In vitro affinities of various halogenated benzamide derivatives as potential radioligands for non-invasive quantification of D2-like dopamine receptors

Article abstract of DOI:10.1016/j.bmc.2007.07.017

Benzamide derivatives as radiotracers have played an important role in diagnosing malfunction in dopaminergic neurotransmission. A variety of halogenated and two unsubstituted benzamide derivatives were synthesised and their in vitro affinities to dopaminergic, serotonergic and adrenergic receptors and their lipophilicities were determined. As references IBZM (3), raclopride (4) and FLB457 (5) were tested as well. The two iodinated compounds NAE (27) and NADE (28) displayed K_i values of 0.68 and 14 nM for the D₂ receptor. The well-established radiotracers FP (1) and DMFP (2) showed affinities in the same range as did the brominated compounds NABrE (29) and NABrDE (30). The log D_7.4 values of 2.91 for NAE (27) and of 2.81 for NADE (28) are in the range of those found for IBZM (3), FP (1) and DMFP (2). These facts allow to expect good properties for the two iodinated compounds NAE (27) and NADE (28) regarding in vivo imaging with SPECT.

Full text of DOI:10.1016/j.bmc.2007.07.017

Bioorganic & Medicinal Chemistry 15 (2007) 6819–6829
In vitro affinities of various halogenated benzamide derivatives
as potential radioligands for non-invasive quantification
of D2-like dopamine receptors
Daniela Stark,a Markus Piel,a Harald Hubner,b Peter Gmeiner,b
¨
Gerhard Grunderc and Frank Ro¨scha,*
¨
aInstitute of Nuclear Chemistry, Johannes Gutenberg-University, Fritz-Straßmann-Weg 2, D-55128 Mainz, Germany
bInstitute of Medicinal Chemistry, Friedrich-Alexander University, Schuhstrasse 19, D-91052 Erlangen, Germany
cDepartment of Psychiatry and Psychotherapy, RWTH Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany
Received 8 January 2007; revised 12 July 2007; accepted 17 July 2007
Available online 19 August 2007
Abstract—Benzamide derivatives as radiotracers have played an important role in diagnosing malfunction in dopaminergic neuro-
transmission. A variety of halogenated and two unsubstituted benzamide derivatives were synthesised and their in vitro affinities to
dopaminergic, serotonergic and adrenergic receptors and their lipophilicities were determined. As references IBZM (3), raclopride
(4) and FLB457 (5) were tested as well. The two iodinated compounds NAE (27) and NADE (28) displayed Ki values of 0.68 and
14 nM for the D2 receptor. The well-established radiotracers FP (1) and DMFP (2) showed affinities in the same range as did the
brominated compounds NABrE (29) and NABrDE (30). The logD7.4 values of 2.91 for NAE (27) and of 2.81 for NADE (28) are in
the range of those found for IBZM (3), FP (1) and DMFP (2). These facts allow to expect good properties for the two iodinated
compounds NAE (27) and NADE (28) regarding in vivo imaging with SPECT.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Especially their extraordinarily high selectivity for D2/
D3 receptors led to the development of various benzam-
ide derivatives as radioactively labelled compounds for
positron emission tomography (PET) and single photon
emission computed tomography (SPECT) (Fig. 1).2–5
Abnormalities of dopaminergic neurotransmission have
been implicated in a variety of neuropsychiatric diseases
such as Parkinson’s disease, schizophrenia and drug
abuse. Pharmaceuticals for the treatment of these condi-
tions target dopamine receptors (D1-like receptors: D1,
D5; D2-like receptors: D2, D3, D4), dopamine transport-
ers and dopamine synthesis. D2 receptor antagonists
have been used for decades for the treatment of schizo-
phrenia and related disorders. They belong to a broad
array of chemical classes such as butyrophenones (e.g.,
haloperidol), thioxanthenes (e.g., flupenthixole) and
benzamides (e.g., amisulpride). Among those, the benza-
mides stand out due to their high selectivity for D2-like
dopamine receptors, their reversibility in binding and
their high affinity.1
[11C]raclopride for PET and
[
123I]iodobenzamide
([123I]IBZM) for SPECT have been used for almost
two decades for quantification of D2/D3 receptors in a
broad range of scientific and clinical applications.6,7 Re-
cently, substituted benzamides with a fluorine-18 label
have been developed for broader clinical use, because
the fluorine-18 label offers the advantage of a longer
half-life compared to the carbon-11 label of e.g.,
[11C]raclopride. Two of the most promising compounds
are [18F]fallypride ([18F]FP) and [18F]desmethoxyfally-
pride ([18F]DMFP).8,9 However, due to their only mod-
erate affinity, most of these tracers, including
[11C]raclopride, [123I]IBZM, or [18F]DMFP, allow for
quantification of D2/D3 receptors only in brain regions
with high D2 receptor densities, like the striatum.
[18F]fallypride on the other hand, due to its very high
affinity, seems to be an ideal tracer for the study of both
striatal and extrastriatal receptors in a single PET scan.
Tracer affinity is of crucial importance for its kinetics in
Keywords: Benzamides; Dopamine receptors; In vitro affinities.
*
Corresponding author. Tel.: +49 6131 3925302; fax: +49 6131
3924692; e-mail: frank.roesch@uni-mainz.de
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.07.017

6820
D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
OMe O
OMe O
MeO
N
N
H
H
N
N
FP (1)
DMFP (2)
F
F
OMe O
OMe O
OMe O
Cl
MeO
N
N
H
N
H
H
N
N
N
OH
OH
I
Cl
Br
raclopride (4)
FLB 457 (5)
IBZM (3)
Figure 1. Structure of FP (1), DMFP (2), IBZM (3), raclopride (4) and FLB 457 (5).
brain, and tracers with very high affinity give new in-
sights into the role of extrastriatal dopamine systems
and antipsychotic drug action.9,10
sodium cyanide as catalyst. The obtained (S)-1-allyl-
pyrrolidine-2-carboxamide (8) was reduced with sodium
bis(2-methoxyethoxy)aluminium dihydride (SDMA) to
give the desired compound 9.19
A first intent was to make these favourable properties of
FP and DMFP available to SPECT. Therefore the fluoro-
propyl moiety at the 5-position of the aromatic ring was
substituted by iodine. The obtained compounds
N-allyl-epidepride (NAE, 27)11,12 and the new compound
N-allyl-desmethoxyepidepride (NADE, 28)13,14 were
tested in vitro. For the racemate of NAE (27) in vitro
binding affinities towards D2 receptors have already
been reported (KD = 0.033 nM, logP7.4 = 2.72).15
The required benzoic acid derivatives were synthesised
from their benzaldehydes or benzoic acid derivatives fol-
lowing the pathways illustrated for the dimethoxy
(Scheme 2) and monomethoxy derivatives (Scheme 3).
The benzoic acid derivatives 13, 16 and 25 are commer-
cially available. 5-Iodo-2-methoxybenzoic acid (22) was
obtained by methylation of the respective 5-iodo-2-
hydroxybenzoic acid (18) (Scheme 3).20,21 The bromine
analogue benzoic acid derivatives 14 and 23 were ob-
tained by methylation and oxidation of the respective
To investigate the influence of other halogen substituents
at the five position of the aromatic ring analogue bromine
derivatives, N-allyl-bromo-epidepride (NABrE, 29)12 and
N-allyl-bromo-desmethoxyepidepride (NABrDE, 30),13,14
chlorine derivatives, N-allyl-chloro-epidepride (NAClE,
31) and N-allyl-chloro-desmethoxyepidepride (NAClDE,
32) and the unsubstituted derivatives, N-allyl-benzamide
(NAB, 33) and N-allyl-desmethoxybenzamide (NADB,
34) were synthesised. In first pharmacological experiments
the lipophilicities and affinities of these benzamide deriva-
tives to the different dopamine receptors, serotonin and
adrenergic receptors were determined in receptor binding
assays.
aldehydes 10 and 19 (Schemes
2
and 3).20,22
5AChloro-2,3-dimethoxybenzoic acid (15) was synthes-
ised by oxidising the aldehyde derivative 11. 5-Chloro-
2-methoxybenzoic acid (24) was synthesised by
methylating 5-chloro-2-hydroxybenzoic acid (20) and
hydrolysing the ester intermediate. For the synthesis of
5-(3-hydroxypropyl)-2,3-dimethoxybenzoic acid (17)
and 5-(3-hydroxypropyl)-2-methoxybenzoic acid (26) a
procedure described by Mukherjee23 was used starting
from 3-(3,4-dimethoxyphenyl)propan-1-ol (12) and
3-(4-methoxyphenyl)propan-1-ol (21) (Schemes 2 and 3).
The benzoic acid derivatives 13–17 and 22–26 were cou-
pled with (S)-1-allyl-2-aminomethylpyrrolidine (9) via
their mixed anhydrides using ethyl chloroformiate
(Scheme 4).
2. Chemistry
The molecules 1 and 2, and 27–34 were synthesised by
reacting the respective benzoic acid derivatives 13–17
and 22–26 with (S)-1-allyl-2-aminomethylpyrrolidine
(9). 16 The pyrrolidinyl compound was prepared follow-
ing a stereo-conservative route established by Ho¨gberg
et al. (Scheme 1).17,18 In three steps, starting with the
amino acid L-proline (6), (S)-1-allyl-2-aminomethylpyrr-
olidine (9) was prepared. The alkylation of 6 with allyl
bromide was followed by ammonolysis of the so ob-
tained allyl ester, (S)-allyl-1-allylpyrrolidine-2-car-
boxylate (7), with ammonia in methanol employing
The 3-fluoropropyl derivatives 1 and 2 were synthesised
as described elsewhere (Scheme 4).23
3. Results and discussion
3.1. In vitro evaluation
3.1.1. Affinities. To determine the binding affinities of
the synthesised compounds NAE (27), NADE (28),

D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
6821
O
O
H2N
O
c
N
N
a
b
N
O
N
H2N
H
HO
6
7
8
9
Scheme 1. Synthesis of 9 according to the route established by Hoegberg et al.17,18 Reagents : (a) allyl bromide, K2CO3, DMSO; (b) NH3/methanol,
NaCN; (c) SDMA/toluene.
OMe
D2-family and the related GPCRs we established a radi-
oligand binding assay.24 Utilizing stably transfected
CHO cells expressing the human dopamine receptor
R1
R3
MeO
COOH
MeO
cond.
subtypes D2 short, D2long,
25 D326 and D4.427 and the radi-
oligand [3H]spiperone we examined the affinities to the
D2-family. Furthermore, binding to the D1 receptor
was investigated using porcine striatal membranes and
the selective radioligand [3H]SCH 23390. To get evi-
dences for the selectivity of the test compounds the affin-
R2
R2
13-17
10-12
ities to the related serotonin receptor subtypes 5-HT1A
,
Cpd. R1
R2
-
R3
Cond.
Cpd.
R2
5-HT2 and the adrenergic receptor a1 were examined
with porcine cortical membranes and the selective radio-
ligands [3H]8-OH-DPAT, [3H]ketanserin and [3H]prazo-
sin, respectively.28 The resulting Ki values are depicted in
Table 1.
-
-
-
13
14
15
16
17
I
10
11
-
OH
Br
CHO
CHO
-
a
Br
OMe Cl
b
Cl
-
-
H
12
OMe (CH2)3OH
H
c
(CH2)3OH
3.1.2. Selectivity. The figures displayed in Table 1 and
the graph in Figure 2 clearly show that the compounds
synthesised have a low affinity for the D1 receptor.
The Ki values of all tested compounds for the D1 sub-
type ranged from 10 to 40 lM (Table 1). The affinities
for compounds 1 and 2, and 27–30 are within the range
of those found for IBZM (3), raclopride (4) and FLB457
(5), which have been applied as radiotracers in research
to examine D2-like receptor related issues with PET and
SPECT. For the D1 receptor, affinities are up to 10,000-
fold lower than for the D2-like receptors and between
10- and 100-fold lower than for the serotonin and adren-
ergic receptor subtypes.
Scheme 2. Synthesis of dimethoxybenzoic acids. Reagents: (a) K2CO3,
MeI, 2-butanone; acetone, KMnO4, H2O; (b) acetone, KMnO4, H2O;
(c) n-butyllithium, THF, CO2; 13 and 16 are commercially available.
OMe
R1
R3
COOH
cond.
R2
R2
Ki values for all examined compounds for the dopami-
nergic receptor subtype D4.4, the serotonergic receptor
subtypes 5-HT1A, 5-HT2 and the adrenergic receptor
subtype a1 range from 100 nM to 4.5 lM (Fig. 2). The
halogenated compounds NAE (27), NADE (28), NAB-
rE (29), NABrDE (30) display Ki values for the 5-HT1A
receptor in the range of 140–225 nM. Ki values for the
D4.4 receptor subtype range from 210 to 1700 nM for
these compounds. Affinities for the D4 receptor subtype
are in the high nM to low lM range.
18-21
22-26
Cpd.
R1
R2
R3
Cond. Cpd.
R2
18
19
20
-
OH
OMe
OH
-
I
CHO
CHO
COOH
-
a
b
c
22
23
24
25
26
I
Br
Br
Cl
Cl
-
H
21
OMe
(CH2)3OH
H
d
(CH2)3OH
The affinities for the D2short, D2long and D3 receptor sub-
type are in the range of 0.4–35 nM for all examined
compounds (Table 1 and Fig. 2). For these three recep-
tor subtypes Ki values are up to 25,000-fold higher than
those found for the D1 receptor. Of the compounds syn-
thesised, NAE (27) and NABrE (29) show the highest
affinity for the D2short/D2long receptor with Ki values of
0.7 nM, and 0.9 nM, respectively, and for the D3 recep-
tor with Ki values of 0.5 nM and 0.6 nM, respectively.
To sum up, the results of the studies concerning the
selectivity of the benzamides it can be clearly said that
Scheme 3. Synthesis of monomethoxybenzoic acids. Reagents: (a)
MeI, NaH, DMF, LiOH, acetone, KMnO4, H2O; (b) acetone,
KMnO4, H2O; (c) NaOH, CH2Cl2, (C4H9)4NI, DMSO, NaOH; (d)
n-butyllithium, THF, CO2; 25 is commercially available.
NABrE (29), NaBrDE (30), FP (1) and DMFP (2) as
well as for the reference substances IBZM (3), raclopride
(4) and FLB 457 (5) to the receptors of the dopamine

6822
D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
O
R1
R1
MeO
MeO
COOH
+
N
N
N
cond.
H
H2N
R2
R2
13-17 and 22-26
9
1-2 and 27-34
Cpd. R1
Cond. R2
Cpd. R1
Cond. R2
27
28
29
30
31
32
33
OMe
a
a
a
a
a
a
a
I
34
35
36
1
H
a
a
b
c
a
b
c
H
H
I
OMe
OMe
OMe
H
CH2CH2CH2OH
CH2CH2CH2OTs
CH2CH2CH2F
OMe
H
Br
Br
Cl
Cl
H
OMe
H
37
38
2
CH2CH2CH2OH
CH2CH2CH2OTs
CH2CH2CH2F
H
OMe
H
Scheme 4. Synthesis of the compounds 1 and 2, and 27–34 employing chloroethyl formiate and triethylamine. Reagents: (a) ethyl chloroformiate
(C2H5)3N, 9; (b) 4-methylbenzene-1-sulfonylchloride, pyridine, CH2Cl2, 35 or 37; (c) KF, Kryptofixꢁ2.2.2, K2CO3, MeCN, 36 or 38.
Table 1. Binding affinities of the synthesised benzamide derivatives 1 and 2, 27–30, and the reference compounds 3–5 to dopaminergic, serotonergic
and adrenergic receptor subtypes (Ki values in nM)
Compound
Kia (nM SEM)
pD1
hD2short
hD2long
hD3
hD4.4
p5-HT6A
p5-HT2
pa6
[3H]SCH23990 [3H]spiperone [3H]spiperone [3H]spiperone [3H]spiperone [3H]8-HO-DPAT [3H]ketanserin [3H]prazosin
27 NAE
18,000 500
13,000 1000
0.74 0.17
15 0.50
0.88 0.12
27 2.5
0.68 0.065 0.46 0.010
14 4.0 11 1.0
0.85 0.015 0.60 0.075
250 30
630 11
210 10
150 15
170 98
140 40
490 65
1100 170
2000 150
1600 100
28 NADE
29 NABrE
30 NABrDE 17,000
2400 1200
1100 640
2100 800
3700 300
4500 50
13,000
0
0
23 1.0
2.2 0.050
30 4.0
22 2.5
1.6 0.30
33 3.6
1700 100
1300 250
3000 400
570 30
230 5.0
1100 120
2300 750
1100 50
4400 600
2200 50
2000
0
1
2
3
4
5
FP
DMFP
IBZM
18,000 2000
30,000 1500
12,000 1500
2.1 0.15
30 5.0
970 340
1900 100
1900 50
3000 100
830 95
4.2 0.75
31 2.2
1.6 0.33
4.2 0.45 4.2 0.69
17 1.7 15 1.5
0.65 0.0090 0.42 0.045
2000 900
3500 500
Raclopride 37,000
FLB457 15,000
0
0
3100 150
210 3.4
1200
0
a Ki values in nM SEM are based on the means of 2–4 experiments each done in triplicate.
all compounds display a high affinity for the D2 and D3
receptor subtypes in the low nM to high pM range.
trend can clearly be seen from the Ki values for the fluo-
rinated and iodinated compound pairs for the D2 recep-
tor (Table 1). The Ki values for the fluorinated
compounds FP (1) (two methoxy groups) and DMFP
(2) (one methoxy group) are 2.2 and 30 nM, respec-
tively. The Ki value for 1 is 13-fold lower than for 2.
The Ki values gained for the iodinated compounds
NAE (27) and NADE (28) are 0.7 and 19 nM. The affin-
ity of the compound carrying two methoxy groups, 27, is
27-fold higher than the affinity of the compound carry-
ing just one methoxy group.
The selectivity for the serotonergic system of all exam-
ined compounds represented by two subtypes is less
than for the D2-like receptors by a factor of about 10
for the 5-HT1A and by a factor of about and over 100
to the 5-HT2 receptor subtype. Looking at the adrener-
gic a1 receptor, affinities are about a factor of 100 lower
than those found for the D2-like receptors.
3.2. Structure–affinity relationship
Compounds carrying two methoxy groups (1, 27, 29)
show the best affinities for those receptor subtypes. Ki
values are 0.7, 0.9 and 2.2 nM, respectively, for both
D2 subtypes, D2short and D2long. FLB 457 (5) follows this
rule as well.
Regarding the affinities of compounds 1 and 2, 27–30
and 3–5 for the D2short/D2long and D3 receptor subtypes
some tendencies can be seen that are related to their
structure (cf. Fig. 3).
Different studies in the literature4 have shown that the
addition of a second methoxy group at the 3-position
of the aromatic ring (position A, Fig. 3) results in a
strong increase in affinity for D2-like receptors. This
Another tendency described in literature4 concerns the
change of the substituent at the nitrogen atom of the
pyrrolidinyl ring (position B, Fig. 3). Changing an ethyl
group into an allyl moiety enhances the affinity for the

D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
6823
40000
30000
20000
NAE
40
30
20
10
0
NADE
NABrE
NABrDE
FP
DMFP
IBZM
Raclopride
FLB 457
D
D
D
3
10000
5000
2long
2short
4000
3000
2000
1000
0
D2long
D3
D1
D2short
D4.4
5-HT1a 5-HT2
α1
Receptor
Figure 2. Affinities to various receptor subtypes for the synthesised benzamide derivatives (Ki in nM).
of the compounds. The difference in the Ki values is
negligible.
OMe
O
A
N
3
N
B
H
3.3. Lipophilicities
5
The lipophilicities of 1–5 and 27–34 were determined
using the HPLC method according to the OEC guideline
for the testing of chemicals.29 Soerenson buffer was used
as eluent and logD7.4 values calculated from retention
times of the respective substances.
C
Figure 3. Modification sites of the benzamide lead structure (A, 3-
position of aromatic ring; B, nitrogen of pyrrolidinyl moiety; C, 5-
position of aromatic ring).
The calculated logD7.4 values are displayed in Table 2.
All compounds examined showed logD7.4 values which
are within the range of those found for already estab-
lished radiotracers like IBZM (3), FP (1) and DMFP (2).
D2 receptor. The Ki values found for FLB 457 (5) and
for NABrE (29) to the D2short/D2long receptor (1.6/
0.65 nM and 0.9 nM) show this effect (Table 1). The
two compounds differ only in the moiety attached to
the nitrogen atom of the pyrrodinyl ring. The affinity
for D2short of 29 is almost twice as high as the affinity
of 5, to D2long the affinity of 29 is about a third lower
compared to the value for 5. From the Ki values ob-
tained for the allyl compounds 27–30 for the D2 receptor
one can conclude that the ethyl compounds 3–5 show
lower affinities than corresponding allyl compounds.
In a more general scope the difference in substitution
does not seem to have an extensive effect on the affinities
for the D2 receptor subtypes.
Table 2. Lipophilicities/logD7.4 values of synthesised benzamide
derivatives 1–5 and 27–34
Compound
Name
LogD7.4
27
28
29
30
31
32
33
34
1
NAE
2.91
2.81
2.83
2.71
n/a
NADE
NaBrE
NaBrDE
NaClE
The substitutions at the 5-position of the aromatic ring
(position C, Fig. 3) seem to exert less influence on the
binding for the D2 receptor. Looking at the influence
on the Ki values of the three different halogen atoms
directly placed at the 5-position of the aromatic ring
(iodine, bromine, chlorine and unsubstituted) no trend
can be seen. Even the 3-fluoropropane moiety at the
5-position does not have dramatic effects on the affinities
NaClDE
NAB
n/a
n/a
NADB
FP
n/a
2.66
2.63
3.13
2.18
n/a
2
DMFP
IBZM
3
4
Raclopride tartrate
FLB457
5

6824
D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
This fact gives rise to the assumption that those com-
pounds will have similarly good properties for the use
as radioligands for molecular imaging.
shifts were reported in parts per million (ppm). FD mass
spectrometry was performed on a Finnigan MAT90-
Spectrometer.
All synthesised benzamide derivatives were purified by
HPLC (system: Sykam S 1100 Solvent Delivery System,
S 8110 Low Pressure Gradient Mixer, Rheodyne 9725i
Inject Valve; Linear UVIS-205 Absorbance Detector;
Axxiom Chromatography 900-200 Pyramid; software:
Pyramid version 2.07; column: LiChrospher 100RP 18
EC-5l, 250 · 20 mm; loop, 100 lL; flow, 5 mL/min) be-
fore carrying out the receptor binding studies.
4. Conclusions
For the two iodinated compounds of which NAE (27)
displays a 3-fold higher affinity for the D2 receptor than
FP (1) (Ki = 2.2 nM) and NADE (28) with a 1.5-fold
higher affinity than DMFP (2) (Ki = 30 nM), excellent
properties for molecular imaging can be expected.
Comparing the values obtained for the iodinated com-
pounds with the ones obtained for FP (1) and DMFP
(2) allows to expect similar properties for the two iodin-
ated compounds NAE (27) and NADE (28) regarding
selectivity and in vivo imaging potential. The bromi-
nated compounds NABrE (29) and NABrDE (30) show
Ki values for the D2 receptor which are in the same
range as those for the iodinated analogues NAE (27)
and NADE (28).
5.1.1. N-(S)-Allyl-1-allylpyrrolidine-2-carboxylate (7).
Twenty-one grams (0.18 mol) L-proline (6) and 61 g
(0.44 mol) K2CO3 were suspended in 200 mL of dry
DMSO. Under stirring 53 g (0.43 mol) of allyl bromide
was added dropwise at ambient temperature over 4 h.
After the addition was completed the reaction mixture
was stirred overnight at room temperature and then
poured onto ice water. The aqueous phase was extracted
with diethyl ether (4· 250 mL). The organic extracts
were dried over Na2SO4 and the solvent evaporated un-
der reduced pressure. The obtained viscous liquid was
purified through column chromatography on silica gel
(eluent: n-hexane/ethyl acetate, 4:1). Thirty grams of
crude product yielded 9.82 g (0.05 mol; 28%) of a col-
Of the structural elements having an influence on the
affinities of benzamides for the D2 receptor the addition
of a second methoxy group at the 3-position of the aro-
matic ring has the most noticeable effect. The enhance-
ments in affinities that can be related to changes at the
nitrogen atom of the pyrrolidinyl ring or the 5-position
of the aromatic ring are less obvious.
1
ourless liquid. H NMR (400 MHz, CDCl3)d 5.91–5.70
(m, 2H, ACH@CH2); 5.29–4.96 (m, 4H, ACH@CH2);
4.57–4.49 (d, 2H, AOACH2ACH@CH2); 3.35 (dd, 1H,
ACH (2)); 3.04–2.81 (m, 2H, NACH2ACH@CH2);
2.59–2.50 (m, 2H, CH2 (5)); 2.30–1.97 (m, 2H, CH2
(3)); 1.81–1.60 (m, 2H, CH2 (4)); 13C NMR (400 MHz,
CDCl3) d 173.82 (C@O); 135.33 (OACH2ACH@CH2);
132.12 (NACH@CH2); 118.36 (OACH2ACH@CH2);
117.43 (NACH2ACH@CH2); 65.17 (OACH2ACH
CH2); 65.13 (C (2)); 57.63 (NACH2ACH@CH2); 53.42
(C (5)); 29.51 (C (5)); 23.07 (C (3)); 23.07 (C (4)); MS
(FD) m/z (% rel int.) 195.7 (100.0 [M]+); 431.1 (11.92
[M+NPM]+); 196.7 (0.79 [M+1]+).
The logD7.4 values of 2.91 for NAE (27) and of 2.81 for
NADE (28) are in the range of those found for IBZM
(3), FP (1) and DMFP (2).
The affinities for D2-like receptors determined for IBZM
(3) are 6-fold lower than the value found for NAE (27)
and about five times higher than the value obtained for
NADE (28). This fact gives reason to the assumption
that better resolution and specificity can be achieved in
SPECT by using the new iodinated compounds.
5.1.2. N-(S)-1-Allylpyrrolidine-2-carboxamide (8). Five
grams (26 mmol) of (S)-1-allylpyrrolidine-2-carboxylate
(7) and 135 mg of NaCN were dissolved in 100 mL of
methanolic ammonia (9 M). The reaction mixture was
kept at 35 ꢂC for 45 h. Methanol was then removed un-
der vacuum, the residue taken up in diethyl ether and
washed with brine. The organic phase was dried over
Na2SO4, the solvent removed under vacuum and the res-
idue was recrystallised from diisopropyl ether. 2.42 g
(16 mmol; 60%) of a white crystalline solid was ob-
5. Experimental
5.1. Chemistry
Unless otherwise noted all chemicals were used without
further purification. Moisture sensitive reactions were
carried out under an argon or nitrogen atmosphere using
dry solvents over molecular sieve (Fluka). 5-Iodo-2,3-
dimethoxybenzoic acid (13) was purchased from Apin
Chemicals. S-(À)-IBZM (3) was purchased from Sigma
RBI, FLB 457 (5) from ABX and S-(À)-raclopride(+)-
tartrate salt (4) from Sigma. All other chemicals, includ-
ing the benzoic acid derivatives 16 and 25, were purchased
from either Merck, Aldrich, Acros or Fluka.
1
tained. Mp 79–80 ꢂC. H NMR (200 MHz, CDCl3) d
7.24 (br s, 1H, NHAH); 5.93–5.73 (m, 2H, NH-H,
ACH@CH2); 5.22–5.04 (m, 2H, ACH@CH2); 3.68–
2.97 (m, 3H, NACH2 ACH@CH2,ACHA (2)); 2.39–
1.63 (m, 6H, CH2 (3, 4, 5)); MS (FD) m/z (% rel int.)
154.7 (100.0 [M]+); 155.6 (13.04 [M+1]+); 309.9 (0.80
[2M]+); 110.6 (0.14 [MÀCONH2].
Two-hundred, three-hundred and four-hundred
megahertz NMR spectra were recorded on a Bruker
200-MHz FT NMR Spectrometer AC 200, a Bruker
300-MHz FT NMR Spectrometer AC 300 or a Bru-
ker-Biospin DRX 400 MHz spectrometer. Chemical
5.1.3. N-(S)-1-Allyl-2-aminomethylpyrrolidine (9). In a
three-necked round bottomed flask 70 mL (0.25 mol)
SDMA (70% in toluene) was added to 280 mL of dry
toluene and heated to 70 ꢂC. Twelve grams (79 mmol)

D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
6825
of (S)-1-allylpyrrolidine-2-carboxamide (8) were dis-
solved in 60 mL of dry THF and added dropwise to
the SDMA solution over the period of 1 h. The reaction
mixture was stirred for four additional hours at 70 ꢂC
and then cooled to room temperature. The mixture
was acidified with 2 M HCl (pH 2–3) and then washed
with diethyl ether. The pH of the aqueous phase was ad-
justed to 10 by addition of NaOH solution (45%). The
aqueous phase was then extracted with ethyl acetate
(5· 200 mL). The organic phase was dried over Na2SO4
and the solvent was removed under reduced pressure.
The remaining crude product was distilled under vac-
uum (approx. 65 mbar) to yield 2 g (14 mmol, 18%, bp
KMnO4 and 40 mL of water was added. After 22 h of
stirring at room temperature the reaction mixture was
filtered over Celite and the filtrate acidified with concen-
trated HCl. The precipitate was filtered, dried and puri-
fied through recrystallisation from water to yield 643 mg
1
(2.5 mmol; 35%) of a white solid. H NMR (200 MHz,
d6-DMSO) d 7.36 (d, 1H, arom. H (6)); 7.28 (d, 1H,
arom. H (4)); 3.84 (s, 3H, AOCH3 (2)); 3.72 (s, 3H,
AOCH3 (3)); MS (FD) m/z (% rel int.) 263.0 (100.0
[M]+); 261.7 (97.40 [M]+).
5.1.6. 5-Bromo-2-methoxybenzoic acid (23). The proce-
dure for 14 was followed with 6.5 g (30 mmol) 5-bromo-
2-methoxybenzaldehyde (19) as starting compound.
103–112 ꢂC) of
a
colourless liquid. 1H NMR
1
(200 MHz, CDCl3) d 5.96–5.76 (m, 1H, ACH@CH2);
5.18–4.99 (m, 2 H, ACH@CH2); 3.60–2.57 (m, 5H,
CH (2), CH2 (7), ACH2ACH@CH2); 2.43–2.10 (m,
2H, NH2); 1.89–1.32 (m, 6 H, ACH2ACH2ACH2A (3–
5)); MS (FD): m/z (% rel int.) = 141.7 (100.0 [M+1]+);
140.7 (96,13 [M]+); 110.7 (2.81 [MÀCH2NH2]).
Yield: 2.1 g (9 mmol; 30%) of a white solid. H NMR
(200 MHz, d6-DMSO) d 12.95 (br s, 1H, ACOOH); 7.72
(d, 1H, arom. H (6)); 7.66 (d, 1H, arom. H (4)); 7.09 (d,
1H, arom. H (3)); 3.80 (s, 3H, AOCH3); MS (FD) m/z
(% rel int.) 230.7 (100.0 [M]+); 232.7 (80.81 [M]+).
5.1.7. 5-Chloro-2,3-dimethoxybenzoic acid (15). The pro-
cedure for 14 was followed with 5.2 g (26 mmol) of
5-chloro-2,3-dimethoxybenzaldehyde (11) as starting
compound. Yield: 750 mg (3 mmol, 14%) of a white solid
was obtained. 1H NMR (300 MHz, d6-DMSO) d 7.27 (s, 1
H, arom. H (6)); 7.15 (s, 1H, arom. H (4)); 3.80 (s, 3 H,
AOCH3(2)); 3.67 (s, 3 H, AOCH3(3)); MS (FD) m/z (%
rel int.) 216.2 (100.0 [M]+); 218.2 (30.88 [M]+).
5.1.4. 5-Iodo-2-methoxybenzoic acid (22). 8.3 g
(30 mmol) of 2-hydroxy-5-iodobenzoic acid (18) was dis-
solved in 20 mL of dry DMF under argon. 2.5 g
(63 mmol) NaH (60% adsorbed on mineral oil) were
added. The mixture was cooled to room temperature,
9.85 g (4.3 mL; 70 mol) of iodomethane was added and
the mixture was stirred at 70 ꢂC for 48 h. The solvent
was removed under vacuum, the residue was taken up in
water and 35 mL of a 1-M LiOH solution was added.
The mixture was stirred at 70–80 ꢂC until the cleavage
was completed (ꢀ2 h). The mixture was cooled down to
room temperature, filtered and the filtrate was acidified
(pH 3–4) with dilute HCl (10%). The precipitate was fil-
trated, dried and purified through column chromatogra-
phy on silica gel with ethyl acetate/n-hexane, 95:5 as
eluent to yield 3 g (12 mmol, 42%) of a white crystalline
solid. 1H NMR (200 MHz, d6-DMSO) d 12.89 (br s, 1H,
ACOOH); 7.86 (d, 1H, arom. H (6)); 7.77 (dd, 1H, arom.
H (4)); 6.96 (d, 1H, arom. H (3)); 3.79 (s, 3H, AOCH3),
MS (FD) m/z (% rel int.) 278.6 (100.0 [M]+); 279.6 (8.57
[M+1]+); 264.6 (0.77 [MÀCH3]+).
5.1.8. 5-Chloro-2-methoxybenzoic acid (24). 7.6 g of
NaOH was dissolved in 590 mL of water. Five hundred
and eighty millilitres of CH2Cl2 was added, followed by
4.4 g of tetrabutyl ammonium iodide and 20 g of
5-chloro-2-hydroxybenzoic acid (20). Under vigorous
stirring 33 mL of DMSO was added dropwise and the
mixture was stirred at room temperature for 4 h. Distilla-
tion gave 9.9 g (46%, 49 mmol) of a colourless liquid.
50 mL of 1 M NaOH was added to 2.0 g of the ester. After
stirring at room temperature overnight 2 M HCl was
added until a precipitate formed. The aqueous phase
was extracted with ether (four portions of 50 mL). The or-
ganic phase was dried with MgSO4, the solvent removed
under in vacuo and 1.6 g (83%, 8 mmol) of a white solid
was isolated. 1H NMR (300 MHz, d6-DMSO) d 7,66
(dd, 1H, arom. H (6)); 7,59 (dd, 1H, arom. H (4)); 7,06
(dd, 1H, arom. H (3)); 3,80 (s, 3 H, AOCH3); MS (FD)
m/z (% rel int.) 186.2 (100.0 [M]+); 188.2 (28.39 [M]+).
5.1.5. 5-Bromo-2,3-dimethoxybenzoic acid (14). Six
grams (26 mmol) 5-bromo-2-hydroxy-3-methoxy-benz-
aldehyde (10) was dissolved in 50 mL of 2-butanone. 5.4
g (39 mmol) of K2CO3 and 2.5 mL of iodomethane
(39 mmol) were added. The mixture was kept at 80 ꢂC
for 22 h and then concentrated to dryness. The residue
was dissolved in 100 mL of ethyl acetate and washed with
1 M NaOH and brine. The organic phase was dried over
MgSO4, the solvent removed under reduced pressure
and the crude product (6.75 g) was further purified by
column chromatography on silica gel with ethyl acetate/
n-hexane, 2:8 as eluent. 2.3 g (9 mmol; 36%) of
5.1.9. 5-(3-Hydroxypropyl)-2,3-dimethoxybenzoic acid
(17). 3-(3,4-Dimethoxyphenyl)propan-1-ol (12) was
treated according to the procedure described for 14 to
yield 62% of the title compound 17. 1H NMR
(200 MHz, CDCl3/d4-MeOH) d 6.98 (d, 1H, arom. H
(6)); 6.90 (d, 1H, arom. H (4)); 3.88 (s, 3H, OCH3 (2));
3.86 (s, 3H, OCH (3)); 3.60 (t, 2H, ArACH2ACH2A
3
1
5-bromo-2,3-dimethoxybenzaldehyde was obtained. H
CH2OH), 2.68 (t, 2H, ArACH2ACH2ACH2OH), 1.97–
1.81 (m, 2H, ArACH2ACH2ACH2OH).
NMR (200 MHz, CDCl3) d 10.32 (s, 1H, ACOH); 7.51
(d, 1H, arom. H (6)); 7.21 (d, 1H, arom. H (4)); 3.95
(s, 3H, AOCH3 (2)); 3.88 (s, 3H, AOCH3 (3)); MS (FD)
m/z (% rel int.) 247.0 (100.0 [M]+); 245.0 (96.91 [M]+).
5.1.10. 5-(3-Hydroxypropyl)-2-methoxybenzoic acid (26).
Two grams 3-(4-methoxyphenyl)propan-1-ol (21)
(12 mmol) was dissolved in 20 mL dry THF and cooled
to À78 ꢂC. Under a nitrogen atmosphere 14.6 mL of an
n-butyllithium solution in n-hexane (15%; 24 mmol) was
1.6 g (7 mmol) 5-bromo-2,3-dimethoxybenzaldehyde
was dissolved in 100 mL of acetone and 2.1 g (13 mmol)

6826
D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
added and the mixture was stirred at À78 ꢂC for 30 min.
The mixture was allowed to warm to room temperature,
stirred for 30 min and poured into a suspension of dry
ice in diethyl ether. The solvent was removed under re-
duced pressure, the residue dissolved in water and ex-
tracted with diethyl ether. The aqueous phase was
acidified, extracted with ethyl acetate and the solvent
evaporated under reduced pressure to give 2.15 g
din-2-yl)methyl)-5-iodo-2-methoxybenzamide (NADE)
(28) using 14 as the benzoic acid derivative. The title
1
compound was obtained in 86% yield as yellow oil. H
NMR (400 MHz, CDCl3) d 8.85 (br s, 1H, N-H); 7.69
(d, 1H, arom. H (6)); 7.10 (d, 1H, arom. H (4)); 6.14–
6.03 (m, 1H, ACH2ACH@CH2); 5.43–5.38 (m, 2H,
ACH2ACH@CH2); 4.04 (s, 3H, OCH3 (2)); 3.84 (s,
3H, OCH3 (3)); 3.96–3.91 (m, 2H, ANHACH2ACH);
3.89–3.86 (m, 1H, ANHACH2ACHA); 3.77–3.69 (m,
1H, ACH2ACH@CH2); 3.50–3.42 (m, 1H, ACH2A
CH@CH2); 2.94–2.88 (m, 2H, CH2ACH2ACH2AN
(11)); 2.24–1.86 (m, 4H, ACH2ACH2ACH2AN (9,
10)); MS (FD) m/z (% rel int.) 385.0 (100.0 [M]+);
383.0 (98.29 [M]+).
(85%, 10 mmol) of
a
yellow solid. 1H NMR
(200 MHz, CDCl3) d 7.99 (d, 1H, arom. H (6)); 7.37
(dd, 1H, arom. H (4); 6.99 (d, 1H, arom. H (3)); 4.04
(s, 3H, OCH3); 3.64 (t, 2H, ArACH2ACH2ACH2OH),
2.70 (t, 2H, ArACH2ACH2ACH2OH), 1.93–1.77 (m,
2H, ArACH2ACH2ACH2OH).
5.1.11. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-iodo-2,3-
dimethoxybenzamide (NAE) (27). Synthesis followed the
same procedure as for N-(((S)-1-allylpyrrolidin-2-yl)-
methyl)-5-iodo-2-methoxybenzamide (NADE, 28) using
5-iodo-2,3-dimethoxybenzoic acid (13) as the benzoic
acid derivative. The title compound was obtained in
82% yield as a yellow oil. 1H NMR (400 MHz, CDCl3)d
8.23 (br s, 1H, NAH); 7.97 (d, 1H, arom. H (6)); 7.22 (d,
1H, arom. H (4)); 5.88–5.78 (m, 1H, ACH2ACH@CH2);
5.16–5.01 (m, 2H, ACH2ACH@CH2); 3.81 (s, 6H, 2·
OCH3); 3.71–3.63 (m, 1H, ANHACH2ACHA); 3.43–
3.23 (m, 2H, ANHACH2ACH); 3.07–2.78 (m, 2H,
ACH2ACH@CH2); 2.64–2.15 (m, 2H, CH2ACH2A
CH2AN (11)); 1.68–1.55 (m, 4H, ACH2ACH2ACH2AN
(9,10)); MS (FD) m/z (% rel int.) 430.7 (100.0 [M]+);
431.8 (29.08 [M+1]+).
5.1.14. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-bromo-2-
methoxybenzamide (NABrDE) (30). Synthesis followed
the same procedure as for N-(((S)-1-allylpyrrolidin-2-
yl)methyl)-5-iodo-2-methoxybenzamide (NADE) (28)
using 23 as the benzoic acid derivative. The title com-
1
pound was obtained in 86% yield as a yellow oil. H
NMR (200 MHz, d6-DMSO) d 8.31 (br s, 1H, N-H);
7.88 (d, 1H, arom. H (6)); 7.63 (dd, 1H, arom. H (4));
7.13 (d, 1H, arom. H (3)); 5.93–5.77 (m, 1H, ACH2A
CH@CH2); 5.23–5.04 (m, 2H, ACH2 ACH@CH2);
3.88 (s, 3H, OCH3); 3.54–2.47 (m, 5H, ANHACH2A
CHA, ANHACH2ACHA, ACH2ACH@CH2); 2.23–
1.46 (m, 6H, ACH2ACH2 ACH2A (9–11)); MS (FD)
m/z (% rel int.) 352.7 (100.0 [M]+); 354.7 (96.13 [M]+);
353.7 (18.61 [M+1]+); 355.7 (13.31 [M+1]+).
5.1.15. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-chloro-2,3-
dimethoxybenzamide (NAClE) (31). Synthesis followed the
same procedure as for N-(((S)-1-allylpyrrolidin-
2-yl)methyl)-5-iodo-2-methoxybenzamide (NADE) (28)
using 15 as the benzoic acid derivative. The title
compound was obtained in 55% yield as a colourless
oil. 1H NMR (300 MHz, CDCl3) d 8.38 (br s, 1H,
N-H); 7.66 (d, 1H, arom. H (6)); 6.96 (d, 1H, arom. H
(4)); 5.89–5.88 (m, 1H, ACH2ACH@CH2); 5.22–5.07
(m, 2H, ACH2ACH@CH2); 3.81 (s, 6H, OCH3); 3.78–
3.71 (m, 1H, ANHACH2ACH); 3.45–3.12 (m, 2H,
ANHACH2ACHA); 2.92–2.74 (m, 2H, ACH2ACH@
CH2); 2.74–1.25 (m, 2H, CH2ACH2ACH2AN (11));
1.94–1.65 (m, 4H, ACH2ACH2ACH2AN (9, 10)).
5.1.12. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-iodo-2-
methoxybenzamide (NADE) (28). Two hundred and
forty grams (0.84 mmol) 5-iodo-2-methoxybenzoic acid
(22) was dissolved in 6 mL CH2Cl2 and cooled to 0 ꢂC
(ice bath). Subsequently 0.15 mL (1.10 mmol) triethyl
amine and 0.1 mL (1.0 mmol) ethyl chloroformiate in
2 mL of CH2Cl2 were added under stirring at 0 ꢂC. After
1 h a mixture of 140 mg (1 mmol) N-(S)-1-allyl-2-ami-
nomethylpyrrolidine (9) and 0.15 mL (1.1 mmol) triethyl
amine in 5 mL CH2Cl2 was added to the reaction mix-
ture and stirred for another 1.5 h at 0 ꢂC. The solvent
was evaporated under reduced pressure; the residue ta-
ken up in CH2Cl2, the organic phase was washed with
water and was dried over Na2SO4. After removal of
the solvent the crude product was purified by column
chromatography yielding 306 mg (0.76 mmol, 76%) of
a yellow oil using ethyl acetate/methanol 8/2 as eluent.
1H NMR (400 MHz, CDCl3) d 8.44 (d, 1H, arom. H
(6)); 8.22 (br s, 1H, N-H); 7.66 (dd, 1H, arom. H (4));
6.70 (d, 1H, arom. H (3)); 5.91–5.80 (m, 1H, ACH2A
CH@CH2); 5.20–5.03 (m, 2H, ACH2ACH@CH2); 3.89
(s, 3H, OCH3); 3.70–3.66 (m, 1H, ANHACH2ACHA);
3.45–3.28 (m, 2H, -NHACH2ACH); 3.10–2.84 (m, 2H,
ACH2ACH@CH2); 2.68–2.18 (m, 2H, CH2ACH2A
CH2AN (11)); 1.76–1.55 (m, 4H, ACH2ACH2ACH2AN
(9, 10)); MS (FD) m/z (% rel int.) 400.9 (100.0 [M]+);
802.4 (30.89 [2M]+); 401.9 (23.26 [M+1]+).
5.1.16. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-chloro-2-
methoxybenzamide (NAClDE) (32). Synthesis followed
the same procedure as for N-(((S)-1-allylpyrrolidin-2-
yl)methyl)-5-iodo-2-methoxybenzamide (NADE) (28)
using 24 as the benzoic acid derivative. The title com-
pound was obtained in 39% yield as colourless liquid.
1H NMR (300 MHz, CDCl3) d 8.33 (br s, 1H, NAH);
7.74 (d, 1H, arom. H (6)); 7.51 (dd, 1H, arom. H (4));
7.18 (d, 1H, arom.
H (3)); 5.94–5.80 (m, 1H,
ACH2ACH@CH2); 5.22–5.06 (m, 2H, ACH2ACH@
CH2); 3.88 (s, 3H, OCH3); 3.40 (m, 1H, ANHACH2A
CHA); 3.20–2.99 (m, 2H, ANHACH2ACHA); 2.88–2.61
(m, 2H, ACH2ACH@CH2); 2.22–1.76 (m, 2H, ACH2
(11); 1.67–1,45 (m, 4H, ACH2ACH2ACH2A (9, 10)).
5.1.13. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-bromo-
2,3-dimethoxybenzamide (NABrE) (29). Synthesis fol-
lowed the same procedure as for N-(((S)-1-allylpyrroli-
5.1.17. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-2,3-dimeth-
oxybenzamide (NAB) (33). Synthesis followed the same

D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
6827
procedure as for N-(((S)-1-allylpyrrolidin-2-yl)methyl)-
5-iodo-2-methoxybenzamide (NADE) (28) using 16 as
the benzoic acid derivative. The title compound was ob-
tained in 36% yield as a colourless liquid. 1H NMR
(300 MHz, CDCl3) d 8.43 (br s, 1H, N-H); 7.76 (d,
1H, arom. H (6)); 7.11 (t, 1H, arom. H (5)); 7.01 (d, 1H,
arom. H (4)); 5.92–5.90 (m, 1H, ACH2ACH @CH2);
5.23–5.08 (m, 2H, ACH2ACH@CH2); 3.88 (s, 6H,
OCH3); 3.83–3.77 (m, 1H, ANHACH2 ACH); 3.52–
3.36 (m, 2H, ANHACH2ACHA); 3.19–2.88 (m, 1H,
ACH2ACH@CH2); 2.32–1.91 (m, 2H, CH2ACH2A
CH2AN (11)); 1.72–1.69 (m, 4H, ACH2ACH2ACH2AN
(9, 10)).
m/z (% rel int.) 516.9 (100.0 [M]+); 1032.9 (47.00
[2M]+); 1033.9 (26.78 [2M+1]+).
5.1.19.3. Compound 1. 1H NMR (400 MHz, CDCl3) d
(ppm): 7.49 (d, 1H, arom. H (6)); 6.80 (d, 1H, arom. H
(4)); 5.87–5.95 (m, 1H, ACH2ACH@CH2); 5.02–5.20
(2d, 2H, ACH2ACH@CH2); 4.31–4.47 (dt, 2H,
ArACH2ACH2ACH2F, J = 48.0 Hz); 3.82 (2s, 6H,
OCH3); 3.75–2.78 (m, 5H, ANHACH2ACHA;
ACH2ACH@CH2; ANHACH2ACHA); 2.67 (t, 2H,
ArACH2ACH2ACH2F); 2.13–2.2 (m, 2H, ACH2ACH2
ACH2A (11)); 1.90–2.03 (m, 2H, ArACH2ACH2A
CH2F; J = 26 Hz); 1.52–1.89 (m, 4H, ACH2ACH2A
CH2A (9, 10)): MS (FD): m/z (% rel int.) = 364.8
(100.0 [M]+); 365.8 (57.3 [M]+).
5.1.18. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-2-methoxy
benzamide (NADB) (34). Synthesis followed the same
procedure as for N-(((S)-1-allylpyrrolidin-2-yl)methyl)-
5-iodo-2-methoxybenzamide (NADE) (28) using 25 as
the benzoic acid derivative. The title compound was ob-
tained in 62% yield as a colourless liquid. 1H NMR
(300 MHz, CDCl3) d 8.40 (br s, 1H, N-H); 8.17 (d,
1H, arom. H (6)); 7.43 (t, 1H, arom. H (5)); 7.04 (t,
1H, arom. H (4)); 6.94 (d, 1H, arom. H (3)); 5.91–5.89
(m, 1H, ACH2ACH@CH2); 5.22–5.08 (m, 2H,
ACH2ACH@CH2); 3.93 (s, 3H, OCH3); 3.77–3.70 (m,
1H, ANHACH2ACHA); 3.51–3.16 (m, 2H, -NHA
CH2ACHA); 3.10–2.84 (m, 2H, ACH2ACH@CH2);
2.81–2.21 (m, 2H, ACH2ACH2ACH2A (11)); 1.95–
1.64 (m, 4H, AC H2ACH2ACH2A (9, 10)).
5.1.20. N-(((S)-1-allylpyrrolidin-2-yl)methyl)-5-(3-hydro-
xypropyl)-2-methoxybenzamide (37). Synthesis followed
the same procedure as for N-(((S)-1-allylpyrrolidin-2-
yl)methyl)-5-iodo-2-methoxybenzamide (NADE) (28)
using 26 as the benzoic acid derivative yielding 81% of
the title compound 37.
1H NMR (200 MHz, CDCl3): d (ppm) = 8.00 (d, 1H,
arom. H (6)); 7.22 (dd, 1H, arom. H (4)); 6.87 (d, 1H,
arom. H (3)); 5.72–5.98 (m, 1H, ACH2ACH@CH2);
4.99–5.19 (m, 2H, ACH2ACH@CH2); 3.90 (s, 3H,
OCH3); 3.61 (t, 2H, ArACH2ACH2ACH2OH); 3.53–
2.75 (br, 6H, ANHACH2ACHA; ACH2ACH@CH2;
ANHACH2ACHA; ACH2ACH2ACH2- (11)); 2.64
(t, 2H, ArACH2ACH2ACH2OH); 2.10–2.29 (m, 1H,
ACH2ACH2ACH2A (11)); 1.52–2.00 (m, 6H, ACH2A
CH2ACH2A (9, 10); ArACH2ACH2ACH2OH).
5.1.19. N-(((S)-1-Allylpyrrolidin-2-yl)methyl)-5-(3-fluoro-
propyl)-2,3-dimethoxybenzamide (FP) (1). Synthesis was
carried out in analogy to the synthesis of N-(((S)-1-allyl-
pyrrolidin-2-yl)methyl)-5-(3-fluoropropyl)-2-methoxyb-
enzamide (2), starting out from 3-(3,4-dimeth-
oxyphenyl)propan-1-ol (12), coupled alcohol 35,
tosylated compound 36 and finally FP (1) affording
comparable yields.
5.1.21. 3-(3-(((S)-1-allylpyrrolidin-2-yl)methylcarbamoyl)-
4-methoxyphenyl)propyl-4-methylbenzenesulfonate (38).
Two hundred and eighty grams N-(((S)-1-allylpyrroli-
din-2-yl)methyl)-5-(3-hydroxypropyl)-2-methoxybenza-
mide 37 and 130 lL pyridine were dissolved in 2 mL
dichloromethane and the solution was cooled to 0–
5 ꢂC. One hundred and seventy milligrams (0.85 mmol)
of 4-methylbenzene-1-sulfonyl chloride was added and
the reaction mixture was stirred for 2 h at 0–5 ꢂC and
then for 3 h at room temperature. The solution was
washed with water and the aqueous phase was extracted
with ethyl acetate. The solvent was removed under re-
duced pressure. The residue was taken up in diethyl
ether and washed with potassium hydroxide solution
(10%) and water. The solvent was removed under re-
duced pressure and the crude product purified by col-
umn chromatography on silica gel with ethyl acetate/
methanol, 4:1 as eluent. The product was obtained as
viscous yellow oil in 48% yield (183 mg). 1H NMR
(200 MHz, CDCl3) d (ppm): 7.93 (d, 1H, arom. H (6));
7.76 (d, 2H, tos.), 7.23 (d, 2H, tos.); 7.15 (dd, 1H, arom.
H (4)); 6.83 (d, 1H, arom. H (3)); 5.78–5.95 (m, 1H,
ACH2ACH@CH2); 5.05–5.22 (m, 2H, ACH2ACH@CH2);
3.98 (t, 2H, ArACH2ACH2ACH2OTos); 3.89 (s, 3H,
OCH3); 3.49–2.74 (br, 6H, ACH2ACH2ACH2A (11);
ACH2ACH@CH2; ANHACH2ACHA); 2.61 (t, 2H,
ArACH2ACH2ACH2OTos); 2.38 (s, 3H, tosACH3);
2.15–2.29 (m, 1H, ANHACH2ACHA); 1.56–1.98 (m,
6H, ACH2ACH2ACH2A (9, 10); ArACH2ACH2A
1
5.1.19.1. Compound 35. H NMR (400 MHz, CDCl3)
d 7.47 (d, 1H, arom. H (6)); 6.80 (d, 1H, arom. H (4));
5.78–5.89 (m, 1H, ACH2ACH@CH2); 5.00–5.15 (m,
2H, ACH2ACH@CH2); 3.81 (s, 3H, OCH3 (2)); 3.80 (s,
3H, OCH3 (3)); 3.67–3.74 (m, 1H, ANHAC H2ACHA);
3.59 (t, 2H, ArACH2ACH2ACH2OH); 3.42–2.78 (m,
4H; ANHACH2ACHA; ANHACH2ACHA; ACH2A
CH@CH2); 2.63 (t, 2H, ArACH2ACH2ACH2OH);
2.15–2.18 (m, 1H, ACH2ACH2ACH2A (11)); 1.61–1.87
(m, 7H, ACH2ACH2ACH2A (11); ACH2ACH2ACH2A
(9, 10); ArACH2AC H2ACH2OH).
1
5.1.19.2. Compound 36. H NMR (400 MHz, CDCl3)
d (ppm): 7.75 (d, 2H, tos.); 7.44 (d, 1H, arom. H
(6));7.32 (d, 2H, tos.); 6.82 (d, 1H, arom. H (4)); 5.78–
5.98 (m, 1H, ACH2ACH@CH2); 5.01–5.25 (m, 2H,
ACH2ACH@CH2); 3.99 (t, 2H, ArACH2ACH2A
CH2OTos); 3.86 (s, 3H, OCH3 (2)); 3.84 (s, 3H, OCH3
(3));
3.80–2.77
(br,
5H,
ANHACH2ACHA;
ANHACH2ACHA; ACH2ACH@CH2); 2.64 (t, 2H,
ArACH2ACH2ACH2OTos); 2.39 (s, 3H, tos-CH3);
2.13–2.28 (m, 1H, ACH2ACH2ACH2A (11)); 1.59–
2.03 (m, 7H, ACH2ACH2ACH2A (11); ACH2ACH2A
CH2A (9, 10); ArACH2ACH2ACH2OTos); MS (FD)

6828
D. Stark et al. / Bioorg. Med. Chem. 15 (2007) 6819–6829
CH2OTos); MS (EI, 70 eV): m/z (% rel int.) 468 (0.49,
[m]+), 457 (1.29, [MAC2H5]+), 347 (2.26, [MAC7H7O2S]+),
110 (100.0, [C7H11N]+); FD: m/z (% rel int.) 487 (100.0,
[M+1]+), 333 (6.45, [(M+1)AC7H7O2S]+).
Data analysis of the resulting competition curves was
accomplished by non-linear regression analysis using
the algorithms in PRISM (GraphPad Software, San
Diego, CA). Ki values were derived from the corre-
sponding EC50 data utilizing the equation of Cheng
and Prusoff.31
5.1.22. N-(((S)-1-allylpyrrolidin-2-yl)methyl)-5-(3-fluoro-
propyl)-2-methoxybenzamide (DMFP) (2). One hundred
milligrams 3-(3-(((S)-1-allylpyrrolidin-2-yl)methyl-car-
bamoyl)-4-methoxyphenyl)propyl 4-methylbenzene-sul-
fonate 38 (0.19 mmol), 16 mg potassium fluoride
(0.28 mmol), 26 mg dehydrated potassium carbonate
(0.12 mmol) and 70 mg Kryptofixꢁ2.2.2. (0.28 mmol)
were dissolved in 4 mL of dry acetonitrile and refluxed
for 16 h. The reaction mixture was allowed to cool
down, the solvent was removed under reduced pressure
and the obtained crude product purified by column
chromatography on silica gel using methanol/ethyl ace-
tate, 1:1 as eluent. The product was obtained as a
brownish viscous mass with a yield of 79% (44 mg).
1H NMR (200 MHz, CDCl3) d (ppm): 7.71 (d, 1H,
arom. H (6)); 7.27 (dd, 1H, arom. H (4)); 6.98 (d, 1H,
arom. H (3)); 5.75–5.97 (m, 1H, ACH2ACH@CH2);
5.02–5.24 (m, 2H, ACH2ACH@CH2); 4.17–4.47 (dt,
2H, ArACH2ACH2ACH2F, J = 47.3 Hz); 3.85 (s, 3H,
OCH3); 3.59–2.86 (br, 6H, ACH2ACH2ACH2A (11);
ACH2ACH@CH2; ANHACH2ACHA); 2.62 (t, 2H,
ArACH2ACH2ACH2F); 2.21–2.37 (m, 1H, ANH
ACH2ACHA); 1.52–2.00 (m, 6H, ACH2ACH2ACH2A
5.3. Lipophilicity
Lipophilicities were determined using the HPLC system
described above with a LiChrospher 100 RP 18 EC-5l
column. Soerensen buffer was used as eluent. Retention
times for compounds 1–4 and 27–30 were determined.
Retention times for a number of reference substances
of known logP were assessed as well. From the obtained
retention times the capacity factor k was calculated for
all compounds. Plotting logk against logP gives the ref-
erence curve which is used to find the logP values for
compounds 1–4 and 27–30. LogD7.4 values of the syn-
thesised compounds were calculated using this reference
curve and the determined retention times.
Acknowledgment
We thank Christian Mersch for the synthesis of com-
pounds 31–34.
(9, 10); ArACH2ACH ACH2F); MS (FD): m/z (% rel
2
int.) 334.3 (100.0, [M]+), 670.1 (10.6, [2M+2]+).
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