Synthesis and evaluation of N1-alkylindole-3-ylalkylammonium compounds as nicotinic acetylcholine receptor ligands

Article abstract of DOI:10.1016/j.bmc.2012.04.050

In this study thirty-three novel indole derivatives were designed and synthesized based on the structure of deformylflustrabromine B (1), a metabolite isolated from the marine bryozoan Flustra foliacea L. The syntheses were carried out using standard methodologies and in good yields. The molecules were tested for their affinities for the α4β2*, α3β 4*, α7* and (α1)₂β1γδ nicotinic acetylcholine receptor (nAChR) subtypes. Binding assays showed that, among these ligands, compound 7c exhibited the highest affinity with K _i = 136.1, 93.9 and 862.4 nM for the α4β2*, α3β4*, and α7* nAChRs subtypes, respectively. These results indicated that the indole core might be a useful scaffold for the development of new potent and selective nAChR ligands.

Full text of DOI:10.1016/j.bmc.2012.04.050

Bioorganic & Medicinal Chemistry 20 (2012) 3719–3727
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and evaluation of N1-alkylindole-3-ylalkylammonium compounds
as nicotinic acetylcholine receptor ligands
Edwin G. Pérez a,c, , Bruce K. Cassels b,c, Christoph Eibl d, , Daniela Gündisch d,
⇑
a Facultad de Química, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Casilla 306, Correo 22, Santiago, Chile
b Department of Chemistry, Faculty of Sciences, University of Chile, Casilla 653, Santiago, Chile
c Millennium Institute for Cell Dynamics and Biotechnology, Plaza Ercilla 847, Santiago, Chile
d Institute of Pharmacy, Department of Pharmaceutical Chemistry, University of Bonn, An der Immenburg 4, 53121 Bonn, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study thirty-three novel indole derivatives were designed and synthesized based on the structure
of deformylflustrabromine B (1), a metabolite isolated from the marine bryozoan Flustra foliacea L. The
syntheses were carried out using standard methodologies and in good yields. The molecules were tested
Received 12 April 2011
Revised 17 April 2012
Accepted 25 April 2012
Available online 2 May 2012
for their affinities for the
types. Binding assays showed that, among these ligands, compound 7c exhibited the highest affinity with
Ki = 136.1, 93.9 and 862.4 nM for the
4b2⁄, 3b4⁄, and 7⁄ nAChRs subtypes, respectively. These results
a a a a1)2b1cd nicotinic acetylcholine receptor (nAChR) sub-
4b2⁄, 3b4⁄, 7⁄ and (
a
a
a
Keywords:
Nicotinic acetylcholine receptors
Affinity
Indolylalkylamines
Structure–activity relationships
indicated that the indole core might be a useful scaffold for the development of new potent and selective
nAChR ligands.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Natural compounds acting on the central nervous system have
played an important role in drug discovery and are the source of
Nicotinic acetylcholine receptors (nAChR) are prototypical li-
gand-gated ion channels that mediate fast synaptic transmission.1
These receptors are pentameric proteins comprising either five
numerous therapeutic agents,6 and the cholinergic system is a
target frequently mentioned in the literature.7–9 Among them,
bungarotoxins, conotoxins, methyllycaconitine, anatoxin-a and
epibatidine have often been discussed as molecular probes for
the receptor but rarely as potential drugs because of their toxicity
and/or low selectivity, while nicotine and cytisine have been used
to facilitate smoking cessation in various formulations (e.g., tablets,
gum, spray, patches and herbal preparations). Finally, varenicline,
inspired in the structure of cytisine, was launched on the market
in 2006 and is commercialized as a smoking cessation agent.10
Although marine natural products appear frequently in the lit-
erature as potent agents acting on the CNS, they have usually been
overlooked and have only recently arisen as possibly valuable drug
leads. Among them, those with an indole moiety represent a rich
group with tremendous potential for the design and development
of drugs for the treatment of various psychiatric diseases and
disorders.11,12
copies of the same (or different)
two different types of subunits (
or two 1, one b1, one and one d (or
cular subtype, symmetrically arranged around a central ion pore.2
Nine different types of subunits ( 2– 10) and three kinds of b
a
subunit(s) or combinations of
and b) in the neuronal subtypes,
) subunit in the neuromus-
a
a
c
e
a
a a
subunits (b2–b4) have been cloned and characterized as constitu-
ents of neuronal nAChR. The physiological ligand of nAChR is
acetylcholine (ACh); however, tobacco components such as nico-
tine (Nic) and [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone]
(NNK) are known to be high-affinity agonists of nAChR, and nico-
tine is the primary addictive component of tobacco smoke.3–5
Binding of ligands such as ACh, Nic or NNK induces a conforma-
tional change in the receptor that opens the ion channel to
transmit signals at neuromuscular junctions and synapses in
the central and peripheral nervous systems.2 Charged amino acids
line the channel pore and select the ions that pass through the
channel.3
Tryptamine [2-(1H-indol-3-yl)ethanamine] derivatives deform-
ylflustrabromine B (1) and deformylflustrabromine (2), isolated
from the widespread marine bryozoan Flustra foliacea L., showed
weak binding affinities at
and deformylflustrabromine (2) was identified as a positive allo-
steric modulator (PAM) of
4b2 nAChR.14,15 Quite recently it was
a7 and a
4b2 nAChRs, respectively,13
a
⇑
Corresponding author.
E-mail address: eperezh@uc.cl (E.G. Pérez).
shown that compound 2 not only potentiates the responses to both
partial and full agonists but has no effect when it is co-applied with
Present address: Department of Pharmaceutical Sciences, College of Pharmacy,
University of Hawaii at Hilo, 34 Rainbow Drive, Hilo, HI 96720, USA.
antagonists.16 Deformylflustrabromine
B (1) did not increase
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.04.050

3720
E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
responses when co-applied with ACh on
inhibited ACh-induced responses in a7 and a
a
4b2 nAChR, but instead
gaseous dimethylamine to generate N,N-dimethylindole-3-
ylglyoxylamide (9). This amide was then N1-alkylated (10a–c)
followed by reduction with LiAlH4 to afford N1-alkyl-N10,N10
4b2 receptors.15 The
fact that 1 displaces radioligands from these nAChR subtypes indi-
cates that its inhibitory activity might be due, at least in part, to
orthosteric binding. As this compound might be an antagonist at
these two nAChR subtypes, in this study we synthesized a series
of N1-alkylindole-3-ylalkylamine homologues of 1, and their
methiodides, and evaluated them for their binding affinities at
-
dimethyltryptamines 6d–f. The corresponding trimethylammoni-
um iodides (7e–g) were obtained by adding MeI (Scheme 2).
To obtain compound 7h, an N10-cyclic tryptamine (Scheme 3),
the intermediate chloroamide (11), produced as described above
using pyrrolidine instead of dimethylamine, was reduced with
LiAlH4, the tryptamine analogue 12 was N1-alkylated with prenyl
bromide, and finally the methylammonium iodide was obtained
by adding MeI.
the three major neuronal subtypes of nAChR (
a4b2, a7, and
a3b4) and, for selected compounds, on the muscle subtype.
The synthesis of N1-prenylgramines (N1-prenylindol-3-yl-N,
N-dimethylmethanamines 15a–b) and their methiodides (16a–b)
involved three steps (Scheme 4). Treatment of indole-3-carboxal-
dehydes 13a–b with NaH and prenyl bromide in dry THF gave
N1-prenylindole-3-carboxaldehydes 14a–b, and subsequent reduc-
tive amination using dimethylamine and NaBH4 in MeOH followed
by quaternization using MeI produced the desired compounds.
The synthesis of N1-alkylated gramines 15c–e with longer alkyl
chains (C8, C10, C12) was effected via a Mannich reaction of N1-
alkylated indoles 17c–e with dimethylamine and formaldehyde.
Trimethylammonium iodides 16c–e were obtained as mentioned
above (Scheme 5).
H
H
N
N
N
H
N
Br
Br
2
1
The synthetic steps followed to obtain N1-alkylhomotryptamines
(3-(1H-indol-3-yl)propanamines 21a–c) and their methiodides
(22a–c) are depicted in Scheme 6. N,N-Dimethyl-3-indolepropana-
mide (19) prepared from commercially available indole-3-propionic
acid (18) was N1-alkylated with the appropriate alkyl bromides (C8,
2. Results and discussion
2.1. Chemistry
C
10, C12), and these intermediates (20a–c) were reduced with LiAlH4
6-Bromo-N10-Boc-N10-methyltryptamine (3a) and its debromi-
nated derivative (3b) were synthesized as previously described,17,18
and N1-alkylated using NaH as base and the corresponding alkyl
halides to produce 4a–d. These compounds were N-Boc-deprotec-
ted using TFA, and the secondary amines (5a–d) were converted
to the tertiary amines (6a–c) and quaternized to 7a–d using
(CHO)n/NaBH4, and MeI, respectively (Scheme 1).
as described above to afford the desired homotryptamines. The
trimethylammonium iodides were obtained by adding MeI.
The synthesis of N1-octylisogramine (N1-octylindol-2-yl-N,N-
dimethylmethanamine, 26) was accomplished by amidation of
indole-2-carboxylic acid (23) with dimethylamine to produce 24
which was N1-alkylated with NaH and octyl bromide to produce
25. This compound was reduced with LiAlH4 affording the
expected dimethylaminomethyl derivative (26). Trimethylammo-
nium iodide 27 was obtained as mentioned before. Scheme 7.
To extend the tryptamine series, we further synthesized N10,N10
dimethyltryptamines 6d-f and N10,N10,N10-trimethyltryptaminium
iodides 7e–g, alkylated on N1 with longer alkyl chains (C8, C10
12), to determine the importance of the substitution on the basic
-
,
C
2.2. Biological results and discussion
nitrogen and the optimal length of the chain attached to the indole
nitrogen. To obtain these compounds, the synthetic route involved
an initial coupling using indole (8) and oxalyl chloride to produce
the corresponding glyoxalyl chloride which was treated with
The presence of a bromine atom at C6 of the indole ring, the
length of the chain joining the indole C3 to the basic nitrogen,
N
N
R1
R2
iii
N
N
6a-c
Boc
N
Boc
H
i
ii
N
N
R1
R1
N
R1
R2
H
R2
iv
I
N
3a-b
a : R 1 = H
b : R1 = Br
4a-d
5a-d
a : R 1 = H; R2 = methyl
b : R1 = H; R2 = allyl
N
R1
1
c : R = H; R2 = prenyl
R2
d : R1 = Br; R2 = prenyl
7a-d
Scheme 1. Reagents and conditions: (i) NaH, THF, 0 °C to rt, 30 min, R2Br, rt, 16 h; (ii) TFA, DCM, rt, 2 h; (iii) (CHO)n, NaBH4, MeOH, rt, 2 h; (iv) MeI, acetone, rt, 16 h.

E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
3721
I
N
N
N
N
O
O
O
O
v
i, ii
iv
iii
N
N
N
N
H
N
H
R
R
R
8
9
10a-c
6d-f
7e-g
a : R = octyl
b : R = decyl
c : R = dodecyl
e : R = octyl
f : R = decyl
g : R = dodecyl
d : R = octyl
e : R = decyl
f : R = dodecyl
Scheme 2. Reagents and conditions: (i) (CO)2Cl2, Et2O, 0 °C; (ii) Me2NH(g), DCM, rt, 80% two steps; (iii) NaH, THF, 0 °C to rt, 30 min, RBr, rt, 16 h; (iv) LiAlH4, THF, reflux, 4 h; (v)
MeI, acetone, rt, 16 h.
N
I
N
N
O
O
iv, v
iii
i, ii
N
N
H
N
H
N
H
7h
8
12
11
Scheme 3. Reagents and conditions: (i) (CO)2Cl2, Et2O, 0 °C; (ii) pyrrolidine, DCM, rt, 85% two steps; (iii) LiAlH4, THF, reflux, 4 h, 79%; (iv) NaH, THF, 0 °C to rt, 30 min, 1-
bromo-3-methyl-2-butene, rt, 16 h; (v) MeI, acetone, 16 h, 80% two steps.
O
O
I
H
H
N
N
ii
iii
i
N
N
N
N
R
R
R
R
H
16a-b
15a-b
13a-b
14a-b
a : R = H
b : R = Br
Scheme 4. Reagents and conditions: (i) NaH, THF, 0 °C to rt, 30 min, 1-bromo-3-methyl-2-butene rt, 16 h; (ii) Me2NH(g), 2 h, NaBH4, MeOH, rt, 2 h; (iii) MeI, acetone, rt, 16 h.
I
N
N
ii
i
iii
N
N
N
H
N
R
R
R
8
17c-e
15c-e
16c-e
c : R = octyl
d : R = decyl
e : R = dodecyl
Scheme 5. Reagents and conditions: (i) Bu4NBr, NaOH, H2O, toluene, RBr, rt, 16 h; (ii) Me2NHaq, HCHO, AcOH/H2O, rt, 24 h; (iii) MeI, acetone, rt, 16 h.

3722
E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
O
O
O
N
OH
N
i, ii
iii
N
N
N
R
H
H
18
19
20a-c
I
N
N
iv
v
N
N
R
R
21a-c
22a-c
a : R = octyl
b : R = decyl
c : R = dodecyl
Scheme 6. Reagents and conditions: (i) CDI, DMF, 0 °C, 1 h; (ii) Me2NH(g), THF, 2 h, 86% two steps; (iii) NaH, THF, 0 °C to rt, 30 min, RBr, rt, 16 h; (iv) LiAlH4, THF, reflux, 4 h; (v)
MeI, acetone, rt, 16 h.
O
O
N
O
N
i, ii
iv
iii
N
OH
N
N
H
H
(
)
7
23
24
25
v
I
N
N
N
N
(
)
7
(
)
7
26
27
Scheme 7. Reagents and conditions: (i) SOCl2, THF, rt, 16 h; (ii) Me2NHaq, rt,10 min, 80% two steps; (iii) NaH, THF, 0 °C to rt, 30 min, 1-bromooctane, rt, 16 h, 73%; (iv) LiAlH4,
THF, reflux, 4 h, 95%; (v) MeI, acetone, rt,16 h, 87%.
the substitution on the latter and the length of the alkyl group (C4
to C12 on the indole nitrogen were systematically varied.
of affinity for
lication on compounds 1 and 2 their affinities for the
a
4b2⁄ and
a
7⁄ nAChR. Although in the original pub-
3b4⁄ nAChR
)
a
Radioligand receptor binding assays were carried out to determine
the compounds’ abilities to compete for [3H]epibatidine and
[3H]metyllycaconitine (MLA) binding sites using different tissue
preparations (Table 1) and to gain insight into structure-affinity
relationships.
were not determined, our present findings indicate that early stud-
ies on this ganglionic receptor subtype should not be neglected in
view of the possibility of new compounds acting on the periphery
instead of, or in addition to the CNS. The activity of the dimethyl-
tryptamine analogues increased slightly with increasing length of
the alkyl chain bound to the indole nitrogen from methyl to
dimethylallyl (prenyl, 3-methyl-2-butenyl), but when the chain
Membrane fractions from rat forebrain, calf adrenals, and Tor-
pedo californica electroplax were used to study the interactions
with the
a
4b2⁄,
a
3b4⁄, and (
a
1)2b1
c
d nAChR subtypes by dis-
was lengthened to octyl, the Ki value rose above 10 lM (Table 1).
placement of [3H]epibatidine. Test compounds were incubated
with membrane fractions from rat forebrain to evaluate their affin-
We found that N,N,N-trimethyltryptaminium derivatives 7b and
7c, with an allyl (2-propenyl) or a dimethylallyl chain on the indole
nitrogen, have nanomolar affinities for all three neuronal nAChR
subtypes. Unlike their dimethyltryptamine counterparts, they bind
ities for
a
7⁄ nAChR by competition with [3H]MLA (Table 1).19–21
Most of the compounds synthesized had negligible binding
affinities for all three neuronal nAChR subtypes. However there
were some exceptions, among which moderate-to-high affinities
(Ki as low as 93.9 nM, almost the same as nicotine) were seen for
almost equally strongly to
cantly, though much more weakly, to
shows low micromolar affinity for the muscle subtype, It is intrigu-
a
4b2⁄ and
a
a
3b4⁄ nAChR and signifi-
7⁄ nAChR, and 7c even
a
4b2⁄ and
showed low micromolar affinity for
displacement could be detected up to 50
type. In our hands, binding of 5d to
3b4⁄ receptors was not appre-
ciably stronger than to
4b2⁄ nAChR.
Interestingly, dimethyltryptamine derivatives 6a–c have low
micromolar affinities for the
3b4⁄ subtype in spite of their lack
a
3b4⁄ nAChR. As noted previously, compound 1 (=5d)
7⁄ nAChR, and no radioligand
M for the
4b2⁄ sub-
ing that introduction of a bromine atom at C6 of the isopentenyl
a
compound 7d leads to
receptors, mainly due to a more than 60-fold fall in affinity for
the latter subtype. Apparently the dimethylallyl group on the
a
preference for
a
4b2⁄ over
a
3b4⁄
l
a
a
a
indole nitrogen is close to optimal for
because both shorter (methyl, 7a; allyl, 7b) and longer (octyl, 7e)
a
3b4⁄ nAChR affinity
a
chains showed higher Ki values, and decyl and dodecyl derivatives

E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
3723
Table 1
3. Conclusions
Radioligand binding affinities of tryptamine (5 = N-methyl, 6 = N,N-dimethyl,
7 = N,N,N-trimethyltryptaminium), gramine (15 = N,N-dimethyl, 16 = N,N,N-trimethy-
lammonium), homotryptamine (21 = N,N-dimethyl, 22 = N,N,N-trimethylammonium),
and isogramine (26, 27) derivatives for different nAChR subtypes
In summary, this preliminary work allowed the very modest
nAChR affinity (Ki >10,000 nM) of the natural lead compound
deformylflustrabromine B to be raised to levels close to that of
nicotine (i.e. Ki value at the
for nicotine, 75.3 nM). Most of the active compounds showed some
slight selectivity for the
paucity of positive results makes it difficult to discern any struc-
ture–activity relationship. However, the indole core, attached to a
short aminoalkyl substituent and bearing
substituent on N1, has provided unprecedented examples of
arylalkylamine derivatives with good nAChR affinity. Further
modification, for instance by substitution on the benzene ring of
the indole moiety, is now an attractive approach in the quest for
subtype-selective nicotinic ligands.
Compound
a
4b2*
a
3b4*
a
7*
(a1)2b1cd
b
a3b4 nAChR subtype for 7c, 93.9 nM;
rat brain
Ki (nM)
(
calf adrenalb
rat brainc
T. californica
Ki (nM)
(
Ki (nM)
(
electroplaxb
SEM)a
SEM)a
SEM)a
Ki (nM) ( SEM)a
a
4b2⁄ subtype. Unfortunately, the relative
Nicotine
5a
5b
5c
5d = 1
6a
6b
6c
6d
6e
6f
7a
7b
7c
7d
7e
7f
7g
0.85 (0.16)
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
517.1
75.3 (8.9)
>10,000
>10,000
>10,000
>10,000
3,676
2,846
1,823
>10,000
>10,000
>10,000
2,011
129 (14)
n.d.
n.d.
>10,000
17,000
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
>10,000
n.d.
n.d.
>10,000
>10,000
2359.3
>10,000
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d
n.d.
n.d
n.d
n.d.
n.d
n.d
n.d.
a medium-length
d
n.d.
>10,000
>10,000
>10,000
n.d.
n.d.
>10,000
6795.5
862.4
1534.2
n.d.
n.d.
n.d.
n.d.
n.d.
4. Experimental section
4.1. Chemistry
365.5
93.9
5,334
136.1
412.0
527.0
>10,000
>10,000
>10,000
n.d.
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>1,000
3404
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
1380
>10,000
>10,000
>10,000
435.0
4.1.1. General information
7h
Melting points were determined on a Reichert Galen III hot
plate microscope apparatus and are uncorrected. 1H NMR spectra
were recorded on Bruker AMX 300, Bruker Avance 400, or Bruker
Avance 500 instruments at 300, 400 or 500 MHz, respectively.
13C NMR spectra were recorded on the same instruments at 75,
100 or 125 MHz. Chemical shifts are reported in d values (parts
per million, ppm) relative to an internal standard of tetramethylsil-
ane in CDCl3 or DMSO-d6 and coupling constants (J) are given in
Hertz. Precoated silica gel 60 plates (Merck 60 F254 0.2 mm) were
used for TLC. TLC spots were visualized by spraying with Drag-
endorff’s reagent or by exposing to iodine vapor.
15a
15b
15c
15d
15e
16a
16b
16c
16d
16e
21a
21b
21c
22a
22b
22c
26
n.d.
>10,000
>10,000
>10,000
>10,000
>1,000
>5000
>10,000
>10,000
n.d.
>10,000
>10,000
>1,000
>10,000
>10,000
>10,000
>10,000
202.5
705.6
>10,000
>10,000
>10,000
>10,000
>10,000
243.5
>10,000
>10,000
>10,000
>10,000
4.1.2. N1,N10-Dimethyl-N10-Boc-tryptamine (4a)
To a suspension of sodium hydride (0.044 g, 1.7 mmol) in anhy-
drous THF (10 mL) was added N10-methyl-N10-Boc-tryptamine (3a,
0.387 g, 1.5 mmol) at 0 °C. The mixture was stirred for 30 min at rt,
and then MeI (0.240 g, 1.7 mmol) dissolved in THF (5 mL) was
added at room temperature. The reaction mixture was allowed to
stir for 16 h, and then quenched with water (10 mL). The suspen-
sion was extracted with EtOAc (3 Â 15 mL), the organic layer was
dried over anhydrous MgSO4 and filtered, and the solvent was re-
moved in vacuo. Chromatography on silica gel (hexane:EtOAc
60:40) gave 0.326 g (80%) of the title compound as a clear oil. 1H
NMR (500 MHz, CDCl3): d 7.60 (d, 1H, J = 5.5 Hz), 7.27 (d, 1H,
J = 8.0 Hz), 7.20 (t, 1H, J = 7.5 Hz), 7.09 (t, 1H, J = 7.0 Hz), 6.82 (s,
1H), 3.72 (s, 3H), 3.47 (t, 2H, J = 7.5 Hz), 2.94 (t, 2H, J = 7.5 Hz),
2.86 (s, 3H,), 1.33 (s, 9H). 13C NMR (125 MHz, CDCl3): d 155.7,
137.0, 127.8, 126.6, 121.5, 118.76, 118.70, 111.7, 109.1, 79.10,
49.76, 34.18, 32.53, 28.28 (3C), 23.83.
27
n.d.
a
b
c
Values are the means from at least 3–5 independent assays.
By displacement of [3H]epibatidine.
By displacement of [3H]methyllycaconitine.
Ref.7. n.d. = not determined.
d
*
Naturally expressed nAChRs which may contain other subunits in addition to
those indicated.
7f-7g are practically inactive at this receptor subtype. Although
most of the secondary and tertiary (including cyclic) amines are
inactive at submicromolar concentrations, some trimethyltrypta-
minium compounds have affinities up to three orders of magnitude
higher than those of the natural products 1 and 2. This is in agree-
ment with the trends reported by Dwoskin et al. for several series
of amine and ammonium compounds and other antagonists such
as hexamethonium and decamethonium.22
4.1.3. N1,N10-Dimethyltryptamine
To
a
solution of N1,N10-dimethyl-N10-Boc-tryptamine (4a)
Of the five gramine derivatives tested (15a–15e) only 15b,
which is the single brominated member of this subgroup, proved
(0.3 g, 1.1 mmol) in DCM (2 mL) at room temperature was added
TFA (0.2 mL). The deep red mixture was stirred for 2 h and then
quenched with a saturated solution of NaHCO3 (2 mL). The mixture
was extracted with DCM (3 Â 5 mL), and the organic layer was
dried over anhydrous MgSO4 and filtered. Chromatography
(DCM:MeOH:TEA 9:0.5:0.5) afforded 0.17 g (85%) of the title prod-
uct as a clear liquid. 1H NMR (oxalate salt, 500 MHz, DMSO-d6): d
8.85 (s, 1H), 7.58 (d, 1H, J = 8.0 Hz), 7.39 (d, 1H, J = 8.0 Hz), 7.19
(s, 1H), 7.15 (t, 1H, J = 7.0 Hz), 7.03 (t, 1H, J = 7.0 Hz), 3.72 (s, 3H),
3.13 (t, 2H, J = 7.5 Hz), 3.02 (t, 2H, J = 7.5 Hz), 2.28 (s, 3H). 13C
NMR (125 MHz, DMSO-d6): d 164.7, 136.8, 127.8, 127.2, 121.5,
active, with a low micromolar Ki, at
sponding N-methylgraminiums (16a–16e), three (16a–16c) have
submicromolar affinities for 4b2 nAChR, and here again the bro-
minated 16b is the most potent. However, 16c was the only one
to show micromolar affinity for 3b4 nAChR. Neither one of the
isogramine derivatives (26, 27) showed any activity.
None of the homotryptamines (21a–21c) showed any activity.
Of their quaternary salts, only 22a exhibited fairly high affinity
a4b2 nAChR. Of the five corre-
a
a
for the
on the indole nitrogen.
a4b2 receptor subype. This compound bears an octyl chain

3724
E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
118.7, 118.6, 109.8, 108.8, 48.8, 32.6, 32.4, 21.6. Anal. Calcd for
14H18N2O4: C, 60.42; H, 6.52; N, 10.07. Found: C, 60.11; H, 6.77;
N, 9.96.
CDCl3): d 185.5, 167.7, 138.2, 137.0, 126.5, 123.8, 123.1, 122.5,
113.3, 110.2, 47.44, 37.53, 34.48, 31.73, 29.80, 29.09 (2C), 26.88,
22.59, 14.06.
C
4.1.4. N1,N10,N10-Trimethyltryptamine (6a)
4.1.8. N,N-Dimethyl-2-(1-octyl-1H-indol-3-yl)ethanamine
(N1-octyl-N10,N10-dimethyltryptamine, 6d)
To a suspension of LiAlH4 (2.00 g, 52.6 mmol) in dry THF
(200 mL) at 0 °C, was added dropwise a solution of N,N-dimethyl-
To a suspension of paraformaldehyde (0.045 g, 1.5 mmol) in
MeOH (10 mL) at room temperature was added N1,N10-dimethyl-
tryptamine (5a, 0.056 g, 0.3 mmol) and the mixture was stirred
for 0.5 h. Then to the above solution was added NaBH4 (0.06 g,
1.5 mmol) at room temperature, and the resulting mixture
was stirred for another 2 h and quenched with a saturated solution
of NaHCO3 (5 mL). The mixture was extracted with DCM
(3 Â 20 mL), and the organic layer was dried over anhydrous
MgSO4 and filtered. Chromatography (DCM:MeOH:TEA 9:0.5:0.5)
gave 0.04 g (75%) of the title product as a clear liquid. 1H NMR
(oxalate salt, 500 MHz, DMSO-d6): d 10.10 (s, 1H), 7.61 (d, 1H,
J = 8.0 Hz), 7.39 (d, 1H, J = 8.0 Hz), 7.19 (s, 1H), 7.16 (t, 1H,
J = 7.0 Hz), 7.03 (t, 1H, J = 7.0 Hz), 3.73 (s, 3H), 3.24 (t, 2H,
J = 7.5 Hz), 3.07 (t, 2H, J = 7.5 Hz), 2.80 (s, 6H). 13C NMR
2-(1-octyl-1H-indol-3-yl)-2-oxoacetamide
(10a,
2.00 g,
6.07 mmol) in dry THF. The mixture was refluxed with stirring
for 4 h and was cooled to rt and then in an ice-water bath. Aqueous
THF (1:1) was added carefully, the solid was removed by filtration
and the volatiles were evaporated under reduced pressure. Chro-
matography (DCM:MeOH 9:1) gave 1.17 g (64%) of the desired
product as a clear oil. 1H NMR (oxalate salt, 300 MHz, DMSO-d6):
d 7.76 (d, 1H, J = 7.6 Hz), 7.47 (d, 1H, J = 8.4 Hz), 7.41 (s, 1H), 7.16
(t, 1H, J = 7.2 Hz), 7.06 (t, 1H, J = 7.2), 5.86 (d, 1H, J = 3.6 Hz), 5.48
(d, 1H, J = 10.4 Hz), 4.14 (t, 2H, J = 9.0 Hz), 3.81 (dd, 1H,
J1 = 10.4 Hz J2 = 13.6 Hz), 3.51 (d, 1H, J = 13.2 Hz), 3.25 (s, 6H),
1.72 (t, 2H, J = 6.4 Hz), 1.24 (m, 10H), 0.84 (t, 3H, J = 4.8 Hz). 13C
NMR (oxalate salt, 75 MHz, DMSO-d6): d 165.0 136.6, 126.8,
125.8, 121.9, 120.1, 119.3, 115.0, 110.5, 70.33, 62.46, 53.95 (2C),
45.94, 31.67, 30.37, 29.08 (2C), 26.75, 22.50, 14.39. Anal. Calcd
for C22H34N2O4: C, 67.66; H, 8.78; N, 7.17. Found: C, 67.60; H,
8.88; N, 7.19.
(125 MHz, DMSO-d6):
d 136.8, 127.7, 127.2, 121.5, 118.71,
118.65, 118.6, 109.8, 108.7, 57.00, 42.32 (2C), 32.43, 20.16. Anal.
Calcd for C15H20N2O4: C, 61.63; H, 6.90; N, 9.58. Found: C, 61.98;
H, 7.01; N, 9.67.
4.1.5. N1,N10,N10,N10-Tetramethyltryptaminium iodide (7a)
To
a
solution of N1,N10-dimethyltryptamine (5a, 0.05 g,
0.26 mmol) in acetone (5 mL), iodomethane (0.14 g, 1.0 mmol)
was added and the reaction mixture was stirred for 16 h. Then,
Et2O was added and the solid collected by filtation to afford
4.1.9. N,N,N-Trimethyl-2-(1-octyl-1H-indol-3-yl)ethanaminium
iodide (N1-octyl-N10,N10,N10-trimethyltryptaminium iodide, 7e)
Prepared in a similar fashion as described above (7a) by
replacing N1,N10-dimethyltryptamine with N,N-dimethyl-2-(1-oc-
tyl-1H-indol-3-yl)ethanamine (6d, 0.5 g, 1.7 mmol) to afford
0.66 g (90%) of a white solid: mp 223–226 °C (dec). 1H NMR
(400 MHz, DMSO-d6): d 7.76 (d, 1H, J = 7.6 Hz), 7.47 (d, 1H,
J = 8.4 Hz), 7.41 (s, 1H), 7.16 (t, 1H, J = 7.2 Hz), 7.06 (t, 1H,
J = 7.2), 5.86 (d, 1H, J = 3.6 Hz), 5.48 (d, 1H, J = 10.4 Hz), 4.14 (t,
2H, J = 9.0 Hz), 3.81 (dd, 1H, J1 = 10.4 Hz J2 = 13.6 Hz), 3.51 (d,
1H, J = 13.2 Hz), 3.27 (s, 9H), 1.72 (t, 2H, J = 6.4 Hz), 1.24 (m,
10H), 0.84 (t, 3H, J = 4.8 Hz). 13C NMR (100 MHz, DMSO-d6): d
136.6, 126.8, 125.8, 121.9, 120.1, 119.3, 115.0, 110.5, 70.33,
62.46, 53.95 (3C), 45.94, 31.67, 30.37, 29.08 (2C), 26.75, 22.50,
14.39. Anal. Calcd for C21H35IN2: C, 57.01; H, 7.97; N, 6.33. Found:
C, 56.93; H, 8.07; N, 6.42.
0.08 g (88%) of
a
white solid: mp 220 °C (dec). 1H NMR
(500 MHz, DMSO-d6): d 8.29 (s, 1H), 7.58 (d, 1H, J = 8.0 Hz), 7.40
(d, 1H, J = 8.0 Hz), 7.22 (s, 1H), 7.16 (t, 1H, J = 7.0 Hz), 7.05 (t, 1H,
J = 7.0 Hz), 3.74 (s, 3H), 3.17 (t, 2H, J = 7.5 Hz), 3.01 (t, 2H,
J = 7.5 Hz), 2.61 (s, 9H). 13C NMR (125 MHz, DMSO-d6): d 136.9,
127.9, 127.2, 121.5, 118.7, 118.5, 109.9, 108.4, 48.78, 32.72,
32.49, 21.62. Anal. Calcd for C14H21IN2: C, 48.85; H, 6.15; I, 36.87.
Found: C, 49.02; H, 6.03; I, 36.80
4.1.6. 2-(1H-Indol-3-yl)-N,N-dimethyl-2-oxoacetamide (9)
To a solution of indole (8, 6.00 g, 51.2 mmol) in dry Et2O (50 mL)
was added dropwise oxalyl chloride (7.80 g, 61.9 mmol, 1.2 eq) at
0 °C with stirring. After 30 min, the yellow solid was filtered and
washed with cold Et2O (50 mL). A suspension of this yellow solid
in dry DCM was treated with dry gaseous dimethylamine for
10 min and the mixture was stirred for 3 h at rt, the solvent was
removed under reduced pressure, and water (200 mL) was added.
The aqueous suspension was extracted with EtOAc (3 Â 150 mL),
and the organic phase was dried over anhydrous MgSO4 and fil-
tered. The product, crystallized as a white solid in EtOH, weighed
8.37 g (80% two steps): mp 158–160 °C. 1H NMR (500 MHz,
DMSO-d6): d 12.25 (s, 1H), 8.10 (d, 1H, J = 8.0 Hz), 8.09 (s, 1H),
7.52 (dd, 1H, J1 = 1.5 Hz, J2 = 6.5 Hz), 7.25 (m, 2H), 2.98 (s, 3H),
2.90 (s, 3H). 13C NMR (125 MHz, DMSO-d6): d 186.8, 167.5,
137.04, 137.01, 125.0, 123.6, 122.6, 121.0, 113.1, 112.7, 36.90,
33.54.
4.1.10. 1-(1H-Indol-3-yl)-2-(pyrrolidin-1-yl)ethane-1,2-dione
(11)
Prepared in a similar fashion as described above (9) using indole
(8, 2.0 g, 17.1 mmol) and replacing dimethylamine with pyrroli-
dine (3.5 g, 50 mmol) giving 3.38 g (82%, two steps) of a white so-
lid: mp 124–126 °C. 1H NMR (500 MHz, DMSO-d6): d 12.22 (s, 1H),
8.16 (s, 1H), 8.11 (d, 1H, J = 8.5 Hz), 7.52 (dd, 1H, J1 = 1.5 Hz,
J2 = 6.5 Hz), 7.25 (m, 2H), 3.47 (t, 2H, J = 7.0 Hz), 3.38 (t, 4H,
J = 7.0 Hz), 1.84 (m, 4H). 13C NMR (125 MHz, DMSO-d6): d 186.5,
165.4, 137.4, 137.0, 125.3, 123.6, 122.6, 121.1, 112.8, 112.7,
46.65, 45.06, 25.66, 23.65.
4.1.11. 3-(2-(Pyrrolidin-1-yl)ethyl)-1H-indole (12)
4.1.7. N,N-Dimethyl-2-(1-octyl-1H-indol-3-yl)-2-oxoacetamide
(10a)
Prepared in a similar fashion as described above (6d) by replac-
ing N,N-dimethyl-2-(1-octyl-1H-indol-3-yl)-2-oxoacetamide with
1-(1H-indol-3-yl)-2-(pyrrolidin-1-yl)ethane-1,2-dione (11, 2.0 g,
8.26 mmol) to afford 1.4 g (79%) of a clear liquid. 1H NMR
(500 MHz, CDCl3): d 8.25 (s, 1H) 7.61 (d, 1H, J = 7.5 Hz), 7.31 (d,
1H, J = 7.5 Hz), 7.16 (t, 1H, J = 8.5 Hz), 7.09 (t, 1H, J = 8.5 Hz), 6.98
(d, 1H, J = 2.0 Hz), 3.00 (m, 2H), 2.81 (m, 2H), 2.63 (m, 4H), 1.82
(m, 4H). 13C NMR (125 MHz, CDCl3): d 136.2, 127.4, 121.8, 121.4,
119.1, 118.8, 114.4, 111.0, 57.17, 54.18, 25.01, 23.44.
Prepared in a similar fashion as described above (4a) using 9
(2.00 g, 6.08 mmol) and replacing MeI with 1-bromooctane
(1.40 g, 7.3 mmol). Chromatography (hexane:EtOAc 8:2) afforded
2.48 g (77%) of the title compound as a clear oil. 1H NMR
(400 MHz, CDCl3): d 8.38 (t, 1H, J = 5.6 Hz), 7.93 (s, 1H), 7.61 (m,
3H), 4.16 (t, 2H, J = 7.6 Hz), 3.14 (s, 3H), 3.10 (s, 3H), 1.91 (m,
2H), 1.31 (m, 10H), 0.90 (t, 3H, J = 6.4 Hz). 13C NMR (100 MHz,

E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
3725
4.1.12. 1-Methyl-1-(2-(1-(3-methylbut-2-enyl)-1H-indol-3-yl)-
ethyl)pyrrolidinium iodide (7h)
4.1.16. N,N-Dimethyl(1-octyl-1H-indol-3-yl)methanamine
(N1-octylgramine, 15c)
Prepared in a similar fashion as described above (4a) using 3-(2-
(pyrrolidin-1-yl)ethyl)-1H-indole (12, 1.0 g, 4.7 mmol) and replac-
ing MeI with 1-bromo-3-methyl-2-butene (1.1 g, 5.2 mmol). This
compound was quaternized without prior purification in the next
reaction as described above (5a) by replacing N1,N10-dimethyltryp-
tamine with the recently prepared product to yield 1.58 g (80% two
steps) of a deliquescent solid. 1H NMR (400 MHz, DMSO-d6): d 7.65
(d, 1H, J = 7.6 Hz), 7.42 (d, 1H, J = 7.5 Hz), 7.27 (s, 1H), 7.16 (t, 1H,
J = 7.6), 7.06 (t, 1H, J = 7.6), 5.31 (m, 1H), 4.73 (d, 2H, J = 7.0 Hz),
3.60 (m, 6H,), 3.19 (m, 2H,), 3.16 (s, 3H), 2.13 (m, 4H), 1.82 (s,
3H), 1.72 (s, 3H). 13C NMR (100 MHz, DMSO-d6): d 136.2, 136.0,
127.6, 126.8, 121.9, 120.8, 119.1 (2C), 110.4, 108.6, 63.97, 63.92,
62.48, 48.04, 43.81, 25.95, 25.87, 21.60, 19.81, 18.32. Anal. Calcd
for C20H29IN2Á3H2O: C, 50.21; H, 7.37; N, 5.86. Found: C, 50.11;
H, 7.22, N, 5.95.
To a solution of aqueous formaldehyde (37%, 1.1 g, 14 mmol) in
AcOH (15 mL) was added aqueous DMA (40%, 5.0 g, 45 mmol) fol-
lowed by 1-octyl-1H-indole (17c, 3.00 g, 13.1 mmol). The reaction
mixture was stirred at rt for 24 h and was then diluted with 2 N
NaOH to raise the pH to > 10. The aqueous solution was extracted
with DCM (3 Â 50 mL), the combined organic extracts were dried
over anhydrous Na2SO4 and volatiles removed under reduced pres-
sure. Chromatography (DCM:MeOH 9:1) gave the desired product,
2.85 g (76%), as a clear liquid. 1H NMR (oxalate salt, 400 MHz,
DMSO-d6): d 7.73 (d, 1H, J = 8.0 Hz), 7.57 (s, 1H), 7.49 (d, 1H,
J = 8.4 Hz), 7.20 (t, 1H, J = 7.2 Hz), 7.12 (t, 1H, J = 8.4 Hz), 4.38 (s,
2H), 4.16 (t, 2H, J = 6.8 Hz), 2.71 (s, 6H), 1.74 (t, 2H, J = 6.8 Hz),
1.19 (m, 10H), 0.80 (t, 3H, J = 6.8 Hz). 13C NMR (100 MHz, DMSO-
d6): d 165.42, 136.3, 132.1, 128.0, 122.4, 120.3, 119.2, 110.8,
102.7, 51.51 (2C), 46.01, 41.61, 31.52 (2C), 29.98, 29.40, 28.80,
26.53, 22.42, 14.33. Anal. Calcd for C21H32N2O4: C, 66.99; H, 8.57;
N, 7.44. Found: C, 66.90; H, 8.66; N, 7.41.
4.1.13. 1-(3-Methylbut-2-enyl)-1H-indole-3-carbaldehyde (14a)
Prepared in a similar fashion as described above (4a) using 1H-
indole-3-carbaldehyde (13a, 2.0 g, 13.8 mmol) and replacing MeI
with 1-bromo-3-methyl-2-butene (3.1 g, 15 mmol). Chromatogra-
phy using DCM afforded 2.7 g (92%) of the title compound as pale
yellow crystals: mp 80–82 °C. 1H NMR (300 MHz, CDCl3): d 12.11
(s, 1H), 7.98 (s, 1H),7.81 (d, 1H, J = 5.7 Hz), 7.21 (d, 1H, J = 5.7 Hz),
6.94 (m, 2H), 5.33 (m, 1H), 4.79 (d, 2H, J = 7.2 Hz), 1.78 (s, 3H),
1.73 (s, 3H). 13C NMR (75 MHz, CDCl3): d 184.5, 139.0, 137.8,
137.3, 125.6, 123.8, 122.9, 122.0, 118.0, 117.8, 110.2, 44.75,
25.73, 18.17.
4.1.17. N,N,N-Trimethyl(1-octyl-1H-indol-3-yl)methanaminium
iodide (N-methyl-N1-octylgraminium iodide, 16c)
Prepared in a similar fashion as described above (7a) by replac-
ing N1,N10-dimethyltryptamine with N,N-dimethyl(1-octyl-1H-in-
dol-3-yl)methanamine (15c, 1.0 g, 3.5 mmol), to afford 1.3 g
(86%) of a white solid: mp 198–200 °C (dec). 1H NMR (400 MHz,
DMSO-d6): d 7.85 (d, 1H, J = 7.6 Hz), 7.74 (s, 1H), 7.57 (d, 1H,
J = 8.0 Hz), 7.23 (t, 1H, J = 7.2 Hz), 7.17 (t, 1H, J = 7.6 Hz), 4.70 (s,
2H), 4.24 (t, 2H, J = 6.8 Hz), 3.05 (s, 9H), 1.78 (t, 2H, J = 6.8 Hz),
1.22 (m, 10H), 0.83 (t, 3H, J = 6.4 Hz). 13C NMR (100 MHz, DMSO-
d6): d 136.3, 133.6, 128.6, 122.4, 120.7, 119.3, 111.0, 101.4, 60.84,
51.65 (2C), 51.61, 46.23, 31.62, 30.03, 29.05, 28.98, 26.64, 22.49,
14.40. Anal. Calcd for C20H33IN2: C, 56.07; H, 7.76; N, 6.54. Found:
C, 55.96; H, 7.79; N, 6.63.
4.1.14. N,N-Dimethyl(1-(3-methylbut-2-enyl)-1H-indol-3-yl)-
methanamine (N1-prenylgramine, 15a)
Through
a solution of 1-(3-methylbut-2-enyl)-1H-indole-3-
carbaldehyde (14a, 1.0 g, 4.7 mmol) in MeOH (25 mL) was bubbled
dry dimethylamine (DMA) for 10 min and the mixture was stirred
for 1 h. NaBH4 (0.6 g, 16 mmol) was added carefully over 10 min
and the mixture was stirred for additional 3 h. Then the solution
was carefully diluted with water and extracted with DCM
(3 Â 100 mL). The combined organic layers were washed twice
with brine, dried over anhydrous Na2SO4 and the solvent was evap-
orated. The mixture was purified by chromatography (DCM:MeOH
9:1) to give 0.7 g (62%) of a clear liquid. 1H NMR (300 MHz, CDCl3):
d 7.66 (d, 1H, J = 7.8 Hz), 7.31 (d, 1H, J = 8.1 Hz), 7.20 (t, 1H,
J = 7.5 Hz), 7.11 (t, 1H, J = 7.2 Hz), 7.10 (s, 1H), 5.36 (m, 1H), 4.66
(d, 2H, J = 6.9 Hz), 3.67 (s, 2H), 2.30 (s, 6H), 1.81 (s, 3H), 1.76 (s,
3H). 13C NMR (75 MHz, CDCl3): d 136.3, 136.1, 128.6, 127.4,
121.4, 119.9, 119.2 (2C), 110.6, 109.6, 54.14, 44.97 (2C), 44.08,
25.75, 18.08. Anal. Calcd for C18H24N2O4: C, 65.04; H, 7.28; N,
8.43. Found: C, 64.88; H, 7.40; N, 8.51.
4.1.18. 3-(1H-Indol-3-yl)-N,N-dimethylpropanamide (19)
To a solution of 3-indolylpropionic acid (4.00 g, 21.2 mmol) in
dry THF (500 mL) was added carbonyldiimidazole (DCI, 3.56 g,
22 mmol) and the mixture was stirred under nitrogen for 1.5 h.
Then, the mixture was treated with gaseous DMA for 10 min and
stirred for 16 h. The mixture was diluted with water (300 mL), ex-
tracted with EtOAc (4 Â 200 mL), dried over anhydrous Na2SO4 and
concentrated under reduced pressure. Chromatography (EtOAc:-
MeOH 95:5) gave the desired product 4.20 g (92%) as a white solid:
mp 137–139 °C. 1H NMR (400 MHz, DMSO-d6): d 8.41 (s broad, 1H),
7.61 (d, 1H, J = 8.0 Hz), 7.35 (d, 1H, J = 8.0 Hz), 7.18 (t, 1H,
J = 7.2 Hz), 7.11 (t, 1H, J = 7.6 Hz), 7.01 (s, 1H), 3.14 (t, 2H,
J = 7.6 Hz), 2.96 (s, 3H), 2.90 (s, 3H), 2.71 (t, 2H, J = 8.0 Hz). 13C
NMR (100 MHz, DMSO-d6): d 172.9, 136.4, 127.3, 121.9, 121.8,
119.2, 118.7, 115.4, 111.3, 37.24, 35.47, 34.25, 20.96.
4.1.15. N,N,N-Trimethyl(1-(3-methylbut-2-enyl)-1H-indol-3-yl)-
methanaminium iodide (N-methyl-N1-prenylgraminium iodide,
16a)
4.1.19. N,N-Dimethyl-3-(1-octyl-1H-indol-3-yl)propanamide
(20a)
Prepared in a similar fashion as described above (7a) by replac-
ing N1,N10-dimethyltryptamine with N,N-dimethyl(1-(3-methyl-
but-2-enyl)-1H-indol-3-yl)methanamine (15a, 0.3 g, 1.2 mmol),
to yield 0.4 g (87%) of a white solid: mp 212–215 °C (dec).1H
NMR (400 MHz, DMSO-d6): d 7.84 (d, 1H, J = 7.6 Hz), 7.69 (s, 1H),
7.50 (d, 1H, J = 8.0 Hz), 7.23 (t, 1H, J = 7.2 Hz), 7.17 (t, 1H,
J = 7.6 Hz), 5.36 (t, 1H, J = 6.8 Hz), 4.83 (d, 2H, J = 7.2 Hz), 4.68 (s,
2H), 3.04 (s, 9H), 1.83 (s, 3H), 1.72 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): d 136.6, 136.3, 133.2, 128.7, 122.4, 120.8, 120.3,
119.3, 111.1, 101.6, 60.89, 51.72, 51.68 (2C), 44.36, 25.84, 18.40.
Anal. Calcd for C17H25IN2: C, 53.13; H, 6.56; N, 7.29. Found: C,
53.02; H, 6.65; N, 7.23.
Prepared in a similar fashion as described above (4a) using 3-
(1H-indol-3-yl)-N,N-dimethylpropanamide (19, 1.00 g, 4.63 mmol)
and replacing MeI with 1-bromooctane (1.07 g, 5.55 mmol). Chro-
matography using EtOAc afforded 1.32 g (87%) of the title com-
pound as a pale yellow liquid. 1H NMR (400 MHz, CDCl3): d 7.59
(d, 1H, J = 8.0 Hz), 7.30 (d, 1H, J = 8.0 Hz), 7.19 (t, 1H, J = 7.2 Hz),
7.09 (t, 1H, J = 7.6 Hz), 6.94 (s, 1H), 4.05, (t, 2H, J = 7.2 Hz), 3.11
(t, 2H, J = 7.6 Hz), 2.95 (s, 3H), 2.90 (s, 3H), 2.69 (t, 2H, J = 8.4 Hz),
1.80 (t, 2H, J = 6.8 Hz), 1.28 (m, 10H), 0.87 (t, 3H, J = 6.4 Hz). 13C
NMR (100 MHz, CDCl3): d 172.9, 136.3, 127.7, 125.5, 121.3, 118.9,
118.6, 114.0, 109.4, 46.21, 37.24, 35.43, 34.49, 31.81, 30.35,
29.26, 29.20, 27.07, 22.64, 20.89, 14.05.

3726
E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
4.1.20. N,N-Dimethyl-3-(1-octyl-1H-indol-3-yl)propan-1-amine
(21a)
mide with N,N-dimethyl-1-octyl-1H-indole-2-carboxamide (25,
1.00 g, 3.33 mmol). Chromatography (DCM:MeOH 9:1) yielded
0.9 g (95%) of a clear liquid. 1H NMR (oxalate salt, 400 MHz,
DMSO-d6): d 7.51 (d, 1H, J = 7.6 Hz), 7.43 (d, 1H, J = 8.4 Hz), 7.13
(t, 1H, J = 7.6 Hz), 7.00 (t, 1H, J = 7.2 Hz), 6.60 (s, 1H), 4.23 (m,
4H), 2.60 (s, 6H), 1.58, (m, 2H), 1.19 (m, 10H), 0.79 (t, 3H,
J = 6.4 Hz). 13C NMR (100 MHz, DMSO-d6): d 164.5, 138.1, 137.2,
127.3, 122.3, 120.9, 119.9, 110.8, 104.9, 43.37, 42.91, 42.83,
31.63, 30.30, 29.17, 29.06, 26.65, 22.49, 14.37. Anal. Calcd for
Prepared in a similar fashion as described above (6d) by replac-
ing N,N-dimethyl-2-(1-octyl-1H-indol-3-yl)-2-oxoacetamide with
N,N-dimethyl-3-(1-octyl-1H-indol-3-yl)propanamide (20a, 0.8 g,
2.4 mmol) giving 0.57 g (73%) of a clear liquid. 1H NMR (oxalate
salt, 300 MHz, DMSO-d6): d 8.51 (d, 1H, J = 7.4 Hz), 7.33 (d, 1H,
J = 7.8 Hz), 7.15 (s, 1H), 7.05 (t, 1H, J = 7.6 Hz), 6.94 (t, 1H,
J = 7.4 Hz), 4.05 (t, 2H, J = 6.8 Hz), 3.01 (t, 2H, J = 7.6 Hz), 2.74 (s,
3H), 2.71 (s, 3H), 2.52 (t, 2H, J = 7.6 Hz), 2.03 (m, 2H), 1.73 (t, 2H,
J = 6.8 Hz), 1.18 (m, 10H), 0.80 (t, 3H, J = 6.4 Hz). 13C NMR
(75 MHz, DMSO-d6): d 164.6, 136.6, 127.2, 125.9, 121.0, 118.5,
118.2, 112.0, 109.6, 65.35, 54.86, 52.21, 45.23, 31.10, 29.81, 28.53
(2C), 26.24, 23.05, 21.95, 21.40, 13.84. Anal. Calcd for
C21H32N2O4: C, 66.99; H, 8.57; N, 7.44. Found: C, 66.90; H, 8.55;
N, 7.60.
4.1.25. N,N,N-Trimethyl(1-octyl-1H-indol-2-yl)methanaminium
iodide (27)
C23H36N2O4: C, 68.29; H, 8.97; N, 6.92. Found: C, 68.36; H, 8.92;
Prepared in a similar fashion as described above (8a) by replac-
ing N1,N10,N10-trimethyltryptamine with N,N-dimethyl(1-octyl-
1H-indol-2-yl)methanamine (26, 0.5 g, 1.7 mmol), to afford 0.65 g
(87%) of a white solid: mp 189–192 °C (dec). 1H NMR (400 MHz,
DMSO-d6): d 7.60 (d, 1H, J = 8.0 Hz), 7.52 (d, 1H, J = 8.4 Hz), 7.21
(t, 1H, J = 7.6 Hz), 7.06 (t, 1H, J = 7.6 Hz), 6.80 (s, 1H), 4.78 (s, 2H),
4.30 (t, 1H, J = 7.2 Hz) 3.08 (s, 9H), 1.55, (m, 2H), 1.15 (m, 10H),
0.78 (t,3H, J = 6.4 Hz). 13C NMR (100 MHz, DMSO-d6): d 139.8,
138.1, 137.6, 127.2, 123.3, 121.6, 120.5, 111.6, 109.0, 59.43, 52.18
(2C), 43.56, 31.59, 30.11, 29.18, 29.03, 26.45, 22.47, 14.37. Anal.
Calcd for C20H33IN2: C, 56.07; H, 7.76; N, 6.54. Found: C, 56.14;
H, 7.85; N, 6.53.
N, 7.02.
4.1.21. N,N,N-Trimethyl-3-(1-octyl-1H-indol-3-yl)propan-1-
aminium iodide (22a)
Prepared in a similar fashion as described above (7a) by replac-
ing N1,N10,N10-trimethyltryptamine with N,N-dimethyl-3-(1-octyl-
1H-indol-3-yl)propan-1-amine (21a, 0.2 g, 0.64 mmol), to afford
0.3 g (88%) of a white solid: mp 167–169 °C. 1H NMR (300 MHz,
DMSO-d6): d 7.51 (d, 1H, J = 6.0 Hz), 7.34 (d, 1H, J = 6.3 Hz), 7.19
(s, 1H), 7.08 (t, 1H, J = 5.4 Hz), 6.96 (t, 1H, J = 7.2), 4.06 (t, 2H,
J = 5.1 Hz), 3.35 (m, 2H), 3.03 (s, 9H), 2.68 (t, 2H, J = 5.7 Hz), 2.03
(m, 2H), 1.68 (t, 2H, J = 5.1 Hz), 1.20 (m, 10H), 0.78 (t, 3H,
J = 4.8 Hz). 13C NMR (75 MHz, DMSO-d6): d 136.5, 127.7, 126.4,
121.5, 119.0, 118.8, 112.5, 110.1, 52.77 (2C), 52.73, 45.78, 31.72,
30.36, 29.78, 29.56, 29.42,26.78, 23.60, 22.53, 21.96, 14.39. Anal.
Calcd for C22H37IN2: C, 57.89; H, 8.17; N, 6.14. Found: C, 57.98;
H, 8.12; N, 6.07.
4.2. Biological assays
4.2.1. Materials
( )-[3H]Epibatidine (33–56.2 Ci/mmol) was obtained from Perk-
inElmer/NEN Life Science Products (Cologne, Germany).[3H]MLA
(20–100 Ci/mmol) was purchased from Biotrend (Cologne, Ger-
many). All other chemicals used were obtained from Sigma-Aldrich
(Deisenhofen, Germany). Frozen Sprague–Dawley rat brains were
purchased from Pel-Freez Biologicals (Rogers, AR, USA.), Torpedo
californica electric organs were purchased from Marinus, Inc.
4.1.22. N,N-Dimethyl-1H-indole-2-carboxamide (24)
To a solution of indole-2-carboxylic acid (23, 2.00 g, 12.4 mmol)
in dry THF (20 mL) was added SOCl2 (5 mL) and the mixture was
stirred at rt for 16 h. Then, the volatiles were evaporated and the
viscous liquid was dissolved in DCM (20 mL). To this solution
was added 40% aqueous DMA (5.6 g, 50 mmol) and the mixture
was stirred for 10 min. Water (20 mL) was added, and the mixture
was extracted with DCM (4 Â 25 mL), and the combined organic
phases were dried over anhydrous Na2SO4 and concentrated under
reduced pressure. The product was crystallized in MeOH to pro-
duce 1.86 g (80%) of brown crystals: mp 77–78 °C. 1H NMR
(CA, USA), and calf adrenals were obtained from
slaughterhouse.
a local
4.2.2. Membrane preparation and binding assays
Crude membrane fractions (P2) from rat brains were isolated as
previously described23,24 and P1 membrane fractions were ob-
tained from calf adrenals and Torpedo californica electroplax. All as-
says were carried out as previously described in HEPES-salt
solution (HSS) containing HEPES (15 mM), NaCl (120 mM), KCl
(5.4 mM), MgCl2 (0.8 mM), and CaCl2 (1.8 mM) and at 22 °C per-
formed in duplicate. Briefly, nonspecific binding was determined
(400 MHz, DMSO-d6):
d 11.46 (s broad, 1H), 7.55 (d, 1H,
J = 8.0 Hz), 7.38 (d, 1H, J = 8.0 Hz), 7.13 (t, 1H, J = 7.2 Hz), 6.98 (t,
1H, J = 7.6 Hz), 6.81 (s, 1H), 3.20 (s, 3H), 3.05 (s, 3H). 13C NMR
(100 MHz, DMSO-d6):
d 163.1, 136.2, 130.7, 127.53, 127.49,
123.7, 121.8, 120.1, 112.53, 112.48, 105.0.
in the presence of 300
used as a radioligand (
l
a
M (À)-nicotine if ( )-[3H]epibatidine was
4b2⁄,
a3b4⁄,
a12b1cd). Also, each assay
4.1.23. N,N-Dimethyl-1-octyl-1H-indole-2-carboxamide (25)
Prepared in a similar fashion as described above (4a) using N,N-
dimethyl-1H-indole-2-carboxamide (24, 1.00 g, 5.32 mmol) and
replacing MeI with 1-bromooctane (1.13 g, 5.55 mmol). Chroma-
tography using EtOAc afforded 1.17 g (73%) of the title compound
as a clear liquid. 1H NMR (400 MHz, DMSO-d6): d 7.68 (d, 1H,
J = 8.0 Hz), 7.42 (d, 1H, J = 8.0 Hz), 7.32 (t, 1H, J = 7.2 Hz), 7.17 (t,
1H, J = 7.6 Hz), 6.65 (s, 1H), 4.35 (t, 1H, J = 7.6 Hz), 3.22 (s, 6H),
1.81 (m, 2H), 1.31 (m, 10H, J = 4.4 Hz), 0.92 (t, 3H, J = 6.8 Hz). 13C
NMR (100 MHz, DMSO-d6): d 164.7, 137.1, 131.6, 126.6, 123.0,
121.6, 120.0, 110.2, 103.9, 44.33 (2C), 31.81, 30.45, 29.25 (2C),
26.98, 22.65, 14.10.
sample of a total volume of 0.5 ml contained 60 lg of membrane
protein, 0.5 nM ( )-[3H]epibatidine, and 0.2 ml of a test compound.
After 90 min incubations were terminated by vacuum filtration
through Whatman GF/B glass fiber filters, presoaked in 1%
poly(ethyleneimine) using a Brandel 24-channel cell harvester.
The radioactivity was measured using a liquid scintillation counter
(Tri-Carb 2100 TR, Packard, Dreieich, Germany). For
assays, nonspecific binding was measured in the presence of
M methyllycaconitine (MLA). Each assay sample contained
l of the test compound, 100
l [3H]MLA to achieve a final con-
centration of 2 nM, and 100 l resuspended membranes. After
a7⁄ binding
1
l
50
l
l
l
180 min (at 22 °C) incubation was terminated by rapid filtration
under vacuum through Whatman GF/B filters presoaked in 1%
poly(ethyleneimine). The radioactivity bound to the filters was
measured using a liquid scintillation counter.
4.1.24. N,N-Dimethyl(1-octyl-1H-indol-2-yl)methanamine (26)
Prepared in
a similar fashion as described above (11a)
by replacing N,N-dimethyl-2-(1-octyl-1H-indol-3-yl)-2-oxoaceta-

E. G. Pérez et al. / Bioorg. Med. Chem. 20 (2012) 3719–3727
3727
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Competition binding data were analyzed using nonlinear
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off25 equation based on the measured IC50 values and Kd = 10 pM
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Acknowledgments
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E. G. P. was a recipient of a DAAD fellowship. This work was
supported by FONDECYT grant 1040776 and ICM grant P05-001-F.
Supplementary data
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