Novel 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methylbenzofuran derivatives as selective α2C-adrenergic receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2006.12.094

The synthesis of a series of 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methyl-2-arylbenzofuran and 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methylbenzofuran-2-carboxamide derivatives as novel α_2C-adrenergic receptor antagonists are described. Their affinity at three different human α₂-adrenergic receptors is reported, and some of these compounds exhibited high affinity for the α_2C-adrenergic receptor with high subtype selectivity. Among them, compound 10e has been found to show the anti-l-dopa-induced dyskinetic activity in marmosets. The structure-activity relationship of these compounds is also discussed.

Full text of DOI:10.1016/j.bmcl.2006.12.094

Bioorganic & Medicinal Chemistry Letters 17 (2007) 1616–1621
Novel 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-
yl)methylbenzofuran derivatives as selective
a2C-adrenergic receptor antagonists
Koji Hagihara,*, Hajime Kashima, Kyoichiro Iida, Junichi Enokizono, Shin-ichi Uchida,
Hiromi Nonaka,à Masako Kurokawa and Junichi Shimada
Pharmaceutical Research Center, Kyowa Hakko Kogyo Co., Ltd, 1188 Shimotogari, Nagaizumi-cho,
Sunto-gun, Shizuoka 411-8731, Japan
Received 29 September 2006; revised 18 December 2006; accepted 25 December 2006
Available online 25 January 2007
Abstract—The synthesis of a series of 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methyl-2-arylbenzofuran and 4-(6,7-di-
methoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methylbenzofuran-2-carboxamide derivatives as novel a2C-adrenergic receptor antago-
nists are described. Their affinity at three different human a2-adrenergic receptors is reported, and some of these compounds
exhibited high affinity for the a2C-adrenergic receptor with high subtype selectivity. Among them, compound 10e has been found
to show the anti-L-dopa-induced dyskinetic activity in marmosets. The structure–activity relationship of these compounds is also
discussed.
Ó 2007 Elsevier Ltd. All rights reserved.
Adrenergic receptors (ARs) are membrane proteins
belonging to the superfamily of G-protein-coupled
receptors and are pharmacologically classified into a1-,
a2-, and b-ARs.1 In particular, a2-ARs are further sub-
divided into a2A, a2B, and a2C subtypes, encoded by dif-
ferent genes in different species.2 This knowledge has led
to a search for selective ligands for each subtype.
ization or even lifetime nursing home care.3–5 There
are no pharmaceutical agents presently approved for
the treatment of dyskinesia.
Idazoxan (1) and yohinbine (2) are known to be potent
and selective a2-AR antagonists. Henry et al. reported
that idazoxan (1) and yohinbine (2) reduced L-dopa-in-
duced dyskinesia in the MPTP-treated marmoset model
of PD. Furthermore, they described that coadministra-
tion of idazoxan (1) with L-dopa can provide an anti-
parkinsonian action more than twice the length of that
seen with L-dopa alone.6 Besides idazoxan (1) and
yohinbine (2), a potent a2-AR antagonist fipamezole
(JP-1730) was recently reported to reduce L-dopa-in-
duced dyskinesia in the MPTP-treated marmoset model
of PD.7 On the other hand, according to studies using
the knockout mouse of each subtype of a2-AR, it was
supposed that a2A- and a2B-AR may participate in low-
ering and raising of blood pressure, respectively, howev-
er, a2C-AR probably does not take part in the regulation
of blood pressure.8 Based on the above facts, we
assumed that selective a2-AR antagonists would be
anti-dyskinetic and anti-parkinsonian agents with a little
influence to the cardiovascular system.
Parkinson’s disease (PD) is the second most common
progressive neurological disorder resulting from the
degeneration of nerve cells (neurons) in a region of the
brain that controls movement. It has been reported that
within 5 years of beginning treatment with the L-3,4-di-
hydroxyphenylalanine (L-dopa), 40–80% of patients
develop dyskinesia, a severely disabling condition with
chaotic and uncontrollable movements of limbs, face,
and mouth, that often necessitates long-term hospital-
Keywords: a2-Adrenergic receptor; Anti-dyskinesia; Antagonist;
Benzofuran.
*
Corresponding author. Tel.: +81 72 223 5583; fax: +81 72 221
0410; e-mail: koji.hagihara@kyowa.co.jp
Present address: Sakai Research Laboratories, Pharmaceutical
Research Center, Kyowa Hakko Kogyo Co., Ltd, 1-1-53 Takasu-
cho Sakai-ku, Sakai-city, Osaka 590-8554, Japan.
à
The discovery of a novel series of triazolopyrimidines (e.g.
3) as a2C-AR antagonists and their structure–activity
Present address: Drug Discovery, Fuence Co., Ltd, W207 RIKEN,
2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.12.094

K. Hagihara et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1616–1621
1617
relationship (SAR) were recently reported.9 During the
SAR studies, it was revealed that 6,7-dimethoxy-tetrahy-
droisoquinoline (6,7-DMTHIQ) structure is important to
represent high a2C-AR affinity and subtype selectivity.
However, subtype selectivity of 3, one of the optimized
compounds, was insufficient.
OMe
OH
OMe
OH
OMe
OH
b
c
a
P+Ph3Br-
5
OH
CHO
Br
Br
e
Br
6
6a (C-5)
6b (C-6)
7a (C-5)
7b (C-6)
5a (C-5)
5b (C-6)
OMe
O
OMe
O
OMe
O
d
Ar
Ar
Ar
5
R3R4N
Br
OHC
4
HCl
9a (C-5)
9b (C-6)
8a (C-5)
8b (C-6)
10a-m, r, s (C-4)
11(C-5)
HN
H
N
O
O
N
N H
H
H
OH
MeO2C
Scheme 1. Reagents and conditions: (a) NaBH4, MeOH, rt; (b) Ph3P,
aq. HBr, CH3CN, reflux; (c) ArCOCl, Et3N, toluene, reflux; (d)
n-BuLi, THF, ꢀ90 °C, then DMF; (e) NaBH(OAc)3, R3R4NH,
(CH2Cl)2, rt.
Idazoxan (1)
Yohinbine (2)
OMe
NH2
N
O
O
MeO
MeO
N
N
R1
N
N
OMe
OMe
R2
N
4
3
OMe
OH
OMe
OMe
CN
CN
a
b
c
O
O
CHO
12
CHO
In the drug design approach, replacement of the core
scaffold of a known active to another one is known as
one of effective techniques to find new active
chemotypes. We therefore focused our attention to the
structural homology between triazolopyrimidine and
other ring systems. With the aim of further enhancing
subtype selectivity, we decided to replace the core struc-
ture to the benzofuran scaffold which was thought to be
easier to introduce functional groups at various positions
and make several types of benzofuran analogs which
have 6,7-DMTHIQ. We herein describe the synthesis of
4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)meth-
yl-2-arylbenzofuran, 4-(6,7-dimethoxy-1,2,3,4-tetrahydro-
isoquinolin-2-yl)methylbenzofuran-2-carboxamide, and
13
14
OMe
OMe
CN
CO2H
d
e
O
O
OMe
OMe
OMe
OMe
N
N
10n
15
O
NR5R6
OMe
O
OMe
OMe
N
10o-q
their regioisomers (4), and the SAR study as novel a2C
-
Scheme 2. Reagents and conditions: (a) K2CO3, KI, 3-(bromomethyl)-
benzonitrile, DMF, reflux; (b) MFA, (Cl2PO)2O, rt; (c) NaBH(OAc)3,
6,7-DMTHIQ, (CH2Cl)2, rt; (d) 5 mol/L aq. NaOH, (CH2OH)2,
150 °C; (e) R5R6NH, EDCI, HOBt, DMF, rt.
AR selective antagonists (see Table 1).10
The target compounds were synthesized as shown in
Schemes 1–6. 4- or 5-Aminomethyl-2-arylbenzofuran
derivatives 10a–m, r, s and 11 were synthesized as shown
in Scheme 1. 2-Arylbenzofurans 8a and b were derived
from commercially available bromosalicyl-aldehydes
5a and b by known literature procedures, respectively.11
Halogen-metal exchange was accomplished by treat-
ment of 8 with butyllithium at ꢀ90 °C, and obtained
Ar–Li species were quenched quickly with DMF at
ꢀ90 °C to suppress generation of regioisomers of 9.12
Reductive amination of a formyl group with 6,7-
DMTHIQ gave target compounds 10a–m and 11,
respectively. Compounds 10r and s were also synthe-
sized by a similar method as above using 1,2,3,4-tetrahy-
droisoquinoline or 4-phenylpiperadine, respectively.
OMe
OH
OMe
OH
OMe
OMe
OH
b
c
O
a
OH
P+Ph3Br-
CHO
18
16
17
12
OMe
OMe
OHC
MeO
MeO
O
O
e
d
N
19
20
Scheme 3. Reagents and conditions: (a) NaBH4, MeOH, rt; (b) Ph3P,
aq. HBr, CH3CN, reflux; (c) PhCOCl, Et3N, toluene, reflux; (d) TiCl4,
Cl2CHOCH3, CH2Cl2, ꢀ20 °C to rt; (e) NaBH(OAc)3, 6,7-DMTHIQ,
(CH2Cl)2, rt.
Compounds 10n–q were prepared as shown in Scheme 2.
O-Alkylation of ortho-vanillin 12 followed by intra-mo-
lecular cyclizaion in basic condition gave cyano-phen-
ylbenzofuran 13 at one effort. Formylation using
N-methylformanilide (MFA) and (Cl2PO)2O13 proceed-
ed regioselectively to give 14. Other formylation
conditions, such as using DMF-POCl3,13 ðCH3ÞSþS
Table 1. Binding activity of a2C-AR antagonists
Compound
Binding affinity
(Ki, nM)a,b
a2A
a2B
a2C
Idazoxan (1)
Yohinbine (2)
3
8
100
15
19
1.9
19
1.8
400
ðCH3ÞBF4ꢀ-ðPhSÞ CH,14
TFA–hexamethylene-tetr-
370
3
amine (HMT),15 and TiCl4-Cl2CHOCH3,16 were not
effective due to low regioselectivity and low yield.
a The assay protocol is described in Ref. 18.
b Values are means of at least two independent assays.

1618
OMe
K. Hagihara et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1616–1621
Table 2. Binding affinity of 2-arylbenzofuran derivatives
OMe
OMe
O
NR5R6
O
O
O
O
O
c
a.b
OMe
O
OMe
OH
Ar
CHO
OMe
OMe
N
22
N
21
OMe
OMe
N
OMe
OMe
10
23a-g
b
Compound
Ar
Binding affinity (Ki, nM)a,b
OMe
OMe
OMe
a2A
a2B
a2C
O
O
O
O
O
O
d
e
O
10a
204
160
8.0
OH
HN
HN
23h, i
NMe2
NMe2
CHO
CHO
R3R4N
24
25
N
Scheme 4. Reagents and conditions: (a) 6,7-DMTHIQ, NaBH(OAc)3,
(CH2Cl)2, rt; (b) aq. NaOH, MeOH–H2O, rt; (c) R5R6NH, EDCI,
HOBt, DMF or CHCl3, rt; (d) Me2NCH2CH2NH2, EDCI, HOBt,
DMF, rt; (e) R3R4NH, NaBH(OAc)3, (CH2Cl)2, rt.
10b
10c
10d
10e
10f
10g
10h
10i
135
330
9.6
NTd
NTd
1742
11%c
2552
NTd
857
NTd
NTd
752
62%c
35%c
20
N
OMe
OH
OMe
OMe
OH
N
a
b
O
O
OH
OHC
CHO
OHC
OHC
c, d
27
28
26
OMe
MeO
MeO
O
O
N
MeO
Me
HN
20%c
804
54%c
19
N
29
Me
Scheme 5. Reagents and conditions: (a) HMT, TFA, reflux; (b)
Cs2CO3, BrCH2CO2Et, DMF, reflux; (c) Me2NCH2CH2NH2, EDCI,
HOBt, DMF, rt; (d) 6,7-DMTHIQ, NaBH(OAc)3, (CH2Cl)2, rt.
OMe
NTd
299
56%c
11
OMe
OMe
OMe
OMe
OHC
O
O
O
O
O
O
a
b
F
OMe
OMe
OMe
CHO
c
Me
Me
21
30
31
F
10j
3%c
13%c
NTd
949
52%c
41%c
18
OMe
OMe
MeO
MeO
OHC
O
O
O
O
d, e
N
Me
HN
OH
NTd
304
N
10k
10l
Me
F
Me
Me
33
32
Scheme 6. Reagents and conditions: (a) H2, Pd(OH)2/C, EtOH, rt; (b)
TiCl4, Cl2CHOCH3, CH2Cl2, ꢀ20 °C to rt; (c) aq. NaOH, MeOH–
H2O, rt; (d) Me2NCH2CH2NH2, EDCI, HOBt, DMF, rt; (e) 6,7-
DMTHIQ, NaBH(OAc)3, (CH2Cl)2, rt.
F3C
10m
10n
10o
10p
10q
NTd
NTd
NTd
29%c
216
NTd
NTd
NTd
31%c
584
18%c
42%c
48%c
54%c
9.4
CF3
Reductive amination with 6,7-DMTHIQ and hydrolysis
of a cyano group afforded carboxylic acid 15, which was
transferred to amides 10o–q by the standard peptide
coupling method (EDCI and HOBt).
CN
O
NH
Me
NH
OH
NH
NMe2
6-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)-
methyl-2-arylbenzofuran 20 was synthesized as shown in
Scheme 3. Formylation of 18, which was derived from
ortho-vanillin 12, gave a mixture of 3-, 4-, and 6-for-
myl-2-phenylbenzofurans. Compound 19 was isolated
from the mixture by silica gel column chromatography
and gave 20 by same method described in Scheme 1.
O
O
a The assay protocol is described in Ref. 18.
Scheme 4 shows the preparation of various 4-amin-
omethylbenzofuran-2-carboxamide derivatives. Reduc-
tive amination of 2117 with 6,7-DMTHIQ and
following hydrolysis of the ester group afforded carbox-
b Values are means of at least two independent assays.
c %Inhibition at 0.1 lM (n = 2).
d Not tested.

K. Hagihara et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1616–1621
1619
Table 3. Binding affinity of benzofuran-2-carboxamide derivatives
ylic acid 22, which was converted to amides 23a–g.
Amidation of 24, derived by hydrolysis of ester 21, with
N,N-dimethylethylenediamine using EDCI and HOBt
proceeded cleanly to give 25 without affecting a formyl
group. Reductive amination of the formyl group affor-
ded 23h and i.
OMe
O
O
NR5R6
OMe
N
23
OMe
Compound
NR5R6
Binding affinity (Ki, nM)a,b
5-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)-
methylbenzofuran-2-carboxamide derivative 29 was
synthesized as illustrated in Scheme 5. Formylation of
vanillin 26 using HMT–TFA15 gave dialdehyde 27 in
moderate yield. The benzofuran scaffold was synthesized
by using ethyl bromoacetate and cesium carbonate in
DMF to afford 28. Compound 29 was derived from 28
by a similar manner as that described above.
a2A
a2B
a2C
Me
N
H
23a
NTc
NTc
20%d
OH
N
H
23b
23c
23d
23e
23f
23g
NTc
NTc
454
141
42
NTc
NTc
2068
1535
857
6%d
9%d
9.4
NHAc
NMe2
N
H
Introduction of 6,7-DMTHIQ at the C-6 position was
performed as illustrated in Scheme 6. C-4 Position of
the benzofuran scaffold was blocked by a methyl group
to introduce a formyl group regioseletively. The formyl
group was introduced at ortho-position of the methoxy
group to afford 31, which was transferred by the same
method as that shown in Scheme 4 to give the target
compound 33. All substances we prepared were charac-
N
H
H
N
4.2
NH2
N
1
0.8
terized by H NMR and mass spectroscopy.
N
H
[3H]MK-912 binding experiments were conducted using
membranes from human hepatoma cells HepG2. In
addition, in order to determine the selectivity over the
other a2 receptor subtypes, [3H]MK-912 binding exper-
iments using membranes from human colon cells HT-
29 expressing the a2A receptors and COS-7 cells trans-
fected with the human a2B receptors were performed.18
The a2-AR affinity data of the benzofuran derivatives
are shown in Tables 2–6.
186
1364
3.5
N
N
a The assay protocol is described in Ref. 18.
b Values are means of at least two independent assays.
c Not tested.
d %Inhibition at 0.1 lM (n = 2).
Table 4. Binding inhibitory activity of benzofuran derivatives
OMe
O
We initially examined the effect of replacement from
the triazolopyrimidine to the benzofuran (Table 2).
Compound 10a showed a slight increase in potency
(a2C-AR Ki = 7.7 nM) and retained a2-subtype selectivi-
ty compared to those of the original compound 3.
2-(Pyridyl)benzofuran 10b retained a2C-AR affinity
and subtype selectivity. Other 2-pyridyl derivatives 10c
and d exhibited reduced affinity for a2C-AR. 2-Phenyl
derivative 10e exhibited substantial improvement in sub-
type selectivity. Encouraged by these results, we investi-
gated the effect of substituents on the phenyl ring of 10e.
Introduction of a meta-methoxy group (10g) was accom-
panied by an increase in subtype selectivity for a2A-AR
affinity, whereas introduction of a methoxy group at the
ortho- or para-position (10f and h) resulted in reduction
of the activity for a2C-AR. On the other hand, the ortho-
fluorophenyl (10i) and ortho-CF3 (10l) groups were both
effective comparing with the corresponding meta- or
para-substitution in terms of potency. The meta-cyano
group (10n) also reduced a2C-AR affinity. Among the
meta-amide groups (10o–q), only N-[2-(N,N-dimethyla-
mino)ethyl]amide (10q) was found to retain a2C-AR
affinity and subtype selectivity.
R3R4N
Compound
R3R4N
Inhibition % at 0.1 lMa,b
a2A
a2B
a2C
N
10r
30
51
54
10s
NTc
NTc
29
N
N
a The assay protocol is described in Ref. 18.
b Values are means of at least two independent assays.
c Not tested.
The results of 10o–q prompted us to design less complex
benzofuran derivatives in which an amide moiety is at-
tached to the C-2 position directly. We therefore synthe-
sized a set of benzofuran-2-carboxamide derivatives
having a similar side chain as those of 10o–q. The bind-
ing affinity for these compounds is shown in Table 3.
Compounds 23a–c exhibited significant loss of potency
for a2C-AR, however, 23d showed high affinity. These
results were parallel to those of compounds 10o–q.
Compounds with various diamino side chains 23e–g also
showed the potent affinity; especially, compound 23f
having a quinuclidinyl group showed the potent activity
However, we found it interesting that the activity of
those derivatives with meta-amide groups (10o–q) varied
depending on the substituents.

1620
K. Hagihara et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1616–1621
Table 5. Binding inhibitory activity of benzofuran derivatives
In vivo activity of the compounds 10e and 23d
against L-dopa-induced dyskinesia in MPTP-treated
common marmosets, previously primed by exposure
to L-dopa to exhibit dyskinesia, was assessed.19 Com-
pound 10e showed potent anti-L-dopa-induced dyski-
netic activity (2.5 mg/kg, po) without influence to
the cardiovascular system. However, significant activ-
ity was not observed in the case of compound 23d
(30 mg/kg, po). The PK study of 10e and 23d by cas-
sette dosing in marmosets (at 2.5 mg/kg each) re-
vealed that AUC of 23d (144 ng h/mL) was low in
comparison with that of 10e (11 ng h/mL).20 Low
intestinal absorption of 23d due to the presence of
two basic nitrogen atoms would be one of the rea-
sons for low anti-L-dopa-induced dyskinetic activity
of 23d. We are estimating that selective a2C-AR
antagonists will have therapeutic potential for the
treatment of L-dopa-induced dyskinesia. Detailed
pharmacological properties of these compounds will
be reported elsewhere.
OMe
O
O
Me
HN
N
R3R4N
Me
Compound
R3R4N
Inhibition % at 0.1 lMa,b
a2A
a2B
a2C
23h
88
51
94
N
23i
80
33
68
N
N
a The assay protocol is described in Ref. 18.
b Values are means of at least two independent assays.
Table 6. Binding inhibitory activity of benzofuran derivatives
OMe
O
MeO
MeO
6
5
R1
N
R2
In conclusion, a novel class of a2C-AR antagonists has
been identified by exploration of the benzofuran deriva-
tives by replacement of core structure. 2-Arylbenzofuran
derivatives and benzofuran-2-carboxamide derivatives
were shown to have potent a2C-AR affinity. Compound
10e exhibited anti-L-dopa-induced dyskinetic activity in
the MPTP-treated marmoset model.
Compound R1
R2
Positiona
Inhibition % at
0.1 lMb,c
a2A
a2B
a2C
11
20
H
5
6
5
6
NTd NTd 19
NTd NTd 39
NTd NTd 41
H
Acknowledgments
O
NMe2
NMe2
29
H
We express our gratitude to Ms. Naomi Yomoda and
Ms. Mayumi Ono for their excellent technical assis-
tance. We are grateful to Dr. Hitoshi Arai for his accu-
rate suggestions and valuable discussions. We also thank
Kyoko Tsutsumi for measuring MS spectra.
N
H
O
33
Me
20
15
65
N
H
a Substituted position on benzofuran.
b The assay protocol is described in Ref. 18.
c Values are means of at least two independent assays.
d Not tested.
Supplementary data
Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.bmcl.2006.12.094.
against a2C-AR (Ki = 0.8 nM). Subtype selectivity was
obviously different to that of 2-arylbenzofurans.
References and notes
Next, we examined the effect of the 6,7-DMTHIQ moi-
ety on the potency and subtype selectivity (Tables 4, 5).
Compound 10r retained potency against a2C-AR. How-
ever, subtype selectivity was lower than that of the 6,
7-DMTHIQ derivative 10e. Replacement with 1-phenyl-
piperazinyl (10s) showed a loss of potency. Compounds
23h and i showed potent activity against a2C-AR, how-
ever, subtype selectivity of these compounds was low.
Therefore, it was verified that the 6,7-DMTHIQ group
is important to show high subtype selectivity as well as
potency against a2C-AR. Furthermore, we examined
the substitution pattern of the 6,7-DMTHIQ moiety.
Substitution of the moiety at the C-5 or C-6 position
was not effective to exhibit high activity against
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18. a2-AR binding was evaluated in in vitro assay to define
their affinity at the three subtypes. Cell membrane was
prepared from HepG2, which is a human hepatoma cell
line and has been reported that only the a2C receptor
subtype among three a2 receptor subtypes is expressed, a
human colon cell line HT-29 expressing the a2A receptors,
and COS-7 cells transfected with the human a2B receptors,
according to description by Schaak et al.21 Competition
assays were started by mixing 1 nmol/L [3H]MK-912 with
or without test compounds and the perspective mem-
branes (50 lg for a2A, 1 lg for a2B, and 100–150 lg for
a2C), in assay buffer [50 mmol/L Tris–HCl (pH 7.5),
7. Savola, J.-M.; Hill, M.; Engstrom, M.; Merivuori, H.;
Wurster, S.; McGuire, S. G.; Fox, S. H.; Crossman, A. R.;
Brotchie, J. M. Mov. Dissord. 2003, 18, 872.
8. MacDonald, E.; Kobilka, B. K.; Scheinin, M. Trends
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9. Kashima, H.; Uesaka, N.; Suzuki, T.; Nonaka, H.;
Enokizono, J.; Uchida, S.; Kanda, T.; Ushiki. J.; Shiozaki,
S.; Shimada, J. Abstracts of Papers, The Japanese Phar-
maceutical Society, 25th Medicinal Chemistry Sympo-
sium, November 29–December 1, 2006, Nagoya.
0.5 mmol/L MgCl2]. The assays were incubated at 25 °C
for 30 min and terminated by filtration through Whatman
GF/C filters under reduced pressure using a MT-24 cell
harvester. Filters were washed three times with ice-cold
assay buffer and placed in scintillation vials. Bound
radioactivity was determined using a liquid scintillation
counter, Packard TRI-CARB 4530. Non-specific binding
was assessed in the presence of 1 lmol/L phentolamine for
a2A and 10 lmol/L yohimbin for a2B and a2C adrenergic
receptors.
10. Hagihara, K.; Kashima, H.; Iida, K.; Otsubo, N.; Nonaka,
H.; Enokizono, J.; Uchida, S.; Kurokawa, M.; Kanda, T.;
Arai, H.; Shimada, J. Abstracts of Papers, The Japanese
Pharmaceutical Society, 25th Medicinal Chemistry Sym-
posium, November 29–December 1, 2006, Nagoya.
11. (a) Corre, M.; Hercouet, A. Tetrahedron 1981, 37, 2855;
(b) Corre, M.; Hercouet, A. Tetrahedron 1981, 37, 2861;
(c) Corre, M.; Hercouet, A. Tetrahedron 1981, 37, 2866.
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19. Pearce, R. K.; Jackson, M.; Smith, L.; Jenner, P.;
Marsden, C. D. Mov. Disord. 1995, 10, 731.
20. Compounds 10e and 23d were simultaneously adminis-
tered by po route to a marmoset at a dose of 2.5 mg/kg
each. Blood samples were collected at appropriate time
points and centrifuged to obtain plasma samples. Plasma
concentrations of the both compounds were measured by
LC/MS/MS. The area under plasma concentration time
curve (AUC) was calculated by a trapezoidal method.
21. Schaak, S.; Cayla, C.; Blaise, R.; Quinchon, F.; Paris, H.
J. Pharmacol. Exp. Ther. 1997, 281, 983.