New piperidinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine derivatives as selective 5-HT1A receptor agonists with highly potent anti-ischemic effects

Article abstract of DOI:10.1016/j.bmcl.2005.04.059

A series of new piperidinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine derivatives were synthesized. Among these compounds, 4-methyl-2-(1,2,3,6- tetrahydropyridin-4-yl)pyrimidine derivative 23 (SUN N5147) exhibited sub-nanomolar affinity for 5-HT_1A receptor with 1000-fold selectivity over both dopamine D₂ and α₁-adrenergic receptors and remarkable neuroprotective activity in a transient middle cerebral artery occlusion (t-MCAO) model.

Full text of DOI:10.1016/j.bmcl.2005.04.059

Bioorganic & Medicinal Chemistry Letters 15 (2005) 2990–2993
New piperidinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine
derivatives as selective 5-HT1A receptor agonists with
highly potent anti-ischemic effects
Katsuhide Kamei,a,* Noriko Maeda,a Ryoko Katsuragi-Ogino,a Makoto Koyama,a
Mika Nakajima,a Toshio Tatsuoka,b Tomochika Ohnoa and Teruyoshi Inoueb
aDaiichi Suntory Biomedical Research Co., Ltd, 1-1-1, Wakayamadai, Shimamoto-cho, Mishima-gun, Osaka 618-8513, Japan
bDaiichi Suntory Pharma Co., Ltd, Mori Bldg. No. 31, 5-7-2, Kojimachi, Chiyoda-ku, Tokyo 102-8530, Japan
Received 1 March 2005; accepted 22 April 2005
Abstract—A series of new piperidinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine derivatives were synthesized. Among these
compounds, 4-methyl-2-(1,2,3,6-tetrahydropyridin-4-yl)pyrimidine derivative 23 (SUN N5147) exhibited sub-nanomolar affinity
for 5-HT1A receptor with 1000-fold selectivity over both dopamine D2 and a1-adrenergic receptors and remarkable neuroprotective
activity in a transient middle cerebral artery occlusion (t-MCAO) model.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Acute ischemic stroke is one of the major causes of
death. Many pharmacological treatments by means of
so-called neuroprotective drugs such as glutamate recep-
tor antagonists and Ca and/or Na channel blockers have
been tried; however, they have not been successful in
improving clinical outcome in patients.1 Recently, cere-
bral serotonergic neuron has been suggested to be
involved in cerebral ischemic conditions. Serotonin
(5-HT) and its receptors are known to play important
roles in various physiological and pathophysiological
processes.2 The 5-HT1A receptor, which is one of numer-
ous 5-HT receptor subtypes, has been generally accepted
to have a role in psychiatric disorders such as depres-
sion, anxiety, and psychosis.3 It has also been reported
that 5-HT1A receptor agonists have protective effects
in cerebral ischemic conditions,4–6 due to hyperpolariza-
tion of cell membrane and glutamate release inhibition.7
Figure 1. Buspirone and 4-(4-aminobutyl)-3-chloro-1,4-benzoxazepin-
5(4H)-one derivatives.
prolactin stimulation and extrapyramidal symptoms.9
In the treatment of cerebral ischemia, it is also consid-
ered that a selective affinity for the 5-HT1A receptor over
a1-adrenergic receptor is very important because a1-ad-
renergic receptor antagonists cause hypotensive effects
and worsen clinical states.
Buspirone (Fig. 1) is a well-known 5-HT1A receptor ago-
nist and it has been useful in the treatment of anxiety
and depression.8 This compound, however, shows a
poor selectivity for 5-HT1A receptor versus dopamine
D2 receptor and causes undesirable side effects such as
The alignment of primary sequences of 5-HT1A, dopa-
mine D2, and a1-adrenergic receptors show a high
degree of homology in the transmembrane regions of
G-protein coupled receptors (GPCRs).10 Biogenic amine
receptors, which are the rhodopsin family of GPCRs,
share a comparable transmembrane structure formed
by a highly organized heptahelical transmembrane
bundle.11 As a consequence, it is difficult to discover a
*
Corresponding author. Tel.: +81 75 962 8194; fax: +81 75 962
6448; e-mail: Katsuhide_Kamei@dsup.co.jp
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.04.059

K. Kamei et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2990–2993
2991
selective 5-HT1A receptor agonist over dopamine D2 and
a1-adrenergic receptors and many researchers around
the world have been working on this issue.12–14 We have
also reported 1,4-benzoxazepine (1,4-BZO) derivatives
which are selective 5-HT1A receptor agonists with potent
anti-ischemic effects.15 In order to improve affinity and
selectivity for the 5-HT1A receptor, we have attempted
to modify amine moiety of 1,4-BZO derivatives. In the
present report, we describe the synthesis of novel pipe-
ridinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine
derivatives and their favorable binding profiles. Their
neuroprotective effects in an in vivo transient middle
cerebral artery occlusion (t-MCAO) model are also
presented.
oxychloride and the subsequent deprotection with TFA.
A piperidine compound 8 was derived by hydrogenation
in the presence of Pd/C from 5 and deprotection with
TFA. 3-(2-Pyrimidinyl)-1,2,5,6-tetrahydropyridine
9
and 3-(2-pyrimidinyl)piperidine 10, which are regio-iso-
mers of 6 and 8, were synthesized as the same way above
from 3-piperidone instead of 4-piperidone. Reaction
yields of alkylation of 3-piperidone with 2-stannylpyrim-
idine 2 and dehydration were lower than expected.
Later during our study, we successfully made an
improvement in the synthesis of 4-(2-pyrimidinyl)-
1,2,3,6-tetrahydropyridine 6 via 2-(4-pyridinyl)pyrimi-
dine 13a (route B). Isonicotinonitrile 11 was converted
to isonicotinamidine hydrochloride 12 by condensation
with 1,1,3,3-tetramethoxypropane to give 2-(4-pyridi-
nyl)pyrimidine 13a.17 Compound 13a was regio-selec-
tively alkylated with benzylchloride, giving quaternary
ammonium derivative 14a quantitatively. 1,2,3,6-Tetra-
hydro-4-(2-pyrimidinyl)piperidine 6 was obtained in
high yield by the reduction of 14a with NaBH4 and
the subsequent deprotection by 1-chloroethyl chlorofor-
mate. We were also able to synthesize of 4-(4-methylpyr-
imidin-2-yl)-1,2,3,6-tetrahydropyridine 16 in good yield
in the same way. Compounds 18–23 were prepared from
3-chloro-4-(4-chlorobutyl)-1,4-benzoxazepin-5(4H)-one
1718 by amination with the corresponding amines.19
2. Chemistry
Pyrimidine derivatives were prepared by the pathway
shown in Scheme 1. Tin–lithium exchange at the 2-posi-
tion of pyrimidine at ꢀ78 ꢁC resulted in 2-lithiopyrimi-
dine,16 and subsequent alkylation with N-Boc-4-
piperidone gave N-Boc-4-hydroxy-4-(2-pyrimidinyl)pi-
peridine 3 in moderate yield. 4-Hydroxy-4-(2-pyrimidi-
nyl)piperidine 4 was obtained by the deprotection of 3
with TFA. 4-(2-Pyrimidinyl)-1,2,3,6-tetrahydropyridine
6 was synthesized by dehydration of 3 with phosphorus
Scheme 1. Reagents and conditions: (a) n-Bu3SnLi, THF, ꢀ78 ꢁC to rt; (b) (i) n-BuLi, THF, ꢀ78 ꢁC; (ii) N-Boc-4-piperidone, THF, ꢀ78 ꢁC to rt; (c)
(i) TFA, CH2Cl2; (ii) NaOH aq; (d) POCl3, pyridine; (e) H2, 10% Pd/C, EtOH; (f) (i) n-BuLi, THF, ꢀ78 ꢁC; (ii) N-Boc-3-piperidone, THF, ꢀ78 ꢁC to
rt; (g) (i) cat. NaOMe, MeOH; (ii) NH4Cl; (h) 1,1,3,3-tetramethoxypropane or acetylacetaldehyde dimethyl acetal, 1,4-dioxane, reflux; (i) BnCl,
CH3CN, reflux; (j) NaBH4, EtOH; (k) (i) ClCOOCH(Cl)CH3, 1,2-dichloroethane, reflux; (ii) MeOH, reflux; (l) amine (HNRR0), NaI, Et3N, CH3CN,
reflux.

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K. Kamei et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2990–2993
3. Results and discussion
(IC50 ratio = 4124) and a1-adrenergic (IC50 ratio = 1324)
receptors.
Compounds 18–23 were evaluated for their binding affin-
ity to 5-HT1A, dopamine D2 and a1-adrenergic receptor
by radioligand binding assays (Table 1). The specific
ligands and tissue sources used were as follows: (a)
5-HT1A serotonergic receptor: [3H]8-OH-DPAT (8-hy-
droxy-2-(N,N-di-n-propylamino)tetralin), rat hippocam-
pus membranes; (b) dopamine D2 receptor: [3H]
raclopride, rat striatum membranes; (c) a1-adrenergic
receptor: [3H]prazosin, rat cerebral cortex membranes.
We investigated in vivo neuroprotective effects of 19, 23,
and Buspirone in a rat model of transient focal cerebral
ischemia. Using the intraluminal suture method of Koiz-
umi et al.,20 male Wistar rats were subjected to a t-
MCAO. The evaluated compounds and vehicle (saline)
were administered at a dose of 1 mg/kg sc immediately
after the occlusion. Three days after reperfusion, seven
coronary brain sections were prepared from rats sub-
jected to ischemia. Coronal sections were stained with
physiological saline including 0.2% 2,3,5-triphenyltet-
razolium chloride. After staining, sections were analyzed
for total area and cerebral infarction area and the cere-
bral infarction volume ratio was calculated.21 Com-
pound 23 exhibited a highly potent anti-ischemic effect
(73% inhibition) (Fig. 2). Compound 19 and Buspirone
also showed potent activities (65% and 53% inhibition,
respectively).
While alcohol derivative 18 showed a very weak affinity
for 5-HT1A receptor, tetrahydropyridine derivative 19
and its piperidine derivative 20 displayed higher 5-
HT1A receptor affinity and selectivity over both dopa-
mine D2 and a1-adrenergic receptors. IC50 ratios of both
19 and 20 were improved from the previous reported15
piperazine derivative 24 and 25. Compounds 21 and
22, which are regio-isomers of 19 and 20, showed re-
duced 5-HT1A receptor affinity. Compound 23 bearing
methyl group at the 4-position of pyrimidine moiety of
19 exhibited the highest affinity (IC50 = 0.185 nM) and
selectivity for 5-HT1A receptor over dopamine D2
All the tested compounds reduced the ischemic hyper-
thermia at the neuroprotective dose (about 2 ꢁC). It is
known that 5-HT1A agonists possess a hypothermic
Table 1. Structures and the receptor binding data of pyrimidine derivatives
Compound
NRR0
IC50 (nM)
IC50 ratio
5-HT1A
2650
D2
a1
D2/5-HT1A
—
a1/5-HT1A
18b
19b
20b
21c
22c
23c
24c,d
NTa
9560
3.6
1.38
5.81
494
1800
893
NTa
763
51
924
2000
384
NTa
245
43
358
310
11
670
344
4.8
79.6
314
—
—
0.185
0.770
4124
66
1324
56
25c,d
1.59
11.0
199
55
544
125
5.0
342
265
Buspirone
2920
a Not tested.
b Hydrochloride.
c Fumarate.
d Ref. 15.

K. Kamei et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2990–2993
2993
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Figure 2. Effect of 23 on cerebral infarction in rats subjected to
transient focal ischemia (60 min middle cerebral artery occlusion).
Compound 23 (1 mg/kg) was administered sc immediately after
occlusion of the MCA. Each datum represents mean SEM. n = 5;
*p < 0.05, versus saline (unpaired t-test).
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effect.22 In order to investigate a hypothermic effect in
this model, we evaluated 4-dimethylaminoantipyrine,
which is an antipyretic drug, at a dose of 200 mg/kg ip
immediately after t-MCAO. Although it caused hypo-
thermia to the same degree as 19 and 23, it showed no
anti-ischemic effect (21% inhibition). These results indi-
cate that pharmacological effect for 5-HT1A receptor
agonist is involved in the mechanism of neuroprotective
effect of 19 and 23.
´
´
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In conclusion, we presented the synthesis and biological
evaluation of pyrimidine derivatives. 1,2,3,6-Tetrahyd-
ropyridinyl-pyrimidine derivatives 19 and 23 show not
only highly potent affinity for 5-HT1A receptor but good
selectivity over dopamine D2 and a1-adrenergic recep-
tors. Since 4-methyl-2-(1,2,3,6-tetrahydropyridin-4-
yl)pyrimidine derivative 23 (SUN N5147) exhibited the
highest 5-HT1A receptor affinity with 1000-fold selectiv-
ity over both dopamine D2 and a1-adrenergic receptors
and remarkable neuroprotective activity in a t-MCAO
model, it might be more suitable as a therapeutic agent
for ischemic neuronal damage. Further investigations of
pharmacological profile of 23 are in progress.
18. Kamei, K.; Maeda, N.; Tatsuoka, T. Tetrahedron Lett.
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19. All compounds were fully characterized by spectral
methods. Representative data of compound 23 (fumarate);
colorless solid; mp 121–124 ꢁC; 1H NMR (400 MHz,
DMSO-d6): d 1.65–1.73 (m, 4H), 2.46 (s, 3H), 2.48–2.57
(m, 4H), 2.73–2.80 (m, 2H), 2.95–3.40 (m, 2H), 3.80–3.88
(m, 2H), 6.63 (s, 2H), 7.09 (s, 1H), 7.15–7.17 (m, 1H), 7.25
(d, 1H, J = 5 Hz), 7.34 (t, 1H, J = 8 Hz), 7.58–7.62 (m,
1H), 7.78–7.80 (m, 1H), 8.63 (d, 1H, J = 5 Hz); IR (KBr)
cmꢀ1: 3424, 2940, 2582, 1655, 1578, 1454, 1372, 1330,
1249; FAB-MS m/z: 425 [MH]+. Anal. Calcd for
C27H29ClN4O6: C, 59.94; H, 5.40; N, 10.36. Found: C,
60.05; H, 5.28; N, 10.23.
20. Koizumi, J.; Yoshida, Y.; Nakagawa, T.; Oneda, G. Jpn.
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21. Cerebral infarction volume ratio (%) = (sum of cerebral
infarction area of five sections · 2 mm/sum of total area of
five sections · 2 mm) · 100; saline: 14.669 1.706; com-
pound 23: 4.002 2.937. Inhibition 73%.
Acknowledgments
We wish to thank Dr. Y. Hayashi for useful suggestions
for the binding assays. Thanks are also due to Dr. H.
Annoura for his encouragement throughout this work
and Mr. T. Toba for helpful advice during the prepara-
tion of the manuscript.
References and notes
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