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A. Kling et al. / Bioorg. Med. Chem. Lett. 15 (2005) 5567–5573
Table 5. Functional profiles for 33 and 34
Compounds
[
35S]GTPc S Emax (%)
5-HT1AIC50 (nM)a
FLIPR Emax (%)
5-HT1B IC50 (nM)a
33
34
4
6
316
1304
7
9
35
85
a Values are geometric means of two or three experiments.
Acknowledgments
We thank S. Heitz, P. Karl, V. Ott, S. Pister, K. Britze,
H. Schulke, C. Thiem, and S. Triebel for chemical syn-
¨
thesis, S. Bopp, P. Goeck-Sturm, E. Ka¨fer, M. Loucka,
M. Mayrer, S. Muller, S. Petersen-Werner, S. Manzano,
¨
M. Nebel, G. Plotzky, M. Schanzenba¨cher, and T.
Schowalter for assay development and screening, L.
King for PK studies, S. Butty, B. Degner, and I. Groth
for in vivo experiments, and C. Krack, M. Diehl, T.
Kro¨nung, K. Lang, and M. Schienemann for analytical
support. Many thanks to Hans Schoemaker for his
contributions and inspiring discussions.
Table 6. Counter screening results for 33 and 34
Receptor Ki (nM)
33
34
5-HT2A
5-HT2C
5-HT5A
5-HT7
D3
180
1.200
5.500
>10.000
>10.000
520
>1.000
4.480
1.300
1.460
118
1.180
1.200
13.7
D2L
a1
Values are geometric means of two or three experiments.
lated [3H]5-HT-release from rat brain cortical slices.
At concentrations of 0.1 and 1 lM, compound 33
evoked a dose-dependent increase of [3H]5-HT-release
confirming the antagonist mode of action. Pharmaco-
kinetic studies of 33 in rat showed metabolic stability
and bioavailability after iv- and po-dosing (2 and
10 mg/kg, respectively), and good CNS penetration
(10 mg/kg po; F: 11 %; brain plasma ratio of 10.2/
AUC0–8h). Upon in vivo examination in the mouse
forced swim test, a behavioral model to assess antide-
pressant efficacy,35 compound 33 did not show any
significant activity up to 30 mg/kg ip.
References and notes
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additional behavioral assays and different species to
confirm our hypothesis and to further validate the ratio-
nale for the synthesis of dual 5-HT1A/B antagonists.
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In summary, we have identified novel and potent com-
bined 5-HT1 autoreceptor ligands containing the N-4-
aryl-piperazinyl-N0-ethyl-5,6,7,8-tetrahydropyrido[40,
30:4,5]thieno[2,3-d]pyrimidin-4(3H)-one
core.
The
compounds prepared displayed affinities in the low nano-
molar range for human 5-HT1A, 5-HT1B, and 5-HT1D
receptor subtypes. Furthermore, several analogues
exhibited an antagonist mode of action for both the 5-
HT1A and 5-HT1B receptors. In general, the structural
modifications we applied had only limited effect on in vi-
tro binding, but major impact on the intrinsic activity for
the 5-HT1A and 5-HT1B receptor subtypes. Although we
achieved our initial goal, the rational design of balanced
5-HT1A/B antagonists still presents a major challenge
since the SAR with respect to the mode of action is not
fully understood. Compounds 33 and 34 were chosen
as most promising representatives and submitted to fur-
ther characterization in in vitro and in vivo testing. In
counter screening, both compounds showed high selec-
tivity against a set of related receptors with the exception
of a1 adrenoceptors. Although 33 was shown to increase
[3H]5-HT release from rat brain cortical slices, an antide-
pressant-like effect in vivo in the mouse forced swim test
could not be demonstrated. Further studies using 33 as
tool compound will be conducted to evaluate the poten-
tial of dual 5-HT1A/B antagonists.
14. Barnes, N. B.; Sharp, T. Neuropharmacology 1999, 38,
1083.
15. Heiser, J. F.; Wilcox, C. S. CNS Drugs 1998, 10, 343.