Syntheses and properties of the major hydroxy metabolites in humans of blonanserin AD-5423, a novel antipsychotic agent

Article abstract of DOI:10.1016/j.bmcl.2004.12.028

Two major metabolites in humans of blonanserin, 2-(4-ethyl-1-piperazinyl)- 4-(4-fluorophenyl)-5,6,7,8,9,10-hexahydrocycloocta-[b]pyridine (code name AD-5423), were synthesized. The first, 7-hydroxylated AD-5423, was synthesized through a four-step process

Full text of DOI:10.1016/j.bmcl.2004.12.028

Bioorganic & Medicinal Chemistry Letters 15 (2005) 1055–1059
Syntheses and properties of the major hydroxy metabolites
in humans of blonanserin AD-5423, a novel antipsychotic agent
Takeshi Ochi,a,* Masato Sakamoto,b Akira Minamida,b Kenji Suzuki,c Tomohiko Ueda,c
Teruaki Une,d Hiroshi Toda,b Kazuya Matsumotob and Yoshiaki Terauchib
aPharmaceutical Research and Technology Center, Dainippon Pharmaceutical Co., Ltd, 5-51, Ebie 1-chome, Fukushima-ku,
Osaka 553-0001, Japan
bPharmacokinetics Research Laboratories, Dainippon Pharmaceutical Co., Ltd, Enoki 33-94, Suita, Osaka 564-0053, Japan
cChemistry Research Laboratories, Dainippon Pharmaceutical Co., Ltd, Enoki 33-94, Suita, Osaka 564-0053, Japan
dPharmacology and Microbiology Research Laboratories, Dainippon Pharmaceutical Co., Ltd, Enoki 33-94, Suita,
Osaka 564-0053, Japan
Received 8November 2004; revised 10 December 2004; accepted 10 December 2004
Available online 30 December 2004
Abstract—Two major metabolites in humans of blonanserin, 2-(4-ethyl-1-piperazinyl)-4-(4-fluorophenyl)-5,6,7,8,9,10-hexahydrocy-
cloocta-[b]pyridine (code name AD-5423), were synthesized. The first, 7-hydroxylated AD-5423, was synthesized through a four-
step process starting from 4-fluorobenzoylacetonitrile (1), and the second, 8-hydroxylated AD-5423, a nine-step process also from
1. The optical resolution, structures, and receptor binding properties of the metabolites were documented.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
5423 derivatives to confirm chemical structures of
metabolites and for additional biological studies.
Blonanserin (AD-5423), having dopamine D2 and sero-
tonin 5-HT2 receptor antagonist properties, is a novel
antipsychotic agent now under clinical development.1–3
Some antipsychotics often produce oversedative and/or
autonomic side effects, probably because of their adren-
aline-a1 receptor antagonist properties. The potent sero-
tonin 5-HT2 antagonism, together with weak
adrenaline-a1 and virtually no dopamine D1 antagonist
properties suggests that blonanserin is expected to offer
an advantageous clinical profile.1 In pharmacokinetic
studies, many metabolites (deethyl form, N-oxide form,
etc.) of the agent were detected and identified in ani-
mals.4 However, hydroxy forms were not identified
and four hydroxy isomers were estimated in the in vitro
metabolism study using rat liver microsomes (unpub-
lished). In the mass balance study using 14C-labeled
compound in humans, 7- and 8-hydroxylated AD-5423
were suggested as major metabolites. We describe prep-
aration of enantiomerically pure 7- and 8-hydroxy AD-
2. Chemistry
7-Hydroxylated AD-5423 (6) was synthesized in a four-
step process as shown in Scheme 1. First, the starting
material, 1,5-cyclooctanonedione (2)5 was synthesized
from the commercially available 1,5-cyclooctanediol by
PCC oxidation. Then, 4-fluorobenzoylacetonitrile (1)6
was condensed to the compound 2 by heating with
PPA to give the compound 3, which provides a basic
framework of the target.7 The compound 3 was con-
verted to the triflate 4 by CF3SO2Cl, followed by
NaBH4 reduction to yield the alcohol 5. Finally, con-
densation of 5 with N-ethylpiperazine gave the 7-
hydroxylated AD-5423 (6).8
8-Hydroxylated AD-5423 (16) was synthesized in a nine-
step process as shown in Scheme 2. First, condensation
of 1 with cyclooctanone 7 through the above described
method gave the compound 8, which was converted to
the corresponding 2-chloro derivative 9 by treatment
with POCl3.1 The compound 9 was then converted
to the N-oxide 10 with m-CPBA, which underwent
Keywords: Blonanserin; AD-5423; Hydroxyl metabolites; Antipsy-
chotic agent.
*
Corresponding author. Tel.: +81 6 6454 8461; fax: +81 6 6455
8356; e-mail: takeshi-ochi@dainippon-pharm.co.jp
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.12.028

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T. Ochi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1055–1059
Scheme 1. Reagents and conditions: (a) PPA; (b) CF3SO2Cl, pyridine; (c) NaBH4, MeOH; (d) N-ethylpiperazine.
chlorination using POCl3 and Et3N to yield the 2,10-di-
chloro derivative 11. Elimination of HCl from 11 using
DBU and subsequent oxidation of the resultant com-
pound 12 with SeO2 and HCOOH gave the 8-oxyformyl
derivative 13. Deformylation with HCl followed by
reduction of the olefin 14 with H2 and PtO2 gave the
alcohol 15. Finally, condensation of 15 with N-ethylpip-
erazine gave the 8-hydroxylated AD-5423 (16) Figure 1.9
of 6a and 16b are shown in Figures 2 and 3, respectively.
In addition, the absolute configuration of hydroxy cen-
ter for each isomer was also confirmed by the improved
Mosher method using 2-methyl-2-(1-naphthyl)propionic
acid (MaNP acid),12 a powerful chiral auxiliary Scheme
3.
3. Biological results and discussion
Chemical structures of the two hydroxylated AD-5423
derivatives, 6 and 16, were confirmed by mass spectro-
metry (MS) and nuclear magnetic resonance spectrometry
(NMR).8,9
The in vitro metabolism study using human liver micro-
somes (unpublished) revealed that the main stereoiso-
mers were 6a of the 7-hydroxy and 16b of the 8-hydroxy
metabolites. These findings indicate that the hydroxyl
groups of the two major stereoisomers of human metab-
olites are situated on the same side of their eight-mem-
bered rings.
A chiral resolution of the compound 6 (12 g) by pre-
parative HPLC using a CHIRALCEL AD column was
then conducted to give the optically pure alcohols, 6a
(S-configuration, 4.2 g) and 6b (R-configuration, 5.2 g),
with an enantiomeric purity of >98%ee.10 Similarly,
the compound 16 (10 g) was resolved using a CHIRAL-
CEL OJ column to give optically pure 16a (4.5 g) and
16b (4.4 g) with >98%ee.10
The four isomers (6a, 6b, 16a, and 16b) and AD-5423
were examined for their binding affinity to the human
D2L and 5HT2A receptors (Table 1). The binding affinity
of AD-5423 is >25.7 and >11.9 times higher than those
of the pair of 6a and 6b, and of 16a and 16b isomers,
respectively. Therefore, introduction of a hydroxyl
group at 7- and 8-positions on the eight-membered ring
reduced the affinity to both receptors.
The absolute configurations of 6a (S-configuration) and
16b (R-configuration) were determined by X-ray crystal-
lography of their HBr salt,11 and the ORTEP diagrams

T. Ochi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1055–1059
1057
Scheme 2. Reagents and conditions: (a) PPA; (b) POCl3; (c) m-CPBA, CHCl3; (d) POCl3, Et3N, CHCl3; (e) DBU, DMSO; (f) SeO2, HCOOH,
dioxane; (g) HCl, MeOH; (h) H2, PtO2, EtOH; (i) N-ethylpiperazine.
Figure 1. The chemical structure of AD-5423 and [14C]AD-5423.
The stereo isomers 6b and 16b having R-configuration at
the hydroxy group exhibited a higher affinity than 6a
and 16a. Concentrations of these metabolites in human
plasma are currently investigated in our clinical pharma-
cokinetic studies, and pharmacological role of the
metabolites will be taken into consideration in the
course of development of AD-5423.
4. Conclusion
In summary, the synthesis and properties of hydroxy
metabolites (6 and 16) of blonanserin (AD-5423) in hu-
mans have been described. Synthesis of 6 and 16 were
achieved in four- and nine-step processes from com-
pound 1, respectively. Subsequent optical resolution of

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T. Ochi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1055–1059
Figure 2. The ORTEP drawing of 6a with thermal at 50% probabilities.
Figure 3. The ORTEP drawing of 16b with thermal at 50% probabil-
ities.
Scheme 3. Reagents and conditions: (a) CHIRALCEL AD column, mobile phase of MeOH/Et2NH (100:0.1); (b) CHIRALCEL OJ column, mobile
phase of hexane/EtOH/Et2NH (90:10:0.1).
Table 1. Binding affinity to recombinant human D2L and 5HT2A
receptors
6 and 16 were performed by preparative HPLC using a
Compds
Configuration of hD2L receptor h5HT2A receptor
Ki (nM)a
chiral column. Additionally, in an in vitro metabolism
study, it was revealed that the main metabolites in hu-
mans were 6a (S-configuration) and 16b (R-configura-
tion), whose absolute configuration were determined
by X-ray crystallography. All stereoisomers had affini-
ties less than one tenth of the parent AD-5423 to the
human D2L and 5HT2A receptors. Isomers 6b and 16b
with R-configuration exhibited a higher affinity to the
receptors than their respective isomers.
hydroxyl center
Ki (nM)a
AD-5423f
6a
6b
0.14 0.002
21.2 1.0
6.20 0.35
11.9 0.3
3.60 0.03
0.81 0.22
18.5 2.7
14.7 2.4
17.9 0.9
9.67 0.77
S
R
S
R
16a
16b
a Data are expressed as the mean SEM of three independent
experiments.

T. Ochi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1055–1059
1059
1.53 (m, 2H, CH2), 1.63 (m, 2H, CH2), 1.76 and 2.20 (m,
2H, CH2), 2.53 (q, J = 7.0 Hz, 2H, CH2), 2.53 (m, 2H,
CH2), 2.61 (m, 4H, CH2 ), 2.83 (ddd, J = 13.3, 7.8, 3.8 Hz,
1H) and 2.66 (ddd, J = 13.3, 10.2, 3.5 Hz, 1H) (CH2), 3.58
(m, 4H, CH2), 3.58(m, 1H, CH), 6.30 (s, 1H, CH), 7.07
Acknowledgements
The authors thank Dr. Siro Kato and Dr. Hisashi Miya-
zaki for helpful discussion.
(m, 2H, CH), 7.18(m, 2H, CH) ppm;
13C NMR
References and notes
(400 MHz, CDCl3) d 11.71, 26.78, 27.68, 32.20, 36.18,
39.25, 45.05, 52.34, 52.44, 72.39, 106.01, 114.73 (d,
J = 21.5 Hz), 121.75, 129.71 (d, J = 7.5 Hz), 136.68
(d, J = 3.7 Hz), 150.30, 156.80, 158.56, 161.75 (d,
J = 245.2 Hz) ppm; MS (APCI) m/z (relative intensity):
384 ([MH+], 100).
1. Oka, M.; Hino, K. Drug. Future 1992, 17, 9–11.
2. Hino, K.; Kai, N.; Sakamoto, M.; Murata, T.; Oka, M.;
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10. Optical resolution of 6 and 16 were performed at Daicel
Chemical Industries, Ltd.
3. Suzuki, K.; Hiyama, Y.; Une, T.; Fujiwara, I. Anal. Sci.
2002, 18, 1289–1290.
27
11. Spectral data, for 6a: mp 194–196 °C (EtOH); ½aꢀD
27
4. Matsuda, M.; Toda, H.; Ishiwata, A.; Mizuki, Y.; Fujii T.;
Miyazaki H. Abstracts of Papers, 140, 5th International
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E. J. Med. Chem. 1979, 22, 1385–1389.
ꢁ15.1 (c 1.0, MeOH); for 6b: mp 194–196 °C (EtOH);
27
½aꢀD ꢁ28.3 (c 1.0, MeOH); for 16a: mp 170–172 °C
27
(MeOH + CH3CN); ½aꢀD +28.4 (c 1.0, MeOH); for 16b:
mp 170–172 °C (MeOH + CH3CN); ½aꢀD ꢁ28.4 (c 1.0,
MeOH); for HBr salt of 6a: mp 172–174 °C (CH3CN);
27
½aꢀD ꢁ15.1 (c 1.0, MeOH); IR (KBr) mmax 3326 cmꢁ1; H
NMR (400 MHz, CDCl3) d 1.25 (t, J = 7.3 Hz, 3H), 1.23–
1.33 (m, 1H), 1.40–1.50 (m, 1H) 1.54–1.67 (m, 3H), 1.76–
1.88 (m, 1H), 2.44–2.52 (m, 1H), 2.59 (m, 1H), 2.72–2.85
(m, 2H), 2.95–3.14 (m, 4H), 3.18(m, 2H), 3.27–3.35 (m,
1H), 3.54 (m, 2H), 4.32 (br s, 1H), 4.40 (m, 2H), 6.54 (s,
1H), 7.25–7.35 (m, 4H), 9.49 (m, 1H) ppm; MS (APCI) m/
z (relative intensity): 384 ([MH+ of free base], 100). For
1
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731.
8. Spectral data for 6: 1H NMR (400 MHz, CDCl3) d 1.12 (t,
J = 7.1 Hz, 3H, CH3), 1.41 and 1.71 (m, 2H, CH2), 1.42
(br s, 1H, OH), 1.71 (m, 2H, CH2), 1.78and 1.94 (m, 2H,
CH2), 2.46 (q, J = 7.1 Hz, 2H, CH2), 2.55 (m, 4H, CH2),
2.55 (m, 1H) and 2.66 (ddd, J = 14.5, 9.9, 4.0 Hz, 1H)
(CH2), 2.85 (m, 2H, CH2), 3.53 (m, 4H, CH2), 3.56 (m, 1H,
CH), 6.29 (s, 1H, CH), 7.08(m, 2H, CH), 7.22 (m, 2H,
CH) ppm; 13C NMR (400 MHz, CDCl3) d 11.93, 23.79,
26.61, 35.58, 37.07, 40.25, 45.27, 52.33, 52.57, 72.19,
105.83, 114.77 (d, J = 21.7 Hz), 121.74, 129.72 (d,
J = 8.0 Hz), 136.66 (d, J = 3.1 Hz), 150.17, 157.09,
158.43, 161.76 (d, J = 247.1 Hz) ppm; MS (APCI) m/z
(relative intensity): 384 ([MH+], 100).
27
HBr salt of 16b: mp 271–273 °C (i-PrOH + CH3CN); ½aꢀD
+28.4 (c 1.0, MeOH); IR (KBr) mmax 3402 cmꢁ1; 1H NMR
(400 MHz, CDCl3) d 1.25 (t, J = 7.3 Hz, 3H), 1.30–
1.60 (m, 5H), 2.01 (m, 1H), 2.46–2.54 (m, 2H), 2.73
(m, 1H), 2.91 (m, 1H), 2.96–3.14 (m, 4H), 3.19 (m, 2H),
3.38(m, 1H), 3.55 (m, 2H), 4.39 (s, 1H), 4.41 (m, 2H),
6.55 (s, 1H), 7.23–7.33 (m, 4H), 9.47 (m, 1H) ppm; MS
(APCI) m/z (relative intensity): 384 ([MH+ of free base],
100).
12. Harada, N.; Watanabe, M.; Kawahara, S.; Sugio, A.;
Kasai, Y.; Ichikawa, A. Tetrahedron: Asymmetry 2000, 11,
1249–1253.
1
9. Spectral data for 16: H NMR (400 MHz, CDCl3) d 1.16
(t, J = 7.0 Hz, 3H, CH3), 1.35 (br s, 1H, OH), 1.46 and