Synthesis and antimycobacterial activity of 5-aryl-1-isonicotinoyl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyrazole derivatives

Article abstract of DOI:10.1016/S0014-827X(01)01098-9

5-Aryl-1-isonicotinoyl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyrazole derivatives were synthesized and tested for their in vitro antimycobacterial activity. The compounds showed an interesting activity against a strain of Mycobacterium tuberculosis and a human strain of M. tuberculosis H4.

Full text of DOI:10.1016/S0014-827X(01)01098-9

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Il Farmaco 56 (2001) 593–599
Synthesis and antimycobacterial activity of
5-aryl-1-isonicotinoyl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyrazole
derivativesꢀ
Maria Grazia Mamolo a,*, Daniele Zampieri a, Valeria Falagiani a, Luciano Vio a,
Elena Banfi b
a Dipartimento di Scienze Farmaceutiche, Uni6ersita` di Trieste, Piazzale Europa 1, I-34127 Trieste, Italy
b Dipartimento di Scienze Biomediche (Sez. Microbiologia), Uni6ersita` di Trieste, Via Fleming 22, I-34127 Trieste, Italy
Received 31 July 2000; accepted 29 January 2001
Abstract
5-Aryl-1-isonicotinoyl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyrazole derivatives were synthesized and tested for their in vitro an-
timycobacterial activity. The compounds showed an interesting activity against a strain of Mycobacterium tuberculosis and a
human strain of M. tuberculosis H4. © 2001 Elsevier Science S.A. All rights reserved.
Keywords: 5-Aryl-1-isonicotinoyl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyrazole derivatives; Antimycobacterial activity
aspirates. The activity of these compounds toward
strains of M. gordonae, M. bo6is, Candida albicans,
Escherichia coli and Staphylococcus epidermidis was
also determined.
1. Introduction
4,5-Dihydro-1H-pyrazole derivatives were described
for their antibacterial [1–5] and antifungal [1,4,6] activ-
ities. In our search for new antimycobacterial agents we
synthesized a series of 1,3,5-trisubstituted 4,5-dihydro-
1H-pyrazoles (3a–3m) (Table 3), in which the nitrogen
at position 1 of the pyrazoline cycle was linked to the
isonicotinoyl residue in order to verify whether that
substitution might confer antimycobacterial properties
to the compounds. Moreover, with position 3 was
connected the 2-pyridinyl substituent which, together
with the nitrogen atoms on the cycle, partially resem-
bled the 2-pyridinecarboxamidrazone moiety present in
compounds characterized by antimycobacterial proper-
ties [7–12]. All the synthesized compounds were tested
for their antimycobacterial activity toward a strain of
Mycobacterium tuberculosis H37Rv and toward a strain
of M. tuberculosis H4, isolated from human bronchial
2. Chemistry
The synthesis of 5-aryl-1-isonicotinoyl-3-(pyridin-2-
yl)-4,5-dihydro-1H-pyrazoles (3a–3m) (Table 3) was
carried out (Scheme 1) by reacting isonicotinoyl chlo-
ride with the corresponding 5-aryl-3-(pyridin-2-yl)-4,5-
dihydro-1H-pyrazoles (2a–2m) (Table 2) which in turn
were prepared from the corresponding 3-aryl-1-
(pyridin-2-yl)-propenones (1a–1m) (Table 1) by treat-
ment with hydrazine hydrate. However, when
a,b-unsaturated ketones 1c, 1f, 1h, 1i and 1k–1m were
allowed to react with hydrazine hydrate, very unstable
products were obtained from which the corresponding
4,5-dihydro-1H-pyrazoles (2) could not be isolated, ac-
cording to the literature findings for similar compounds
[13]. The crude products were directly used for the
following reaction (see Section 3). Any attempt to
obtain compounds 3a–3m by reacting propenone
derivatives 1a–1m with isoniazid was unsuccessful.
ꢀ A preliminary account of this work was presented at the Italian–
Hungarian–Polish Joint Meeting on Medicinal Chemistry (Divisione
di Chimica Farmaceutica), Giardini Naxos-Taormina, 28 September–
1 October 1999.
* Corresponding author.
E-mail address: mamolo@univ.trieste.it (M. Grazia Mamolo).
0014-827X/01/$ - see front matter © 2001 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(01)01098-9

594
M. Grazia Mamolo et al. / Il Farmaco 56 (2001) 593–599
1
pyrazolines with ortho-substituted phenyl residues,
whose l values are in the range 5.98–6.10 ppm, and the
corresponding methine protons of the pyrazolines bear-
ing meta- and para-substituted phenyl rings, whose l
values are in the range 5.72–5.77 ppm. This spectral
behavior is not in agreement with compounds derived
from the tautomeric form B, in which the methine
protons have a more homogeneous magnetic environ-
ment. Moreover, the ortho-substituted phenyl groups
present in the pyrazoline derivatives 2b, 2e produce a
similar downfield shift of the methine protons with
respect to the resonance of the corresponding protons
of the para-substituted derivatives 2d, 2g. On the basis
of these findings, we assigned to the obtained com-
pounds 3a–3m the structure corresponding to the
5-aryl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyrazole deriva-
tives 2a–2m. The known a,b-unsaturated ketones 1a–
1d, 1g, 1k, 1m were prepared according to the
literature. The general synthetic procedure is described
in Section 3 for the preparation of the new compounds
1e, 1f, 1h, 1i, 1j, 1l (Table 1).
The H NMR spectra of compounds 2a, 2b, 2d, 2e,
2g, 2j and 3a–3m reveal the presence of three doublets
of doublet signals due to the magnetically nonequiva-
lent protons HA (upfield H of CH2) and HB (downfield
H of CH2), and to the vicinal methine proton HX. The
values of the coupling constants between the protons
are consistent with the expected structures. However,
the pyrazoline derivatives 2a–2m may react with isoni-
cotinoyl chloride in two of the possible tautomeric
forms, viz. 5-aryl-3-(pyridin-2-yl)-4,5-dihydro-1H-pyra-
zoles (A) or 3-aryl-5-(pyridin-2-yl)-4,5-dihydro-1H-
pyrazoles (B), to give the corresponding 1-isonicotinoyl
derivatives whose 1H NMR spectra would be very
similar. From the 1H NMR spectra of the obtained
compounds it appears that there exists a difference in
the chemical shifts between the methine protons of the
3. Experimental
3.1. Chemistry
Melting points were determined with a Bu¨chi 510
capillary apparatus, and are uncorrected. Infrared spec-
tra in nujol mulls were recorded on a Jasco FT 200
spectrophotometer. Proton nuclear magnetic resonance
(1H NMR) spectra were determined on a Varian Gem-
ini 200 spectrometer; chemical shifts are reported as l
(ppm) relative to tetramethylsilane as internal standard,
deuterochloroform as solvent. Reaction courses and
product mixtures were routinely monitored by thin-
layer chromatography on silica gel precoated F254
Merck plates. EI MS spectra (70 eV) were taken on a
VG 7070 spectrometer. Elemental analyses (C, H, N)
were performed on a Carlo Erba analyzer and were
within 90.3 of the theoretical value.
3.1.1. 3-Aryl-1-(pyridin-2-yl)-propenones (1e, 1f, 1h,
1i, 1j, 1l)
To a mixture of 27 mmol of the appropriate aromatic
aldehyde (dissolved in 5 ml of methanol) and 22 ml of
10% sodium hydroxide, 3.27 g (27 mmol) of 2-
acetylpyridine was added dropwise under cooling (0–
5°C) and stirring. After the addition was complete the
reaction mixture was stirred for 2 h keeping the temper-
ature below 10°C. The resulting solid was collected by
filtration, washed thoroughly with ice-cold water, dried
in a vacuum dessicator and recrystallized from absolute
ethanol (Table 1).
Scheme 1.

M. Grazia Mamolo et al. / Il Farmaco 56 (2001) 593–599
595
Table 1
Compounds 1a–1m
Compound
R
m.p. (°C)
IR (cm−1) (CꢀO)
Formula (C, H, N)
Ref.
1a
1b
1c
1d
1e
1f
1g
1h
1i
H
70–72
90–92
94–96
100–102
95–97
84–86
97–99
72–74
72–74
84–86
74–76
73–75
83–85
1685
1698
1678
1674
1698
1697
1699
1680
1670
1672
1677
1684
1663
C14H11NO
C14H10NOC1
C14H10NOC1
[14]
[14]
[14]
[15]
2-Cl
3-Cl
4-Cl
2-Br
3-Br
4-Br
2-F
3-F
4-F
2-CH3
3-CH3
4-CH3
C
14H10NOC1
C14H10NOBr
C14H10NOBr
C14H10NOBr
[16]
C14H10NOF
C14H10NOF
C14H10NOF
C15H13NO
1j
1k
1l
[16]
[15]
C
15H13NO
1m
C15H13NO
3.1.2. 5-Phenyl-3-(pyridin-2-yl)-4,5-dihydro-
1H-pyrazole (2a)
1H-pyrazole 2a dissolved in 15 ml of absolute ethanol
was added at room temperature (r.t.). To the stirred
solution, 4.35 g (43 mmol) of triethylamine was added
dropwise and the reaction mixture was further stirred
for 3 h. The precipitated solid was filtered, washed with
water, dried in a vacuum dessicator and recrystallized
from absolute ethanol to obtain 2.4 g (52%) of 3a; m.p.
187–89°C.
To a solution of 3 g (14 mmol) of 1a in 25 ml of
ethanol, 1.43 g (28 mmol) of 98% hydrazine monohy-
drate was added dropwise under stirring. After addition
the reaction mixture was further stirred for 1 h and
concentrated under reduced pressure. The solid precipi-
tate was collected by filtration and immediately crystal-
lized from absolute ethanol to obtain 1.8 g (85%) of 2a;
m.p. 55°C.
1
IR (Nujol, cm−1): 1647. H NMR (CDCl3, TMS): l
3.46 (dd, 1H, HA, upfield H of CH2; JAB=18.68 Hz,
1
IR (Nujol, cm−1): 3312. H NMR (CDCl3, TMS): l
J
J
AX=5.13 Hz), 3.92 (dd, 1H, HB, downfield H of CH2;
BA=18.68 Hz, JBX=11.72 Hz), 5.80 (dd, 1H, HX,
3.23 (dd, 1H, HA, upfield H of CH2; JAB=17.14 Hz,
J
J
AX=8.71 Hz), 3.65 (dd, 1H, HB, downfield H of CH2;
BA=17.14 Hz, JBX=10.90 Hz), 4.98 (dd, 1H, HX,
CH; JXA=5.13 Hz, JXB=11.72 Hz), 7.25–8.75 (m,
13H, arom. and pyr.). MS; m/z: 328 [M+]. Anal.
(C20H16N4O): C, H, N.
Analogously, the compounds 3b–3m were prepared.
Yields and melting points of compounds 3a–3m are
reported in Table 3 and their spectral data are recorded
in Table 4.
Yields of compounds 3c, 3f, 3h, 3i, 3k–3m, prepared
starting from the crude products of the reaction be-
tween the corresponding a,b-unsaturated ketones 1 and
hydrazine hydrate, were calculated on the basis of the
amount of ketone employed.
CH; JXA=8.71 Hz, JXB=10.90 Hz), 6.17 (br s, 1H,
NH, disappearing on deuteration), 7.06–8.57 (m, 9H,
arom. and pyr.). MS; m/z: 223 [M+]. Anal. (C14H13N3):
C, H, N.
Analogously, the compounds 2b, 2d, 2e, 2g, 2j were
prepared. Yields, melting points and spectral data are
reported in Table 2.
The very unstable compounds 2c, 2f, 2h, 2i and
2k–2m were not isolated. At the end of the reaction the
solution was evaporated to dryness in vacuo and the
oily residue was directly used for the following reaction.
3.2. Microbiology
3.1.3. 1-Isonicotinoyl-5-phenyl)-3-(pyridin-2-yl)-
4,5-dihydro-1H-pyrazole (3a)
The determination of the antitubercular and antimy-
cobacterial activity was performed by the agar dilution
method [17] in quadrant plates containing Middlebrook
To a solution of 3.74 g (21 mmol) of isonicotinoyl
chloride hydrochloride in 15 ml of dichloromethane, 3.1
g (14 mmol) of 5-phenyl-3-(pyridin-2-yl)-4,5-dihydro-

Table 2
Spectral data of compounds 2a–2m
Comp.
R
H
Yield (%)
63
m.p. (°C)
Formula (C, H, IR (nujol,
1H NMR (DMSO, TMS) (l)
Mass m/z [M+
]
N)
cm−1
)
2a
55
C14H13N3
3312
3.23 (dd, 1H, HA, upfield H of CH2; JAB=17.14 Hz, JAX=8.71 Hz), 3.65 (dd, 1H, HB, 223
downfield H of CH2; JBA=17.14 Hz, JBX=10.90 Hz), 4.98 (dd, 1H, HX, CH;
JXA=8.71 Hz, JXB=10.90 Hz), 6.17 (br s, 1H, NH, disappearing on deuteration),
7.06–8.57 (m, 9H, arom. and pyr.)
2b
2-Cl
61
96–9
C14H12N3Cl
3320
3.09 (dd, 1H, HA; JAB=17.21 Hz, JAX=9.52 Hz), 3.80 (dd, 1H, HB; JBA=17.21 Hz,
257, 259
/
J
BX=10.62 Hz), 5.37 (overlapped dd, 1H, HX), 6.20 (br s, 1H, NH, disappearing on
deuteration), 7.10–8.40 (m, 8H, arom. and pyr.)
a
a
a
a
a
a
2c
2d
3-Cl
4-Cl
58
92–4
C14H12N3Cl
3340
3.10 (dd, 1H, HA; JAB=17.21 Hz, JAX=9.52 Hz), 3.60 (dd, 1H, HB; JBA=17.21 Hz,
257, 259
J
BX=11.35 Hz), 4.90 (overlapped dd, 1H, HX), 6.17 (br s, 1H, NH, disappearing on
5
deuteration), 7.07–8.60 (m, 8H, arom. and pyr.)
(
2e
2-Br
61
95–7
C14H12N3Br
3343
3.01 (dd, 1H, HA; JAB=16.85 Hz, JAX=9.16 Hz), 3.76 (dd, 1H, HB; JBA=16.85 Hz,
301, 303
J
BX=11.35 Hz), 5.27 (overlapped dd, 1H, HX), 6.27 (br s, 1H, NH, disappearing on
593
deuteration), 7.02–8.50 (m, 8H, arom. and pyr.)
a
a
a
a
a
a
2f
2g
3-Br
4-Br
599
63
93–5
C14H12N3Br
3300
2.95 (dd, 1H, HA; JAB=17.30 Hz, JAX=9.65 Hz), 3.48 (dd, 1H, HB; JBA=17.30 Hz,
301, 303
J
BX=11.20 Hz), 4.95 (overlapped dd, 1H, HX), 6.20 (br s, 1H, NH, disappearing on
deuteration), 7.10–8.85 (m, 8H, arom. and pyr.)
a
a
a
a
a
a
a
a
a
a
a
2h
2i
2j
2-F
3-F
4-F
a
56
96–8
C14H12N3F
3240
3.16 (dd, 1H, HA; JAB=17.21 Hz, JAX=9.16 Hz), 3.63 (dd, 1H, HB; JBA=17.21 Hz,
241
J
BX=10.62 Hz), 4.95 (overlapped dd, 1H, HX), 6.21(br s, 1H, NH, disappearing on
deuteration), 6.96–8.56 (m, 8H, arom. and pyr.)
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
2k
2l
2m
2-CH3
3-CH3
4-CH3
a
a
a The compounds were not isolated (see Section 3).

M. Grazia Mamolo et al. / Il Farmaco 56 (2001) 593–599
597
formed by the agar dilution method; Mueller–Hinton
agar (Oxoid) and Sabouraud dextrose agar (Oxoid)
were used for bacterial and fungal strains, respectively,
to prepare quadrant plates with serial dimethylsulfoxide
twofold dilutions of the different chemicals tested. A 20
ml sample of each 104 ml−1 microbial suspension was
inoculated on to each chemical-containing quadrant.
Control plates consisted of Mueller–Hinton agar or
Sabouraud dextrose agar alone, culture medium with
dimethylsulfoxide and culture medium with known an-
timicrobial drugs, like ampicillin (10 mg/disk) for bacte-
rial strain or econazole (10 mg/disk) for C. albicans. All
the plates were then incubated at 37°C overnight.
and Cohn 7H11 agar, supplemented with Middlebrook
ADC or OADC enrichments. Serial dimethylsulfoxide
twofold dilutions of the different chemicals tested were
included in the agar layer and suspensions of different
Mycobacterium spp. strains, prepared in sterile saline
containing 0.2% fatty acid-free albumin and 0.02%
polysorbate 80, were plated on to each quadrant. Con-
trol plates with known antitubercular drugs were in-
cluded and all the plates were incubated at 37°C in 5%
CO2 for 4 weeks, after which viable counting was
performed. We employed four different strains of My-
cobacterium spp.: M. tuberculosis H37Rv reference
strain, M. tuberculosis H4 clinical isolate, M. gordonae
and M. bo6is from our bacterial collection. The mini-
mal inhibitory concentration (MIC) was defined for
each chemical as the lowest dilution associated with at
least a 99% reduction in the number of viable colonies.
Results are shown in Table 5.
4. Results and discussion
A series of 5-aryl-1-isonicotinoyl-3-(pyridin-2-yl)-4,5-
dihydro-1H-pyrazole derivatives 3a–3m have been syn-
thesized with the aim of evaluating their
antimycobacterial activity toward a strain of M. tuber-
culosis H37Rv and a strain of M. tuberculosis H4,
isolated from human bronchial aspirates. All the syn-
thesized compounds exhibited an interesting in vitro
antimycobacterial activity against the tested strains of
M. tuberculosis, their MIC values ranging from 8 to 16
mg/ml (Table 5). However, none of the compounds
exhibited any antimycobacterial activity against the
strains of M. bo6is and M. gordonae at the maximal
employed concentration (64 mg/ml). Compounds 3a–
3m were inactive against the tested strains of C. albicans
and E. coli, and exhibited a very low activity toward the
strain of S. epidermidis. Since the substituents on the
phenyl residue at the 5-position on the cycle do not
exert any important modulatory role on the activity,
pyrazoline derivatives, modified by the replacement of
the substituted phenyl residue with heterocyclic rings,
may lead to compounds with higher antimycobacterial
activity. The presence of the 2-pyridinyl residue at
3-position on the pyrazoline cycle may exert an
important role on the activity of the tested com-
pounds because 3,5-diaryl-1-isonicotinoyl-4,5-dihydro-
1H-pyrazole derivatives were found to be inactive
against M. tuberculosis H37Rv [18]. However, it cannot
be ruled out that the rather constant activity of com-
pounds 3a–3m depends on a release of isoniazid in the
biological medium, even if no degradation of the com-
pounds in solution was observed after several months.
If the activity of compounds 3a–3m is due to the
release of isoniazid, the lack of antimycobacterial activ-
ity of the above 3,5-diaryl-1-isonicotinoyl-4,5-dihydro-
1H-pyrazole derivatives [18] might be attributed to the
inhibition of isoniazid release through a possible stabi-
lizing effect of a hydrogen bond between the hydroxy
The other microbial strains tested were E. coli, S.
epidermidis and C. albicans. The bacterial strains were
grown overnight in Mueller–Hinton broth and the
fungal strain was grown overnight in Sabouraud dex-
trose broth; the test inocula were prepared diluting the
overnight suspension to a density of 104 microorgan-
isms per milliliter. The MIC determinations were per-
Table 3
Compounds 3a–3m
Comp.
R
Yield (%)
m.p. (°C)
Formula (C, H, N)
C20H16N4O
3a
3b
3c
3d
3e
3f
3g
3h
3i
H
52
69
186–9
181–3
126–9
218–220
162–4
115–7
234–6
174–7
178–181
194–7
156–8
171–3
213–6
2-Cl
3-Cl
4-Cl
2-Br
3-Br
4-Br
2-F
3-F
4-F
2-CH3
3-CH3
4-CH3
C20H15N4Ocl
C20H15N4Ocl
C20H15N4Ocl
C20H15N4Obr
C20H15N4Obr
C20H15N4Obr
C20H15N4OF
C20H15N4OF
C20H15N4OF
C20H15N4O
35 a
65
60
33 a
62
40 a
38 a
69
3j
3k
3l
42 a
40 a
41 a
C20H15N4O
C21H18N4O
3m
a The yield was calculated on the basis of the amount of a,b-unsat-
urated ketone employed in the synthesis (see Section 3).

598
M. Grazia Mamolo et al. / Il Farmaco 56 (2001) 593–599
Table 4
Spectral data of compounds 3a–3m
Comp.
3a
3b
3c
R
IR (nujol,
1H NMR (DMSO, TMS) (l)
Mass m/z [M+
]
cm−1
)
H
1647
3.46 (dd, 1H, HA, upfield H of CH2; JAB=18.68 Hz, JAX=5.13 Hz), 3.92 (dd, 1H,
HB, downfield H of CH2; JBA=18.68 Hz, JBX=11.72 Hz), 5.80 (dd, 1H, HX, CH;
328
J
XA=5.13 Hz, JXB=11.72 Hz), 7.25–8.75 (m, 13H, arom. and pyr.)
3.30 (dd, 1H, HA; JAB=18.68 Hz, JAX=5.13 Hz), 3.95 (dd, 1H, HB; JBA=18.68 Hz, 362, 364
BX=11.62 Hz), 6.04 (dd, 1H, HX; JXA=5.13 Hz, JXB=11.62 Hz), 7.13–8.69 (m,
2-Cl
3-Cl
4-Cl
3-Br
3-Br
4-Br
2-F
3-F
4-F
1623
1650
1637
1650
1649
1668
1644
1646
1638
J
12H, arom. and pyr.)
3.40 (dd, 1H, HA; JAB=18.62 Hz, JAX=5.19 Hz), 3.93 (dd, 1H, HB; JBA=18.62 Hz, 362, 364
JBX=11.60 Hz), 5.74 (dd, 1H, HX; JXA=5.19 Hz, JXB=11.60 Hz), 7.0–8.8 (m, 12H,
arom. and pyr.)
3d
3e
3.40 (dd, 1H, HA; JAB=18.62 Hz, JAX=5.19 Hz), 3.90 (dd, 1H, HB; JBA=18.62 Hz, 362, 364
JBX=11.60 Hz), 5.75 (dd, 1H, HX; JXA=5.19 Hz, JXB=11.60 Hz), 7.05–8.8 (m,
12H, arom. and pyr.)
3.30 (dd, 1H, HA; JAB=18.31 Hz, JAX=4.39 Hz), 4.00 (dd, 1H, HB; JBA=18.31 Hz, 406, 408
JBX=11.72 Hz), 6.10 (dd, 1H, HX; JXA=4.39 Hz, JXB=11.72 Hz), 6.85–8.85 (m,
12H, arom. and pyr.)
3f
3.46 (dd, 1H, HA; JAB=18.68 Hz, JAX=4.76 Hz), 3.95 (dd, 1H, HB; JBA=18.68 Hz, 406, 408
JBX=11.72 Hz), 5.75 (dd, 1H, HX; JXA=4.76 Hz, JXB=11.72 Hz), 7.10–8.8 (m,
12H, arom. and pyr.)
3g
3h
3i
3.44 (dd, 1H, HA; JAB=18.68 Hz, JAX=5.13 Hz), 3.94 (dd, 1H, HB; JBA=18.68 Hz, 406, 408
JBX=11.72 Hz), 5.75 (dd, 1H, HX; JXA=5.13 Hz, JXB=11.72 Hz), 7.15–8.80 (m,
12H, arom. and pyr.)
3.47 (dd, 1H, HA; JAB=18.68 Hz, JAX=5.49 Hz), 3.96 (dd, 1H, HB; JBA=18.68 Hz, 346
JBX=12.09 Hz), 5.98 (dd, 1H, HX; JXA=5.49 Hz, JXB=12.09 Hz), 7.15–8.8 (m,
12H, arom. and pyr.)
3.45 (dd, 1H, HA; JAB=18.68 Hz, JAX=5.13 Hz), 3.93 (dd, 1H, HB; JBA=18.68 Hz, 346
JBX=12.09 Hz), 5.77 (dd, 1H, HX; JXA=5.13 Hz, JXB=12.09 Hz), 7.0–8.8 (m, 12H,
arom. and pyr.)
3j
3.42 (dd, 1H, HA; JAB=18.68 Hz, JAX=4.76 Hz), 3.90 (dd, 1H, HB; JBA=18.68 Hz, 346
JBX=11.72 Hz), 5.75 (dd, 1H, HX; JXA=4.76 Hz, JXB=11.72 Hz), 6.90–8.90 (m
12H, arom. and pyr.)
3k
3l
2-CH3 1645
3-CH3 1644
4-CH3 1641
2.50 (s, 3H, CH3), 3.30 (dd, 1H, HA; JAB=18.68 Hz, JAX=4.76 Hz), 3.95 (dd, 1H,
HB; JBA=18.68 Hz, JBX=11.72 Hz), 5.99 (dd, 1H, HX; JXA=4.76 Hz, JXB=11.72
Hz), 7.0–8.94 (m, 12H arom. and pyr.)
2.30 (s, 3H, CH3), 3.43 (dd, 1H, HA; JAB=18.92 Hz, JAX=4.88 Hz), 3.90 (dd, 1H,
HB; JBA=18.92 Hz, JBX=11.60 Hz), 5.74 (dd, 1H, HX; JXA=4.88 Hz, JXB=11.60
Hz), 6.9–8.8 (m, 12H, arom. and pyr.)
2.30 (s, 3H, CH3), 3.45 (dd, 1H, HA; JAB=18.68 Hz, JAX=5.13 Hz), 3.90 (dd, 1H,
HB; JBA=18.68 Hz, JBX=11.72 Hz), 5.72 (dd, 1H, HX; JXA=5.13 Hz, JXB=11.72
Hz), 7.0–8.8 (m, 12H, arom. and pyr.)
342
342
342
3m
group in the ortho position on the 3-aryl residue and
the nitrogen atom at the 2-position in the pyrazoline
cycle of these compounds. It will be of interest to verify
if analogous 3,5-diaryl-pyrazoline derivatives without
the ortho-hydroxy substituent on the phenyl ring at the
3-position on the cycle may exhibit antimycobacterial
properties. On the other hand, compounds 3a–3m are
characterized by the presence in the 3-position of the
2-pyridinyl substituent, which can contribute to the
activity. The replacement of the isonicotinoyl group in
compounds 3a–3m with other acyl derivatives may be
important in order to establish the possible significance
of the 2-pyridinyl residue with respect to the antimy-
cobacterial activity. On the basis of these consider-
ations, the synthesis and the antimycobacterial activity
evaluation of new pyrazoline derivatives are now in
progress.
Acknowledgements
The authors would like to thank Dr. M. Cebulec for
the microanalyses. This research was carried out
with the financial support of the Italian MURST
(60%).

M. Grazia Mamolo et al. / Il Farmaco 56 (2001) 593–599
599
Table 5
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Activity of the 5-aryl-1-isonicotinoil-3-(pyridin-2-yl)-4,5-dihydro-1H-
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Comp. MIC (mg/ml)
M. tuberculosis
H37Rv
M. tuberculosis H4 clinical isolate a
3a
3b
3c
3d
3e
3f
8
8
8
8
8
8
8
8
8
16
16
16
16
16
16
8
8
3g
3h
3i
3j
3k
3l
8
16
16
16
8
8
16
16
3m
16
a M. tuberculosis strains resulted sensitive to isoniazid (5 mg/disk)
and rifampicin (30 mg/disk).
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