Synthesis and molecular docking studies of glucose-linked isonicotinoyl- 1, 3, 4-thiadiazolidines as antitubercular agents

Article abstract of DOI:10.2174/1570178614666170608130326

Background: The recent emergence of multidrug-resistant strains of M. tuberculosis that are resistant to two major effective drugs, viz. isoniazid and rifampicin, stimulated us to make an attempt for the development of a new class of potent antitubercular

Full text of DOI:10.2174/1570178614666170608130326

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Letters in Organic Chemistry, 2018, 15, 15-22
RESEARCH ARTICLE
ISSN: 1570-1786
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Synthesis and Molecular Docking Studies of Glucose-linked Isonicotinoyl-
1,3,4-Thiadiazolidines as Antitubercular Agents
BENTHAM
S
CIENCE
Snehal A. Chavan1,*, Avinash G. Ulhe1, Baliram N. Berad1 and Rupesh V. Chikhale2,3
1Department of Chemistry, Mahatma Jyotiba Phule Educational Campus, Rashtrasant Tukadoji Maharaj Nagpur Uni-
2
versity, Nagpur, India; Advanced Centre for Treatment, Research and Education in Cancer (ACTREC) Tata Memorial
Centre, Kharghar, Navi Mumbai, India; 3Division of Pharmacy and Optometry, University of Manchester, Manchester,
UK
Abstract: Background: The recent emergence of multidrug-resistant strains of M. tuberculosis that are
resistant to two major effective drugs, viz. isoniazid and rifampicin, stimulated us to make an attempt
for the development of a new class of potent antitubercular agents by modifying the structures of exist-
ing drugs. Aiming this, an efficient synthesis of glucose linked-isonicotinoyl-1,3,4-thiadiazolidines has
been carried out.
Method: The title compounds have been synthesized through cyclocondensation reaction of 1-
isonicotinoyl-4-aryl thiosemicarbazides with N-tetra-O-acetyl-β-D-glucopyranosyl isocyanodichloride.
The structures of newly synthesized compounds were verified by IR, 1H NMR, 13C NMR, mass spec-
A R T I C L E H I S T O R Y
trometry and elemental analyses. The title compounds were evaluated for their in vitro antitubercular
potency against M. tuberculosis H37Rv strain using Lowenstein-Jensen method.
Received: November 21, 2016
Revised: April 08, 2017
Results: A few title compounds were found to be equipotent with the reference drug rifampicin, while
Accepted: May 03, 2017
moderately potent, when compared with the reference drug isoniazid. These compounds were sub-
DOI:
10.2174/1570178614666170608130326
jected to molecular docking studies and their results were found to be in agreement with the in vitro
studies.
Conclusion: We reported simple and efficient protocol for the synthesis of series of bioactive glucose-
linked isonicotinoyl-1,3,4-thiadiazolidines by utilizing N-tetra-O-acetyl-β-D-glucopyranosyl isocyano-
dichloride as a suitable reagent for glycosylation. This approach is a valuable addition to the fast-
developing field of glucose-linked heterocycles and might be used to develop new potential drugs. We
demonstrated the introduction of isonicotinoyl and glucosyl moieties in single molecular framework
which may prove beneficial for developing new class of antitubercular agents.
Keywords: 1,3,4-Thiadiazolidines, antitubercular agents, glucopyranosyl isocyanodichloride, isonicotinoyl thiosemicarbazide,
M. tuberculosis H37Rv strain, isoniazid, molecular docking.
1. INTRODUCTION
Isoniazid also called as isonicotinohydrazide, is the drug
which has been put into practice for the treatment of
tuberculosis [3]. Although isoniazid possesses significant
bactericidal activity, and a critical component of the first-line
anti-tuberculous regimens, in the last two decades, resistance
to isoniazid has been increasingly reported [2]. The above
facts explicate the need for the development of new class of
safe and more efficient anti-tuberculosis drugs.
Over 6 million new cases of tuberculosis were reported to
World Health Organization (WHO) in 2014 [1]. The global
TB control efforts have been facing formidable challenges
due to the emergence of multidrug-resistant tuberculosis
(MDR-TB), and extensively drug resistant tuberculosis
(XDR-TB), defined as MDR-TB with additional resistance
to fluoroquinolones and at least one of the injectable second-
line drugs like capreomycin, kanamycin, and amikacin [2].
Easy incorporation into various synthetic strategies, makes
isoniazid a highly versatile molecule [3]. This potential
property of isoniazid can be explored further for synthesizing
a large number of derivatives that are effective against my-
cobacterial infections [3]. The structurally modified isoniazid
framework possessing chemically blocked hydrazine unit, is
*Address correspondence to this author at the Department of Chemistry,
Faculty of Science, Rashtrasant Tukadoji Maharaj Nagpur University, Nag-
pur, India; Tel: +919730799470; E-mail: i_snehal123@yahoo.com
1875-6255/18 $58.00+.00
© 2018 Bentham Science Publishers

16 Letters in Organic Chemistry, 2018, Vol. 15, No. 1
Chavan et al.
N
N
O
N
R
CH3
OH
N
H
N
CH3
N
N
N
N
O
O
N
S
H3C
Analgesic
S
R
N
Anti-tubercular
Antimicrobial
Fig. (1). Biologically active molecules with isonicotinoyl moiety.
known to exhibit a high level of antitubercular activity [4]. 1-
Isonicotinoyl-4-aryl thiosemicarbazides are reported to be
widely used as a precursor for the synthesis of various het-
erocyclic compounds [5, 6].
using KBr disk on Perkin Elmer FT-IR KBr spectrophotome-
ter. 1H and 13C NMR data were obtained in CDCl3 and
DMSO-d6 as solvents and tetramethylsilane (TMS) as inter-
nal reference on a Brucker Avance II 400 NMR spectrome-
ter. Mass spectra were recorded on a Waters Micromass Q-
Tof micro instrument using electron impact (EI) at an ioniz-
ing potential of 70eV. Optical rotations were measured by
Equip-Tronics Digital Polarimeter EQ-801. Reactions were
monitored by TLC using aluminum sheet Silica Gel 60 F254
(Merck).
Isonicotinoyl nucleus is a biologically active heterocyclic
functionality that is related to a broad range of pharmacol-
ogical activities due to the position of nitrogen atom in the
ring [7]. Various isonicotinoyl derivatives are found to be
biologically interesting and display antitubercular [8, 9],
antimicrobial [5, 10-13], antioxidant [14], anticancer [15],
analgesic [16], anti-viral and antifungal activities [3, 11] as
shown in Fig. (1). In addition to this, pyridinyl-1,3,4-
thiadiazoles are known to possess antibacterial and antifun-
gal activities [17].
2.2. General Procedure for the Synthesis of N-tetra-O-
acetyl-β-D-glucopyranosyl isocyanodichloride (4)
N-Tetra-O-acetyl-β-D-glucopyranosyl isocyanodichloride
(4) was synthesized by previously [22-24] reported method.
The method involved excessive chlorination of N-tetra-O-
acetyl-β-D-glucopyranosyl isothiocyanate to yield compound 4.
On the other hand, the characteristic property of the car-
bohydrate fragments to get actively transported, is used for
creating promising and efficient drugs by N-glycosylation of
many amino compounds, including heterocyclic and natural
physiologically active compounds [18].
2.3. General Procedure for the Synthesis of 1-
isonicotinoyl 4-aryl thiosemicarbazides (3a-f)
The glycosylation of physiologically active compounds
(or their individual fragments) at the glycoside site of sugars
provides an efficient possible pathway for the preparation of
drugs with low toxicity, as the introduction of carbohydrate
fragments into the structure of physiologically active com-
pounds not only improves their water solubility but also sig-
nificantly reduces toxicity [18b, 19]. Moreover, the glycone
part offers ample opportunity for fine tune up of lipophilic-
ity, which is one of the fundamental features determining
“druglikeness” [20]. Furthermore, the chemical modification
of natural scaffolds is one of the potential strategies for the
development of new antitubercular drugs [21].
Compounds 3a-f were prepared according to a the re-
ported method [7]. Briefly, a mixture of isoniazid (1, 0.01
mol) and an appropriate aryl isothiocyanate (2, 0.015 mol)
was refluxed in absolute ethanol for 4 h. Progress of the re-
action was monitored by TLC. A white solid product ob-
tained on cooling was filtered and washed with diethyl ether.
The crude product was recrystallized from ethanol to afford
the desired product 3. Compounds 3a-f were identified by
the comparison of analytical data (melting points and 1H
NMR data) with literature reports [21, 25].
2.3.1. Characterization Data of 1-Isonicotinoyl 4-phenyl
thiosemicarbazide (3a)
In view of the connection between the biological activi-
ties of isonicotinoyl and carbohydrate moieties, we have
reported here a simple and convenient protocol for the syn-
thesis of bioactive glucose-linked isonicotinoyl-1,3,4-
thiadiazolidines through cyclocondensation reaction and
demonstrated that the title compounds possess antitubercular
activity comparable to rifampicin. N-Tetra-O-acetyl-β-D-
glucopyranosyl isocyanodichloride was used as an intermedi-
ate for glycosylation and 1-isonicotinoyl-4-aryl thiosemicar-
bazide was used for incorporating isonicotinoyl moiety.
Yield 90%; mp 190-192oC; IR (KBr) νmax: 3266 and 3118
(N-H), 1681 (O=C-N), 1384 (C-N), 1255 (C=S) cm-1; 1H
NMR (DMSO-d6, 400 MHz): δ = 10.82, (1H, s, NH), 9.82
(1H, s, NH), 9.74 (1H, s, NH), 8.73 (2H, dd, pyridiyl H),
7.87 (2H, d, pyridiyl H), 7.49 (2H, d, ArH), 7.31 (2H, t,
ArH), 7.15 (1H, t, ArH).
2.4. General Procedure for the Synthesis of 5-Arylimino-
3-isonicotinoyl-2-tetra-O-acetyl-β-D-glucopyranosyli-
mino-1,3,4-thiadiazolidines (6a-f)
2. EXPERIMENTAL
2.1. Materials and Method
All melting points were uncorrected and measured using
an electro-thermal apparatus. FT-IR spectra were recorded
To a solution of an appropriate 1-isonicotinoyl 4-aryl
thiosemicarbazide (3, 0.01 mol) in a 2:1 CHCl3-DMF mix-
ture, N-tetra-O-acetyl-β-D-glucopyranosyl isocyanodichlo-

Synthesis and Molecular Docking Studies of Glucose-linked
Letters in Organic Chemistry, 2018, Vol. 15, No. 1 17
2.4.1.3. 5-(3-methylphenyl)imino-3-isonicotinoyl-2-tetra-O-
acetyl-β-D-glucopyranosylimino-1,3,4-thiadiazolidine (6c):
ride (4, 0.01 mol) was added slowly. The reaction mixture
was refluxed for 5 h. The hydrogen chloride gas was evolved
during the reaction which was clearly noted with moist blue
litmus paper. The reaction was monitored by TLC and after
completion of the reaction, the reaction mixture was cooled
followed by dilution with dichloromethane. The organic
layer was washed with water, dried over the surface of anhy-
drous sodium sulfate and distilled off to afford product 5. It
was triturated with aqueous saturated solution of sodium
bicarbonate for 10 min. It was then extracted with ethyl ace-
tate and dried over the surface of anhydrous sodium sulfate.
The dried organic layer was concentrated under reduced
pressure and evaporated to afford compound 6 as creamish
coloured solid residue which was recrystallized from chloro-
form-petroleum ether.
Yield 71%; mp 175–177°C; [α] 25 D + 70 (c 0.5, EtOH); Rf
0.49 (50% EtOAc : hexane); IR (KBr) νmax: 3317 (N-H),
1752 (O=C-O), 1637 (C=N), 1367 (C-N), 740 (C-S) cm-1; 1H
NMR (CDCl3, 400 MHz): δ = 8.83-7.77 (4H, m, pyridyl H),
7.73-7.14 (4H, m, ArH), 7.35 (1H, s, NH), 5.36 (1H, t, J =
9.5 Hz, H1), 5.10-3.87 (6H, m, H2-H7), 2.40 (3H, s, CH3),
2.10 -1.98 (12H, m, CH3-C=O); 13C NMR (CDCl3, 400
MHz): δ = 169.8 (C=O), 169.4 (C=O), 169.2 (C=O), 168.8
(C=O), 160.5 (C=O), 156.1 (C=N), 150.7 (C=N), 150.3
(pyridine-C), 138.3 (pyridine-C), 134.0 (pyridine-C), 130.8
(Ar-C), 128.9 (Ar-C), 125.6 (Ar-C), 123.0 (Ar-C), 121.7
(Ar-C), 121.6 (Ar-C), 119.1 (Ar-C), 117.7 (Ar-C), 114.5
(Ar-C), 82.3 (glucose-C), 72.9 (glucose-C), 70.6 (glucose-
C), 67.6 (glucose-C), 66.0 (glucose-C), 61.5 (glucose-C),
21.2 (CH3), 20.7 (CH3-C=O), 20.5 (CH3-C=O), 20.3 (CH3-
C=O), 20.3 (CH3-C=O); MS (m/z): 641 [M]+; Anal. Calcd
for C29H31N5O10S: N, 10.91; S, 5.00. Found: N, 10.84; S,
4.94.
2.4.1. Characterization Data of the Compounds
2.4.1.1. 5-(4-phenyl)imino-3-isonicotinoyl-2-tetra-O-acetyl-
β-D-glucopyranosylimino-1,3,4-thiadiazolidine (6a)
Yield 86%; mp 133-135oC; [α] 25 D + 50 (c 0.5, EtOH); Rf
0.56 (50% EtOAc: hexane); IR (KBr) νmax: 3267 (N-H),
1753 (O=C-O), 1622 (C=N), 1369 (C-N), 751 (C-S) cm-1; 1H
NMR (CDCl3, 400 MHz): δ = 8.78 (2H, d, J = 4.4 Hz, pyri-
dine-H), 8.01 (1H, bs, NH), 7.83 (4H, dd, J = 5.2 Hz, pyri-
dine-H), 7.54 (2H, d, J = 8.0 Hz, ArH), 7.41 (2H, t, J = 7.6
Hz, ArH), 7.14 (1H, t, J = 7.6 Hz, ArH), 5.36 (1H, t, J = 9.6
Hz, H1), 5.32-3.83 (6H, m, H2-H7), 2.08 -2.02 (12H, m, CH3-
C=O); 13C NMR (CDCl3+DMSO-d6, 400 MHz): δ = 169.6
(C=O), 169.2 (C=O), 169.9 (C=O), 168.7 (C=O), 162.9
(C=O), 160.5 (C=N), 156.0 (C=N), 150.5 (pyridine-C),
138.3 (pyridine-C), 130.8 (Ar-C), 128.8 (Ar-C), 122.0 (Ar-
C), 119.0 (Ar-C), 117.3 (Ar-C), 82.5 (glucose-C), 70.4 (glu-
cose-C), 67.7 (glucose-C), 67.6 (glucose-C), 61.5 (glucose-
C), 20.4 (CH3-C=O), 20.3 (CH3-C=O), 20.2 (CH3-C=O),
20.1 (CH3-C=O); MS (m/z): 627 [M]+, 523 (100%) [M-
C6H4NO+2]+, Anal. Calcd for C28H29N5O10S: N, 11.16; S,
5.11. Found: N, 11.00; S, 5.20.
2.4.1.4. 5-(4-methylphenyl)imino-3-isonicotinoyl-2-tetra-O-
acetyl-β-D-glucopyranosylimino-1,3,4-thiadiazolidine (6d)
Yield 79%; mp 117–119°C; [α] 25 D + 80 (c 0.5, EtOH); Rf
0.49 (50% EtOAc : hexane); IR (KBr) νmax: 3314 (N-H),
1752 (O=C-O), 1618 (C=N), 1368 (C-N), 757 (C-S) cm-1; 1H
NMR (CDCl3, 400 MHz): δ = 8.83-7.73 (4H, m, pyridyl H),
7.40-7.20 (4H, m, ArH), 5.36 (1H, t, J = 9.5 Hz, H1), 5.09-
3.87 (6H, m, H2-H7), 2.38 (3H, s, CH3), 2.10 -1.99 (12H, m,
CH3-C=O); 13C NMR (CDCl3, 400 MHz): δ = 170.0 (C=O),
169.9 (C=O), 169.3 (C=O), 169.0 (C=O), 162.5 (C=O),
154.0 (C=N), 150.1 (C=N), 148.9 (pyridine-C), 139.2 (pyri-
dine-C), 134.5 (pyridine-C), 129.7 (Ar-C), 124.5 (Ar-C),
121.8 (Ar-C), 120.2 (Ar-C), 119.9 (Ar-C), 115.0 (Ar-C),
82.5 (glucose-C), 72.7 (glucose-C), 70.3 (glucose-C), 67.0
(glucose-C), 66.5 (glucose-C), 61.9 (glucose-C), 21.0 (CH3),
20.9 (CH3-C=O), 20.5 (CH3-C=O), 20.4 (CH3-C=O), 20.2
(CH3-C=O); MS (m/z): 627 [M]+, 549 (100%) [M-(C7H7)-
1]+; Anal. Calcd for C29H31N5O10S: N, 10.91; S, 5.00. Found:
N, 10.82; S, 5.15.
2.4.1.2. 5-(4-methoxyphenyl)imino-3-isonicotinoyl-2-tetra-
O-acetyl-β-D-glucopyranosylimino-1,3,4-thiadiazolidine
(6b)
2.4.1.5. 5-(4-chlorophenyl)imino-3-isonicotinoyl-2-tetra-O-
acetyl-β-D-glucopyranosylimino-1,3,4-thiadiazolidine (6e)
Yield 81%; mp 90–92°C; [α] 25 D + 70 (c 0.5, EtOH); Rf
0.48 (50% EtOAc : hexane); IR (KBr) νmax: 3307 (N-H),
1745 (O=C-O), 1610 (C=N), 1369 (C-N), 752 (C-S) cm-1; 1H
NMR (CDCl3, 400 MHz): δ = 8.76 (2H, d, J = 4.8 Hz, pyri-
dine H), 7.78 (2H, dd, J = 5.2, 6.0 Hz, pyridine H), 7.44 (2H,
d, J = 8.8 Hz, ArH), 7.34 (1H, bs, NH), 6.94 (1H, d, J = 8.8
Hz, ArH), 5.47-3.88 (7H, m, H1-H7), 3.82 (3H, s, OCH3)
2.09 -2.02 (12H, m, CH3-C=O); 13C NMR (CDCl3+DMSO-
d6, 400 MHz): δ = 169.7 (C=O), 169.3 (C=O), 169.0 (C=O),
168.8 (C=O), 160.7 (C=O), 155.8 (C=N), 154.7 (C=N),
150.5 (pyridine-C), 131.4 (pyridine-C), 130.8 (Ar-C), 129.5
(Ar-C), 118.8 (Ar-C), 114.6 (Ar-C), 114.1 (Ar-C), 81.3 (glu-
cose-C), 72.0 (glucose-C), 67.7 (glucose-C), 61.6 (glucose-
C), 55.1 (-OCH3), 20.4 (CH3-C=O), 20.3 (CH3-C=O), 20.2
(CH3-C=O), 20.1 (CH3-C=O); MS (m/z): 657 [M]+; Anal.
Calcd for C29H31N5O11S: N, 10.65; S, 4.88. Found: N, 10.45;
S, 4.74.
Yield 82%; mp 172–174°C; [α] 25 D + 90 (c 0.5, EtOH); Rf
0.47 (50% EtOAc : hexane); IR (KBr) νmax: 3318 (N-H),
1752 (O=C-O), 1610 (C=N), 1369 (C-N), 723 (C-S) cm-1; 1H
NMR (CDCl3, 400 MHz): δ = 8.83-7.15 (8H, m, ArH), 5.36
(1H, t, J = 9.92 Hz, H1), 5.13-3.87 (6H, m, H2-H7), 2.10 -
2.01 (12H, m, CH3-C=O); 13C NMR (CDCl3, 400 MHz): δ =
169.7 (C=O), 169.1 (C=O), 169.0 (C=O), 168.5 (C=O),
161.5 (C=O), 153.0 (C=N), 150.1 (C=N), 147.4 (pyridine-
C), 137.5 (pyridine-C), 134.8 (pyridine-C), 128.5 (Ar-C),
126.5 (Ar-C), 124.8 (Ar-C), 123.7 (Ar-C), 120.4 (Ar-C),
117.0 (Ar-C), 83.4 (glucose-C), 72.6 (glucose-C), 70.4 (glu-
cose-C), 67.3 (glucose-C), 66.2 (glucose-C), 61.7 (glucose-
C), 21.0 (CH3-C=O), 20.8 (CH3-C=O), 20.7 (CH3-C=O),
20.4 (CH3-C=O); MS (m/z): 549 [M-(C6H4Cl)]+; Anal. Calcd
for C28H28ClN5O10S: N, 10.58; S, 4.84. Found: N, 10.40; S,
4.74.

18 Letters in Organic Chemistry, 2018, Vol. 15, No. 1
Chavan et al.
2.4.1.6. 5-(2-methoxyphenyl)imino-3-isonicotinoyl-2-tetra-
O-acetyl-β-D-glucopyranosylimino-1,3,4-thiadiazolidine
(6f)
test compound. The standard strain M. tuberculosis H37Rv
was tested with known drugs isoniazid and rifampicin. [27].
3.2. Molecular Docking Study
Yield 67%; mp 85–87°C; [α] 25 D + 50 (c 0.5, EtOH); Rf
0.48 (50% EtOAc : hexane); IR (KBr) νmax: 3317 (N-H),
1752 (O=C-O), 1623 (C=N), 1368 (C-N), 752 (C-S) cm-1; 1H
NMR (CDCl3, 400 MHz): δ = 8.82-7.83 (4H, m, pyridine H),
7.77-6.94 (4H, m, ArH), 5.39-3.84 (7H, m, H1-H7), 3.96 (3H,
s, OCH3) 2.10 -2.00 (12H, m, CH3-C=O); 13C NMR (CDCl3,
400 MHz): δ = 169.5 (C=O), 169.8 (C=O), 169.2 (C=O),
167.5 (C=O), 161.6 (C=O), 156.8 (C=N), 153.5 (C=N),
150.1 (pyridine-C), 133.3 (pyridine-C), 131.4 (Ar-C), 127.2
(Ar-C), 119.6 (Ar-C), 115.3 (Ar-C), 113.1 (Ar-C), 82.5 (glu-
cose-C), 72.5 (glucose-C), 67.9 (glucose-C), 61.1 (glucose-
C), 56.1 (-OCH3), 21.0 (CH3-C=O), 20.8 (CH3-C=O), 20.6
(CH3-C=O), 20.4 (CH3-C=O); MS (m/z): 657 [M]+, 535
In order to evaluate the newly synthesized molecules and
look into the binding mode of the compounds within the tar-
get proteins molecular docking studies was carried out with
help of Glide docking module of Schrodinger [28]. Crystal
structure was obtained from Protein Data Bank (RCSB-
PDB) for the Crystal structure of the enoyl-ACP reductase of
Mycobacterium tuberculosis (InhA) in the apo-form and in
complex with the active metabolite of isoniazid pre-formed
by a biomimetic approach (PDB ID: 4TRM) [29]. The com-
pound library was generated for maximum number of possi-
ble conformations using LigPrep module of Schrodinger and
docking with protein was carried out using Glide docking
module version 15.4.
(100%) [M-(C7H7O)-1]+; (C7H7O
=
4-methoxyphenyl
group); Anal. Calcd for C29H31N5O11S: N, 10.65; S, 4.88.
Found: N, 10.30; S, 4.75.
4. RESULTS AND DISCUSSION
4.1. Chemistry
3. BIOLOGICAL ASSAY
3.1. Antitubercular Assay
The reaction sequence for the preparation of 5-arylimino-
3-isonicotinoyl-2-tetra-O-acetyl-β-D-glucopyranosylimino-
1,3,4-thiadiazolidines (6a-f) is outlined in Scheme 1. Ini-
tially, 1-isonicotinoyl-4-aryl thiosemicarbazides (3a-f) were
synthesized by refluxing a mixture of isoniazid (1) and dif-
ferent aryl isothiocyanates (2a-f) in absolute ethanol for 4 h
by a previously reported method [7]. In the next step, com-
pounds 3a-f were condensed with an intermediate N-tetra-O-
acetyl-β-D-glucopyranosyl isocyanodichloride (4) [22-24] in
a refluxing medium of 2:1 CHCl3-DMF for 5 h to yield a salt
form of the product 5a-f. During the intermolecular cyclo-
condensation reaction, evolution of hydrogen chloride gas
was clearly noted as tested with moist blue litmus paper.
Finally, compounds 5a-f were basified with saturated solu-
tion of sodium bicarbonate to reproduce the title compounds
(6a-f) as free bases in 67-86% yields. The plausible mecha-
nism for cyclocondensation of compounds (3a-f) to com-
pounds (6a-f) is depicted in Scheme 2.
Antitubercular activity determination of the title com-
pounds 6a-f against M. tuberculosis H37Rv was performed
by slightly modified Lowenstein–Jensen method described
earlier [26], where 250 μg/mL dilution of each test com-
pound prepared in DMSO was added in liquid Lowenstein–
Jensen medium. The media was then sterilized by inspissa-
tion method. A culture of M. tuberculosis H37Rv growing on
Lowenstein–Jensen medium was harvested in 0.85 % saline
in bijou bottles. These tubes were then incubated for 24 h at
37°C and then M. tuberculosis H37Rv were streaked (5×104
bacilli per tube). These tubes were then incubated at 37°C.
Growth of bacilli was seen after 12, 22 days and finally 28
days of incubation. Compound containing tubes were com-
pared with control tubes where medium alone was incubated
with M. tuberculosis H37RV.
The concentration at which no development of colonies
occurred or <20 colonies was taken as MIC concentration of
N C
S
O
O
OAc
a
b
N
N
C
C
S
O
H
N
AcO
AcO
Cl
Cl
N C
HN
C
HN NH2
NH
AcO
R
4
2a-f
3a-f
1
R
O
O
C
N
N
H
R
H
N
R
C
N
N
N
N
c
N
N
OAc
O
OAc
. HCl
S
S
O
AcO
AcO
AcO
AcO
N
AcO
AcO
5a-f
6a-f
R: a:-H; b:-4-OCH3; c:-3-CH3; d:-4-CH3; e:-4-Cl; f:-2-OCH3
Scheme (1). Synthetic protocol for the title compounds. Reagents and Conditions: a EtOH, Reflux, 4h; b CHCl3-DMF, Reflux, 5h; c satu-
rated solution of NaHCO3.

Synthesis and Molecular Docking Studies of Glucose-linked
Letters in Organic Chemistry, 2018, Vol. 15, No. 1 19
R
O
H
O
H
N
N
C
N
N
N
C
R
N
H
C
N
-HCl
C
N
H
3a-f
OAc
S
SH
OAc
C
O
Cl
AcO
AcO
O
Cl
Cl
N
AcO
AcO
N C
AcO
AcO
-HCl
4
O
N
H
R
C
N
N
N
OAc
. HCl
S
O
AcO
AcO
N
AcO
5a-f
NaHCO3
6a-f (Free bases)
Scheme (2). Plausible mechanism for the formation of title compounds 6a-f.
The physical and spectral data of compounds 3a-f were
matched with the reported values [21, 25]. The IR spectrum
of compound 3a showed an absorption band at 3266 and
3118 cm-1 which indicated the presence of NH functional
group. The presence of an absorption band at 1255 cm-1 was
4.2. Biological Activity
The title compounds 6a-f were screened for their in-vitro
antitubercular activity against Mycobacterium tuberculosis
H37Rv strain using Lowenstein-Jensen agar method [26]. All
the screened compounds, including the reference drugs viz.
isoniazid and rifampin have shown 99% inhibition against
M. tuberculosis H37Rv strain. It is evident from the results
presented in Table 1, that amongst the screened compounds,
compounds 6a and 6e are highly potent compounds of the
series with MIC (50 μg/mL) equivalent with the reference
drug rifampicin. Compounds 6b and 6d are moderately po-
tent (62.5 μg/mL) while compounds 6c and 6f have shown
very less potency (100 and 250 μg/mL) as compared to the
reference drug isoniazid and rifampin.
1
attributed to C=S. The H NMR spectrum of 3a, showed a
singlet at δ 10.82 ppm and a doublet at δ 9.78 ppm for NH
protons. The aromatic protons resonated within the range of
δ 8.73-7.15 ppm.
Designed series of molecules 6a-f were characterized by
1
IR, H NMR, 13C NMR and mass spectrometry techniques
before evaluating for their in vitro antitubercular activity.
The IR spectral study of the compounds 6a-f showed two
strong bands in the range of 3318-3267 cm-1 and 1745-1753
cm-1 due to N-H and ester carbonyl stretching, respectively.
It is interesting to note that, the unsubstituted phenyl ring
and the monosubstituted phenyl ring with electron withdraw-
ing chloro group at para position, demonstrated positive
influence on inhibitory activity against M. tuberculosis
H37Rv strain whereas the electron donating methyl and
methoxy groups at meta or para position exhibited negative
influence on the inhibitory activity.
1
The H NMR spectral analysis of compounds 6a-f showed a
characteristic triplet for anomeric proton (H1) of glucosyl
ring at δ 5.36 ppm. The coupling constant (J) within the
range of 9.5-9.9 Hz indicated glucosyl moiety to be β-
anomer [30]. A multiplet due to the glucosyl ring protons
(H2-H7) in the range of δ 5.47-3.83 ppm was also observed.
The acetyl protons of other glucosyl moiety resonated as a
1
multiplet within δ 2.10-1.98 ppm. In addition, the H NMR
The positive influence on antitubercular activity is sup-
ported by the fact that the overall lipophilicity of molecule
can be increased by the strong electron withdrawing sub-
stituents such as nitro, chloro and fluoro at the para position
of the aromatic ring which in turn facilitates diffusion of a
molecule through the biological membranes to reach its site
of action [27, 31, 32]. The least activity of compound 6f
among the series of compounds was attributed to the electron
donating methoxy group at ortho position. The results en-
lighten the major influence of electronic properties of the
substituents on the antitubercular activity. Furthermore, the
presence of acetylated glycosyl moiety may result in in-
creased bioactivity since it can cross through the cell mem-
branes more readily than unprotected glycosyl due to im-
spectra of compounds 6a-f exhibited a broad singlet centered
at δ 8.01-7.34 ppm due to the NH-attached to phenyl ring.
The aromatic protons also appeared in their respective region
as were other protons of the substituents. The 13C NMR
spectra of the newly synthesized compounds 6a-f showed the
signal for β anomeric carbon of the glucosyl ring within the
range of δ 81.3-83.4 ppm along with other glucosyl carbons.
It also displayed thiadiazolidine, pyridine and phenyl ring
carbon signals. The mass spectral studies of the title com-
pounds 6a-f showed molecular ion peaks M+ and [M+1]+
which were in good agreement with the molecular mass of
the corresponding compounds.

20 Letters in Organic Chemistry, 2018, Vol. 15, No. 1
Chavan et al.
Table 1. In vitro antitubercular activity of compounds 6a-f against M. tuberculosis H37Rv.
O
C
N
H
N
R
N
N
N
OAc
S
O
AcO
AcO
AcO
Entry
R
% Inhibition
MICa, μg/ml
6a
6b
6c
H
99
99
99
50
4-OCH3
3-CH3
62.5
100
6d
6e
4-CH3
4-Cl
99
99
99
99
99
62.5
50
6f
2-OCH3
----
250
0.2
40
Isoniazidb
Rifampinb
-----
a: Minimum Inhibitory Concentration.
b: Standard Reference Drug.
O
C
N
N
O
C
R
R
NH
S
NH
S
in vitro deacetylation
N
N
N
N
N
N
OAc
OH
O
O
AcO
AcO
HO
HO
AcO
HO
6a-f
7a-f
R: a:-H; b:-4-OCH3; c:-3-CH3; d:-4-CH3; e:-4-Cl; f:-2-OCH3
Scheme (3). In vitro conversion of acetyl group to the hydroxyl groups carried out by the enzymatic activity after transfer of drug molecule
into the microorganism.
proved solubility of the respective bioactive compounds [33,
34].
interacts with nitrogen atom from pyridine ring forming a
hydrogen bond. Residues Arg409 and Asp396 form hydro-
gen bonds with the hydroxy group of glucopyranosyl moitey.
The dock score was found to be -5.317 which is above the
standard drug isoniazid and rifampicin at -4.125 and -5.021
respectively. Similarly compound 7e interacts with formation
of hydrogen bonds between Gln393 and the secondary nitro-
gen from the thiadiazole ring, Gln633 interacts with nitrogen
atom from pyridine ring forming a hydrogen bond, Asp396
forms hydrogen bonds with the hydroxy group of glu-
copyranosyl moiety. This compound exhibits a dock score of
-5.289 which is higher than the standard compounds as men-
tioned earlier.
4.3. Molecular Docking Studies
To investigate further regarding the antimycobacterial
activity of the newly synthesized compounds we carried out
molecular docking studies. The present synthesis is based on
derivatization of active drug moiety isoniazid hence we se-
lected the enoyl-ACP reductase of Mycobacterium tubercu-
losis (PDB ID 4TRM) as target as it is an important reduc-
tase enzyme required for the biosynthesis of mycolic acids
which is an important component of the cell wall. The crystal
structure was refined for the missing loops and residues us-
ing Glide module of the Shrodinger and then subject to mo-
lecular docking with the 6a-f and 7a-f compounds. The
docking was carried out under the extra precision mode with
receptor and the ligands in flexible mode, calculations were
made for each of the interacting residues, energy and dock
score was recorded. The interpretation of results are pre-
sented in Fig. (2), it can be observed that ligands are binding
on the same region as that of isoniazid.
It is important to note that the compounds of series 6a-f
and 7a-f differ from each other with respect to presence of
acetyl group (Scheme 3), this aspect of the present study is
important because as it is known that once drug moiety en-
ters an organism it undergoes deacetylation, thus the com-
pounds 6a-f will be converted to 7a-f in the in vitro condi-
tions. In case of these molecules it is observed that com-
pounds 6b and 6e have exhibited comparable activity to the
drug rifampicin, these compounds are analogous to com-
pounds 7b and 7e. Moreover, the interacting residues are
common for the experimental and the standard drug which
The compound 7b interacts with residues from the recep-
tor with formation of hydrogen bonds between Gln393 and
the secondary nitrogen from the thiadiazole ring, Gln633

Synthesis and Molecular Docking Studies of Glucose-linked
Letters in Organic Chemistry, 2018, Vol. 15, No. 1 21
Fig. (2). a, b) Molecular docking poses for compound 7b in 3D and 2D form presenting interaction between ligand and residues Gln393,
Arg409, Asp396 and Gln633. c, d) Molecular docking poses for compound 7e in 3D and 2D form representing interaction between ligand
and residues Gln393, Asp396 and Gln633.
signifies that the active site cavity is common for both the
types of compounds.
CONSENT FOR PUBLICATION
Not applicable.
CONCLUSION
CONFLICT OF INTEREST
In the present investigation, we have reported a simple
and efficient protocol for the synthesis of series of bioactive
glucose-linked isonicotinoyl-1,3,4-thiadiazolidines by utiliz-
ing N-tetra-O-acetyl-β-D-glucopyranosyl isocyanodichloride
as a suitable reagent for glycosylation. This approach is a
valuable addition to the fast-developing field of glucose-
linked heterocycles and might be used to develop new poten-
tial drugs. We demonstrated the introduction of isonicotinoyl
and glucosyl moieties in single molecular framework which
may prove beneficial for developing new class of antituber-
cular agents. The title compounds were analyzed by molecu-
lar docking approach and were evaluated for their in vitro
antitubercular activity against M. tuberculosis H37Rv strain.
Among the title compounds, compound 6a, 6b and 6e
showed more potential as antitubercular agent than the series
of compounds. It is conceivable that such type of compounds
possessing good to moderate antitubercular activity can be
further modified to exhibit better potency than the standard
drugs in future.
The authors declare no conflict of interest, financial or
otherwise.
ACKNOWLEDGEMENTS
One of the authors, Snehal A. Chavan is thankful to
Council of Scientific and Industrial Research (CSIR), New
Delhi, for the financial support in the form of Senior Re-
search Fellowship (File No. 09/128(0086)/2012-EMR-I
dated 22/06/2012). The authors are also grateful to Micro-
care Laboratory, Surat, for in vitro antitubercular screening,
the Director, Sophisticated Analytical Instrumentation Facil-
ity (SAIF), Panjab University, Chandigarh and Sophisticated
Instrumentation Facility (SIF), VIT University, Vellore, for
spectral analysis.
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