Talipexole variations as novel bitopic dopamine D2 and D3receptor ligands

Article abstract of DOI:10.1039/c9md00379g

We linked 2-aminothiazoloazepane scaffolds with phenylpiperazine pharmacophores to generate bitopic dopamine receptor ligands. Highest D₂R/D₃R binding affinities up to pK_i values of 7.74 were observed for compounds containing a 1-(2,3-dichlorophenyl)piperazinoyl moiety, maintaining affinity with deaminated 5,6,7,8-tetrahydro-4H-thiazoloazepine derivatives.

Full text of DOI:10.1039/c9md00379g

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DOI: 10.1039/C9MD00379G
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Talipexole variations as novel bitopic dopamine D2 and D3
receptor ligands
Lars Stanka, Annika Franka, Stefanie Hagenowa and Holger Stark*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
We linked 2-aminothiazoloazepane scaffolds with (Figure 1). In these compounds dopamine´s catechol moiety is
phenylpiperazine pharmacophores to generate bitopic replaced by a bioisosteric aminothiazole, that was found to
dopamine receptor ligands. Highest D2R/D3R binding bind to the D2R and D3R in nanomolar concentration ranges
affinities up to pKi values of 7.74 were observed for when coupled to arylpiperazines.7,8 The aminothiazole
compounds containing a 1-(2,3-dichlorophenyl)piperazinoyl derivative talipexole (Figure 1, Table 1) was developed as
moiety,
thiazoloazepane derivatives.
maintaining
affinity
with
deaminated dopamine D2R/D3R agonist for symptomatic treatment of PD
and is approved by the Japanese Pharmaceuticals and Medical
Devices Agency (PMDA). Talipexole features incorporation of
Targeting the dopamine receptor in neuropsychiatric diseases its basic amine into a ring system, thereby lacking stereo-
like Parkinson´s disease (PD) became a common strategy.1 selectivity of compounds D-210 and D-219. Reducing
Although numerous drugs are applied, few live up to the stereochemistry in molecules is beneficial for drug
challenges presented by the receptor’s particularities. The development as it facilitates synthesis, purification and
dopamine receptors are divided into two families according to simplifies clinical development. Thus, talipexole derivatives
their G-protein coupling and signalling pathways: D1-like were coupled to arylpiperazines or other motifs via different
receptors (D1 and D5 receptor subtypes) activate, while D2-like alkyl linkers, to achieve bitopic ligands containing two basic
receptors (D2, D3 and D4 receptor subtypes) inhibit adenylyl centres without stereo-chemical properties. The second motif
cyclase. Especially dopamine D2 and D3 receptors (D2R/D3R) are did include classic scaffolds like (2,3-dichlorophenyl)piperazine
highly investigated for their specific receptor properties and or (2-methoxyphenyl)piperazine, but also unusual motifs to
treatment opportunities in PD or schizophrenia. Recent generate more versatile bitopic compounds. The objective was
research puts emphasis on the development of bitopic ligands to modify binding selectivity compared to talipexole.
bearing two pharmacophores to target the orthosteric binding Additionally, the influence of amination or deamination of
pocket (OBP) and a secondary allosteric binding pocket (SBP), these aminothiazoles were evaluated to explore bioisosteric
found within the receptors.2,3 The SBP is not as highly exchange of catechols.
conserved as the OBP in the D2R and D3R. Hence, bitopic
ligands provide higher subtype selectivity or modified
pharmacodynamic properties such as functional selectivity or
kinetic interaction with additional binding regions.4 For the
design of bitopic ligands at the D2R and D3R various scaffolds
are described to yield satisfying binding affinities.2,5,6 They
usually contain at least one basic centre to allow for
interaction with the highly conserved aspartate residue in the
OBP. Among those promising scaffolds are (2-
methoxyphenyl)piperazines
and
(2,3-dichlorophenyl)-
piperazines as shown with compounds D-210 and D-219
aInstitute of Pharmaceutical and Medicinal Chemistry, Heinrich Heine University
Düsseldorf, Universitaetsstr. 1, 40225 Duesseldorf, Germany; E-mail: stark@hhu.de
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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Journal Name
HO
N
brominated and subsequently converted with tVhieiowuArrteicale Oinnlinae
Hantzsch thiazole synthesis, yielding 5, a mixture of two
NH2
H2N
N
DOI: 10.1039/C9MD00379G
S
HO
2-aminothiazole isomers. Due to their similar physicochemical
properties, the resulting isomers were not separated, but
instead used without further purification in the next steps.
They were either directly deprotected using strong acid (6) or
deaminated with isopentyl nitrite in THF, followed by
deprotection (8 and 9). Secondary amines 6, 8 and 9 were each
isolated by column chromatography after the deprotection
step. The regioisomer of 6 was neither isolated nor used for
further synthesis. Alcohols 10a–g were converted to the
respective aldehydes 11a–g by Swern oxidation (Scheme 2).
11g was obtained by deprotection of N-(4,4-diethoxybutyl)-
adamantane-1-carboxamide. The aldehydes 11a–h were used
without further purification for reductive amination of either
thiazoloazepane 6, 8 or 9 to form target compounds 12–14.
Compounds were investigated for their binding affinities
(Table 1) in [3H]spiperone displacement studies in binding
buffer (120 mM NaCl, 5 mM KCl, 1 mM CaCl2, 1 mM MgCl,
50 mM Tris) using crude membrane extracts prepared from
stably transfected CHO-K1 cells, overexpressing human D2S and
D3 receptors as described previously.7 CHO-K1 cells (American
Type Culture Collection, Rockville, MD; CCL 61) were
transfected using pAXhD2 and pSVD3 plasmids respectively.
CHO-K1 cells for D3R transfection were deficient in
dihydrofolate reductase. The final constructs of stably
transfected CHO-K1 cell lines for D2sR and D3R were kindly
donated by Prof. Dr. Shine (Australia) and Prof. Dr. Sokoloff
Dopamine
pKi (hD2S) = 6.27
pKi (hD3) = 7.64
Talipexole
pKi (hD2S) = 6.21
pKi (hD3) = 7.17
N
H2N
S
R
N
N
N
CH3
D-210, R=2-OCH3
pKi (hD2L) = 6.78
pKi (hD3) = 8.29
D-219, R=2,3-diCl
pKi (hD2L) = 7.16
pKi (hD3) = 8.74
H3C
N
O
O
N
N
S
R
(1), R=H2N-
pKi (hD2S) = 8.55
pKi (hD3) = 8.52
(2), R=H-
pKi (hD2S) = 8.49
pKi (hD3) = 8.07
Figure 1 Structures and pKi values of dopamine8, talipexole9 and bitopic
D2/D3 receptor ligands.7,8
The three scaffolds 2-aminothiazolo[4,5-d]azepane 6, thiazolo-
[4,5-d]azepane 8 and thiazolo[4,5-c]azepane 9 were prepared
according to Scheme 1. Carboxybenzyl (Cbz)-protected
piperidone underwent ring expansion by means of freshly
synthesized ethyl diazoacetate 2 and a Lewis acid to form the
azepanone derivative 3. Cleavage of the β-keto ester with a
strong base produced 4. The α-keto position of 4 was
(France),
respectively.
N
S
N
S
N
Cbz
H2N
N
Cbz
O
N
O
Cbz
1
O
O
O
d
a
b
c
N
Cbz
N Cbz
O
H2N
S
S
N
N
N2
H3C
N
Cbz
N
Cbz
H3C
O
3
4
2
5
7
e
e
e
S
N
S
N
N
S
O
O
H2N
NH
NH
NH
Cbz=
8
6
9
Scheme 1 Synthesis of thiazoloazepanes. Reagents and conditions: (a) Boron trifluoride diethyl etherate, Et2O, −78°C, 1 h; (b) KOH, EtOH/H2O, reflux, 2.5 h;
(c) Br2, CHCl3, rt, until completion, followed by thiourea, EtOH, rt to reflux, 2 h; (d) Isopentyl nitrite, THF, reflux, 2 h; (e) 6 N HCl, iPrOH, reflux, 10 h.
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C9MD00379G
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Cl
Cl
R2
N
N
S
n
R1
N
R1
NH
I =
N
N
N
S
N
N
N
N
II =
1
2
1
12a-b
13a-h R1=H-,
6
8
R =H2N-, R =I-II, n=3
R =H2N-
1
b
R2=I-VI, n=1-3
R =H-
N
III =
O
H3C O
N
N
IV =
V =
R2
a
R2
n
n
HO
O
N
S
N
10a-g
11a-h
b
O
VI =
NH
O
H3C
S
S
N
N
N
N
NH
N
9
14
Scheme 2 Coupling of thiazoloazepanes to arylpiperazines. Reagents and conditions: (a) Oxalyl chloride, dimethyl sulfoxide, Et3N, DCM, −50°C, 0.5 h;
(b) Na(OAc)3BH, 1,2-dichloroethane, rt, overnight.
Table 1 In vitro binding affinities at human dopamine D2S and D3 receptors of bitopic talipexole derivatives.
N
R1
N
R2
CH2
n
S
hD2S pKi
hD3 pKi
R1
n
R2
x̅
(± S.E.M.)
x̅
(± S.E.M.)
Compound
Talipexole
6.219
7.179
H2N-
1
(± 0.02)
(± 0.03)
Cl
N
Cl
7.65
(± 0.09)
7.59
(± 0.11)
12a
12b
H2N-
H2N-
4
4
N
N
N
5.56
(± 0.07)
5.42
(± 0.11)
N
N
Cl
N
Cl
7.74
(± 0.05)
7.55
(± 0.09)
13a
13b
H-
H-
4
4
N
N
N
N
5.60
(± 0.09)
5.51
(± 0.15)
N
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4.38
(± 0.01)
4.91
13c
13d
13e
13f
13g
13h
14
H-
H-
H-
H-
H-
H-
2
2
3
4
4
4
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N
N
(± 0.21)
DOI: 10.1039/C9MD00379G
O
H3C O
6.82
(± 0.15)
6.62
(± 0.05)
N
N
H3C O
7.19
(± 0.10)
6.78
(± 0.13)
N
N
H3C O
7.07
(± 0.07)
6.51
(± 0.19)
N
N
5.20
(± 0.27)
5.42
(± 0.18)
N
S
N
O
5.26
(± 0.20)
6.35
(± 0.17)
NH
S
H3C O
N
6.75
(± 0.21)
6.59
(± 0.12)
N
N
N
CH2
3
pKi values are derived by incubating membrane preparations from CHO-K1 cells, stably expressing the human D2sR (25 µg/well) or D3R (20 µg/well) with the
compound and [3H]spiperone (0.2 nM) for 120 min at RT. Data represent mean (x
) ± standard error of mean (S.E.M.) of at least three independent
̅
experiments (two for compounds 13c-13e and 12b), each performed in triplicates with seven appropriate concentrations or in duplicates with eleven
concentrations.
Among bitopic talipexole derivatives, highest affinities at the not conducted. The necessity of the 2-amino moiety for
D2R and the D3R were found for compounds, sharing a 1-(2,3- thiazoles as catechol bioisosteres is also still disputed. In most
dichloro)piperazine moiety (12a, 13a). Compared to cases the amino function was preserved due to initial
talipexole,9 12a and 13a showed improved D2R/D3R affinity, assumptions of its pivotal importance or completely replaced
while minor D3R preference is abolished in these bitopic by different bioisosteric hetereocycles.11,12 However, the
ligands. On the contrary, the tetrathydrobenzothiazoles D-210 importance and arrangement of hydrogen-bond donor and
and D-219 (Figure 1) showed D3R preference.8 Interestingly, acceptor capacities of heterocyclic catechol bioisosteres are
slight D3R preference was found for the adamantane-1- not fully understood. While aromatic planar systems provide
carboxamide (13h). A pair of 2-aminothiazoles and their π-stacking interactions with aromatic amino acids in the
deaminated analogues (12a
& 13a, 12b & 13b) were binding pocket, endo/exocyclic hydrogen-bond donor
synthesized, in order to evaluate the impact of the aromatic properties (e.g. hydroxyl and amino groups) are hypothesized
amino group on D2R/D3R affinity. Since the deamination was to be compensable by hydrophobic interactions or either
performed without loss of affinity, the deaminated core motif water-mediated ligand-receptor interactions.12,13 Thus, potent
was chosen as our preferred pharmacophore for the design of and selective heterocyclic ligands, lacking hydrogen donor
further bitopic dopamine receptor ligands. It has to be noted, functions or even non-aromatic, but conjugated bitopic enyne-
that deamination of compound 13f could contribute to these type ligands are described.14-16 Modification on hydrogen-bond
findings but was not performed in this mini-series. Variation of donor and acceptor capacities, i.e. deamination of the 2-
the alkyl linker lengths between the two pharmacophores of aminothiazole provides alterations of physicochemical
deaminated
1-(2-methoxyphenyl)piperazine-coupled properties, being decisive for drug-likeness and bioavailability
talipexole derivatives showed minor influences on D2R/D3R of drug candidates. Accordingly, deaminated thiazoles,
affinity with a slight tendency for D2R preference with providing only proton acceptor properties, may be novel
prolonged linker lengths (13f & 13e > 13d). These findings are suitable catechol bioisosteres to fit the D2R/D3R binding
in good accordance with bitopic (de)aminated benzothiazoles pocket. However, the homobivalent compound 13g showed
(compounds (1) and (2), Figure 1) coupled to analogous only marginal affinity at both dopamine receptors. This
arylpiperazine motifs.7 In contrast to that, a small series of demonstrates the more dominant impact on receptor binding
structural related tetrathydrobenzothiazoles, e.g., D-210 and by the arylpiperazine pharmacophore rather than the
D-219 (Figure 1), achieved D3R preference, showing negligible thiazoloazepane moiety of the presented bitopic ligands.
affinity differences for two and four carbon linker.8,10 The Repositioning of the azepane nitrogen led to decrease of D2R
influence of the highly flexible alkyl lengths on dopamine affinity (13e vs. 14). Although some of the compounds could
receptor subtype selectivity remains controversial,3 but improve on binding affinity compared to talipexole, they
appears less crucial for (de)aminated thiazoles. However, it lacked desired selectivity. Nonetheless, they provide valuable
would have been interesting to perform these alterations with insights into SAR of bioisosteric exchange with aminothiazoles.
compounds 12a and 12b, but within this small series that was In silico evaluation of these compounds could yield structural
4 | J. Name., 2012, 00, 1-3
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11 J. Maillard, P. Delauny, M. Langlois, B. Portevin,VJie.wLAergticeleaiOanlninde
C. Manuel, Eur. Med. Chem., 1984, 19D, O45I:11–04.150369./C9MD00379G
12 F. Boeckler and P. Gmeiner, Pharmacol. Ther., 2006, 112,
281–333.
rationale for their lack of selectivity and grant optimization
proposals for further derivatization of the thiazoloazepane
motif.17
13 F. Boeckler and P. Gmeiner, Biochim. Biophys. Acta, 2007,
1768, 871–887.
14 M. Dörfler, N. Tschammer, K. Hamperl, H. Hübner and P.
Gmeiner, J. Med. Chem., 2008, 51, 6829–6838.
Conclusions
As an advantage over the tetrathydrobenzothiazoles (D-210
and D-219),8 synthesized talipexole derivatives are achiral, do
not require stereo-selective synthesis with further
characterization of enantiomers, and therefore may be more
favourable for drug development. With this small series of
bitopic talipexole derivatives it could be shown that
deamination of bitopic thiazole-type ligands is well tolerated
by D2Rs/D3Rs. By increasing the library of bitopic ligands,
further exploration regarding the possibilities of this targeting
approach is facilitated and 1-(2,3-dichloro)piperazines,
connected via flexible alkyl linker are proven valuable
pharmacophores to increase dopamine receptor affinity within
bitopic compounds. Synthesis of deaminated thiazoles to
adjust physicochemical properties provides suitable scaffolds
for bitopic dopamine D2R/D3R ligands, awaiting prospective
modification for lead optimization to further improve affinity
and modulate subtype selectivity.
15 J. Elsner, F. Boeckler, F. W. Heinemann, H. Hübner and P.
Gmeiner, J. Med. Chem., 2005, 48, 5771–5779.
16 C. Hiller, R. C. Kling, F. W. Heinemann, K. Meyer, H. Hübner
and P. Gmeiner, J. Med. Chem., 2013, 56, 5130–5141.
17 M. Michino, T.Beuming, P. Donthamsetti, A. Hauck Newman,
J. A. Javitch and L. Shi, Pharmacol. Rev., 2015, 67, 198-213.
Conflicts of interest
There are no conflicts to declare. AF and HS are kindly funded
by the GRK2158, HS was also supported by the EU COST
Actions CA15135 and CA18133. The CHO-K1 cell lines for D2sR
and D3R were kindly donated by Prof. Shine (Australia) and
Prof. Sokoloff (France), respectively.
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