Structural studies of 4-aminoantipyrine derivatives

Article abstract of DOI:10.1016/j.molstruc.2005.05.016

Reaction of 4-aminoantipyrine with acetylacetone, ethyl acetoacetate, benzoyl isothiocyanate, phenyl isothiocyanate, maleic anhydride and methoxymethylene Meldrum's acid afforded a series of new antipyrine derivatives. The antibacterial activity of the synthesized compounds against Micrococcus luteus ATCC 9341, Staphilococcus aureus ATCC 29737, and Escherichia coli ATCC 8739 was evaluated and the minimal inhibitory concentration determined. Modest activity was found only to the maleamic acid obtained from the reaction of 4-aminoantipyrine and maleic anhydride. ¹H NMR investigation of this maleamic acid showed that it is slowly converted to the corresponding toxic maleimide. The structures of three derivatives were determined by X-ray diffraction analysis.

Full text of DOI:10.1016/j.molstruc.2005.05.016

Journal of Molecular Structure 752 (2005) 32–39
www.elsevier.com/locate/molstruc
Structural studies of 4-aminoantipyrine derivatives
a,
a
Silvio Cunha , Shana M. Oliveira , Manoel T. Rodrigues Jr. , Rodrigo M. Bastos ,
a
a
*
a
Jailton Ferrari , Cecılia M.A. de Oliveira , Lucılia Kato , Hamilton B. Napolitano ,
b
b
c
´
´
Ivo Vencatod, Carlito Lariuccid
a
´
Instituto de Quımica, Universidade Federal da Bahia, Campus de Ondina, 40170-290 Salvador—BA, Brazil
b
´ ´
Instituto de Quımica, Universidade Federal de Goias, CP 131, 74001-970 Goiania—GO, Brazil
ˆ
c
ˆ ´ ´ ´
Ciencias Exatas e Tecnologicas, Universidade Estadual de Goias, BR 153, Km 98, 75133-050 Anapolis—GO, Brazil
d
´ ´
Instituto de Fısica, Universidade Federal de Goias, CP 131, 74001-970 Goiania—GO, Brazil
ˆ
Received 4 March 2005; revised 25 April 2005; accepted 9 May 2005
Available online 1 July 2005
Abstract
Reaction of 4-aminoantipyrine with acetylacetone, ethyl acetoacetate, benzoyl isothiocyanate, phenyl isothiocyanate, maleic anhydride
and methoxymethylene Meldrum’s acid afforded a series of new antipyrine derivatives. The antibacterial activity of the synthesized
compounds against Micrococcus luteus ATCC 9341, Staphilococcus aureus ATCC 29737, and Escherichia coli ATCC 8739 was evaluated
and the minimal inhibitory concentration determined. Modest activity was found only to the maleamic acid obtained from the reaction of
4-aminoantipyrine and maleic anhydride. 1H NMR investigation of this maleamic acid showed that it is slowly converted to the
corresponding toxic maleimide. The structures of three derivatives were determined by X-ray diffraction analysis.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Enaminones; Thioureas; Meleimide
1. Introduction
derivatives in search for antibacterial agents. In this work,
we describe our results concerning the syntheses, X-ray
structural analysis, and the antimicrobial activity of these
substances.
The syntheses of 4-aminoantipyrine derivatives have
attracted the attention of several research groups due to their
potential biological activities [1]. In this context, broad
spectra of bioactive 4-aminoantipyrine derivatives and their
metal complexes have been investigated and diversities of
bioactivities such as analgesic [2,3], antiinflammatory [3],
antimicrobial [4,5], and anticancer activity [6] have been
reported. The antibacterial activity caught our attention
because antimicrobial resistance developed by important
pathogens has increased in the last decade [7]. Besides,
emerging and re-emerging bacterial infectious diseases still
causes death and disability worldwide [8].
2. Experimental
2.1. Reagents and techniques
´
Melting points were determined on a Microquımica
MQAPF 301 hot plate apparatus and are uncorrected.
Infrared spectra were recorded as KBr discs on a FT-IR
BOMEM MB100 instrument. NMR spectra were obtained
1
As part of our continuing interest on the syntheses of
potential bioactive compounds [9], including enaminone
[10], we undertook the syntheses of 4-aminoantipyrine
for H at 300 MHz and for 13C at 75 MHz using a Varian
Gemini 300 spectrometer. Chemical shifts are reported in
ppm units downfield from reference (internal TMS). EIMS
spectra were measured on a HP MSD 5973 apparatus with
direct probe insertion at 70 eV. Elemental analyses were
performed on a 2400 CHN Perkin Elmer. Meldrum’s acid
and methoxymethylene Meldrum’s acid were prepared
according to known procedures [11]. The single crystal
X-ray data collections of compounds 7 and 14 were carried
*
Corresponding author. Tel.: C55 71 32375784; fax: C55 71 32374117.
E-mail address: silviodc@ufba.br (S. Cunha).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.05.016

S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
33
1
´
out on a Nonius CAD-4 diffractometer at Instituto de Fısica/
1528, 1490, 1157. H NMR (CDCl3): 2.27 (3H, s); 3.13
(3H, s); 7.25–7.63 (8H, m); 7.86 (2H, d, J 7.7 Hz); 9.36 (1H,
s); 11.53 (1H, s). 13C NMR (CDCl3): 12.1 (CH3); 35.8
(CH3); 109.4 (C); 124.4 (CH); 126.9 (CH); 127.6 (CH);
129.0 (CH); 129.2 (CH); 131.7 (C); 133.5 (CH); 134.7 (C);
151.8 (C); 161.3 (C); 166.7 (C); 181.5 (C). Anal. calcd for
C19H18SN4O2: C, 62.28%; H, 4.95%; N, 15.29%. Found: C,
62.02%; H, 5.02%; N, 15.21%.
UFG. Compound 11 was collected at the University of
Pittsburgh during ACA 2003 Summer Course at Kappa
CCD at low temperature.
2.2. Synthetic procedures
2.2.1. (Z)-4-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-
1H-4-pyrazolylamino)-3-penten-2-one (3)
A net solution of 4-aminoantipyrine (1.05 g, 0.51 mmol)
and acetylacetone (1 mL, 1.0 mmol) was left at room
temperature with stirring for 20 min. The yellow solid that
formed was decanted and triturated with ethyl ether,
affording 3 (1.61 g, 80%, m.p. 127.3–129.0 8C). IR (KBr):
2.2.4. 4-Anilino(thioxo)methylamino-1,5-dimethyl-
2-phenyl-2,3-dihydro-1H-3-pyrazolone (9)
To a solution of 4-aminoantipyrine (1.04 g, 5.1 mmol) in
benzene (10 mL) phenyl isothiocyanate (0.65 mL,
5.4 mmol) was added dropwise under stirring and ice-bath
cooling. The reaction mixture was left for 3 h at room
temperature after which time the solvent was evaporated
and crude solid was triturated with petroleum ether.
Recrystallization with CH2Cl2/petroleum (4:1) ether
afforded 9 (1.57 g, 91%, m.p. 198–200 8C) as yellow
needles. IR (KBr): nmax (cmK1) 3420, 3277, 1632, 1567,
1
nmax (cmK1) 1674, 1617, 1561, 1270. H NMR (CDCl3):
dZ1.95 (s, 3H); 2.05 (3H, s); 2.21 (3H, s); 3.06 (3H, s); 5.20
(1H, s); 7.25–7.47 (5H, m); 11.52 (1H, s). 13C NMR
(CDCl3): 10.6 (CH3); 19.3 (CH3); 29.1 (CH3); 36.1 (CH3);
97.4 (CH); 110.6 (C); 124.1 (CH); 126.9 (CH); 129.2 (CH);
134.8 (C); 150.8 (C); 162.0 (C); 163.3 (C); 196.4 (C). MS,
m/z (%): 287 (0.9) [MCC2], 286 (8) [MCC1], 285 (42)
[MC], 195 (48%). Anal. calcd for C16H19N3O2: C, 67.35%;
H, 6.71%; N, 14.73%. Found: C, 67.42%; H, 6.72%; N,
14.61%.
1
1532, 1294. H NMR (CDCl3CDMSO-D6): 2.24 (3H, s);
3.12 (3H, s); 7.11 (1H, t, J 7.2 Hz); 7.26–7.33 (3H, m); 7.38
(2H, d, J 7.2 Hz); 7.46–7.51 (4H, m); 8.85 (1H, br s); 9.82
(1H, s). 13C NMR (CDCl3CDMSO-D6): 11.0 (CH3); 35.6
(CH3); 108.8 (C); 123.9 (CH); 124.5 (CH); 126.4 (CH);
128.1 (CH); 128.9 (CH); 134.8 (C); 139.7 (CH); 161.7 (C);
181.4 (C). Anal. calcd for C18H18SN4O: C, 63.88%; H,
5.36%; N, 16.56%. Found: C, 63.72%; H, 5.20%; N,
16.33%.
2.2.2. Ethyl (Z)-3-(1,5-dimethyl-3-oxo-2-phenyl-2,
3-dihydro-1H-4-pyrazolylamino)-2-butenoate (5)
A net solution of 4-aminoantipyrine (0.80 g, 3.92 mmol)
and ethyl acetoacetate (1 mL, 7.85 mmol) was left at
room temperature with stirring for 20 min. The yellow
solid that formed was decanted and triturated with ethyl
ether, affording 1.64 g. To the ethyl ether solution
petroleum ether was added and allowed to cool in the
freezer (K25 8C) and more 0.09 g of the yellow solid
precipitated, affording 5a (1.73 g, 95%, m.p. 128–130 8C).
IR (KBr): nmax (cmK1) 3245, 1679, 1661, 1605, 1540, 1135.
1H NMR (CDCl3): 1.26 (3H, t, J 7.2 Hz); 1.92 (3H, s); 2.22
(3H, s); 3.06 (3H, s); 4.12 (2H, q, J 7.2 Hz); 4.71 (1H, s);
7.29–7.48 (5H, m); 9.39 (1H, s). 13C NMR (CDCl3): 10.5
(CH3); 14.6 (CH3); 19.5 (CH3); 36.2 (CH3); 58.6 (CH2);
85.8 (CH); 111.2 (C); 123.9 (CH); 126.7 (CH); 129.2 (CH);
134.9 (C); 151.5 (C); 161.7 (C); 162.6 (C); 170.4 (C). Anal.
calcd for C17H21N3O3: C, 64.75%; H, 6.71%; N, 13.32%.
Found: C, 64.72%; H, 6.68%; N, 13.41%.
2.2.5. (Z)-3-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-
1H-4-pyrazolylcarbamoyl)-2-propenoic acid (11)
A solution of 4-aminoantipyrine (0.10 g, 0.5 mmol) and
maleic anhydride (0.05 g, 0.5 mmol) in ethyl acetate
(10.0 mL) was left at room temperature with stirring for
30 min (the solution turned yellow and a precipitate began
to form after 15 min), after which time the solid that formed
was separated from the solvent and was recrystallized from
CHCl3 affording 11 (0.15 mg, 99.6%, m.p. 177.6–179.9 8C)
as a pale yellow solid. IR (KBr): nmax (cmK1) 3349, 1676,
1646. 1H NMR (CDCl3): 2.27 (s, 3H), 3.27 (s, 3H),
5.95 (1H, d, J 12.9 Hz), 6.40 (1H, d, J 12.9 Hz), 7.36 (2H, d,
J 7.2 Hz), 7.50–7.60 (3H, m); 10.82 (1H, s).
2.2.6. 1-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-
4-pyrazolyl)-2,5-dihydro-1H-2,5-azoledione (12)
2.2.3. 1,5-Dimethyl-3-oxo-2-phenyl-4-phenylcarboxamido
(thioxo)methylamino-2,3-dihydro-1H-pyrazole (7)
To a solution of 4-aminoantipyrine (2.01 g, 10.0 mmol)
in CHCl3 (8.0 mL) a solution of maleic anhydride (1.01 g,
10.0 mmol) in CHCl3 (3.0 mL) was added dropwise with
stirring and ice-bath cooling for 15 min., after which time
the solvent was evaporated. To the solid that formed acetic
anhydride (5.0 mL) and sodium acetate (0.51 g, 6.2 mmol)
was added and the reaction mixture was heated at reflux for
30 min, and then it was cooled to room temperature and
10 mL of water was added and extracted with CH2Cl2 (2!
10 mL). The organic phase was dried with MgSO4, filtered
To a solution of 4-aminoantipyrine (1.97 g, 9.7 mmol) in
benzene (10 mL) benzoyl isothiocyanate (1.4 mL,
10.4 mmol) was added dropwise under stirring and ice-
bath cooling. The reaction mixture was left for 3 h at room
temperature after which time the solvent was evaporated
and crude solid was triturated with petroleum ether.
Recrystallization with CH2Cl2/petroleum (4:1) ether
afforded 7 (3.16 g, 89%, m.p. 210 8C) as yellow needles.
IR (KBr): nmax (cmK1) 3420, 3127, 1677, 1648, 1625, 1590,

34
S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
and the solvent evaporated under reduced pressure. The
residual maroon oleo was treated with CH2Cl2/petroleum
ether (4:1) affording a pale maroon oil. The solvent was
decanted from the oleo and the residue was dried under
reduced pressure, yielding 12 (1.89 g, 62%, m.p. 29.4–
32.0 8C) as a hygroscope bright yellow solid. IR (KBr): nmax
2.4. Antibacterial assay
The bacteria used in this experiment were Micrococcus
luteus ATCC 9341, Staphilococcus aureus ATCC 29737,
and Escherichia coli ATCC 8739. For the bioautography
bioassay [15], pure compounds were applied to Silica gel
TLC plates at concentrations of 1–3 mg in EtOH or CHCl3.
TLC plates were dried until complete removal of solvents.
The inoculum was prepared by culturing each organism in
sterile Miller–Hinton broth at 37 8C to a turbidity equivalent
to McFarland 0.5 standard (108 CFU/mL). One microliter of
each diluted inoculum (104K106 CFU/mL) was added in
10 mL of Mueller-Hinton agar medium (MHA-DIFCO),
and distributed over TLC plates. After the solidification, the
TLC plates were incubated at 36 8C for 24 h. Plates were
sprayed with a 2 mg/mL of 3-(4,5-dimethylthiazol-2-yl)-
2,5-diphenyltetrazolium bromide (MTT, thiazolyl blue) and
the clear zones on the chromatogram indicated inhibition of
growth. The minimal inhibitory concentration was deter-
mined by serial dilution using 96-well microplates [16]. The
compounds were solubilized in 0.5 mL of the dimethyl
sulfoxide (DMSO) and diluted in a sterile 0.85% saline
solution containing Tween 80. This solution was added into
the first column of the wells on the microplates and serially
diluted in Miller–Hinton broth to obtain a concentration
range of 15.6–1000 mg/mL. The wells in the dilution series
were inoculated with the cultures prepared as described
above. Finally, microplates were incubated overnight at
37 8C and the results were marked by observing the change
of color when p-iodonitrotetrazolium violet (INT, Sigma)
was added. Negative control (DMSO and Miller–Hinton
broth) as well as positive control (chlorophenicol) were
included in each assay. All data represent two replicated
experiments per microorganism.
1
(cmK1) 1716, 1655, 1567, 1488, 1297. H NMR (CDCl3):
2.18 (3H, s); 3.20 (3H, s); 6.86 (s, 2H); 7.30–7.53 (m, 5H).
13C NMR (CDCl3): 10.9 (CH3); 35.4 (CH3); 124.8 (CH);
124.4 (CH); 127.3 (CH); 129 (CH); 129.2 (CH); 134.3 (C);
133.8 (CH); 152.8 (C); 160.9 (C); 163.3 (C); 169.1 (C).
2.2.7. 5-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-
4-pyrazolylaminomethylene)-2,2-dimethyl-1,3-dioxane-4,
6-dione (14)
A solution of Meldrum’s acid (0.15 g, 1.1 mmol) in
trimethyl orthoformate (1.5 mL,19.6 mmol) was heated at
reflux for 3 h after which time the solvent was evaporated.
The solid that formed was dissolved in CH3OH (2 mL) and
4-aminoantipyrine (0.21 g, 1.0 mmol) in CH3OH (3 mL)
was added and the solution was allowed to stand at room
temperature with stirring for 15 min (a precipitate began to
form after a few minutes). The solvent was evaporated and
the crude solid was recrystallized from CH2Cl2/petroleum
ether (4:1) affording 14 (0.28 g, 78%, m.p. 211–212 8C) as
yellow needles. IR (KBr): nmax (cmK1) 3206, 1717, 1674,
1
1585. H NMR (CDCl3): 1.72 (6H, s); 2.34 (3H, s); 3.13
(3H, s); 7.31–7.37 (3H, m); 7.45–7.50 (2H, m); 9.07 (1H, d,
J 13.8 Hz); 10.99 (1H, d, J 14.1 Hz). 13C NMR (CDCl3):
10.2 (CH3); 26.8 (CH3); 35.8 (CH3); 86.4 (C); 104.7 (C);
109.8 (C); 124.4 (CH); 127.5 (CH); 129.3 (CH); 133.7 (C);
144.1 (C); 155.5 (CH); 158.8 (C); 162.8 (C); 165.9 (C).
Anal. calcd for C18H19N3O5: C, 60.50%; H, 5.36%; N,
11.76%. Found: C, 60.62%; H, 5.26%; N, 11.77%.
2.3. Crystal structure determination of compounds 7,
11 and 14
3. Results and discussions
Single crystal X-ray diffraction data of 7 and 14 were
collected using a CAD-4 diffractometer [12] while data for 11
was collected using Kappa CCD diffractometer [13]. The
structures were solved by direct methods and refined by full-
matrixleast-squaresonF2 foralldatausingSHELXL97[14]. The
hydrogenatoms were addedatcalculatedpositions and refined
using a riding model, except for those involved in H-bonds,
whose coordinates were refined isotropically. Anisotropic
displacement parameters were used for all non-H atoms.
The crystallographic data for structures in this paper have
been deposited with the Cambridge Crystallographic Data
Center as supplementary publication numbers CCDC
252825 for 7 and CCDC 252826 for 14. Copies of the
data can be obtained free of charge via www.ccdc.cam.ac.
uk/conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Center, CCDC, 12 Union Road, Cambridge
CB21EZ, UK. Fax: C44 1223 336033; e-mail: deposit@
ccdc.camac.uk.).
To synthesize the derivatives of 4-aminoantipyrine (1), a
group of ambident eletrophiles was selected which could be
converted into test compounds. In this way, enaminone
derivatives of 1 were prepared by the procedure described
earlier [17]. Thus, 4-aminoantipyrine and acetylacetone (2)
were refluxed in toluene with azeotropic removal of water,
but poor yield was obtained after tedious purification. To
overcome this, the reaction was performed without solvent,
and a solution of 4-aminoantipyrine in an excess of
acetylacetone afforded enaminone 3 with improved yield
(80%). Using this modification of the reported protocol [17]
of enaminone’s synthesis, amine 1 was reacted with ethyl
acetoacetate (4) affording enaminone 5 in 95% yield. In
addition to the above ambident eletrophiles, we extended
the reaction of 1 to benzoyl isothiocyanate (6), phenyl
isothiocyanate (8), maleic anhydride (10) and Meldrum’s
acid derivative 13, whereby thioureas 7 and 9, maleamic
acid 11 and enaminone 14 were obtained in excellent yields

S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
35
O
H
O
O
O
N
2
3
N
N
80%
O
O
H
O
O
O
4
N
OEt
5
N
N
95%
O
C
N C S
N
S
O
7
6
N
89%
N
H
N
H
O
N
N
C S
N
N
S
8
NH
9
N
2
O
1
89%
N
N
O
O
H
H
10
O
O
N
H
O
N
O
N
O
N
99%
62%
N
H
N
O
O
O
12
11
O
O
O
N
O
O
N
13
H
OCH
N
O
O
O
3
O
14
O
78%
Scheme 1.
(Scheme 1). All derivatives but 11 and 12 [2] are substances
not previously described.
involving the group COOH forming a quasi-planar pseudo
seven-membered ring. One intermolecular N14–H14/O15i
(iZ1-x, 2-y, 1-z) H-bond between the amide groups of two
neighboring molecules link them in a centrosymmetric
dimeric form about the B-face.
The structure of 11 was unambiguously assigned through
its crystal structure determination, in agreement with a
previous X-ray study of the same compound, leading us to
use the previously obtained for comparison throughout the
paper [18]. Besides, compounds 7 and 14 had their
structures assigned by X-ray crystallography. The
ORTEP-3 [19] representations of compounds 7, 11, and
14 are shown in Fig. 1. Regarding the crystal structure of 7
(Fig. 2 and Table 1), there is one intramolecular
N14–H14/O20 H-bond forming a pseudo planar six-
membered ring. The dihedral angle between rings (N1–C5)
and (C6–C11) is 55.54(5)8. The crystal data and structure
refinement parameters of 7 and 14 are given in Table 2.
In the molecular structure of 11 (Fig. 2 and Table 1) there
is one strong intramolecular O21–H21/O20 H-bond
The crystal structure of 14 (Fig. 2 and Table 1) shows one
intramolecular N14–H14/O24 H-bond forming a pseudo
planar six-membered ring together with a non-classical
bifurcate intramolecular H-bond involving C16–H16/O15
and C16–H16/O23 that support two quasi-planar pseudo
five-membered rings, resulting in an almost flattened
molecule. The dihedral angle between rings (N1–C5) and
(C6–C11) is 47.53(6)8.
When maleamic acid 11 was left in CDCl3 in the NMR
tube it was slowly converted into maleimide 12 (Fig. 3).
After 1 day, the proportion 11:12 was 1:1 (Fig. 3b), based on
the integral of methyl groups between 2 and 4 ppm in the 1H

36
S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
Fig. 1. ORTEP-3 [19] drawings of the molecules 7, 11, and 14, with the atom-numbering schemes. The displacement ellipsoids are drawn at the 30%
probability levels.
NMR spectrum (it is important to point out that the
spectrum of 11, Fig. 3a, should be recorded immediately
after sample preparation). This proportion changed to 1:1.8,
1:3.2 and 1:4.6 after 4, 7, and 15 days, respectively, and only
signals of compound 12 were detected after 22 days of
sample preparation. Other structural features corroborated
the conversion of maleamic acid 11 into maleimide 12.
The acid hydrogen at 10.82 ppm was not observed after 15
days (Fig. 3a–e), and, moreover, the doublets referent to
the chemically non-equivalent olefinic hydrogens of 11
became one singlet integrated to two hydrogens (Fig. 3a–f),
in agreement to structure 12. In addition, the formation of
12 was alternatively accomplished by the treatment of
maleamic acid 11 with sodium acetate in CHCl3 (maleimide
12 was described as an oil [2], but we found it as
1
hygroscopic solid, see Section 2), and the H NMR data
were identical to the obtained by the slow conversion. The
transformation of 11 into 12 in the CDCl3 solution can
be attributed to trace of acid in this deuterated solvent. A
literature search reveals that spontaneous conversion of
maleamic acid into maleimide is not a common feature [20].
Maleimide 12 was described as an analgesic compound
more active than aspirin and paracetamol, but with high
toxic effect also [2].
The antibacterial activity of the 4-aminoantipyrine and
its derivatives was evaluated by means of direct

S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
37
Table 1
H-bonding for compounds 7, 11, and 14
˚
D–H (A)
˚
˚
H/A (A)
D/A (A)
!(DHA)
(degrees)
Compound 7
0.81(3)
1.96(3)
2.617(2)
138(2)
N14–H14/
O20
Compound 11
1.03(2)
1.46(2)
1.91(2)
2.483(2)
2.821(2)
175(2)
171(2)
O21–H21/
O20
0.92(2)
N14–H14/
O15i
Compound 14
0.91(3)
2.00(3)
2.20(3)
2.50(3)
2.700(2)
2.930(2)
2.815(2)
133(3)
128(2)
98(2)
N14–H14/
O24
1.00(3)
1.00(3)
C16–H16/
O15
C16–H16/
O23
Symmetry operation: (i) 1Kx, 2Ky, 1Kz
Table 3. Derivative 11 was the unique active compound
showing a modest growth inhibition at concentrations
ranging between 125 and 250 mg/mL against all the bacteria
tested. The others were less potent with MICR1000 mg/mL.
However, compound 11 is slowly converted to the highly
toxic [2] compound 12 in solution phase, as indicated by the
NMR study.
Table 2
Crystal data and structure refinement for compounds 7 and 14
Identification code
7
14
Molecular formula
Formula weight
Temperature (K)
Space group
C19H18N4O2S
366.43
293(2)
C18H19N3O5
357.36
293(2)
P21/c
P21/c
˚
a (A)
˚
b (A)
˚
c (A)
16.134(4)
8.3286(8)
13.853(2)
90
17.813(1)
10.664(1)
9.388(1)
90
a (degrees)
b (degrees)
g (degrees)
106.08(1)
90
96.316(9)
90
3
˚
V (A )
1788.6(5)
4
1772.5(3)
4
Z
Dcal (g cmK3
)
1.361
1.339
Fig. 2. The packing diagrams of molecules 7, 11, and 14. Dashed lines
indicate hydrogen bonds. H atoms not involved in hydrogen bonds have
been omitted.
m (mmK1
)
1.787
0.828
Absorption corr.: Tmax
,
0.633, 0.574
none
Tmin
Ranges of h,k, l
K1/19, 9/0, K16/16
K1/21, K12/0,
K11/11
3472
No. of measured ref.
3489
bioautography in a TLC bioassay against M. luteus ATCC
9341, S. aureus ATCC 29737, and E. coli ATCC 8739.
Among them, the derivatives 7, 9, 11 and 14 exhibited mild
to good antibacterial activity in the preliminary screening at
1 and 3 mg concentrations. All compounds were then tested
for minimal inhibitory concentration (MIC) by serial
microdilution technique. Their MIC (mg/mL) are shown in
No. of independent ref.,
3134, 0.027
3150, 0.0124
Rint
Data/restraints/
3134/0/248
3150/0/254
parameters
Robs
0.0504
0.0531
0.1349
1.139
0.0470
0.0608
0.1359
1.034
Rall
Rw (all data)
S

38
S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
Fig. 3. 1H NMR spectra of maleamic acid 11 in CDCl3 solution, showing its conversion into maleimide 12. The captions a, b, c, d, e, and f correspond to the
spectrum of the same sample recorded after 0, 1, 4, 7, 15, and 22 days of preparation, respectively.
Table 3
Acknowledgement
Antimicrobial activity of aminoantipyrine derivatives
Compound
MIC (mg/mL)a
The authors gratefully acknowledge the financial
support of Conselho Nacional de Desenvolvimento
´ ´
Cientıfico e Tecnologico—CNPq and Fundac¸a˜o de
M. luteus
S. aureus
E. coli
7
1000
O1000
125
1000
O1000
250
1000
500
9
`
Amparo a Pesquisa do Estado da Bahia—FAPESB.
11
14
PCb
250
We also thank the Brazilian Agencies for fellowships
to S.M.O. (PIBIC-UFBa/CNPq), J.F. (CAPES), H.B.N.
(FAPESP), M.T.R. Jr. (CNPq), R.M.B. (CNPq) and I.V.
(CNPq); S.C. thanks CNPq for a research fellowship.
1000
!3.9
1000
!3.9
1000
!3.9
a
Minimal inhibitory concentration.
b
PC (positive control—chloranphenicol).

S. Cunha et al. / Journal of Molecular Structure 752 (2005) 32–39
39
[12] Enraf-Nonius, CAD4/PC Version 1.2, Enraf-Nonius, Delft, The
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