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Table 1. Receptor binding affinities of compounds 2, 3, and comparison with compounds 1a and 1b (pIC50 values)
Compd
5-HT2A
5-HT2C
H1
a1A
a2A
a2C
5-HT1A
5-HT1D
D2L
6.06
8.06
5.72
D3
D4
1a
1b
2
7.64
8.46
6.41
<6
7.91
8.98
7.90
6.04
8.17
8.63
<6
7.78
6.27
7.84
6.4
6.43
6.32
<6
<6
5.73
6.06
<6
<6
6.01
6.7
<6
<6
6.18
6.87
<6
6.77
9.26
5.78
6.88
8.58
6.60
<6
3
<6
<6
<6
<6
Biological Results and Discussion
nitrogen atom in the 7-position of the tetracyclic system,
did not show high or moderate affinity for any receptor
except for H1. As it was expected from those binding
data 3 was inactive in our mCPP test.
The affinities for histamine-H1 receptor as well as for
different human serotonergic, dopaminergic and adre-
nergic receptors of the two target compounds that could
be synthesised were measured by means of radioligand
binding assays as it was described in our previous arti-
cles.10 The experiments to measure the in vivo activity
of the compounds in our mCPP challenge test were
performed in male Wistar rats, weighing between 200
and 220 g, following the method described by Meert
and co-workers.5 The test compounds were adminis-
tered subcutaneously 45 min after intravenous injection
of mCPP. Two activity criteria were measured: disin-
hibition (partial antagonism of mCPP) and exploration
(full antagonism of mCPP).5 Table 1 shows the binding
affinity of compounds 2, 3 and reference compounds 1a
(R1=R2=H) and 1b (R1=H, R2=11-Cl) for several
receptors.
In conclusion, we have synthesised two new tetracyclic
structures, namely 2-(dimethylaminomethyl)-2,3,3a,8-
tetrahydroisoxazolo[3,2-a]pyrido[3,4-c]-[2]benzazepine
(2) and 2 - (dimethylaminomethyl) - 2,3,3a,8 - tetra-
hydroisoxazolo[3,2-a]pyrido[3,2-c]-[2]benzazepine (3).
In addition we have described a new method for the
synthesis of pyridobenzazepines. Compound 2 showed
quite remarkable selectivity for 5-HT2C receptor, but
did not show affinity for H1 receptor in contrast to its
tetrahydrodibenzoisoxazoloazepine analogues. Com-
pound 2 was active subcutaneously in our mCPP chal-
lenge test as well, what indicates it could be considered
as a 5-HT2C antagonist. Larger scale resynthesis and
separation of 2 into its enantiomers is currently in pro-
gress, our hope being to be able to identify one of them
as a new potent and selective 5-HT2C antagonist. Phar-
macological results of those pure enantiomers will be
the subject for further publications.
As can be seen in Table 1, compound 2 showed a quite
remarkable selectivity for the human 5-HT2C receptor
over 5-HT2A receptor. Furthermore, and most interest-
ing, is its lack of affinity for H1 receptor and other ser-
otonergic receptors. Only weak affinity was observed for
D4 and a1 receptors. Comparing the receptor binding
data of compound 2 with compounds 1a and 1b it can
be deduced that the replacement of the carbon atom
present in the 11-position by a nitrogen atom dropped
the affinity for H1 receptors, which was of the same
order of magnitude as that for 5-HT2 receptors in the
dibenzoisoxazoloazepine series. Even more all com-
pounds from those series were proved to be indeed new
5-HT2A/2C receptor antagonists, while 2 might be
defined as a rather selective 5-HT2C antagonist. It is
noteworthy as well that the presence of halogen atoms
in the 11-position enhanced the affinity for the dopamine
receptors, but on the contrary replacement of that CH by
nitrogen even decreased this affinity. The 5-HT2C antag-
onistic activity of compound 2 was confirmed in our in
vivo mCPP challenge test (Table 2). It was quite potent in
the disinhibition test and moderately potent in the
exploration test. On the other hand, compound 3, with the
Acknowledgements
The authors would like to thank Ms. Valle Ancos,
Alcira Del Cerro and Victoria Perez for their experi-
mental work performed. They would also like to thank
Mr. Willy Van Gorp for his help in management and
coordination of all data generated.
References and Notes
1. Hoyer, D.; Clarke, D. E.; Fozard, J. R.; Hartig, P. R.;
Martin, G. R.; Mylecharane, E. J.; Saxena, P. R.; Humphrey,
P. P. A. Pharmacol. Rev. 1994, 46, 157.
2. Sanders-Bush, E. and Mayer, S. E. In Goodman & Gilman’s
The Pharmacological Basis of Therapeutics, 9th ed.; Hardman,
J. G., Limbird, L. E., Molinoff, P. B., Ruddon, R. W., Good-
man, L. S., Gilman, A. G., Eds.; McGraw-Hill: New York,
1996; p 249.
3. Gibson, E. L.; Barnfield, A. M. C.; Curzon, G. Neuro-
pharmacology 1994, 33, 457.
4. Kennett, G. A.; Whitton, P.; Shah, K.; Curzon, G. Eur.
J. Pharmacol. 1989, 164, 445.
5. Meert, T. F.; Melis, W.; Aerts, N.; Clincke, G. Behav.
Pharmacol. 1997, 8, 353.
6. Whitton, P.; Curzon, G. Psychopharmacology 1990, 100, 138.
7. Rodgers, R. J.; Cole, J. C.; Cobain, M. R.; Daly, P.;
Doran, P. J.; Eells, J. R.; Wallis, P. Behav. Pharmacol. 1992, 3,
621.
Table 2. Activity in our mCPP challenge test, disinhibition and
exploration measurements after sc administration,5 of compounds 2
and 3
Compd
mCPP (disin.)
ED50 (mg/kg)
mCPP (expl.)
ED50 (mg/kg)
1a
1b
2
0.01
0.16
0.16
>2.5
>2.5
2.5
8. Di Matteo, V.; Di Giovanni, G.; Esposito, E. CNS Drug
Rev. 2000, 6, 195.
3
>2.5
>2.5