Synthesis of 1,2,4-triazole derivatives containing benzothiazoles as pharmacologically active molecule

Article abstract of DOI:10.3109/14756366.2010.535794

In attempt to make significant pharmacologically active molecule, we report here the synthesis and in vitro antimicrobial and antitubercular activity of various series of 3-(3-pyridyl)-5-(4-nitrophenyl)-4-(N-substituted-1,3- benzothiazol-2-amino)-4H-1,2,4-triazole. The antimicrobial activity of title compounds were examined against two Gram-positive bacteria (Staphylococcus aureus, Streptococcus pyogenes), two Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), and three fungi (Candida albicans, Aspergillus niger, Aspergillus clavatus) using the broth microdilution method and antitubercular activity H₃₇Rv using Lowenstein-Jensen agar method.

Full text of DOI:10.3109/14756366.2010.535794

Journal of Enzyme Inhibition and Medicinal Chemistry, 2011; 26(4): 527–534
© 2011 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2010.535794
ORIGINAL ARTICLE
Synthesis of 1,2,4-triazole derivatives containing
benzothiazoles as pharmacologically active molecule
Navin B. Patel, and Imran H. Khan
Department of Chemistry, Veer Narmad South Gujarat University, Surat, Gujarat, India
Abstract
In attempt to make significant pharmacologically active molecule, we report here the synthesis and in vitro
antimicrobial and antitubercular activity of various series of 3-(3-pyridyl)-5-(4-nitrophenyl)-4-(N-substituted-1,3-
benzothiazol-2-amino)-4H-1,2,4-triazole. The antimicrobial activity of title compounds were examined against two
Gram-positive bacteria (Staphylococcus aureus, Streptococcus pyogenes), two Gram-negative bacteria (Escherichia coli,
Pseudomonas aeruginosa), and three fungi (Candida albicans, Aspergillus niger, Aspergillus clavatus) using the broth
microdilution method and antitubercular activity H37Rv using Lowenstein-Jensen agar method.
Keywords: 1,2,4-Triazole, antimicrobial activity, antitubercular activity
Introduction
our oxadiazole were reported to possess antitubercular
activity.19,20 It is established that these compounds tar-
get the sterol demethylase, a mixed-function oxidase
involved in sterol synthesis in eukaryotic organisms.21
e unraveling of Mycobacterium genome sequence
has revealed that a protein having homology to one
of the above mixed oxidase function is present in
Mycobacterium tuberculosis.22 In view of this data, we
aimed the synthesis, antimicrobial, and antitubercular
evaluation of new substituted 1,2,4-triazole derivatives.
We have incorporated triazoles with pyridine and ben-
zothiazole derivatives, which possess wide variety of
biological activity.
Tuberculosis (TB) is the leading infectious cause of
death in the world today, with ∼3 million deceasing
every year. An increase in the global burden of TB with
the worldwide mortality rate of 23% is a major concern
in the socioeconomic and health sectors.1–5 e synergy
of this disease with HIV infection and the emergence
of multidrug resistance and extensively drug resistance
tuberculosis (MDRTB and XDRTB) pose a threatening
global challenge.6–8 Although a number of lead mole-
cules exist today to develop new drugs, no new chemi-
cal entity has emerged for clinical use for over the last
45 years in the treatment of this disease.9,10 erefore,
there is an urgent need to develop new drugs, acting
through a novel mechanism of action for the chemo-
therapy of TB.
Experimental section
Chemistry
Recently, certain triazole-based compounds were
reported to possess antimicrobial activities.11–13 It is
believed that aryl-azolyl-ethane moiety, present in
many azole antifungal drugs, serves as pharmacophore
in compounds having Mycobacterium killing activity.14,15
Many azole derivatives have also been shown to pos-
sess interesting antimycobacterial activity in addition to
antifungal activity.16–18 In addition, closer analogues of
All chemicals were of analytical grade and use directly.
All melting points were determined in PMP-DM scien-
tific melting point apparatus and are uncorrected. e
completion of the reaction was checked by TLC using
Merck silica gel 60 F254 and spots were visualized under
UV radiation. IR spectra were recorded on Perkin-Elmer
RX 1 FT-IR spectrophotometer in KBr (γmax in cm−1). H
1
Address for Correspondence: Navin B. Patel, Department of Chemistry, Veer Narmad South Gujarat University, Surat–395007, Gujarat, India.
E-mail: drnavin@satyam.net.in
(Received 08 March 2010; revised 25 July 2010; accepted 24 October 2010)
527

528 N.B. Patel and I.H. Khan
NMR spectra were recorded in CDCl3 on a Bruker Avance
II 400 NMR spectrometer (400 MHz) using TMS as inter-
nal standard (δ in ppm). 13C NMR spectra were recorded
in CDCl3 on a Bruker Avance II 400 NMR spectrometer
operating at 400 MHz (δ in ppm). e microanalyses
were performed on a Heraeus Carlo Erba 1180 CHN ana-
lyzer. e mass spectra were recorded on micromass Q-T
of micro (TOF MS ES+).
ppm. Anal. calcd. for C8H9N3OS: C, 49.21; H, 4.65; N,
21.52; Found: C, 49.25; H, 4.62; N, 21.48%.
(2f). Yield 68%; m.p. 198–200°C; IR (KBr): 3445 (NH2),
1
3218 (NH), 1624 (C=N), 1428 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.79 (s, 2H, NH2, disappeared on
D2O exchange), 8.90 (s, 1H, NH, disappeared on D2O
exchange), 7.82–8.21 (m, 3H, 3CH) ppm. Anal. calcd. for
C7H6N3ClS: C, 42.11; H, 3.03; N, 17.76; Found: C, 42.15; H,
3.07; N, 17.79%.
Substituted 2-hydrazino-1,3-benzothiazole (2a–j) was
prepared by the literature procedure.23,24
(2g) Yield 69%; m.p. 167–169°C; IR (KBr): 3439 (NH2),
1
3220 (NH), 1638 (C=N), 1435 (thiazole) cm−1; H NMR
General procedure for synthesis of 2-hydrazino
benzothiazoles
(400 MHz, CDCl3) δ 4.83 (s, 2H, NH2, disappeared on
D2O exchange), 8.92 (s, 1H, NH, disappeared on D2O
exchange), 2.83 (s, 3H, CH3), 7.31–7.69 (m, 3H, 3CH)
ppm. Anal. calcd. for C8H9N3S: C, 53.61; H, 5.06; N, 23.44;
Found: C, 53.65; H, 5.01; N, 23.38%.
(2a–j). Concentrated hydrochloric acid (0.067 mol)
was added drop wise with stirring to hydrazine hydrate
(0.12 mol) at 5–6°C followed by ethylene glycol (30mL);
thereafter substituted 2-amino-1,3-benzothiazole (1a–j)
(20 mmol) was added in portions and the resultant
mixture was refluxed for 2–3 h and cooled at room tem-
perature. e reaction progress was monitored by TLC
using toluene:ethylacetate (75:25) as mobile phase. e
reaction mixture was filtered and resulting precipitate
was washed with distilled water. e resulting crude was
crystallized from ethanol. e other compounds of the
series were prepared by similar procedure.
(2h). Yield 60%; m.p. 199–201°C; IR (KBr): 3440 (NH2),
1
3200 (NH), 1631 (C=N), 1445 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.88 (s, 2H, NH2, disappeared on
D2O exchange), 8.95 (s, 1H, NH, disappeared on D2O
exchange), 7.06–8.82 (m, 3H, 3CH) ppm. Anal. calcd. for
C7H6N4O2S: C, 40.00; H, 2.88; N, 26.65; Found: C, 40.04; H,
2.85; N, 26.61%.
(2i). Yield 68%; m.p. 248–250°C; IR (KBr): 3449 (NH2),
1
3212 (NH), 1640 (C=N), 1439 (thiazole) cm−1; H NMR
(2a). Yield 70%: m.p. 204–206°C. IR (KBr): 3435 (NH2),
(400 MHz, CDCl3) δ 4.86 (s, 2H, NH2, disappeared on
D2O exchange), 8.94 (s, 1H, NH, disappeared on D2O
exchange), 7.81 (s, 1H, CH), 7.98 (s, 1H, CH) ppm. Anal.
calcd. for C7H5N3Cl2S: C, 35.91; H, 2.15; N, 17.95; Found:
C, 35.88; H, 2.19; N, 17.92%.
1
3200 (NH), 1631 (C=N), 1442 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.83 (s, 2H, NH2, disappeared on
D2O exchange), 8.94 (s, 1H, NH, disappeared on D2O
exchange), 7.28–7.64 (m, 3H, 3CH) ppm. Anal. calcd. for
C7H6N3FS: C, 45.89; H, 3.30; N, 22.94; Found: C, 45.91; H,
3.31; N, 22.98%.
(2j). Yield 63%; m.p. 239–241°C; IR (KBr): 3449 (NH2),
1
3220 (NH), 1640 (C=N), 1445 (thiazole) cm−1; H NMR
(2b). Yield 61%; m.p. 200–202°C; IR (KBr): 3449 (NH2),
(400 MHz, CDCl3) δ 4.82 (s, 2H, NH2, disappeared on
D2O exchange), 8.92 (s, 1H, NH, disappeared on D2O
exchange), 7.55–7.87 (m, 3H, 3CH) ppm. Anal. calcd. for
C7H6N3ClS: C, 42.11; H, 3.03; N, 17.76; Found: C, 42.07; H,
3.01; N, 18.00%.
1
3212 (NH), 1623 (C=N), 1451 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.83 (s, 2H, NH2, disappeared on
D2O exchange), 8.90 (s, 1H, NH, disappeared on D2O
exchange), 7.63–7.93 (m, 3H, 3CH) ppm. Anal. calcd. for
C7H6N3SBr: C, 34.44; H, 2.48; N, 17.21; Found: C, 34.40; H,
2.45; N, 17.19%.
2-(3-Pyridyl)-5-(4-nitrophenyl)-1,3,4-oxadiazole (5)
A mixture of nicotinoyl hydrazide (4) (5 mmol) and
4-nitro benzoic acid (5 mmol) in phosphorus oxy-
chloride (5 mL) was refluxed on water bath for 9 h. e
progress of the reaction was monitored by TLC using
toluene:ethylacetate:methanol (70:20:10) as mobile
phase. After the completion of reaction, it was cooled
and poured onto crushed ice with continuous stirring.
e solid mass separated was neutralized with sodium
bicarbonate solution (10% w/v). e resulting solid
thus obtained was collected by filtration, washed well
with cold water, dried, and crystallized from absolute
ethanol.
(2c). Yield 67%; m.p. 210–212°C; IR (KBr): 3445 (NH2),
1
3220 (NH), 1640 (C=N), 1448 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.81 (s, 2H, NH2, disappeared on
D2O exchange), 8.92 (s, 1H, NH, disappeared on D2O
exchange), 7.04–7.79 (m, 3H, 3CH) ppm. Anal. calcd. for
C7H6N4O2S: C, 40.00; H, 2.88; N, 26.65; Found: C, 39.97; H,
2.90; N, 26.68%.
(2d). Yield 62%; m.p. 198–200°C; IR (KBr): 3449 (NH2),
1
3222 (NH), 1620 (C=N), 1439 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.82 (s, 2H, NH2, disappeared on
D2O exchange), 8.94 (s, 1H, NH, disappeared on D2O
exchange), 2.45 (s, 3H, CH3), 7.26–7.71 (m, 3H, 3CH)
ppm. Anal. calcd. for C8H9N3S: C, 53.61; H, 5.06; N, 23.44;
Found: C, 53.57; H, 5.08; N, 23.47%.
(5). Yield 65%; m.p. 121–123°C; IR (KBr): 1667 (C=N),
1
1284, 1078 (C-O-C) cm−1; H NMR (400 MHz, CDCl3) δ
(2e). Yield 65%; m.p. 193–195°C; IR (KBr): 3439 (NH2),
9.38 (s, 1H, CH), 8.83 (dd, 1H, J= 3.48 Hz, CH), 8.39–8.48
(m, 5H, 5CH), 7.61 (t, 1H, CH) ppm; 13C NMR (400 MHz,
CDCl3) δ 160.22 (C2-oxadiazole), 159.58 (C5-oxadiazole),
149.50, 146.88, 145.38, 135.83, 129.65, 128.68, 124.68,
124.29, 123.34 (aromatic ring) ppm; MS (m/z): 268 (M+);
1
3208 (NH), 1628 (C=N), 1448 (thiazole) cm−1; H NMR
(400 MHz, CDCl3) δ 4.80 (s, 2H, NH2, disappeared on
D2O exchange), 8.94 (s, 1H, NH, disappeared on D2O
exchange), 3.86 (s, 1H, OCH3), 7.16–7.65 (m, 3H, 3CH)

Synthesis of 1,2,4-triazole derivatives 529
Anal. calcd. for C13H8N4O3: C, 58.21; H, 3.01; N, 20.89;
Found: C, 58.17; H, 3.04; N, 20.85%.
compounds of the series were prepared by similar proce-
dure (Scheme 1).
(6a). Yield 66%; m.p. 210–212°C; IR (KBr): 3434 (NH),
1
General procedure for the synthesis of 3-(3-pyridyl)-5-
(4-nitrophenyl)-4-(N-substituted-1,3-benzothiazol-2-
amino)-4H-1,2,4-triazole (6a–j)
1649 (C=N) cm−1; H NMR (400 MHz, CDCl3) δ 7.73 (s,
1H, NH), 9.38 (s, 1H, CH), 8.84 (dd, 1H, J= 4.0 Hz, CH),
8.39–8.49 (m, 5H, 5CH), 7.60 (t, 1H, CH), 7.06–7.26 (m,
3H, benzothiazole-H); 13C NMR (400 MHz, CDCl3) δ
163.48 (C3-triazole), 163.35 (C5-triazole), 152.91, 149.66,
147.94, 145.66, 138.43, 134.42, 132.66, 131.12, 129.03,
129.12, 128.15, 124.55, 124.19, 121.91, 113.66, 109.85
(aromatic ring) ppm; MS (m/z): 433 (M+); Anal. calcd. for
C20H12N7O2FS: C, 55.42; H, 2.79; N, 22.62; Found: C, 55.38;
H, 2.81; N, 22.71%.
A mixture of 2-(3-pyridyl)-5-(4-nitrophenyl)-1,3,4-ox-
adiazole (5) (5 mmol) and substituted 2-hydrazino-1,3-
benzothiazole (2a–j) (5 mmol) in dry pyridine (10 mL)
was refluxed for 18–24 h. e reaction was monitored
by TLC on silica gel using ethyl acetate:toluene (2.5:7.5).
It was then cooled and poured on to crushed ice. e
reaction mass was neutralized by dilute hydrochloric
acid and resulting solid was washed with cold water,
dried, and crystallized from absolute ethanol. e other
(6b). Yield 62%; m.p. 199–201°C; IR (KBr): 3432 (NH),
1
1646 (C=N) cm−1; H NMR (400 MHz, CDCl3) δ 7.79 (s,
NH2
i
N
S
N
ii
NH2
NH NH2
S
R
R
R
1 a-j
2 a-j
O
O
O
CH3
O
OH
NH2
NH
iii
+
N
O2N
N
3
4
iv
N
N
O
5
N
NO2
N
N
N
v
NH
3a-j
5
+
N
NO2
N
S
R
6 a-j
i. NH4SCN,Br2, Glacial acetic acid, NH3; ii. Hydrazine Hydrate, conc. HCl, Ethylene Glycol;
iii. NH2NH2.H2O, ethanol, refluxed; iv. POCl3, reflux 9h;
v. dry pyridine, refluxed
R = a. 6-F,
b. 6-Br,
d. 6-CH3,
e. 6-OCH3,
f. 6-Cl,
g. 4-CH3,
h. 4-NO2,
i. 5-Cl,6-Cl,
j. 4-Cl
c. 6-NO2,
Scheme 1. Synthetic protocol for the compounds 6a–j.

530 N.B. Patel and I.H. Khan
1H, NH), 9.37 (s, 1H, CH), 8.82 (dd, 1H, J= 4.0 Hz, CH),
8.40–8.51 (m, 5H, 5CH), 7.56 (t, 1H, CH), 7.61-7.76 (m, 3H,
benzothiazole-H); 13C NMR (400 MHz, CDCl3) δ 163.28
(C3-triazole), 162.69 (C5-triazole), 153.03, 149.82, 147.69,
145.60, 136.69, 134.28, 133.15, 131.43, 129.03, 128.15,
127.78, 124.49, 124.16, 123.09, 118.99, 111.63 (aromatic
ring) ppm; MS (m/z): 494 (M+), 496 (M+2); Anal. calcd.
for C20H12N7O2BrS: C, 48.59; H, 2.45; N, 19.83; Found: C,
48.63; H, 2.41; N, 19.79%.
CDCl3) δ 163.18 (C3-triazole), 162.65 (C5-triazole), 20.82
(CH3), 152.88, 148.93, 146.98, 143.47, 134.28, 132.47,
132.25, 131.07, 129.18, 128.96, 128.82, 127.57, 124.53,
123.98, 122.04, 120.96 (aromatic ring) ppm; MS (m/z):
429 (M+); Anal. calcd. for C21H15N7O2S: C, 58.73; H, 3.52;
N, 22.83; Found: C, 58.81; H, 3.57; N, 22.87%.
(6h). Yield 67%; m.p. 171–173°C; IR (KBr): 3442 (NH),
1659 (C=N) cm−1; 1H NMR (400 MHz, CDCl3) δ 7.75 (s, 1H,
NH), 9.37 (s, 1H, CH), 8.82 (dd, 1H, J= 4.0 Hz, CH), 8.39–
8.48 (m, 5H, 5CH), 7.60 (t, 1H, CH), 8.22 (d, 1H, J= 8.16
Hz, CH), 8.56 (d, 1H, J= 8.14 Hz, CH), 6.63 (t, 1H, CH);
13C NMR (400 MHz, CDCl3) δ 162.94 (C3-triazole), 162.45
(C5-triazole), 152.21, 148.83, 147.74, 144.36, 138.06,
134.67, 132.10, 131.98, 131.81, 129.23, 128.07, 127.60,
124.20, 123.91, 122.55, 120.65 (aromatic ring) ppm; MS
(m/z): 460 (M+); Anal. calcd. for C20H12N8O4S: C, 52.17; H,
2.63; N, 24.34; Found: C, 52.21; H, 2.67; N, 24.37%.
(6c). Yield 69%; m.p. 186–188°C; IR (KBr): 3449
1
(NH), 1652 (C=N) cm−1; H NMR (400 MHz, CDCl3) 7.80
(s, 1H, NH), 9.38 (s, 1H, CH), 8.83 (dd, 1H, J= 3.8 Hz, CH),
8.36–8.47 (m, 5H, 5CH), 7.62 (t, 1H, CH), 7.33 (d, 1H,
J= 8.16 Hz, CH), 7.56 (d, 1H, J= 7.85 Hz, CH), 8.74 (s, 1H,
CH); 13C NMR (400 MHz, CDCl3) δ 162.94 (C3-triazole),
162.53 (C5-triazole), 152.96, 148.83, 147.74, 146.61, 141.77,
134.48, 132.86, 132.32, 129.03, 129.53, 129.31, 124.61,
124.19, 121.98, 110.58, 119.72 (aromatic ring) ppm; MS
(m/z): 460 (M+); Anal. calcd. for C20H12N8O4S: C, 52.17; H,
2.63; N, 24.34; Found: C, 52.21; H, 2.59; N, 24.31%.
(6i). Yield 68%; m.p. 205–207°C; IR (KBr): 3449 (NH),
1
1649 (C=N) cm−1; H NMR (400 MHz, CDCl3) δ 7.88 (s,
1H, NH), 9.36 (s, 1H, CH), 8.81 (dd, 1H, J= 3.8 Hz, CH),
8.38–8.50 (m, 5H, 5CH), 7.59 (t, 1H, CH), 7.59 (s, 1H, CH),
7.66 (s, 1H, CH); 13C NMR (400 MHz, CDCl3) δ 163.34
(C3-triazole), 162.89 (C5-triazole), 152.35, 149.74, 147.82,
144.86, 134.29, 133.72, 133.50, 129.69, 129.41, 128.02,
128.75, 124.46, 124.02, 123.37, 123.78, 121.74 (aromatic
ring) ppm; MS (m/z): 484 (M+), 486 (M+2), 488 (M+4);
Anal. calcd. for C20H11N7O2Cl2S: C, 49.60; H, 2.29; N, 20.24;
Found: C, 49.64; H, 2.26; N, 20.21%.
(6j). Yield 65%; m.p. 191–193°C; IR (KBr): 3438 (NH),
1661 (C=N) cm−1; 1H NMR (400 MHz, CDCl3) δ 7.76 (s, 1H,
NH), 9.37 (s, 1H, CH), 8.81 (dd, 1H, J= 4.0 Hz, CH), 8.38–
8.51 (m, 5H, 5CH), 7.61 (t, 1H, CH), 6.91–7.30 (m, 3H,
benzothiazole-H); 13C NMR (400 MHz, CDCl3) δ 163.42
(C3-triazole), 162.96 (C5-triazole), 152.59, 148.96, 146.89,
144.86, 134.12, 131.65, 131.32, 131.59, 128.02, 127.81,
124.47, 124.08, 123.18, 120.29, 120.18, 118.79 (aromatic
ring) ppm; MS (m/z): 449 (M+), 451 (M+2); Anal. calcd.
for C20H12N7O2ClS: C, 53.40; H, 2.69; N, 21.79; Found: C,
53.34; H, 2.72; N, 21.83%.
(6d). Yield 70%; m.p. 179–180°C; IR (KBr): 3447 (NH),
1
1661 (C=N) cm−1; H NMR (400 MHz, CDCl3) δ 2.34 (s,
3H, CH3), 7.82 (s, 1H, NH), 9.37 (s, 1H, CH), 8.82 (dd, 1H,
J= 4.0 Hz, CH), 8.39–8.52 (m, 5H, 5CH), 7.56 (t, 1H, CH),
7.05-7.50 (m, 3H, benzothiazole-H); 13C NMR (400 MHz,
CDCl3) δ 163.07 (C3-triazole), 162.61 (C5-triazole), 22.91
(CH3), 152.93, 149.57, 148.01, 144.75, 135.28, 135.07,
131.31, 129.05, 129.92, 128.79, 128.52, 124.61, 124.21,
124.02, 121.27, 121.38 (aromatic ring) ppm; MS (m/z):
429 (M+); Anal. calcd. for C21H15N7O2S: C, 58.73; H, 3.52;
N, 22.83; Found: C, 58.77; H, 3.47; N, 22.78%.
(6e). Yield 71%; m.p. 189–191°C; IR (KBr): 3449 (NH),
1655 (C=N) cm−1; 1H NMR (400 MHz, CDCl3) δ 3.82 (s, 3H,
OCH3), 7.76 (s, 1H, NH), 9.36 (s, 1H, CH), 8.81 (dd, 1H,
J= 4.0 Hz, CH), 8.39–8.48 (m, 5H, 5CH), 7.59 (t, 1H, CH),
6.84–7.28 (m, 3H, benzothiazole-H); 13C NMR (400 MHz,
CDCl3) δ 163.38 (C3-triazole), 162.82 (C5-triazole), 52.59
(OCH3), 152.91, 149.99, 147.76, 147.35, 143.02, 134.36,
132.60, 132.44, 131.13, 129.13, 128.42, 124.23, 124.08,
119.15, 113.98, 106.25 (aromatic ring) ppm; MS (m/z):
445 (M+); Anal. calcd. for C21H15N7O3S: C, 56.62; H, 3.39;
N, 22.01; Found: C, 56.66; H, 3.41; N, 21.98%.
(6f). Yield 65%; m.p. 204–206°C; IR (KBr): 3442 (NH),
1657 (C=N) cm−1; 1H NMR (400 MHz, CDCl3) δ 7.80 (s, 1H,
NH), 9.36 (s, 1H, CH), 8.82 (dd, 1H, J= 3.8 Hz, CH), 8.37–
8.48 (m, 5H, 5CH), 7.52 (t, 1H, CH), 7.59–7.76 (m, 3H,
benzothiazole-H); 13C NMR (400 MHz, CDCl3) δ 163.34
(C3-triazole), 162.85 (C5-triazole), 152.87, 148.97, 147.32,
144.44, 134.08, 131.52, 131.05, 129.09, 127.81, 127.62,
126.85, 125.47, 124.33, 123.84, 121.95, 121.52 (aromatic
ring) ppm; MS (m/z): 449 (M+), 451 (M+2); Anal. calcd.
for C20H12N7O2ClS: C, 53.40; H, 2.69; N, 21.79; Found: C,
53.42; H, 2.73; N, 21.83%.
Antimicrobial activity
e minimum inhibitory concentrations (MICs) of syn-
thesized compounds were carried out by broth microdi-
lution method as described by Rattan.25 Antibacterial
activity was screened against two Gram-positive bacte-
ria (Staphylococcus aureus MTCC 96 and Streptococcus
pyogenes MTCC 442) and two Gram-negative bacteria
(Escherichia coli MTCC 443 and Pseudomonas aeruginosa
MTCC 2488). Ampicillin was used as a standard antibac-
terial agent. Antifungal activity was screened against three
fungal species Candida albicans MTCC 227, Aspergillus
niger MTCC 282, and Aspergillus clavatus MTCC 1323.
Griseofulvin was used as a standard antifungal agent.
All MTCC cultures were collected from Institute of
Microbial Technology, Chandigarh and tested against
above mentioned known drugs. Mueller hinton broth
was used as nutrient medium to grow and dilute the drug
suspension for the test. Inoculum size for test strain was
(6g). Yield 65%; m.p. 192–194°C; IR (KBr): 3435 (NH),
1
1660 (C=N) cm−1; H NMR (400 MHz, CDCl3) δ 2.61 (s,
3H, CH3), 7.76 (s, 1H, NH), 9.36 (s, 1H, CH), 8.82 (dd, 1H,
J= 3.8 Hz, CH), 8.38–8.49 (m, 5H, 5CH), 7.59 (t, 1H, CH),
7.09–7.28 (m, 3H, benzothiazole-H); 13C NMR (400 MHz,

Synthesis of 1,2,4-triazole derivatives 531
adjusted to 108 colony-forming unit (CFU) per millilitre by
comparing the turbidity. Dimethyl sulphoxide (DMSO)
was used as diluents to get desired concentration of
drugs to test upon standard bacterial strains. Serial dilu-
tions were prepared in primary and secondary screening.
e control tube containing no antibiotic was immedi-
ately subcultured (before inoculation) by spreading a
loopful evenly over a quarter of plate of medium suitable
for the growth of the test organism and put for incuba-
tion at 37°C overnight. e tubes were then incubated
overnight. e MIC of the control organism was read to
check the accuracy of the drug concentrations. e low-
est concentration inhibiting growth of the organism was
recorded as the MIC. All the tubes not showing visible
growth (in the same manner as control tube described
earlier) was subcultured and incubated overnight at
37°C. e amount of growth from the control tube before
incubation (which represents the original inoculum) was
compared. Subcultures might show similar number of
colonies indicating bacteriostatic, a reduced number of
colonies indicating a partial or slow bactericidal activity
and no growth if the whole inoculum has been killed.
e test must include a second set of the same dilutions
inoculated with an organism of known sensitivity. Each
synthesized drug was diluted obtaining 2000 μg/mL con-
centration, as a stock solution. In primary screening, 500,
250, and 125 μg/mL concentrations of the synthesized
drugs were taken. e active synthesized compounds
found in this primary screening were further tested in
a second set of dilution against all microorganisms. e
drugs found active in primary screening were similarly
diluted to obtain 100, 50, 25, 12.5, 6.250, 3.125, and 1.5625
μg/mL concentrations. e highest dilution showing at
least 99% inhibition is taken as MIC.
Results and discussion
Chemistry
2-Amino-6-flouro-1,3-benzothiazole 1a on treatment
of hydrazine hydrate, concentrated hydrochloric acid,
and ethylene glycol yields 2-hydrazino-6-flouro-1,3-
benzothiazole 2a. IR spectra of 2a showed broad stretch-
ing band around 3425 and 3200 cm−1 for NH and NH2.
1H NMR spectrum showed a singlet at δ 4.83 and δ 8.93,
which were accounted for NH2 and NH, which vanished
on D2O exchange. Ethyl nicotinate 3 on treatment with
hydrazine hydrate yields nicotinoyl hydrazide 4; the IR
spectra of 4 showed stretching band around 3335 and
3278 cm−1 due to amine/amide NH, whereas strong
stretching band at 1610 cm−1 was attributed to amide car-
1
bonyl. H NMR spectrum showed a singlet at δ 4.51 and
δ 9.81, which were accounted for NH2 and NH, which
vanished on D2O exchange. Intermolecular cyclization of
nicotinoyl hydrazide 4 with 4-nitrobenzoic acid in pres-
ence of phosphorus oxy chloride affords 2-(3-pyridyl)-5-
1
(4-nitrophenyl)-1,3,4-oxadiazole 5. Disappearance of H
NMR resonances observed with NH and NH2 functions in
the 1H NMR spectrum of 5 proved that ring closure start-
ing from 4 resulted in the formation of 1,3,4-oxadiazole
ring. is was further substantiated by the 13C NMR data
of 5, which showed a peak at δ 160.22 and δ 159.58 due to
C2 and C5 of oxadiazole. Mass spectrum of 5 displayed a
molecular ion peak at m/z 268 that confirmed its molec-
ular weight. Condensation of 5 with various substituted
2-hydrazino-1,3-benzothiazole 2a–j in pyridine results
in 3-(3-pyridyl)-5-(4-nitrophenyl)-4-(N-substituted-1,3-
benzothiazol-2-amino)-4H-1,2,4-triazole 6a–j. Absence
of 1H NMR resonances observed with NH2 function of 2a
and appearance of signal at δ 7.73 for NH was observed
1
in H NMR of 6a proved the condensation of 2 and 5
resulted in the formation of 1,2,4-triazole ring. is was
substantiated by 13C NMR data of 6a that showed a peak
at δ 163.48 and δ 163.35 due to C3 and C5 of triazole. Mass
spectrum of 6 displayed a molecular ion at m/z 433 that
confirmed its molecular weight.
Antitubercular activity
Drug susceptibility and determination of MIC of the
test compounds against M. tuberculosis H37Rv were per-
formed by L.J. agar (MIC) method25–28 where primary
1000, 500, 250 and secondary 200, 100, 62.5, 50, 25, 12.5,
6.25, 3.25 μg/mL dilutions of each test compound were
added; liquid L.J. medium and then media were steril-
ized by inspissation method. A culture of M. tuberculosis
H37Rv growing on L.J. medium was harvested in 0.85%
saline in bijou bottles. All test compounds that make
first stock solution of 2000 μg/mL concentration of
compounds were prepared in DMSO. ese tubes were
then incubated at 37°C for 24 h followed by streaking of
M. tuberculosis H37Rv (5 × 104 bacilli per tube). ese
tubes were then incubated at 37°C. Growth of bacilli was
seen after 12 days, 22 days, and finally 28 days of incuba-
tion. Tubes having the compounds were compared with
control tubes where medium alone was incubated with
M. tuberculosis H37Rv. e concentration at which no
development of colonies occurred or <20 colonies was
taken as MIC concentration of test compound. e stan-
dard strain M. tuberculosis H37Rv was tested with known
drug rifampicin.
Antibacterial activity
e MICs of the tested compounds are shown in Tables 1
and 2. e results revealed that substituted 2-hydrazino
benzothiazoles were moderately active against bacteria
except 2e, which showed good activity against S. aureus
and E. coli while 1,3,4-oxadiazole 5 exhibited quite good
activity to some extent. Most of 1,2,4-triazole derivative
were found good activity (62.5–250 μg/mL) against S.
aureus. Compounds 6b, 6c, 6f, 6g, and 6j exhibited pro-
nounced activity (62.5–125 μg/mL) against S. aureus. All
the compounds exhibited moderate activity (150–250
μg/mL) except 6b and 6j (62.5 μg/mL) against S. pyo-
genes. Compounds 6b, 6f, 6g, 6h, and 6j possessed good
activity (100–125 μg/mL) except 6c showed pronounced
activity (62.5 μg/mL) while others displayed moderate
activity (150–250 μg/mL) against E. coli. Compounds
6c and 6d showed good activity (100 μg/mL) except 6i

532 N.B. Patel and I.H. Khan
6c, 6g, 6i, and 6j showed good activity toward Gram-
negative bacteria. Compounds 2e, 6c, 6g, and 6j were
found active against Gram-positive and Gram-negative
bacteria.
showed very good activity (62.5 μg/mL) while others
possessed moderate activity (150–250 μg/mL) against P.
aeruginosa. Compounds 6b, 6c, 6f, 6g, and 6j exhibited
good activity against Gram-positive bacteria, whereas
Table 1. Minimum inhibitory concentrations (MICs, μg/mL) for the title compounds.
Gram-positive bacteria
Gram-negative bacteria
S. aureus
MTCC 96
500
S. pyogenes
MTCC 442
250
E. coli
MTCC 443
250
P. aeruginosa
Compound
R
6-F
MTCC 2488
250
2a
2b
6-Br
250
500
500
500
2c
2d
2e
2f
6-NO2
6-CH3
6-OCH3
6-Cl
500
500
250
250
250
250
100
500
200
250
62.5
100
125
500
500
125
2g
2h
2i
2j
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
500
500
250
250
500
250
500
250
250
500
100
125
500
500
250
250
5
—
100
125
500
250
6a
6-F
250
250
250
500
6b
6c
6d
6e
6-Br
100
62.5
500
125
250
6-NO2
6-CH3
6-OCH3
6-Cl
62.5
250
62.5
150
100
250
100
250
125
500
250
6f
125
500
125
250
6g
6h
6i
6j
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
100
1000
250
100
250
500
125
200
1000
100
250
500
62.5
250
62.5
100
100
Ampicillin
—
250
100
100
Table 2. Minimum inhibitory concentrations (MICs, μM) for the title compounds.
Gram-positive bacteria
Gram-negative bacteria
S. aureus
MTCC 96
2732
S. pyogenes
E. coli
P. aeruginosa
MTCC 2488
1366
Compound
R
6-F
MTCC 442
1366
MTCC 443
1366
2a
2b
6-Br
1024
2049
2049
2049
2c
2d
2e
2f
2g
2h
2i
2j
6-NO2
6-CH3
6-OCH3
6-Cl
2380
2380
1190
1190
1396
1396
558.6
320.5
502.5
1396
2793
1025
1282
641.0
628.1
1396
2512
2512
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
2793
2793
2380
1190
2380
1190
1068
2136
427.3
1256
534.2
1256
2512
2512
5
6a
6b
6c
6d
6e
6f
6g
—
373.1
577.3
202.4
135.8
582.7
561.8
278.4
233.1
1086
466.4
577.3
126.5
1086
1865
932.8
1154
6-F
577.3
253.0
135.8
349.6
1123
6-Br
506.0
217.4
233.1
561.8
556.6
582.7
434.7
124.1
556.8
286.5
6-NO2
6-CH3
6-OCH3
6-Cl
582.7
280.9
1113
278.4
233.1
271.7
1033
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
2331
6h
6i
6j
543.4
516.5
139.2
286.5
2066
222.7
716.3
222.7
286.5
Ampicillin
—

Synthesis of 1,2,4-triazole derivatives 533
has been selected for further development, and studies to
acquire more information about structure–activity rela-
tionships are in progress in our laboratories.
Antifungal activity
In vitro antifungal activities (MICs) of the synthesized
compounds are shown in Tables 3 and 4. e results
showed that 2-hydrazino benzothiazoles 2a–i possessed
good activity (250–500 μg/mL) against C. albicans except
2j (1000 μg/mL). Compounds 2a–j displayed moderate
to weak activity (250–500 μg/mL) against A. niger and
A. clavatus, whereas 1,3,4-oxadiazole 5 exhibited weak
activity against all three fungi. Compounds 6c, 6d, 6e,
6f, 6i, and 6j showed good activity (250–500 μg/mL),
whereas 6a and 6h exhibited pronounced activity (100
μg/mL) against C. albicans. Compounds 6a, 6h, and 6i
exhibited moderate activity (200–250 μg/ml), whereas
remaining compounds showed weak activity against A.
niger. Compounds 6d and 6h displayed moderate activ-
ity (200–250 μg/mL), whereas rest of the compounds
showed weak activity against A. clavatus. Compounds 2f,
2g, 2h, 6a, 6d, and 6h were found active against all the
three fungal species.
Table 4. Minimum inhibitory concentrations (MICs, μM) for the
title compounds.
Fungal species
C. albicans
MTCC 227
1366
A. niger
A. clavatus
Compound
R
6-F
MTCC 282 MTCC 323
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
5
6a
6b
6c
6d
6e
5464
2049
2380
2793
2564
1005
1396
1190
2136
2512
>2731
577.3
>2024
1086
1165
1123
2227
>2331
434.8
0516
>2227
284.0
5464
2049
4761
5586
1282
1265
1117
952.3
4273
2512
>2731
2309
>2024
2173
582.7
2247
2227
>2331
434.8
1033
>2227
284.0
6-Br
2049
6-NO2
6-CH3
6-OCH3
6-Cl
2380
1396
2564
1265
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
2793
952.3
2136
5025
—
>2731
230.9
>2024
1086
6-F
6-Br
Antitubercular activity
6-NO2
6-CH3
6-OCH3
6-Cl
e encouraging results from the antibacterial studies
impelled us to go for preliminary screening of synthesized
compounds against M. tuberculosis are summarized in
Table 5. From the preliminary examination of the antitu-
bercular activity results, compound 2e containing hydraz-
ide group showed better activity (50 μg/mL) against M.
tuberculosis and compounds 6a, 6e, and 6j showed good
activity (50–62.5 μg/mL). Due to the better activity against
tested microorganisms and mycobacteria, compound 6j
582.7
561.8
1113
6f
6g
6h
6i
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
>2331
217.4
1033
6j
1113
Griseofulvin
—
1420
Table 3. Minimum inhibitory concentrations (MICs, μg/mL) for
the title compounds.
Table 5. Minimum inhibitory concentrations (MICs, μg/mL and
μM) for the title compounds.
Fungal species
MIC values of M.
tuberculosis H37Rv
C. albicans
MTCC 227
250
A. niger
A. clavatus
Compound
R
6-F
μg/mL
250
500
250
1000
50
μM
1366
2049
1109
5586
256.4
1005
2793
2380
1068
502.5
3731
461.6
126.5
543.4
233.1
140.44
556.8
2331
217.4
413.2
111.3
48.66
% Inhibition
98%
96%
98%
95%
98%
96%
95%
97%
98%
96%
95%
96%
98%
96%
98%
96%
94%
97%
96%
98%
98%
98%
Compound
R
6-F
MTCC 282 MTCC 323
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
5
6a
6b
6c
6d
6e
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
5
6a
6b
6c
6d
6e
1000
500
1000
500
6-Br
6-Br
500
6-NO2
6-CH3
6-OCH3
6-Cl
6-NO2
6-CH3
6-OCH3
6-Cl
500
500
1000
1000
250
250
500
500
500
200
500
500
250
100
1000
200
62.5
250
100
62.5
250
1000
100
200
50
250
200
250
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
500
250
200
200
250
200
500
500
1000
500
1000
>1000
100
500
—
—
>1000
250
>1000
1000
>1000
1000
250
6-F
6-F
6-Br
6-Br
>1000
500
>1000
500
6-NO2
6-CH3
6-OCH3
6-Cl
6-NO2
6-CH3
6-OCH3
6-Cl
250
500
250
500
1000
1000
>1000
200
6f
6g
6h
6i
6f
6g
6h
6i
500
1000
>1000
200
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
4-CH3
4-NO2
5-Cl, 6-Cl
4-Cl
>1000
100
500
250
500
6j
6j
500
>1000
100
>1000
100
Rifampicin
—
40
Griseofulvin
—
500

534 N.B. Patel and I.H. Khan
11. Banfi, E., Scialino, G., Zampieri, D., Mamolo, M.G., Vio, L.,
Ferrone, M., Fermeglia, M., Paneni, M.S., Pricl, S. Antifungal
and antimycobacterial activity of new imidazole and triazole
Conclusion
A series of newer analogues 1,2,4-triazoles were synthe-
sized by the introduction of 2-hydrazino benzothiazoles
to 1,3,4-oxadiazoles and accessed for antimicrobial and
antitubercular activity. Modification of substituents
on benzothiazoles ring with various electron-releasing
and electron-withdrawing substituents improved the
activity. e analogues with halogen, methyl, and
nitro substituents emerged as promising antibacterials
showing better to moderate activity, whereas analogues
bearing nitro substituent showed better antifungal activ-
ity. It was also observed that the promising antimicrobials
have proved to be better antituberculars. Specially, com-
pound 6j due to their better activity against H37Rv strain,
is the best choice for the preparation of new derivatives
in order to improve antitubercular activity in future.
derivatives.
A combined experimental and computational
approach. J. Antimicrob. Chemother. 2006, 58, 76–84.
12. Ulusoy, N., Gürsoy, A., Otük, G. Synthesis and antimicrobial
activity of some 1,2,4-triazole-3-mercaptoacetic acid derivatives.
Farmaco 2001, 56, 947–952.
13. Muhi-Eldeen Z, Nadir M, Aljobory NR, Husseen F, Stohs SJ.
Synthesis and antimicrobial evaluation of 3-(4-tert-amino-2-
butynyl)thio and alkyl/alkenylthio-4,5-disubstituted-4H-1,2,4-
triazoles. Eur. J. Med. Chem. 1991, 26, 237–241.
14. Küçükgüzel, I., Tatar, E., Küçükgüzel, S.G., Rollas, S., De
Clercq, E. Synthesis of some novel thiourea derivatives obtained
from
5-[(4-aminophenoxy)methyl]-4-alkyl/aryl-2,4-dihydro-
3H-1,2,4-triazole-3-thiones and evaluation as antiviral/anti-
HIV and anti-tuberculosis agents. Eur. J. Med. Chem. 2008, 43,
381–392.
15. Banfi, E., Mamolo, M.G., Zampieri, D., Vio, L., Monti Bragadin, C.
Antimycobacterial activity of N1-[1-[3-aryl-1-(pyridin-2-, 3- or
4-yl)-3-oxo] propyl]-2-pyridinecarboxamidrazones. J. Antimicrob.
Chemother. 2001, 48, 705–707.
16. Jackson, C.J., Lamb, D.C., Kelly, D.E., Kelly, S.L. Bactericidal and
inhibitoryeffectsofazoleantifungalcompoundsonMycobacterium
smegmatis. FEMS Microbiol. Lett. 2000, 192, 159–162.
17. Guardiola-Diaz, H.M., Foster, L.A., Mushrush, D., Vaz, A.D. Azole-
antifungalbindingtoanovelcytochromeP450fromMycobacterium
tuberculosis: implications for treatment of tuberculosis. Biochem.
Pharmacol. 2001, 61, 1463–1470.
18. McLean, K.J., Marshall, K.R., Richmond, A., Hunter, I.S., Fowler, K.,
Kieser, T., Gurcha, S.S., Besra, G.S., Munro, A.W. Azole antifungals
are potent inhibitors of cytochrome P450 mono-oxygenases
and bacterial growth in mycobacteria and streptomycetes.
Microbiology 2002, 30, 314–318.
Acknowledgements
e authors are thankful to Veer Narmad South Gujarat
University for providing necessary facilities and research
fellowship. We also thank SAIF Lucknow for elemental
analysis and SAIF Chandigarh for spectral analysis of
the compounds and D. Rajani, Microbial Laboratory,
Surat, for antimicrobial and antimycobacterial activity.
Declaration of interest
19. Dabiri, M., Salehi, P., Baghbanzadeh, M., Bahramnejad, M. A
facile procedure for the one-pot synthesis of unsymmetrical
2,5-disubstituted 1,3,4-oxadiazoles. Tetrahedron Lett. 2006, 47,
6983–6986.
e authors report no conflict of interest. e authors
alone are responsible for the content and writing of the
article.
20. Navarrete-Vázquez,
G.,
Molina-Salinas,
G.M.,
Duarte-
Fajardo, Z.V., Vargas-Villarreal, J., Estrada-Soto, S., González-
Salazar, F., Hernández-Núñez, E., Said-Fernández, S. Synthesis
and antimycobacterial activity of 4-(5-substituted-1,3,4-oxadiazol-
2-yl)pyridines. Bioorg. Med. Chem. 2007, 15, 5502–5508.
21. Podust, L.M., Poulos, T.L., Waterman, M.R. Crystal structure
of cytochrome P450 14alpha-sterol demethylase (CYP51) from
Mycobacterium tuberculosis in complex with azole inhibitors. Proc.
Natl. Acad. Sci. U.S.A. 2001, 98, 3068–3073.
References
1. Stokstad, E. Infectious disease. Drug-resistant TB on the rise.
Science 2000, 287, 2391.
2. WHO Global Tuberculosis Programme—Tuberculosis Fact Sheet,
2002. World Health Organization. Global Tuberculosis Control,
WHO Report 2001, 2002.
22. Bellamine, A., Mangla, A.T., Nes, W.D., Waterman, M.R.
Characterization and catalytic properties of the sterol 14alpha-
demethylase from Mycobacterium tuberculosis. Proc. Natl. Acad.
Sci. U.S.A. 1999, 96, 8937–8942.
23. Barnett, C.J. Exchange Amination Process for Preparing
2-Hydrazinobenzothiazoles. U.S. Patent 3,937,714.
24. Kumar, V., Roy, R.K., Kumar, V., Kukshal, A., Yadav, V.P. Synthesis
and antimicrobial activity of 2-(6-substituted-1,3-benzothiazol-
2-yl)-N-(4-halophenyl)hydrazinecarbothiomide. J. Indian Chem.
Soc. 2008, 85B, 333–335.
25. Rattan, A. Antimicrobials in Laboratory Medicine. New Delhi:
Churchill BI Livingstone, 2000, pp. 85–108.
26. Anargyros, P., Astill, D.S., Lim, I.S. Comparison of improved
BACTEC and Lowenstein-Jensen media for culture of mycobacteria
from clinical specimens. J. Clin. Microbiol. 1990, 28, 1288–1291.
27. Shah, R.R., Mehta, R.D., Parikh, A.R. Studies on isoniazide
derivatives: preparation and antimicrobial activity of 2-aryl-3-
(pyridylcarbomyl)-5-carboxymethyl-4-thiazolidinones. J. Indian
Chem. Soc. 1985, 62B, 255–257.
28. Desai, N.C., Shukla, H.K., Tahker, K.A. Some new 2-aryl-3-
isonicotamido-4-thiazolidinones and their 5-carboxymethyl
homologues as potential antitubercular and antibacterial agent.
J. Indian Chem. Soc. 1984, 61B, 239–240.
3. World Health Organization, Geneva, Switzerland, WHO/CDS/
TB/2001, 287. http://www.who.int/mediacentre/factsheets/
who104/en/index.html
4. Mooran, N. WHO issues another gloomy tuberculosis report. Nat.
Med. 1996, 2, 377.
5. Dye, C., Scheele, S., Dolin, P., Pathania, V., Raviglione, M.C.
Global burden of tuberculosis: estimated incidence, prevalence
and mortality by country. J. Am. Med. Assoc. 1999, 282,
677–686.
6. Dooley, S.W., Jarvis, W.R., Martone, W.J., Snider, D.E. Jr. Multidrug-
resistant tuberculosis. Ann. Intern. Med. 1992, 117, 257–259.
7. Raviglione, M.C., Snider, D.E. Jr, Kochi, A. Global epidemiology of
tuberculosis. Morbidity and mortality of a worldwide epidemic.
JAMA 1995, 273, 220–226.
8. Farmer, P., Bayona, J., Becerra, M., Furin, J., Henry, C., Hiatt, H.,
Kim, J.Y., Mitnick, C., Nardell, E., Shin, S. e dilemma of MDR-TB
in the global era. Int. J. Tuberc. Lung Dis. 1998, 2, 869–876.
9. Hudson, A., Imamura, T., Gutteridge, W., Kanyok, T., Nunn, P. e
Current Anti-TB Drug Research and Development Pipeline. WHO
TDR/PRD/03.1W Geneva, 2003.
10. Tripathi, R.P., Tewari, N., Dwivedi, N., Tiwari, V.K. Fighting
tuberculosis: an old disease with new challenges. Med. Res. Rev.
2005, 25, 93–131.