Synthesis and anti-tubercular evaluation of 4-quinolylhydrazones

Article abstract of DOI:10.1016/S0968-0896(02)00071-8

A series of 4-quinolylhydrazones were synthesized and tested against Mycobacterium tuberculosis H37Rv. Preparation of the title compounds was achieved by reaction of 4-quinolylhydrazine and aryl- or heteroaryl-carboxaldehyde. For the most of derivatives interesting antitubercular properties were showed; two compounds (3₂ and 3₂₅), identified as the most active, were tested also against Mycobacterium avium.

Full text of DOI:10.1016/S0968-0896(02)00071-8

Bioorganic & Medicinal Chemistry 10 (2002) 2193–2198
Synthesis and Anti-tubercular Evaluation of 4-Quinolylhydrazones
Luisa Savini,* Luisa Chiasserini, Alessandra Gaeta and Cesare Pellerano
`
Dipartimento Farmaco Chimico Tecnologico, Universita degli Studi di Siena, Via A. Moro, 53100 Siena, Italy
Received 16 October 2001; revised 20 December 2001; accepted 6 February 2002
Abstract—A series of 4-quinolylhydrazones were synthesized and tested against Mycobacterium tuberculosis H37Rv. Preparation of
the title compounds was achieved by reaction of 4-quinolylhydrazine and aryl- or heteroaryl-carboxaldehyde. For the most of
derivatives interesting antitubercular properties were showed; two compounds (32 and 325), identified as the most active, were tested
also against Mycobacterium avium. # 2002 Elsevier Science Ltd. All rights reserved.
Introduction
3-phenyl-4-thioxo-2H-1,3-benzoxazine-2(3H)-ones,
-dithiones13 and fluoroquinolones (ciprofloxacin, oflox-
acin, levofloxacin, sparfloxacin, gatifloxacin and moxi-
floxacin).14
Tuberculosis (TB), an infection of Mycobacterium
tuberculosis still remains the leading cause of worldwide
death among infectious diseases;1,2 one-third of the
population is infected with M. tuberculosis and the
World Health Organization (WHO) estimates that
within the next 20 years about 30 million people will
catch tuberculosis.3ꢀ7
Within a programaimed at developing new quinoline
derivatives, we previously synthesized numerous quino-
lylhydrazones, some of which resulted were endowed
with anti-mycoplasmal, anti-bacterial, anti-cestode,
anti-viral, anti-tumoral and anti-tubercular proper-
ties.15ꢀ24
The resurgence of TB is associated with the emergence
of HIV/AIDS epidemic8 and the fast development of
multidrug resistant TB bacterial strains.9,10 In the
developing world, probably 50% of HIV seropositive
individuals are co-infected with TB. Therefore taking into
account what is reported above there is a pressing need to
develop new and more effective anti-tubercular agents.
Therefore, as a consequence of previous researches and
on the basis of the obtained results, a series of 4-quino-
lylhydrazones 3, with various substituents on quinoline
nucleus and with aryl- or heteroaryl-hydrazonic moiety,
were synthesized as potential anti-tubercular agents.
Among the new structures recently reported as potential
anti-tubercular of particular interest seems to be some
2,6-bis(alkylthio)4-pyridinecarboxamides,11 N-alkyl-1,2-
dihydro-2-thioxo-3-pyridinecarbothioamides,12 6-chloro-
The new synthesized quinolylhydrazones 3 and the
starting quinolylhydrazines 2 were tested against M.
tuberculosis H37Rv and interesting anti-tubercular
properties resulted for most of the title compounds.
Scheme 1. R,R0, Ar as defined in Table 1.
*Corresponding author. Tel.: +39-0577-234304; fax: +39-0577-234333; e-mail: savini@unisi.it
0968-0896/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(02)00071-8

2194
L. Savini et al. / Bioorg. Med. Chem. 10 (2002) 2193–2198
Chemistry
The 4-quinolylhydrazine 2 necessary for preparation of
4-quinolylhydrazones 3 were obtained fromthe corre-
sponding 4-chloroquinoline 1 and hydrazine hydrate as
we previously described.24
The synthesis of 4-quinolylhydrazones 3 was carried
out, according to the previously described procedure,18
by reaction of equimolar amounts of 4-hydrazino-
quinoline 2 and the appropriate carboxaldehyde in
EtOH, as illustrated in Scheme 1.
The structures assigned to the synthesized compounds
are in good agreement with elemental analyses, IR and
Table 1. Physicochemical data and molecular formula of derivatives 2 and 3
Compd
R
R0
Ar
Mp (ꢁC)
250–253
Cryst. solvent
Molecular formula
a
21
22
23
24
H
7-OCH3
7-OCH3
8-OCH3
6-OCH3
a
CH3
CH3
C6H5
H
CH3
H
CH3
H
CH3
H
CH3
H
CH3
H
CH3
CH3
H
H
H
H
CH3
CH3
CH3
CH3
CH3
H
a
a
.
C11H13N3O HCl
25
26
27
28
29
210
7-OC2H5
7-OC2H5
6-n.C4H9
6-n.C4H9
6-n.OC4H9
6-n.OC4H9
6-Cyclohexyl
6-Cyclohexyl
7-Cl
EtOH
a
b
c
b
c
.
C15H19N3 HCl
211
212
287–291
EtOH anhyd.
c
a
213
214
b
7-Cl
5,7-Cl
5,7-Cl
6-F
215
216
217
31
184–187
202–205
EtOH
EtOH
C9H7Cl2N3
C10H9Cl2N3
a
H
4-OCH3–naphthyl
2-OCH3–naphthyl
4-OCH3–naphthyl
4-N(C2H5)2–C6H4
2-OCH3–naphthyl
4-OCH3–naphthyl
4-N(C2H5)2–C6H4
3,4-(OCH2O)–C6H3
4-OCH3–naphthyl
2-OCH3–naphthyl
4-OCH3–naphthyl
4-N(C2H5)2–C6H4
2-OCH3–naphthyl
4-OCH3–naphthyl
4-N(C2H5)2–C6H4
4-NHCOCH3–C6H4
5-NO2–2–furyl
195 (dec.)
118–121
235–238
201 (dec.)
202 (dec.)
286–289
128–132
215 (dec.)
261–262
95 (dec.)
200–202
119–122
232–235
231–234
115–118
138 (dec.)
Benzene
EtOH
EtOH
EtOH-H2O
EtOH
EtOH
EtOH-H2O
EtOH
EtOH-H2O
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH-H2O
C21H17N3O
.
C22H19N3O2 1/4H2O
32
33
34
35
36
37
38
39
7-OCH3
7-OCH3
7-OCH3
7-OCH3
7-OCH3
7-OCH3
7-OCH3
8-OCH3
7-OC2H5
7-OC2H5
7-OC2H5
7-OC2H5
7-OC2H5
7-OC2H5
6-OCH3
6-OCH3
6-n.C4H9
6-n.C4H9
6-n.C4H9
6-n.OC4H9
6-n.OC4H9
6-Cyclohexyl
6-Cyclohexyl
6-Cyclohexyl
6-Cyclohexyl
6-Cyclohexyl
6-Cyclohexyl
7-Cl
C22H19N3O2
.
C21H24N4O 1/4H2O
.
C23H21N3O2 H2O
.
C23H21N3O2 HCl H2O
.
.
C22H26N4O H2O
C19H17N3O3
C23H21N3O2
.
C23H21N3O2 1/2H2O
C23H21N3O2
.
C22H26N4O 1/2H2O
C24H23N3O2
310
311
312
313
314
315
316
H
H
CH3
CH3
CH3
C6H5
C6H5
H
CH3
CH3
H
CH3
H
H
CH3
CH3
CH3
CH3
H
.
C24H23N3O2 3/4H2O
.
C23H28N4O H2O
C25H22N4O2
C23H21N3O2
C25H25N3O
C26H27N3O
C22H23N3O2
C25H25N3O2
C26H27N3O2
C27H17N3O
C26H27N3O
C23H25N3
d
317
318
319
320
321
322
323
4-OCH3–naphthyl
4-OCH3–naphthyl
3,4-(OCH2O)–C6H3
4-OCH3–naphthyl
4-OCH3–naphthyl
4-OCH3–naphthyl
195–196
237–239
202–204
204–205
209–210
182–184
EtOH-H2O
EtOH
EtOH
EtOH
EtOH-H2O
EtOH
b
324
1-C6H5–2,5–CH3–3–pyrrolyl
C6H5
325
326
327
252–254
163–166
290–292
EtOH-H2O
EtOH-H2O
DMF
4-N(C2H5)2–C6H4
4-OCH3–naphthyl
1-C6H5–2,5–CH3–3–pyrrolyl
2-OCH3–naphthyl
4-OCH3–naphthyl
4-N(C2H5)2–C6H4
2-OCH3–naphthyl
4-OCH3–naphthyl
4-N(C2H5)2–C6H4
3,4-(OCH2O)–C6H3
4-OCH3–naphthyl
3,4-(OCH2O)–C6H3
4-OCH3–naphthyl
4-OCH3–naphthyl
C27H34N4
C28H29N3O
b
328
329
330
331
237–239
132–136
245–248
259–262
224–226
249–252
223–225
164–167
218–220
158–160
269–271
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
C21H16ClN3O
.
C21H16ClN3O 3/4H2O
H
H
CH3
CH3
CH3
H
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
5,7-Cl
5,7-Cl
5,7-Cl
e
C20H21ClN4
C22H18ClN3O
C22H18ClN3O
C21H23ClN4
332
333
334
335
336
337
338
339
C17H11Cl2N3O2
.
C21H15Cl2N3O 1/4H2O
H
CH3
CH3
CH3
C18H13Cl2N3O2
C22H17Cl2N3O
C22H18FN3O
5,7-Cl
6-F
aRef 24.
bRef 25.
cRef 26.
dRef 15.
eRef 27.

L. Savini et al. / Bioorg. Med. Chem. 10 (2002) 2193–2198
2195
1H NMR spectral data. The IR spectra of quinolylhydra-
zones 3 have a weak band between 3350 and 3170 cmꢀ1
due to the stretching vibration of the NH group. In the
1H NMR spectra a singlet appears between 8.3–9.2 d,
which is typical of the aldehyde proton. Physicochemical
properties are summarized in Table 1.
Pharmacology
The in vitro evaluation of antituberculosis activity was
carried out at the GWL Hansen’s Disease Center within
the Tuberculosis Antimicrobial Acquisition Coordinat-
ing Facility (TAACF) screening programfor the dis-
covery of novel drugs for treatment of tuberculosis. Under
the direction of the US National Institute of Allergy and
Infectious Diseases (NIAID), Southern Research Insti-
tute coordinates the overall program. The purpose of
the screening programis to provide a resource whereby
new experimental compounds can be tested for their
capacity to inhibit the growth of virulent M. tuberculosis.
Table 2. In vitro evaluation of antimicrobial activity versus Myco-
bacterium tuberculosis H37Rv [minimum inhibitory concentration
(MIC ) in mg/mL]
Compd
M. tuberculosis
MIC
(mg/mL)
% Inhibition MIC
IC50
SI
(mg/mL) (mg/mL)
b
21
<12.5
>12.5
>12.5
<12.5
>12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
>12.5
>12.5
>12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
>12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
<12.5
>12.5
>12.5
>12.5
>12.5
<12.5
0.031
97
94
54
99
88
98
99
99
99
99
99
100
98
97
82
12.5
12.5
22
23
24
25
26
27
28
29
6.25
12.5
6.25
6.25
3.78
25.2
0.60
2.02
Biological tests have been performed according to the
method described in refs 28–30 and the results are
reported in Tables 2–4.
b
13.40
7.77
5.94
10.28
5.31
2.14
0.62
0.95
1.64
0.85
4.28
6.16
12.5
210
211
212
213
214
215
216
217
31
6.25
6.25
6.25
12.5
12.5
Results and Discussion
53.54
76.97
Fromthe primary screening against
M. tuberculosis
87
69
H37Rv the maiority of the tested compounds showed an
inhibitory activity between 95 and 100%, therefore
these compounds were submitted to a second level assay
to evaluate the actual minimum inhibitory concentra-
tion (MIC) and to assess cytotoxicity towards the
VERO cell line and selectivity index (SI), defined as the
ratio of the measured IC50 in VERO cells to the MIC.
100
100
100
100
100
99
100
100
100
100
100
100
100
100
100
95
3.13
6.25
0.78
12.5
3.13
1.56
12.5
12.5
1.56
3.13
6.25
6.25
6.25
1.56
3.50
73
7.20
7.20
23
1.10
11.68
9.23
0.58
7.00
a
32
33
34
35
36
37
b
b
38
39
5.40
2.70
0.43
1.73
On the basis of the obtained data we can remark the
interesting anti-tubercular properties showed by some
quinolylhydrazones 3. The activity is significantly affec-
ted by substituents both on quinoline nucleus and
hydrazonic moiety. On quinoline nucleus the most
effective substituents resulted 6-cyclohexyl, 7-methoxy,
7-ethoxy and 7-chloro, while, as for the hydrazonic
moiety, greater effectiveness resulted for para- and
310
311
312
313
314
315
<4.20 <0.70
6.40
6.90
3.60
6.20
1.02
1.10
2.31
0.50
12.5
12.5
12.5
b
316
317
b
72
318
319
320
321
322
323
324
100
100
100
100
100
100
100
100
100
100
100
99
6.25
5.70
9.80
6.80
3.40
5.20
13.20
12.60
64
0.91
1.57
1.09
0.54
6.67
4.22
2.02
10.24
7.76
8.4
6.25
6.25
6.25
0.78
3.13
6.25
6.25
1.56
1.56
1.56
6.25
3.13
3.13
6.25
0.78
6.25
Table 3. Evaluation of anti-Mycobacterium avium activity
Compd
MIC (mg/mL)a
SI
38
39
325
3.13
25
3.13
23.32
0.29
20.45
a
325
326
327
328
12.1
13.1
6.60
4.23
aMICs are determined in the MABA against a strain of M. avium (A
TCC 25291).
b
329
330
331
332
333
334
99
3.40
1.09
100
100
100
100
4
10
4
53
3.30
3.40
11.90
0.56
4.36
1.9
Table 4. Macrofage assay
Compd
MIC (mg/mL)
SI
EC90
EC99
EC90/MIC
b
335
336
337
338
b
32
39
325
6.25
0.78
6.25
11.68
9.23
10.24
0.65
>1
0.80
2.00
>1
1.61
0.10
>1.28
0.13
b
b
b
339
Rifampin (RMP)
100
90
3.13
1.90
0.61
The columns labeled EC90 and EC99 list the concentrations effecting 90
and 99% reduction in residual mycobacterial growth after 7 days
compared to untreated controls. Compounds with EC90>16ÂMIC (as
reported in the column labeled EC90/MIC) are considered inactive.
aMIC against M. tuberculosis Erdman was 3.13.
bInsoluble in DMSO, unable to test.

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L. Savini et al. / Bioorg. Med. Chem. 10 (2002) 2193–2198
ortho-methoxynaphtyl substituents. MIC values for
those compounds ranged from 0.78 to 3.13 mg/mL
(Table 2). The chlorodisubstitution led to inactive deri-
vatives (335ꢀ39). As far as the substitution in position 2
of quinoline nucleus is concerned the methyl appears to
be most favourable group. Quinolylhydrazines 2, even if
endowed with appreciable inhibiting action, showed a
SI generally below 4, with the only exception of 213 and
214 with a SI=4.28 and 6.16 respectively, while for some
quinolylhydrazones (32,3,5,22,25,26,27) a significantly higher
SI was found (Table 2).
preparation of the unknown 4-quinolylhydrazines (25,
211, 215, 216) are also described in this section; analytical
and physicochemical data are reported in Table 1.
Spectroscopic data (IR and H NMR) are fully con-
sistent with the proposed structures.
1
7-Ethoxy-4-hydrazinoquinoline hydrochloride (25). Equi-
molar amounts of 7-ethoxy-4-chloroquinoline and
hydrazine hydrate (85%) in anhydrous ethanol were
heated under reflux for 7–8 h. The corresponding
hydrazinoquinoline hydrochloride precipitated already
in the course of refluxing and completely after cooling.
The obtained precipitate was purified by recrystalliza-
tion (65% yield).
Three compounds (32, 33 and 325), with a high SI value
(11.68, 9.23, and 10.24, respectively), were then tested
for efficacy in vitro in a TB-infected macrophage model,
showing good values of EC90 and EC99. Furthemore,
these compounds were evaluated for their inhibitory
activity against a single strain of M. avium, an oppor-
tunistic pathogen which has been associated with
tuberculosis in patients infected by HIV (Table 3). As
for compounds 32 and 325, which showed a SI of 23.32
and 20.45 respectively, further evaluation in additional
M. avium assays is in progress.
6-Cyclohexyl-4-hydrazinoquinoline hydrochloride (211).
The compound was obtained, according to the method
described for 25, by refluxing equimolar amounts of
6-cyclohexyl-4-chloroquinoline and hydrazine hydrate
(85%) for 8 h (61% yield).
4-Hydrazino-5,7-dichloroquinoline (215). 4,5,7,-Trichloro-
quinoline (21.5 mmol, 5 g) and hydrazine hydrate (85%)
(25 mL) in anhydrous ethanol were refluxed for 9–10 h.
After cooling and dilution with water the 4-hydrazino-
5,7-dichloroquinoline (215) precipitated, it was collected,
and recrystallized (60% yield).
It is important to point out the low toxicity particularly
shown by quinolylhydrazones 32 and 325 active against
M. tuberculosis H37Rv and M. avium.
In conclusion, for the development of our research, it
seems advisable to synthesize new derivatives with sui-
tably chosen substituents both on the quinoline nucleus
and hydrazonic moiety. Additional tests are required in
order to obtain more definitive and clear answers from
structure–activity relationships.
2-Methyl-4-hydrazino-5,7-dichloroquinoline (216). The
compound was obtained by refluxing, for 3–4 h, the
2-methyl-4,5,7-trichloroquinoline (20.29 mmol, 5 g) and
hydrazine hydrate (85%) (25 mL) under the same con-
ditions described above for compound 215 (80% yield).
General procedure
4-quinolylhydrazones (3)
for
the
preparation
of
Experimental
Chemistry
The title compounds were prepared from 4-quino-
lylhydrazine or its HCl salt and the appropriate carb-
oxaldehyde in EtOH for 1–2 h. After cooling and
diluting with H2O the quinolylhydrazone 3 precipitated
fromthe reaction mixture; it was collected and purified by
crystallization fromthe suitable solvent (Table 1) (70–
90% yields). In those instances where 4-hydrazinoquino-
line hydrochloride was employed, an equimolar amount
of NaOAc was added to the mixture to liberate the free
Melting points were determined on a Kofler blok or on
a Buchi 510 apparatus and are uncorrected. Elemental
analyses were performed on a Perkin-Elmer 240 C Ele-
mental Analyzer by Laboratories of Dipartimento
Farmaco Chimico Tecnologico, Universita di Siena
(Italy) and the data for C, H, and N are within Æ0.4%
of the theoretical values. IR spectra were determined in
Nujol mull on a Perkin-Elmer FT-IR 1600 spectro-
1
base for reaction. The H NMR spectral data of some
representative 4-quinolylhydrazones are here described.
1
photometer. H NMR spectra were recorded on a Var-
ian XL-200 or AC200 Bruker instruments. The chemical
shifts (d) are relative to Me4Si used as internal standard;
the following abbreviations were used: s=singlet,
t=triplet, dd=double doublet, q=quartet, qt=quintet,
st=sextet, m=multiplet, u=unresolved, b=broad. The
coupling constants J were in Hertz. TLC on silica-gel
plates (Merck, 60, F254) was used for purity check and
reaction monitoring. Column chromatography on silica
gel (Merck, 70–230 mesh and 230–400 mesh ASTH for
flash chromatography) was applied when necessary, to
isolate and purify the different reactions products.
37. (DMSO-d6) d 1.09 (t, 6H, 2 CH3CH2N); 2.44 (s, 3H,
CH3); 3.35 (q, 4H, 2 CH3CH2N); 3.84 (s, 3H, OCH3);
6.68 (d, 2H, PhH, Jorto=8.6); 6.97–7.08 (m, 3H, ArH
and H-3 quinoline); 7.53 (d, 2H, PhH, Jorto=8.6); 8.12
(d, 1H, H-5, J5ꢀ6=9.2); 8.19 (s, 1H, CH¼N); 10.55 (bs,
1H, NH, D2O exchangeable).
313. (DMSO-d6) d 1.38 (s, 3H, CH3CH2O); 2.48 (s, 3H,
CH3); 4.00 (s, 3H, OCH3); 4.14 (q, 2H, CH3CH2O);
7.01–7.11 (m, 3H, H-3 quinoline and 2 ArH); 7.38–7.52
(m, 2H, ArH); 7.63 (t, 1H, ArH); 7.88–8.00 (m, 2H,
ArH); 8.24 (d, 1H, ArH, Jorto=9.06); 9.07 (s, 1H,
CH¼N); 9.30 (d, 1H, ArH, Jorto=8.6); 10.98 (bs, 1H,
NH, D2O exchangeable).
All the reagents were of the best available commercial
quality and were used without further purification. The

L. Savini et al. / Bioorg. Med. Chem. 10 (2002) 2193–2198
2197
318. (DMSO-d6) d 0.96 (t, 3H, CH3CH2CH2CH2–); 1.39
(st, 2H, CH3CH2CH2CH2–); 1.72 (qt, 2H,
Coordinating Facility (TAACF), Southern Research
Institute, Frederick, MD, USA, through a research and
development contract of our University with the US
National Institute of Allergy and Infectious Diseases.
Thanks are addressed to Dr. Joseph A. Maddry
(TAACF) for his collaboration. This work was sup-
ported by financial assistance fromItalian Murst (ex
60% and ex 40%).
CH3CH2CH2CH2–); 2.81 (t, 2H, CH3CH2CH2CH2–);
4.06 (s, 3H, OCH3); 7.13 (d, 1H, H-3 quinoline,
J3ꢀ2=8.2); 7.31 (bs, 1H, ArH); 7.52–7.79 (m, 5H,
ArH); 7.93 (d, 1H, ArH, Jorto=8.1); 8.16 (s, 1H, ArH);
8.29 (d, 1H, H-2 quinoline, J2ꢀ3=8.2); 8.98 (ud, 2H,
1ArH and CH¼N); 10.95 (bs, 1H, NH, D2O
exchangeable).
323. (DMSO-d6) d 1.39–1.63 and 1.92–2.27 (2m, 10H,
cyclohexyl); 2.51–2.72 (m, 1H cyclohexyl); 4.06 (s, 3H,
OCH3); 7.13 (d, 1H, H-3 quinoline J3ꢀ2=8.4); 7.62–7.80
(m, 6H, ArH); 7.94 (d, 1H, ArH); 8.17 (ud, 1H, H-5
quinoline); 8.30 (d, 1H, H-2 quinoline, J2ꢀ3=8.4); 9.01
(bs, 2H, ArH and CH¼N); 11.70 (bs, 1H, NH, D2O
exchangeable).
References and Notes
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337. (DMSO-d6) d 2.56 (s, 3H, CH3); 6.10 (s, 2H,
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Acknowledgements
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