Structure-activity relationship of 5-chloro-2-methyl-3-(1,2,3,6- tetrahydropyridin-4-yl)-1H-indole analogues as 5-HT6 receptor agonists

Article abstract of DOI:10.1016/j.ejmech.2013.03.006

To further investigate the structure-activity relationship (SAR) of the 5-hydroxytryptamine type 6 (5-HT₆) receptor agonist 5-chloro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole (EMD386088, 6), a series of 2-methyl-3-(1,2,3,6-tetrahydr

Full text of DOI:10.1016/j.ejmech.2013.03.006

European Journal of Medicinal Chemistry 63 (2013) 578e588
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
Structureeactivity relationship of 5-chloro-2-methyl-3-
(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole analogues as 5-HT6
receptor agonists
,
a,
Cecilia Mattsson a , Peder Svensson 1, Henning Boettcher b, Clas Sonesson a
*
a Medicinal Chemistry, NeuroSearch Sweden AB, Biotech Center, Arvid Wallgrens Backe 20, SE-413 46 Gothenburg, Sweden
b Merck KGaA, Merck Serono Research, Small Molecule Platform, Frankfurter Strasse 250, 64293 Darmstadt, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
To further investigate the structureeactivity relationship (SAR) of the 5-hydroxytryptamine type 6 (5-
HT6) receptor agonist 5-chloro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole (EMD386088, 6),
a series of 2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indoles were synthesized, and in vitro affinity
to, and functional activity at 5-HT6 receptors was tested. We focused on substituents made at the indole
N1-, 2- and 5-positions and these were found to not only influence the affinity at 5-HT6 receptors but also
the intrinsic activity leading to antagonists, partial agonists and full agonists. In order for a compound to
demonstrate potent 5-HT6 receptor agonist properties, the indole N1 should be unsubstituted, an alkyl
group such as 2-methyl is needed and finally halogen substituents in the indole 5-position (fluoro, chloro
or, bromo) were essential requirements. However, the introduction of a benzenesulfonyl group at N1-
position switched the full agonist 6 to be a 5-HT6 receptor antagonist (30). A few compounds within the
2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indoles were also screened for off-targets and generally
they displayed low affinity for other 5-HT subtypes and serotonin transporter protein (SERT).
Ó 2013 Elsevier Masson SAS. All rights reserved.
Received 12 December 2012
Received in revised form
28 February 2013
Accepted 3 March 2013
Available online 14 March 2013
Keywords:
5-HT6
5-Hydroxytryptamine type 6 receptor
agonist
3-(1,2,3,6-Tetrahydropyridin-4-yl)-1H-
indole
EMD386088
1. Introduction
[3,4]. 5-HT6 receptors are found in striatal (on medium spiny neu-
rons), limbic and specific cortical areas, and their distribution is
The 5-hydroxytryptamine (serotonin) type 6 (5-HT6) receptor is
one of the most recent additions to the large family of serotonin (1,
Fig. 1) receptors and was first identified in the early 1990s [1]. The
exclusive localization of 5-HT6 receptor to the central nervous sys-
tem (CNS), combined with the fact that a number of known anti-
psychotics and antidepressants display high affinity for this
receptor, has resulted in widespread interest in this particular re-
ceptor [2]. The 5-HT6 receptor is a seven transmembrane-spanning
G protein-coupled receptor, which is linked positively to the ade-
nylate cyclase second messenger system. No subtypes of this re-
ceptor have yet been detected. Messenger ribonucleic acid (mRNA)
for the 5-HT6 receptor is expressed post-synaptically by non-
serotonin-containing neurons in the serotonin projection field
almost superimposable tothat of dopamine receptors. This suggests,
therefore, that 5-HT6 receptors may be involved in the control of
motor function, mood, reward and motivation, making them an
interesting drug target for CNS disorders such as schizophrenia,
depression and epilepsy. They may also be of relevance to the un-
derstanding and treatment of obesity, impaired memory and
cognitive function, and drug abuse [5]. Selective 5-HT6 receptor
antagonists were discovered a few years after the discovery of the 5-
HT6 receptor (Sleight et al., 1998) [6] and several are already in
clinical development for the treatment of cognitive disorders and
obesity [6e9]. The lack of a selective agonist, combined with limited
knowledge of the receptor’s transduction mechanisms and in-
consistencies in the pharmacological and neurochemical effects of
the antagonists, hampers the understanding of 5-HT6 receptor
pharmacology [10]. New selective 5-HT6 agonists based on different
chemical motifs are needed as pharmacological tools, therefore, to
evaluate the significance of the 5-HT6 receptor system. All currently
known 5-HT6 receptor agonists are based on the 5-HT (1) scaffold,
and the first reported agonists had an alkyl group in the 2 position (2
and 3, Fig. 1) [11e14]. More recently, a series of 5-HT6 receptor ag-
onists have been reported that are built on the two chemical motifs 4
* Corresponding author. Tel.: þ46 (0)709 518355.
E-mail addresses: cecilia.m.mattsson@gmail.com (C. Mattsson), peder.svensson@
astrazeneca.com (P. Svensson), henning.boettcher@merckgroup.com (H. Boettcher),
clas.sonesson@gmail.com (C. Sonesson).
1
Present address: AstraZeneca R&D Mölndal, CVGI IMed, SE-431 83 Mölndal,
Sweden.
0223-5234/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2013.03.006

C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
579
potent antagonist) [32,33]. Furthermore, Holenz et al. have re-
ported an elegant study on the chemical motif 4, from which potent
5-HT6 receptor antagonists and agonists can be developed
depending on the properties of the aryl-sulfonamide group (R-
group) used [18]. This means that the substitution in this position is
a very crucial one that needs fine-tuning, depending on whether an
agonist or antagonist is required.
1 5-HT
2 EMTD
3 ST1936
While investigating analogues of compound 6, we concluded
that small alkyl groups (methyl and ethyl) in the 2-position allowed
agonist properties to be retained, whereas larger groups decreased
not only the receptor binding affinity but also the intrinsic activity
of the compound. In the 5-position of the indole nucleus, only
methoxy and chlorine groups were synthesized and tested. Both
were found to be agonists, with the chlorine group being the most
potent (6, EC50 ¼ 1.0 nM) [26]. To further study the structuree
affinity relationships (SAFIR) and functionality of analogues of
compound 6, we synthesized and tested (in vitro) their affinity to
and functional activity at 5-HT6 receptors. We focused on the N1-
and 5-positions in the indole nucleus (R1 and R3, respectively), but
also report some examples where R2 was varied (11, Fig. 3).
4 X = O, N
5 X = CH, N
6 EMD386088
Fig. 1. 5-Hydroxytryptamine type 6 (5-HT6) receptor agonists.
2. Results and discussion
and 5 (Fig.1), wherethe R-group is defined bya largearylsubstituent
[15e25]. From these two series, it is very clear that the 5-HT6 re-
ceptor can accommodate large groups in both the N1 and 5 positions
when the basic amino group is substituted on an ethyl side chain.
The amino group has also beenincorporatedin ringconstraints, such
as the pyrrolidine and piperidine ring, which retains agonist prop-
erties. Sevenyears ago, we discovered a new 5-HT6 receptor agonist,
5-chloro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole
(EMD386088, 6, Fig. 1). This compound is a potent agonist with an
IC50 of 7.4 nM, and good selectivity over all other 5-HT receptors,
except for the 5-HT3 receptor (only a 6-fold difference) [26]. Com-
pound 6 is the first 5-HT6 receptor agonist reported wherein the side
chain does not constitute an ethyl amino group. Since 2005, this
agonist has been used as a pharmacological tool compound in
several studies [27e30], for example 6 has been shown to have an-
tidepressant and anxiolytic effects in rats [31].
From a structureeactivity relationship (SAR) perspective, it is
interesting to note that when the 4-substituted piperidene/piper-
idine moiety is used in other chemical series, the compounds
generated are potent 5-HT6 receptor antagonists. When the sub-
stitution is in the 5-position of the indole nucleus, as in compound
7 [18], or in the N1-position, as in 8 (Fig. 2) [32], both compounds
are potent 5-HT6 receptor antagonists. However, moving the ni-
trogen in the tetrahydropyridine ring one step yields a modest
partial agonist 1-(benzenesulfonyl)-3-(1,2,3,6-tetrahydropyridin-
5-yl)indole (9, Ki ¼ 4.6 nM, EC50 ¼ 159 nM, 41%, Fig. 2) [33], while
the saturated analogue 10 (Ki ¼ 2 nM with EC50 ¼ 24 nM, Fig. 2) is a
full 5-HT6 receptor agonist, (when the enantiomers are separated
one enantiomer behaves as a full agonist whereas the other is a
2.1. Chemistry
The different 2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole derivatives were prepared by acid-catalysed condensation
between a 2-methyl-1H-indole and 4-piperidone (6, 12e23, 27e29,
Scheme 1) in 25e100% yield [34]. The 5-substituted-2-methyl-1H-
indoles used were either synthesized according to Scheme 1 or
commercially available i.e., 5-chloro-2-methyl-1H-indole (31), 5-
bromo-2-methyl-1H-indole (35), 5-fluoro-2-methyl-1H-indole
(36), 2-methyl-5-nitro-1H-indole (37), 5-methoxy-2-methyl-1H-
indole (42) and 2-methyl-1H-indole (49). Indole carboxylic esters
have been used for synthesis of 2-methyl-1H-indoles [35]. We used
5-methylsulfonyl-1H-indole-2-carboxylic acid (40, Scheme 1) as a
precursor for 2-methyl-5-methylsulfanyl-1H-indole (41). Heating
with large excess of LiAlH4 (10 equiv) yielded simultaneous reduc-
tion of both functional groups to 41 in low yield (16%). Other de-
rivatives of 2-methyl-1H-indoles were made by known chemistry
transformations of the 5-hydroxy group (43), 5-bromine (35) and 5-
amino (47) indole substituents. 5-methoxy-2-methyl-1H-indole
(42, Scheme 1) was de-methylated in excellent yield with BBr3 to
yield the 5-hydroxy derivate (43, 98%) [36]. The 5-hydroxy derivate
43 was used for alkylation with Mitsunobu chemistry to yield 5-
isopropoxy-2-methyl-1H-indole (44) in 69% yield, and also con-
verted with 1,1,1-trifluoro-N-phenyl-N-(trifluoromethylsulfonyl)
methanesulfonamide [PhN(SO2CF3)2] to yield corresponding triflate
(45) in moderate yield (68%). Compound 46 was synthesized by
nucleophilic substitution with 2-methyl-1H-indol-5-ol (43) and 1-
fluoro-2-nitrobenzene (microwave irradiation) in moderate yield
7
8
9
10
Fig. 2. Piperidene/piperidineindole 5-hydroxytryptamine type 6 (5-HT6) receptor ligands connected to an arylsulfonyl group in position 1 or 5.

580
C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
nitrogen (6) was first protected with a tert-butoxycarbonyl (BOC)
group (50, 96% yield) [38], then alkylated at the indole N1-position
and subsequently deprotected to yield 30 (25%).
R1 = -H, -Me, -Et, -nPr, -SO2Ph
R2 = -H, -Me
R3 = -H, -F, -Cl, -Br, -OMe, -OSO2CF3, -OiPr, -OPh(2-NO2),
-SMe, -CN, -NO2, -NHSO2Ph, -Ph, -(3-thienyl)
2.2. Biological activity
11
By exploring the substitution at the aromatic side in the indole
ring, we found that the 5-position can tolerate a wide range of
physical properties (Table 1), with the chloro (6), bromo (12), nitro
(19) and phenoxy [eOPh(2-NO2), 20] groups being the most potent.
However, it seems that negative steric interactions may occur, since
the phenyl (23) and 3-thienyl (22) compounds reduced affinity for
the 5-HT6 receptor drastically. Compared to the bulky phenoxy
group (20), these two substituents expand in an extended form
seen from the point of attachment, while the phenoxy has a bent
geometrical shape that seems to fit into the binding cavity. This is
further supported by the even more bulky phenylsulfone amide
(17), which also binds with high affinity and has similar geometrical
shape. These ligands probably interact with a hydrophobic region
proposed in previous studies, indicating that a flexible aromatic
group enhances binding in the indole 5-position [16,18,39]. How-
ever, both the triflate (16), iso-propoxy (21) and methoxy (14)
groups display low affinity, although exchanging the oxygen atom
with a sulphur atom yields a more lipophilic substituent and the
activity is increased (IC50 ¼ 20 nM, 18). It is more likely, therefore,
that the interaction is driven by hydrophobic interaction, which is
in good agreement with the tryptamine series, and further supports
Fig. 3. Generic structure of 5-hydroxytryptamine type 6 (5-HT6) receptor agonists.
(36%). This nucleophilic aromatic substitution needed a strong
electron-withdrawing group to proceed (eNO2); attempts to
remove the nitro group were unsuccessful, reduction to an aniline
was possible, but during diazotization conditions the indole was
decomposed and compound 46 was used, therefore, without any
further transformations. Palladium-catalysed cross-coupling
(Suzuki) with 5-bromo-2-methyl-1H-indole (35) was used for
introducing different aromatic systems: 2-methyl-5-phenyl-1H-
indole (38, 48%, Scheme 1) and 2-methyl-5-(3-thienyl)-1H-indole
(39, 84%) [37]. 2-methyl-1H-indol-5-amine (47, Scheme 1) was
transformed to the corresponding N-(2-methyl-1H-indol-5-yl)
benzenesulfonamide (48) in good yield (89%) [18]. Alkylation of
5-chloro-2-methyl-1H-indole (31, Scheme 1) at the indole
nitrogen, under basic conditions with the appropriate alkyl halide,
provided the N1-substituted indoles (32e34) [34] in 40e79% yield
[14]. To prepare 1-(benzenesulfonyl)-5-chloro-2-methyl-3-(1,2,3,6-
tetrahydropyridin-4-yl)indole (30, Scheme 2), the piperidene
35
ii
47
40
viii
i
38 R3 = -Ph
39 R3 = -(3-thienyl)
41
48
R3 = -Br (35), -F (36),
ix
ix
-NO2 (37), -H (49)
ix
42 R3 = -OMe
31 R1 = -H
32 R1 = -Me
33 R1 = -Et
34 R1 = -nPr
43 R3 = -OH
ix
ix
44 R3 = -OiPr
45 R3 = -OSO2CF3
6, 12-23 R1 = H
27 R1 = -Me, 28 R1 = -Et, 29 R1 = -nPr
1. iii
2. iv or v
ix
vii
1. iii
2. vi
42
46
31
Scheme 1. Synthesis of various 2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indoles. Reagents and conditions: (i) LiAlH4, dioxane, 110 ꢀC; (ii) phenylboronic acid/3-
thiopheneboronic acid, Pd(PPh3)4, toluene, ethanol, aqueous NaHCO3, reflux; (iii) BBr3, CH2Cl2, room temperature; (iv) 2-propanol, diethyl azodicarboxylate, Ph3P, CH2Cl2; (v)
PhN(SO2CF3)2, triethylamine, CH2Cl2; (vi) 1-fluoro-2-nitrobenzene, Cs2CO3, dimethylformamide, microwave irradiation 10 min, 140 ꢀC; (vii) NaH, dimethylformamide, alkyl halide,
heat; (viii) PhSO2Cl, pyridine, room temperature; (ix) 4-piperidone,HCl, H3PO4, acetic acid, 80 ꢀC.

C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
581
activity, indicating that there must be a specific interaction with the
receptor site or influence on the conformation of the piperidene
ring that is important for intrinsic activity (see Conformational
analysis). Compounds lacking a methyl group in position 2 (25,
26) seem to be partial agonists at 5-HT6 receptors whereas sub-
stitution with a methyl group (6, 12e14) yields compounds with
maximal IA. However, when the size is increased to a phenyl group
(24), a silent antagonist is achieved, indicating how important this
group is for the pharmacological property in this class of com-
pounds. These results are in good agreements with the tryptamine
series published by Glennon et al. [14] In the 5-chloro-2-methyl-3-
(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole series, the influence of
different N1-alkyl groups on 5-HT6 receptor affinity was also
investigated (27e29, Table 1). The results indicate that attaching an
N1-alkyl group decreased affinity considerably. The findings are
also in good agreement with data from published 5-HT6 receptor
agonist studies in the tryptamine series [14]. In contrast, attaching
an arylsulfonyl group to the N1-position in other chemical series,
such as 1-(benzenesulfonyl)-3-(1,2,3,6-tetrahydropyridin-4-yl)
indole, increased the affinity for the 5-HT6 receptor (8, Fig. 2) [32].
In our series, increased affinity was also observed for compound 30
(IC50 ¼ 2 nM). When the compound was tested for functional ac-
tivity, it was discovered to be a 5-HT6 receptor antagonist (inhibi-
tion of 5-HT induced stimulation of cAMP accumulation in HeLa
1. ii
2. iii
i
6
50
30
Scheme
2. Synthesis
of
1-(benzenesulfonyl)-5-chloro-2-methyl-3-(1,2,3,6-
tetrahydropyridin-4-yl)indole (30). Reagents and conditions: (i) di-tert-butyl dicar-
bonate (BOC), CH2Cl2, room temperature; (ii) PhSO2Cl, NaH, dimethylformamide, room
temperature; (iii) trifluoroacetic acid, CH2Cl2, room temperature.
that hydrogen-bond formation of a methoxy or hydroxy group is
not important for binding at the 5-HT6 receptor [39]. According to
Table 1, intrinsic activity (IA) varies with different substituents in
position 5. Interestingly, the chloro (6), bromo (12), fluoro (13) and
methoxy (14) groups display full agonist activity when the alkyl
group in position 2 is a methyl. The nitro (19), thiomethyl (18),
triflate (16) and the bulky aminosulfone (17) analogues were found
to be partial agonists [16,18]. Furthermore, the presence of an alkyl
group in position 2 seems to be very significant for high intrinsic
Table 1
5-HT6 receptor binding affinity and functional cAMP data for different 3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indoles: variation in N1-, 2- and 5-position at the indole ring.
R3
R2
R1
IC50 (nM)
EC50 (nM)
IA (%)
Functional activity
a
b
Cmpd
6g
eCl
eBr
eF
eOMe
eH
eOSO2CF3
eNHSO2Ph
eSMe
eNO2
eOPh(2-NO2)
eOiPr
e(3-thienyl)
ePh
eMe
eMe
eMe
eMe
eMe
eMe
eMe
eMe
eMe
eMe
eMe
eMe
eMe
ePh
eH
eH
eMe
eMe
eMe
eMe
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
eH
7.4 (ꢁ1.6)c
1.0 (ꢁ0.40)d
92d
100
100
100
78
AGO
AGO
AGO
AGO
pAGO
pAGO
pAGO
pAGO
pAGO
e
12
13
14g
15
16
17
18
19
20
21
22
23
24g
25
26g
27
28
29
30
10
2.7
30
80
5.3
5.8
200
50
1100
32
65
29e
20
21f
60f
58
6.6
32
ND
ND
ND
ND
0
130
200
ND
10
9
100
700
1000
2
20
79
40
28
ND
ND
ND
ND
0
44
55
ND
ND
ND
0f
e
e
e
eH
eCN
eOMe
eCl
eCl
ANTh
pAGO
pAGO
e
eMe
eEt
enPr
eSO2Ph
100
80
ND
e
eCl
eCl
ND
e
ANTh
2e
0f
Abbreviations: 5-HT6, 5-hydroxytryptamine type 6 receptor; AGO, full agonist; pAGO, partial agonist; ANT, antagonist; BHK, baby hamster kidney; cAMP, 30-50-cyclic
adenosine monophosphate; Cmpd, compound; HEK, human embryonic kidney; IA, intrinsic activity; [3H]LSD, [3H]Lysergic acid diethylamide; ND, not determined; SEM,
standard error of the mean.
a
Displacement of [3H]LSD binding to cloned human 5-HT6 receptors stably expressed in HEK cells [40], single determination.
Stimulation of cAMP production to cloned human 5-HT6 receptors stably expressed BHK cells [6], single determination.
b
c
Mean of four determinations (ꢁSEM).
d
Mean of three determinations (ꢁSEM).
e
Measurement done by Cerep (Poitiers, France), displacement of [3H]LSD binding to cloned human 5-HT6 receptors stably expressed in CHO cells [1], mean of two
determinations.
f
Measurement done by Cerep (Poitiers, France), stimulation of cAMP production in cloned human 5-HT6 receptors stably expressed BHK cells [40], single determination.
Previously published by Mattsson et al. [26].
Confirmed to be antagonists by inhibition of cAMP production of 5-HT induced stimulation of cAMP accumulation in HeLa cells stably expressing the human 5-HT6
g
h
receptors [40].

582
C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
cells stably expression the human 5-HT6 receptors [40]) which is in
line with what has been reported previously for this type of sub-
stitution [32]. This means that despite the presence of the 2-methyl
group, the compound is an antagonist and secondly, that this alkyl
group is tolerated in the antagonist binding mode.
In addition, a number of the new compounds (12, 13, 15, 16, 19,
22e24 and 26) were further screened for “off-target” affinities for
5-HT receptors (5-HT1A, 5-HT1B/1D, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4
and, 5-HT7) and serotonin transporter protein (SERT, Table 2). In
general, they displayed low affinity for these receptors and SERT,
except for 5-HT1B/1D where compound 12 (bromo), 16 (triflate) and,
22 [-(3-thienyl)] turned out to bind with high affinity. Comparing
the full agonists 6,12 and,13, a switch from a chloro group (6) in the
indole 5-position to a fluoro (13) or bromo (12) yields a lower
selectivity for 5-HT1B/1D receptors. A comparison between the
different selectivity profiles of the two 5-methoxy derivatives [26
(2-H) [41],14 (2-methyl)] yields that a 2-methyl group increases the
selectivity towards 5-HT1A (107-fold), 5-HT1B (51-fold) and 5-HT1D
(>50-fold) receptors.
Fig. 4. Alignment of 15 (thick bonds, green carbons), its 2-H analogue (white small
sphere on the 2-H) and 24 (thin bonds, green carbons) against LSD (thin bonds, grey
carbons). Abbreviations: LSD, (þ)-lysergic acid diethylamide. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
2.3. Conformation analysis
(þ)-Lysergic acid diethylamide (LSD) is a high-affinity partial
agonist at 5-HT6 receptors, with a Ki of 2 nM. It is proposed that the
ergoline moiety of LSD should represent the optimal conformation
by which tryptamine ligands bind to 5-HT6 receptors. This is
because the ergoline skeleton locks the aminoethyl side chain in
the tryptamine substructure, in a fully extended fashion [39,45e
47]. Rigid body alignment against LSD of three 3-(1,2,5,6-
tetrahydropyridin-4-yl)-1H-indoles (4-THPI) with eH, emethyl
(15) or ephenyl (24) in the indole 2-position is shown in Fig. 4.
Low-energy conformations from stochastic searches were used for
LSD and the 4-THPI analogues in the rigid body alignment. All
calculations were performed in the 2011.10 release of Chemical
Computing Group’s (www.chemcomp.com) Molecular Operating
Environment (MOE) software using the MMFF94s force field [48]
and born salvation [49]. Rotational profile calculations on the
bond between the piperidene and the indole rings for all three 4-
THPI analogues revealed a flat energy profile for all angles, except
angles close to 0 or 180ꢀ (i.e. the steric interactions seemed to
dominate over pi-system conjugation, even for the 2-H analogue).
In the alignment between LSD and the 4-THPI structures, there are
matches between N1 in the indole rings and the basic nitrogens.
Table 2
Selectivity data for other 5-HT receptors and serotonin transporter protein (SERT).a
No
R3/R2
5-HT IC50 (nM)a
1A 1B
SERT IC50 (nM)
1D
2A
2C
3
4
7
6b
eCl/eMe
eBr/eMe
eF/eMe
eOMe/eMe
eH/eMe
eOSO2CF3/eMe
eNO2/eMe
e(3-thienyl)/eMe
ePh/eMe
eH/ePh
eOMe/eH
660
660
>1000
430
5700
>1000
890
>1000
>1000
>1000
4
180
75
200
310
890
29
570
12
140
>1000
6
110
130
160
>1000
1200
35
310
33
390
>1000
20
240
400
950
>1000
1500
>1000
1000
>1000
>1000
50
450
420
700
>1000
2900
990
>1000
>1000
>1000
100
34
ND
ND
>1000
2300
ND
ND
ND
620
ND
ND
9800
1000
ND
ND
ND
ND
ND
3000
480
4500
4800
1900
>1000
>1000
>1000
>1000
>1000
>1000
ND
12
13
14b
15
16
19
22
23
24d
26c
3100
9800
>1000
1800
>1000
690
3700
ND
ND
ND
270
>1000
>1000
300
ND
ND
Abbreviations: 5-HT, 5-hydroxytryptamine; SERT, serotonin transporter protein; ND, not determined; h, human.
a
Binding methods according to Bartoszyk et al. [43] and Heinrich et al. [44], 5-HT1A ([3H]-8-OH-DPAT, rat), 5-HT1B ([125I]-iodocyanopindolol, rat), 5-HT1D ([3H]-5-HT, calf),
5-HT2A ([3H]-ketanserin, h), 5-HT2C ([3H]-mesulergine, h), 5-HT3 ([3H]-GR65630, NG 108 cells), 5-HT4 ([3H]-GR113808, guinea pig), 5-HT7 ([3H]-LSD, h) and, SERT ([3H]-5-HT,
rat), single determination.
b
Previously published by Mattsson et al. [26].
Selectivity profile reported before i.a., Macor et al. [41].
5-HT2A/2C reported before Crawforth et al. [42].
c
d

C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
583
This may explain the high affinity found in this series of 5-HT6 li-
4.1.2. General procedure for the synthesis of the 2-methyl-3-
(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole analogues (6, 12e23,
27e29)
gands. The 2-methyl (15) moiety overlaps better with LSD than
does the 2-H on the slightly extended hydrophobic volume that LSD
occupies in this region. The 2-phenyl (24) moiety extends even
further in this direction and could, therefore, participate in other
interactions that may explain its antagonistic profile.
2-Methyl-1H-indole derivatives (0.5e6 mmol, 1 equiv) were
stirred at 80 ꢀC in acetic acid (2 mL/1 mmol), 4-piperidone hydro-
chloride hydrate (1.5e18 mmol, 3 equiv) and 1 M phosphoric acid
(1 mL/1 mmol) were added. After 1e2 h, the mixture was poured
into ice/ammonia, and extracted with ethyl acetate (3 ꢂ 25 mL). The
combined organic layers were washed with water and brine, dried,
and evaporated in vacuo to give the title compounds. The crude
products were purified by silica gel column chromatography (ethyl
acetateemethanol, gradient) and most of them were converted to
the corresponding salts by dissolving the free base in methanol or
ethanol and adding one equivalent of oxalic acid or ethanolic HCl
solution. The solvent was removed and azeotroped with absolute
ethanol in vacuo followed by recrystallization from appropriate
solvents.
3. Conclusions
The physicochemical properties of the aromatic substituent in
the indole position 5 influence both the affinity and intrinsic ac-
tivity at 5-HT6 receptors. The substitution with chloro, bromo, nitro
and phenoxy substituents yields high-affinity ligands. However,
only the halogens (fluoro, chloro and bromo) and the methoxy
group induce full agonist properties. Structural features as the 2-
methyl group was also found to be important for full agonist
properties compared to the unsubstituted analogues, while sub-
stitution at the indole nitrogen (N1) with a benzenesulfonyl group
(30) switched the potent agonist 6 to be a 5-HT6 receptor antago-
nist (30). Therefore, by fine-tuning the R1, R2 and R3 substituents
within the 3-(1,2,3,6-tetrahydropyridine-4-yl)-1H-indole series, 5-
HT6 antagonists, partial agonists and full agonists can be achieved.
In addition, the selectivity profile towards other 5-HT subtypes and
SERT was in general good, with an exception for 5-HT1B/1D where
compounds 12 (bromo), 16 (triflate) and 22 [-(3-thienyl)] turned
out to bind with high affinity.
4.1.3. 5-Chloro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole (6)
The product was obtained in 81% yield from 5-chloro-2-methyl-
1H-indole. ESIMS: m/z 247.1 (M þ H)þ. 1H NMR (CD3OD, 300 MHz)
d
: 2.37e2.42 (m, 5H), 3.02 (t, J ¼ 5.1 Hz, 2H), 3.46 (s, 2H), 5.66 (s,
1H), 6.96 (dd, J ¼ 8.4, 1.8 Hz, 1H), 7.19 (d, J ¼ 8.7 Hz, 1H), 7.43 (d,
J ¼ 2.1 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d: 12.58, 30.72, 43.87,
45.53, 112.46, 115.48, 118.91, 121.41, 125.18, 125.45, 130.01, 132.14,
134.35, 135.28. Conversion to the oxalate salt and recrystallization
in methanol/diethyl ether gave 6 as a yellow powder. mp 196e
197 ꢀC (dec). Anal. (C14H15ClN2,C2H2O4) C, H, N.
4. Experimental section
4.1. Chemistry
4.1.4. 5-Bromo-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole (12)
4.1.1. Materials and methods
The product was obtained in 100% yield from 5-bromo-2-
All 1H NMR and 13C NMR experiments were performed on a
Varian VXR4000 or 300 MHz spectrometer (Varian, Darmstadt,
methyl-1H-indole. ESIMS: m/z 291.0, 293.0 (M þ H)þ. 1H NMR
(CD3OD, 300 MHz)
d
: 2.36e2.40 (m, 5H), 3.01 (t, J ¼ 5.7 Hz, 2H),
Germany). Chemical shifts are reported as
d
(ppm) relative to tet-
3.44 (s, 2H), 5.65 (s, 1H), 7.08e7.15 (m, 2H), 7.56 (s, 1H). 13C NMR
(CD3OD, 75 MHz) : 12.56, 30.74, 43.87, 45.54,112.89,112.93,115.38,
ramethylsilane (TMS) as internal standard. The following abbrevi-
ations are used: singlet (s), doublet (d), doublet of doublet (dd),
triplet (t), quadruplet (q), multiplet (m), broad singlet (br s). Elec-
trospray ionization mass spectra (ESIMS) were recorded on Agilent
1200 Series Liquid Chromatography/Mass Selective Detector (Agi-
lent Technologies, Stockholm, Sweden). Low resolution mass
spectra (EI, 70 eV) were recorded on HP5700 mass detector inter-
faced with a HP 5970 A gas chromatograph (Agilent Technologies,
Stockholm, Sweden) equipped with a fused silica column HP-1.
Melting points were determined using a Büchi 545 instrument
and are uncorrected (Kebo lab, Göteborg, Sweden). Elemental an-
alyses (C, H, N) were performed by Merck KGaA (Darmstadt, Ger-
d
121.99, 124.02, 125.26, 130.67, 132.10, 134.20, 135.51. Conversion to
the oxalate salt and recrystallization in ethanol/diethyl ether gave
12 as
a redebrown powder. Anal. (C14H15BrN2,C2H2O4,H2O)
C, H, N.
4.1.5. 5-Fluoro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole (13)
The product was obtained in 100% yield from 5-fluoro-2-
methyl-1H-indole. ESIMS: m/z 231.1 (M þ H)þ. 1H NMR (CD3OD,
300 MHz)
d
: 2.35e2.40 (m, 5H), 2.99 (t, J ¼ 5.7 Hz, 2H), 3.42 (s, 2H),
5.63 (s, 1H), 6.70e6.80 (m, 1H), 7.10e7.16 (m, 2H). 13C NMR (CD3OD,
75 MHz) : 12.73, 30.63, 43.89, 45.54, 104.20, 104.52, 108.96, 109.31,
many). The microwave heating was performed in
a
Smith
d
Synthesizer single-mode microwave cavity producing continuous
irradiation at 2450 MHz (Personal Chemistry AB, Uppsala, Sweden).
For further instructions see Alterman et al. [50] All purifications
were made at a Flash Master II automated flash chromatography
system (Biotage, Stockholm, Sweden), equipped with 20 g columns
packed with E. Merck silica gel 60 (0.040e0.063 mm) using
gradient solvent system isooctane/ethyl acetate/methanol. The
starting materials were purchased from commercial suppliers and
were used without purification 5-chloro-2-methyl-1H-indole, 5-
methoxy-2-methyl-1H-indole, 2-methyl-5-nitro-1H-indole, 5-
bromo-2-methyl-1H-indole, 5-fluoro-2-methyl-1H-indole and 2-
methyl-1H-indole. Compounds 6 [26], 14 [26,51], 15 [34] are
known but made by method reported within this publication.
Compounds 24 [52], 25 [41], and 26 [26,51] are known and syn-
thesized by published methods. Purity of all target compounds
where assessed as greater than 95% by elemental analysis (C, H, N).
111.87, 112.00, 115.84, 115.90, 124.76, 129.13, 129.26, 132.34, 133.44,
134.67, 157.45, 160.51. Crystallized as base to yield a yellow powder.
mp 163e165 ꢀC. Anal. (C14H15FN2,0.5H2O) C, H, N.
4.1.6. 5-Methoxy-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole (14)
The product was obtained in 100% yield from 5-methoxy-2-
methyl-1H-indole. ESIMS: m/z 243.1 (M þ H)þ. 1H NMR (CD3OD,
300 MHz)
d
: 2.36 (s, 3H), 2.44 (s, 2H), 3.02 (t, J ¼ 5.7 Hz, 2H), 3.45
(s, 2H), 3.77 (s, 3H), 5.65 (s, 1H), 6.67 (dd, J ¼ 8.7, 2.4 Hz, 1H), 6.97
(s, 1H), 7.10 (d, J ¼ 9 Hz, 1H). NMR (CD3OD, 75 MHz)
d
: 12.67,
30.75, 43.96, 45.59, 56.47, 102.62, 111.04, 111.91, 115.58, 124.44,
129.28, 132.23, 132.80, 133.36, 155.01. Conversion to the HCl salt
and recrystallization in methanol/diethyl ether gave 14 as a
brown powder. mp 226e228 ꢀC. Anal. (C15H18N2O,HCl,1/3H2O)
C, H, N.

584
C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
4.1.7. 2-Methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole (15)
The product was obtained in 50% yield from 2-methyl-1H-
3.43 (br s, 2H), 5.69 (s, 1H), 6.82 (dd J ¼ 8.4, 2.2 Hz, 1H), 6.90 (d,
J ¼ 8.7 Hz, 1H), 7.20e7.25 (m, 2H), 7.37 (d, J ¼ 8.4 Hz, 1H), 7.58 (t,
J ¼ 8.4 Hz, 1H), 8.01 (dd, J ¼ 8.1, 1.5 Hz, 1H), 11.17 (s, 1H). 13C NMR
indole. ESIMS: m/z 213.1 (M þ H)þ. 1H NMR (CD3OD, 300 MHz)
d:
2.38 (s, 3H), 2.46 (br s, 2H), 3.00 (t, J ¼ 5.7 Hz, 2H), 3.43 (br s, 2H),
(DMSO-d6, 75 MHz) d: 12.72, 29.90, 42.85, 44.76, 109.45, 111.85,
5.65 (br s, 1H), 6.91e7.02 (m, 2H), 7.22 (dd, J ¼ 7.8, 2.1 Hz, 1H), 7.46
113.03, 114.58, 118.13, 122.06, 124.67, 125.25, 127.78, 130.18, 132.63,
133.49, 134.53, 139.98, 147.27, 151.92. Crystallized as base to yield a
yellow powder. mp 187e188 ꢀC (dec). Anal. (C20H19N3O3,0.5H2O) C,
H, N.
(d, J ¼ 7.0 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d: 12.61, 30.79, 43.93,
45.58, 111.36, 115.58, 119.64, 119.74, 121.41, 124.42, 128.90, 132.40,
132.74, 136.94. Conversion to the oxalate salt and recrystallization
in ethanol/diethyl ether gave 15 as a yellow powder. mp 180e
181 ꢀC (dec). Anal. (C14H16N2,C2H2O4) C, H, N.
4.1.13. 5-Isopropoxy-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-
1H-indole (21)
4.1.8. [2-Methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indol-5-yl]
trifluoromethanesulfonate (16)
The product was obtained in 61% yield from 5-isopropoxy-2-
methyl-1H-indole (44). ESIMS: m/z 271.1 (M þ H)þ. 1H NMR
The product was obtained in 73% yield from (2-methyl-1H-
indol-5-yl) trifluoromethanesulfonate (45). ESIMS: m/z 361.0
(CD3OD, 300 MHz)
d
: 1.26 (d, J ¼ 6 Hz, 6H), 2.35e2.42 (m, 5H), 2.98
(t, J ¼ 5.5 Hz, 2H), 3.41 (s, 2H), 4.42 (heptamer, J ¼ 6.1 Hz, 1H), 5.63
(s, 1H), 6.68 (dd, J ¼ 8.7, 2.1 Hz, 1H), 7.02 (d, J ¼ 2.1 Hz, 1H), 7.13 (d,
(M þ H)þ. 1H NMR (CD3OD, 400 MHz)
d: 2.41 (s, 3H), 2.44 (t,
J ¼ 4.30 Hz, 2H), 3.06 (t, J ¼ 5.66 Hz, 2H), 3.49 (q, J ¼ 2.73 Hz, 2H),
5.71 (tt, J ¼ 3.32,1.56 Hz,1H), 6.94 (dd, J ¼ 8.79, 2.54 Hz,1H), 7.29 (d,
J ¼ 8.59 Hz,1H), 7.37 (d, J ¼ 2.34 Hz,1H). 13C NMR (CD3OD,101 MHz)
J ¼ 8.4 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d: 12.75, 22.65, 30.77,
43.92, 45.58, 73.02, 107.17, 111.81, 113.49, 115.49, 124.46, 129.32,
132.63, 132.68, 133.40, 152.49. Conversion to the oxalate salt and
recrystallized in ethanol/diethyl ether gave 21 as a redebrown
powder. mp 179e182 ꢀC (dec). Anal. (C17H22N2O,C2H2O4,0.5H2O)
C, H, N.
d: 12.57, 29.73, 43.34, 44.86, 111.74, 112.35, 114.20, 115.45, 115.90,
118.63, 121.81, 123.96, 124.99, 128.88, 131.89, 135.74, 136.06, 144.68.
Conversion to the oxalate salt and recrystallization in methanol/
diethyl ether gave 16 as a yellow powder. mp 201e203 ꢀC. Anal.
(C15H15F3N2O3S,C2H2O4) C, H, N.
4.1.14. 2-Methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-5-(3-thienyl)-
1H-indole (22)
4.1.9. N-[2-Methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indol-5-
yl]benzenesulfonamide (17)
The product was obtained in 85% yield from 2-methyl-5-(3-
thienyl)-1H-indole (39). ESIMS: m/z 295.1 (M þ H)þ. 1H NMR
The product was obtained in 25% yield from N-(2-methyl-1H-
(CD3OD, 300 MHz) d: 2.38 (s, 3H), 2.42e2.53 (m, 2H), 3.04 (t,
indol-5-yl)benzenesulfonamide (48). ESIMS: m/z 368.0 (M þ H)þ.1H
J ¼ 5.7 Hz, 2H), 3.46 (d, J ¼ 3 Hz, 2H), 5.70 (s,1H), 7.23 (d, 8.4 Hz,1H),
NMR (CD3OD, 400 MHz)
d
: 2.26e2.47 (m, 5H), 3.01 (t, J ¼ 5.65 Hz,
7.31 (dd, J ¼ 8.4, 1.8 Hz, 1H), 7.39 (s, 3H), 7.70 (s, 1H). 13C NMR
2H), 3.45 (d, J ¼ 2.61 Hz, 2H), 5.55 (s, 1H), 6.74 (dd, J ¼ 8.69, 2.03 Hz,
(75 MHz, CDCl3) d: 12.60, 30.91, 43.97, 45.62, 111.64, 116.02, 117.39,
1H), 6.99e7.17 (m, 2H), 7.40 (t, J ¼ 7.68 Hz, 2H), 7.47e7.57 (m, 1H),
118.97, 120.69, 124.82, 126.55, 127.56, 128.49, 129.35, 132.68, 133.25,
136.38, 145.45. Conversion to the oxalate salt and recrystallized in
methanol/diethyl ether gave 22 as a yellow powder. mp 230e
232 ꢀC. Anal. (C18H18N2S,0.75C2H2O4,0.25H2O) C, H, N.
7.60e7.68 (m, 2H).13C NMR (CD3OD,101 MHz)
d: 12.84, 30.77, 44.00,
45.66, 111.65, 115.81, 116.06, 119.35, 124.61, 128.62, 129.12, 129.93,
132.51, 133.62, 133.99, 135.39, 141.35. mp 187e188 ꢀC.
Anal. (C20H21N3O2S,H2O) C, H, N.
4.1.15. 2-Methyl-5-phenyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole (23)
4.1.10. 2-Methyl-5-methylsulfanyl-3-(1,2,3,6-tetrahydropyridin-4-
yl)-1H-indole (18)
The product was obtained in 72% yield from 2-methyl-5-phenyl-
The product was obtained in 56% yield from 2-methyl-5-
1H-indole (38). ESIMS: m/z 289.1 (M þ H)þ. 1H NMR (CD3OD,
methylsulfanyl-1H-indole (41). ESIMS: m/z 259.1 (M þ H)þ. 1H
300 MHz) d: 2.36 (s, 3H), 2.44 (s, 2H), 2.96 (s, 2H), 3.35e3.38 (m, 2H),
NMR (CDCl3, 300 MHz)
d: 1.97 (br s, 2H), 2.37 (s, 3H), 2.48 (s, 3H), 3.14
5.66 (s, 1H), 7.19e7.36 (m, 5H), 7.56 (d, J ¼ 6 Hz, 2H), 7.68 (s, 1H). 13
C
(t, J ¼ 5.7 Hz, 2H), 3.57 (s, 2H), 5.75 (s, 1H), 7.14e7.15 (m, 2H), 7.58 (s,
NMR (CD3OD, 75 MHz) d: 12.68, 30.91, 43.91, 45.58, 111.70, 116.06,
1H), 8.53 (br s, 1H). 13C NMR (CDCl3, 75 MHz)
d: 12.69, 19.21, 30.30,
118.08, 121.11, 124.88, 126.97, 128.04, 129.45, 129.57, 132.56, 133.26,
133.47, 136.48, 144.30. Conversion to the oxalate salt and recrystal-
lization in ethanol/diethyl ether gave 23 as a yellow powder. mp
221e223 ꢀC. Anal. (C20H20N2,0.75C2H2O4,0.25H2O) C, H, N.
43.42, 45.30, 110.77, 120.57, 120.92, 123.26, 125.19, 127.14, 128.40,
130.51, 131.70, 133.97. Conversion to the oxalate salt and recrystal-
lization in ethanol/diethyl ether gave 18 as an orange powder. mp
192e193 ꢀC. Anal. (C15H18N2S,C2H2O4,0.25H2O) C, H, N.
4.1.16. 5-Chloro-1,2-dimethyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-
1H-indole (27)
4.1.11. 2-Methyl-5-nitro-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
indole (19)
The product was obtained in 86% yield from 5-chloro-1,2-
The product was obtained in 100% yield from 2-methyl-5-nitro-
dimethyl-1H-indole (32). ESIMS: m/z 261.0 (M þ H)þ. 1H NMR
1H-indole. ESIMS: m/z 258.1 (M þ H)þ. 1H NMR (CD3OD, 300 MHz)
(CD3OD, 300 MHz)
d
: 2.38e2.28 (m, 5H), 2.94 (t, J ¼ 5.5 Hz, 2H),
d
: 2.41e2.45 (m, 5H), 3.07 (t, J ¼ 5.7 Hz, 2H), 3.48e3.71 (m, 2H), 5.74
3.35e3.43 (m, 5H), 5.51 (s, 1H), 6.94, (dd, J ¼ 8.4, 1.8 Hz, 1H), 7.03 (d,
(s, 1H), 7.28 (d, J ¼ 8.7 Hz, 1H), 7.91 (dd, J ¼ 8.7, 2.1 Hz, 1H), 8.38 (d,
J ¼ 8.7 Hz, 1H), 7.39, (d, J ¼ 1.8 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d:
J ¼ 2.1 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d
: 12.56, 30.79, 43.84,
11.12, 29.74, 30.97, 43.83, 45.53,110.81,115.64,118.90,121.39,125.53,
126.12, 129.05, 131.94, 135.71, 136.22. Conversion to the HCl salt and
recrystallization in ethanol/diethyl ether gave 27 as a yellow pow-
der. mp 253e255 ꢀC. Anal. (C15H17ClN2,HCl,0.25H2O) C, H, N.
45.58, 111.34, 116.48, 117.09, 117.95, 126.45, 128.27, 131.41, 136.54,
140.07, 142.33. Crystallized as base to yield a yellow powder. mp
217e219 ꢀC (dec). Anal. (C14H15N3O2,0.5H2O) C, H, N.
4.1.12. 2-Methyl-5-(2-nitrophenoxy)-3-(1,2,3,6-tetrahydropyridin-
4-yl)-1H-indole (20)
4.1.17. 5-Chloro-1-ethyl-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-
yl)-1H-indole (28)
The product was obtained in 82% yield from 2-methyl-5-(2-
The product was obtained in 46% yield from 5-chloro-1-ethyl-2-
nitrophenoxy)-1H-indole (46). ESIMS: m/z 350.0 (M þ H)þ. 1H
methyl-1H-indole (33). ESIMS: m/z 275.0 (M þ H)þ. 1H NMR
NMR (DMSO-d6, 300 MHz)
d
: 2.35 (s, 2H), 2.42 (s, 3H), 2.93 (br s, 2H),
(CD3OD, 400 MHz)
d: 1.28 (t, J ¼ 7.08 Hz, 3H), 2.42 (s, 3H), 2.64e2.87

C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
585
(m, 2H), 3.49 (t, J ¼ 6.07 Hz, 2H), 3.88 (d, J ¼ 3.03 Hz, 2H), 4.16 (q,
J ¼ 7.33 Hz, 2H), 5.67 (br s, 1H), 7.06 (dd, J ¼ 8.72, 1.90 Hz, 1H), 7.29
(d, J ¼ 8.59 Hz, 1H), 7.48 (d, J ¼ 2.02 Hz, 1H). 13C NMR (CD3OD,
The organic portion was dried (MgSO4) and the solvent was
removed under reduced pressure. The residue was purified by flash
chromatography on silica gel (ethyl acetate/methanol, gradient) to
give the title compounds.
101 MHz) d: 11.22, 15.60, 27.72, 39.09, 42.54,43.51, 111.51, 114.09,
119.06, 119.87, 122.14, 126.24, 129.13, 132.82, 135.46, 135.96. Con-
version to the HCl salt and recrystallization in methanol/diethyl
ether gave 28 as a yellow powder. mp 247e250 ꢀC. Anal.
(C16H19ClN2,HCl) C, H, N.
4.1.21. 5-Chloro-1,2-dimethyl-indole (32)
The product was obtained in 64% yield from 5-chloro-2-methyl-
1H-indole. MS m/z (relative intensity, 70 eV) 179 (bp), 178 (97), 143
(20), 128 (20), 115 (36); ESIMS: m/z 180.1 (M þ H)þ. 1H NMR (CDCl3,
4.1.18. 5-Chloro-2-methyl-1-propyl-3-(1,2,3,6-tetrahydropyridin-4-
yl)-1H-indole (29)
300 MHz) d: 2.34 (s, 3H), 3.52 (s, 3H), 6.12 (s, 1H), 7.03 (s, 2H), 7.42
(s, 1H). 13C NMR (CDCl3, 75 MHz)
d: 12.63, 29.35, 99.20, 109.55,
Theproductwasobtainedin76%yieldfrom5-chloro-2-methyl-1-
118.84, 120.41, 124.74, 128.86, 135.66, 138.25.
propyl-1H-indole (34). ESIMS: m/z 289.1 (M þ H)þ. 1H NMR (CD3OD,
300 MHz)
d
: 0.87 (t, J ¼ 7.2 Hz, 3H),1.67 (sextet, J ¼ 7.2 Hz, 2H), 2.35e
4.1.22. 5-Chloro-1-ethyl-2-methyl-indole (33)
2.40 (m, 5H), 3.00 (t,J ¼ 5.5 Hz, 2H), 3.42(s, 2H), 3.96 (t, J¼ 7.2Hz, 2H),
5.59 (s,1H), 6.97 (dd, J ¼ 8.4, 2.1 Hz,1H), 7.17 (d, J ¼ 8.4 Hz,1H), 7.40 (d,
The product was obtained in 79% yield from 5-chloro-2-methyl-
1H-indole. MS m/z (relative intensity, 70 eV) 195 (18), 193 (Mþ, 52),
J ¼ 2.1 Hz,1H). 13C NMR (CD3OD, 75 MHz)
d: 11.21,11.58, 24.40, 31.02,
180 (33), 178 (bp), 143 (18). 1H NMR (CDCl3, 300 MHz)
d
: 1.25 (t,
J ¼ 7.2 Hz, 3H), 2.35 (s, 3H), 4.02 (q, J ¼ 7.2 Hz, 2H), 6.13 (s, 1H), 7.05
(q, 2H), 7.44 (s, 1H). 13C NMR (CDCl3, 75 MHz)
: 12.47, 15.08, 37.76,
43.87, 45.56, 45.65, 111.24, 115.94, 119.00, 121.47, 125.57, 126.31,
129.28, 132.10, 135.22, 135.77. Conversion to the oxalate salt and
recrystallization in methanol/diethyl ether gave 29 as a yellow
powder. mp 151e154 ꢀC. Anal. (C17H21ClN2,C2H2O4,0.5H2O) C, H, N.
d
99.52, 109.60, 118.96, 120.39, 124.67, 129.10, 134.52, 137.44.
4.1.23. 5-Chloro-2-methyl-1-propyl-indole (34)
4.1.19. 1-(Benzenesulfonyl)-5-chloro-2-methyl-3-(1,2,3,6-
tetrahydropyridin-4-yl)indole (30)
The product was obtained in 40% yield from 5-chloro-2-methyl-
1H-indole. MS m/z (relative intensity, 70 eV) 209 (15), 207 (Mþ, 41),
tert-butyl
4-(5-chloro-2-methyl-1H-indol-3-yl)-3,6-dihydro-
180 (32), 178 (bp), 143 (12). 1H NMR (CD3OD, 300 MHz)
d: 0.83 (t,
2H-pyridine-1-carboxylate (50, 0.68 g, 1.96 mmol) was dissolved in
4 mL anhydrous dimethylformamide at 0 ꢀC and 60% NaH (0.094 g,
2.35 mmol) was added. The mixture was stirred under N2 until
evolution of H2 gas ceased (approx. 30 min). Benzenesulfonyl
chloride (0.38 g, 2.15 mmol) was added and the mixture was
allowed to stir for 2 h. Brine was added and the reaction mixture
was extracted with ethyl acetate. The organic portion was dried
(MgSO4) and the solvent was removed under reduced pressure to
afford 0.37 g in 38% yield of tert-butyl 4-[1-(benzenesulfonyl)-5-
chloro-2-methyl-indol-3-yl]-3,6-dihydro-2H-pyridine-1-
J ¼ 7.5 Hz, 3H), 1.66 (q, J ¼ 7.5 Hz, 2H), 2.32 (s, 3H), 3.92 (t, J ¼ 7.5 Hz,
2H), 6.08 (s, 1H), 6.97 (dd, J ¼ 8.4, 1.8 Hz, 1H), 7.13 (d, J ¼ 8.7 Hz, 1H),
7.34 (d, J ¼ 2.1 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d: 11.50, 12.71,
24.33, 45.46, 100.43, 111.16, 119.64, 121.12, 125.55, 130.55, 136.56,
139.35.
4.1.24. 2-Methyl-5-phenyl-1H-indole (38)
5-bromo-2-methyl-1H-indole (0.5 g, 2.38 mmol) was dissolved
in anhydrous toluene (50 mL) and Pd(PPh3)4 (0.12 g, 0.11 mmol)
was added. The resulting solution was allowed to stir for 30 min
under nitrogen flow. Phenylboronic acid (0.43 g, 3.57 mmol) was
dissolved in 15 mL absolute ethanol and added to the reaction,
followed by saturated 25 mL aqueous NaHCO3. The reaction
mixture was heated to reflux overnight. The solvent was evapo-
rated and the residue was dissolved in water and ethyl acetate. The
organic portion was dried (MgSO4) and the solvent was removed
under reduced pressure. The residue was purified by flash chro-
matography on silica gel (isooctane/ethyl acetate, gradient) to give
the title compound in 48% yield (0.23 g, 0.48 mmol). MS m/z
(relative intensity, 70 eV) 207 (Mþ, bp), 206 (74), 178 (10), 165 (10),
carboxylate. 1H NMR (CDCl3, 400 MHz)
d: 1.54 (s, 9H), 2.35 (br s,
2H), 2.55 (s, 3H), 3.66 (t, J ¼ 5.6 Hz, 2H), 4.10 (br s, 2H), 5.68 (br s,
1H), 7.26 (dd, J ¼ 9.2, 2 Hz, 1H), 7.33 (d, J ¼ 2 Hz, 1H), 7.41e7.55 (m,
2H), 7.57e7.62 (m, 1H), 7.78 (dd, J ¼ 7.2, 1.2 Hz, 2H), 8.16 (d,
J ¼ 9.2 Hz, 1H). The residue was re-dissolved in dichloromethane
(20 mL) and 1 mL TFA was added. After 2 h at room temperature
(RT), the reaction was quenched with 10% Na2CO3 and extracted
with CH2Cl2 and dried. The residue was purified by flash chroma-
tography on silica gel (ethyl acetate/methanol, gradient) to give the
title compound (0.19 g, 25%). ESIMS: m/z 387.1 (M þ H)þ. 1H NMR
(CD3OD, 400 MHz)
d
: 2.23 (dd, J ¼ 4.87, 2.71 Hz, 2H), 2.53 (s, 3H),
152 (7); ESIMS: m/z 208.1 (M þ H)þ. 1H NMR (CD3OD, 300 MHz)
d
:
3.02 (t, J ¼ 5.69 Hz, 2H), 3.43 (d, J ¼ 2.98 Hz, 2H), 5.68 (d, J ¼ 1.62 Hz,
1H), 7.22 (dd, J ¼ 8.80, 2.03 Hz, 1H), 7.37 (d, J ¼ 2.17 Hz, 1H), 7.48 (t,
J ¼ 7.85 Hz, 2H), 7.55e7.65 (m, 1H), 7.78 (dd, J ¼ 8.53, 1.22 Hz, 2H),
2.37 (s, 3H), 6.14 (s, 1H), 7.19e7.36 (m, 5H), 7.56e7.63 (m, 3H). 13
C
NMR (CD3OD, 75 MHz)
d: 13.51, 100.77, 111.53, 118.54, 120.85,
126.85, 127.98, 129.51, 131.07, 133.47, 137.36, 137.45, 144.25.
8.10 (d, J ¼ 8.94 Hz, 1H). 13C NMR (CD3OD, 101 MHz)
d: 13.96, 30.39,
43.74, 45.58, 117.02, 119.99, 124.93, 125.28, 127.61, 129.84, 130.18,
130.63, 130.81, 132.68, 135.48, 135.71, 136.07, 140.11. Conversion to
the oxalate salt and recrystallization in ethanol/methanol/diethyl
4.1.25. 2-Methyl-5-(3-thienyl)-1H-indole (39)
5-Bromo-2-methyl-1H-indole (0.5 g, 2.38 mmol) was dissolved
in anhydrous toluene (50 mL) and Pd(PPh3)4 (0.12 g, 0.11 mmol)
was added. The resulting solution was allowed to stir for 30 min
under nitrogen flow. 3-Thiopheneboronic acid (0.45 g, 3.57 mmol)
was dissolved in 15 mL absolute ethanol and added to the reaction,
followed by saturated 25 mL aqueous NaHCO3. The reaction
mixture was heated to reflux overnight. The solvent was evapo-
rated and the residue was dissolved in water and ethyl acetate. The
organic portion was dried (MgSO4) and the solvent was removed
under reduced pressure. The residue was purified by flash chro-
matography on silica gel (isooctane/ethyl acetate, gradient) to give
the title compound in 84% yield (0.42 g, 1.96 mmol). MS m/z
(relative intensity, 70 eV) 213 (Mþ, bp), 212 (73),167 (9),139 (4),106
ether gave 30 as
a
yellow powder. mp 185e186 ꢀC. Anal.
(C20H19ClN2O2S,C2H2O4) C, H, N.
4.1.20. General procedure for the alkylation of 5-chloro-2-methyl-
1H-indole (32e34)
5-Chloro-2-methyl-1H-indole (0.9e5.1 mmol, 1 equiv) was
dissolved in 2e4 mL anhydrous dimethylformamide at 0 ꢀC and 60%
NaH (1.1e6.2 mmol, 1.2 equiv) was added, The mixture was stirred
under N2 until evolution of H2 gas ceased (approx. 30 min). Iodo-
ethane, iodomethane or 1-iodopropane (1.1e6.2 mmol, 1.2 equiv)
was added and the mixture was allowed to stir for 12 h. Brine was
added and the reaction mixture was extracted with ethyl acetate.
(8). 1H NMR (CDCl3, 300 MHz)
d: 2.38 (s, 3H), 6.21 (s, 1H), 7.22 (d,

586
C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
J ¼ 8.23 Hz, 1H), 7.35 (dd, J ¼ 6.30, 0.76, 2H), 7.38e7.46 (m, 1H), 7.72
(s, 2H). 13C NMR (CDCl3, 75 MHz)
: 13.65, 100.70, 110.38, 117.47,
118.53, 120.18, 125.61, 126.79, 127.96, 129.52, 135.45, 135.77, 143.81.
(relative intensity, 70 eV) 279 (Mþ, 53),146 (bp),118 (66),117 (27), 91
(11). 1H NMR (CDCl3, 400 MHz)
: 2.45 (s, 3H), 6.26 (dd, J ¼ 2.15,
d
d
0.98 Hz,1H), 6.99 (dd, J ¼ 8.79, 2.54 Hz,1H), 7.25 (d, J ¼ 4.69 Hz,1H),
7.39 (d, J ¼ 2.34 Hz, 1H), 8.03 (br s, 1H). 13C NMR (CDCl3, 101 MHz)
d:
4.1.26. 2-Methyl-5-methylsulfanyl-1H-indole (41)
13.77, 101.26, 110.94, 111.95, 113.94, 114.09, 117.28, 120.47, 123.66,
129.38, 134.84, 137.94, 143.70.
A solution of the 5-methylsulfonyl-1H-indole-2-carboxylic acid
(0.5 g, 1.97 mmol) in dioxan (10 mL) was added drop-wise to an ice-
cooled suspension of lithium aluminium hydride (1.48 g,
38.9 mmol) in dioxan (10 mL). The mixture was refluxed for 15 h
and after cooling, excess lithium aluminium hydride was destroyed
with 3 M sodium hydroxide solution/water. Inorganic salts were
filtered off. Dioxane was evaporated and the residue extracted with
ethyl acetate, dried (MgSO4) and evaporated to yield an oil which
was purified by flash chromatography on silica gel (isooctane/ethyl
acetate, gradient) to give the title compound in 0.055 g (16%). MS
m/z (relative intensity, 70 eV). 177 (Mþ, bp), 162 (99), 130 (20), 118
(26), 117 (25). ESIMS: m/z 178.0 (M þ H)þ. 1H NMR (CDCl3,
4.1.30. 2-Methyl-5-(2-nitrophenoxy)-1H-indole (46)
A heavy-walled Pyrex tube was charged with 2-methyl-1H-
indol-5-ol (43, 0.2 g, 1.35 mmol), 1-fluoro-2-nitrobenzene (0.21 mg,
1.49 mmol), Cs2CO3 (0.5 g, 1.53 mmol) in dimethylformamide
(4 mL). The reaction mixture was exposed to microwave irradiation
(140 ꢀC) for 10 min. This procedure was repeated five times. The
pooled reactions were diluted with ethyl acetate, and extracted
with water and 10% aqueous Na2CO3. The organic phases were
separated, pooled, dried (MgSO4) and concentrated to give the
crude product. Purification was performed using flash chromatog-
raphy on silica gel (isooctane/ethyl acetate, gradient) to give the
title compound in 36% yield (0.66 g, 2.46 mmol). MS m/z (relative
intensity, 70 eV) 268 (Mþ, 49), 220 (16), 207 (11), 146 (bp), 118 (63).
300 MHz)
d
: 2.36 (s, 3H), 2.48 (s, 3H), 6.13 (s,1H), 7.12 (s, 2H), 7.50 (s,
1H), 7.74 (s, 1H). 13C NMR (CDCl3, 75 MHz)
d: 13.55, 18.76, 99.95,
110.68, 120.40, 122.84, 127.40, 129.79, 134.72, 135.90.
ESIMS: m/z 269.0 (M þ H)þ. 1H NMR (CDCl3, 300 MHz)
d: 2.40 (s,
4.1.27. 2-Methyl-1H-indol-5-ol (43)
3H), 6.19 (s,1H), 6.86 (q, J ¼ 8.4 Hz, 2H), 7.06 (t, J ¼ 7.2 Hz,1H), 7.21e
7.26 (m, 2H), 7.37 (t, J ¼ 7.8 Hz,1H), 7.92 (d, J ¼ 8.4 Hz,1H), 8.09 (br s,
To a cooled (0 ꢀC), stirred solution of 5-methoxy-2-methyl-1H-
indole (3.5 g, 21.7 mmol) in dichloromethane (200 mL), boron tri-
bromide 1 M in dichloromethane solution (10 mL, 108 mmol) was
added drop-wise. The reaction mixture was allowed to stir at RT for
2 h, before being poured into ice water, and extracted with ethyl
acetate. The organic phase was washed with water and brine, dried
(Na2SO), filtered, and concentrated in vacuo to afford the title
compound (3.13 g, 98%). MS m/z (relative intensity, 70 eV) 147 (Mþ,
82), 146 (bp), 118 (16), 117 (14), 91 (11). ESIMS: m/z 148.0 (M þ H)þ.
1H). 13C NMR (CDCl3, 75 MHz)
d: 13.54, 100.49, 100.60, 111.32,
113.93, 118.52, 121.36, 125.35, 129.71, 133.51, 133.89, 137.14, 140.13,
148.21, 152.96.
4.1.31. N-(2-Methyl-1H-indol-5-yl)benzenesulfonamide (48)
To
a solution of 2-methyl-1H-indol-5-amine (47, 0.98 g,
6.7 mmol) in 10 mL pyridine, was added benzenesulfonyl chloride
(1.4 g, 8.0 mmol) in portions over 10 min. The reaction was stirred at
RT for 4 h, and then quenched with 10% HCl and ethyl acetate. The
organic phase was dried with MgSO2, filtrated and the solvent
evaporated. The crude product was further purified with flash
chromatograph (ethyl acetate/methanol), 1.72 g (6.0 mmol) in 89%
yield. MS m/z (relative intensity, 70 eV) 286 (Mþ, 27), 207 (9), 145
(bp), 118 (26), 77 (17); ESIMS: m/z 287.1 (M þ H)þ. 1H NMR (CD3OD,
1H NMR (CD3OD, 400 MHz)
d
: 2.34 (s, 3H), 5.94 (s, 1H), 6.55 (dd,
J ¼ 8.59, 2.34 Hz, 1H), 6.79 (d, J ¼ 2.34 Hz, 1H), 7.05 (d, J ¼ 8.59 Hz,
1H). 13C NMR (CD3OD, 101 MHz)
: 13.50, 99.71, 104.65, 110.73,
111.54, 131.27, 132.87, 137.34, 151.07.
d
4.1.28. 5-Isopropoxy-2-methyl-1H-indole (44)
At RT, diethyl azodicarboxylate (DEAD, 0.672 mL, 4.27 mmol)
was slowly added to a solution of 2-methyl-1H-indol-5-ol (43,
0.42 g, 2.85 mmol), Ph3P (1.49 g, 5.7 mmol) and propan-2-ol
(0.214 g, 3.56 mmol), in 40 mL of CH2Cl2. The mixture was stirred
at RT until the reaction was complete (TLC analysis) and then
quenched with methanol (3 mL). Water was added and the mixture
was extracted with CH2Cl2. The organic extracts were washed with
water and brine, dried over MgSO4, and concentrated to give the
crude product. Purification was performed using flash chromatog-
raphy on silica gel (isooctane/ethyl acetate, gradient) to give the
title compound in 69% yield (0.31 g, 1.63 mmol). MS m/z (relative
intensity, 70 eV) 189 (Mþ, 40), 147 (bp), 146 (72), 118 (13), 117 (11).
300 MHz)
(m, 2H), 7.41 (m, 2H), 7.49 (m, 1H), 7.63 (m, 2H); 13C NMR (CD3OD,
75 MHz) : 13.62, 100.59, 111.51, 116.16, 118.70, 128.52, 129.81,
d: 2.35 (s, 3H), 5.98 (s,1H), 6.68 (dd, J ¼ 8.8, 2 Hz,1H), 7.05
d
129.92, 130.86, 133.67, 136.40, 138.15, 141.23.
4.1.32. tert-Butyl 4-(5-chloro-2-methyl-1H-indol-3-yl)-3,6-
dihydro-2H-pyridine-1-carboxylate (50)
A solution of 5-chloro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-
yl)-1H-indole (6, 0.17 g, 0.70 mmol) and di-tert-butyl dicarbonate
(0.17 g, 0.77 mmol) in dichloromethane (0.6 M) was stirred for 1 h.
The reaction mixture was quenched with aqueous 10% Na2SO4 and
the organic phase was evaporated (0.70 g, 96%) as a white solid.
ESIMS: m/z 190.0 (M þ H)þ. 1H NMR (CD3OD, 300 MHz)
d
: 1.26 (d,
ESIMS:m/z 345.1 (M ꢃ H)ꢃ.1H NMR (CD3OD, 400 MHz)
d: 1.50 (s, 9H),
J ¼ 6 Hz, 6H), 2.36 (s, 3H), 4.42 (pentamer, J ¼ 6 Hz, 1H), 6.01 (s, 1H),
2.36 (s, 3H), 2.45 (s, 2H), 3.58e3.65 (m, 2H), 4.05 (s, 2H), 5.61 (s, 1H),
6.97 (dd, J ¼ 8.8, 2 Hz,1H), 7.18 (d, J ¼ 8.4 Hz,1H), 7.38 (d, J ¼ 2 Hz,1H).
6.64 (dd, J ¼ 8.7, 2.4 Hz, 1H), 6.94 (d, J ¼ 2.4 Hz, 1H), 7.11 (d,
J ¼ 8.4 Hz, 1H). 13C NMR (CD3OD, 75 MHz)
d: 13.52, 22.59, 72.95,
100.18, 107.30, 111.66, 113.36, 131.01, 133.63, 137.42, 152.46.
4.2. Biology
4.1.29. (2-Methyl-1H-indol-5-yl) trifluoromethanesulfonate (45)
2-methyl-1H-indol-5-ol (43, 0.41 g, 2.78 mmol), triethylamine
(0.71 g, 6.96 mmol), and 1,1,1-trifluoro-N-phenyl-N-(trifluorometh-
ylsulfonyl)methanesulfonamide PhN(SO2CF3)2 (1.49 g, 4.17 mmol)
were dissolved in CH2Cl2 (20 mL), and the mixture was stirred at RT.
After 2 h the mixture was diluted with CH2Cl2 (100 mL), washed
with 10% aqueous Na2CO3, dried over MgSO4 and concentrated to
give the crude product. Purification was performed using flash
chromatography on silica gel (isooctane/ethyl acetate, gradient) to
give the title compound in 68% yield (0.53 g, 1.89 mmol). MS m/z
4.2.1. Materials and methods
Foetal calf serum (FCS; Life Technologies, Karlsruhe, Germany)
was heat-inactivated at 54 ꢀC for 30 min immediately after the first
thawing. Phosphate-buffered saline and minimum essential me-
dium MEM-a were obtained from Life Technologies (Karlsruhe,
Germany). Serotonin creatinine sulphate was purchased from
Merck KGaA (Darmstadt, Germany). cAMP was measured using a
Biotrak cAMP enzyme immunoassay kit (Amersham-Pharmacia,
Uppsala, Sweden). For functional testing of 5-HT6 ligands, BHK cells
were stably transfected with the human 5-HT6 receptor.

C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
587
4.2.2. Method of 3H-LSD binding assay for 5-HT6 receptor
[4] R.P. Ward, D.M. Dorsa, Molecular and behavioral effects mediated by Gs-
coupled adenosine A2a, but not serotonin 5-HT4 or 5-HT6 receptors
following antipsychotic administration, Neuroscience 89 (1999) 927e938.
[5] J. Arnt, C.K. Olsen, 5-HT6 receptor ligands and their antipsychotic potential,
Int. Rev. Neurobiol. 96 (2011) 141e161.
[6] A.J. Sleight, F.G. Boess, M. Bos, B. Levet-Trafit, C. Riemer, A. Bourson, Charac-
terization of Ro 04-6790 and Ro 63-0563: potent and selective antagonists at
human and rat 5-HT6 receptors, Br. J. Pharmacol. 124 (1998) 556e562.
[7] J. Arnt, B. Bang-Andersen, B. Grayson, F.P. Bymaster, M.P. Cohen,
N.W. DeLapp, B. Giethlen, M. Kreilgaard, D.L. McKinzie, J.C. Neill,
D.L. Nelson, S.M. Nielsen, M.N. Poulsen, J.M. Schaus, L.M. Witten, Lu
The test was performed according to Kohen et al. with modifi-
cations as follows [40]. Compounds were dissolved in DMSO
(1 mM) and diluted to the appropriate concentrations with test
buffer (20 mM HEPES, 0.1% ascorbic acid, adjusted to pH 7.4 with
NaOH). 20
37 ꢀC with 80
burg; spec. act. 80e90 Ci/mmol, 1 nM final concentration) and
100 l of membrane suspension (23 g protein, RB-HS6; Receptor
m
l of the compound solution was incubated for 1 h at
ml
3H-LSD (TRK-1041, Amersham Pharmacia, Frei-
m
m
AE58054,
a 5-HT6 antagonist, reverses cognitive impairment induced by
Biology Inc., Beltsville, MD, USA). The reaction was terminated by
rapid filtration (GFB filter, Whatman, pre-soaked for 1 h with 0.1%
aqueous polyethyleneimine). Filters were washed three times with
3 mL test buffer (see above) and transferred to mini vials. After
addition of 2 mL scintillant (Ultima Gold, Packard, Frankfurt, Ger-
many) radioactivity was determined in a liquid scintillation counter
(Packard, Frankfurt, Germany). Calculation of IC50/Ki-values was
performed with RS1 (BBN Software Cooperation).
subchronic phencyclidine in a novel object recognition test in rats, Int. J.
Neuropsychopharmacol. 13 (2010) 1021e1033.
[8] D.J. Heal, S.L. Smith, A. Fisas, X. Codony, H. Buschmann, Selective 5-HT6 re-
ceptor ligands: progress in the development of a novel pharmacological
approach to the treatment of obesity and related metabolic disorders, Phar-
macol. Ther. 117 (2008) 207e231.
[9] N.V. Ruiz, G. Oranias Olsina, Patents, Int. Rev. Neurobiol. 94 (2010) 35e66.
[10] F. Borsini, F. Bordi, T. Riccioni, 5-HT6 pharmacology inconsistencies, Pharma-
col. Biochem. Behav. 98 (2010) 169e172.
[11] A. Tassone, G. Madeo, T. Schirinzi, D. Vita, F. Puglisi, G. Ponterio, F. Borsini,
A. Pisani, P. Bonsi, Activation of 5-HT6 receptors inhibits corticostriatal glu-
tamatergic transmission, Neuropharmacology 61 (2011) 632e637.
[12] T. Riccioni, F. Bordi, P. Minetti, G. Spadoni, H.M. Yun, B.H. Im, G. Tarzia,
H. Rhim, F. Borsini, ST1936 stimulates cAMP, Ca2þ, ERK1/2 and Fyn kinase
through a full activation of cloned human 5-HT6 receptors, Eur. J. Pharmacol.
661 (2011) 8e14.
[13] V. Valentini, R. Frau, F. Bordi, F. Borsini, G. Di Chiara, A microdialysis study
of ST1936, a novel 5-HT6 receptor agonist, Neuropharmacology 60 (2011)
602e608.
[14] R.A. Glennon, M. Lee, J.B. Rangisetty, M. Dukat, B.L. Roth, J.E. Savage,
A. McBride, L. Rauser, S. Hufeisen, D.K. Lee, 2-Substituted tryptamines: agents
with selectivity for 5-HT(6) serotonin receptors, J. Med. Chem. 43 (2000)
1011e1018.
[15] J. Holenz, P.J. Pauwels, J.L. Diaz, R. Merce, X. Codony, H. Buschmann, Medicinal
chemistry strategies to 5-HT(6) receptor ligands as potential cognitive en-
hancers and antiobesity agents, Drug Discov. Today 11 (2006) 283e299.
[16] D.C. Cole, W.J. Lennox, S. Lombardi, J.W. Ellingboe, R.C. Bernotas, G.J. Tawa,
H. Mazandarani, D.L. Smith, G. Zhang, J. Coupet, L.E. Schechter, Discovery of 5-
arylsulfonamido-3-(pyrrolidin-2-ylmethyl)-1H-indole derivatives as potent,
selective 5-HT6 receptor agonists and antagonists, J. Med. Chem. 48 (2005)
353e356.
[17] I. Kendall, H.A. Slotten, X. Codony, J. Burgueno, P.J. Pauwels, J.M. Vela,
K.C. Fone, E-6801, a 5-HT6 receptor agonist, improves recognition memory by
combined modulation of cholinergic and glutamatergic neurotransmission in
the rat, Psychopharmacology (Berlin) 213 (2011) 413e430.
4.2.3. Cell culture
Recombinant BHK cells were grown in 75 cm2 cell culture flasks
with a filter, in a culture medium consisting of MEM-a medium
with 10% dialysed, heat-inactivated FCS, at 37 ꢀC under a humidi-
fied atmosphere containing 5% CO2. New medium was added every
2 days. The cells were subcultured once weekly.
4.2.4. Stimulation of cAMP formation [6]
Cells were grown to semi-confluence, and harvested by treat-
ment with a solution of 5 mM EDTA in PBS at 37 ꢀC for 2 min. The
cells were suspended in culture medium, counted, transferred into
a 96-well micro titer plate with 10,000 cells/well, and incubated for
at least 12 h until complete adherence. Immediately prior to the
experiment, the cell culture medium was replaced after careful
washing with 180
and/or serotonin were added in 20
m
l serum-free MEM-
a
medium. Test compounds
, producing 200
ml MEM-
a
ml
total volume per well. For the determination of agonistic effects,
test compounds were added to the cells. For the determination of
antagonistic effects, test compounds were incubated in the pres-
[18] J. Holenz, R. Merce, J.L. Diaz, X. Guitart, X. Codony, A. Dordal, G. Romero,
A. Torrens, J. Mas, B. Andaluz, S. Hernandez, X. Monroy, E. Sanchez,
E. Hernandez, R. Perez, R. Cubi, O. Sanfeliu, H. Buschmann, Medicinal chem-
istry driven approaches toward novel and selective serotonin 5-HT6 receptor
ligands, J. Med. Chem. 48 (2005) 1781e1795.
[19] E. Alcalde, N. Mesquida, S. Lopez-Perez, J. Frigola, R. Merce, Indene-based
scaffolds. 2. An indole-indene switch: discovery of novel indenylsulfonamides
as 5-HT6 serotonin receptor agonists, J. Med. Chem. 52 (2009) 675e687.
[20] D.C. Cole, J.R. Stock, W.J. Lennox, R.C. Bernotas, J.W. Ellingboe, S. Boikess,
J. Coupet, D.L. Smith, L. Leung, G.M. Zhang, X. Feng, M.F. Kelly, R. Galante,
P. Huang, L.A. Dawson, K. Marquis, S. Rosenzweig-Lipson, C.E. Beyer,
L.E. Schechter, Discovery of N1-(6-chloroimidazo[2,1-b][1,3]thiazole-5-
sulfonyl)tryptamine as a potent, selective, and orally active 5-HT(6) recep-
tor agonist, J. Med. Chem. 50 (2007) 5535e5538.
ence of 0.1 mM serotonin. The cells were incubated in the presence
of test compounds for 45 min. The culture supernatant was care-
fully removed and the cells were washed once with PBS. Intracel-
lular cAMP was determined with the Biotrak cAMP Enzyme
Immunoassay following the descriptions of the manufacturer.
Acknowledgements
We thank Anna Sandahl, Mikael Andersson, and Elin Hammar
for help with the synthetic chemistry experiments. For review of
the manuscript, we thank Abigail Woollard.
[21] L.E. Schechter, Q. Lin, D.L. Smith, G. Zhang, Q. Shan, B. Platt, M.R. Brandt,
L.A. Dawson, D. Cole, R. Bernotas, A. Robichaud, S. Rosenzweig-Lipson,
C.E. Beyer, Neuropharmacological profile of novel and selective 5-HT6 re-
ceptor agonists: WAY-181187 and WAY-208466, Neuropsychopharmacology
33 (2008) 1323e1335.
Appendix A. Supplementary data
[22] R.C. Bernotas, S. Lenicek, S. Antane, D.C. Cole, B.L. Harrison, A.J. Robichaud,
G.M. Zhang, D. Smith, B. Platt, Q. Lin, P. Li, J. Coupet, S. Rosenzweig-Lipson,
C.E. Beyer, L.E. Schechter, Novel 1-aminoethyl-3-arylsulfonyl-1H-pyrrolo
[2,3-b]pyridines are potent 5-HT(6) agonists, Bioorg. Med. Chem. 17 (2009)
5153e5163.
[23] R.C. Bernotas, S. Antane, R. Shenoy, V.D. Le, P. Chen, B.L. Harrison,
A.J. Robichaud, G.M. Zhang, D. Smith, L.E. Schechter, 3-(Arylsulfonyl)-1-(aza-
cyclyl)-1H-indoles are 5-HT(6) receptor modulators, Bioorg. Med. Chem. Lett.
20 (2010) 1657e1660.
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.ejmech.2013.03.
006. These data include MOL files and InChiKeys of the most
important compounds described in this article.
References
[24] G. de Foubert, M.J. O’Neill, T.S. Zetterstrom, Acute onset by 5-HT(6)-receptor
activation on rat brain brain-derived neurotrophic factor and activity-
regulated cytoskeletal-associated protein mRNA expression, Neuroscience
147 (2007) 778e785.
[1] F.J. Monsma Jr., Y. Shen, R.P. Ward, M.W. Hamblin, D.R. Sibley, Cloning and
expression of a novel serotonin receptor with high affinity for tricyclic psy-
chotropic drugs, Mol. Pharmacol. 43 (1993) 320e327.
[25] R.A. Glennon, U. Siripurapu, B.L. Roth, R. Kolanos, M.L. Bondarev, D. Sikazwe,
M. Lee, M. Dukat, The medicinal chemistry of 5-HT6 receptor ligands with a
focus on arylsulfonyltryptamine analogs, Curr. Top. Med. Chem. 10 (2010)
579e595.
[26] C. Mattsson, C. Sonesson, A. Sandahl, H.E. Greiner, M. Gassen, J. Plaschke,
J. Leibrock, H. Bottcher, 2-Alkyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-
[2] M.L. Woolley, C.A. Marsden, K.C. Fone, 5-HT6 receptors, Curr. Drug Targets CNS
Neurol. Disord. 3 (2004) 59e79.
[3] C. Gerard, S. el Mestikawy, C. Lebrand, J. Adrien, M. Ruat, E. Traiffort,
M. Hamon, M.P. Martres, Quantitative RT-PCR distribution of serotonin 5-HT6
receptor mRNA in the central nervous system of control or 5,7-
dihydroxytryptamine-treated rats, Synapse 23 (1996) 164e173.

588
C. Mattsson et al. / European Journal of Medicinal Chemistry 63 (2013) 578e588
indoles as novel 5-HT6 receptor agonists, Bioorg. Med. Chem. Lett. 15
(2005) 4230e4234.
[40] R. Kohen, M.A. Metcalf, N. Khan, T. Druck, K. Huebner, J.E. Lachowicz,
H.Y. Meltzer, D.R. Sibley, B.L. Roth, M.W. Hamblin, Cloning, characterization,
[27] G. Castaneda-Corral, H.I. Rocha-Gonzalez, C.I. Araiza-Saldana, M. Ambriz-
Tututi, G.C. Vidal-Cantu, V. Granados-Soto, Role of peripheral and spinal 5-
HT6 receptors according to the rat formalin test, Neuroscience 162 (2009)
444e452.
and chromosomal localization of a human 5-HT6 serotonin receptor,
J. Neurochem. 66 (1996) 47e56.
[41] J.E. Macor, C.A. Burkhart, J.H. Heym, J.L. Ives, L.A. Lebel, M.E. Newman,
J.A. Nielsen, K. Ryan, D.W. Schulz, L.K. Torgersen, 3-(1,2,5,6-Tetrahydropyrid-
[28] A. Meneses, G. Perez-Garcia, G. Liy-Salmeron, D. Flores-Galvez, C. Castillo,
E. Castillo, The effects of the 5-HT(6) receptor agonist EMD and the 5-HT(7)
receptor agonist AS19 on memory formation, Behav. Brain Res. 195 (2008)
112e119.
[29] H.M. Yun, H. Rhim, 5-HT6 receptor ligands, EMD386088 and SB258585,
differentially regulate 5-HT6 receptor-independent events, Toxicol. In Vitro
25 (2011) 2035e2040.
4-yl)pyrrolo[3,2-b]pyrid-5-one: a potent and selective serotonin (5-HT1B)
agonist and rotationally restricted phenolic analogue of 5-methoxy-3-
(1,2,5,6-tetrahydropyrid-4-yl)indole, J. Med. Chem. 33 (1990) 2087e2093.
[42] J. Crawforth, S. Goodacre, R. Maxey, S. Bourrain, S. Patel, R. Marwood,
D. O’Connor, R. Herbert, P. Hutson, M. Rowley, 3-(4-Piperidinyl)- and 3-(8-
aza-bicyclo[3.2.1]oct-3-yl)-2-phenyl-1H-indoles as bioavailable h5-HT2A an-
tagonists, Bioorg. Med. Chem. Lett. 10 (2000) 2701e2703.
[30] X. Zhang, P.E. Andren, R.A. Glennon, P. Svenningsson, Distribution, level,
pharmacology, regulation, and signaling of 5-HT6 receptors in rats and mar-
mosets with special reference to an experimental model of parkinsonism,
J. Comp. Neurol. 519 (2011) 1816e1827.
[43] G.D. Bartoszyk, C. Van Amsterdam, H.E. Greiner, W. Rautenberg, H. Russ,
C.A. Seyfried, Sarizotan, a serotonin 5-HT1A receptor agonist and dopamine
receptor ligand. 1. Neurochemical profile, J. Neural Transm. 111 (2004)
113e126.
[31] A. Nikiforuk, T. Kos, A. Wesolowska, The 5-HT6 receptor agonist EMD 386088
produces antidepressant and anxiolytic effects in rats after intrahippocampal
administration, Psychopharmacology (Berlin) 217 (2011) 411e418.
[32] D.C. Cole, J.W. Ellingboe, W.J. Lennox, H. Mazandarani, D.L. Smith, J.R. Stock,
[44] T. Heinrich, H. Bottcher, R. Gericke, G.D. Bartoszyk, S. Anzali, C.A. Seyfried,
H.E. Greiner, C. Van Amsterdam, Synthesis and structureeactivity relationship
in a class of indolebutylpiperazines as dual 5-HT(1A) receptor agonists and
serotonin reuptake inhibitors, J. Med. Chem. 47 (2004) 4684e4692.
[45] C.D. Unsworth, P.B. Molinoff, Characterization of a 5-hydroxytryptamine re-
ceptor in mouse neuroblastoma N18TG2 cells, J. Pharmacol. Exp. Ther. 269
(1994) 246e255.
[46] M.G. Russell, R. Dias, Memories are made of this (perhaps): a review of se-
rotonin 5-HT(6) receptor ligands and their biological functions, Curr. Top.
Med. Chem. 2 (2002) 643e654.
G.
Zhang,
P.
Zhou,
L.E.
Schechter,
N1-Arylsulfonyl-3-(1,2,3,6-
tetrahydropyridin-4-yl)-1H-indole derivatives are potent and selective 5-
HT6 receptor antagonists, Bioorg. Med. Chem. Lett. 15 (2005) 379e383.
[33] D.C. Cole, W.J. Lennox, J.R. Stock, J.W. Ellingboe, H. Mazandarani, D.L. Smith,
G. Zhang, G.J. Tawa, L.E. Schechter, Conformationally constrained N1-
arylsulfonyltryptamine derivatives as 5-HT6 receptor antagonists, Bioorg.
Med. Chem. Lett. 15 (2005) 4780e4785.
[34] K. Freter, 3-Cycloalkenylindoles, J. Org. Chem. 40 (1975) 2525e2529.
[35] D.S.C. Black, N. Kumar, L.C.H. Wong, Synthesis of 4,6-dimethoxyindoles, Aust.
J. Chem. 39 (1986) 15e20.
[47] B.L. Roth, S.C. Craigo, M.S. Choudhary, A. Uluer, F.J. Monsma Jr., Y. Shen,
H.Y. Meltzer, D.R. Sibley, Binding of typical and atypical antipsychotic agents
to
5-hydroxytryptamine-6
and
5-hydroxytryptamine-7
receptors,
J. Pharmacol. Exp. Ther. 268 (1994) 1403e1410.
[36] K. Torisu, K. Kobayashi, M. Iwahashi, Y. Nakai, T. Onoda, T. Nagase, I. Sugimoto,
Y. Okada, R. Matsumoto, F. Nanbu, S. Ohuchida, H. Nakai, T. Masaaki, Devel-
opment of prostaglandin D2 receptor antagonist: discovery of highly potent
antagonists, Bioorg. Med. Chem. 12 (2004) 4685e4700.
[37] G.M. Carrera, G.S. Sheppard, Synthesis of 6- and 7-arylindoles via palladium-
catalyzed cross-coupling of 6- and 7-bromoindole with arylboronic acids,
Synlett (1994) 93e94.
[48] T.A. Halgren, Merck molecular force field. I. Basis, form, scope, parameteri-
zation, and performance of MMFF94, J. Comput. Chem. 17 (1996) 490e519.
[49] M. Wojciechowski, B. Lesyng, Generalized born model: analysis, refinement,
and applications to proteins, J. Phys. Chem. B 108 (2004) 18368e18376.
[50] M. Alterman, A. Hallberg, Fast microwave-assisted preparation of aryl and
vinyl nitriles and the corresponding tetrazoles from organo-halides, J. Org.
Chem. 65 (2000) 7984e7989.
[38] J. Wei, B.A. Pio, H. Cai, S.P. Meduna, S. Sun, Y. Gu, W. Jiang, R.L. Thurmond,
L. Karlsson, J.P. Edwards, Pyrazole-based cathepsin S inhibitors with improved
cellular potency, Bioorg. Med. Chem. Lett. 17 (2007) 5525e5528.
[39] R.A. Glennon, M. Bondarev, M. Lee, 5-HT6 serotonin receptor binding of
indolealkylamines: a preliminary structureeaffinity investigation, Med. Chem.
Res. 9 (1999) 108e117.
[51] J. Guillaume, C. Dumont, J. Laurent, L. Nedelec, (Tetrahydro-1,2,3,6 pyridinyl-
4)-3
1 H-indoles: synthese, proprietes serotoninergique et anti-dop-
aminergiques, Eur. J. Med. Chem. 22 (1987) 33e43.
[52] D.J. Hallett, U. Gerhard, S.C. Goodacre, L. Hitzel, T.J. Sparey, s. Thomas,
M. Rowley, Neighboring group participation of the indole nucleus: an unusual
DAST-mediated rearrangement reaction, J. Org. Chem. 65 (2000) 4984e4993.