Synthesis and antidepressant activity of optical isomers of 2-(4-benzylpiperazin-1-yl)-1-(5-chloro-6-methoxynaphthalen-2-yl) propan-1-ol (SIPI5056)

Article abstract of DOI:10.1016/j.bmcl.2009.11.108

Four optical isomers of SIPI5056 were synthesized and evaluated for their antidepressant activities and acute toxicities as novel multiple reuptake inhibitors of monoamine transmitters. Chiral alanines were used as educts to prepare their respective target compounds in nine steps. Pharmacological results showed that the (1R,2S)-SIPI5056 isomer has higher inhibitory activity and lower toxicity than other three isomers and is worthy of further development.

Full text of DOI:10.1016/j.bmcl.2009.11.108

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1256–1259
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antidepressant activity of optical isomers of
2-(4-benzylpiperazin-1-yl)-1-(5-chloro-6-methoxynaphthalen-2-yl)
propan-1-ol (SIPI5056)
*
Zhijie Weng, Jianqi Li
Shanghai Institute of Pharmaceutical Industry, 1111 North Zhongshan Road, Shanghai 200437, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four optical isomers of SIPI5056 were synthesized and evaluated for their antidepressant activities and
acute toxicities as novel multiple reuptake inhibitors of monoamine transmitters. Chiral alanines were
used as educts to prepare their respective target compounds in nine steps. Pharmacological results
showed that the (1R,2S)-SIPI5056 isomer has higher inhibitory activity and lower toxicity than other
three isomers and is worthy of further development.
Received 19 August 2009
Revised 22 October 2009
Accepted 20 November 2009
Available online 27 November 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Optical isomer
Antidepressant
Triple reuptake inhibitor
Depression is one of the most common neuropsychiatric condi-
tions with a lifetime prevalence approaching 17%. Depression also
ranks as one of the most significant causes of disability worldwide,
second only to ischemic.1 Drugs that interfere with the reuptake of
biogenic amines have been used to treat depression for several
decades. Early medications such as tricyclic antidepressants and
monoamine oxidase inhibitors are effective but possess many side
effects that limit their clinical applications. Selective serotonin
reuptake inhibitors (SSRIs) or noradrenaline reuptake inhibitors
(SNRIs) are as effective as the traditional antidepressants with few-
er side effects due to their improved selectivity towards a single
monoamine transporter.
depressant activity in our patents.13 Wherein we discovered that
2-(4-benzylpiperazin-1-yl)-1-(5-chloro-6-methoxynaphthalen-2-
yl) propan-1-ol, (1, SIPI5056) has dual reuptake inhibitory activity
for 5-HA and NA neurotransmitters.
Structurally, compound 1 has two chiral carbon centers and
therefore contains four optical isomers. Our previous research had
successfully separated the erythro conformation from the threo,
even though it was still a racemic mixture of two optical isomers
for each conformation. Nevertheless, our in vitro studies indicated
that the erythro conformation of 1 was a triple reuptake inhibitor
whereas the threo was a dual reuptake inhibitor. The results of the
acutetoxicitystudies (mice, po) showedthat theLD50 value of theer-
ythro was more than 1.5 g/kg, while it was about 220 mg/kg for the
threo conformation, suggesting that the overall acute toxicity of er-
ythro racemic mixture was much lower than that of threo racemic
mixture as well as most of antidepressants on the market.
Recently, dual reuptake inhibitors of both serotonin and nor-
adrenaline, such as Venlafaxine and Duloxetine have gained accep-
tance in the market, because of their effective actions on both
severe depression and chronic depression.2–5
Success research on the dual reuptake inhibitors led scientists to
develop triple reuptake inhibitors, molecules that inhibit reuptakes
of all three neurotransmitters, 5-HT, NA, and DA collectively. The pre-
clinical and clinical research revealed that the triple reuptake drugs in
study produce a more rapid onset of action and possess greater effi-
cacy than traditional antidepressants,6–10 these are, for example,
DOV-21947 (by DOV pharmaceutical, Phase II), SEP-225289 (by
Sepracor, Phase II), and NS-2359 (by Neuroserch, Phase II).11
Previously, we disclosed the synthesis of certain aryl alkanol
piperazine derivatives12 and the biological evaluation of their anti-
The overall activities of the racemic mixture in erythro confor-
mation has demonstrated its antidepressive potency and safety as
a novel triple reuptake inhibitor, however, it still contains two
optical isomers, (1S,2R) and (1R,2S), respectively, which may pos-
sess difference in activity and safety. On the other hand, although
the threo racemic mixture displays much high overall toxicity, it is
possible that the toxicity is due to one of the two optical isomers.
Thereby it is necessary to carry out the comparable research on
bioactivity and safety with each individual optical isomers of
SIPI5056 in order to find the optimal drug candidate with high effi-
cacy and low toxicity for further preclinical development.
Four individual optical isomers shown in Table 1 were prepared
through 9 steps from their respective chiral alanines as chiral educts,
* Corresponding author. Tel.: +86 21 55514600; fax: +86 21 65312830.
E-mail address: lijianqb@126.com (J. Li).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.11.108

Z. Weng, J. Li / Bioorg. Med. Chem. Lett. 20 (2010) 1256–1259
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Table 1
In vitro reuptake inhibiting activities of target compounds 1-1–1-4 for 5-HT, NA, DA receptors
OH
H
1
N
N
2
H
O
1
Cl
½ ꢁ (c 1, CH3OH)
a 2D5
Compd
Formula
Config.
Yield (%)
IC50
NA
1.4
(lM)
5-HT
DA
Venlafaxine
0.35
>1000
1.15
>1000
10.0
1-1
1-2
1-3
1-4
C25H29ClN2O2ꢂ2HClꢂ2H2O
C25H29ClN2O2ꢂ2HClꢂ2H2O
C25H29ClN2O2ꢂ2HClꢂ2H2O
C25H29ClN2O2ꢂ2HClꢂ2H2O
(1R,2S)
(1S,2S)
(1S,2R)
(1R,2R)
34.0
8.5
33.2
8.4
ꢃ8.05
+50.6
+8.54
ꢃ50.1
0.012
0.825
0.548
0.375
0.185
0.425
7.0
1.25
>1000
according to the methods described in Scheme 1. The N-methoxy-N-
methyl-2-(methoxycarbomylamino) propionamide (5) was pre-
pared from alanine according to the procedure described in the
literature.14 Compound 8 was synthesized by Grignard reaction of
5 and 7, then was chloro-substituted, reduced and hydrolyzed to
obtain the key compound 11, 11 reacted with 14 to form the piper-
azinering. 15wasamixtureoftwoepimerides, whichshoweddiffer-
ent Rf values in thin-layer chromatography and was separated by
normal silica gel (200–300 mesh) column chromatography (dichlo-
romethane/methanol, 20:1 v/v) to yield two optical isomers. There-
when the AIP (aluminum isopropoxide) was used as a reductant,
compound 11 was obtained as a erythro-isomer with no threo-iso-
mer, which is probably due to the formation of intermediate com-
pound 16 and followed by hydrolyzation to generate erythro-
isomer only (Scheme 2). The compound 16 had been obtained
and detected by mass and 1H NMR.19
The conformation inherited from its chiral alanine starting
material was confirmed by comparing the coupling constants from
their collective NMR spectra. The definitive configuration of (1R,2S)
isomer (1-1) was examined by X-ray diffraction (Fig. 1). Crystallo-
graphic data (excluding structure factors) for the structure in this
paper have been submitted to the Cambridge Crystallographic Data
Centre as supplementary publication numbers CCDC 740153. Cop-
ies of the data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44 (0)1223-
336033 or e-mail: deposit@ccdc.cam.ac.uk].
fore, (1R,2S)/(1S,2S) isomerwasprepared from
L
-alanineand(1S,2R)/
(1R,2R) isomer was prepared from
D-alanine through the above syn-
thetic process.15–18 The yields and the optical rotation values of each
optical isomers were shown in Table 1. The optical purity of each iso-
mer was determined to be ee% >99% by chair HPLC analysis (Daicel
OJ-H chiral column, 5
ane/isopropanol/diethylamine, 80:20:0.1 v/v/v; Temperature:
l
m, 250 ꢀ 4.6 mm; Mobile phase: N-hex-
Rat synaptosomes were prepared from cerebral cortex and used
in 3H-labeled 5-HT, NA, and DA to test reuptake inhibitory effects
of isomers.20,21 The (1S,2R) and (1R,2S) isomers were found to have
higher reuptake inhibiting activities in vitro for 5-HT, NA, and DA
30 °C; Detection: UV, 230 nm).
Compound 9 was reduced with NaBH4 to yield 10 as a mixture
of two isomers, the ratio of erythro/threo was about 4:1. However,
O
O
O
O
c
a
b
*
O
*
*
HO
*
HO
N
Cl
O
NHCOOCH3
*
NH2
NHCOOCH3
3
NHCOOCH3
e
NHCOOCH3
O
2
4
5
Br
d
8
MgBr
f
O
O
6
7
O
OH
OH
NHCOOCH3
*
g
NH2
NHCOOCH3
*
*
h
O
O
O
k
Cl
Cl
Cl
11
10
9
N
j
Cl
Cl
N
i
H
OH
HO
N
OH
HO
N
14
13
12
OH
OH
l
N
N
N
*
*
*
O
O
Cl
Cl
15
1
Scheme 1. Reagents and conditions: (a) methyl chloroformate, 1 N NaOH, rt; (b) SOCl2, CH2Cl2, ꢃ10 °C; (c) N,O-dimethyl hydroxyamine hydrochloride, CH2Cl2, rt; (d) Mg,
THF, 70 °C; (e) THF, ꢃ78 °C; (f) NaClO/NaCl/40% H2SO4, CH2Cl2, rt; (g) NaBH4, CH3OH, rt; (h) 30% KOH/H2O, CH3OH, reflux; (i) PhCH2Cl, Na2CO3, 80 °C; (j) SOCl2, toluene, 65 °C;
(k) TEA, CH3CN, reflux; (l) silica gel (200–300 mesh) column chromatography, dichloromethane/methanol, 20:1 v/v.

1258
Z. Weng, J. Li / Bioorg. Med. Chem. Lett. 20 (2010) 1256–1259
O
O
*
NH
O
OH
m
*
n
*
*
*
NHCOOCH3
NH2
O
O
O
Cl
Cl
9
Cl
16
11
Scheme 2. Reagents and conditions: (m) AIP, IPA, 60 °C; (n) 30% KOH/H2O, CH3OH, reflux.
Acknowledgments
The authors acknowledge the financial support from National
Natural Science Foundation of China. We would like to gratefully
acknowledge Dr. Wenxin Dong (Shanghai Institute of Pharmaceu-
tical Industry, China) for in vitro and in vivo studies, Mr. Jialiang
Zhong (Shanghai Institute of Pharmaceutical Industry, China) for
X-ray crystallography studies. We would also like to thank Profes-
sor Lei Fu (Shanghai Jiao Tong University, China) for helpful
discussion.
References and notes
1. Butler, R.; Carney, S.; Cipriani, A.; Geddes, J.; Hatcher, S.; Price, J.; Von Korff, M.
Am. Fam. Phys. 2006, 73, 1999.
Figure 1. The stereochemical structure projection of compound 1-1.
2. Mariappan, P.; Alhasso, A.; Ballantyne, Z.; Grant, A.; N’Dow J. Eur. Urol. 2007, 51,
67.
3. Elliott, R. M. Clin. Proc. 1994, 69, 1069.
4. Rosenzweig-Lipson, S.; Beyer, C. E.; Hughes, Z. A.; Khawaja, X.; Rajarao, S. J.;
Malberg, J. E.; Rahman, Z.; Ring, R. H.; Schechter, L. E. Pharmacol. Ther. 2007,
113, 134.
Table 2
In vivo antidepressant activity and acute toxicity of target compounds 1-1–1-4 in
mouse
Compd
Config.
ED50 (mg/kg)
LD50 (mg/kg)
5. Capriotti, T. Medsurg. Nurs. 2006, 15, 241.
6. D’Aquila, P. S.; Collu, M.; Gessa, G. L.; Serra, G. Eur. J. Pharmacol. 2000, 405, 365.
7. Eshleman, A. J.; Carmolli, M.; Cumbay, M.; Martens, C. R.; Neve, K. A.; Janowsky,
A. J. Pharmacol. Exp. Ther. 1999, 289, 877.
8. Meyer, J. H.; Kruger, S.; Wilson, A. A.; Christensen, B. K.; Goulding, V. S.;
Schaffer, A.; Minifie, C.; Houle, S.; Hussey, D.; Kennedy, S. H. NeuroReport 2001,
12, 4121.
TST
FST
1-1
1-2
1-3
1-4
(1R,2S)
(1S,2S)
(1S,2R)
(1R,2R)
12.6
27.9
16.5
24.5
28.9
1030–1202
300–400
1171–1259
200–250
*
—
24.5
*
—
9. Izumi, T.; Inoue, T.; Kitagawa, N.; Shimanaka, S.; Takahashi, Y.; Kusumi, I.;
Odagaki, Y.; Denda, K.; Ohmori, T. J. Affect Disord. 2000, 61, 127.
10. Lammers, C. H.; Diaz, J.; Schwartz, J. C. Mol. Psychiatry 2000, 5, 378.
11. Skolnick, P.; Krieter, P.; Tizzano, J.; Basile, A.; Popik, P.; Czobor, P.; Lippa, A. C. N.
S. Drug Rev. 2006, 12, 123.
12. Li, J. Q.; Huang, L. Y.; Dong, W. X.; Weng, Z. J.; Jin, H.; Ni, X. L.; Zhang, S. J.;
Huang, C. F.; Gu, F. H. Chin. J. Med. Chem. 2006, 16, 270.
13. Li, J. Q.; Huang, L. Y.; Dong, W. X.; Ge, X.; Shi, C. J. C. N. Patent ZL02111934.1,
2002.
*
No statistically significant changes compared with the blank group.
(Table 1), while the (1S,2S) and (1R,2R) isomers were 5-HT, NA
reuptake inhibitors with no DA reuptake inhibitive effect. The tri-
ple inhibitory activity of (1R,2S) isomer was remarkably stronger
than that of other three isomers.
14. Tsuchihashi, G.; Mitamura, S.; Kitajima, K.; Kobayashi, K., U.S. Patent 4,496,755,
1985.
The isomers demonstrated efficacy in two depression related
behavioral models. The ED50 values of four isomers were measured
by the means of single oral dosing mouse forced tail suspension
test (TST) and mouse forced swimming test (FST). The results
showed that the ED50 value of (1R,2S) isomer was 12.6 mg/kg,
(1S,2R) isomer was 16.5 mg/kg, (1S,2S) isomer was 27.9 mg/kg
and (1R,2R) isomer was 24.5 mg/kg in the tail suspension test.
The results of the forced swimming displayed that the ED50 of
(1R,2S) isomer was 28.9 mg/kg, (1S,2R) isomer was 24.5 mg/kg,
(1S,2S) and (1R,2R) isomers were statistically no significant
changes compared with the blank group. The antidepressant activ-
ity of (1R,2S) was the strongest among four isomers (Table 2).
The acute toxicities of isomers were also studied in mouse and
the results demonstrated that the LD50 of four optical isomers was
as follows: (1R,2S) 1030–1202 mg/kg, (1S, 2R) 1171-1259 mg/kg,
(1S,2S) 300–400 mg/kg (1R,2R) 200–250 mg/kg, respectively. The
acute toxicity of erythro-isomers was significantly lower than that
of threo-isomers (Table 2).
15. (1R,2S)-SIPI5056 (1-1): Yield 2.0 g (34%) of a white solid. Mp: 242–243 °C. 1H
NMR (400 MHz, CDCl3 + D2O): d 0.88–0.90 (d, 3H, J = 6.8, 3H, CH3), 2.58–2.86
(m, 9H, CH, piperazine-H), 4.04 (s, 3H, OCH3), 5.13–5.14 (d, 1H, J = 3.2, CH),
7.26–8.19 (m, 10H, ArH); EI-MS m/z: 425 (M+); Anal. Calcd for
C25H29ClN2O2ꢂ2HClꢂ2H2O: C, 56.24; H, 6.51; N, 5.25. Found: C, 56.04; H, 6.36;
N, 5.30.
16. (1S,2S)-SIPI5056 (1-2): Yield 0.5 g (8.5%) of a white solid. Mp: 240–241 °C. 1H
NMR (400 MHz, CDCl3 + D2O): d 0.95–0.97 (d, J = 6.4, 3H, CH3), 3.49–3.97 (m,
9H, CH, piperazine-H), 4.36 (s, 3H, OCH3), 4.80–4.83 (d, 1H, J = 9.6, CH), 7.48–
8.12 (m, 10H, ArH); EI-MS m/z: 425 (M+); Anal. Calcd for
C25H29ClN2O2ꢂ2HClꢂ2H2O: C, 56.24; H, 6.51; N, 5.25. Found: C, 56.44; H, 6.21;
N, 5.30.
17. (1S,2R)-SIPI5056 (1-3): Yield 1.95 g (33.2%) of a white solid. Mp: 241–243 °C.
1H NMR (400 MHz, CDCl3 + D2O): d 1.05–1.07 (d, J = 6.8, 3H, CH3), 3.47–4.00
(m, 9H, CH, piperazine-H), 3.99 (s, 3H, OCH3), 5.15–5.16 (d, 1H, J = 3.2, CH),
7.45–8.10 (m, 10H, ArH); EI-MS m/z: 425 (M+); Anal. Calcd for
C25H29ClN2O2ꢂ2HClꢂ2H2O: C, 56.24; H, 6.51; N, 5.25. Found: C, 56.37; H, 6.38;
N, 5.24.
18. (1S,2R)-SIPI5056 (1-4): Yield 0.49 g (8.4%) of a white solid. Mp: 240–242 °C. 1H
NMR (400 MHz, CDCl3 + D2O): d 1.06–1.08 (d, J = 6.8, 3H, CH3), 3.42–4.08 (m,
9H, CH, piperazine-H), 4.41 (s, 3H, OCH3), 4.92–4.94 (d, 1H, J = 9.6, CH), 7.54–
8.21 (m, 10H, ArH); EI-MS m/z: 425 (M+); Anal. Calcd for
C25H29ClN2O2ꢂ2HClꢂ2H2O: C, 56.24; H, 6.51; N, 5.25. Found: C, 56.15; H, 6.28;
N, 5.26.
In summary, we have prepared four optical isomers of SIPI5056.
The (1R,2S) and (1S,2R) isomers were triple reuptake inhibitors,
while the (1S,2S) and (1R,2R) isomers were dual reuptake inhibitors.
(1R,2S)-SIPI5056 had higher inhibitory activity and lower toxicity
than other three isomers and is worthy of further development.
19. 5-(1-Chloro-2-methoxynaphthalen-6-yl)-4-methyloxazolidin-2-one (16):
a
white solid. 1H NMR (400 MHz, CDCl3 + D2O): d 0.82–0.84 (d, J = 6.4 3H, CH3),
4.04 (s, 3H, OCH3), 4.25–4.29 (m, 1H, CH), 5.85–5.87 (d, 1H, J = 7.6, OCH), 7.25–
8.25 (m, 10H, ArH); EI-MS m/z: 291 (M+).

Z. Weng, J. Li / Bioorg. Med. Chem. Lett. 20 (2010) 1256–1259
20. Preparation of synaptosomes: Rats were decapitated, the brains rapidly excised, synaptosomes and 10
1259
l
l solution of compound were added (all done at 4 °C).
and frontal cortex dissected out on ice-cold saline (4 °C). The 3 g tissue was
homogenized in 30 ml of ice-cold 0.32 M sucrose and then centrifuged (1500g)
for 10 min (4 °C). The pellet was discarded and the supernatant centrifuged
(20,000g) for 30 min (4 °C). After refined, the pellet was resuspended in buffer
and immediately used. Protein content was determined with kit of total
protein.
After mixing, the tubes were incubated 5 min in 37 °C. Uptake was started by
addition of 10 l [3H]-5-HT, [3H]-NA or [3H]-DA (300 nM), after another
l
mixing, the tubes were incubated again 5 min in 37 °C. The reaction was
stopped by cooling the tubes in ice; the samples were then filtered through
glass fiber filters and washed twice with artificial cerebral fluid. After drying in
60–70 °C, the filter membranes were put into scintillation tubes. Filter-bound
radioactivity was counted by scintillation spectrometry. The difference in [3H]-
5-HT, [3H]-NA or [3H]-DA at 37 °C and 0 °C was taken as a measure of active
uptake.
21. Reuptake of monoamine transmitters: According to the method described by
literatures (Br. J. Pharmacol. 1997, 122, 302 and 1992, 105, 147), in the tubes,
1.0 ml artificial cerebral fluid (adding oxygen in advance), 20 ll suspension of