N-acetyl-5-arylalkoxytryptamine analogs: Probing the melatonin receptors for MT1-selectivity

Article abstract of DOI:10.1002/ardp.201100125

A series of melatonin analogs obtained by the replacement of the ether methyl group with larger arylalkyl and aryloxyalkyl substituents was prepared in order to probe the melatonin receptors for MT₁-selectivity. The most MT₁-selective agents 11 and 15 were substituted with a Ph(CH ₂)₃ or a PhO(CH₂)₃ group. Compounds 11 and 15 displayed 11.5-fold and 11-fold higher affinity for the MT₁ receptors than for the MT₂ subtype. Interestingly, in our binding assay 11 and 15 have shown considerably higher MT₁-affinity and selectivity than the reference ligand, the dimeric agomelatine 1a. The synthesis and pharmacological evaluation of a novel series of MLT analogs obtained by replacing the ether methyl group with arylalkyl and aryloxyalkyl moieties is described here. The results indicate for compounds 11 and 15 considerably higher MT₁-affinity and selectivity than the reference ligand, the dimeric agomelatine 1a. Copyright

Full text of DOI:10.1002/ardp.201100125

666
Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
Full Paper
N-Acetyl-5-arylalkoxytryptamine Analogs: Probing the
Melatonin Receptors for MT1-Selectivity
Christian Markl1, William P. Clafshenkel2, Mohamed I. Attia1y, Shalini Sethi2,
Paula A. Witt-Enderby2, and Darius P. Zlotos3
1 Institute of Pharmacy and Food Chemistry, Pharmaceutical Chemistry, University of Wu¨rzburg, Wu¨rzburg,
Germany
2 Division of Pharmaceutical Sciences, School of Pharmacy, Duquesne University, Pittsburgh, PA, USA
3 The German University in Cairo, Department of Pharmaceutical Chemistry, New Cairo City, Cairo, Egypt
A series of melatonin analogs obtained by the replacement of the ether methyl group with larger
arylalkyl and aryloxyalkyl substituents was prepared in order to probe the melatonin receptors for
MT1-selectivity. The most MT1-selective agents 11 and 15 were substituted with a Ph(CH2)3 or a
PhO(CH2)3 group. Compounds 11 and 15 displayed 11.5-fold and 11-fold higher affinity for the
MT1 receptors than for the MT2 subtype. Interestingly, in our binding assay 11 and 15 have
shown considerably higher MT1-affinity and selectivity than the reference ligand, the dimeric
agomelatine 1a.
Keywords: Melatonin analogs / Melatonin receptors / MT1 receptor / MT2 receptor
Received: April 5, 2011; Revised: May 11, 2011; Accepted: May 13, 2011
DOI 10.1002/ardp.201100125
Introduction
The optimal distance between the dimer head groups for
MT1-selectivity was determined to be three methylene groups
[4]. The resulting compound 1a behaved as MT1 antagonist
and displayed 224-times higher affinity for the MT1 receptors
(Ki ¼ 0.5 nM) than for the MT2 receptors (Ki ¼ 112 nM)
expressed in the HEK-cells. In the CHO-cells, the correspond-
ing Ki MT1/Ki MT2 ratio was reduced to 38 [5]. Extension of the
spacer to four methylene units to give compound 1b resulted
in a reduced MT1-selectivity in HEK-cells (121-fold) and similar
MT1-selectivity in CHO-cells (54-fold) when compared to
the C3-analog 1a [5]. Recently, a series of heterodimer analogs
of 1b, formally obtained by replacement of one of its agome-
latine units with various aryl moieties showing MT1-selectiv-
ity between 5- and 93-fold (CHO-cells) has been synthesized [6].
The most MT1-selective ligand in this series is the biphenyl-
carboxylic acid analog 1c. The findings indicate that a biva-
lent ligand is not necessary to achieve MT1 selectivity.
Another dimeric MT1-selective agent was obtained by direct
coupling of two agomelatine units via the aromatic carbon
atoms to give the agonist 2 [4]. Diverse monomeric ligands
displayed only moderate MT1-selectivity with the 4-phenyl-
butyl substituted benzoxazole analog 3 [7] and the hexyloxy
The neurohormone melatonin (N-acetyl-5-methoxytrypt-
amine, MLT, Fig. 1) exerts its diverse physiological actions
mostly through activation of the two high affinity G-protein-
coupled MT1 and MT2 receptors [1].
An accurate characterization of melatonin receptor-medi-
ated functions requires MT1 and MT2-selective ligands. While
many series of MT2-selective agents have been published
in the last decade, pronounced MT1-selectivity is still a
challenge with only few examples of MT1-selective agents
reported up to date [2]. A common structural feature in
the recently reported MT2-selective ligands, most of them
behaving as antagonists, is a lipophilic substituent located
out of the plane of their core nucleus in a position corre-
sponding to N1 or C2 of MLT [3]. The most MT1-selective
agents (Table 1) are dimers of the non-selective agonist ago-
melatine obtained by connecting two agomelatine units via
their ether oxygen atoms by a polymethylene spacer.
Correspondence: Darius P. Zlotos, The German University in Cairo,
Department of Pharmaceutical Chemistry, New Cairo City, 11835 Cairo,
Egypt.
E-mail: darius.zlotos@guc.edu.eg
Fax: þ20 27581041
yCurrent address: Department of Pharmaceutical Chemistry, College of
Pharmacy, King Saud University, Riyadh, Saudi Arabia
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Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
N-Acetyl-5-arylalkoxytryptamine Analogs
667
Table 1. MT1-Selective ligands and their binding constants Ki [nM]
at the MT1 and MT2 receptors.
NHCOMe
MeO
MT1
MT2
N
H
NHAc
AcHN
Figure 1. Structure of melatonin (MLT).
0.5 a
3.9 b
112 a
149 b
1a
chromane analog 4 [4] being the most selective examples.
The only common structural feature of MT1-selective
ligands seems to be the the presence of a bulky hydrophobic
substituent in a position topologically equivalent to the
methoxy group of MLT. However, the optimal length of this
substituent, as well as the nature of the terminal aromatic
ring generating MT1-selectivity has not been investigated
until now. In this paper, we describe the synthesis and
pharmacological evaluation of a novel extensive series of
MLT analogs obtained by replacement of the ether methyl
group with arylalkyl and aryloxyalkyl moieties of different
chain lengths. The binding affinities of the novel compounds
for the human MT1 and MT2 melatonin receptors expressed
in CHO-cells were determined and compared to those of the
most known MT1-selective reference compound 1a tested in
the same binding assay.
(CH2 )3
O
O
NHAc
AcHN
0.6 a
3.1 b
73 a
1b
1c
2
167 b
(CH2)4
O
O
NHAc
CO2H
0.55 b
51 b
(CH2)4
O
O
Results and discussion
AcNH
3.2 a
5.2 b
253 a
246 b
Chemistry
The dimeric agomelatine 1a was prepared from O-demethyl-
agomelatine and 1,3-dibromopropane using K2CO3 in MeCN
as described by Descamps-Francois et al. [3] in 66% yield.
However, as we observed a considerably different melting
point (mp 113–1168C) from the one reported (mp 101–1038C)
[3], compound 1a was fully characterized by NMR, MS, HPLC
and combustion analysis to confirm its structure. Moreover, a
by-product, O-allyl-O-demethylagomelatine, was observed as a
result of HBr elimination from the monoalkylated intermedi-
ate. In order to obtain the corresponding dimer of MLT 5, the
same reaction conditions were applied to N-acetyl-5-hydroxy-
tryptamine 6 yielding the allyl ether 7 as a major product.
The desired dimeric MLT 5 could be obtained in 35% yield
under liquid-liquid-liquid phase transfer catalysis conditions
(TBAB, NaOH, NaCl, toluene, H2O) [8] using 1-bromo-3-chloro-
propane as starting material (Scheme 1). All other target
compounds were prepared by alkylation of 6 with different
alkyl halides. For the commercially available 6, we developed
two new synthetic approaches starting from the lower-priced
5-benzyloxyindole-3-acetonitrile (Scheme 1). A two step reac-
tion sequence involved reduction of the nitrile group using
NaBH4, NiCl2 ꢀ 6 H2O, Ac2O followed by debenzylation of the
resulting (benzyloxyindolyl)-ethylacetamide 8 by means of
ammonium formate, 10% Pd/C. A more convenient one step
NHAc
H
N
3
0.63 c
22 c
O
O
N
NHAc
O
1.2 a
3.4 b
29 a
21 b
H3C
4
(CH2 )5
O
a
b
HEK-cells, CHO-cells, NIH3T3-cells
c
reaction applied Raney Ni-Pd/C catalytic hydrogenation in
the presence of Ac2O. O-Alkylation of 6 with a variety
of arylalkylhalides was carried out using the standard
procedure (K2CO3, CH3CN, 18 h reflux) to give the target
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Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
Discussion
To our surprise, the reference MT1-selective ligand, the
dimeric agomelatine 1a, displayed a much lower affinity
for the MT1 receptors (Ki ¼ 112 nM) than the affinity reported
by Descamps-Francois et al. [3] and Audinot et al. (Ki ¼ 3.9 nM)
[4]. Moreover, instead of the expected high MT1-selectivity
(Ki MT2/Ki MT1 ¼ 38) [4] we observed lower selectivity (3.2-fold)
for the MT1 subtype. It should be mentioned that the same
cell-lines (CHO-cells) were used in both laboratories.
Moreover, MLT competition assays run in parallel as control
experiments gave similar MT1 (0.46 nM vs. 0.22 nM [5]) and
MT2 (0.95 nM vs. 0.35 nM [5]) binding constants. Though these
differences cannot be explained, these findings underscore
the importance of running multiple reference compounds
when conducting pharmacological analyses of compounds
that have ideally different binding profiles to minimize the
variability of results between labs. This then allows for better
more direct comparisons of the pharmacological data
obtained from the different laboratories.
CN
NHAc
Ph
O
Ph
O
(i)
N
H
N
H
(ii)
8
(iii)
NHAc
NHAc
HO
RO
(iv)
N
N
H
H
6
method A: 9, 11, 13, 15, 19
(v)
method B: 7, 10, 12, 14,
16-18, 20
The structure of agomelatine has been derived from MLT by
the bioisosteric replacement of the indole ring with a
naphthalene scaffold. In order to examine which of the
two ring systems generates higher MT1-selectivity, we syn-
thesized a dimeric MLT 5 obtained by connecting two MLT
units via C3 spacer. Compound 5 displayed a 4-fold lower
affinity for the MT1 receptors (Ki ¼ 464 nM) and an 8-fold
lower affinity for the MT2 subtype (Ki ¼ 2828 nM) than the
dimeric agomelatine 1a resulting in an increased MT1-selec-
tivity ratio of 6. The higher affinities of the agomelatine
analog for both MLT receptor subtypes are in agreement with
the binding profile of the monomers, as agomelatine displays
higher binding for both receptors than MLT [3].
NHAc
AcHN
O
O
N
N
H
H
5
Scheme
1. Reagents
and
conditions:
(i)
NaBH4,
Ac2O, NiCl2 ꢀ 6 H2O, MeOH, rt, 20 h; (ii) ammonium formate, 10%
Pd/C, EtOH, reflux, 2 h; (iii) Raney Ni, 10% Pd/C, 400 kPa H2, THF,
Ac2O, 508C, 12 h; (iv) method A: K2CO3, CH3CN, respective alkyla-
tion agent, reflux, 18 h, method B: Cs2CO3, CH3CN, respective
alkylation agent, 608C, 4 h; (v) NaOH, NaCl, TBAB, H2O,
Br-(CH2)3-Cl, toluene, 508C, 3 h.
A common structural feature of MT1-selective ligands is the
the presence of a bulky hydrophobic substituent in a position
topologically equivalent to the methoxy group of MLT. In
order to examine the optimal length of this substituent, as
well as the nature of the terminal aromatic ring generating
MT1-selectivity, we replaced the ether methyl group of MLT
with arylalkyl and aryloxyalkyl moieties of different chain
lengths. The allyl (7) and 2-naphthyl (9) analogs displayed low
nanomolar affinities for both MT1 and MT2 receptors without
pronounced subtype selectivity. The O-benzyl derivative (8) main-
tained the high affinity for the MT2 receptors (Ki ¼ 1.8 nM)
when compared to MLT (Ki ¼ 1 nM) while its binding for
the MT1-subtype was 30-times reduced (Ki ¼ 14.6 nM) relative
to the parent compound resulting in 8-fold selectivity
toward the MT2 receptors. Compound 8 has already been
reported to be MT2-selective displaying 18-fold higher affinity
for MT2-receptors (Ki ¼ 6.6 nM) than for the MT1-receptors
(Ki ¼ 118 nM) expressed in NIH3T3 cells [9]. The differences
in binding affinities and selectivity ratio can most likely be
explained by different cell lines used in both binding assays.
ethers 9, 11, 13, 15, and 19 (see Table 2 for structures). The
remaining target compounds 7, 10, 12, 14, 16–18, and 20 were
obtained according to a modified alkylating protocol using
Cs2CO3 as base, lower temperature (608C) and shorter reac-
tion time (4 h).
Pharmacology
The affinity of the target compounds for human MT1 or MT2
melatonin receptors expressed in CHO cells was measured by
competition binding analysis using the radioligand, 2-[125I]-iodo-
melatonin. Melatonin competition assays were run in parallel
and the affinity of melatonin for the MT1 or MT2 melatonin
receptors was in the range of the reported literature. For the
sake of comparison, the most MT1-selective ligand reported to
date, the dimeric agomelatine analog 1a, was included in
our study The results are compiled in Table 2. One of the most
MT1-selective ligands 15 was subjected to functional studies
using cyclic AMP assay in CHO cells expressing human MT1
or MT2 receptors. The results are shown in Fig. 2.
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Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
N-Acetyl-5-arylalkoxytryptamine Analogs
669
Table 2. Binding affinitya of compounds 1a and 5–20 for the human MT1 and MT2 receptors expressed in CHO cells obtained in competition
radioligand binding assays using 2-[125I]-iodomelatonin.
R
O
NHAc
N
H
R
MT1 pKi ꢁ SEM (Ki, nM)
MT2 pKi ꢁ SEM (Ki, nM)
Ki MT2/Ki MT1
1a
MLT
5
–
6.95 ꢁ 0.03 (112)
9.34 ꢁ 0.10 (0.46)
6.33 ꢁ 0.02 (464)
6.45 ꢁ 0.03 (355)
9.02 ꢁ 0.09 (0.95)
5.55 ꢁ 0.04 (2828)
3.2
2.1
6.1
–CH3
(CH2)3O
NHAc
N
H
–
7
9
–CH –CH CH
2
8.20 ꢁ 0.03 (6.3)
8.09 ꢁ 0.14 (8.1)
8.76 ꢁ 0.01 (1.7)
7.74 ꢁ 0.02 (18.3)
0.27
2.3
–
2
8
–CH2-Ph
–(CH2)2-Ph
–(CH2)3-Ph
–(CH2)4-Ph
–(CH2)5-Ph
–(CH2)2-OPh
–(CH2)3-OPh
7.84 ꢁ 0.02 (14.6)
9.83 ꢁ 0.12 (0.15)
8.40 ꢁ 0.12 (3.9)
8.33 ꢁ 0.08 (4.7)
7.13 ꢁ 0.07 (74)
8.97 ꢁ 0.09 (1.1)
8.10 ꢁ 0.08 (7.9)
7.31 ꢁ 0.06 (49.2)
8.74 ꢁ 0.12 (1.8)
9.72 ꢁ 0.04 (0.19)
7.35 ꢁ 0.41 (45.0)
7.99 ꢁ 0.02 (10.2)
8.09 ꢁ 0.07 (8.2)
8.57 ꢁ 0.05 (2.7)
7.06 ꢁ 0.15 (87)
7.78 ꢁ 0.03 (16.7)
0.12
1.3
10
11
12
13
14
15
16
11.5
2.2
0.11
2.5
11
0.34
(CH2)3O
17
8.38 ꢁ 0.04 (4.1)
8.13 ꢁ 0.02 (7.4)
1.8
(CH2)3O
18
19
7.63 ꢁ 0.03 (23.6)
7.15 ꢁ 0.04 (71.6)
7.74 ꢁ 0.22 (18.1)
6.84 ꢁ 0.02 (145)
0.77
2.0
(CH2)3O
O
(CH2)3
N
O
20
–(CH2)5–CH3
8.31 ꢁ 0.08 (4.9)
8.18 ꢁ 0.12 (6.6)
1.3
a
pKi values were calculated from IC50 values obtained from competitive curves according to the method of Cheng and Prusoff [12] and
are the mean of three determinations.
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Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
Figure 2. Functional analysis of melatonin (1 pM–10 nM; closed circles) in the absence or presence of 15 (10 nM; open circles) to inhibit
forskolin-induced cAMP accumulation in CHO cells expressing the human MT1 melatonin receptor (MT1-CHO) or human MT2 melatonin
receptor (MT2-CHO). Each data point represents the average ꢁ SEM of two experiments. Where appropriate, curves were fit by non-linear
regression analysis by 1-site fit to obtain potency (IC50) and maximal inhibitory values using GraphPad Prism software.
Elongation of the benzyl side chain in 8 by one methylene
group led to a complete loss of MT2-selectivity. The resulting
phenylethyl analog 10 exhibited the highest affinities for
melatonin receptors of the whole series (Ki ¼ 0.15 and 0.19
nM for MT1 and MT2). A further increase in chain length
reversed the subtype selectivity generating the most MT1-
selective agent 11. Compound 11 with a C3 spacer between
MLT and the phenyl group displayed a 11.5-fold higher bind-
ing for the MT1 (Ki ¼ 3.9 nM) than for the MT2 receptors
(Ki ¼ 45 nM). Its MT1-selectivity is 3.6-times higher than that
of the reference agent 1a. A further elongation of the poly-
methylene spacer abolished MT1-selectivity. In the C4-homo-
log 12, the additional CH2-group caused a 4-fold increase of
binding for MT2 receptors (Ki ¼ 10.2 nM) while the MT1-
affinity was unchanged (Ki ¼ 4.7 nM) when compared to
the C3 analog 11 resulting in considerable reduction of
MT1-selectivity. The C5-homolog 13 displayed a 16-fold
decrease of binding to MT1 receptors (Ki ¼ 74 nM) and
unchanged MT2-affinity relative to the C4-analog 12 generat-
ing a 9-fold selectivity for the MT2 receptors. The data in the
homologous C1-C5 series 8, 10–13 revealed the optimal chain
length for MT1 -selectivity to be C3 which is in agreement with
the results in the dimeric agomelatine series [3]. Introduction
of a second ether oxygen to the most MT1-selective ligand 11
maintained its superior pharmacological profile. The result-
ing phenyloxy analog 15 displayed an 11-fold higher affinity
for the MT1 (Ki ¼ 7.9 nM) than for the MT2 receptors (Ki ¼ 87
nM). Reduction of the spacer length from C3 to C2 resulted in
loss of MT1-selectivity giving a high-affinity non-selective
ligand 14 (Ki ¼ 1.1 and 2.7 nM for MT1 and MT2).
16 represents a structural modification of the reference
ligand 1a obtained by the removal of the ethylacetamide
side chain from one naphthyl moiety and replacement of
the other naphthyl scaffold by the indole ring. These struc-
tural changes led to a 2.3-fold decrease of MT1 (49 nM) and 21-
fold decrease of MT2-affinity (16.7 nM) generating a reversed
3-fold preference toward the MT2 subtype.
Another replacement of the phenyl group by the phthal-
imide moiety in the MT1-selective agent 11 to give compound
19 also led to reduced both MT1-affinity (71.6 nM) and selec-
tivity (MT1-selectivity ratio 2). Finally, compound 20 bearing a
hexyl group which is also present in the MT1-selective ligand
4 exhibited nearly the same binding constants to both MLT
receptor subtypes (Ki ¼ 4.9 and 6.6 nM for MT1 and MT2).
Functional analysis of one of the two most MT1-selective
ligands, 15, showed it to have agonist activity at both MT1
(MT1-CHO) and MT2 (MT2-CHO) receptors expressed in CHO
cells. As shown in Fig. 2, melatonin (1 pM–10 nM) inhibited
forskolin-induced cAMP accumulation in MT1-CHO cells in a
concentration-dependent manner with a potency (IC50) value
of 32 pM and a maximum inhibition (49%) occurring
at 10 nM melatonin. The addition of 15 (10 nM) with
melatonin (1 pM–10 nM) did not competitively antagonize
melatonin’s actions at MT1 receptors but rather acted as an
agonist producing a maximal inhibitory (ꢂ63%) effect on
forskolin-induced cAMP accumulation when combined with
a concentration of melatonin (i.e., 1 pM) that produced no
inhibition alone. Similarly, melatonin (1 pM–10 nM) inhib-
ited forskolin-induced cAMP accumulation in MT2-CHO cells
with a potency value of 1.6 pM and maximum inhibition
(ꢂ53%) occurring at 10 nM melatonin. 15 (10 nM), added
in combination with melatonin (1 pM–10 nM) did not
competitively antagonize melatonin’s actions at MT2
receptors but acted as an agonist producing a 25% further
inhibition of forskolin-induced cAMP accumulation to that
The structure of the MT1-selective ligand 15 was further
modified by replacing the terminal phenyl group with
bulkier aromatic ring systems, such as 2-naphthyl (16),
1-naphthyl (17) and biphenyl (18) resulting in loss of
MT1-selectivity. It is worth noting that the 2-naphthyl analog
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Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
N-Acetyl-5-arylalkoxytryptamine Analogs
671
m/z (%) ¼ 499 (Mþ, 7), 498 (19), 440 (31), 439 (96), 381 (21), 380
(71), 368 (21), 212 (21), 211 (100), 210 (30), 199 (33), 197 (16), 190
(25), 183 (23), 171 (18), 170 (26), 169 (30), 158 (15). 157 (48), 153
(21), 141 (23), 140 (14), 128 (20). Anal. calcd. for C27H28N2O3: C,
74.67; H, 6.87; N, 5.62. Found: C, 74.95; H, 7.04; N, 5.38; RP-HPLC
tR ¼ 18.3 min.
produced by 1 pM melatonin alone. For both MT1-CHO
and MT2-CHO cell lines, 15, added in combination with
melatonin, produced maximum inhibition of forskolin-
induced cAMP accumulation at all concentrations of
melatonin tested.
In summary, a novel series of MLT analogs obtained by the
systematic replacement of the ether methyl group with
larger arylalkyl and aryloxyalkyl substituents was prepared
in order to probe the melatonin receptors for MT1-selectivity.
The most MT1-selective agents 11 and 15 were substituted
with a Ph(CH2)3 or a PhO(CH2)3 group confirming the optimal
chain length for MT1-selectivity to be C3. Interestingly, in our
binding assay, 11 and 15 have shown considerably higher
MT1-affinity and selectivity than the standard highly
MT1-selective ligand, the dimeric agomelatine 1a. Our find-
ings are useful for the future design of MT1-selective ligands.
N-[2-(5-{3-[3-(2-Acetylamino-ethyl)-1H-indol-5-yloxy]-
propoxy}-1H-indol-3-yl)ethyl]acetamide (5)
A mixture of 6 (215 mg, 0.985 mmol), sodium hydroxide (50 mg,
1.23 mmol), sodium chloride (488 mg, 8.37 mmol), TBAB
(253 mg, 0.787 mmol) and water (1.5 mL) was stirred in a sealed
tube until completely dissolved. 1-Bromo-3-chloropropane
(77 mg, 0.491 mmol) und toluene (1.5 mL) were added and the
three-layer-emulsion was stirred rapidly (1000 rpm) at 508C for
3 h. Ethyl acetate (40 mL) and water (40 mL) were added, the
organic phase was separated, and the aqueous phase was
extracted with ethyl acetate (2 ꢃ 30 mL). The combined organic
layers were dried (Na2SO4) and evaporated under reduced pres-
sure. The crude product was purified by a two-step silica gel
chromatography (1. chloroform/methanol/ammonia, 10:1:0.1;
2. THF/ammonia, 10:0.1). 5 was isolated as a pale yellow solid
(83 mg, 35%), mp 2208C (decomp.). 1H-NMR (d6-DMSO): d 1.85
(s, 6H), 2.21–2.29 (m, 2H), 2.81 (t, 4H, J ¼ 7.3 Hz), 3.34 (qua, 4H,
J ¼ 6.7 Hz), 4.21 (t, 4H, J ¼ 6.2 Hz), 6.68 (dd, 2H, J ¼ 2.2, 8.7 Hz),
7.11 (d, 2H, J ¼ 2.2 Hz), 7.14 (s, 2H), 7.27 (d, 2H, J ¼ 8.7 Hz), 7.68
(br, 2H), 10.69 (br, 2H). 13C-NMR (d6-DMSO): d 22.7, 25.2, 29.2, 38.9,
64.9, 101.3, 111.5, 111.7, 111.9, 123.3, 127.6, 131.5, 152.1, 169.1.
HRMS-ESI m/z [M þ Na]þ calcd. for C27H32N4O4Na: 499.2315,
found: 499.2315; RP-HPLC tR ¼ 13.7 min.
Experimental
Chemistry
Melting points were determined using a capillary melting point
apparatus (Gallenkamp, Sanyo) and are uncorrected. Column
chromatography was carried out on silica gel 60 (0.063–
0.200 mm) obtained from Merck. A Bruker AV-400 spectrometer
was used to obtain 1H-NMR (400 MHz) and 13C-NMR (100 MHz)
spectra respectively. Proton chemical shifts are referred to CHCl3
(7.24 ppm) and DMSO-d6 (2.55 ppm). Coupling constants (J values)
are given in hertz (Hz). Carbon chemical shifts are referred to
CDCl3 (77.00 ppm) and DMSO-d6 (39.50 ppm). The NMR reso-
nances were assigned by means of HH-COSY, HMQC, and
HMBC experiments. EI mass spectra were determined on a
Finnigan MAT 8200 and on ESI-microTOF spectrometers.
Elemental analysis was performed by the microanalytical section
of the Instiute of Inorganic Chemistry, University of Wu¨rzburg.
All reactions were carried out under an argon atmosphere. All
chemicals were purchased from commercial suppliers and used
directly without any further purification. Agomelatine was
synthesized as previously reported [10]. HPLC analysis was per-
formed on an Agilent 1100 HPLC system with a Synergi MAX RP
C-12 column (4 mm, 150 ꢃ 4.60 mm). 99.9% methanol/0.1%
formic acid (mobile phase B) and 99.9% water/0.1% formic acid
(mobile phase A) were used at a flow rate 1.0 mL/min in linear
gradient eluation of 10 to 100% B over 18 min holding 4 min at
100% B; compound purities obtained by integration of chromato-
grams at l ¼ 254.8 nm were ꢄ95% throughout.
N-{2-[5-(benzyloxy)-1H-indol-3-yl]ethyl}acetamide (8)
NaBH4 (0.790 g, 21.0 mmol) was cautiously added to a stirred
solution of 5-benzyloxyindole-3-acetonitrile (0.770 g, 3.00 mmol),
acetic anhydride (0.60 mL, 6 mmol) and NiCl2 ꢀ 6 H2O (0.71 g,
3.00 mmol) in methanol (30 mL) at 08C. A black precipitate was
formed following a vigorous reaction and once the reaction had
subsided, stirring was continued at room temperature for 20 h.
Methanol was removed under vacuum and the residue was dis-
solved in ethyl acetate (40 mL) and NaHCO3 (20 mL), filtered, and
the precipitate was washed with ethyl acetate (3 ꢃ 10 mL). The
combined organic layer was dried (Na2SO4) and evaporated
under reduced pressure to give 0.860 g (93%) of crude 8 as
light brown viscous oil which was used as such in the next step.
RP-HPLC tR ¼ 15.2 min.
N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]acetamide (6)
(Method A)
A solution of 5-benzyloxyindole-3-acetonitrile
(525 mg, 2.00 mmol) in THF (12 mL) and acetic anhydride
(2.65 mL) was hydrogenated over Raney nickel and 10% Pd/C
(145 mg) at 400 kPa H2 for 12 h at 508C. The catalysts were
filtered off on Celite1 and washed with THF. The filtrate was
concentrated in vacuo and the residue was purified by column
chromatography (CHCl3/MeOH, 4:1) to give 311 mg (71%) of 6 as a
colorless foam. (Method B) A mixture of 8 (0.310 g, 1.0 mmol),
ammonium formate (0.300 g, 4.76 mmol) and 10% Pd/C (0.600 g)
in ethanol (30 mL) was heated at reflux for 2 h. The reaction
mixture was cooled to room temperature and filtered. The
filtrate was evaporated under reduced pressure to afford
0.190 g (85%) of pure 6 as a pale yellow viscous oil. The spectral
data of 6 were identical with those previously documented [11].
N-[2-(7-{3-[8-(2-Acetylaminoethyl)naphthalen-2-yloxy]-
propoxy}-naphthalen-1-yl)ethyl]acetamide (1a)
1a was synthesized from O-demethylagomelatine and 1,3-dibro-
mopropane according to a previously described procedure [3]
applying an additional purification step by column chromatog-
raphy (silica, gel, ethyl acetate to THF gradient eluation).
Contrary to the reported melting point (mp 101–1038C, toluene),
a different melting point (mp 113–1168C, toluene) was observed.
The 1H-NMR data were identical to those previously reported [3].
13C-NMR (CDCl3): d 20.7, 26.8, 31.0, 37.6, 62.4, 101.5, 116.2, 121.2,
124.5, 124.9, 126.9, 128.1, 130.9, 132.3, 154.7, 167.4. MS (EI):
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672
C. Markl et al.
Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
General procedure (method A) for the synthesis of N-{2-[5-
(substituted alkoxy)-1H-indol-3-yl]ethyl}acetamides (9, 11,
13, 15, and 19)
A mixture of 6 (1 equiv.), anhydrous K2CO3, (2 equiv.), the respec-
tive alkylating agent (1.5 equiv.), and a catalytical amount of KI
(10 mg) in dry acetonitrile (20 mL) was heated at reflux for 18 h.
The reaction mixture was cooled to room temperature, filtered
and the filtrate was evaporated under vacuum to afford the crude
products which were purified by column chromatography
(chloroform/methanol/ammonia, 10:1:0.1).
N-{2-[5-(3-phenoxypropoxy)-1H-indol-3-yl]ethyl}-
acetamide (15)
Compound 15 (0.200 g, 56%) was obtained from 6 (0.220 g,
1.008 mmol) and 3-phenoxypropyl bromide (0.370 g, 1.72 mmol)
in the presence of K2CO3 (0.28 g, 2.02 mmol) as light brown solid
mp 112–1148C. 1H-NMR (CDCl3): d 1.79 (s, 3H), 2.12–2.19 (m 2H),
2.76–2.82 (m, 2H), 3.40–3.47 (m, 2H), 4.04–4.11 (m, 4H), 5.66 (br.,
1H), 6.74–7.19 (m, 9H), 8.43 (br., 1H). 13C-NMR (CDCl3): d 23.3,
25.3, 29.6, 39.9, 64.6, 65.5, 101.8, 112.1, 122.4, 112.8, 114.6, 120.7,
123.1, 127.8, 129.5, 131.8, 153.2, 158.9, 170.4. MS (EI): m/z
(%) ¼ 352 (Mþ, 32), 293 (100), 280 (13), 159 (37). Anal. calcd.
for C21H24N2O3: C, 71.57; H, 6.86; N, 7.95. Found: C, 71.20; H,
6.90; N, 8.03; RP-HPLC tR ¼ 16.2 min.
N-{2-[5-(Naphthalen-2-ylmethoxy)-1H-indol-3-yl]ethyl}-
acetamide (9)
Compound 9 (0.140 g, 47%) was obtained from 6 (0.180 g,
2-(bromomethyl)naphthalene
N-(2-{5-[3-(1,3-Dioxo-1,3-dihydro-2H-isoindol-2-yl)-
propoxy]-1H-indol-3-yl}ethyl)-acetamide (19)
0.83 mmol)
and
(0.280 g,
1.25 mmol) in the presence of K2CO3 (0.230 g, 1.66 mmol) as
pale yellow solid mp 56–588C. 1H-NMR (CDCl3): d 1.77 (s, 3H),
2.79 (t, 2H, J ¼ 6.8 Hz), 3.41–3.46 (m, 2H), 5.14 (s, 2H), 5.52 (br.,
1H), 6.83 (d, 1H, J ¼ 2.3 Hz), 6.87 (dd, 1H, J ¼ 2.5, 8.8 Hz), 7.07 (d,
1H, J ¼ 2.8 Hz), 7.12–7.15 (m, 1H), 7.36–7.38 (m, 2H), 7.47 (dd, 1H,
J ¼ 1.8, 8.8 Hz), 7.72–7.81 (m, 4H), 8.21 (br., 1H). 13C-NMR (CDCl3):
d 23.3, 25.3, 39.8, 71.2, 102.4, 112.1, 112.6, 113.0, 123.0,
125.6, 125.9, 126.2, 126.4, 127.8, 127.9, 128.0, 128.3, 131.9,
133.1, 133.4, 135.1, 153.2, 170.3. MS (EI): m/z (%) ¼ 358 (Mþ,
14), 299 (19), 286 (10), 141 (100). Anal. calcd. for C23H22N2O2:
C, 77.07; H, 6.19; N, 7.82. Found: C, 76.75; H, 7.04; N, 7.00; RP-
HPLC tR ¼ 16.8 min.
Compound 19 (0.120 g, 29%) was obtained from 6 (0.220 g,
1.008 mmol) and 2-(3-chloropropyl)-1H-isoindole-1,3-(2H)-dione
(0.340 g, 1.51 mmol) in the presence of K2CO3 (0.280 g,
2.02 mmol) as light brown solid, mp 60–628C. 1H-NMR (CDCl3):
d 1.81 (s, 3H), 2.05–2.11 (m, 2H), 2.79 (t, 2H, J ¼ 6.7 Hz), 3.42–3.47
(m, 2H), 3.82 (t, 2H, J ¼ 6.9 Hz), 3.95 (t, 2H, J ¼ 5.9 Hz), 5.81
(br., 1H), 6.62 (dd, 1H, J ¼ 2.5, 8.8 Hz), 6.84–6.87 (m, 2H), 7.08
(d, 1H, J ¼ 8.8 Hz), 7.58–7.60 (m, 2H), 7.69–7.72 (m, 2H), 8.51
(br., 1H). 13C-NMR (CDCl3): d 23.3, 25.2, 28.4, 35.6, 39.8, 66.6,
101.9, 111.9, 112.4, 112.7, 122.9, 123.2, 127.7, 131.8, 132.1,
133.9, 152.9, 168.4, 170.3. MS (EI): m/z (%) ¼ 405 (Mþ, 13), 346
(33), 333 (23) 188 (100), 160 (31). Anal. calcd. for C23H23N3O4:
C, 68.13; H, 5.72; N, 10.36. Found: C, 67.84; H, 5.79; N, 10.45;
RP-HPLC tR ¼ 14.4 min.
N-{2-[5-(3-phenylpropoxy)-1H-indol-3-yl]ethyl}acetamide
(11)
Compound 11 (0.100 g, 50%) was obtained from 6 (0.130 g,
0.60 mmol) and (3-bromopropyl)benzene (0.170 g, 0.90 mmol)
in the presence of K2CO3 (0.17 g, 1.2 mmol) as a light brown
viscous oil. 1H-NMR (CDCl3): d 1.81 (s, 3H), 2.02–2.08 (m, 2H), 2.76
(t, 2H, J ¼ 8.2 Hz), 2.83 (t, 2H, J ¼ 7.07 Hz), 3.45–3.50 (m, 2H),
3.93 (t, 2H, J ¼ 6.7 Hz), 5.54 (br., 1H), 6.79 (dd, 1H, J ¼ 2.5, 8.6 Hz),
6.89–6.94 (m, 2H), 7.10–7.20 (m, 6H), 8.16 (br., 1H). 13C-NMR
(CDCl3): d 23.4, 25.3, 31.1, 32.3, 39.8, 67.9, 101.8, 112.0, 112.9,
122.9, 125.9, 126.2, 127.8, 128.4, 128.5, 128.6, 141.8, 153.4, 170.2.
MS (EI): m/z (%) ¼ 336 (Mþ, 29), 277 (100), 264 (73), 159 (46). Anal.
calcd. for C21H24N2O2: C, 74.97; H, 7.19; N, 8.33. Found: C, 74.75;
H, 7.21; N, 8.39; RP-HPLC tR ¼ 16.6 min.
General procedure (method B) for the synthesis of N-{2-[5-
(substituted alkoxy)-1H-indol-3-yl]ethyl}acetamides (7, 10,
12, 14, 16–18 and 20)
A
mixture of 6 (1.00 mmol), cesium carbonate (1.710 g,
5.25 mmol) and the respective alkylating agent (1.03 mmol) in
abs. acetonitrile (10 mL) was stirred at 608C for 4 h. The reaction
mixture was concentrated in vacuo, the residue was diluted with
THF and filtered through a Celite1 pad. The filtrate was collected
and concentrated in vacuo. The crude product was purified by
silica gel chromatography (CHCl3/methanol, 10:1). Further puri-
fication was carried out for 14, 16–18 and 20 by recrystallization
from THF/MTBE.
N-{2-[5-(5-phenylpentyl)oxy)-1H-indol-3-yl]ethyl}-
acetamide (13)
N-[2-(5-Allyloxy-1H-indol-3-yl)-ethyl]acetamide (7)
Compound 13 (0.130 g, 35%) was obtained from 6 (0.230 g,
1.05 mmol) and (5-bromopentyl) benzene (0.360 g, 1.58 mmol)
in the presence of K2CO3 (0.290 g, 2.10 mmol) as dark yellow
viscous oil. 1H-NMR (CDCl3): d 1.4–1.48 (m, 2H), 1.57–1.65 (m, 2H),
1.70–1.77 (m, 2H), 1.81 (s, 3H), 2.55 (t, 2H, J ¼ 7.7 Hz), 2.82 (t, 2H,
J ¼ 6.7 Hz), 3.44–3.49 (m, 2H), 3.89 (t, 2H, J ¼ 6.6 Hz), 5.60
(br., 1H), 6.76 (dd, 1H, J ¼ 2.5, 8.8 Hz), 6.84–6.94 (m, 2H), 7.06–
7.20 (m, 6H). 13C-NMR (CDCl3): d 23.4, 25.3, 25.9, 29.4, 31.3, 35.9,
39.8, 68.9, 101.7, 112.0, 112.5, 112.9, 122.9, 125.7, 127.8, 128.3,
128.5, 131.7, 142.6, 153.5, 170.3. MS (EI): m/z (%) ¼ 364 (Mþ, 32),
305 (100), 292 (38), 159 (56). Anal. calcd. for C23H28N2O2: C, 75.79;
H, 7.74; N, 7.69. Found: C, 75.35; H, 7.94; N, 7.75; RP-HPLC
tR ¼ 17.8 min.
Compound 7 (137 mg, 53%) was obtained from 6 (218 mg) and
3-bromopropene (125 mg, 1.03 mmol) as colorless viscous oil.
1H-NMR (CDCl3): d 1.90 (s, 3H), 2.82–2.97 (m, 2H), 3.48–3.62
(m, 2H), 4.55 (d, 2H, J ¼ 4.5 Hz), 5.26 (dd, 1H, J ¼ 1.7, 10.4 Hz),
5.42 (dd, 1H, J ¼ 1.7, 17.2 Hz), 5.67 (br, 1H), 6.01–6.16 (m, 1H),
6.80–7.09 (m, 3H), 7.23 (d, 1H, J ¼ 8.1 Hz), 8.30 (br, 1H). 13C-NMR
(CDCl3): d 23.4, 25.2, 39.7, 69.8, 102.1, 112.0, 112.5, 112.9, 117.4,
122.9, 127.7, 131.7, 133.8, 152.9, 170.2. MS (EI): m/z (%) ¼ 258 (Mþ,
8), 237 (30), 236 (16), 235 (100), 224 (24), 222 (68), 199 (16), 186
(16), 159 (21), 158 (20), 146 (25), 145 (20). Anal. calcd.
for C15H18N2O2: C, 69.74; H, 7.02; N, 10.84. Found: C, 69.29; H,
7.20; N, 10.64; RP-HPLC tR ¼ 13.1 min.
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Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
N-Acetyl-5-arylalkoxytryptamine Analogs
673
solid, mp 147–1488C. 1H-NMR (d6-DMSO): d 1.83 (s, 3H), 2.38 (qui,
2H, J ¼ 6.1 Hz), 2.79 (t, 2H, J ¼ 7.3 Hz), 3.32 (qua, 2H, J ¼ 6.8 Hz),
4.30 (t, 2H, J ¼ 6.2 Hz), 4.40 (t, 2H, J ¼ 6.1 Hz), 6.80 (dd, 1H,
J ¼ 2.3, 8.7 Hz), 7.03–7.16 (m, 3H), 7.26 (d, 1H, J ¼ 8.7 Hz),
7.43–7.58 (m, 4H), 7.90 (d, 1H, J ¼ 8.1 Hz), 7.94 (t, 1H,
J ¼ 5.4 Hz), 8.25 (d, 1H, J ¼ 7.6), 10.69 (br, 1H). 13C-NMR (d6-
DMSO): d 23.7, 25.2, 30.0, 39.4, 64.7, 64.9, 101.4, 105.2, 111.4,
111.9, 112.3, 119.9, 121.4, 123.3, 125.2, 126.2, 126.4, 127.4, 127.5,
127.6, 131.5, 140.0, 152.1, 154.0, 168.9. MS (EI): m/z (%) ¼ 403 (17),
402 (Mþ, 60), 344 (22), 343 (88), 330 (22), 200 (100), 186 (23), 159
(22), 158 (21), 157 (20), 146 (26), 115 (25). Anal. calcd.
for C25H26N2O3: C, 74.60; H, 6.51; N, 6.96. Found: C, 74.25; H,
6.69; N, 7.02; RP-HPLC tR ¼ 17.7 min.
N-[2-(5-Phenethyloxy-1H-indol-3-yl)-ethyl]acetamide (10)
Compound 10 (210 mg, 65%) was obtained from 6 (218 mg) and
(2-bromoethyl)benzene (191 mg, 1.03 mmol) as colorless viscous
oil. 1H-NMR (CDCl3): d 1.98 (s, 3H), 2.83 (t, 2H, J ¼ 6.0 Hz), 3.05 (t,
2H, J ¼ 7.1 Hz), 3.48 (qua, 2H, J ¼ 6.0 Hz), 4.15 (t, 2H, J ¼ 7.1 Hz),
5.56 (br, 1H), 6.79 (dd, 1H, J ¼ 1.8, 8.6 Hz), 6.91 (s, 1H), 6.95 (d, 1H,
J ¼ 1.8 Hz), 7.13–7.28 (m, 6H), 8.17 (br, 1H). 13C-NMR (CDCl3): d 20.9,
25.2, 35.0, 39.7, 69.7, 101.7, 112.0, 112.5, 112.9, 122.9, 126.4, 127.7,
128.4, 129.0, 131.7, 138.5, 153.1, 170.1. HRMS-ESI m/z [M þ Na]þ
calcd. for C20H22N2O2Na: 345.1578, found: 345.1573; RP-HPLC
tR ¼ 15.9 min.
N-{2-[5-(4-Phenylbutoxy)-1H-indol-3-yl]-ethyl}acetamide
(12)
Compound 12 (60 mg, 17%) was obtained from 6 (218 mg) and
(4-chlorobutyl)benzene (173 mg, 1.03 mmol) as colorless viscous
oil. 1H-NMR (CDCl3): d 1.54 (qui, 2H, J ¼ 6.8 Hz), 1.64 (qui, 2H,
J ¼ 6.8 Hz), 1.96 (s, 3H), 2.61 (t, 2H, J ¼ 6.8 Hz), 2.83 (t, 2H,
J ¼ 6.3 Hz), 3.48 (qua, 2H, J ¼ 6.3 Hz), 3.93 (t, 2H, J ¼ 6.8 Hz),
5.58 (br, 1H), 6.77 (dd, 1H, J ¼ 2.3, 8.7 Hz), 6.89 (s, 1H), 6.94 (d, 1H,
J ¼ 2.3 Hz), 7.07–7.24 (m, 6H), 8.19 (br, 1H). 13C-NMR (CDCl3):
d 20.9, 25.0, 25.2, 29.1, 35.6, 39.7, 68.7, 101.7, 111.9, 112.5, 112.8,
122.8, 125.7, 127.7, 128.2, 128.4, 131.6, 142.3, 153.4, 170.2. HRMS-
ESI m/z [M þ Na]þ calcd. for C22H26N2O2Na: 373.1891, found:
373.1886; RP-HPLC tR ¼ 17.2 min.
N-(2-{5-[3-(Biphenyl-4-yloxy)-propoxy]-1H-indol-3-yl}-
ethyl)acetamide (18)
18 (236 mg, 55%) was obtained from 6 (218 mg) and 4-(3-bromo-
propoxy)biphenyl (300 mg, 1.03 mmol) as white solid, mp 1418C.
1H-NMR (d6-DMSO): d 1.84 (s, 3H), 2.31 (qui, 2H, J ¼ 5.9 Hz), 2.81
(t, 2H, J ¼ 7.1 Hz), 3.30–3.40 (m, 2H), 4.23 (t, 2H, J ¼ 5.6 Hz),
4.34 (t, 2H, J ¼ 6.1 Hz), 6.80 (dd, 1H, J ¼ 2.3, 8.7 Hz), 7.09–7.18
(m, 4H), 7.20–7.54 (m, 4H), 7.82–7.92 (m, 4H), 7.96 (br, 1H), 10.68
(br, 1H). 13C-NMR (d6-DMSO): d 22.7, 25.2, 28.9, 39.5, 64.5,
64.7, 101.4, 111.5, 112.0, 112.3, 114.9, 123.3, 126.1, 126.7,
127.6, 127.7, 128.8. 131.5, 132.5, 139.8, 152.1, 158.2, 169.0.
MS (EI): m/z (%) ¼ 429 (Mþ, 12), 428 (36), 370 (26), 369 (100),
357 (16), 355 (52), 200 (27), 185 (15), 159 (25), 146 (19). Anal.
calcd. for C27H28N2O3: C, 75.68; H, 6.59; N, 6.54. Found: C, 75.30;
H, 6.64; N, 6.81; RP-HPLC tR ¼ 18.0 min.
N-{2-[5-(2-Phenoxyethoxy)-1H-indol-3-yl]ethyl}acetamide
(14)
Compound 14 (186 mg, 55%) was obtained from 6 (218 mg) and
(2-bromoethoxy)benzene (207 mg, 1.03 mmol) as pale yellow
crystals, mp 150–1518C. 1H-NMR (CDCl3): d 1.90 (s, 3H), 2.91
(t, 2H, J ¼ 6.0 Hz), 3.55 (qua, 2H, J ¼ 6.0 Hz), 4.25–4.40
(m, 4H), 5.33 (br, 1H), 6.87–7.02 (m, 5H), 7.08 (s, 1H), 7.22–7.31
(m, 3H), 8.07 (br, 1H). 13C-NMR (CDCl3): d 23.4, 25.3, 39.8, 66.7,
67.6, 102.3, 112.0, 112.7, 113.1, 114.7, 121.0, 122.9, 127.7, 129.5,
131.9, 153.1, 158.7, 170.2. MS (EI): m/z (%) ¼ 338 (Mþ, 28), 280 (21),
279 (100), 266 (71), 159 (41), 146 (25), 145 (22). Anal. calcd.
for C20H22N2O3: C, 70.99; H, 6.55; N, 8.28. Found: C, 70.60;
H, 6.71; N, 8.37; RP-HPLC tR ¼ 15.1 min.
N-[2-(5-Hexyloxy-1H-indol-3-yl)-ethyl]acetamide (20)
Compound 20 (206 mg, 68%) was obtained from 6 (218 mg) and
1-bromohexane (170 mg, 1.03 mmol) as white solid, mp 1758C.
1H-NMR (CDCl3): d 0.89 (t, 3H, J ¼ 6.9 Hz), 1.27–1.38 (m, 4H), 1.45
(qui, 2H, J ¼ 7.2 Hz), 1.78 (qui, 2H, J ¼ 6.8 Hz), 1.89 (s, 3H), 2.89 (t,
2H, J ¼ 6.2 Hz), 3.54 (qua, 2H, J ¼ 6.2 Hz), 3.97 (t, 2H, J ¼ 6.6 Hz),
5.75 (br, 1H), 6.84 (dd, 1H, J ¼ 1.8, 8.8 Hz), 6.93 (s, 1H), 7.01 (d, 1H,
J ¼ 1.8 Hz), 7.23 (d, 1H, J ¼ 8.8 Hz), 8.48 (br, 1H). 13C-NMR
(CDCl3): d 14.0, 22.5, 23.2, 25.2, 25.7, 29.4, 31.3, 39.7, 68.9,
101.6, 111.9, 112.3, 112.7, 122.8, 125.6, 127.6, 131.5, 170.0.
MS (EI): m/z (%) ¼ 302 (Mþ, 37), 244 (18), 243 (100), 231 (15),
230 (69), 159 (63), 146 (44). Anal. calcd. for C18H26N2O2:
C, 71.49; H, 8.67; N, 9.26. Found: C, 71.39; H, 8.77; N, 9.36;
RP-HPLC tR ¼ 17.2 min.
N-(2-{5-[3-(Naphthalen-2-yloxy)propoxy]-1H-indol-3-yl}-
ethyl)acetamide (16)
Compound 16 (173 mg, 43%) was obtained from 6 (218 mg) and
2-(3-bromopropoxy)naphthalene (273 mg, 1.03 mmol) as white
1
solid mp 1408C. H-NMR (d6-DMSO): d 1.84 (s, 3H), 2.31 (qui, 2H,
J ¼ 5.9 Hz), 2.81 (t, 2H, J ¼ 7.1 Hz), 3.30–3.42 (m, 2H), 4.23 (t, 2H,
J ¼ 5.6 Hz), 4.34 (t, 2H, J ¼ 6.1 Hz), 6.80 (dd, 1H, J ¼ 2.3, 8.8 Hz),
7.09–7.17 (m, 2H), 7.20–7.30 (m, 2H), 7.34–7.44 (m, 2H), 7.45–7.54
(m, 1H), 7.81–7.91 (m, 3H), 7.96 (br, 1H), 10.64 (br, 1H). 13C-NMR
(d6-DMSO): d 22.7, 25.1, 28.9, 39.4, 64.5, 64.7, 101.4, 106.7, 111.4,
111.9, 112.3, 118.7, 123.3, 123.5, 126.3, 126.7, 127.4, 127.6, 128.4,
129.2, 131.5, 134.3, 152.1, 156.4, 169.0. MS (EI): m/z (%) ¼ 403 (16),
402 (Mþ, 60), 344 (24), 343 (100), 330 (56), 200 (32), 185 (27), 172
(17), 159 (35), 146 (24), 127 (15). Anal. calcd. for C25H26N2O3: C,
74.60; H, 6.51; N, 6.96. Found: C, 74.34; H, 6.77; N, 6.95; RP-HPLC
tR ¼ 17.5 min.
Pharmacology
Competition binding analysis
All synthesized compounds were tested for their binding
affinity and selectivity for each of the melatonin receptor
subtypes, MT1 and MT2 using competition binding analysis.
Briefly, cells expressing the human MT1 or MT2 melatonin
receptor (MT1-CHO, MT2-CHO) were grown to confluence on
10 cm cell culture plates until they reached approximately
80% confluence. Next, cells were washed, lifted, and added to
tubes containing 80–100 pM.
N-(2-{5-[3-(Naphthalen-1-yloxy)propoxy]-1H-indol-3-yl}-
ethyl)acetamide (17)
Compound 17 (229 mg, 57%) was obtained from 6 (218 mg) and
1-(3-bromopropoxy)naphthalene (273 mg, 1.03 mmol) as white
2-[125I]-iodomelatonin in the absence (total binding) or
presence of melatonin (1 fM to 1 mM) or the test compounds
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www.archpharm.com

674
C. Markl et al.
Arch. Pharm. Chem. Life Sci. 2011, 344, 666–674
Yocca, in The IUPHAR compendium of receptor characterization
and classification (Ed.: D. Girdlestone), IUPHAR Media, London
2000, pp. 271–277.
(1 pM to 1 mM). The reactions were incubated for 1 h at 258C,
and then terminated following the addition of cold Tris-HCl
solution (50 mM, pH 7.4) and filtered through glass
fiber filters (Schleicher and Schuell, Keene, NH) saturated
in polyethylenimine 0.5% solution (v/v). Radioactive counts
were counted using a gamma counter. Data points were fit by
1- or 2-site nonlinear regression analysis based upon the
lowest residual sum of squares (GraphPad Prism) and affinity
constants (Ki) values were calculated.
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(b) P. J. Garrat, A. Tsotinis, Mini Rev. Med. Chem. 2007, 7, 1075–
1088; (c) G. Spadoni, A. Bedini, in Melatonin: From Molecules to
Therapy (Eds: S. R. Pandi-Perumal, D. P. Cardinali), Nova
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The cAMP accumulation assays were carried out by Enzyme
Immuno Antibody (EIA) kit according to manufacturer’s
directions. Stable CHO cell lines expressing human MT1 or
human MT2 receptors were cultured on 10 cm plates in F-12
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lation was expressed as a percentage of forskolin response
within each group. Curves were fit using non-linear
´ `
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The authors have declared no conflict of interest.
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