Synthesis and circular dichroism of optically active 1,3-disubstituted isochromans of dopamine D4 antagonist activity

Article abstract of DOI:10.1016/j.tetasy.2010.08.006

The C-1 epimers of the 3-methyl-6,7-dimethoxy analogues of the D ₄ antagonist sonepiprazole 1b and 5-HT_1D agonist PNU-109291 1a containing both the isochroman and p-methoxyphenylpiperazine chromophores were prepared in order to study

Full text of DOI:10.1016/j.tetasy.2010.08.006

Tetrahedron: Asymmetry 21 (2010) 2356–2360
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis and circular dichroism of optically active 1,3-disubstituted
isochromans of dopamine D4 antagonist activity
Gábor Kerti a, Tibor Kurtán a, , Katalin E. Kövér b, Sándor Sólyom c, István Greiner d, Sándor Antus a,e
⇑
a Department of Organic Chemistry, University of Debrecen, PO Box 20, H-4010 Debrecen, Hungary
b Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4010 Debrecen, Hungary
c IVAX Drug Research Institute Ltd, H-1323 Budapest, Hungary
d Richter Gedeon Nyrt., P.O. Box 27, H-1475, Budapest 10, Hungary
e Research Group for Carbohydrates of the Hungarian Academy of Sciences, PO Box 55, 4010 Debrecen, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 July 2010
Accepted 11 August 2010
The C-1 epimers of the 3-methyl-6,7-dimethoxy analogues of the D4 antagonist sonepiprazole 1b and 5-
HT1D agonist PNU-109291 1a containing both the isochroman and p-methoxyphenylpiperazine chro-
mophores were prepared in order to study the applicability of circular dichroism for the assignment of
the configuration of 1,3-disubstituted isochromans and test their dopamine D4 antagonist activity.
Ó 2010 Elsevier Ltd. All rights reserved.
Dedicated to Prof. András Lipták on the
occasion of his 75th birthday
5
8
4
1. Introduction
R1
R2
6
3
2
O
There are several synthetic optically active isochroman deriva-
tives reported with remarkable pharmacological activities, such as
selective 5-HT1D agonist,1 D1 agonist2 and D4 antagonist3, which
are promising for the treatment of migraines, Parkinson’s disease
and schizophrenia, respectively. Moreover, it has been shown that
the absolute configurations of these isochroman derivatives play a
decisive role in their pharmacological activities; the (S)-enantiomer
of the 5-HT1D agonist 1a (PNU-109291)1a and the selective D4 antag-
onist sonepiprazole 1b (U-101387)3 possessed a superior affinity for
the binding site compared to the (R)-enantiomer, while the (1R,3S)-
enantiomer of 2 (A68930) is almost exclusively responsible for the
observed selective D1 agonist activity of the racemate (Chart 1).2a
In spite of the apparent importance of chirality in these deriva-
tives, there is no direct and general method for the assignment of
the configuration of the isochroman skeleton available which can
1
7
N
N
R2
OMe
SO2NH2
R1
CONHMe
H
1
a
b
OH
HO
O
NH2 HCl
be used on
lg quantity of a non-crystalline derivative. Thus, so
far X-ray diffraction2c,3 and analogous techniques1a,2a have been
applied to determine the absolute configurations of optically active
isochromans. Herein, we outline a general method for the configu-
rational assignment of 1,3-disubstituted isochromans that exploits
the combination of heteronuclear couplings constants or NOE ef-
fect and CD data.
(1R,3S)-2 (A68930)
Chart 1. Structures of pharmacologically active synthetic isochromans.
configurations of the epimeric isochroman derivatives were stud-
ied by the measurements of their heteronuclear coupling constants
and CD spectra. The activities of the prepared isochromans were
tested on dopamine D4 receptors in radio ligand binding assays.
In a simple sequence, both C-1 epimers of the 3-methyl-6,7-
dimethoxy analogues of the 5-HT1D agonist PNU-109291 1a
containing both isochroman and p-methoxyphenylpiperazine
chromophores were prepared and the relative and absolute
2. Results and discussion
In order to study the chiroptical properties of pharmacologically
active 1,3-disubstituted isochromans of potential pharmacological
⇑
Corresponding author. Tel.: +36 52 512 900 22466; fax: +36 52 512 744.
E-mail address: kurtant@tigris.klte.hu (T. Kurtán).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.08.006

G. Kerti et al. / Tetrahedron: Asymmetry 21 (2010) 2356–2360
2357
absolute configuration. The three-bond carbon–proton coupling
constants also confirmed that the C-1 ethoxycarbonyl substituent
of (1S,3S)-4a has an axial orientation and the half-chair conforma-
tion of the hetero ring is not distorted to relieve the 1,3-diaxial
interaction. In contrast, the small 3JC3,1H value (<2 Hz) of (1R,3S)-5a
and the NOE effect between the axial 1-H and 3-H protons
allowed its assignment as cis, that is, (1R,3S). The absolute configu-
rations of the isochroman derivatives have recently been studied by
circular dichroism and a correlation was established between the
helicity of the hetero ring and the 1Lb band Cotton effect (CE),7
which was used to determine the absolute configurations of 3-
substituted isochroman natural products, pseudoanguillosporins
A and B.8
According to this correlation, the P-helicity (Scheme 2) of the
hetero ring results in a positive 1Lb band CE regardless of the nat-
ure(s) and position(s) of the substituent(s) on the aromatic ring. In
both (1S,3S)-4a and (1R,3S)-5a, the hetero rings adopt a P-helicity
with equatorial 3-methyl group, as indicated in Scheme 2 and in
agreement with the rule, their 1Lb band CEs are positive at about
280 nm (Table 1). In contrast, below 250 nm, the CD spectra of
the epimers were markedly different reflecting their different C-1
absolute configurations.
Since the absolute configuration of C-3 was known in 4a and 5a,
the determination of the relative configuration gave the absolute
configuration of C-1, making the CD analysis redundant. However,
for the 1,3-disubstituted isochromans of unknown absolute config-
uration, the sign of the 1Lb CE allows us to determine the helicity of
the hetero ring which in combination with the relative configura-
tion deduced from heteronuclear coupling constants and/or NOE
effects, gives the absolute configuration. For 1-monosubstituted
isochromans, only the helicity of the heteroring can be determined
from the sign of the measured 1Lb CE, which also gives the absolute
configuration of C-1.
H
H3CO
H3CO
OH
(S)-3
EtO
OEt
TMSOTf/
dry MeCN
OEt
O
H3CO
H3CO
CH3
O
H3CO
H3CO
CH3
+
O
R
R
(1S,3S)-4a-d
(1R,3S)-5a-d
4,5
R
a
b
c
d
COOEt
i
COOH
N
N
OCH3
ii
A =
COA
iii
CH2A
Scheme 1. Reagents: (i) LiOH, THF; (ii) 4-methoxyphenylpiperazine, EDC, dry
CH2Cl2; (iii) BH3, THF.
activity, (1S,3S)-4d and (1R,3S)-5d analogues of the 5-HT1D agonist
1a were synthesized (Scheme 1).
This was achieved by an oxa-Pictet–Spengler cyclization4 of the
optically active secondary alcohol (+)-(S)-3, readily available from
the bioreduction of the corresponding ketone,5 with ethyl-3,3-
diethoxypropionate in the presence of trimethylsilyl triflate
(TMSOTf), which resulted in a 1:2 mixture of epimers (1S,3S)-4a
and (1R,3S)-5a, which were subsequently separated by column
chromatography. The inherent (S)-C-3 stereogenic centre allowed
the assignment of the configuration at C-1 by means of the hetero-
nuclear coupling constants and an NOE effect, since it was not ef-
fected during the ring closure. The three-bond carbon–proton
The isochroman epimers (1S,3S)-4a and (1R,3S)-5a served as
starting materials for a three-step synthesis of isochroman deriva-
tives (1S,3S)-4d and (1R,3S)-5d possessing potential dopaminergic
activity (Scheme 1).
Esters (1S,3S)-4a and (1R,3S)-5a were hydrolysed to the corre-
sponding carboxylic acids (1S,3S)-4b and (1R,3S)-5b by lithium
hydroxide in THF in high yield (93–95%). Similar to the ester pre-
cursors, the carboxylic acid derivatives (1S,3S)-4b and (1R,3S)-5b
also had positive 1Lb CE around 280 nm (Fig. 1) in accordance with
the P-helicity of their hetero ring. Coupling with 4-methoxyphen-
ylpiperazine provided the amides (1S,3S)-4c and (1R,3S)-5c, which
in contrast to the ester derivatives, had near mirror image CD spec-
tra in the region 350–180 nm (Fig. 2). It is evident that with the
introduction of the methoxyphenylpiperazine moiety, the relative
orientation of the two aryl chromophores, that is, the absolute con-
figuration of C-1, determines the CD spectra, which overrides the
contribution from the helicity of the isochroman ring.
coupling constants of (1S,3S)-4a (3JC3,1H = 6.0 Hz; JC1,3H = 1–2 Hz)
3
and the absence of an NOE effect6 between its 1-H and 3-H protons
proved the trans relative configuration and hence the (1S,3S)-4a
H
H
R
3
3
H
Me
Me
1
1H
R
4
4
O
O
2
2
ωC-8,C-8a,C-1,O > 0
ωC-8,C-8a,C-1,O > 0
The reduction of the amides with borane in THF resulted in
(1S,3S)-4d and (1R,3S)-5d with 75% and 85% overall yields, respec-
tively. For (1S,3S)-4d and (1R,3S)-5d, similar three-bond heteronu-
clear NMR coupling constants were measured as for (1S,3S)-4a and
P-helicity
P-helicity
Scheme 2. Preferred P-helicity conformations of the fused heteroring in (1S,3S)-4a–d
and (1R,3S)-5a–d with axial and equatorial C-1 substituents, respectively.
Table 1
CD data of isochromans (1S,3S)-4a–d and (1R,3S)-5a–d in acetonitrile
Compound
CD: kmax (nm) (De)
(1S,3S)-4a
(1R,3S)-5a
(1S,3S)-4b
(1R,3S)-5b
(1S,3S)-4c
(1R,3S)-5c
(1S,3S)-4d
(1R,3S)-5d
290sh (+0.50), 281 (+0.62), 274sh (+0.47), 228 (+4.00), 223sh (+3.94), 210 (+4.35)
288sh (+0.22), 283 (+0.30), 241 (ꢀ0.91), 229 (+0.40), 220 (ꢀ0.23), 205 (+15.95)
290sh (+0.67), 286sh (+0.83), 281 (+0.86), 227 (+5.96), 211sh (+5.61), 196 (ꢀ7.28)
289 (+0.20), 284sh (+0.18), 277sh (+0.13), 241 (ꢀ1.03), 229 (+0.09), 220 (ꢀ0.78), 201 (+19.31), 193 (ꢀ6.09)
313sh (+0.04), 304 (+0.06), 289sh (ꢀ0.19), 285 (ꢀ0.26), 230 (+5.53), 206 (ꢀ11.70), positive below 198 nm
315sh (ꢀ0.03), 309 (ꢀ0.04), 292sh (+0.78), 282 (+1.08), 242 (ꢀ0.67), 227sh (+1.19), 207 (+25.68), 195 (ꢀ15.77)
288 (+0.82), 282 (+0.89), 232 (+7.28), 213 (ꢀ2.88), 199 (+6.35)
288 (+0.07), 240 (ꢀ2.72), 206.5 (+9.25), 196 (ꢀ4.80)

2358
G. Kerti et al. / Tetrahedron: Asymmetry 21 (2010) 2356–2360
Table 2
Results of the biochemical assays of the compounds tested
Compound Concent ration
M)
Inhibition (%)
(l
Dopamine
D4,2
Dopamine
D4,4
Dopamine
D4,7
4a
5a
4c
5c
4d
10
10
10
10
10
10
0
ꢀ1
1
3
1
46
6
3
ꢀ2
ꢀ1
6
4
66
34
being stored when awaiting the assay. According to the literature
data, the (1R)-sonepiprazole 1b has an inferior D4 antagonist activ-
ity compared to its (1S)-enantiomer. The conformationally more ri-
gid amides (1S,3S)-4c had practically no activity on the tested
dopamine D4 receptors and the 4a and 5a precursors did not show
either activity (Scheme 3).
Figure 1. CD spectra of (1S,3S)-4b (dashed line) and (1R,3S)-5b (solid line) in
acetonitrile with the 1Lb region enlarged.
4. Conclusion
(1R,3S)-5a, respectively, which confirmed that the large axial C-1
substituent of (1S,3S)-4d did not distort the half-chair conforma-
tion of the hetero ring and thus the compounds in both series 4
and 5 have P-helicity (Scheme 1, Scheme 2, Fig. 2).
Both C-1 epimers of the 3-methyl-6,7-dimethoxy analogues of
the 5-HT1D agonist PNU-109291 were prepared in order to study
the applicability of the isochroman helicity rule in the 1,3-disubsti-
tuted isochromans and in the presence of a remote aryl chromo-
phore. Their absolute configurations and the conformations of
their hetero ring were determined by means of their three-bond
heteronuclear coupling constants. Although the p-methoxyphenyl
group is separated by several single bonds from the C-1 stereogen-
ic centre, their 1Lb band CE does not follow the isochroman helicity
rule and the absolute configuration of the C-1 stereogenic centre
determines the CD spectra. However, the near mirror image CEs
below 250 nm are indicative of the C-1 absolute configuration of
the epimers and can be used for the configurational assignment
of C-1 in analogous compounds. Pharmacological studies revealed
that (1S,3S)-4d showed moderate non-selective antagonist activity
on dopamines D4,2, D4,4, D4,7. It was also demonstrated that the
isochroman helicity rule can be safely used for the configurational
assignment of 1,3-disubstituted isochromans such as (1S,3S)-4a,b
and (1R,3S)-5a,b; i.e. in the absence of an interacting C-1 aromatic
substituent.
With the amide carbonyl group reduced as in (1S,3S)-4d and
(1R,3S)-5d, the C-1 side-chain became more flexible leading to
multiple conformations and hence significantly different 1Lb CE in
(1S,3S)-4d and (1R,3S)-5d as a result of the interaction of the isoch-
roman chromophore and the p-methoxyphenyl group. Although
both of them had positive CE in the 1Lb region, which apparently
follows the isochroman helicity rule, it cannot be applied due to
the aforementioned consideration. A CD calculation of the epimers
(1S,3S)-4d and (1R,3S)-5d would be highly demanding considering
the large conformational freedom of the C-1 substituent.
3. Pharmacological study
The activity of the prepared compounds were tested on dopa-
mine D4,2, D4,4, D4,7 receptors with radio ligand binding assays
using human recombinant CHO-K1 cells and spiperone and
haloperidol as reference compounds (Scheme 3).9 Compound
(1S,3S)-4d showed 66% inhibition with a dopamine D4,2 receptor
at 10
dopamine D4,4
l
M concentration and smaller inhibition activities with
D4,7 receptors (Table 2). Unfortunately, the
,
(1R,3S)-5d could not be tested, since it partially decomposed while
O
NH
O
N
N
F
spiperone
OH
O
N
Cl
F
haloperidol
Figure 2. CD spectra of (1S,3S)-4c (dashed line) and (1R,3S)-5c (solid line) in
acetonitrile with the 250–350 nm region enlarged.
Scheme 3. Structure of the reference compounds spiperone and haloperidol.

G. Kerti et al. / Tetrahedron: Asymmetry 21 (2010) 2356–2360
2359
5.2. General procedure for the preparation of 5b, 4b
5. Experimental
5.1. General
5.2.1. (+)-[(1R,3S)-6,7-Dimethoxy-3-methyl-3,4-dihydro-1H-
isochromen-1-yl]acetic acid 5b
To a solution of 5a (50 mg, 0.17 mmol) in THF (5 ml), an aque-
ous solution of lithium hydroxide (0.3 M, 2.2 ml) was added and
the mixture was stirred at room temperature for 18 h. The volatiles
were then removed in vacuo and the residue was acidified with
1 M HCl. The resulting cloudy mixture was extracted with CH2Cl2
(3 ꢁ 15 ml) and the combined organic layer was washed with
brine, dried (Na2SO4), filtered and concentrated. The residue was
purified by preparative TLC (toluene/acetic acid 9:1) to give 5b
(43 mg, 95%). The product was crystallized (from CH2Cl2/hexane
Melting points were determined on a Kofler hot-stage appara-
tus and are uncorrected. Elemental analysis was measured with a
Carlo-Elba analyser Tpy 1106. The NMR spectra were recorded on
a Bruker-AMX 500 (1H: 500 MHz; 13C: 125 MHz) Bruker WP 200
SY (1H: 200 MHz) spectrometer using TMS as an internal standard.
Chemical shifts were reported in ppm. Optical rotation was deter-
mined with a Perkin–Elmer 241 polarimeter. CD spectra were
recorded on a J-810 spectropolarimeter. The CD spectra were mea-
sured in millidegrees and normalized into
D
emax (l molꢀ1 cmꢀ1)/k
1:10): mp 119–121 °C; ½a D20
ꢂ
¼ þ117:5 (c 1.28, CH2Cl2); 1H NMR
(nm) units. In the UV spectra, the red shift of the tweezer Soret band
indicated that complexation took place. IR spectra were recorded on
a Perkin Elmer 16 PC FTIR spectrometer and absorption bands pre-
(500 MHz, CDCl3) d 1.35 (d, J = 6.2 Hz, 3H, CH3), 2.59 [dd, J = 15.7,
2.2 Hz, 1H, CH2a(CO)],), 2.70 (dd, J = 15.7, 11.4 Hz, 4-CH2a), 2.76
[dd, J = 15.7, 8.5 Hz, 1H, CH2b(CO)], 3.00 (dd, J = 15.7, 3.6 Hz, 4-
CH2b), 3.81–3.88 (m, 7H, 3-H, 2 ꢁ OCH3), 5.16 (dd, J = 8.5, 3.3 Hz,
1H, 1-H), 6,55 (s, 1H, Ar-H), 6.58 (s, 1H, Ar-H); 13C NMR
(125 MHz, CDCl3) d 21.62 (CH3), [36.23 (CH2(CO)], 42.28 (C-4),
56.49 (OCH3), 71.60 (C-3), 73.59 (C-1), 107.62 (C-Ar), 112.10
(C-Ar), 126.71, 127.87 (C-8a, C-5a), 143.97 (C-7), 148.13 (C-6),
sented in cmꢀ1. Precoated silica gel plates (Kieselgel 60 F254
,
0.25 mm, Merck) were used for analytical and preparative TLC.
High resolution FAB mass spectra were measured on a JEOL JMS-
DX303 HF mass spectrometer using a glycerol matrix and Xe
ionizing gas.
3
3
175.69 (CO), JC3,1H = 2.0 Hz, JC1,3H = 1–2 Hz; IR (KBr): 2972,
2934, 2836, 1740, 1316, 1252, 1104 cmꢀ1
Anal. Calcd for
14H18O5: C, 63.15; H, 6.81. Found: C, 63.03; H, 6.83.
5.1.1. (+)-Ethyl-[(1S,3S)-6,7-dimethoxy-3-methyl-3,4-dihydro-
1H-isochromen-1-yl]acetate 4a and (+)-ethyl-[(1R,3S)-6,7-
dimethoxy-3-methyl-3,4-dihydro-1H-isochromen-1-yl]acetate 5a
.
C
Trimethylsilyl triflate (50 ll) was added to a mixture of 3
5.2.2. (+)-[(1S,3S)-6,7-Dimethoxy-3-methyl-3,4-dihydro-1H-
isochromen-1-yl]acetic acid 4b
(300 mg, 1.53 mmol) and ethyl-(3,3-diethoxy)propionate (0.44 ml,
2.28 mmol) in acetonitrile (10 ml). The reaction mixture was
heated at a gentle reflux for 30 min. The mixture was washed with
NaHCO3 solution (15 ml) and extracted with CH2Cl2 (3 ꢁ 15 ml),
dried (Na2SO4), filtered and concentrated in vacuo to give 568 mg
of a colourless oil, which contained two components (5a:4a) in a
ratio of 5:3, separated by column chromatography (hexane/ethyl
acetate 4:1). Eluted first was 5a (225.3 mg, 50%), which was then
Solid (93%). The product was crystallized from hexane: mp 135–
136 °C; ½a 2D0
ꢂ
¼ þ21:1 (c 0.88, CH2Cl2); 1H NMR (500 MHz, CDCl3) d
1.32 (d, J = 6.2 Hz, 3H, CH3), 2.62 [m, 2H, CH2(CO)], 2.77 (d,
J = 14.5 Hz, 4-CH2a), 2.76 (m, 1H, 4-CH2b), 3.84 (s, 3H, OCH3),
3.85 (s, 1H, OCH3), 4.08 (m, 1H, 3-H), 5.32 (d, J = 8.5, Hz, 1H, 1-
H), 6,53 (s, 1H, Ar-H), 6.58 (s, 1H, Ar-H); 13C NMR (125 MHz, CDCl3)
d 21.29 (CH3), 35.40 [CH2(CO)], 38.22 (C-4), 56.49 (OCH3), 65.28
(C-3), 72.10 (C-1), 108.11 (C-Ar), 111.77 (C-Ar), 125.88, 128.20
(C-8a, C-5a), 148.08, 148.53 (C-6, C-7), 170.05 (CO), 3JC3,1H = 6.0 Hz,
3JC1,3H = 1–2 Hz; IR (KBr): 3160, 2966, 2926, 2832, 1714, 1294,
1250, 1108 cmꢀ1. Anal. Calcd for C14H18O5: C, 63.15; H, 6.81.
Found: C, 63.08; H, 6.80.
crystallized from hexane: mp 92–94 °C; ½a D20
¼ þ108:2 (c 1.27,
ꢂ
CHCl3); 1H NMR (500 MHz, CDCl3) d 1.29 (t, J = 7.5 Hz, 3H, CH2–
CH3), 1.30 (d, J = 6.0 Hz, 3H, CH–CH3), 2.56 (dd, J = 13.9, 2.0 Hz,
1H, 4-Hb), 2.67–2.70 (m, 2H, H-4a, 1’-Hb), 2.89 (dd, J = 15.0,
4.0 Hz, 1H, 1’-Ha), 3.76–3.83 (m, 1H, 3-H), 3.83 (s, 3H, OCH3),
3.85 (s, 3H, OCH3), 4.21 (q, J = 7.5 Hz, 2H, CH2–CH3), 5.17 (m, 1H,
1-H), 6.55 (s, 1H, Ar-H), 6.57(s, 1H, Ar-H); 13C NMR (125 MHz,
CDCl3) d 14.20 (CH2–CH3), 21.55 (CH–CH3), 35.96 (C-1’), 42.18 (C-
4), 55.84 (OCH3), 55.96 (OCH3), 60.51 (CH2–CH3), 70.62 (C-3),
73.54 (C-1), 107.18 [CH,(Ar)], 111.45 [CH,(Ar)], 126.57 (C-5a),
128.65 (C-8a), 147.20 (C-6), 147.78 (C-7), 171.50 (CO).
5.3. General procedure for the preparation of 4c, 5c
5.3.1. (+)-1-{[(1S,3S)-6,7-Dimethoxy-3-methyl-3,4-dihydro-1H-
isochromen-1-yl]acetyl}-4-(4-methoxyphenyl) piperazine 4c
To a cooled (0 °C) solution of 4b (22 mg, 0.08 mmol) and
N-(p-methoxyphenyl)piperazine (20.6 mg, 0.11 mmol) in dichloro-
methane (5 ml), EDC (47.5 mg, 0.25 mmol) and N,N-dimethylami-
nopyridine (5 mg, 0.04 mmol) were added. The reaction mixture
was allowed to warm to ambient temperature and it was stirred
for further 2 h. The reaction mixture was concentrated in vacuo,
suspended in water (5 ml) and then extracted with CH2Cl2
(3 ꢁ 15 ml). The combined organic layer was dried (Na2SO4), fil-
tered and concentrated. The residue was purified by preparative
TLC (toluene/acetic acid 8:1) to give 4c (35 mg, 96%) as a reddish
3
3JC3,1H = 2.0 Hz, JC1,3H = 1–2 Hz; IR (KBr): 2990, 2968, 2832, 1734,
1248, 1234 cmꢀ1. Anal. Calcd for C16H22O5: C, 65.29; H, 7.53.
Found: C, 65.43; H, 7.50.
Eluted second was 4a (140.7 mg, 31%), which was crystallized
from hexane: mp 98–101 °C; ½a D20
ꢂ
¼ þ30:2 (c 1.25, CHCl3); 1H
NMR (500 MHz, CDCl3) d 1.26–1.33 (m, 6H, CH–CH3, CH2–CH3),
2.58–2.62 (m, 2H, 4-H), 2.69 [dd, J = 14.5, 4.0 Hz, 1H, CH2a(CO)],
2.90 [dd, J = 15.0, 10.5 Hz, 1H, CH2b(CO)], 3.83 (s, 3H, OCH3), 3.85
(s, 3H, OCH3), 4.05 (m, 1H, 3-H), 4.23 (m, 2H, CH2–CH3), 5.30 (m,
1H, 1-H), 6.53 (s, 1H, Ar-H), 6.57 (s, 1H, Ar-H); 13C NMR
oil: ½a 2D0
ꢂ
¼ þ6:4 (c 1.35, CHCl3); 1H NMR (200 MHz, CDCl3) d 1.30
(125 MHz, CDCl3)
d 14.27 (CH2–CH3), 21.24 (CH–CH3), 35.26
(d, J = 6.0 Hz, 3H, CH3), 2.72 [dt, J = 16.0, 3.5 Hz, 2H, CH2(CO)],
3.11 [overlapped, 4H, 2 ꢁ N–CH2(CO)], 3.12 [overlapped, 2H, N–
CH2(Ar)], 3.65–3.67 [m, 2H, N–CH2(Ar)], 3.74 (s, 3H, OMe), 3.80
(s, 3H, OCH3), 3.82 (s, 3H, OCH3), 3.87–3.92 (m, 2H, 4-H), 3.97–
4.02 (m, 1H, 3-H), 5.39–5.40 (m, 1H, 1-H), 6.56 (s, 1H, Ar-H), 6.65
(s, 1H, Ar-H), 6.85 (d, J = 9.0 Hz, 2H, Ar-H), 6.91 (d, J = 9.0 Hz, 2H,
Ar-H); 13C NMR (125 MHz, CDCl3) d 21.00 (CH3), 35.15 [CH2(CO)],
39.73 [N–CH2(CO)], 41.91 (C-4), 46.10 [N–CH2(CO)], 50.85 [N–
CH2(Ar)], 51.47 [N–CH2(Ar)], 55.45 (OCH3), 55.79 (OCH3), 55.94
(OCH3), 64.90 (C-3), 72.02 (C-1), 108.02 (C-5), 111.09 (C-8),
[CH2(CO)], 41.79 (C-4), 55.86 (OCH3), 55.96 (OCH3), 60.63 (CH2–
CH3), 64.33 (C-3), 71.98 (C-1), 107.86 [CH,(Ar)], 111.42 [CH,(Ar)],
125.50 (C-5a), 128.17 (C-8a), 146.50 (C-7), 147.20 (C-6), 171.12
3
3
(CO). JC3,1H = 6.0 Hz, JC1,3H = 1–2 Hz; IR (KBr): 2972, 2932, 2836,
1732, 1278, 1252, 1230, 1106 cmꢀ1. Anal. Calcd for C16H22O5: C,
65.29; H, 7.53. Found: C, 65.26; H, 7.52.

2360
G. Kerti et al. / Tetrahedron: Asymmetry 21 (2010) 2356–2360
114.42 (C-Ar), 118.89 (C-Ar), 125.09 (C-5a), 128.45 (C-8a), 145.00
(C-6), 147.45 (C-7), 147.75 (C-q-Ar), 154.39 (C-q-Ar), 169.70
OCH3), 3.79 (s, 3H, OCH3), 4.70 (m, 1H, 1-H), 6.48 (s, 1H, Ar-H),
6.54 (s, 1H, Ar-H), 6.73–6.85 (m, 4H, Ar-H); 13C NMR (125 MHz,
CDCl3) d 22.20 (CH3), 33.60 (CH2), 36.50 (C-4), 50.70 (N–CH2),
53.70 [CH2(pip)], 54.86 [CH2(pip)(Ar)], 55.90 (OCH3), 56.30
(2 ꢁ OCH3), 70.90 (C-3), 75.50 (C-1), 107.70 (C-5), 111.71 (C-8),
114.70 (C-Ar), 118.50 (C-Ar), 127.16 (C-5a), 129.85 (C-8a), 145.40
(CO); IR (KBr): 2930, 2856, 2834, 1634, 1250, 1076 cmꢀ1
.
5.3.2. (+)-1-{[(1R,3S)-6,7-Dimethoxy-3-methyl-3,4-dihydro-1H-
isochromen-1-yl]acetyl}-4-(4-methoxy-phenyl)piperazine 5c
Reddish oil (96%): ½a D20
ꢂ
¼ þ79:5 (c 1.47, CHCl3); 1H NMR
(C-6), 147.05 (C-7), 147.81 (N–C-q-Ar), 153.42 (C-q-Ar); J1H-C3
3
(500 MHz, CDCl3) d 1.28 (d, J = 6.0 Hz, 3H, CH3), 2.62 (m, 2H,
4-H), 2.91 [overlapped, 2H, N–CH2(CO)], 3.08–3.13 [overlapped,
4H, 2 ꢁ N–CH2(Ar)], 3.64–3.66 [overlapped, 2H, CH2a(CO), 3-H],
3.67–3.68 [overlapped, 2H, N–CH2(CO)], 3.76 (s, 3H, OCH3), 3.83
(s, 3H, OCH3), 3.84 (s, 3H, OCH3), 4.08 [m, 1H, CH2b(CO)], 5.20
(m, 1H, 1-H), 6.57 (s, 1H, Ar-H), 6.69 (s, 1H, Ar-H), 6.86 (d,
J = 9.0 Hz, 2H, Ar-H), 6.92 (d, J = 9.0 Hz, 2H, Ar-H); 13C NMR
(125 MHz, CDCl3) d 21.77 (CH3), 35.99 (C-4), 40.35 [N–CH2(CO)],
41.92 [CH2(CO)], 46.44 [N–CH2(CO)], 50.90 [N–CH2(Ar)], 51.30
[N–CH2(Ar)], 55.42 (OCH3), 55.78 (OCH3), 55.94 (OCH3), 70.43 (C-
3), 74.83 (C-1), 107.33 (C-5), 111.19 (C-8), 114.39 (C-Ar), 118.87
(C-Ar), 126.12 (C-5a), 128.84 (C-8a), 145.07 (C-6), 147.41 (C, C-7),
147.64 (C-q-Ar), 154.30 (C-q-Ar), 170.38 (CO); IR (KBr): 2964,
= 2.0 Hz, 3J3H-C1 = 1–2 Hz; IR (KBr): 2930, 2830, 1248, 1104 cmꢀ1
.
6. Pharmacological assays
6.1. Radio ligand binding assays at human recombinant CHO-K1
cells (dopamine D4,2 receptor)
The incubation buffer: 50 mM Tris–HCl, pH 7.4, 1.4 mM ascorbic
acid, 0.001% BSA, 150 mM NaCl.
The samples were incubated for 2 h at 25 °C. Ligand: 0.5 nM
[3H] spiperone, vehicle: 1% DMSO, Non-specific ligand: 10
lM
haloperidol, KD: 0.32 nM, Bmax: 0.55 pmol/mg protein, specifics
binding: 90%.
2832, 1634, 1248, 1104 cmꢀ1
.
6.2. Radio ligand binding assays at human recombinant CHO-K1
cells (dopamine D4,4 receptor)
5.4. General procedure for the preparation of 4d, 5d
5.4.1. (+)-1-{2-[(1S,3S)-6,7-Dimethoxy-3-methyl-3,4-dihydro-
1H-isochromen-1-yl]ethyl}-4-(4-methoxyphenyl)piperazine 4d
A solution of 4c (40 mg, 0.09 mmol) in THF (15 ml) was cooled to
0 °C and treated with a 1 M solution of borane in THF (0.27 ml,
0.27 mmol). The cooling bath was removed and the mixture heated
at reflux for 4 h. Then a 1 M solution of borane in THF (0.1 ml,
0.1 mmol) was added to the mixture, which was then heated at re-
flux for an additional 3 h. The reaction was then cooled to 0 °C and
slowly quenched with aqueous 1 M HCl (1.05 ml) and refluxed for
an additional 1.5 h. The solution was cooled to room temperature
and the volatiles were removed in vacuo. The resulting aqueous res-
idue was diluted with brine and the pH was set to 14 with aqueous
NaOH, followed by extraction with CH2Cl2 (3 ꢁ 15 ml). The com-
bined organic layer was washed with brine, dried (Na2SO4), filtered
and concentrated in vacuo. The residue was purified by preparative
TLC (toluene/acetic acid 2:1) to give 4d (33.2 mg, 86%), which was
The incubation buffer: 50 mM Tris–HCl, pH 7.4, 1.4 mM ascorbic
acid, 0.001% BSA, 150 mM NaCl.
The samples were incubated for 2 h at 25 °C. Ligand: 1.2 nM
[3H] spiperone, vehicle: 1% DMSO, non-specific ligand: 10
lM
haloperidol, KD: 0.46 nM, Bmax: 0.63 pmol/mg protein, specifics
binding: 85%.
6.3. Radio ligand binding assays at human recombinant CHO-K1
cells (dopamine D4,7 receptor)
The incubation buffer: 50 mM Tris–HCl, pH 7.4, 1.4 mM ascorbic
acid, 0.001% BSA, 150 mM NaCl.
The samples were incubated for 2 h at 25 °C. Ligand: 1.5 nM
[3H] spiperone, vehicle: 1% DMSO, non-specific ligand: 10
lM
haloperidol, KD: 0.48 nM, Bmax: 0.77 pmol/mg protein, specifics
binding: 85%.
crystallized from hexane: mp 123–124 °C; ½a D20
¼ þ14:9 (c 0.11,
ꢂ
CHCl3); 1H NMR (500 MHz, CDCl3) d 1.34 (d, J = 6.2 Hz, 3H, CH3),
1.90 (m, 1H, CH2a), 2.14 (m, 1H, CH2b), 2.60 (dd, J = 16.0, 9.7 Hz,
2H, 4-H), 2.67 [overlapped, 3H, CH2(pip)(Ar), N–CH2a], 2.68 (over-
lapped, 1H, N–CH2b), 2.69 [overlapped, 2H, CH2(pip)], 2.70 [over-
lapped, 2H, CH2(pip)(Ar)], 3.13 [overlapped, 2H, CH2(pip)], 3.70 (s,
3H, OCH3), 3.78 (s, 6H, 2 ꢁ OCH3), 4.04–4.07 (m, 1H, 3-H), 4.86
(dd, J = 10.7, 2.5 Hz, 1H, 1-H), 6.56 (s, 1H, Ar-H), 6.59 (s, 1H, Ar-H),
6.86 (d, J = 9.1 Hz, 2H, Ar-H), 6.93 (d, J = 9.1 Hz, 2H, Ar-H); 13C
NMR (125 MHz, CDCl3) d 21.38 (CH3), 33.34 (CH2), 35.46 (C-4),
50.62 [CH2(pip)], 53.55 [CH2(pip)(Ar)], 55.57 (OCH3), 55.77 (N–
CH2), 55.89 (OCH3), 56.02 (OCH3), 63.71 (C-3), 73.44 (C-1), 108.24
(C-5), 111.41 (C-8), 114.46 (C-Ar), 118.18 (C-Ar), 125.29 (C-5a),
129.81 (C-8a), 145.73 (C-7), 147.43 (C-6), 147.68 (N-C-q-Ar),
Acknowledgements
Antus, S., Kurtán, T., Kövér, K. E., Kerti G. thank the National Of-
fice for Research and Technology, Hungarian Scientific Research
Fund (NKTH, K-68429, OTKA, K-81701), János Bolyai Foundation
and Ferenc Deák Fellowship for the financial support.
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3
3
153.82 (C-q-Ar), JC3,1H = 4.9 Hz, JC1,3H = 1–2 Hz; IR (KBr): 2940,
2820, 1246, 1106 cmꢀ1. Anal. Calcd for C25H34N2O4: C, 70.39; H,
8.03; N, 6.57. Found: C, 70.32; H, 8.06; N, 6.58.
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1H-isochromen-1-yl]ethyl}-4-(4-methoxyphenyl)piperazine 5d
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Oil (87%): ½a 2D0
ꢂ
¼ þ67:1 (c 0.54, CHCl3); 1H NMR (500 MHz, CDCl3)
d 1.15 (d, J = 6.1 Hz, 3H, CH3), 2.00 (m, 1H, CH2a), 2.23 (overlapped,
1H, CH2b), 2.56 (overlapped, 1H, 4-Ha), 2.59 [overlapped, 2H, CH2(pi-
p)(Ar)], 2.63 (overlapped, 1H, 4-Hb), 2.67 [overlapped, 2H, CH2(pi-
p)(Ar)], 2.70 [overlapped, 4H, 2 ꢁ CH2(pip)], 3.15 (overlapped, 2H,
N–CH2), 3.39 (overlapped, 1H, 3-H), 3.62 (s, 3H, OCH3), 3.77 (s, 3H,
}
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