Structure-activity relationship study of N 6-(2-(4-(1 H -Indol-5-yl)piperazin-1-yl)ethyl)- N 6-propyl-4,5,6,7- tetrahydrobenzo[ d ]thiazole-2,6-diamine analogues: Development of highly selective D3 dopamine receptor agonists along with a highly potent D2/D3 agonist and their pharmacological characterization

Article abstract of DOI:10.1021/jm300268s

In our effort to develop multifunctional drugs against Parkinson's disease, a structure-activity-relationship study was carried out based on our hybrid molecular template targeting D2/D3 receptors. Competitive binding with [ ³H]spiroperidol was used to evaluate affinity (K_i) of test compounds. Functional activity of selected compounds in stimulating [ ³⁵S]γS binding was assessed in CHO cells expressing either human D2 or D3 receptors. Our results demonstrated development of highly selective compounds for D3 receptor (for (-)-40K_i, D3 = 1.84 nM, D2/D3 = 583.2; for (-)-45K_i, D3 = 1.09 nM, D2/D3 = 827.5). Functional data identified (-)-40 (EC₅₀, D2 = 114 nM, D3 = 0.26 nM, D2/D3 = 438) as one of the highest D3 selective agonists known to date. In addition, high affinity, nonselective D3 agonist (-)-19 (EC₅₀, D2 = 2.96 nM and D3 = 1.26 nM) was also developed. Lead compounds with antioxidant activity were evaluated using an in vivo PD animal model.

Full text of DOI:10.1021/jm300268s

Article
pubs.acs.org/jmc
Structure−Activity Relationship Study of N6-(2-(4-(1H-Indol-5-yl)
piperazin-1-yl)ethyl)-N6-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-
2,6-diamine Analogues: Development of Highly Selective D3
Dopamine Receptor Agonists along with a Highly Potent D2/D3
Agonist and Their Pharmacological Characterization
Mark Johnson,† Tamara Antonio,‡ Maarten E. A. Reith,‡,§ and Aloke K. Dutta*,†
†Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, United States
§
‡Department of Psychiatry and Department of Pharmacology, New York University, New York, New York 10016, United States
S
* Supporting Information
ABSTRACT: In our effort to develop multifunctional drugs against Parkinson’s disease, a structure−activity-relationship study
was carried out based on our hybrid molecular template targeting D2/D3 receptors. Competitive binding with [3H]spiroperidol
was used to evaluate affinity (Ki) of test compounds. Functional activity of selected compounds in stimulating [35S]GTPγS
binding was assessed in CHO cells expressing either human D2 or D3 receptors. Our results demonstrated development of
highly selective compounds for D3 receptor (for (−)-40 Ki, D3 = 1.84 nM, D2/D3 = 583.2; for (−)-45 Ki, D3 = 1.09 nM, D2/
D3 = 827.5). Functional data identified (−)-40 (EC50, D2 = 114 nM, D3 = 0.26 nM, D2/D3 = 438) as one of the highest D3
selective agonists known to date. In addition, high affinity, nonselective D3 agonist (−)-19 (EC50, D2 = 2.96 nM and D3 = 1.26
nM) was also developed. Lead compounds with antioxidant activity were evaluated using an in vivo PD animal model.
in the striatum of the midbrain.8 D2 and D3 receptor subtypes
occur post- and presynaptically. In the latter location they
INTRODUCTION
Dopaminergic receptor systems have been targeted for the
■
function as autoreceptors that regulate DA synthesis,
development of pharmacotherapeutic agents for a number of
metabolism, and release.9 It is noteworthy that D2 and D3
CNS related disorders, including drug addiction, schizophrenia,
receptor subtypes share 50% overall amino acid sequence
homology and 75−80% in their agonist binding sites. As a
result, development of ligands selective for either subtype is a
challenging task.10,11
depression, and Parkinson’s disease (PD). Dopamine (DA)
receptor agonists have been employed more extensively in the
treatment of Parkinson’s disease than any other type of
pharmacotherapy. Levodopa (L-dopa), the immediate pre-
cursor to endogenous DA, is the current gold-standard
treatment option for PD. DA receptors belong to the family
of transmembrane proteins known as G-protein-coupled
receptors (GPCRs). DA receptors are widely distributed in
the CNS, are also present in the periphery, and are divided into
five subtypes. On the basis of the stimulatory action on adenylyl
cyclase, D1 and D5 are grouped together as D1 type. D2−D4
receptors are classified as D2 type because of their inhibitory
action on adenylyl cyclase activity.1−7 Interestingly, the D3
receptor was found to have a distribution in the brain that is
somewhat different from that of the D2 receptor. The highest
levels of D3 receptor expression were found to be in the limbic
region of the brain, while D2 receptor expression is most dense
Parkinson’s disease (PD) is a progressive, neurodegenerative
disorder that results from the death of DA-producing cells in
the substantia nigra region of the midbrain. Common
symptoms include resting tremor, muscular rigidity, bradyki-
nesia, postural instability, and cognitive psychiatric complica-
tions.12−14 Although the etiology of PD is not yet clear and may
be multifactorial, oxidative stress and mitochondrial dysfunction
are thought to play a central role in the pathology of the
disease. Recent studies on various genetic mutations have
provided new insights into the disease process.15−17 Oxidative
Received: February 26, 2012
Published: May 29, 2012
© 2012 American Chemical Society
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Figure 1. Molecular structure of dopamine D3-receptor-preferring agonists.
a
Scheme 1
a
Reagents and conditions: (a) n-propylamine, NaCNBH3, AcOH, CH2Cl2; (b) 2-bromoethanol, K2CO3, CH3CN reflux; (c) (COCl)2, DMSO,
Et3N, CH2Cl2, −78 °C to rt; (d) 2, Na(OAc)3BH, CH2Cl2; (e) aq HBr (48%), reflux; (f) indole-5-, -2- or -3-carbaldeyde, Na(OAc)3BH, CH2Cl2.
stress has been strongly implicated in midbrain dopaminergic
cell death.15 Toxicity from endogenous and exogenous origins,
caused by oxidative mechanisms, has been implicated as a
fundamental process in progressive nigral cell loss.18 Along with
motor fluctuations and wearing off after long-term treatment,
side effects associated with L-dopa treatment and the eventual
oxidation of DA derived from L-dopa have been speculated to
produce further oxidative stress.19
In addition, α-synuclein, a presynaptic protein involved in
fibrillization, has been implicated in the pathogenesis of
PD.20,21 A recent report demonstrated that in cultured
human dopaminergic neurons, accumulation of α-synuclein
induces apoptosis in the presence of DA and reactive oxygen
species.22 Furthermore, an interaction between calcium,
cytosolic DA, and α-synuclein has been implicated in the loss
of DA neurons in the substantia nigra.23 In this case, DA-
dependent neurotoxicity is mediated by a soluble protein
complex containing α-synuclein.24 Therefore, α-synuclein,
together with oxidized DA, could have synergistic effects in
terms of disease susceptibility and progression.
It is increasingly evident that for a complex disease such as
PD, a drug aimed at one target site will only partially address
the therapeutic need of the disease. Thus, it is hypothesized
that multifunctional drugs, having multiple pharmacological
activities, will be more effective in the case of PD.25 Our
approach in developing such agents involves alleviating
symptoms of the disease, along with preventing or halting the
neurodegeneration process. Our drug development approach
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a
Scheme 2
a
Reagents and conditions: (a) triisopropylsilyl chloride, NaH, THF; (b) 4, PdCl2[P(o-tol)3]2, NaOt-Bu, xylenes, reflux; (c) CF3COOH, CH2Cl2; (d)
(2-bromoethoxy)-tert-butyldimethylsilane, K2CO3, CH3CN, reflux; (e) (Boc)2O, DMAP, THF; (f) n-Bu4NF, THF; (g) (COCl)2, DMSO, Et3N,
CH2Cl2, −78 °C to rt; (h) ( )-, (−)-, or (+)-pramipexole, Na(OAc)3BH, CH2Cl2; (i) CF3COOH, CH2Cl2; (j) 2, Na(OAc)3BH, CH2Cl2; (k) aq
HBr (48%), reflux.
encompasses and incorporates some of the critical pathogenic
factors implicated in PD.26,27 We have designed a novel, hybrid,
molecular template by combining known D2/D3 agonists with
D2/D3 antagonist fragments, which led to the development of
a number of D3-preferring agonists.28−33 One such compound,
D-264, was shown to be neuroprotective in two PD animal
models.34 Furthermore, we demonstrated that our D3-
preferring agonist, D-264, significantly improved behavioral
syndromes in both acute MPTP and progressive lactacystin
mouse models of PD.34 Moreover, D-264 exhibited pro-
nounced neuroprotection in both MPTP- and lactacystin-
lesioned animal models, in which degeneration of dopaminergic
pathways is known to occur. The neuroprotective effect of D-
264 was attributed, in part, to activation of the D3 receptor.
Structural flexibility in the D2/D3 antagonist fragment of our
hybrid molecular template has allowed us to design and develop
new DA agonists with the capacity to bind iron. Iron has been
implicated in the pathogenesis of PD, likely via increasing
oxidative stress levels.31 In our recent study, we have
demonstrated development of brain penetrant, multifunctional
compounds with agonist activity at D2/D3 receptors along with
capacity to chelate iron. One of our lead compounds in this
series exhibited in vivo neuroprotection in a mouse MPTP
model.31,35
As mentioned above, we have previously reported a hybrid
structure approach as part of our ongoing effort to design and
develop selective agonists for the DA D3 receptor. Our hybrid
approach combines, via suitable linker length, an agonist
binding moiety (aminotetralin or bioisosteric equivalent) with
arylpiperazine fragments. This approach has yielded molecules
that retain agonist activity while exhibiting varying selectivity
for the D3 receptor (Figure 1). Our current structure−activity-
relationship study is focused on introducing several indole
derivatives on the piperazine ring. Our goal is to assess indole
substitution in terms of its effect on selectivity and affinity for
the D3 receptor. It is important to mention that indole
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a
Scheme 3
a
Reagents and conditions: (a) 4, EDCl, HOBT, Et3N, CH2Cl2; (b) CF3COOH, CH2Cl2; (c) (2-bromoethoxy)(tert-butyl)dimethylsilane, (3-
bromopropoxy)(tert-butyl)dimethylsilane or (bromobutoxy)(tert-butyl)dimethylsilane, K2CO3, CH3CN, reflux; (d) (Boc)2O, 4-DMAP, THF; (e) n-
Bu4NF, THF; (f) (COCl)2, DMSO, Et3N, CH2Cl2, −78 °C to rt; (g) ( ), (+), or (−)-pramipexole, Na(OAc)3BH, CH2Cl2; (h) CF3COOH,
CH2Cl2.
derivatives are well-known for their potent antioxidant
activity.36,37 Another goal is to produce synergistic, antioxidant
activity by combining the 2-aminothiazole moiety with an
indole functionality.38
t-Bu in xylenes at reflux, yielded intermediate 12. Successive
deprotection of TIPS and Boc groups with trifluoroacetic acid
gave amine 13, which on selective N-alkylation with (2-
bromoethoxy)-tert-butyldimethylsilane yielded compound 14.
The indole moiety of intermediate 14 was N-protected giving
compound 15, which on TBDMS deprotection yielded alcohol
16. Compound 16 was converted to its aldehyde derivative 17,
under Swern oxidation conditions. Aldehyde 17 was sub-
sequently condensed with ( )-, S-(−)-, or R-(+)-pramipexole
to yield intermediates ( )-18, S-(−)-18, and R-(+)-18, which
were each treated with trifluoroacetic acid to afford final
compounds ( )-19, S-(−)-19, and R-(+)-19. Aldehyde 17 was
further condensed with 5-methoxy-1,2,3,4-tetrahydronaphtha-
len-2-yl)propylamine under reductive amination conditions and
subsequently treated with aqueous HBr (48%) to furnish final
compound 21.
Scheme 3 depicts the synthesis of final compounds ( )-40,
R-(+)-40, S-(−)-40, 41, and 42. Indole-2-carboxylic acid was
reacted with amine 4, under amide coupling conditions, to yield
intermediate 23. Deprotection, followed by selective N-
alkylation with appropriately substituted TBDMS-protected
alkyl halides afforded intermediates 25−27. Protection of the
indole moiety, followed by selective deprotection of the
hydroxyl functionality, gave alcohols 31−33. Alcohols 31−33
CHEMISTRY
■
Scheme 1 outlines the synthesis of 9a, 9b, and 9c. 5-Methoxy-2-
tetralone was first condensed with n-propylamine in the
presence of sodium cyanoborohydride under reductive
amination conditions to yield secondary amine 2. In
preparation of 7, amine 4 was N-alkylated using 2-
bromoethanol to provide alcohol 5. Alcohol 5 was converted,
under Swern oxidation conditions, to its aldehyde derivative.
Condensation of aldehyde 6 with amine 2, using sodium
triacetoxyborohydride as reducing agent, yielded compound 7.
Treatment of intermediate 7 with aqueous HBr (48%)
provided amine 8. Finally, condensation of secondary amine
8 with properly substituted indolecarbaldehydes afforded final
compounds 9a−c.
Scheme 2 describes the synthesis of final compounds ( )-19,
(+)-19, (−)-19, and 21. Commercially available 5-bromoindole
was N-protected using triisopropylsilyl chloride in the presence
of NaH to give intermediate 11. Palladium-catalyzed cross-
coupling of 11 with amine 4, using PdCl2[P(o-tol)3]2 and NaO-
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a
Scheme 4
a
Reagents and conditions: (a) ( )-, (+)-, or (−)-pramipexole, Na(OAc)3BH, CH2Cl2; (b) CF3COOH, CH2Cl2; (c) indole-3-carboxylic acid, EDCl,
HOBT, Et3N, CH2Cl2; (d) indole-5-carboxylic acid, EDCl, HOBT, Et3N, CH2Cl2; (e) 5-methoxy-1H-indole-3-carboxylic acid, EDCl, HOBT, Et3N,
CH2Cl2; (f) BBr3, CH2Cl2, −78 °C to rt; (g) 1H-indole-5-carbaldehyde, Na(OAc)3BH, CH2Cl2.
were subsequently converted to their aldehyde derivative, under
Swern oxidation conditions, to yield 34−36. Aldehyde 34 was
coupled with ( )-, R-(+), and S-(−)-pramipexole, under
reductive amination conditions, to give condensed products
( )-37, R-(+)-37, and S-(−)-37. Deprotection of the indole
moiety afforded final compounds ( )-40, R-(+)-40, and S-
(−)-40. Aldehydes 35 and 36 were condensed with
( )-pramipexole to yield intermediates 38 and 39, which
were deprotected under acidic conditions to furnish final
compounds 41 and 42.
Scheme 4 outlines the synthesis of final compounds ( )-45,
R-(+)-45, S-(−)-45, ( )-46, R-(+)-46, S-(−)-46, 48, and 49.
Aldehyde 6 was coupled with ( )-, (+)-, or (−)-pramipexole to
yield condensed products ( )-43, R-(+)-43, and S-(−)-43.
Subsequent treatment with trifluoroacetic acid yielded depro-
tected intermediates ( )-44, R-(+)-44, and S-(−)-44. Sepa-
rately, under amide coupling conditions, ( )-44, R-(+)-44, and
S-(−)-44 were reacted with either indole-3-carboxylic acid or
indole-5-carboxylic acid to yield final compounds ( )-45, R-
(+)-45, S-(−)-45, ( )-46, R-(+)-46, and S-(−)-46. Reaction of
( )-44 with 5-methoxy-1H-indole-3-carboxylic acid, under
amide coupling conditions, or 1H-indole-5-carbaldehyde
under reductive amination conditions afforded intermediate
47 and final compound 49. Finally, demethylation of 47 with
boron tribromide furnished final compound 48.
RESULTS AND DISCUSSION
■
Our current study is aimed at investigating the molecular and
chemical flexibility, along with basicity, of the arylpiperazine
fragment of our hybrid template as it relates to D2/D3 receptor
binding and functional activity. The present series of
compounds comprise various indole derivatives, as our previous
studies have indicated that an indole substituent in the
arylpiperazine region is well tolerated, producing molecules
with high D2/D3 affinity and preference for D3 receptor.32 We
have carried out our binding studies with rat dopamine D2 and
D3 (rD2 and rD3) receptors expressed in HEK-293 cells and
functional characterization with human D2 and D3 receptors
(hD2 and hD3) expressed in CHO cells. In our own findings,
we did not see any significant difference of affinity of
compounds interacting with either rat or human dopamine
D2 and D3 receptors. An overall high degree of homology
exists between the two species, 95% for D2 and greater than
78% for D3 with somewhat shorter third intracellular loop in
the human version of the D3 receptor.2,39
Table 1 summarizes the binding data for analogues that were
synthesized. Compounds 9a−c, which incorporate the 5-
hydroxyaminotetralin headgroup and a methylene unit
connecting piperazine to indole at various positions, displayed
high affinity for D3 and moderate affinity for D2 receptors.
Among this series of analogues, the 5-substituted indole
derivative 9a displayed the highest selectivity for D3 (Ki, D2
= 269 nM, D3 = 4.17 nM, D2/D3 = 64.5), while 9c (Ki, D2 =
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Table 1. Inhibition Constants for Competition with [3H]Spiroperidol Binding to Cloned Rat D2L and D3 Receptors Expressed
a
in HEK-293 Cells
Ki (nM)
compd
rD2L, [3H]spiroperidol
rD3, [3H]spiroperidol
D2L/D3
(−)-5-OH-DPAT
D-237
D-301
D-264
9a
58.8 11.0
26.0 7.5
269 16
264 40
269 183
183 26
82.1 7.1
46.7 6.6
1.36 0.28
0.83 0.13
2.23 0.60
0.92 0.23
4.17 0.36
5.48 0.86
3.20 0.32
1.92 0.38
2.19 0.39
15.9 3.6
10.4 1.6
4.59 0.15
1.84 0.51
54.1 4.2
2.78 0.25
1.74 0.25
4.17 0.30
1.09 0.14
48.2 8.6
4.10 0.57
1.40 0.29
52.8 8.3
16.8 0.6
8.07 0.93
43.2
31.5
121
253
64.5
33.4
25.6
24.3
17.8
8.46
7.3
9b
9c
( )-19
(−)-19
(+)-19
21
39
5
134 12
76.4 2.4
852 209
1,073 92
2,558 112
928 152
531 119
1,503 67
902 130
1,316 244
1,243 130
1,031 182
2,626 229
1,079 139
132 22
( )-40
(−)-40
(+)-40
41
185.6
583
47.3
334
305
360
828
27.3
303
736
49.7
64.2
16.4
42
( )-45
(−)-45
(+)-45
( )-46
(−)-46
(+)-46
48
49
a
Results are the mean SEM for three to six independent experiments, each performed in triplicate.
82.1 nM, D3 = 3.20 nM, D2/D3 = 25.6) proved to be the most
potent and least selective. Analogues 9a−c exhibited lower
affinity for D2 and in the case of 9a, higher selectivity for D3
compared to parent compound D-237 (9a Ki, D2 = 269 nM,
D2/D3 = 64.5 vs D-237 Ki, D2 = 26.0 nM, D2/D3 = 31.5). A
similar 5-substituted indole derivative, 21, lacks a linking carbon
between piperazine and indole and displayed low selectivity and
lost some potency (Ki, D2 = 76.4 nM, D3 = 10.4 nM, D2/D3 =
7.3) for the D3 receptor compared to counterparts 9a−c.
Compound 49, analogous to 9a−c, with 2-aminothiazole
substitution in the agonist headgroup maintained D2 receptor
affinity within the range displayed by 9a−c, while D3 affinity
decreased by approximately 2-fold (Ki, D2 = 132 nM, D3 =
8.07 nM, D2/D3 = 16.4).
Previous and current results consistently demonstrate that in
the 2-aminothiazole series of hybrid compounds, the
(−)-isomeric version exhibits the highest affinity for the D3
receptor compared to the (+)-isomer. Bioisosteric equivalent
molecules were synthesized with the aminotetralin headgroup
replaced with 2-aminothiazole. The first of these analogues
incorporated a bond that linked the piperazine moiety directly
to the indole group. The most active optical isomer of this
molecule, (−)-19, displayed the highest affinity for the D2
receptor among the compounds in our study, along with low
selectivity (Ki, D2 = 39 nM, D3 = 2.19 nM, D2/D3 = 17.8). In
contrast, one of the parent compounds, D-301, displayed lower
D2 affinity and higher D3 selectivity (Ki, D2 = 269 nM, D3 =
2.23 nM, D2/D3 = 121) compared to (−)-19. This suggests
that the indole moiety alone does not give rise to selectivity for
either receptor subtype. In order to investigate the effect of
lowering the basicity of the piperazine ring, we synthesized a
number of analogues that incorporate an amide bond at the
piperazine nitrogen atom, distal to the agonist headgroup.
Interestingly, in these molecules, D3 receptor affinity was
maintained in the low nanomolar range, while D2 affinity
dropped significantly to the low micromolar range. The 2-
aminothiazole derived, 3-substituted indoleacyl derivative
(−)-45 displayed the highest selectivity in binding (Ki, D2 =
902 nM, D3 = 1.09 nM, D2/D3 = 828) to D3 receptor in our
current series of molecules. A more than 3-fold increase in D3
selectivity was observed for (−)-45 when compared to previous
lead and parent compound D-264 (D2/D3, 828 vs 253 for
(−)-45 vs D-264). Compound (−)-45 was also more selective
than another lead compound, D-301 (D2/D3, 828 vs 121 for
(−)-45 vs D-301). Our next goal was to synthesize isomeric, 2-
substituted indoleacyl derivative ( )-40, connected to the
piperazine ring via amide linkage. The most active enantiomer,
(−)-40, exhibited high affinity and selectivity for D3 receptor
(Ki, D3 = 1.84 nM, D2/D3 = 583). Next, the isomeric, 5-
substituted, indoleacyl derivative ( )-46 was prepared. The
most active enantiomer, (−)-46, produced a similar high
affinity and selectivity profile for D3 receptor (Ki, D3 = 1.40
nM, D2/D3 = 736). Thus, affinity and selectivity for D3
receptor were similar in isomeric compounds (−)-40, (−)-45,
and (−)-46.
Next, to determine the impact of the linker length on D2/D3
receptor binding, we varied the length of the two-carbon tether
between the agonist headgroup and the arylpiperazine
fragment. The two-carbon linker of ( )-40 was increased to
three and four carbons. Compound 41 (Ki, D2 = 928 nM, D3 =
2.78 nM, D2/D3 = 333.8) contained a three-carbon linker and
displayed an almost 2-fold increase in D3 selectivity compared
to the parent compound ( )-40 (Ki, D2 = 852 nM, D3 = 4.59
nM, D2/D3 = 186). Compound 42 contained a four-carbon
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a
Table 2. Stimulation of [35S]GTPγS Binding to Cloned Human D2 Receptor and D3 Receptor Expressed in CHO Cells
hCHO-D2
[35S]GTPγS EC50 (nM)
hCHO-D3
[35S]GTPγS EC50 (nM)
compd
Emax (%)
Emax (%)
D2/D3
DA
227 11
116 16
33.1 6.6
114 12
86.4 6.2
70.7 14.9
2.96 0.3
100
8.57
100
26.5
141
22.1
438
99.3
126
2.35
D-301
D-264
(−)-40
(−)-45
(−)-46
(−)-19
88.4 3.9
0.82 0.20
1.51 0.22
0.26 0.07
0.87 0.11
0.56 0.14
1.26 0.2
102
2
104
101
5
5
90.0 4.3
103 10
91.6 5.9
100
6
107
107
4
3
98.1 3.3
93.1 4.4
a
EC50 is the concentration producing half-maximal stimulation. For each compound, maximal stimulation (Emax) is expressed as a percent of the Emax
observed with 1 mM (D2) or 100 μM (D3) of the full agonist DA (Emax, %). Results are the mean SEM for three to six independent experiments,
each performed in triplicate.
linker, which increased affinity for both D2 and D3 receptors
(Ki, D2 = 531 nM, D3 = 1.74 nM, D2/D3 = 305) compared to
( )-40 and 41. Finally, we modified ( )-45 to incorporate a
hydroxyl substituent at the 5-position of the indole moiety.
Hydroxyl substitution helped us to study the electronic effects
of an electron-releasing group on the indole nucleus and a
possible contribution of hydrogen-bond interactions in this
region of D2 and D3 receptors. This modification produced
compound 48, which maintained micromolar D2 affinity of the
parent compound, while D3 affinity decreased 4-fold (Ki, D2 =
1,079 nM, D3 = 16.8 nM, D2/D3 = 64.2). This result indicated
that introduction of a 5-hydroxyl group on the indole nucleus
did not have a significant effect on D2 affinity, while D3 affinity
and selectivity were impacted unfavorably.
radical by ( )-40, ( )-45, ( )-46, ( )-19, and ascorbic acid
is shown in Figure 2.40 The scavenging effect is expressed as
The next goal of our study was to investigate the functional
activity of selected compounds at D2/D3 receptors. The most
and least selective D3 ligands, based on binding results, were
selected for functional activity evaluation. Optically active lead
compounds (−)-19,(−)-40, (−)-45, and (−)-46 were tested in
the [35S]GTPγS functional assay to characterize their ability to
stimulate D2/D3 receptors in comparison to the endogenous
ligand DA and to the parent compounds D-264 and D-301.
(−)-40, (−)-45, and (−)-46 each of the three compounds
tested displayed higher functional selectivity and potency for
D3 receptor in comparison to D-264 and DA (Table 2). In
particular, (−)-40 maintained high functional selectivity for D3
receptor (EC50, D2 = 114 nM, D3 = 0.26 nM, D2/D3 = 438),
correlating well with binding data, and exhibited full agonist
activity at both D2 and D3 receptors (Emax close to 100%).
Compound (−)-40 demonstrated a 5-fold increase in func-
tional potency (EC50, D3 = 1.51 vs 0.26 for D-264 vs (−)-40)
and an almost 20-fold increase in functional selectivity (D2/D3
22.1 vs 438 nM for D-264 vs (−)-40) for the D3 receptor when
compared to D-264. On the other hand, in comparison to D-
301, the selectivity was 3-fold higher (EC50 D2/D3 = 438 vs
141). Compounds (−)-45 (EC50, D2 = 86.4 nM, D3 = 0.87
nM, D2/D3 = 99.3) and (−)-46 (EC50, D2 = 70.7 nM, D3 =
0.56 nM, D2/D3 = 126) each exhibited full agonist activity
(Emax not significantly different from 100%) at D2 and D3
receptors, while their selectivity for D3 receptor dropped
considerably when compared to binding data. In contrast to the
above-mentioned indoleacyl derivatives, compound (−)-19 was
exceptionally potent at D2 receptor (EC50, D2 = 2.96 nM and
D3 = 1.26 nM), while also exhibiting high potency for D3
receptor. Thus, (−)-19 was indiscriminate in its binding to D2
and D3 receptors.
Figure 2. DPPH radical scavenging activity by ( )-19, ( )-40,
( )-45, ( )-46, and ascorbic acid.
percent of control. As shown in Figure 2, each compound
inhibited DPPH radical activity dose dependently. The
standard compound, ascorbic acid, had an IC50 of 24.9 μM in
this assay procedure, whereas the IC50 for ( )-19 was 14.5 μM
(n = 3−4 for all compounds tested). All other compounds
exhibited potencies comparable to that of ascorbic acid. It is
clear from the data that compound ( )-19 is nearly twice as
potent as ascorbic acid in quenching the DPPH radical.
Reversal of Reserpine-Induced Hypolocomotion in
Rats by (−)-19, (−)-46, (−)-40, and Ropinirole. Reserpine
induces depletion of catecholamines in nerve terminals,
resulting in a cataleptic condition in rats, which is a well
established animal model for PD.41 Significant reduction of
locomotion of the rats was observed 18 h after the
administration of reserpine (5 mg/kg, sc), which indicated
the development of akinesia in rats (Figure 3). Compound
(−)-19 (5 μmol/kg, sc) was efficacious in significantly reversing
akinesia in rats, compared to reserprine treatment alone, over a
6 h period. Similarly, treatment with the reference drug
ropinirole (5 μmol/kg, sc) produced a significant locomotor
activation compared to control, reaching higher levels of
locomotion but with a much shorter duration of action
compared with (−)-19. On the other hand, compounds (−)-46
and (−)-40 (10 μmol/kg, sc) failed to produce any appreciable
effect in reversing akinesia in reserpine-treated rats.
CONCLUSION
■
Results from binding and functional activity studies indicate
that we have developed a novel class of D3-selective agonists,
based on our hybrid template. Our current series of compounds
include those with low, moderate, and high selectivity for D3
Evaluation of Free Radical Scavenging Activity.
Scavenging of the DPPH (1,1-diphenyl-2-picrylhydrazyl)
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EXPERIMENTAL SECTION
■
Reagents and solvents were purchased from commercial suppliers and
used as received unless otherwise noted. Dry solvent was obtained
following the standard procedure. All reactions were performed under
N2 atmosphere unless otherwise indicated. Analytical silica gel 60 F254
-
coated TLC plates were purchased from EMD Chemicals, Inc. and
were visualized with UV light or by treatment with phosphomolybdic
acid (PMA), Dragendorff’s reagent, or ninhydrin. Whatman Purasil
60A silica gel 230−400 mesh was used for flash column chromato-
graphic purifications. Proton nuclear magnetic resonance (1H NMR)
spectra were measured on a Varian 400 MHz FT NMR spectrometer,
using tetramethylsilane (TMS) as an internal standard. The NMR
solvent used was CDCl3 unless otherwise indicated. Optical rotations
were recorded on Perkin-Elmer 241 polarimeter. Mass spectra were
recorded on Micromass QuattroLC triple quadrupole mass
spectrometer. Melting points were recorded using a MEL-TEMP II
(Laboratory Devices Inc., U.S.) capillary melting point apparatus and
were uncorrected. Elemental analyses were performed by Atlantic
Microlab, Inc. and were within 0.4% of the theoretical value.
5-Methoxy-N-propyl-1,2,3,4-tetrahydronaphthalen-2-amine
(2). Into a stirring solution of n-propylamine (14.9 mL, 181.6 mmol)
and ketone 1 (12.8 g, 72.6 mmol) in CH2Cl2 (70 mL) was added
glacial acetic acid (17.3 mL, 290.5 mmol). After the mixture was stirred
for 0.5 h, NaCNBH3 (11.4 g, 181.6 mmol) was added portionwise at 0
°C, followed by methanol (20 mL). The mixture was allowed to reach
room temperature and stirred overnight. The reaction mixture was
quenched with a saturated NaHCO3 solution at 0 °C and extracted
with ethyl acetate (3 × 100 mL). The combined organic layer was
washed with water, brine and dried over Na2SO4. Solvent was removed
under reduced pressure. Crude product was purified by column
chromatography (EtOAc/MeOH, 9:1) to give compound 2 (11.1 g,
70%). 1H NMR (CDCl3, 400 MHz): δ 0.96 (t, J = 7.2 Hz, 3H), 1.54−
1.65 (m, 3H), 2.09−2.16 (m, 1H), 2.52−2.74 (m, 4H), 2.88−3.07 (m,
3H), 3.81 (s, 3H), 6.66 (d, J = 8.0 Hz, 1H), 6.71 (d, J = 8.4 Hz, 1H),
7.09 (t, J = 8.4 Hz, 1H).
Figure 3. Effects of different drugs (administered sc) upon reserpine
(5.0 mg/kg, sc, 18 h pretreatment) induced hypolocomotion in rats.
Each point represents the mean
SEM for three to six rats.
Horizontal activity was measured as described in Experimental Section.
Representation of horizontal locomotor activity is at discrete 30 min
intervals after the administration of (−)-19 (5 μmol/kg), (−)-46 (10
μmol/kg), (−)-40 (10 μmol/kg), and ropinirole (5 μmol/kg)
compared to control rats, 18 h after reserpine treatment. Differences
among treatments were significant by one-way ANOVA analysis
(F(4.95) = 6.69 (P < 0.0001)): (∗∗) P < 0.01 ((−)-19) or (∗) P <
0.05 (ropinirole) compared to reserpine control (Dunnett’s analysis
after one-way ANOVA).
receptor. D3 selectivity, according to our SAR results, is
influenced by three factors: linker length, molecular structure,
and basicity of the arylpiperazine fragment. Our results indicate
a correlation between basicity of the nitrogen atom that
connects piperazine to the indole ring, with D2/D3 selectivity
and potency. In the case of compound 49, piperazine and
indole are connected via a methylene unit, giving rise to high
basicity of the piperazine nitrogen atom and low selectivity for
D3 receptor (D2/D3 = 16.4 for 49). On the other hand, when
the connecting carbon is a planar sp2 hybridized carbonyl
group, the basicity of the nitrogen atom is low and much higher
selectivity is observed for the D3 receptor (D2/D3 = 583, 828,
and 736 for (−)-40, (−)-45, and (−)-46, respectively). It is also
possible that an electronic effect of carbonyl group on the
indole ring might also additionally play an important role in
selectivity for D3 receptor. In the GTPγS functional assay,
compound (−)-40 exhibited high selectivity for the D3
receptor and is one of the most selective D3 agonists known
to date (D2/D3 = 438). These results indicate that amide
linkage, connecting the piperazine ring to the indole moiety, is
unfavorable in terms of binding to the D2 receptor while
affinity for the D3 receptor remains high. In this regard, in a
recent publication, the importance of the presence of amide
linkage has been shown in highly selective D3 antagonist
compounds.42 The length of the tether between the agonist
headgroup and the arylpiperazine fragment affects the affinity
and selectivity for D2 and D3 receptors. In the series ( )-40,
41, and 42, in which the linker length is increased from n = 2 to
n = 4, an increase in D3 affinity and selectivity occurs.
4-(2-Hydroxyethyl)piperazine-1-carboxylic Acid tert-Butyl
Ester (5). A mixture of compound 4 (10.0 g, 53.7 mmol), 2-
bromoethanol (10.1 g, 80.6 mmol), and K2CO3 (22.3 g, 161.1 mmol)
in CH3CN (100 mL) was refluxed for 14 h according to procedure D.
The crude material was purified by silica gel column chromatography
1
(EtOAc/MeOH, 20:1) to give compound 5 (7.12 g, 58%). H NMR
(CDCl3, 400 MHz): δ 1.40 (s, 9H), 2.40 (t, J = 4.8 Hz, 4H), 2.50 (t, J
= 5.2, 2H), 3.38 (t, J = 4.8 Hz, 4H), 3.58 (t, J = 5.2 Hz, 2H).
Procedure A. 4-(2-Oxoethyl)piperazine-1-carboxylic Acid
tert-Butyl Ester (6). Into a stirring solution of oxalyl chloride (5.5
g, 43.3 mmol) in CH2Cl2 (80 mL) at −78 °C was added DMSO (6.2
mL, 78.7 mmol). The reaction mixture was stirred for 0.5 h, followed
by addition of compound 5 (5.0 g, 21.7 mmol, in 20 mL of CH2Cl2).
The reaction mixture was stirred at the same temperature for 0.5 h,
followed by addition of Et3N (18.2 mL, 179.4 mmol), and stirring was
continued for 1.5 h while allowing the reaction mixture to reach room
temperature. The reaction mixture was quenched by addition of a
saturated solution of NaHCO3 and extracted with CH2Cl2 (3 × 100
mL). The combined organic layer was dried using Na2SO4, and the
solvent was removed under reduced pressure. The crude product was
purified by silica gel column chromatography (EtOAc/MeOH, 20:1)
to give compound 6 (4.96 g, ∼100%).
Procedure B. 4-{2-[(5-Methoxy-1,2,3,4-tetrahydronaphtha-
len-2-yl)propylamino]ethyl}piperazine-1-carboxylic Acid tert-
Butyl Ester (7). Into a stirring solution of amine 2 (4.76 g, 21.7
mmol) in CH2Cl2 (50 mL) was added aldehyde 6 (4.96 g, 21.7 mmol).
After the mixture was stirred for 1 h, NaBH(OAc)3 (8.29 g, 39.1
mmol) was added portionwise and the mixture was stirred for 48 h at
room temperature. The reaction mixture was quenched with a
saturated solution of NaHCO3 at 0 °C and extracted with ethyl acetate
(3 × 100 mL). The combined organic layer was dried over Na2SO4,
and the solvent was removed under reduced pressure. Crude product
was purified by column chromatography (EtOAc/MeOH, 20:1) to
give compound 7 (6.46 g, 69%). 1H NMR (CDCl3, 400 MHz): δ 0.86
(t, J = 7.6 Hz, 3H), 1.20 (s, 9H), 1.30−1.52 (m, 3H), 1.90−2.12 (m,
Furthermore, radical quenching study indicates that com-
pound ( )-19 has potent antioxidant activity. Antioxidant
activity is highly relevant, as there has been a strong implication
of oxidative stress in the pathogenesis of PD. Further evaluation
of the antioxidant activity of these compounds is underway. In
the present in vivo PD animal model, compound (−)-19
produced a significant, long-lasting reversal of hypolocomotion
in reserpinized rats. Our ongoing studies with (−)-19 are
directed at evaluating the full potential of this compound as a
multifunctional, neuroprotective agent against PD.
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1H), 2.20−3.06 (m, 13H), 3.20−3.60 (m, 6H), 3.77 (s, 3H), 6.61 (d, J
= 8 Hz, 1H), 6.67 (d, J = 8 Hz, 1H), 7.05 (t, J = 7.6 Hz, 1H).
6-[(2-Piperazin-1-ylethyl)propylamino]-5,6,7,8-tetrahydro-
naphthalen-1-ol (8). A mixture of compound 7 (6.46 g, 14.9 mmol)
and 48% aqueous HBr (40 mL) was refluxed at 125 °C for 12 h. The
reaction mixture was evaporated to dryness, and a saturated solution of
NaHCO3 was added to it at 0 °C. The reaction mixture was then
extracted with ethyl acetate (3 × 100 mL). The combined organic
layer was dried over Na2SO4, filtered, and concentrated under reduced
pressure to yield compound 8 (3.80 g, 80%). 1H NMR (CD3OD, 400
MHz): δ 1.06 (t, J = 7.2 Hz, 3H), 1.80−2.02 (m, 3H), 2.36−2.48 (m,
1H), 2.60- 2.80 (m, 1H), 2.96−4.02 (m, 18H), 6.61 (d, J = 8 Hz, 1H),
6.66 (d, J = 8 Hz, 1H), 6.96 (t, J = 8 Hz, 1H).
tert-Butyl 4-(1-(Triisopropylsilyl)-1H-indol-5-yl)piperazine-1-
carboxylate (12). A mixture of 11 (22.0 g, 63.0 mmol), 4 (11.71 g,
63.0 mmol), PdCl2[P(O-tol)3]2 (2.47 g, 3.1 mmol), and NaO-t-Bu
(9.08 g, 94.4 mmol) in xylenes (175 mL) was heated at 110 °C for 12
h. The reaction mixture was filtered through Celite and concentrated
in vacuo. The crude residue was purified by column chromatography
1
(EtOAc/hexane, 1:20) to afford compound 12 (13.22 g, 46%). H
NMR (CDCl3, 400 MHz): δ 1.19 (s, 18H), 1.55 (s, 9H), 1.74 (heptet,
J = 6.8 Hz, 3H), 3.14 (bs, 4H), 3.67 (bs, 4H), 6.60 (t, J = 6 Hz, 1H),
6.94 (d, J = 8.8 Hz, 1H), 7.19 (s, 1H), 7.26 (t, J = 2.8 Hz, 1H), 7.47 (d,
J = 8.8 Hz, 1H).
Procedure C. 5-Piperazin-1-yl-1H-indole (13). To a stirring
solution of compound 12 (7.70 g, 16.8 mmol) in CH2Cl2 (15 mL) was
added TFA (15 mL) slowly at room temperature, and the reaction
mixture was stirred for 2 h. Unreacted TFA and solvent were removed
under reduced pressure, and the salt was washed with diethyl ether. A
saturated solution of NaHCO3 was added to the salt, followed by
extraction with CH2Cl2 (3 × 50 mL). The combined organic layer was
dried over Na2SO4, filtered, and evaporated in vacuo to provide
6-({2-[4-(1H-Indol-5-ylmethyl)piperazin-1-yl]ethyl}-
propylamino)-5,6,7,8-tetrahydronaphthalen-1-ol (9a). Amine 8
(200 mg, 0.63 mmol) was reacted with 1H-indole-5-carbaldehyde (91
mg, 0.63 mmol) and NaBH(OAc)3 (240 mg, 1.13 mmol) in CH2Cl2
(15 mL) using procedure B. The crude residue was purified by column
chromatography (MeOH/EtOAc, 1:6) to afford compound 9a (220
1
1
mg, 79%). H NMR (CDCl3, 400 MHz): δ 0.86 (t, J = 7.2 Hz, 3H),
compound 13 (2.88 g, 85%). H NMR (CDCl3, 400 MHz): δ 1.85
1.30−1.52 (m, 3H), 1.90−2.10 (m, 1H), 2.46−3.02 (m, 19H), 3.76 (s,
2H), 6.51 (d, J = 8 Hz, 1H), 6.67 (d, J = 8 Hz, 1H), 6.94 (t, J = 7.6 Hz,
1H), 7.06−7.25 (m, 3H), 7.36 (d, J = 8 Hz, 1H), 7.72 (d, J = 8.2 Hz,
1H), 8.26 (bs, 1H). 13C NMR (CDCl3, 100 MHz): δ 12.0, 22.3, 24.0,
25.7, 29.9, 32.4, 47.9, 52.8, 53.5, 53.6, 53.8, 57.4, 58.7, 111.2, 112.2,
119.6, 121.4, 122.1, 123.6, 124.2, 126.3, 128.2, 136.5, 138.5, 154.2,
171.4. The free base was converted to its hydrochloride salt. Mp 165−
169 °C. Anal. (C30H46.5Cl3.5N4O) C, H, N.
(bs, 1H), 2.80−3.28 (m, 8H), 6.85−7.10 (m, 1H), 7.02−7.40 (m, 4H),
8.31 (bs, 1H).
Procedure D. 5-{4-[2-(tert-Butyldimethylsilanyloxy)ethyl]-
piperazin-1-yl}-1H-indole (14). A mixture of compound 13 (2.88
g, 14.3 mmol), (2-bromoethoxy)-tert-butyldimethylsilane (3.42 g, 14.3
mmol), and K2CO3 (5.93 g, 42.9 mmol) in CH3CN (50 mL) was
refluxed for 14 h. After filtration, acetonitrile was evaporated under
reduced pressure and the crude material was purified by silica gel
column chromatography (EtOAc/hexane, 3:1) to give compound 14
6-({2-[4-(1H-Indol-2-ylmethyl)piperazin-1-yl]ethyl}-
propylamino)-5,6,7,8-tetrahydronaphthalen-1-ol (9b). Amine 8
(200 mg, 0.63 mmol) was reacted with 1H-indole-2-carbaldehyde (91
mg, 0.63 mmol) and NaBH(OAc)3 (240 mg, 1.13 mmol) in CH2Cl2
(15 mL) using procedure B. The crude residue was purified by column
chromatography (MeOH/EtOAc, 1:6) to afford compound 9b (225
1
(4.01 g, 78%). H NMR (CDCl3, 400 MHz): δ 0.02 (s, 6H), 0.83 (s,
9H), 2.30−2.80 (m, 6H), 2.82−3.30 (m, 4H), 3.52−3.82 (m, 2H),
6.25−6.48 (m, 1H), 6.75−7.30 (m, 4H), 8.09 (s, 1H).
5-{4-[2-(tert-Butyldimethylsilanyloxy)ethyl]piperazin-1-yl}-
indole-1-carboxylic Acid tert-Butyl Ester (15). Amine 14 (4.0 g,
11.1 mmol) was reacted with (Boc)2O (2.68 g, 12.2 mmol) and
DMAP (1.49 g, 12.2 mmol) in THF (50 mL) at room temperature
using procedure G. The crude material was purified by column
chromatography over silica gel (EtOAc/hexane, 1:1) to give
compound 15 (5.2 g, ∼100%). 1H NMR (CDCl3, 400 MHz): δ
0.08 (s, 6H), 0.95 (s, 9H), 1.65 (s, 9H), 2.61 (t, J = 6.4 Hz, 2H), 2.73
(t, J = 4.8 Hz, 4H), 3.19 (t, J = 4.8 Hz, 4H), 3.81 (t, J = 6.4 Hz, 2H),
6.47 (d, J = 3.6 Hz, 1H), 7.01 (dd, J = 6.4, 2.4 Hz, 1H), 7.06 (dd, J =
6.4, 2.4 Hz, 1H), 7.53 (s, 1H), 8.00 (s, 1H).
1
mg, 81%). H NMR (CDCl3, 400 MHz): δ 0.90 (t, J = 7.2 Hz, 3H),
1.40−1.71 (m, 3H), 1.96−2.10 (m, 1H), 2.36−3.08 (m, 19H), 3.77 (s,
2H), 5.36 (bs, 2H), 6.39 (s, 1H), 6.60 (dd, J = 7.2 Hz, 1H), 6.95 (t, J =
7.6 Hz, 1H), 7.04−7.12 (m, 2H), 7.17 (t, J = 7.6 Hz, 1H), 7.36 (d, J =
8.4 Hz, 1H), 7.56 (d, J = 8.4 Hz, 1H). 13C NMR (CDCl3, 100 MHz):
δ 12.1, 21.6, 24.0, 25.4, 28.4, 30.0, 31.8, 47.5, 52.5, 52.8, 53.2, 53.6,
55.5, 57.2, 57.8, 103.0, 111.3, 119.9, 120.5, 122.0, 123.7, 126.0, 128.3,
133.8, 136.7, 137.6, 154.6, 178.0. The free base was converted to its
hydrochloride salt. Mp 180−185 °C. Anal. (C28H47Cl4N4O3.5) C, H,
N.
Procedure E. 5-[4-(2-Hydroxyethyl)piperazin-1-yl]indole-1-
carboxylic Acid tert-Butyl Ester (16). Into a stirring solution of
compound 15 (2.0 g, 4.3 mmol) in THF (30 mL) was added n-
tetrabutylammonium fluoride (1.14 g, 4.3 mmol, 1.0 M solution in
THF) at 0 °C. The reaction mixture was then stirred at room
temperature for 1 h. THF was evaporated in vacuo, and the residue
was diluted with CH2Cl2 (50 mL) and washed with water. The water
layer was extracted with CH2Cl2 (3 × 75 mL). The combined organic
layer was washed with brine, dried over Na2SO4, and evaporated. The
crude product was purified by silica gel column chromatography
(EtOAc/MeOH, 20:1) to yield compound 16 (1.49 g, 99%). 1H NMR
(CDCl3, 400 MHz): δ 1.65 (s, 9 H), 2.61 (t, J = 5.2 Hz, 2H), 2.70 (t, J
= 4.8 Hz, 4H), 3.19 (t, J = 4.8 Hz, 4H), 3.67 (t, J = 5.2 Hz, 2H), 6.47
(d, J = 3.6 Hz, 1H), 7.01 (dd, J = 6.8, 2 Hz, 1H), 7.06 (d, J = 2 Hz,
1H), 7.53 (s, 1H), 8.00 (s, 1H).
5-[4-(2-Oxoethyl)piperazin-1-yl]indole-1-carboxylic Acid
tert-Butyl Ester (17). Compound 16 (1.49 g, 4.3 mmol) was reacted
with oxalyl chloride (0.75 mL, 8.6 mmol), DMSO (1.23 mL, 17.3
mmol), and Et3N (3.6 mL, 25.8 mmol) in CH2Cl2 (40 mL) using
procedure A. The crude residue was purified by column chromatog-
raphy using ethyl acetate as solvent to afford compound 17 (1.23 g,
83%).
6-({2-[4-(1H-Indol-3-ylmethyl)piperazin-1-yl]ethyl}-
propylamino)-5,6,7,8-tetrahydronaphthalen-1-ol (9c). Amine 8
(200 mg, 0.63 mmol) was reacted with 1H-indole-3-carbaldehyde (91
mg, 0.63 mmol) and NaBH(OAc)3 (240 mg, 1.13 mmol) in CH2Cl2
(15 mL) using procedure B. The crude residue was purified by column
chromatography (MeOH/EtOAc, 1:6) to afford compound 9c (213
1
mg, 77%). H NMR (CDCl3, 400 MHz): δ 0.85 (t, J = 7.2 Hz, 3H),
1.20−1.56 (m, 2H), 1.80−2.04 (m, 1H), 2.20−3.00 (m, 18H), 3.20−
3.45 (m, 2H), 3.74 (s, 2H), 6.48 (d, J = 7.6 Hz, 1H), 6.57 (d, J = 7.6
Hz, 1H), 6.93 (t, J = 7.2 Hz, 1H), 7.02−7.25 (m, 3H), 7.35 (d, J = 7.6
Hz, 1H), 7.71 (d, J = 7.6 Hz, 1H), 8.24 (s, 1H). 13C NMR (CDCl3,
100 MHz): δ 12.0, 22.5, 25.4, 26.0, 26.7, 29.9, 48.4, 52.9, 53.7, 58.3,
58.6, 63.6, 102.6, 111.0, 117.5, 121.7, 124.0, 124.7, 128.1, 128.8, 135.5,
145.2, 165.9. The free base was converted to its hydrochloride salt. Mp
180−185 °C. Anal. (C28H47Cl4N4O3.5) C, H, N.
5-Bromo-1-(triisopropylsilyl)-1H-indole (11). Into a stirring
solution of NaH (4.03 g, 170.0 mmol) in dry THF (150 mL) was
added compound 10 (16.44 g, 83.9 mmol) portionwise at 0 °C. The
reaction mixture was allowed to stir at room temperature for 1 h,
followed by dropwise addition of triisopropylsilyl chloride (20 g, 103.7
mmol). The reaction mixture was stirred for 12 h and then filtered
through Celite. The crude residue was purified by column
chromatography using hexane as solvent to afford compound 11 (22
g, 75%). 1H NMR (CDCl3, 400 MHz): δ 1.23 (s, 18H), 1.74 (heptet, J
= 7.6 Hz, 3H), 6.64 (d, J = 3.2 Hz, 1H), 7.07 (d, J = 6 Hz, 1H), 7.14
(s, 1H), 7.31 (d, J = 3.2 Hz, 1H), 7.45 (d, J = 8.8, 1H).
5-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)indole-1-carboxylic Acid
tert-Butyl Ester [( )-18]. Compound 17 (175 mg, 0.51 mmol)
was reacted with ( )-pramipexole (108 mg, 0.51 mmol) and
NaBH(OAc)3 (194 mg, 0.92 mmol) in CH2Cl2 (15 mL) according
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to procedure B. The crude product was purified by silica gel column
chromatography (EtOAc/MeOH, 20:1) to yield compound ( )-18
(150 mg, 55%). H NMR (CDCl3, 400 MHz): δ 0.91 (t, J = 6.8 Hz,
1H), 1.35−1.60 (m, 2H), 1.67 (s, 9H), 1.89−2.10 (m, 1H), 2.30−3.30
(m, 20H), 4.94 (bs, 2H), 6.67 (t, J = 3.2 Hz, 1H), 7.09 (dd, J = 8.8, 2.8
Hz, 1H), 7.28 (dd, J = 3.2 Hz, 1H), 7.59 (s, 1H), 7.97 (d, J = 6.4 Hz,
1H).
135.1, 136.2, 140.8, 171.0. [α]25 +15.5° (c 1.0, CH3OH). Mp 115−
D
120 °C. Anal. (C31H37.9F10.5N6O7.2S) C, H, N.
1
tert-Butyl 5-(4-(2-((5-Methoxy-1,2,3,4-tetrahydronaphtha-
len-2-yl)(propyl)amino)ethyl)piperazin-1-yl)-1H-indole-1-car-
boxylate (20). Aldehyde 17 (320 mg, 0.93 mmol) was reacted with
amine 2 (204 mg, 0.93 mmol) and NaBH(OAc)3 (355 mg, 1.68
mmol) in CH2Cl2 (20 mL) using procedure B. The crude material was
purified by column chromatography over silica gel (EtOAc/hexane,
(S)-5-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propyl amino]ethyl}piperazin-1-yl)indole-1-carboxylic Acid
tert-Butyl Ester [(−)-18]. Compound 17 (175 mg, 0.51 mmol)
was reacted with S-(−)-pramipexole (108 mg, 0.51 mmol) and
NaBH(OAc)3 (194 mg, 0.92 mmol) in CH2Cl2 (15 mL) using
procedure B. The crude residue was purified by column chromatog-
raphy (EtOAc/MeOH, 20:1) to afford compound S-(−)-18 (161 mg,
59%). 1H NMR (CDCl3, 400 MHz): δ 0.93 (t, J = 6.8 Hz, 1H), 1.35−
1.60 (m, 2H), 1.68 (s, 9H), 1.89−2.10 (m, 1H), 2.30−3.30 (m, 20H),
4.94 (bs, 2H), 6.67 (t, J = 3.2 Hz, 1H), 7.09 (dd, J = 8.8, 2.8 Hz, 1H),
7.28 (dd, J = 3.2 Hz, 1H), 7.60 (s, 1H), 7.97 (d, J = 6.4 Hz, 1H).
(R)-5-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propyl amino]ethyl}piperazin-1-yl)indole-1-carboxylic Acid
tert-Butyl Ester [(+)-18]. Compound 17 (175 mg, 0.51 mmol) was
reacted with R-(+)-pramipexole (108 mg, 0.51 mmol) and NaBH-
(OAc)3 (194 mg, 0.92 mmol) in CH2Cl2 (15 mL) using procedure B.
The crude residue was purified by column chromatography using
(EtOAc/MeOH, 20:1) to afford compound R-(+)-18 (164 mg, 60%).
1H NMR (CDCl3, 400 MHz): δ 0.91 (t, J = 6.8 Hz, 1H), 1.37−1.60
(m, 2H), 1.67 (s, 9H), 1.89−2.10 (m, 1H), 2.30−3.30 (m, 20H), 4.94
(bs, 2H), 6.67 (t, J = 3.2 Hz, 1H), 7.10 (dd, J = 8.8, 2.8 Hz, 1H), 7.28
(dd, J = 3.2 Hz, 1H), 7.59 (s, 1H), 7.98 (d, J = 6.4 Hz, 1H).
N6-{2-[4-(1H-Indol-5-yl)piperazin-1-yl]ethyl}-N6-propyl-
4,5,6,7-tetrahydrobenzothiazole-2,6-diamine [( )-19]. Com-
pound ( )-18 (150 mg, 0.28 mmol) was reacted with TFA (10
mL) in CH2Cl2 (10 mL) using procedure C. Unreacted TFA and
solvent were removed in vacuo and the salt was washed with diethyl
ether and recrystallized from ethanol to afford compound ( )-19 (106
mg, 38%). 1H NMR (CD3OD, 400 MHz): δ 0.99 (t, J = 7.2 Hz, 3H),
1.52−1.74 (m, 2H), 1.76−2.04 (m, 1H), 2.19 (d, J = 9.2 Hz, 1H),
2.52−2.84 (m, 6H), 3.10−3.58 (m, 13H), 6.50 (d, J = 3.2 Hz, 1H),
7.05 (d, J = 8.8 Hz, 1H), 7.29 (d, J = 3.2 Hz, 1H), 7.34 (d, J = 8.8 Hz,
2H). 13C NMR (CD3OD, 100 MHz): δ 12.0, 22.2, 24.0, 25.1, 47.0,
51.1, 54.4, 54.8, 59.2, 101.4, 101.5, 111.8, 115.3, 116.1, 127.8, 129.7,
135.1, 136.0, 140.7, 171.0. Mp 110−115 °C. Anal. (C30H40F9N6O7.5S)
C, H, N.
1
1:1) to give compound 20 (190 mg, 38%). H NMR (CDCl3, 400
MHz): δ 0.91 (t, J = 7.2 Hz, 3H), 1.33−1.75 (m, 13H), 1.95−2.13 (m,
1H), 2.35−3.23 (m, 18H), 3.81 (s, 3H), 6.55−6.77 (m, 3H), 7.03−
7.15 (m, 3H), 7.58 (d, J = 2.4 Hz, 1H), 7.96 (d, J = 6.8 Hz, 1H).
6-({2-[4-(1H-Indol-5-yl)piperazin-1-yl]ethyl}propylamino)-
5,6,7,8-tetrahydronaphthalen-1-ol (21). A mixture of compound
20 (60 mg, 0.11 mmol) and 48% aqueous HBr (10 mL) was refluxed
for 5 h. The reaction mixture was evaporated to dryness, and the
residue was washed with diethyl ether. Finally, the HBr salt was
recrystallized from ethanol to furnish compound 21 (50 mg, 60%). 1H
NMR (CD3OD, 400 MHz): δ 0.95 (t, J = 7.2 Hz, 3H), 1.41−1.57 (m,
3H), 2.00−2.22 (m, 1H), 2.58−3.18 (m, 19H), 6.61 (d, J = 8 Hz, 1H),
6.75 (d, J = 8 Hz, 1H), 7.08 (t, J = 7.6 Hz, 1H), 7.19−7.38 (m, 3H),
7.51 (d, J = 8 Hz, 1H), 7.90 (d, J = 8.2 Hz, 1H), 8.50 (bs, 1H). Mp
250−260 °C. Anal. (C27H41.4Br4N4O1.7) C, H, N.
Procedure F. 4-(1H-Indole-2-carbonyl)piperazine-1-carbox-
ylic Acid tert-Butyl Ester (23). To a stirring solution of EDCI·HCl
(15.45 g, 80.6 mmol) in CH2Cl2 (150 mL) was added acid derivative
22 (10.39 g, 64.5 mmol) at room temperature. The reaction mixture
was stirred for 0.5 h, followed by addition of amine 4 (10.0 g, 53.7
mmol), HOBT (10.89 g, 80.6 mmol), and Et3N (22.46 g, 161.2
mmol). The reaction mixture was stirred for 3 h, followed by addition
of a saturated solution of NaHCO3. The aqueous layer was extracted
with CH2Cl2 (3 × 150 mL). The combined organic layer was dried
over Na2SO4, evaporated under reduced pressure and the crude
product was purified by flash column chromatography (CH2Cl2/
MeOH, 50:1) to afford compound 23 (15.6 g, 88%). 1H NMR
(CDCl3, 400 MHz): δ 1.49 (s, 9H), 3.56 (t, J = 5.6 Hz, 4H), 3.74−
4.04 (m, 4H), 6.78 (s, 1H), 7.15 (t, J = 7.6 Hz, 1H), 7.30 (t, J = 7.6
Hz, 1H), 7.43 (d, J = 8.4 Hz, 1H), 7.65 (d, J = 8.4 Hz, 1H), 9.14 (bs,
1H).
(1H-Indol-2-yl)piperazin-1-ylmethanone (24). Compound 23
(12 g, 36.4 mmol) was reacted with TFA (20 mL) in CH2Cl21(20 mL)
using procedure C to provide compound 24 (7.85 g, 94%). H NMR
(CDCl3, 400 MHz): δ 2.52−3.04 (m, 4H), 3.60−4.06 (m, 4H), 6.77
(s, 1H), 7.14 (t, J = 7.6 Hz, 1H), 7.27 (d, J = 6.8 Hz, 1H), 7.43 (d, J =
6.8 Hz, 1H), 7.65 (d, J = 6.8 Hz, 1H), 9.50 (bs, 1H).
(S)-N6-{2-[4-(1H-Indol-5-yl)piperazin-1-yl]ethyl}-N6-propyl-
4,5,6,7-tetrahydrobenzothiazole-2,6-diamine [(−)-19]. Com-
pound (−)-18 (150 mg, 0.28 mmol) was reacted with TFA (10
mL) in CH2Cl2 (10 mL) using procedure C. Unreacted TFA and
solvent were removed in vacuo and the salt was washed with diethyl
ether and recrystallized from ethanol to afford compound S-(−)-19
(120 mg, 43%). 1H NMR (CD3OD, 400 MHz): δ 0.98 (t, J = 7.2 Hz,
3H), 1.54−1.74 (m, 2H), 1.76−2.04 (m, 1H), 2.19 (d, J = 9.2 Hz,
1H), 2.52−2.84 (m, 6H), 3.10−3.58 (m, 13H), 6.51 (d, J = 3.2 Hz,
1H), 7.05 (d, J = 8.8 Hz, 1H), 7.29 (d, J = 3.2 Hz, 1H), 7.34 (d, J = 8.8
Hz, 2H). 13C NMR (CD3OD, 100 MHz): δ 12.0, 22.3, 24.0, 25.1, 47.0,
51.1, 54.5, 54.8, 59.2, 101.4, 101.6, 111.8, 115.3, 116.1, 127.8, 129.7,
{4-[2-(tert-Butyldimethylsilanyloxy)ethyl]piperazin-1-yl}-
(1H-indol-2-yl)methanone (25). Compound 24 (2.50 g, 10.9
mmol) was reacted with (2-bromoethoxy)-tert-butyldimethylsilane
(3.13 g, 13.1 mmol) and K2CO3 (4.52 g, 32.7 mmol) in CH3CN (50
mL) using procedure D. The crude material was purified by silica gel
column chromatography using ethyl acetate as solvent to give
1
compound 25 (3.55 g, 84%). H NMR (CDCl3, 400 MHz): δ 0.09
(s, 6H), 0.92 (s, 9H), 2.02−2.80 (m, 6H), 3.01−4.20 (m, 6H), 6.77 (s,
1H), 7.11 (t, J = 7.6 Hz, 1H), 7.25 (t, J = 7.6 Hz, 1H), 7.44 (d, J = 8.0
Hz, 1H), 7.63 (d, J = 8 Hz, 1H), 10.4 (bs, 1H).
{4-[3-(tert-Butyldimethylsilanyloxy)propyl]piperazin-1-yl}-
(1H-indol-2-yl)methanone (26). Compound 24 (2.50 g, 10.9
mmol) was reacted with (3-bromopropoxy)-tert-butyldimethylsilane
(3.31 g, 13.1 mmol) and K2CO3 (4.52 g, 32.7 mmol) in CH3CN (50
mL) using procedure D. The crude material was purified by silica gel
column chromatography (EtOAc/hexane, 1:1) to give compound 26
135.1, 136.0, 140.8, 171.0. [α]25 −11.0° (c 1.0, CH3OH). Mp 115−
D
120 °C. Anal. (C31H37.5F10.5N6O7S) C, H, N.
(R)-N6-{2-[4-(1H-Indol-5-yl)piperazin-1-yl]ethyl}-N6-propyl-
4,5,6,7-tetrahydrobenzothiazole-2,6-diamine [(+)-19]. Com-
pound (+)-18 (150 mg, 0.28 mmol) was reacted with TFA (10 mL)
in CH2Cl2 (10 mL) using procedure C. Unreacted TFA and solvent
were removed in vacuo and the salt was washed with diethyl ether and
recrystallized from ethanol to afford compound R-(+)-19 (140 mg,
1
(3.33 g, 76%). H NMR (CDCl3, 400 MHz): δ 0.06 (s, 6H), 0.90 (s,
9H), 1.52−1.86 (m, 2H), 2.45−2.70 (m, 6H), 3.68 (t, J = 12 Hz, 2H),
3.72−4.20 (m, 4H), 6.78 (s, 1H), 7.14 (t, J = 7.6 Hz, 1H), 7.20−7.32
(m, 2H), 7.43 (d, J = 7.6 Hz, 1H), 7.64 (d, J = 7.6 Hz, 1H), 9.35 (s,
1H).
{4-[4-(tert-Butyldimethylsilanyloxy)butyl]piperazin-1-yl}-
(1H-indol-2-yl)methanone (27). Compound 24 (2.50 g, 10.9
mmol) was reacted with (4-bromobutoxy)-tert-butyldimethylsilane
(3.50 g, 13.1 mmol) and K2CO3 (4.52 g, 32.7 mmol) in CH3CN (50
1
50%). H NMR (CD3OD, 400 MHz): δ 0.98 (t, J = 7.2 Hz, 3H),
1.54−1.78 (m, 2H), 1.76−2.04 (m, 1H), 2.20 (d, J = 9.2 Hz, 1H),
2.52−2.84 (m, 6H), 3.10−3.58 (m, 13H), 6.51 (d, J = 3.2 Hz, 1H),
7.05 (d, J = 8.8 Hz, 1H), 7.29 (d, J = 3.2 Hz, 1H), 7.34 (d, J = 8.8 Hz,
2H). 13C NMR (CD3OD, 100 MHz): δ 12.2, 22.3, 24.0, 25.1, 47.0,
51.2, 54.5, 54.8, 59.2, 101.4, 101.6, 111.8, 115.3, 116.1, 127.8, 129.7,
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Journal of Medicinal Chemistry
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1
mL) using procedure D. The crude material was purified by silica gel
column chromatography (EtOAc/hexane, 2:3) to give compound 27
(4.31 g, 95%). H NMR (CDCl3, 400 MHz): δ 0.05 (s, 6H), 0.90 (s,
9H), 1.47−1.75 (m, 4H), 2.40 (t, J = 6.4 Hz, 2H), 2.53 (t, J = 4.4 Hz,
4H), 3.64 (t, J = 5.6 Hz, 2H), 3.80−4.05 (m, 4H), 6.77 (s, 1H), 7.12
(t, J = 6.8 Hz, 1H), 7.26 (t, J = 7.2 Hz, 1H), 7.43 (d, J = 8.4 Hz, 1H),
7.63 (d, J = 8 Hz, 1H), 10.00 (s, 1H).
Procedure G. 2-{4-[3-(tert-Butyldimethylsilanyloxy)ethyl]-
piperazine-1-carbonyl}indole-1-carboxylic Acid tert-Butyl
Ester (28). To a stirring solution of amine 25 (3.55 g, 9.2 mmol)
in THF (50 mL) were added (Boc)2O (2.21 g, 10.1 mmol) and
DMAP (1.23 g, 10.1 mmol) at room temperature. The reaction
mixture was stirred at the same temperature for 12 h. The crude
mixture was evaporated under reduced pressure, followed by
extraction with CH2Cl2 (3 × 100 mL) in water. The combined
organic layer was dried over Na2SO4, filtered, and concentrated in
vacuo. The crude material was purified by column chromatography
over silica gel using ethyl acetate as solvent to give compound 28 (4.46
g, ∼100%). 1H NMR (CDCl3, 400 MHz): δ 0.05 (s, 6H), 0.09 (s, 9H),
1.62 (s, 9H), 2.48 (t, J = 4 Hz, 2H), 2.56 (t, J = 6 Hz, 2H), 2.63 (t, J =
4 Hz, 2H), 3.38 (t, J = 4 Hz, 2H), 3.76 (t, J = 6 Hz, 4H), 6.60 (s, 1H),
7.20−7.28 (m, 1H), 7.34 (t, J = 7.2 Hz, 1H), 7.53 (d, J = 7.6 Hz, 1H),
8.16 (d, J = 7.6 Hz, 1H).
(EtOAc/MeOH, 9:1) to yield compound 33 (3.72 g, 97%). H NMR
(CDCl3, 400 MHz): δ 0.95−1.70 (m, 13H), 2.30 (t, J = 6 Hz, 4H),
2.37−2.65 (m, 2H), 3.15−3.36 (m, 2H), 3.37−3.55 (m, 2H), 3.55−
3.82 (m, 2H), 6.48 (s, 1H), 7.12 (t, J = 7.6 Hz, 1H), 7.23 (t, J = 8 Hz,
1H), 7.42 (d, J = 8 Hz, 1H), 8.05 (d, J = 8 Hz, 1H).
1
2-[4-(2-Oxoethyl)piperazine-1-carbonyl]indole-1-carboxylic
Acid tert-Butyl Ester (34). Compound 31 (1.0 g, 2.7 mmol) was
reacted with oxalyl chloride (0.47 mL, 5.4 mmol), DMSO (0.76 mL,
10.7 mmol), and Et3N (2.2 mL, 16.1 mmol) in CH2Cl2 (40 mL) using
procedure A. The crude residue was purified by column chromatog-
raphy (EtOAc/MeOH, 20:1) to afford compound 34 (0.81 g, 81%).
2-[4-(3-Oxopropyl)piperazine-1-carbonyl]indole-1-carbox-
ylic Acid tert-Butyl Ester (35). Compound 32 (0.8 g, 2.1 mmol) was
reacted with oxalyl chloride (0.36 mL, 4.1 mmol), DMSO (0.59 mL,
8.3 mmol), and Et3N (1.73 mL, 12.4 mmol) in CH2Cl2 (40 mL) using
procedure A. The crude residue was purified by column chromatog-
raphy (EtOAc/MeOH, 20:1) to afford compound 35 (0.62 g, 78%).
2-[4-(4-Oxobutyl)piperazine-1-carbonyl]indole-1-carboxylic
Acid tert-Butyl Ester (36). Compound 33 (1.0 g, 2.5 mmol) was
reacted with oxalyl chloride (0.43 mL, 5.0 mmol), DMSO (0.71 mL,
10.0 mmol), and Et3N (2.08 mL, 15.0 mmol) in CH2Cl2 (40 mL)
using procedure A. The crude residue was purified by column
chromatography (EtOAc/MeOH, 20:1) to afford compound 36 (0.75
g, 75%).
2-{4-[3-(tert-Butyldimethylsilanyloxy)propyl]piperazine-1-
carbonyl}indole-1-carboxylic Acid tert-Butyl Ester (29). Amine
26 (3.33 g, 8.3 mmol) was reacted with (Boc)2O (2.00 g, 9.1 mmol)
and DMAP (1.11 g, 9.1 mmol) in THF (50 mL) using procedure G.
The crude material was purified by column chromatography over silica
2-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazine-1-carbonyl)indole-1-carboxylic
Acid tert-Butyl Ester [( )-37]. Aldehyde 34 (480 mg, 1.3 mmol)
was reacted with ( )-pramipexole (273 mg, 1.3 mmol) and
NaBH(OAc)3 (451 mg, 2.3 mmol) in CH2Cl2 (25 mL) using
procedure B. The crude material was purified by column
chromatography over silica gel (EtOAc/MeOH, 9:1) to give
1
gel (EtOAc/hexane, 1:1) to give compound 29 (4.04 g, 97%). H
NMR (CDCl3, 400 MHz): δ 0.002 (s, 6H), 0.84 (s, 9H), 1.57 (s, 9H),
1.50−1.80 (m, 2H), 2.20−2.70 (m, 6H), 3.30−3.45 (m, 2H), 3.62 (t, J
= 12 Hz, 2H), 3.66−3.80 (m, 2H), 6.55 (s, 1H), 7.18 (t, J = 7.6 Hz,
1H), 7.29 (t, J = 7.6 Hz, 1H), 7.48 (d, J = 7.6 Hz, 1H), 8.12 (d, J = 8.4
Hz, 1H).
1
compound ( )-37 (0.52 g, 71%). H NMR (CDCl3, 400 MHz): δ
0.85 (t, J = 3.6 Hz, 3H), 1.30−1.65 (m, 2H), 1.60 (s, 9H), 1.95 (d, J =
10.8 Hz, 1H), 2.20−3.10 (m, 16H), 3.15−3.82 (m, 4H), 4.94 (bs, 2H),
6.58 (s, 1H), 7.24 (d, J = 8.4 Hz, 1H), 7.33 (t, J = 6.8 Hz, 1H), 7.53 (d,
J = 6 Hz, 1H), 8.13 (d, J = 6 Hz, 1H).
(R)-2-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazine-1-carbonyl)indole-1-carboxylic
Acid tert-Butyl Ester [(+)-37]. Aldehyde 34 (200 mg, 0.54 mmol)
was reacted with R-(+)-pramipexole (114 mg, 0.54 mmol) and
NaBH(OAc)3 (205 mg, 0.97 mmol) in CH2Cl2 (25 mL) using
procedure B. The crude material was purified by column
chromatography over silica gel (EtOAc/MeOH, 9:1) to yield
2-{4-[4-(tert-Butyldimethylsilanyloxy)butyl]piperazine-1-
carbonyl}indole-1-carboxylic Acid tert-Butyl Ester (30). Amine
27 (4.31 g, 10.4 mmol) was reacted with (Boc)2O (2.50 g, 11.4 mmol)
and DMAP (1.39 g, 11.4 mmol) in THF (50 mL) using procedure G.
The crude material was purified by column chromatography over silica
1
gel (EtOAc/hexane, 1:3) to give compound 30 (4.92 g, 92%). H
NMR (CDCl3, 400 MHz): δ 0.001 (s, 6H), 0.84 (s, 9H), 1.25−1.70
(m, 13H), 2.15−2.40 (m, 4H), 2.42−2.55 (m, 2H), 3.25−3.45 (m,
2H), 3.47−3.65 (m, 2H), 3.67−3.85 (m, 2H), 6.54 (s, 1H), 7.18 (t, J =
7.2 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.48 (d, J = 7.6 Hz, 1H), 8.12 (d,
J = 8.4 Hz, 1H).
1
compound R-(+)-37 (186 mg, 61%). H NMR (CDCl3, 400 MHz):
δ 0.86 (t, J = 3.6 Hz, 3H), 1.30−1.65 (m, 2H), 1.61 (s, 9H), 1.95 (d, J
= 10.8 Hz, 1H), 2.20−3.10 (m, 16H), 3.15−3.82 (m, 4H), 4.94 (bs,
2H), 6.58 (s, 1H), 7.25 (d, J = 8.4 Hz, 1H), 7.33 (t, J = 6.8 Hz, 1H),
7.53 (d, J = 6 Hz, 1H), 8.13 (d, J = 6 Hz, 1H).
(S)-2-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazine-1-carbonyl)indole-1-carboxylic
Acid tert-Butyl Ester [(−)-37]. Aldehyde 34 (300 mg, 0.81 mmol)
was reacted with S-(−)-pramipexole (170 mg, 0.81 mmol) and
NaBH(OAc)3 (308 mg, 1.45 mmol) in CH2Cl2 (25 mL) using
procedure B. The crude material was purified by column
chromatography over silica gel (EtOAc/MeOH, 9:1) to yield
2-[4-(2-Hydroxyethyl)piperazine-1-carbonyl]indole-1-car-
boxylic Acid tert-Butyl Ester (31). Compound 28 (4.46 g, 9.2
mmol) was reacted with n-tetrabutylammonium fluoride (2.39 g, 9.2
mmol, 1.0 M solution in THF) in THF (30 mL) using procedure E.
The crude product was purified by silica gel column chromatography
1
(EtOAc/MeOH, 9:1) to yield compound 31 (3.08 g, 90%). H NMR
(CDCl3, 400 MHz): δ 1.62 (s, 9H), 2.46 (t, J = 4.8 Hz, 2H), 2.54−
2.68 (m, 4H), 3.41 (t, J = 5.2 Hz, 2H), 3.64 (t, J = 5.2 Hz, 2H), 3.72−
3.78 (m, 2H), 6.60 (s, 1H), 7.21−7.28 (m, 1H), 7.35 (t, J = 8.4 Hz,
1H), 7.54 (d, J = 7.6 Hz, 1H), 8.14 (d, J = 7.6 Hz, 1H).
1
compound S-(−)-37 (284 mg, 62%). H NMR (CDCl3, 400 MHz):
2-[4-(3-Hydroxypropyl)piperazine-1-carbonyl]indole-1-car-
boxylic Acid tert-Butyl Ester (32). Compound 29 (4.04 g, 8.1
mmol) was reacted with n-tetrabutylammonium fluoride (2.11 g, 8.1
mmol, 1.0 M solution in THF) in THF (30 mL) using procedure E.
The crude product was purified by silica gel column chromatography
δ 0.83 (t, J = 3.6 Hz, 3H), 1.30−1.65 (m, 2H), 1.61 (s, 9H), 1.95 (d, J
= 10.8 Hz, 1H), 2.20−3.10 (m, 16H), 3.15−3.82 (m, 4H), 4.94 (bs,
2H), 6.58 (s, 1H), 7.25 (d, J = 8.4 Hz, 1H), 7.33 (t, J = 6.8 Hz, 1H),
7.53 (d, J = 6 Hz, 1H), 8.14 (d, J = 6 Hz, 1H).
1
(EtOAc/MeOH, 9:1) to yield compound 32 (2.84 g, 91%). H NMR
2-(4-{3-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]propyl}piperazine-1-carbonyl)indole-1-carbox-
ylic Acid tert-Butyl Ester (38). Aldehyde 35 (220 mg, 0.57 mmol)
was reacted with ( )-pramipexole (121 mg, 0.57 mmol) and
NaBH(OAc)3 (218 mg, 1.03 mmol) in CH2Cl2 (25 mL) using
procedure B. The crude material was purified by column
chromatography over silica gel (EtOAc/MeOH, 9:1) to give
compound 38 (215 mg, 65%). H NMR (CDCl3, 400 MHz): δ 0.86
(t, J = 7.2 Hz, 3H), 1.15−1.85 (m, 13H), 1.96 (d, J = 7.2 Hz, 1H),
2.10−2.85 (m, 15H), 2.90−3.15 (m, 1H), 3.20−3.50 (m, 2H), 3.55−
(CDCl3, 400 MHz): δ 1.30−1.75 (m, 11H), 2.33 (m, 2H), 2.47 (t, J =
4.4 Hz, 4H), 3.29 (m, 2H), 3.63 (t, J = 4.8 Hz, 4H), 6.50 (s, 1H), 7.13
(t, J = 7.6 Hz, 1H), 7.24 (t, J = 7.2 Hz, 1H), 7.43 (d, J = 7.6 Hz, 1H),
8.05 (d, J = 8.4 Hz, 1H).
2-[4-(4-Hydroxybutyl)piperazine-1-carbonyl]indole-1-car-
boxylic Acid tert-Butyl Ester (33). Compound 30 (4.92 g, 9.5
mmol) was reacted with n-tetrabutylammonium fluoride (2.50 g, 9.5
mmol, 1.0 M solution in THF) in THF (30 mL) using procedure E.
The crude product was purified by silica gel column chromatography
1
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3.95 (m, 2H), 6.58 (s, 1H), 7.23 (t, J = 7.6 Hz, 1H), 7.33 (t, J = 7.6
Hz, 1H), 7.52 (d, J = 7.6 Hz, 1H), 8.13 (d, J = 8 Hz, 1H).
121.6, 124.2, 127.4, 128.2, 133.7, 136.9, 163.8, 170.5. Mp 115−120 °C.
Anal. (C32H42F9N6O8.5S) C, H, N.
2-(4-{4-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]butyl}piperazine-1-carbonyl)indole-1-carboxylic
Acid tert-Butyl Ester (39). Aldehyde 36 (233 mg, 0.58 mmol) was
reacted with ( )-pramipexole (123 mg, 0.58 mmol) and NaBH-
(OAc)3 (222 mg, 1.05 mmol) in CH2Cl2 (25 mL) using procedure B.
The crude material was purified by column chromatography over silica
(4-{4-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]butyl}piperazin-1-yl)-(1H-indol-2-yl)methanone
(42). Compound 39 (175 mg, 0.29 mmol) was reacted with TFA (20
mL) in CH2Cl2 (20 mL) using procedure C. Unreacted TFA and
solvent were removed under reduced pressure, followed by washing of
the salt with diethyl ether and recrystallization from ethanol to afford
compound 42 (175 mg, 71%). 1H NMR (CD3OD, 400 MHz): δ 1.03
(t, J = 7.2 Hz, 3H), 1.50−2.02 (m, 6H), 2.03−2.20 (m, 1H), 2.35 (d, J
= 10.8 Hz, 1H), 2.54−3.70 (m, 18H), 3.74−4.01 (m, 1H), 6.90 (s,
1H), 7.08 (t, J = 7.6 Hz, 1H), 7.23 (t, J = 7.6 Hz, 1H), 7.44 (d, J = 8.4
Hz, 1H), 7.62 (d, J = 8.4 Hz, 1H). 13C NMR (CD3OD, 100 MHz): δ
10.0, 18.4, 21.0, 21.7, 22.0, 22.2, 22.7, 51.6, 56.0, 59.1, 105.7, 105.7,
111.8, 120.3, 121.6, 124.2, 127.4, 128.2, 133.2, 136.9, 163.8, 170.6. Mp
100−105 °C. Anal. (C35H43.6F12N6O9.8S) C, H, N.
1
gel (EtOAc/MeOH, 20:1) to yield compound 39 (190 mg, 55%). H
NMR (CDCl3, 400 MHz): δ 0.87 (t, J = 7.2 Hz, 3H), 1.10−1.78 (m,
15H), 1.96 (d, J = 11.2 Hz, 1H), 2.12−2.85 (m, 15H), 2.90−3.15 (m,
1H), 3.25−3.50 (m, 2H), 3.65−3.92 (m, 2H), 4.78 (s, 2H), 6.60 (s,
1H), 7.25 (t, J = 7.6 Hz, 1H), 7.35 (t, J = 7.6 Hz, 1H), 7.54 (d, J = 7.6
Hz, 1H), 8.15 (d, J = 8.4 Hz, 1H).
(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-2-yl)methanone
[( )-40]. Compound ( )-37 (200 mg, 0.35 mmol) was reacted with
TFA (20 mL) in CH2Cl2 (20 mL) using procedure C. Unreacted TFA
and solvent were removed under reduced pressure. The TFA salt was
converted to the free base by extraction using CH2Cl2 (3 × 100 mL)
and a saturated solution of NaHCO3. The crude material was purified
by column chromatography over silica gel to afford compound ( )-40
(228 mg, 80%). 1H NMR (CD3OD, 400 MHz): δ 1.04 (t, J = 7.2 Hz,
3H), 1.70−1.88 (m, 2H), 2.01−2.18 (m, 1H), 2.32 (d, J = 10.8 Hz,
1H), 2.60−3.60 (m, 13H), 3.72−4.20 (m, 6H), 6.85 (s, 1H), 7.07 (t, J
= 8 Hz, 1H), 7.23 (t, J = 8 Hz, 1H), 7.44 (d, J = 8 Hz, 1H), 7.62 (d, J =
8 Hz, 1H). 13C NMR (CD3OD, 100 MHz): δ 14.1, 23.0, 26.0, 26.7,
27.0, 56.6, 57.0, 57.8, 63.1, 109.2, 115.7, 116.3, 124.1, 125.4, 127.9,
131.3, 132.7, 137.4, 137.5, 167.8, 174.4. The free base was converted
to its hydrochloride salt. Mp 270−275 °C. Anal. (C25H40Cl4N6O2S) C,
H, N.
4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazine-1-carboxylic Acid tert-Butyl
Ester [( )-43]. Aldehyde 6 (2.4 g, 10.5 mmol) was reacted with
( )-pramipexole (2.22 g, 10.5 mmol) and NaBH(OAc)3 (4.01 g, 18.9
mmol) in CH2Cl2 (40 mL) using procedure B. The crude material was
purified by column chromatography over silica gel (EtOAc/MeOH,
1
20:1) to yield compound ( )-43 (3.34 g, 75%). H NMR (CDCl3,
400 MHz): δ 0.81 (t, J = 7.2 Hz, 3H), 1.10−1.75 (m, 10H), 1.91 (d, J
= 9.6 Hz, 1H), 2.10−2.75 (m, 15H), 2.97 (m, 1H), 3.36 (m, 4H), 5.29
(bs, 2H).
(R)-4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazine-1-carboxylic Acid tert-Butyl
Ester [(+)-43]. Compound 6 (1.2 g, 5.25 mmol) was reacted with
(R)-(+)-pramipexole (1.11 g, 5.25 mmol) and NaBH(OAc)3 (2.0 g,
9.46 mmol) in CH2Cl2 (25 mL) using procedure B. The crude
material was purified by column chromatography over silica gel
(EtOAc/MeOH, 20:1) to give compound R-(+)-43 (1.63 g, 73%). 1H
NMR (CDCl3, 400 MHz): δ 0.83 (t, J = 7.2 Hz, 3H), 1.10−1.75 (m,
10H), 1.91 (d, J = 9.6 Hz, 1H), 2.10−2.75 (m, 15H), 2.98 (m, 1H),
3.36 (m, 4H), 5.29 (bs, 2H).
(S)-4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazine-1-carboxylic Acid tert-Butyl
Ester [(−)-43]. Compound 6 (1.2 g, 5.25 mmol) was reacted with
(S)-(−)-pramipexole (1.11 g, 5.25 mmol) and NaBH(OAc)3 (2.0 g,
9.46 mmol) in CH2Cl2 (25 mL) using procedure B. The crude
material was purified by column chromatography over silica gel
(EtOAc/MeOH, 20:1) to give compound S-(−)-43 (1.61 g, 71%). 1H
NMR (CDCl3, 400 MHz): δ 0.80 (t, J = 7.2 Hz, 3H), 1.10−1.75 (m,
10H), 1.91 (d, J = 9.6 Hz, 1H), 2.12−2.75 (m, 15H), 2.97 (m, 1H),
3.36 (m, 4H), 5.29 (bs, 2H).
(R)-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-2-yl)methanone
[(+)-40]. Compound (+)-37 (150 mg, 0.26 mmol) was reacted with
TFA (15 mL) in CH2Cl2 (15 mL) using procedure C. Unreacted TFA
and solvent were removed in vacuo and the salt was washed with
diethyl ether and recrystallized from ethanol to afford compound R-
1
(+)-40 (160 mg, 75%). H NMR (CD3OD, 400 MHz): δ 1.05 (t, J =
7.2 Hz, 3H), 1.70−1.88 (m, 2H), 2.01−2.18 (m, 1H), 2.34 (d, J = 10.8
Hz, 1H), 2.60−3.60 (m, 13H), 3.72−4.20 (m, 6H), 6.85 (s, 1H), 7.07
(t, J = 8 Hz, 1H), 7.23 (t, J = 8 Hz, 1H), 7.44 (d, J = 8 Hz, 1H), 7.63
(d, J = 8 Hz, 1H). 13C NMR (CD3OD, 100 MHz): δ 14.1, 23.0, 26.2,
26.7, 27.0, 56.6, 57.0, 57.8, 63.1, 109.3, 115.7, 116.3, 124.1, 125.4,
127.9, 131.3, 132.7, 137.4, 137.6, 167.8, 174.4. [α]25 +25.2° (c 1.0,
D
CH3OH). Mp 100−110 °C. Anal. (C31H38.2F9N6O7.6S) C, H, N.
(S)-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-2-yl)methanone
[(−)-40]. Compound (−)-37 (200 mg, 0.35 mmol) was reacted with
TFA (20 mL) in CH2Cl2 (20 mL) using procedure C. Unreacted TFA
and solvent were removed in vacuo and the salt was washed with
diethyl ether and recrystallized from ethanol to afford compound S-
(−)-40 (237 mg, 83%). 1H NMR (CD3OD, 400 MHz): δ 1.02 (t, J =
7.2 Hz, 3H), 1.73−1.88 (m, 2H), 2.01−2.18 (m, 1H), 2.32 (d, J = 10.8
Hz, 1H), 2.60−3.60 (m, 13H), 3.72−4.20 (m, 6H), 6.85 (s, 1H), 7.08
(t, J = 8 Hz, 1H), 7.23 (t, J = 8 Hz, 1H), 7.44 (d, J = 8 Hz, 1H), 7.62
(d, J = 8 Hz, 1H). 13C NMR (CD3OD, 100 MHz): δ 14.3, 23.0, 26.2,
26.7, 27.0, 56.6, 57.0, 57.8, 63.1, 109.3, 115.7, 116.3, 124.1, 125.4,
N6-(2-Piperazin-1-ylethyl)-N6-propyl-4,5,6,7-tetrahydroben-
zothiazole-2,6-diamine [( )-44]. Compound ( )-43 (3.34 g, 7.88
mmol) was reacted with TFA (20 mL) in CH2Cl2 (20 mL) using
procedure C to give compound ( )-44 (2.30 g, 90%). 1H NMR
(CDCl3, 400 MHz): δ 0.79 (t, J = 7.2 Hz, 3H), 1.25−1.48 (m, 2H),
1.50−1.72 (m, 1H), 1.88 (d, J = 11.2 Hz, 1H), 2.08−3.07 (m, 19H),
5.40 (bs, 2H).
(R)-N6-(2-Piperazin-1-ylethyl)-N6-propyl-4,5,6,7-tetrahydro-
benzothiazole-2,6-diamine [(+)-44]. Compound (+)-43 (1.63 g,
3.84 mmol) was reacted with TFA (15 mL) in CH2Cl2 (15 mL) using
1
procedure C to yield compound R-(+)-44 (1.16 g, 93%). H NMR
127.9, 131.3, 132.7, 137.4, 137.5, 167.8, 174.4. [α]25 −31.2° (c 1.0,
(CDCl3, 400 MHz): δ 0.80 (t, J = 7.2 Hz, 3H), 1.25−1.48 (m, 2H),
1.52−1.72 (m, 1H), 1.88 (d, J = 11.2 Hz, 1H), 2.08−3.07 (m, 19H),
5.40 (bs, 2H).
D
CH3OH). Mp 110−115 °C. Anal. (C31H40F9N6O8.5S) C, H, N.
(4-{3-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]propyl}piperazin-1-yl)-(1H-indol-2-yl)methanone
(41). Compound 38 (200 mg, 0.34 mmol) was reacted with TFA (20
mL) in CH2Cl2 (20 mL) using procedure C. Unreacted TFA and
solvent were removed under reduced pressure, followed by washing of
the salt with diethyl ether and recrystallization from ethanol to afford
compound 41 (266 mg, 94%). 1H NMR (CD3OD, 400 MHz): δ 1.04
(t, J = 7.6 Hz, 3H), 1.65−1.90 (m, 2H), 1.95−2.18 (m, 1H), 2.20−
2.48 (m, 3H), 2.56−3.70 (m, 12H), 3.78−4.40 (m, 5H), 6.90 (s, 1H),
7.08 (t, J = 8 Hz, 1H), 7.23 (t, J = 8 Hz, 1H), 7.44 (d, J = 8.4 Hz, 1H),
7.62 (d, J = 8.4 Hz, 1H). 13C NMR (CD3OD, 100 MHz): δ 10.0, 18.4,
20.1, 21.8, 22.3, 22.7, 51.8, 53.1, 53.6, 59.2, 104.4, 105.7, 111.8, 120.2,
(S)-N6-(2-Piperazin-1-ylethyl)-N6-propyl-4,5,6,7-tetrahydro-
benzothiazole-2,6-diamine [(−)-44]. Compound (−)-43 (1.61 g,
3.80 mmol) was reacted with TFA (15 mL) in CH2Cl2 (15 mL) using
1
procedure C to afford compound S-(−)-44 (1.16 g, 94%). H NMR
(CDCl3, 400 MHz): δ 0.79 (t, J = 7.2 Hz, 3H), 1.25−1.48 (m, 2H),
1.50−1.72 (m, 1H), 1.89 (d, J = 11.2 Hz, 1H), 2.08−3.07 (m, 19H),
5.41 (bs, 2H).
(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-3-yl)methanone
[( )-45]. Indole-3-carboxylic acid (54 mg, 0.33 mmol) was reacted
with compound ( )-44 (90 mg, 0.28 mmol) in the presence of
5837
dx.doi.org/10.1021/jm300268s | J. Med. Chem. 2012, 55, 5826−5840

Journal of Medicinal Chemistry
Article
EDCI.HCl (80 mg, 0.42 mmol), TEA (0.12 mL, 0.83 mmol), and
HOBT (56 mg, 0.41 mmol) in CH2Cl2 (10 mL) using procedure F.
The crude product was purified by flash column chromatography
The crude material was purified by column chromatography over silica
gel (EtOAc/MeOH, 4:1) to furnish compound R-(+)-46 (94 mg,
65%). 1H NMR (CDCl3, 400 MHz): δ 0.89 (t, J = 7.2 Hz, 1H), 1.40−
1.54 (m, 2H), 1.60−1.81 (m, 1H), 1.97 (d, J = 11.2 Hz, 1H), 2.20−
2.72 (m, 14H), 2.90−3.15 (m, 1H), 3.30−4.03 (m, 4H), 4.89 (bs,
2H), 6.57 (s, 1H), 7.16−7.29 (m, 1H), 7.35 (d, J = 8.4 Hz, 1H), 7.71
(s, 1H), 8.84 (s, 1H). 13C NMR (CDCl3, 100 MHz): δ 12.0, 22.5,
25.3, 26.0, 26.7, 48.5, 53.7, 58.3, 58.7, 103.1, 111.4, 117.3, 120.4, 121.4,
1
(EtOAc/MeOH, 4:1) to afford compound ( )-45 (83 mg, 64%). H
NMR (CDCl3, 400 MHz): δ 0.87 (t, J = 7.6 Hz, 3H), 1.30−1.52 (m,
2H), 1.55−1.80 (m, 1H), 1.95 (d, J = 11.6 Hz, 1H), 2.20−2.80 (m,
13H), 2.85−3.10 (m, 1H), 3.50−3.82 (m, 4H), 4.86 (bs, 2H), 7.0−
7.38 (m, 4H), 7.60−7.76 (m, 1H), 9.77 (s, 1H). 13C NMR (CDCl3,
100 MHz): δ 12.0, 14.4, 21.3, 22.5, 25.4, 26.1, 26.8, 48.6, 53.7, 54.2,
58.3, 58.8, 60.6, 111.5, 112.1, 117.6, 120.4, 121.2, 122.8, 125.6, 127.5,
135.9, 145.3, 165.8, 167.2. The free base was converted to its
hydrochloride salt. Mp 170−175 °C. Anal. (C25H38.6Cl4N6O1.3S) C, H,
N.
(R)-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-3-yl)methanone
[(+)-45)]. Indole-3-carboxylic acid (54 mg, 0.33 mmol) was reacted
with compound (+)-44 (90 mg, 0.28 mmol) in the presence of
EDCI·HCl (80 mg, 0.42 mmol), TEA (0.12 mL, 0.83 mmol), and
HOBT (56 mg, 0.41 mmol) in CH2Cl2 (10 mL) using procedure F.
The crude material was purified by column chromatography over silica
gel (EtOAc/MeOH, 4:1) to yield compound R-(+)-45 (87 mg, 67%).
1H NMR (CDCl3, 400 MHz): δ 0.89 (t, J = 7.6 Hz, 3H), 1.30−1.52
125.9, 127.0, 127.5, 136.7, 145.1, 166.1, 172.2. [α]25 +38.6° (c 1.0,
D
CH3OH). The free base was converted to its hydrochloride salt. Mp
200−205 °C. Anal. (C25H40Cl4N6O2S) C, H, N.
(S)-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-5-yl)methanone
[(−)-46]. Indole-5-carboxylic acid (60 mg, 0.37 mmol) was reacted
with compound (−)-44 (100 mg, 0.31 mmol) in the presence of
EDCI·HCl (89 mg, 0.46 mmol), TEA (0.13 mL, 0.93 mmol), and
HOBT (63 mg, 0.46 mmol) in CH2Cl2 (15 mL) using procedure F.
The crude material was purified by column chromatography over silica
gel (EtOAc/MeOH, 4:1) to yield compound S-(−)-46 (95 mg, 66%).
1H NMR (CDCl3, 400 MHz): δ 0.86 (t, J = 7.2 Hz, 1H), 1.40−1.54
(m, 2H), 1.62−1.81 (m, 1H), 1.97 (d, J = 11.2 Hz, 1H), 2.20−2.72
(m, 14H), 2.90−3.15 (m, 1H), 3.30−4.02 (m, 4H), 4.89 (bs, 2H),
6.58 (s, 1H), 7.15−7.29 (m, 1H), 7.35 (d, J = 8.4 Hz, 1H), 7.71 (s,
1H), 8.84 (s, 1H). 13C NMR (CDCl3, 100 MHz): δ 12.2, 22.5, 25.3,
26.1, 26.7, 48.5, 53.7, 58.3, 58.9, 103.1, 111.4, 117.3, 120.4, 121.4,
(m, 2H), 1.57−1.80 (m, 1H), 1.95 (d, J = 11.6 Hz, 1H), 2.20−2.80
(m, 13H), 2.85−3.10 (m, 1H), 3.50−3.82 (m, 4H), 4.87 (bs, 2H),
7.0−7.38 (m, 4H), 7.60−7.76 (m, 1H), 9.77 (s, 1H). 13C NMR
(CDCl3, 100 MHz): δ 12.0, 14.4, 21.4, 22.5, 25.4, 26.1, 26.9, 48.6,
53.7, 54.2, 58.3, 58.8, 60.6, 111.6, 112.1, 117.6, 120.4, 121.2, 122.8,
125.9, 127.1, 127.5, 136.7, 145.1, 166.1, 172.2. [α]25 −34.4° (c 1.0,
D
CH3OH). The free base was converted to its hydrochloride salt. Mp
200−205 °C. Anal. (C25H42.1Cl4.5N6O2.8S) C, H, N.
125.6, 127.5, 135.9, 145.3, 165.9, 167.2. [α]25 +37.4° (c 1.0,
D
CH3OH). The free base was converted to its hydrochloride salt. Mp
185−190 °C. Anal. (C25H40Cl4N6O2S) C, H, N.
(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(5-methoxy-1H-indol-3-yl)-
methanone (47). 5-Methoxy-1H-indole-3-carboxylic acid (213 mg,
1.11 mmol) was reacted with compound ( )-44 (300 mg, 0.93 mmol)
in the presence of EDCI·HCl (267 mg, 1.40 mmol), TEA (0.39 mL,
2.78 mmol), and HOBT (188 mg, 1.40 mmol) in CH2Cl2 (25 mL)
using procedure F. The crude material was purified by column
chromatography over silica gel (EtOAc/MeOH, 6:1) to give
(S)-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-3-yl)methanone
[(−)-45)]. Indole-3-carboxylic acid (54 mg, 0.33 mmol) was reacted
with compound (−)-44 in the presence of EDCI·HCl (80 mg, 0.42
mmol), TEA (0.12 mL, 0.83 mmol), and HOBT (56 mg, 0.41 mmol)
in CH2Cl2 (10 mL) using procedure F. The crude material was
purified by column chromatography over silica gel (EtOAc/MeOH,
1
compound 47 (280 mg, 61%). H NMR (CDCl3, 400 MHz): δ 0.85
1
4:1) to give compound S-(−)-45 (93 mg, 72%). H NMR (CDCl3,
(t, J = 7.2 Hz, 3H), 1.32−1.48 (m, 2H), 1.56−1.76 (m, 1H), 1.93 (d, J
= 10 Hz, 1H), 2.26−2.78 (m, 1H), 2.90−3.10 (m, 1H), 3.52−3.77 (m,
4H), 3.77 (s, 3H), 5.21 (bs, 2H), 6.77 (d, J = 8.4 Hz, 1H), 6.90−7.22
(m, 3H), 10.3 (bs, 1H).
400 MHz): δ 0.85 (t, J = 7.6 Hz, 3H), 1.30−1.52 (m, 2H), 1.55−1.80
(m, 1H), 1.95 (d, J = 11.6 Hz, 1H), 2.20−2.80 (m, 13H), 2.85−3.10
(m, 1H), 3.50−3.82 (m, 4H), 4.86 (bs, 2H), 7.0−7.38 (m, 4H), 7.60−
7.76 (m, 1H), 9.77 (s, 1H). 13C NMR (CDCl3, 100 MHz): δ 12.0,
14.4, 21.3, 22.5, 25.4, 26.1, 26.8, 48.6, 53.8, 54.2, 58.3, 58.8, 60.6,
111.5, 112.1, 117.7, 120.4, 121.2, 122.8, 125.6, 127.5, 135.9, 145.3,
(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(5-hydroxy-1H-indol-3-yl)-
methanone (48). Compound 47 (140 mg, 0.28 mmol) was brought
to −78 °C in CH2Cl2 (15 mL), followed by dropwise addition of BBr3
(0.13 mL, 1.41 mmol). The reaction mixture was allowed to stir for 12
h while gradually attaining room temperature. The reaction was
quenched by the addition of a saturated solution of NaHCO3, and
extraction was with CH2Cl2 (2 × 100 mL). The organic layer was
dried over Na2SO4 and concentrated under reduced pressure. The
crude material was purified by flash column chromatography over silica
165.8, 167.2. [α]25 −33.6° (c 1.0, CH3OH). The free base was
D
converted to its hydrochloride salt. Mp 205−210 °C. Anal.
(C25H41.5Cl4.5N6O2.5S) C, H, N.
(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-5-yl)methanone
[( )-46]. Indole-5-carboxylic acid (60 mg, 0.37 mmol) was reacted
with compound ( )-44 (100 mg, 0.31 mmol) in the presence of
EDCI·HCl (89 mg, 0.46 mmol), TEA (0.13 mL, 0.93 mmol), and
HOBT (63 mg, 0.46 mmol) in CH2Cl2 (15 mL) using procedure F.
The crude material was purified by column chromatography over silica
gel (EtOAc/MeOH, 4:1) to yield compound ( )-46 (102 mg, 71%).
1H NMR (CDCl3, 400 MHz): δ 0.88 (t, J = 7.2 Hz, 1H), 1.40−1.54
(m, 2H), 1.60−1.81 (m, 1H), 1.97 (d, J = 11.2 Hz, 1H), 2.20−2.72
(m, 14H), 2.90−3.15 (m, 1H), 3.30−4.02 (m, 4H), 4.89 (bs, 2H),
6.57 (s, 1H), 7.15−7.29 (m, 1H), 7.35 (d, J = 8.4 Hz, 1H), 7.71 (s,
1H), 8.84 (s, 1H). 13C NMR (CDCl3, 100 MHz): δ 12.0, 22.5, 25.3,
26.0, 26.7, 48.5, 53.7, 58.3, 58.7, 103.1, 111.4, 117.3, 120.4, 121.4,
125.9, 127.0, 127.5, 136.7, 145.1, 166.1, 172.2. The free base was
converted to its hydrochloride salt. Mp 185−190 °C. Anal.
(C25H41Cl4N6O2.5S) C, H, N.
1
gel (EtOAc/MeOH, 2:1) to give compound 48 (80 mg, 59%). H
NMR (CD3OD, 400 MHz): δ 0.91 (t, J = 7.6 Hz, 3H), 1.42−1.58 (m,
2H), 1.62−1.80 (m, 1H), 2.00 (d, J = 8.8 Hz, 1H), 2.40−2.85 (m,
15H), 3.00−3.22 (m, 1H), 3.60−3.88 (m, 4H), 6.74 (dd, J = 8, 1.6 Hz,
1H), 7.04 (d, J = 2.4 Hz, 1H), 7.24 (s, 1H), 7.53 (s, 1H). The free base
was converted to its hydrochloride salt. Mp 210−215 °C. Anal.
(C25.8H43.4Cl4N6O3.9S) C, H, N.
N6-{2-[4-(1H-Indol-5-ylmethyl)piperazin-1-yl]ethyl}-N6-prop-
yl-4,5,6,7-tetrahydrobenzothiazole-2,6-diamine (49). Amine
( )-44 (80 mg, 0.25 mmol) was reacted with 1H-indole-5-
carbaldehyde (36 mg, 0.25 mmol) and NaBH(OAc)3 (94 mg, 0.45
mmol) in CH2Cl2 (15 mL) using procedure B. The crude residue was
purified by column chromatography (EtOAc/MeOH, 4:1) to afford
compound 49 (71 mg, 63%). 1H NMR (CDCl3, 400 MHz): δ 0.86 (t,
J = 7.2 Hz, 3H), 1.32−1.54 (m, 2H), 1.60−1.78 (m, 1H), 1.95 (d, J =
10.4 Hz, 1H), 2.20−2.80 (m, 18H), 2.90−3.10 (m, 1H), 3.63 (s, 2H),
4.87 (bs, 2H), 6.51 (s, 1H), 7.16 (d, J = 8.4 Hz, 1H), 7.19 (s, 1H), 7.33
(d, J = 8.4 Hz, 1H), 7.55 (s, 1H), 8.45 (s, 1H). The free base was
(R)-(4-{2-[(2-Amino-4,5,6,7-tetrahydrobenzothiazol-6-yl)-
propylamino]ethyl}piperazin-1-yl)-(1H-indol-5-yl)methanone
[(+)-46]. Indole-5-carboxylic acid (60 mg, 0.37 mmol) was reacted
with compound (+)-44 (100 mg, 0.31 mmol) in the presence of
EDCI·HCl (89 mg, 0.46 mmol), TEA (0.13 mL, 0.93 mmol), and
HOBT (63 mg, 0.46 mmol) in CH2Cl2 (15 mL) using procedure F.
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converted to its hydrochloride salt. Mp 230−235 °C. Anal.
(C27H49Cl5N6O2S) C, H, N.
ASSOCIATED CONTENT
* Supporting Information
Elemental analysis data for all final targets. This material is
■
S
Evaluation of Potency in Binding to and Activating
Dopamine D2 and D3 Receptors. Binding potency was monitored
by inhibition of [3H]spiroperidol (15.0 Ci/mmol, Perkin-Elmer)
binding to DA rD2 and rD3 receptors expressed in HEK-293 cells in a
buffer containing 0.9% NaCl. Functional activity of test compounds in
activating dopamine hD2 and hD3 receptors expressed in CHO cells
was measured by stimulation of [35S]GTPγS (1250 Ci/mmol, Perkin-
Elmer) binding in comparison to stimulation by the full agonist DA as
described by us previously.29
Evaluation of Antioxidant Activity. DPPH Radical Scaveng-
ing Assay. To a 96-well plate, an amount of 100 μL of methanolic
drug solutions ranging from 20 to 250 μM was added. Next 100 μL of
200 μM methanolic solution of DPPH (1,1-diphenyl-2-picrylhydrazyl)
was added and the plate was shaken vigorously at 30 °C for 20 min.
Control wells received 100 μL of methanol and 100 μL of 200 μM
methanolic DPPH solution. Wells containing only 200 μL of methanol
served as a background correction. The change in absorbance of all
samples and standard (ascorbic acid) was measured at 517 nm. Radical
scavenging activity was expressed as inhibition percentage and was
calculated using the following formula: % scavenging activity =
[(absorbance of control − absorbance of sample)/(absorbance of
control)] × 100.40
Animal Experiments. Drugs and Chemicals. The following
commercially available drugs were used in the experiment: reserpine
hydrochloride (Alfa Aesar) and ropinirole (Sigma Aldrich). The
trifluoroacetate salt of (−)-19 and (−)-40 and the hydrochloride salt
of (−)-46 and ropinirole were dissolved in water. Reserpine was
dissolved in 10−25 μL of glacial acetic acid and further diluted with
5.5% glucose solution. All compounds for this study were administered
subcutaneously (sc) in a volume of 0.1−0.3 mL to each rat.
Animals. In rodent studies, animals were male and female Sprague-
Dawley rats from Harlan (Indianapolis, IN) weighing 220−225 g
unless otherwise specified. Animals were maintained in sawdust-lined
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Phone: 1-313-577-1064. Fax: 1-313-577-2033. E-mail:
adutta@wayne.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is supported by National Institute of Neurological
Disorders and Stroke/National Institutes of Health (Grant
NS047198, A.K.D.). We are grateful to Dr. K. Neve, Oregon
Health and Science University, Portland, OR, for D2L and D3
expressing HEK cells. We are also grateful to Dr. J. Shine,
Garvan Institute for Medical Research, Sydney, Australia, for
D2L expressing CHO cells. We are grateful to Dr. Sanjib Gogoi
and Gyan Modi for help with synthesis and in vivo animal
experiments.
ABBREVIATIONS USED
■
GTPγS, guanosine 5′-[γ-thio]triphosphate; 5-OH-DPAT, 5-
hydroxy-2-(dipropylamino)tetralin; CHO, Chinese hamster
ovary; HEK, human embryonic kidney; L-DOPA, (S)-(3,4-
dihydroxyphenyl)alanine; DPPH, 1,1-diphenyl-2-picrylhydra-
zyl; PD, Parkinson’s disease; DA, dopamine; sc, subcutaneous
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