Design and synthesis of novel potent antinociceptive agents: Methyl-imidazolyl N-acylhydrazone derivatives

Article abstract of DOI:10.1016/S0968-0896(00)00152-8

This paper describes recent results of design, synthesis and pharmacological evaluation of new N-heterocyclic functionalized N-acylhydrazone compounds, belonging to the 2-methyl-imidazolyl-3-acylhydrazone class (4a-e). These compounds were planned by applying the molecular simplification strategy to propose the structural modifications on the previously described functionalized imidazo[1,2-a]pyridine 3-acylhydrazone series (2), which presented an important analgesic profile. This new series (4) was synthesized in order to investigate the possible pharmacophoric contribution of the N-heteroaromatic ring and N-acylhydrazone moieties to the analgesic activity. Compounds 4a-b are the most potent antinociceptive agents from this series. Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(00)00152-8

Bioorganic & Medicinal Chemistry 8 (2000) 2243±2248
Design and Synthesis of Novel Potent Antinociceptive Agents:
Methyl-imidazolyl N-Acylhydrazone Derivativesy
Juliana M. Figueiredo,a Celso de A. Camara,b Emanuel G. Amarante,a
Ana Luisa P. Miranda,a Fulvia M. Santos,a Carlos R. Rodrigues,a
Carlos Alberto M. Fragaa and Eliezer J. Barreiroa,b,
*
a
Â
Laboratorio de AvaliacËaÄo e Sõntese de Substancias Bioativas (LASSBio), Faculdade de Farmacia, Brazil
Â
Ã
Â
b
Â
Instituto de Quõmica, Universidade Federal do Rio de Janeiro, Ilha do FundaÄo, CP 68006, ZIP 21944-970,
Rio de Janeiro, RJ, Brazil
Received 15 October 1999; accepted 15 May 2000
AbstractÐThis paper describes recent results of design, synthesis and pharmacological evaluation of new N-heterocyclic functio-
nalized N-acylhydrazone compounds, belonging to the 2-methyl-imidazolyl-3-acylhydrazone class (4a±e). These compounds were
planned by applying the molecular simpli®cation strategy to propose the structural modi®cations on the previously described
functionalized imidazo[1,2-a]pyridine 3-acylhydrazone series (2), which presented an important analgesic pro®le. This new series (4)
was synthesized in order to investigate the possible pharmacophoric contribution of the N-heteroaromatic ring and N-acylhy-
drazone moieties to the analgesic activity. Compounds 4a±b are the most potent antinociceptive agents from this series. # 2000
Elsevier Science Ltd. All rights reserved.
Introduction
the previously active series (2) (path a, Fig. 1). Thus, we
assume that the imidazole ring introduced in 4, which
represents an isosteric replacement, could imitate the
aromatic system of the lead series (2) and give rise to a
di€erent hydrophobic character to the N-heterocyclic
framework linked to the para-substituted aryl-N-acyl-
hydrazone moiety, considered as the principal pharma-
cophoric unit involved in the analgesic activity.3
In the course of an ongoing research program aimed at
the design, synthesis and pharmacological evaluation of
new bioactive compounds acting at arachidonic acid cas-
cade enzymes level, we described previously the analgesic
and platelet anti-aggregating pro®le of N-phenylpyrazole
4-acylhydrazone (NAH) derivatives (1),1 functionalized
imidazo[1,2-a]pyridine 3-acylhydrazone derivatives (2)2
and N-phenyl-3-methyl-pyrazolo[3,4-b]pyridine 5-acyl-
hydrazone derivatives (3)3 (Fig. 1). Compounds from
series 2, particularly the para-bromophenyl derivative
(2b), presented an important analgesic pro®le when
orally administered to mice in doses of 100 mM.2
In the new imidazolic series of NAH derivatives (4), we
elected only the groups associated with the most active
derivatives in the previous lead series (e.g. 4a±b, NMe2,
Br)1 3 as the para-substituents of the phenyl ring at the
hydrazone motif. In addition, we decided to introduce
the 3,5-di-tert-butylphenol substituent (4e) due to the
known redox properties of this framework,4 which is
present in other anti-in¯ammatory derivatives.5,6 We
also decided to synthesize the unsubstituted phenyl ring
compound (4c) to verify the contribution of the para-
substituents present in 4a±b, as well as the isosteric 2-
furyl derivative (4d).7 9
As our studies progressed with new heterocyclic N-acyl-
hydrazone (NAH) derivatives as candidates to anti-
nociceptive agents, we designed a new class of azahetero-
cyclic NAH derivatives (4a±e). This series was structurally
planned by employing the molecular simpli®cation
strategy to introduce further structural modi®cations on
The rational design of compounds from series 4 may
provide evidence to the contribution of the N-hetero-
cyclic moiety in the anti-in¯ammatory and analgesic
activities, considering that the imidazolic system in the
new series (4) presents a lower hydrophobic character
yThis paper is contribution No. 49 from LASSBio.
*Corresponding author: Dr. LASSBio, Faculdade de Farmacia,
UFRJ, CCS, Cidade Universitaria, PO Box 68006, ZIP 21944-970,
Rio de Janeiro, RJ, Brazil. Tel.: +55-021-562-6644, fax: +55-021-
2733890; e-mail: eliezer@pharma.ufrj.br
0968-0896/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(00)00152-8

2244
J. M. Figueiredo et al. / Bioorg. Med. Chem. 8 (2000) 2243±2248
Scheme 1. Synthetic route for the preparation of imidazolyl NAH
derivatives (4). (a) MnO2, THF, re¯ux, 3 h, 85%; (b) I2, KOH, MeOH,
.
rt, 24 h; (c) NaCN, MnO2, MeOH, rt, 20 h, 70%; (d) NH2NH2 H2O,
EtOH, re¯ux, 1.5 h; (e) (H3C)2CˆO, EtOH, HCl(cat.), re¯ux, 12 h, 75%
(2 steps); (f) Ar-CHO, MeOH, HCl(cat.), re¯ux, 20 h.
chemical shift of the imidazolic hydrogen and C-2,
respectively. Thus, Montgomery and co-workers17 indi-
cated that in structurally related compounds possessing
an electron-withdrawing group (EWG) at C-4 and a
methyl substituent at C-5 from the imidazole ring, the
N-4 tautomer is favored and presents H-2 as a single
Figure 1. Design concept of the new imidazolyl NAH derivatives (4).
1
signal in the H NMR spectra up®eld shifted at d 2.53.
than the previous lead series (2). Furthermore, the
presence of the methyl group in the imidazole ring of 4
ensures the same ortho-relationship with the supposed
pharmacophoric unit as in the lead series (2) and could
prevent the typical tautomerism of the imidazolic system,
as observed in other therapeutically useful imidazolic
compounds.10
Due to the C-2 from the imidazole ring, the signal in the
13C NMR spectra occurs at d 134.2. These data are
consistent with the pattern observed for the ester (7) (see
Experimental). In general, the population of the imida-
zole tautomer can be estimated from the electronic
in¯uence of the ring substituents. In fact, the presence of
the electron-releasing group (ERG) favored the N-5
tautomer while the EWG favored the N-4 tautomer.18
Afterwards, as it was initially established by the syn-
thetic route, the hydrazide derivative (8) was prepared by
treating 7 with an 80% hydrazine hydrate solution.
Unfortunately, although the thin-layer chromatography
(TLC) indicated the formation of a new polar compound,
which was initially assumed as the desired hydrazide (8),
all attempts to obtain this key intermediate from the
reaction mixture were unsuccessful. In order to circum-
vent this experimental limitation, we decided to trap this
intermediate in situ, by carefully adding a carbonyl
compound. None of our attempts to use aromatic alde-
hydes were successful. Fortunately, by adding an excess of
acetone at the ®nal stage of the reaction, as indicated by
TLC analysis, the yield of the corresponding acetone±
hydrazone obtained 9 was almost 80%. The structure of
this stable and crystalline compound was fully spectro-
scopically characterized by the usual methods. The suc-
cess of this procedure over the aromatic aldehyde
addition was probably due to the distinct solubility
properties exhibited by the two di€erent classes of car-
bonyl compounds in the reaction medium. This proce-
dure is particularly advantageous because the hydrazone
adduct (9) can be stocked for several weeks at room
temperature and can be easily prepared in a molar scale.
Results and Discussion
The most convenient method previously developed for the
preparation of the desired imidazolic NAH compounds
(4a±e) was the condensation of imidazolyl hydrazide (8)
with elected aromatic aldehydes, which were performed in
the precedent series.1 3 The key intermediate hydrazide (8)
can be obtained from the oxidation of 5(4)-methyl-4(5)-
hydroxymethyl imidazole (5)11 to the corresponding
methyl ester derivative (7) followed by treatment with
hydrazine hydrate (Scheme 1). Therefore, we initially
decided to use the Yamada method12 for the conversion of
the aldehyde (6) into methyl 5-methylimidazole-4-carbox-
ylate (7). The oxidation of alcohol 511 using MnO2 in
THF,13 in re¯ux, gave a yield of 85% of the corresponding
aldehyde (6), as a pale-yellow solid.14 Unfortunately,
under Yamada conditions (i.e., I2 in methanolic KOH),
we were not able to obtain the desired methyl ester deri-
vative (7) from the aldehyde (6). In order to circumvent
this unexpected result, we proceeded with the investiga-
tion of the oxidation method described by Lai and
Anderson15 using MnO2/NaCN in methanol, directly
over alcohol (5), to obtain methyl ester (7). Fortunately,
this process gave a yield of 70% of methyl ester (7).16
The N-4 tautomer was found to be the major compound
in the ester (7) and its identity was revealed through the
After the key intermediate acetone±hydrazone adduct
(9) was prepared using an ecient method, a `trans-
hydrazonation' reaction was performed by treating 9
1
analysis of H and 13C NMR spectra, considering the

J. M. Figueiredo et al. / Bioorg. Med. Chem. 8 (2000) 2243±2248
2245
with an excess of the appropriate aromatic aldehyde in
acidic conditions (Scheme 1). As a matter of fact, using this
procedure, the new desired imidazolic NAH compounds
(4a±e) were obtained in adequate yields, as illustrated in
Table 1.
N-5 tautomer (conformation B0; Figure 2). However,
this one is 3 kcal/mol less stable.
The analgesic and anti-in¯ammatory activities of the
new imidazolyl hydrazone derivatives (4a±e) were eval-
uated using the acetic acid-induced mice abdominal
constrictions test21 and the carrageenan-induced rat paw
edema test,22 respectively. The results for the analgesic
activity are shown in Table 2. All compounds studied,
initially with a concentration of 100 mmol/kg, were able
to inhibit ca. 70% of abdominal induced constrictions,
with a higher potency than indomethacin (55.4%) and
dipyrone (42.1%), in the same dose. Thus, due to this
high analgesic activity, we decided to investigate these
compounds with half of the dose, i.e., with a con-
centration of 50 mmol/kg. In this concentration, all N-
acylhydrazone derivatives (4a±e) were more active than
dipyrone in the concentration of 100 mmol/kg. The most
potent analgesic compound (4b) showed 61.7% of inhi-
bition of the induced contortions, followed by the para-
dimethylaminophenyl compound (4a), which presented
58% of inhibition. Both compounds (4a±b) were more
active than indomethacin twice as much as its dose.
The (E)±(Z) diastereomeric ratio of these new NAH
compounds (4a±e) was next investigated by spectro-
scopic methods. The careful analysis of 1H and 13C
NMR spectra indicated the presence of the (Z)-isomer
formed in the `trans-hydrazonation' process as the major
one.19 The double-bond con®guration was identi®ed
1
by the HCˆN chemical shift in the H NMR spectra,
occurring in all derivatives, at the range of d 8.35±
8.50 ppm in accordance with previous observations
from the precedent series (1±2)1 3,19 (Table 1).
Molecular modeling studies using AM1 Hamiltonian20
were next carried out with the unsubstituted derivative
(4c) in order to investigate the conformational behavior
of the NAH motif around the C-4 from the imidazole
nucleus. From these studies we were able to observe
that the S-cis-like conformation A of the N-4 tautomer
from compound 4c was ca. 6.0 kcal/mol more stable
than the corresponding S-trans A0 conformation (Fig.
2). Besides, this conformation (A) (Fig. 2) could be
favored by a ®ve-member-like intramolecular hydrogen
bond involving the hydrogen atom of the N-acylhy-
drazone moiety and the nitrogen atom N-3 of the imi-
dazole ring. Hydrogen bonding was also observed in the
The results of the anti-in¯ammatory bioassay for series
4 are shown in Table 3. Compounds 4a±e inhibited sig-
ni®cantly 35±45% of the edema formation for 3 h after
the induction. In this bioassay, 4b was the most active
Table 2. E€ects of 5-methyl-imidazolyl-4-acylhydrazone derivatives
(4a-±e), dipyrone and indomethacin in the inhibition of abdominal
constrictions induced by acetic acid (0.6%, ip) in mice
Compound
Dosea
(mmol/kg)
nb
Constrictions
number
Inhibition
(%)c
Vehicle control
(Arabic gum 5%)
Dipyrone
Indomethacin
4a
Ð
10
93.8Æ4.9
Ð
100
100
100
50
100
50
100
50
100
50
9
14
10
8
9
8
10
7
9
9
10
9
54.3Æ5.5
41.9Æ4.4
31.3Æ5.5
37.5Æ3.4
26.8Æ3.4
34.1Æ2.8
22.5Æ4.9
43.0Æ5.3
26.2Æ3.0
40.2Æ3.3
21.9Æ3.8
43.3Æ3.8
42.1*
55.3*
66.6*
58.0*
71.4*
61.7*
76.0*
51.7*
72.0*
54.8*
76.6*
51.3*
4b
4c
4d
4e
100
50
aAll compounds were administered po.
bn=number of animals.
c% of inhibition obtained by comparison with vehicle control group.
*P<0.05 (Student's t-test). Results are expressed as mean Æ SEM.
Figure 2. Ring isomerism and conformers of the new class of NAH
derivatives (4).
Table 1. Physical properties and yields of 5-methyl-imidazolyl 4-acylhydrazone derivatives (4a±e)
Compound
Molecular formula
Molecular weight
Yield (%)
mp (ꢀC)
d (ppm) N=CH
4a
4b
4c
4d
4e
C
C
14H17N5O
12H11N4OBr
C12H12N4O
271
307
228
218
356
69
76
73
93
60
247±250 (dec.)
>250 (dec.)
>250 (dec.)
158±160
8.35
8.50
8.48
8.47
8.37
C10H10N4O2
C20H28N4O2
176±179

2246
J. M. Figueiredo et al. / Bioorg. Med. Chem. 8 (2000) 2243±2248
Table 3. E€ects of 5-methyl-imidazolyl-4-acylhydrazone derivatives
(4a±e) and indomethacin in the inhibition of carrageenan-induced rat
paw edema
compound (2) by the imidazole ring in the new series of
imidazolyl N-acylhydrazone derivatives (4) represents an
optimization of the analgesic activity in this class of
derivatives. Moreover, compounds 4a and 4b were iden-
ti®ed as the most potent analgesic agents, suggesting that
the imidazole ring plays an important role in the
analgesic activity observed.
Compound
Time nb
(h)a
Dosec
(mmol/kg)
Volume
variation
(mL)d
Inhibition
(%)e
1
Ð
Ð
Ð
267.2Æ47.2
564.8Æ52.1
773.9Æ36.2
104.9Æ13.5
140.3Æ13.8
153.2Æ11.9
169.0Æ19.2
358.1Æ31.7
485.2Æ34.8
116.6Æ10.8
375.4Æ41.9
509.4Æ49.4
153.4Æ22.8
317.3Æ24.1
444.5Æ44.8
191.8Æ25.8
411.1Æ23.6
513.8Æ31.8
157.3Æ22.9
326.4Æ35.1
479.5Æ60.1
Ð
Ð
Ð
Vehicle control
(Arabic gum 5%)
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
9
7
60.7*
75.1*
80.2*
36.7*
36.6*
37.3*
56.4*
33.5*
34.2*
42.6*
43.8*
42.6*
28.2*
27.2*
33.6*
41.1*
42.2*
38.0*
Experimental
Chemistry
Indomethacin
100
100
100
100
100
100
4a
4b
4c
4d
4e
12
11
12
9
Infrared (IR) spectra were obtained with a Perkin±
Elmer 1600 spectrometer by using potassium bromide
plates. Nuclear magnetic resonance (1H NMR and 13C
NMR) spectra were determined in dimethylsulfoxide
(DMSO-d6) containing ca. 1% TMS as an internal
standard with AC 200 Bruker and VXR 300 Varian
and Gemini 300 Varian spectrophotometers. Splitting
patterns are as follows: s, singlet; d, doublet; m, multi-
plet; b, broad. The signals due to the hydrogen attached
to the imidazole ring are indicated as Im-H. The mass
spectra were obtained with a GC/VG Micromass 12 at
70 eV. Microanalysis data was obtained using a Perkin±
Elmer 240a analyzer. Melting points were determined
with a Quimis 340 apparatus and are uncorrected.
8
aTime after carrageenan injection (0.1 mg/paw).
bn=number of animals.
cAll compounds were administered po.
dVolume variation is the di€erence between the volumes of carragee-
nan treated paw and saline treated paw.
The progress of all reactions was monitored by TLC,
which was performed on 2.0Â6.0 cm aluminum sheets
precoated with silica gel 60 (HF-254, Merck) to a
thickness of 0.25 mm. The developed chromatograms
were viewed under ultraviolet light (254±265 nm) and
treated with iodine vapor. Melting points were deter-
mined through a Quimis 120 capillary melting point
apparatus and are uncorrected. The solvents employed
in the reactions were previously distilled.
e% of inhibition obtained by comparison with vehicle control group.
* P<0.05 (Student's t-test). Results are expressed as mean Æ SEM.
compound presenting 56.4% of inhibition at the ®rst
hour with a concentration of 100 mmol/kg.
The anti-in¯ammatory pro®le of this series of NAH (4)
was clearly distinct from that previously described for
compounds of series 2.1,2,23 In fact, the 2-furyl derivative
from the N-phenylpyrazolic series (2) was not able to
present any important e€ect in the carrageenan-induced
rat paw edema test.23,24 Curiously, the corresponding
para-bromophenyl derivative belonging to this series (2)
was not able to present any anti-in¯ammatory activity
in identical concentrations in the same pharmacological
assay.2 Furthermore, the e€ect of these compounds (4)
in the gastric mucosa was also investigated, indicating a
weak ulcerative behavior for compound 4c when used in
the concentration of 300 mmol/kg.
Methyl 5-methyl-imidazole-4-carboxylate (7).15 To a mix-
ture of 2.24 g (20 mmol) of 4(5)-methyl-5(4)-hydroxy-
methyl-imidazole (5) and 1.63 g of sodium cyanide
(33.2 mmol) in 200 mL of methanol, was added 8.7 g
activated manganese dioxide15 (100 mmol) over 5 min.
The mixture was stirred for 20 h at room temperature
and the suspension was ®ltered through Celite, and
washed with dichloromethane (3Â20 mL). The organic
fractions were combined, dried over anhydrous sodium
sulfate, ®ltered and evaporated under reduced pressure,
to give 2.24 g (80%) of the methyl ester (7) as a white
These results suggest that this new series of imidazolic
NAH derivatives (4) presents a very important analgesic
activity pro®le in comparison with the most hydrophobic
series (2) previously described. Therefore, the N-hetero-
aromatic ring of derivatives (4) is probably responsible
for the improvement of the analgesic activity due to the
less hydrophobic character of the imidazolic ring and a
nitrogen atom is sterically less hindered in this series.
solid, mp 171±173 ꢀC; MS (70 eV) relative abundance:
1
140 (M+, 100%), 125 (21%), 109 (95%); IR (KBr) cm
:
1
1708 (n CˆO); H NMR (200 MHz, CDCl3) d 7.62 (s,
1H, Im H-2), 3.95 (s, 3H, OCH3), 2.59 (s, 3H, Im-CH3);
13C NMR (50 MHz, CDCl3) d 163.5 (CˆO), 137.5 (C-5),
135.0 (C-2), 132.0 (C-4), 52.5 (OCH3), 14.0 (Im-CH3).
(Isopropylidene)-5-methyl-imidazole-4-carbohydrazide (9).
One gram of 80% aqueous hydrazine monohydrate
(20 mmol) was added to a solution of 1 g of methyl ester (7)
(7.14 mmol) in 2.5 mL of absolute ethanol and the
resulting mixture was re¯uxed for 4 h. The solvent was
evaporated under reduced pressure and to the crude
resulting oil was added 15 mL of n-hexane, 5 mL of
Conclusions
Our results indicate that the isosteric replacement of the
imidazo[1,2-a]pyridine system from the original lead

J. M. Figueiredo et al. / Bioorg. Med. Chem. 8 (2000) 2243±2248
2247
ethanol, 5 mL of acetone, one drop of hydrochloridric
acid and the mixture was re¯uxed for 2 h. The evapora-
tion under reduced pressure and the ®ltration of the
resulting solid in Buchner furnished 0.91 g (71%) of the
acetone±ꢀhydrazone derivative (9) as a yellow solid, mp
245±250 C (dec.); MS (70 eV) 180 (M+, 5%); 165 (5%),
109 (100%); IR (KBr) cm 1: 3385, 3252 and 3151 (n N±
trans-hydrazonation of 9 with benzaldehyde as a yellow
solid, mp>250 ꢀC; MS (70 eV) relative abundance: 228
1
(M+, 7%), 125 (30%), 109 (100%); IR (KBr) cm
:
3314, 3207 and 3174 (n N±H), 1668 (n CˆO), 1593 (n
CˆC); 1H NMR (200 MHz, DMSO-d6) d 12.50 (br, 1H,
Im-NH), 11.42 (s, 1H, CONH), 8.48 (s, 1H, NˆCH),
7.70 (s, 1H, Im H-2), 7.60 (m, 5H, Ph), 2.55 (s, 3H, Im-
CH3); 13C NMR (50 MHz, DMSO-d6) d 159.8 (CˆO),
145.0 (CHˆN), 134.1 (C-10), 133.7 (Im C-2), 132.8 (Im
C-5), 131.7 (C-30 and C-50), 128.7 (C-20 and C-60), 128.0
(Im C-4), 122.7 (C-40), 10.6 (Im-CH3). Anal. calcd for
C12H12N4O: C, 63.13; H, 5.30; N, 24.56. Found: C,
63.18; H, 5.39; N, 24.48.
1
H), 1668 (n CˆO); H NMR (200 MHz, DMSO-d6) d
9.85 (br, 1H, CONH), 7.60 (s, 1H, Im H-2), 3.50 (br, 2H,
NH2), 2.45 (s, 3H, Im-CH3), 2.00 (s, 3H, NˆCCH3), 1.90
(s, 3H, NˆCCH3); 13C NMR (50 MHz, DMSO-d6) d
160.0 (CˆO), 154.5 (Me2CˆN), 134.0 (C-2), 133.0 (C-
5), 128.5 (C-4), 25.5 (CH3), 17.0 (CH3), 14.0 (Im-CH3).
General procedure for the preparation of N-acylhydra-
zone derivatives (4a±e). Equimolar amounts of the
appropriate aromatic aldehydes and two drops of
hydrochloridric acid, acting as a catalyst, were added to a
solution of acetone±hydrazone derivative (9) in 20 mL of
ethanol. At the end of the reaction, which was monitored
by TLC analysis, compounds 4a±e were isolated by
concentrating the reaction mixture under reduced pres-
sure, followed by the addition of dichloromethane (ca.
25 mL), cooling and ®ltration under vacuum.
(20-Furylidene)-5-methyl-imidazole-4-carbohydrazide (4d).
Derivative 4d was obtained with a yield of 93% by
trans-hydrazonation of 9 with furfuraldehyde as a yellow
solid, mp 158±160 ꢀC; MS (70 eV) relative abundance:
1
218 (M+, 18%), 125 (16%), 109 (100%); IR (KBr) cm
:
3468, 3332 and 3214 (n N±H), 1662 (n CˆO) and 1592 (n
1
CˆC); H NMR (200 MHz, DMSO-d6) d 11.75 (br, 1H,
Im-NH), 8.47 (s, 1H, NˆCH), 8.04 (br, 1H, CONH), 7.82
(s, 1H, C-50), 6.89 (s, 1H, C-30), 6.78 (s, 1H, Im H-2), 6.6
(s, 1H, C-40), 2.6 (s, 3H, Im-CH3); 13C NMR (50 MHz,
DMSO-d6) d 158.7 (CˆO), 149.6 (C5), 144.8 (CHˆN),
136.8 (C-20), 133.6 (Im C-2), 133.3 (Im C-5), 126.6 (Im C-
4), 112.9 (C-40), 112.1 (C-30) and 10.6 (Im-CH3). Anal.
calcd for C10H10N4O2: C, 55.03; H, 4.62; N, 25.68.
Found: C, 55.11; H, 4.69; N, 55.08.
(4-Dimethylaminebenzylidene)-5-methyl-imidazole-4-car-
bohydrazide (4a). Derivative 4a was obtained with a
yield of 69% by trans-hydrazonation of 9 with 4-dime-
thylaminobenzaldehyde as a yellow solid, mp 247±250 ꢀC
(dec.); MS (70 eV) relative abundance: 271 (M+, 74%),
163 (52%), 146 (100%), 125 (7%), 109 (43%); IR (KBr)
cm1: 3468, 3432, 3386 and 3236 (n N±H), 1664 (n CˆO),
(3,5-Di-tert-butyl-4-hydroxybenzylidene)-5-methyl-imida-
zole-4-carbohydrazide (4e). Derivative 4e was obtained
with a yield of 60% by trans-hydrazonation of 9 with
3,5-di-tert-butyl-4-hydroxybenzaldehyde as a yellow
solid, mp 176±179 ꢀC; MS (70 eV) relative abundance:
356 (M+, 25%), 341 (3%), 248 (3%), 233 (17%), 125
(27%), 109 (100%); IR (KBr) cm 1: 3438 (n O±H),
3318, 3376 and 3167 (n N±H), 1651 (n CˆO), 1605 (n
1
1599 (n CˆC); H NMR (200 MHz, DMSO-d6) d 12.70
(br, 1H, Im-NH), 11.00 (br, 1H, CONH), 8.35 (s, 1H,
CHˆN), 7.63 (s, 1H, Im H-2), 7.50 (d, 2H, C-40, J=
15 Hz), 6.75 (d, 2H, C-30, J=15 Hz), 2.96 (N(CH3)2),
2.45 (s, 3H, Im-CH3); 13C NMR (50 MHz, DMSO-d6) d
159.8 (CˆO), 151.6 (C-40), 147.7 (CHˆN), 133.7 (Im C-
2), 132.5 (Im C-5), 128.6 (C-30 and C-50), 128.0 (Im C-4),
122.0 (C-10), 112.0 (C-20 and C-60), 40.0 (N(CH3)2) and
11.0 (Im-CH3). Anal. calcd for C14H17N5O: C, 61.96; H,
6.32; N, 25.82. Found: C, 62.07; H, 6.34; N, 25.90.
1
CˆC); H NMR (200 MHz, DMSO-d6) d 12.34 (br, 1H,
Im-NH), 10.92 (s, 1H, CONH), 8.37 (s, 1H, NˆCH),
7.60 (s, 1H, Im H-2), 7.45 (s, 2H, H6-H2), 7.24 (s, 1H,
OH), 2.48 (s, 3H, Im-CH3), 1.41 (s, 18H, C(CH3)3); 13C
NMR (50 MHz, DMSO-d6) d 159.5 (CˆO), 155.7 (C-40),
147.7 (NˆCH), 139.1 (C-30 and C-50), 133.3 (Im C-4),
132.1 (Im C-2), 129.0 (C-1), 126.0 (Im C-5), 123.6 (C-20
and C-60), 34.4 (C(CH3)3), 30.1 (C(CH3)3), 10.4 (Im-
CH3). Anal. calcd for C20H28N4O2: C, 67.37; H, 7.92;
N, 15.72. Found: C, 67.42; H, 7.89; N, 15.78.
(4-Bromobenzylidene)-5-methyl-imidazole-4-carbohydra-
zide (4b). Derivative 4b was obtained with a yield of
76% by trans-hydrazonation of 9 with 4-bromo-
benzaldehyde, as a yellow solid, mp>250 ꢀC (dec.); MS
(70 eV) relative abundance: 306 (M+, 5%), 308 (5%),
198 (5%), 200 (5%), 125 (33%), 109 (100%); IR (KBr)
cm 1: 3471, 3322, 3386 and 3186 (n N±H), 1668 (n CˆO),
Molecular modeling
1
1591 (n CˆC); H NMR (200 MHz, DMSO-d6) d 12.60
(br, 1H, Im-NH), 11.40 (br, 1H, CONH), 8.50 (s, 1H,
CHˆN), 7.68 (s, 1H, Im H-2), 7.65 (m, 2H, C-20 and C-
60), 7.45 (m, 2H, C-30 and C-50), 2.50 (s, 3H, Im-CH3);
13C NMR (50 MHz, DMSO-d6) d 159.8 (CˆO), 146.4
(CHˆN), 134.8 (Im C-2), 133.7 (C-10), 129.6 (C-40), 129.2
(Im C-5), 128.8 (C-30 and C-50), 127.9 (Im C-4), 126.9 (C-
20 and C-60), 10.7 (Im-CH3). Anal. calcd for C12H11
BrN4O: C, 47.06; H, 3.62; N, 18.30. Found: C, 46.98; H,
3.69; N, 18.38.
All modeling procedures were performed on a Silicon
Graphics workstation IRIX 6.3 (CPU R5000). The
molecular models were built and pre-optimized on the
Builder module of InsightII (Molecular Simulations
Inc., San Diego, CA) and conformational analysis was
done using the CVFF force®eld within Search-Compare
module in InsightII environment (Molecular Simula-
tions Inc., San Diego, CA).
Conformational analysis by molecular mechanics was
done by ®ltering the conformations in a range of 5 kcal/
mol. The starting conformation was, in each case, the
(Benzylidene)-5-methyl-imidazole-5-carbohydrazide (4c).
Derivative 4c was obtained with a yield of 73% by

2248
J. M. Figueiredo et al. / Bioorg. Med. Chem. 8 (2000) 2243±2248
minimized structure after building structures for 4c. The
dihedral angles were de®ned as follows: ꢀ1=0±180ꢀ,
ꢀ2=180ꢀ, ꢀ3=0±360ꢀ with increments of 60ꢀ and ꢀ4=0±
180ꢀ, with increments of 60ꢀ (see Figure 2 for torsion
angle de®nition).
Fellowships from CNPq-Br (to CAC, EJB, ALPM and
CAMF) are gratefully acknowledged. We wish to thank
the analytical laboratory of UFRRJ-Br and NPPN/
UFRJ-Br, for the mass and NMR spectra.
The conformations obtained from molecular mechanics
were then reoptimized by AM1, using the keywords
AM1, MMOK, EF, HESS=1, GRAD and PRECISE.20
Pharmacology
References
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pounds 4a±e were administered orally (100 mmol/kg; 0.1
mL/20 g) as a suspension in 5% Arabic gum in saline
(vehicle). Indomethacin (100 mmol/kg) and dipyrone (100
mmol/kg) were used as standard drugs in the same con-
ditions. Acetic acid solution was administered ip 1 h later.
Ten minutes following ip acetic acid injection, the
number of constrictions per animal was recorded for 20
min. Control animals received an equal volume of vehicle.
Analgesic activity was expressed as % of inhibition of
constrictions when compared with the control group.
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Statistics. Results are expressed as the mean ÆSEM
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Acknowledgements
This work was supported by grants from CNPq-Br
(50.0033/96-5), Fundacao Jose Bonifacio-UFRJ (Br)
(grant 4825-9, 4626-6) and Pronex (FINEP 0888).
24. Ormelli, C. B.; Barreiro, E. J.; Miranda, A. L. P. Abstr.
XIII ReuniaÄo Anual da FederacËaÄo de Sociedades de Biologia
Experimental 1998, 05.003.