.9 mmol) and phenethyl iodide (15.58 g, 65.8 mmol) in THF (2200 mL)

was added LDA (42.7 mL, 76.8 mmol) at –78 °C under N
to 0 °C for 1.5 h and at rt for 1.5 h, the reaction was quenched by the addition of H
mixture was extracted with EtOAc (200 mL). The separable organic layer was washed with sat. Na
20 mL)/H O (100 mL), H O (100 mL), brine (50 mL), and dried over MgSO , filtered, concentrated
2
atmosphere for 15 min. After stirring at –78
2
O (100 mL). This
S
2 2
O
3
(
2
2
4
under reduced pressure. The residue was purified by column chromatography (SiO , n-hexane/EtOAc =
2
1
1
2
/0–4/1) to produce 7a (11.48 g, 82%) as pale yellow oil. H-NMR (CDCl
3
) δ 1.56–1.99 (4H, m),
.15–2.23 (2H, m), 2.38–2.54 (1H, m), 2.54–2.70 (1H, m), 2.76 (1H, ddd, J = 12.9, 12.1, 4.9 Hz), 2.89
(
1H, ddd, J = 12.9, 12.1, 4.5 Hz), 3.37 (1H, ddd, J = 14.0, 8.3, 4.2 Hz), 3.49 (1H, ddd, J = 14.0, 6.4, 4.5
Hz), 7.13–7.33 (5H, m), 7.34–7.48 (3H, m), 7.48–7.56 (2H, m).
5
.4.
(5.00 g, 23.3 mmol), p-methoxyphenethyl iodide (9.17 g, 35.0 mmol), LDA (20.5 mL, 40.8 mmol)
and THF (120 mL) were used as previously described for 7a. The crude product was purified by column
(2RS)-1-Benzoyl-2-[2-(4-methoxyphenyl)ethyl]piperidine-2-carbonitrile (7b)
6
chromatography (SiO , n-hexane/EtOAc = 1/0–4/1) to produce 7b (7.02 g, 85%) as pale yellow oil.
2
1
H-NMR (CDCl
1H, ddd, J = 13.2, 11.7, 4.9 Hz), 2.70 (1H, ddd, J = 13.0, 11.7, 5.3 Hz), 2.83 (1H, ddd, J = 13.0, 12.2,
.9 Hz), 3.36 (1H, ddd, J = 13.9, 8.5, 4.3 Hz), 3.49 (1H, ddd, J = 13.9, 6.4, 4.5 Hz), 3.77 (3H, s), 6.82
2H, ddd, J = 9.4, 2.8, 2.3 Hz), 7.14 (2H, ddd, J = 9.4, 2.8, 2.1 Hz), 7.38–7.48 (3H, m), 7.48–7.55 (2 H,
3
) δ 1.49–2.00 (4H, m), 2.08–2.23 (2H, m), 2.43 (1H, ddd, J = 13.2, 12.2, 5.3 Hz), 2.58
(
4
(
-1
m); IR (KBr) cm 3061, 3028, 2999, 2947, 2866, 2835, 2233, 1659, 1651, 1645, 1612, 1582, 1514,
1
493, 1464, 1447, 1404, 1394, 1354, 1302, 1267, 1248, 1115, 1074, 1034, 1001, 978, 953, 928, 914;
+
LC/MS (ESI) m/z 349 (M+H) .
5
.5.
(2RS)-1-Benzoyl-2-[2-(3-methoxyphenyl)ethyl]piperidine-2-carbonitrile (7c)
6
(5.00 g, 23.3 mmol), p-methoxyphenethyl iodide (9.17 g, 35.0 mmol), LDA (20.5 mL, 40.8 mmol)

and THF (50 mL) were used as previously described for 7a. The crude product was purified by column
chromatography (SiO , n-hexane/EtOAc = 3/1–2/1) to obtain 7c (6.02 g, 73%) as yellow brown oils.
2
1
H-NMR (CDCl
3
) δ 1.40–2.00 (4H, m), 2.15–2.21 (2H, m), 2.40–2.95 (4H, m), 3.34–3.55 (2H, m), 3.79
(
3H, s), 5.73–5.90 (2H, m), 7.16–7.52 (7H, m).
5
.6.
(5.00 g, 23.3 mmol), o-methoxyphenethyl iodide (9.17 g, 35.0 mmol), LDA (20.5 mL, 40.8 mmol)
and THF (120 mL) were used as previously described for 7a. The crude product was purified by column
(2RS)-1-Benzoyl-2-[2-(2-methoxyphenyl)ethyl]piperidine-2-carbonitrile (7d)
6
chromatography (SiO , n-hexane /EtOAc = 1/0–4/1) to obtain 7d (6.30 g, 78%) as pale yellow oil.
2
1
H-NMR (CDCl
1H, ddd, J = 13.8, 9.2, 4.5 Hz), 3.50 (1H, ddd, J = 13.8, 5.7, 4.7 Hz), 3.81 (3H, s), 6.84 (1H, d, J = 8.3
Hz), 6.84–6.92 (1H, m), 7.18 (1H, d, J = 7.3 Hz), 7.18–7.23 (1 H, m), 7.37–7.49 (3H, m), 7.50–7.55 (2H,
3
) δ 1.59–1.95 (4H, m), 2.13–2.34 (2H, m), 2.36–2.60 (2H, m), 2.70–2.96 (2H, m), 3.34
(
-1
m); IR (KBr) cm 3061, 2999, 2943, 2868, 2837, 2233, 1663, 1651, 1601, 1587, 1580, 1495, 1462,
1
9
454, 1447, 1394, 1385, 1350, 1339, 1269, 1244, 1204, 1177, 1161, 1115, 1074, 1049, 1028, 1001, 978,
+
53, 912; LC/MS (ESI) m/z 349 (M+H) .
5
.7.
To a solution of 7a (1.07 g, 3.36 mmol) in toluene (16 mL) was added AlCl
After stirring at 85 °C for 5 h, the reaction was quenched by the addition of 1 N HCl (50 mL). The
precipitate was collected off, and washed with 1 N HCl (20 mL × 3), H O (20 mL × 3), Et O (20 mL ×
) to obtain white powder (686 mg). This powder was dissolved in MeOH/THF = 1/1 (64 mL), and 8 N
NaOH (16 mL) was added to the mixture. After stirring at 85 °C for 2 days, the reaction mixture was
concentrated under reduced pressure. The residue was partitioned between EtOAc (50 mL) and H O (30
mL). The separable organic layer was washed with H O (50 mL), brine (50 mL), and dried over MgSO
(2RS)-3,4-Dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (8a)
3
(1.14 g, 8.40 mmol) at rt.
2
2
3
2
2
4
,

filtered, concentrated under reduced pressure. The residue was purified by column chromatography
1
(
NHSiO
2
, n-hexane /EtOAc = 1/0–9/1) to obtain 8a (245 mg, 34%) as pale yellow oil. H-NMR (CDCl
3
)
δ 1.35–1.90 (7H, m), 2.04 (1H, ddd, J = 13.8, 9.2, 6.4 Hz), 2.42 (1H, ddd, J = 13.8, 5.1 Hz), 2.86 (1H,
ddd, J = 13.1, 9.1, 3.9 Hz), 2.95–3.04 (2H, m), 3.07 (1H, ddd, J = 13.1, 4.9, 4.7 Hz), 7.22 (1H, d, J = 7.5
Hz), 7.30 (1H, dd, J = 7.7, 7.5 Hz), 7.46 (1H, ddd, J = 7.7, 7.5, 1.4 Hz), 8.02 (1H, dd, J = 7.7, 1.4 Hz);
-1
IR (KBr) cm 3319, 3063, 3024, 2930, 2862, 1682, 1601, 1483, 1454, 1435, 1356, 1339, 1327, 1306,
1
2
286, 1271, 1223, 1198, 1167, 1155, 1128, 1101, 1082, 1055, 995, 978, 949, 932, 901; LC/MS (ESI) m/z
+
16 (M+H) .
5
.8.
b (7.02 g, 2.01 mmol), AlCl
mL), and MeOH (100 mL) were used as previously described for 8a. The crude product was purified by
(2RS)-7-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (8b)
7
3
(6.85 g, 50.4 mmol), toluene (100 mL), 8 N NaOH (100 mL), THF (50
column chromatography (NHSiO , n-hexane/EtOAc = 1/0–4/1%) to obtain 8b (260 mg, 5%) as red oil.
2
1
H-NMR (CDCl ) δ 1.37–1.62 (3H, m), 1.62–1.84 (3H, m), 1.93–2.07 (1H, m), 2.41 (1H, ddd, J = 13.8,
3
4
7
.9, 4.9 Hz), 2.80–2.87 (1H, m), 2.88–2.96 (2H, m), 3.07 (1H, ddd, J = 13.4, 4.9, 4.7 Hz), 3.83 (3H, s),
.04 (1H, dd, J = 8.3, 2.8 Hz), 7.13 (1H, d, J = 8.3 Hz), 7.49 (1H, d, J = 2.8 Hz); LC/MS (ESI) m/z 246
+
(
M+H) .
5
.9.
(2RS)-8-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (8c)
CO H (3 mL) at rt, and the
To a solution of 7c (1.0 g, 2.9 mmol) in toluene (10 mL) was added CF
3
2
mixture was stirring at rt for 4 h and concentrated under reduced pressure. The residue was dissolved in
MeOH (10 mL), and 8 N NaOH (1 mL) was added to the mixture. After stirring at 120 °C for 18 h, the
mixture was partitioned between EtOAc and H
2
O. The aqueous layer was extracted with EtOAc. The
SO , filtered, concentrated under
combined organic layer was washed with brine, and dried over Na
2
4

reduced pressure. The residue was purified by column chromatography (NHSiO
2
, n-hexane /EtOAc =
) δ
1
1
1
0/1–5/1) to obtain 8c (0.05 g, 7%) as pale brown oil and 8d (0.27 g, 35%). H-NMR (CDCl
3
.45–1.67 (4H, m), 1.75–1.81 (1H, m), 1.95–2.05 (3H, m), 2.18–2.26 (1H, m), 2.81–3.13 (4H, m), 3.89
(
3H, s), 6.76–6.83 (2H, m), 7.36 (1H, d, J = 8.1 Hz).
5
.10. (2RS)-6-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (8d)
To a solution of 7c (1.0 g, 2.9 mmol) in trifluorobenzene (10 mL) was added trimethylsilyl
trifluoromethanesulfonate (2 g) in an ice-bath, and the mixture was stirring at rt for 18 h and
concentrated under reduced pressure. The residue was dissolved in MeOH (30 mL), and 8 N NaOH (20
mL) was added to the mixture. After stirring at 130 °C for 48 h, the mixture was partitioned between
EtOAc and H
2
O. The aqueous layer was extracted with EtOAc. The combined organic layer was washed
SO , filtered, concentrated under reduced pressure. The residue was
with brine, and dried over Na
2
4
purified by column chromatography (NHSiO , n-hexane /EtOAc = 10/1–5/1) to obtain 8d (0.34 g, 48%)
2
1
as pale brown oil. H-NMR (CDCl
3
) δ 1.31–1.61 (3H, m), 1.61–1.85 (3H, m), 2.02 (2H, ddd, J = 13.8,
9
.2, 6.6 Hz), 2.42 (1H, ddd, J = 13.8, 4.9, 4.9 Hz), 2.84 (1H, ddd, J = 13.4, 9.7, 3.8 Hz), 2.91–3.00 (2H,
m), 3.07 (1H, ddd, J = 13.4, 4.6, 4.6 Hz), 3.84 (3H, s), 6.67 (1H, d, J = 2.4 Hz), 6.83 (1H, dd, J = 8.7,
-
1
2
1
.5 Hz), 7.99 (1H, d, J = 8.7 Hz); IR (KBr) cm 3319, 3001, 2926, 2860, 1672, 1599, 1572, 1495, 1462,
450, 1356, 1340, 1304, 1258, 1227, 1157, 1130, 103, 1082, 1053, 1030, 997, 980. 963, 905; LC/MS
+
(
ESI) m/z 246 (M+H) .
5
.11. (2RS)-2-Bromo-6-methoxy-3,4-dihydronaphthalen-1(2H)-one (10a)
To a solution of 6-methoxy-3,4-dihydronaphthalen-1(2H)-one (9a, 35.6 g, 200 mmol) in THF (600 mL)
was added a solution of phenyltrimethylammonium tribromide (76.4 g, 200 mmol) in THF (400 mL) at
–
78 °C for 1 h under N
2
atmosphere. After stirring at –78 °C to room temperature (rt) for 4 h and at rt for
1
2 h., the precipitation was collected off and washed with EtOAc. The filtrate was concentrated under

reduced pressure. The residue was cooled with refrigerator. The precipitation was collected off and
washed with iPr
n-hexane/iPr
2
O to obtain 10a (42.9 g, 84%) as white powder. Furthermore, the recrystallization form
1
2
O gave colorless plate. H-NMR (CDCl
3
) δ 2.33–2.60 (2H, m), 2.87 (1H, ddd, J = 17.0 Hz,
4
.5 Hz, 4.2 Hz), 3.30 (1H, ddd, J = 17.0 Hz, 9.8 Hz, 6.1 Hz), 3.87 (3H, s), 4.69 (1H, dd, J = 4.2 Hz, 4.2
-
1
Hz), 6.72 (1H, d, J = 2.7 Hz), 6.87 (1H, dd, J = 9.1 Hz, 2.7 Hz), 8.07 (1H, d, J = 9.1 Hz); IR (KBr) cm
3
1
4
007, 2943, 2909, 2839, 1680, 1599, 1568, 1495, 1462, 1454, 1443, 1435, 1429, 1352, 1319, 1302, 1261,
215, 1194, 1159, 1124, 1113, 1086, 1034, 1016, 995, 930; Anal. Calcd for C11
.35. Found: C, 51.75; H, 4.28.
H
11
2
O Br: C, 51.79; H,
5
.12. (2RS)-2-Bromo-5-methoxy-3,4-dihydronaphthalen-1(2H)-one (10b)
To a solution of 9b (4.96 g, 27.3 mmol) in THF (140 mL) were added phenyltrimethylammonium
tribromide (11.00 g, 28.7 mmol) at rt under N atmosphere. After stirring at rt for 2 h, the precipitate was
collected off, and washed with EtOAc. The filtrate was washed with sat. Na (20 mL)/H O (100
mL), H O (50 mL), brine (50 mL), and dried over MgSO , filtered, concentrated under reduced pressure.
The residue was washed with iPr
recrystallization from with iPr
2
2
S
2
O
3
2
2
4
2
O to obtain 10b (3.99 g, 57%) as white powder. Furthermore, the
1
2
O gave white powder: mp 93 °C (n-hexane/iPr
2
O); H-NMR (CDCl
3
) δ
ppm 2.45–2.54 (2H, m), 3.02 (2H, dd, J = 6.1, 6.1 Hz), 3.88 (3H, s), 4.71 (1H, dd, J = 4.5, 4.2 Hz), 7.06
-1
(
1H, d, J = 8.0 Hz), 7.32 (1H, dd, J = 8.0, 8.0 Hz), 7.70 (1H, d, J = 8.0 Hz); IR (KBr) cm 3003, 2949,
2
901, 2837, 1688, 1597, 1582, 1474, 1456, 1437, 1346, 1315, 1300, 1283, 1261, 1211, 1196, 1186, 1151,
+
+
1
123, 1082, 1063, 1032, 995, 922; LC/MS (ESI) m/z 255 M , 257 (M+2) .
5
.13. (2RS)-N-(6-Methoxy-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)acetamide (11a)
To a solution of 10a (42.9 g, 168 mmol) in DMF (850 mL) were added AcOH (21.2 mL, 370 mmol)
and a solution of NaN
3
(22.3 g, 336 mmol) in H O (70 mL) at from –15 °C to –5 °C. After stirring at
2

from –15 °C to 0 °C for 6 h, the reaction was quenched by the addition of H
2
O (1 L). Precipitation was
collected off and washed with EtOAc. The filtrate was concentrated under reduced pressure. The residue
was cooled with refrigerator to produce precipitation, which was collected off and washed with iPr
obtain crude azide compound (38.1 g) as white powder.
2
O to
This material was dissolved in THF (850 mL). To the solution were added Ac
2
O (24.6 mL, 252 mmol)
atmosphere, the mixture
and 10% Pd/C (15.2 g, 40 %w/w) at 0 °C. After stirring at rt for 16 h under H
2
was filtered with Celite. To the filtrate was added 10% Pd/C (15.2 g, 40 %w/w) at rt. After stirring at rt
for 8 h under H atmosphere, the mixture was filtered with Celite. The filtrate was concentrated under
reduced pressure. The residue was purified by column chromatography on SiO with n-hexane/EtOAc
1/5–0/1) as eluent to obtain 11a (13.54 g, 35% in 2 steps) as white powder. Furthermore, the
2
2
(
1
recrystallization form n-hexane/EtOAc gave white needle: mp 151.2–151.3 °C; H-NMR (CDCl
1H, dddd, J = 14.0 Hz, 13.4 Hz, 12.4 Hz, 4.3 Hz), 2.09 (3H, s), 2.80 (1H, dddd, J = 12.4 Hz, 4.9 Hz, 4.5
Hz, 2.5 Hz), 2.95 (1H, ddd, J = 17.1 Hz, 4.3 Hz, 2.5 Hz), 3.24 (1H, ddd, J = 17.1 Hz, 13.0 Hz, 4.5 Hz),
.87 (3H, s), 4.57 (1H, ddd, J = 13.4 Hz, 5.1 Hz, 4.9 Hz), 6.63 (1H, brs), 6.71 (1H, d, J = 2.4 Hz), 6.85
3
) δ 1.85
(
3
-1
(
1H, dd, J = 8.9 Hz, 2.5 Hz), 7.99 (1H, d, J = 8.9 Hz); IR (KBr) cm 3277, 3069, 2943, 2839, 1680,
1
1
6
651, 1601, 1568, 1551, 1537, 1497, 1464, 1454, 1447, 1433, 1373, 1335, 1319, 1250, 1213, 1155, 1109,
+
097, 1051, 1028, 924, 910; LC/MS (ESI) m/z 234 (M+H) ; Anal. Calcd for C13
.48; N, 6.00. Found: C, 66.86; H, 6.42; N, 6.00.
H
15NO : C, 66.94; H,
3
5
.14. (2RS)-1'-Acetyl-6-methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (12a)
To a solution of 11a (6.94 g, 29.8 mmol) in DMF (150 mL) were added 1,4-dibromobutane (18.9 mL,
1
55 mmol) and NaH (40%, 3.14 g, 65.5 mmol) at –78 °C under N
78 °C to rt for 2 h and rt for 3 h, the reaction was quenched by the addition of H
(100 mL ×2). The combined organic layers
2
atmosphere. After stirring at from
–
2
O (100 mL). This
mixture was extracted with EtOAc (100 mL × 4) and CHCl
3

were dried order MgSO
4
, filtered and concentrated under reduced pressure. The residue was purified by
column chromatography (SiO
2
, n-hexane/EtOAc) to obtain 12a (6.53 g, 76%) as white powder.
Furthermore, the recrystallization form n-hexane/EtOAc gave pale purple plate: mp 122–126 °C;
1
H-NMR (CDCl ) δ 1.50–1.66 (1H, m), 1.71–1.86 (3H, m), 1.89–2.01 (1H, m), 2.06 (3H, s), 2.07–2.16
3
(
(
1H, m), 2.58 (1H, ddd, J = 13.0 Hz, 12.8 Hz, 5.1 Hz), 2.72–3.06 (2H, m), 3.16–3.40 (1H, m), 3.69–3.80
1H, m), 3.83 (3H, s), 6.63 (1H, d, J = 2.4 Hz), 6.84 (1H, dd, J = 8.7 Hz, 2.5 Hz), 8.09 (1H, d, J = 8.7
-1
Hz); IR (KBr) cm 3015, 2941, 2866, 1682, 1651, 1634, 1601, 1574, 1495, 1470, 1462, 1454, 1445,
1
1
435, 1427, 1416, 1402, 1398, 1356, 1346, 1337, 1273, 1250, 1225, 1194, 1163, 1142, 1128, 1113, 1105,
+
074, 1030, 1001, 972, 941, 908; LC/MS (ESI) m/z 288 (M+H) ; Anal. Calcd for C17
H
21NO : C, 71.06;
3
H, 7.37; N, 4.87. Found: C, 71.01; H, 7.31; N, 4.85.
5
.15. (2RS)-1'-Acetyl-5-methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (12b)
To a solution of 10b (3.90 g, 15.3 mmol) in DMF (150 mL) were added AcOH (1.95 mL, 33.6 mmol)
and a solution of NaN
stirring at –15 to 0 °C for 4 h, the reaction was quenched by the addition of ice. The precipitate was
collected off, and washed with H O (20 mL ×3) and iPr O (20 mL × 3) to obtain crude azide (2.98 g,
0%) as white powder. This material was used on next step without further purification.
To a solution of crude azide (2.83 g, 13.0 mmol) in THF (60 mL) were added Ac O (2.55 mL, 26.1
atmosphere, the
3
(2.03 g, 30.6 mmol) in H
2
O (14 mL) at –15 to –10 °C under N atmosphere. After
2
2
2
9
2
mmol) and 10% Pd/C (849 mg, 30 %w/w) at rt. After stirring at rt for 1 day under H
2
Ⓡ
mixture was filtered with Celite . The filtrate was concentrated under reduced pressure. The residue was
washed with iPr O (10 mL × 2) to produce red power. Furthermore, recrystallization from
2
n-hexane/EtOAc gave (2RS)-N-(5-Methoxy-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)acetamide (11b) as
red powder (1.84 g).
To a suspension of 50–72% NaH (788 mg, 16.4 mmol) in DMF (30 mL) were added 1,4-dibromobutane

(
4.75 mL, 38.8 mmol) and a solution of 11b (1.74 g, 7.46 mmol) in DMF (10 mL) at 0 °C under N
2
atmosphere. After stirring at 0 °C to rt for 1 h and at rt for 3 h, the reaction was quenched by the addition
of 1 N HCl (50 mL). This mixture was extracted with EtOAc (100 mL × 2). The combined organic
layers were washed with H
2
O (50 mL), brine (50 mL), and dried over MgSO
4
, filtered, concentrated
under reduced pressure. The residue was by column chromatography (SiO
2
, n-hexane/EtOAc = 3/2–2/3)
to obtain 12b (1.03 g, 48%) as white powder. Furthermore, recrystallization from n-hexane/EtOAc gave
1
colorless prism: mp 130–133 °C (n-hexane/EtOAc); H-NMR (CDCl
3
) δ 1.54–1.68 (1H, m), 1.70–1.86
(
4H, m), 1.90–2.20 (2H, m), 2.05 (3H, s), 2.40–2.70 (2H, m), 2.93–3.16 (1H, m), 3.22–3.33 (1H, m),
3
7
1
.69–3.79 (1H, m), 3.84 (3H, s), 6.97 (1H, d, J = 7.6 Hz), 7.28 (1H, dd, J = 7.6, 7.6 Hz), 7.74 (1H, d, J =
-1
.6 Hz); IR (KBr) cm 3071, 2941, 2864, 1691, 1682, 1643, 1634, 1583, 1470, 1439, 1414, 1402, 1344,
315, 1288, 1259, 1225, 1184, 1167, 1146, 1119, 1101, 1057, 1036, 1005, 970, 951, 908; LC/MS (ESI)
+
m/z 288 (M+H) ; Anal. Calcd for C17
H
21NO : C, 71.06; H, 7.37; N, 4.87. Found: C, 70.56; H, 7.32; N,
3
4
.65.
5
.16. (2RS)-6-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (8d)
To a solution of 12a (6.53 g, 22.7 mmol) in EtOH (150 mL) was added cHCl (50.0 mL) at rt. After
stirring under reflux for 3 days, the reaction mixture was concentrated under reduced pressure. The
residue was partitioned between EtOAc (200 mL) and 1 N NaOH (200 mL). The separable organic layer
was washed with brine (100 mL), dried over, MgSO
4
, filtered, and concentrated under reduced pressure.
, n-hexane/EtOAc = 1/0–0/1) to obtain 8d
3.58 g, 64%) as yellow oil, and to recover 12a (1.84 g, 28%).
The residue was purified by column chromatography (SiO
2
(
5
.17. 5-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (8e)
To a solution of 12b (850 mg, 2.96 mmol) in EtOH (30 mL) was added cHCl (10 mL) at rt. After

stirring under reflux for 1 week, the reaction was quenched by the addition of 8 N NaOH (50 mL). This
mixture was extracted with EtOAc (200 mL × 4). The combined organic layers were washed with brine
(
50 mL), dried over MgSO
4
, filtered, concentrated under reduced pressure. The residue was by column
chromatography (NHSiO
2
, n-hexane/EtOAc = 50/1–2/1) to obtain 8e (297 mg, 41%) as yellow oil.
1
H-NMR (CDCl ) δ 1.36–1.62 (3H, m), 1.62–1.79 (3H, m), 1.90–2.02 (1H, ddd, J = 13.8, 10.0, 5.5 Hz),
3
2
2
7
.42 (1H, ddd, J = 13.8, 5.1, 4.9 Hz), 2.67–2.81 (1 H, ddd, J = 18.5, 10.0, 5.5 Hz), 2.81–2.92 (1H, m),
.94–3.05 (1H, m), 3.01–3.12 (1H, m), 3.86 (3H, s), 7.00 (1H, dd, J = 7.9, 0.9 Hz), 7.28 (1H, dd, J = 7.9,
+
.9 Hz), 7.62 (1H, dd, J = 7.9, 0.9 Hz); LC/MS (ESI) m/z 246 (M+H) .
5
.18. (2S)-6-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one D-(R)-mandelate
(
13a).
d hydrochloride (5.2 g, 18.3 mmol) was partitioned between ethyl acetate and 0.1 N NaOH (400 mL),
and the aqueous layer was extracted with ethyl acetate. The combined organic layer was washed with
brine, dried (Na SO ) and concentrated in vacuo. to produce brown oils (4.73 g). To a solution of the oils
8
2
4
in ethanol (100 mL) was added a solution of D-(R)-(-)-mandelic acid (2.78g, 18.3 mmol) in ethanol (100
mL) and diisopropylether (800 mL), and the mixture was stirred at rt for 18 h. The precipitation was
1
filtered off to obtain 13a (2.89 g, 40%) as white crystals: H-NMR (CDCl
3
) δ 1.40–1.80 (6H, m), 2.12
(
1H, dt, J = 5.7 Hz, 12.9 Hz), 2.30–2.36 (1H, m), 2.79–2.86 (1H, m), 2.92–3.04 (2H, m), 3.55–3.63 (1H,
m), 3.87 (3H, s), 4.85 (1H, s), 5.71 (3H, brs), 6.64 (1H, d, J = 2.7 Hz), 6.86 (1H, dd, J = 2.4 Hz, 8.7 Hz),
.05–7.15 (3H, m), 7.37 (2H, dd, J = 1.5 Hz, 7.5 Hz), 7.97 (1H, d, J = 8.4 Hz); Anal. Calcd for
: C, 69.50; H, 6.85; N, 3.52. Found: C, 69.46; H, 6.85; N, 3.54.
7
C
23
H27NO
5
5
.19. (2R)-6-methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one L-(S)-mandelate
13b)
(

The mother liquid of 13a was partitioned between ethyl acetate and 0.1 N NaOH (300 mL), and the
aqueous layer was extracted with ethyl acetate. The combined organic layer was washed with brine,
dried (Na
2
SO ) and concentrated in vacuo. to produce brown oils (2.71 g). To a solution of the oils in
4
ethanol (50 mL) was added a solution of L-(S)-(+)-mandelic acid (1.68 g, 11.1 mmol) in ethanol (50
mL) and diisopropylether (400 mL), and the mixture was stirred at rt for 5 h. The precipitation was
1
filtered off to obtain 13b (3.02 g, 42%) as white crystals: H-NMR (CDCl
3
) δ 1.40–1.80 (6H, m), 2.12
(
1H, dt, J = 5.7 Hz, 12.9 Hz), 2.30–2.36 (1H, m), 2.79–2.86 (1H, m), 2.92–3.04 (2H, m), 3.55–3.63 (1H,
m), 3.87 (3H, s), 4.85 (1H, s), 5.71 (3H, brs), 6.64 (1H, d, J = 2.7 Hz), 6.86 (1H, dd, J = 2.4 Hz, 8.7 Hz),
.05–7.15 (3H, m), 7.37 (2H, dd, J = 1.5 Hz, 7.5 Hz), 7.97 (1H, d, J = 8.4 Hz); Anal. Calcd for
: C, 69.50; H, 6.85; N, 3.52. Found: C, 69.50; H, 6.83; N, 3.54.
.20. (2S)-6-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (14a)
3a (2.82 g, 7.10 mmol) was portioned between EtOAc and 0.2N NaOH, and the aqueous layer was
extracted with EtOAc. The combined organic layer was washed washed with brine, dried over Na SO
filtered, and concentrated under reduced pressure to produce 14a (1.8 g, ~100%) as pale brown oil.
7
C
23
H27NO
5
5
1
2
4
,
2
0
[
α]
D
+31.0° (c = 0.500, MeOH); 98.3% ee [colimm: CHIRALPAK OJ; mobile phase:
n-hexane/EtOH/diethylamine (95/5/01)(v/v/v)].
5
.21. (2R)-6-Methoxy-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one (14b)
3b (2.96 g) was portioned between EtOAc and 0.33N NaOH, and the aqueous layer was extracted
with EtOAc. The combined organic layer was washed washed with brine, dried over Na SO , filtered,
and concentrated under reduced pressure to produce 14a (1.88 g, ~100%) as pale brown oil. [α]
32.7° (c = 0.505, MeOH); 99.7% ee [colimm: CHIRALPAK OJ; mobile phase:
n-hexane/EtOH/diethylamine (95/5/01)(v/v/v)].
1
2
4
2
0
D
–

5
.22. 1'-(2-Phenylethyl)-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one hydrochloride (3a)
A mixture of 8a hydrochloride (0.35 g, 1.4 mmol), N-ethyldisopropylamine (0.54 g, 4.2 mmol) and
potassium carbonate (0.67 g, 4.9 mmol) in DMF (20 mL) was stirred for 1h at rt. To the mixture was
added (2-iodoethyl)benzene (0.97 g, 4.2 mmol) in an ice-bath, and the mixture was stirred at 100 °C for
2
4 h and concentrated in vacuo. The residue was partitioned between ethyl acetate and water, and the
aqueous layer was extracted with ethyl acetate. The combined organic layer was washed with brine,
dried (Na SO ) and concentrated in vacuo. The residue was purified by column chromatography on
2
4
basic silica gel (n-hexane/EtOAc = 10/1– 6/1) to produce brown oils (0.34 g), to a solution of which in
ether (5 mL) was added 4N HCl/EtOAc (0.30 mL, 1.2 mmol) dropwise in an ice-bath, and the
1
precipitaion was filtered off to obtain 3a (0.32 g, 65%) as white crystals: mp 116–117 °C; H-NMR
(
DMSO-d
6
) δ 1.50–2.80 (6H, m), 3.07–3.74 (10H, m), 7.20–7.34 (5H, m), 7.43–7.48 (2H, m), 7.69 (1H,
t, J = 7.5 Hz), 8.03 (1H, d, J = 5.7 Hz), 9.92 (1H, brs); Anal. Calcd for C22
H
25NO·HCl·0.5H O: C,
2
+
7
2.41; H, 7.46; N, 3.84. Found: C, 73.01; H, 7.73; N, 3.76; LC/MS (ESI) m/z 320 (M+H) .
5
.23. (2RS)-1'-[2-(2-Methylphenyl)ethyl]-3,4-dihydro-1H-spiro[naphthalene-2,2'-piperidin]-1-one
hydrochloride (3b)
To a solution of 8a (225 mg, 1.05 mmol) and 1-(2-iodoethyl)-2-methylbenzene (386 mg, 1.57 mmol) in
toluene (5 mL) were added iPr
under reflux for 1.5 days, a solution of 1-(2-iodoethyl)-2-methylbenzene (386 mg, 1.57 mmol) in toluene
5 mL) was added to the mixture. This mixture was stirred under reflux for 1 day, and then, the reaction
was quenched by the addition of H O (20 mL). This mixture was extracted with EtOAc (50 mL). The
separated organic layer was washed with sat. Na (5 mL)/H O (20 mL), H O (20 mL), brine (20
mL), and dried over MgSO , filtered, concentrated under reduced pressure. The residue was by column
chromatography (NHSiO , n-hexane /EtOAc = 1/0–19/1) to obtain free form of 3b as a pale yellow oil
2
NEt (740 L, 4.18 mmol) at rt with silica gel blue tube. After stirring
(
2
S
2 2
O
3
2
2
4
2