N-Substituted 3-(arylamino)-4,5-dihydro-2H-benz[g]indazol-2-yl acetamides with anti-inflammatory and analgesic activities

Article abstract of DOI:10.1016/S0014-827X(00)00055-0

A series of substituted 3-(arylamino)-4,5-dihydro-2H-benz[g]indazol-2-yl acetamides was synthesized and tested in comparison with former analogues. The title compounds showed only weak antiarrhythmic properties but good anti- inflammatory and antinociceptive activity, particularly evident in the morpholino derivative. (C) 2000 Published by Elsevier Science S.A.

Full text of DOI:10.1016/S0014-827X(00)00055-0

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Il Farmaco 55 (2000) 383–388
N-Substituted 3-(arylamino)-4,5-dihydro-2H-benz[g]indazol-2-yl
acetamides with anti-inflammatory and analgesic activities
Silvia Schenone a,*, Olga Bruno a, Angelo Ranise a, Francesco Bondavalli a,
Giuseppe Falcone b, Walter Filippelli b, Barbara Rivaldi b
a Dipartimento di Scienze Farmaceutiche dell’Uni6ersita` di Geno6a, Viale Benedetto XV, 3, I-16132 Genoa, Italy
b Istituto di Farmacologia e Tossicologia, Facolta` di Medicina e Chirurgia, II Uni6ersita` degli Studi Via S. Andrea delle Dame 8,
I-80138 Naples, Italy
Received 8 March 2000; accepted 3 April 2000
Abstract
A series of substituted 3-(arylamino)-4,5-dihydro-2H-benz[g]indazol-2-yl acetamides was synthesized and tested in comparison
with former analogues. The title compounds showed only weak antiarrhythmic properties but good anti-inflammatory and
antinociceptive activity, particularly evident in the morpholino derivative. © 2000 Published by Elsevier Science S.A. All rights
reserved.
Keywords: N-Substituted 4,5-dihydro-2H-benz[g]indazol-2-yl acetamides; Anti-inflammatory agents; Analgesic agents
1. Introduction
It was with these observations in mind that we have
been engaged in the preparation of other analogues of
1 bearing in position 2 of the benzindazole ring a
substituted acetamido moiety instead of an aryl group:
Our previous work dealing with the biological activ-
ity of simple and complex pyrazole derivatives enabled
us to study a series of 2-aryl-3-phenylamino-4,5-dihy-
dro-2H-benz[g]indazoles 1 that showed interesting an-
tiarrhythmic and local anaesthetic activities [1].
In our compounds the rigid tetralone moiety takes
the place of the two phenyl rings present in compounds
2, thus maintaining comparable lipophilic features.
We also tried the effect of the p-substitution with
halogen atoms in the phenylamino group in order to
verify their influence on the pharmacological profile.
On the other hand, diphenyl-substituted pyrazolyl
acetamides 2 were early prepared and tested as an-
tiarrhythmic agents by Bailey [2].
2. Chemistry
The synthetic approach started from 1-tetralone 3
which was reacted with the proper p-substituted
phenylisothiocyanates to give the corresponding oxo-
carbothioamides 4 in good yield.
* Corresponding author. Tel.: +39-010-3538866; fax: +39-010-
3538358.
E-mail address: bondabsr@unige.it (S. Schenone).
0014-827X/00/$ - see front matter © 2000 Published by Elsevier Science S.A. All rights reserved.
PII: S0014-827X(00)00055-0

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S. Schenone et al. / Il Farmaco 55 (2000) 383–388
Comp.
X
NR2
Comp.
X
NR2
6a
6b
6c
6d
6e
H
H
H
H
Cl
NHCH(CH3)2
NH(CH2)2OCH2CH3
NHCH2C6H5
morpholino
NHCH(CH3)2
6f
6g
6h
6i
Cl
Cl
Cl
Br
Br
NH(CH2)2OCH2CH3
NHCH2C6H5
morpholino
NH(CH2)2OCH2CH3
morpholino
6l
Reaction of 4 with ethyl hydrazinoacetate gave the
ethyl esters 5, which in turn, by heating with the
relevant amines, led to the desired substituted amides 6
in good yield.
The direct cyclization of 4 to 5, without isolation of
hydrazone intermediates, was achieved as in the former
series [1] by heating the reaction mixture with a cata-
lytic amount of acetic acid and elimination of hydrogen
sulfide.
internal standard; J in Hz. Analyses for C, H, N were
within 90.3% of the theoretical values.
4.1.1. General procedure for N-aryl-3,4-dihydro-
1(2H)-oxonaphtalene-2-carbothioamides (4a–c)
To a cold solution of 1-tetralone (2.92 g, 20 mmol) in
dry dimethylformamide (DMF, 15 ml), a 60% sodium
hydride dispersion in mineral oil (0.80 g, 20 mmol) was
added and the resulting mixture was stirred at room
temperature (r.t.) until the hydrogen evolution sub-
sided. The proper arylisothiocyanate (21 mmol) was
then added and the mixture was stirred at r.t. for 4 h,
poured cautiously into cold water (100 ml) and ex-
tracted with petroleum ether (b.p. 40–70°C). The
aqueous solution was cooled and acidified with 1 M
HCl (pH 4–5).
3. Pharmacology
Compounds 6a–l were submitted to a preliminary
screening for anti-inflammatory, analgesic, antiarrhyth-
mic and local anaesthetic activities.
The solid precipitate was settled, filtered, washed
with water and finally crystallized from absolute
ethanol.
4. Experimental
4a: yield 80%; ivory–white crystals, m.p. 137–138°C,
lit. [1].
4.1. Chemistry
4b: yield 92%; ivory–white crystals, m.p. 160–162°C.
1
Melting points were determined with a Bu¨chi 530
apparatus. IR spectra were measured in KBr with a
Perkin–Elmer 398 spectrophotometer. H NMR spec-
tra were recorded in CDCl3 solution on a Hitachi
Perkin–Elmer R-600 (60 MHz) instrument, chemical
shifts are reported as l (ppm) relative to TMS as
IR (CHCl3): 3300 and 1664 (NH and CO) cm−1; H
NMR: l 2.2–3.3 (m, 4H, 2CH2), 3.9–4.3 (m, 1H, CH),
7.2–7.7 and 7.8–8.2 (2m, 8H Ar), 11.30 (s, 1H, NH,
disappears with D2O). Anal. C17H14ClNOS (C, H, N).
4c: yield 70%; ivory–white crystals, m.p. 144–145°C.
1
1
IR (CHCl3): 3140 and 1672 (NH and CO) cm−1; H

S. Schenone et al. / Il Farmaco 55 (2000) 383–388
385

386
S. Schenone et al. / Il Farmaco 55 (2000) 383–388
NMR: l 2.6–3.4 (m, 4H, 2CH2), 3.6–4.0 (m, 1H, CH),
7.2–8.3 (m, 8H Ar), 10.82 (br s, 1H, NH, disappears
with D2O). Anal. C17H14BrNOS (C, H, N).
4.1.3. General procedure for N-substituted
3-(arylamino)-4,5-dihydro-2H-benz[g]indazol-2-yl
acetamides (6a–l)
Ethyl acetates 5a–c (10 mmol) and an excess (5 ml) of
the suitable amine were heated at reflux (in the case of
isopropylamine) or at 100°C (in the case of other
amines) for 4 h. Excess amine was removed under re-
duced pressure and the residue was dissolved in chloro-
form (20 ml) and washed with 1 M HCl (10 ml) and
water. The organic phase was dried (anhyd. MgSO4),
filtered and evaporated under reduced pressure to give a
crude solid that was crystallized from absolute ethanol.
Yields, melting points and spectral data of 6a–l are
reported in Table 1.
4.1.2. General procedure for ethyl
3-(arylamino)-4,5-dihydro-2H-benz[g]indazol-2-yl
acetates (5a–c)
To a solution of sodium ethoxide prepared from
sodium (0.46 g, 20 mmol) in absolute ethanol (25 ml),
ethyl hydrazino acetate hydrochloride (3.4 g, 22 mmol)
was added and the resulting suspension was stirred at
r.t. for 5 min. Then the relevant b-oxothioamide and a
small quantity (5 drops) of glacial acetic acid were
added and the mixture refluxed for 12 h. The solvent
was removed under reduced pressure and the residue
treated with water (100 ml), filtered and crystallized
from absolute ethanol.
4.2. Pharmacology
5a: yield 58%; light yellow crystals, m.p. 149–150°C.
Anti-inflammatory activity was evaluated by car-
rageenan-induced paw edema in rats [3]; analgesic ac-
tivity was evaluated by the acetic acid writhing test in
mice [4]; antiarrhythmic activity was evaluated as pro-
tection index against ecgraphic effects from aconitine in
rats [5] and local anaesthetic activity was evaluated as
infiltration anesthesia in rats [6].
1
IR (CHCl3): 3395 and 1740 (NH and CO) cm−1. H
NMR: l 1.23 (t, J=7.2, 3H, CH3), 2.3–2.7 and 2.7–3.1
(2m, 4H, 2CH2), 4.23 (q, J=7.2, 2H, CH2O), 4.89 (s,
2H, CH2ꢀN), 5.56 (s, 1H, NH disappears with D2O),
6.6–7.5 and 7.7–8.1 (2m, 9H Ar). Anal. C21H21N3O2
(C, H, N).
5b: yield 58%; light yellow crystals, m.p. 159–160°C.
1
IR (CHCl3): 3380 and 1739 (NH and CO) cm−1. H
NMR: l 1.25 (t, J=7.2, 3H, CH3), 2.3–2.7 and 2.7–3.1
(2m, 4H, 2CH2), 4.22 (q, J=7.2, 2H, CH2O), 4.87 (s,
2H, CH2N), 5.63 (s, 1H, NH, disappears with D2O),
6.5–7.4 and 7.7–8.10 (2m, 8H Ar), Anal. C21H20ClN3O2
(C, H, N).
5. Result and discussion
As a general consideration, compounds 6a–l poorly
confirm the features of previous congeners 1 showing
only weak antiarrhythmic (Table 2) and no local anaes-
thetic activity.
5c: yield 60%; light yellow crystals, m.p. 143–144°C.
1
IR (CHCl3): 3385 and 1738 (NH and CO) cm−1. H
NMR: l 1.25 (t, J=7.2, 3H, CH3), 2.3–2.7 and 2.7–3.1
(2m, 4H, 2CH2), 4.23 (q, J=7.2, 2H, CH2O), 4.89 (s,
2H, CH2N), 5.59 (s, 1H, NH, disappears with D2O),
6.5–6.9 and 7.7–8.1 (2m, 8H Ar). Anal. C21H20BrN3O2
(C, H, N).
On the other hand a good anti-inflammatory activity
turns out to be present in almost all 6a–l (Table 3) with
a maximum for 6l having an ED50 of 15.91 (12.61–
20.01) and 19.62 (14.91–25.82) mg/kg per o.s. after 3
and 4 h, respectively.
Table 2
Activity against ventricular fibrillation caused by aconitine in albino rats a
Comp.
Dose (mg/kg p.o.)
Appearance time of extrasystoles (s9SEM)
Death time (s9SEM)
b
Control (aconitine HCl)
Quinidine
180916.1
385920.2 c
194915.7
187920.1
232918.6
198915.7
224917.5
307914.5
196920.4
205919.7
198919.7
263922.3
596919.3
1007915.6 c
621916.3
583915.8
712922.3
671918.7
607919.5
785923.4
691916.3
677919.1
647918.5
694917.1
25
50
50
50
50
50
50
50
50
50
50
6a
6b
6c
6d
6e
6f
6g
6h
6i
6l
a Five animals (200–250 g)/group.
b 15 mg/kg i.v. until death.
c Statistically significant value calculated in comparison with the test performed with aconitine only (PB0.01).

S. Schenone et al. / Il Farmaco 55 (2000) 383–388
387
Table 3
Anti-inflammatory activity by carrageenan-induced rat paw edema test a of compounds 6a–l
Comp.
Dose (mg/kg)
Edema inhibition (%) relative to control at the following times (h) after
treatment
1
2
3
4
Indomethacin
5
−45
−32
−38
−45
−58
−39
−58
−61
−55
−64
−58
−71
−68
−55
−26
−50
−39
−66
−34
−47
−50
−44
−58
−47
−63
−73
−63
−39
−45
−50
−56
−45
−41
−58
−39
−52
−43
−63
−78
−68
−35
−53
−57
−63
−42
−50
−53
−35
−59
−39
−57
−70
6a
6b
6c
6d
6e
6f
6g
6h
6i
50
50
50
50
50
50
50
50
50
12.5
25
50
6l
a Each compound was tested on a group of five albino rats (180–250 g). Compounds were given by gastric probe 30 min before carrageenan
(0.1 ml of 1% solution).
Table 4
Acetic acid writhing test: analgesic activity
Comp.
Dose (mg/kg)
Mean number of writhes in 25 min period after treatment9SEM
% Decrease relative to controls
Control
Acetic acid 0.5% 46.195.7
Indomethacin
5
23.693.9
25.395.2
28.694.6
31.593.4
29.593.9
29.293.8
24.195.1
27.296.8
29.594.8
26.396.9
22.897.2
26.897.1
24.196.2
−53
−45
−38
−32
−36
−37
−48
−41
−36
−43
−51
−42
−48
6a
6b
6c
6d
6e
6f
50
50
50
50
50
50
50
12.5
25
50
50
50
6g
6h
6i
6l
with a halogen atom (Br and Cl, respectively) and had
a morpholino–acetamide chain in position 2.
The morpholino–acetamido analogue 6d, without a
p-substitution in the phenyl ring, showed only a consid-
erable anti-inflammatory action.
Evidently the morpholino moiety is the best sub-
stituent among the tested N-substituted acetamides,
whereas the presence of a lipophilic, electron-withdraw-
ing halogen group enhances activity level.
Furthemore a fairly remarkable antinociceptive effect
was evidenced for all compounds 6a–l (Table 4) at a
dose of 50 mg/kg, the most potent being 6h with an
ED50 of 47.91 (26.42–86.87) mg/kg per o.s., showing
the same antinociceptive property of indomethacin (5
mg/kg) at a dose of 50 mg/kg per o.s.
As a matter of fact the change of the aryl moiety in
position 2 of the benzindazole nucleus with a substi-
tuted acetamide function does not confirm the an-
tiarrhythmic action proved by derivatives 1 and typical
of pyrazole–acetamides 2.
Acknowledgements
It is worthwhile noting that compound 6l elicited the
maximum of anti-inflammatory activity and outstand-
ing analgesic effect, whereas the maximum of analgesic
activity was achieved by 6h. Both these derivatives
The authors would like to thank MURST (Cofi-
nanziamento Nazionale) and CNR for financial sup-
port, and A. Panaro, C. Rossi and F. Tuberoni for
analytical support.
carried out in position 3 a phenyl ring p-substituted
.

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S. Schenone et al. / Il Farmaco 55 (2000) 383–388
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