Synthesis and biological screening of thiosemicarbazones of substituted 3-acetylcoumarins having D-glucose moiety

Article abstract of DOI:10.1016/j.bmcl.2020.127664

Thiosemicarbazones 5a-j were synthesized with yields of 45–68% by condensation of 3-acetylcoumarins 3a-j and tetra-O-acetyl-β-D-thiosemicarbazide 4. All obtained thiosemicarbazones were screened for anti-microorganic activities against bacteria (B. subtilis, S. aureus, S. epidermidis, E. coli, P. aeruginosa, K. pneumoniae, S. typhimurium) and fungi (A. niger, C. albicans, S. cerevisiae, and A. flavus). Some compounds had significant inhibitory activity with MICs of 0.78–3.125 μM in comparison with 5a, including 5e,h,i for S. aureus, and 5c,f,i for S. epidermidis (Gram-(+) bacteria), 5c,f,g for E.coli, 5f for K. pneumoniae, 5b,c,g for P. aeruginosa, and 5i for S. typhimurium (Gram-(?) bacteria), 5d,h,i for A. niger, 5i for A. flavus, 5b,d,e,h for C. albicans, and 5i for S. cerevisiae. Compounds exhibited excellent activity against tested microorganism with MIC = 0.78 μM, including 5h,i (against S. aureus), 5h (against C. albicans), and 5i (against S. cerevisiae).

Full text of DOI:10.1016/j.bmcl.2020.127664

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Synthesis and biological screening of thiosemicarbazones of substituted 3-
acetylcoumarins having d-glucose moiety
Vu Ngoc Toan, Nguyen Dinh Thanh, Nguyen Minh Tri
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Reference:
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BMCL 127664
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24 October 2020
28 October 2020
Please cite this article as: Ngoc Toan, V., Dinh Thanh, N., Minh Tri, N., Synthesis and biological screening of
thiosemicarbazones of substituted 3-acetylcoumarins having d-glucose moiety, Bioorganic & Medicinal
Chemistry Letters (2020), doi: https://doi.org/10.1016/j.bmcl.2020.127664
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Synthesis and biological screening of thiosemicarbazones of substituted 3-acetylcoumarins
having D-glucose moiety
Vu Ngoc Toana,b, Nguyen Dinh Thanh*b, Nguyen Minh Tria,b
a Department of Toxicological Chemistry and Radiation, Institute for Advanced Technology
(Vietnam Academy of Military Science and Technology), 17 Hoang Sam, Cau Giay, Ha Noi, Viet
Nam
b Faculty of Chemistry, VNU University of Science (Vietnam National University, Ha Noi), 19 Le
Thanh Tong, Hoan Kiem, Ha Noi, Viet Nam
Abstract
Thiosemicarbazones 5a-j were synthesized with yields of 45−68% by condensation of 3-
acetylcoumarins 3a-j and tetra-O-acetyl-β-D-thiosemicarbazide 4. All obtained thiosemicarbazones
were screened for anti-microorganic activities against bacteria (B. subtilis, S. aureus, S. epidermidis,
E. coli, P. aeruginosa, K. pneumoniae, S. typhimurium) and fungi (A. niger, C. albicans, S.
cerevisiae, and A. flavus). Some compounds had significant inhibitory activity with MICs of
0.78−3.125 μM in comparison with 5a, including 5e,h,i for S. aureus, and 5c,f,i for S. epidermidis
(Gram-(+) bacteria), 5c,f,g for E.coli, 5f for K. pneumoniae, 5b,c,g for P. aeruginosa, and 5i for S.
typhimurium (Gram-(−) bacteria), 5d,h,i for A. niger, 5i for A. flavus, 5b,d,e,h for C. albicans, and
5i for S. cerevisiae. Compounds exhibited excellent activity against tested microorganism with MIC
= 0.78 μM, including 5h,i (against S. aureus), 5h (against C. albicans), and 5i (against S.
cerevisiae).
Keywords: 3-Acetylcoumarins; Antibacterial; Antifungal; D-Glucose; Thiosemicarbazides;
Thiosemicarbazones

Thiosemicarbazides and thiosemicarbazone derivatives had occupied important roles in organic and
medicinal chemistry. These classes of compounds presented chelating properties by using C=S and
NH groups for coordination with metal center.1-3 They could be used as versatile intermediates for
preparing various heterocyclic compounds.4, 5 They exhibited a broad spectrum of potential
pharmacological activities, such as antibacterial,6 antifungal,7 anticancer,8 antimycobacterial,9 and
antidiabetic10 activity. For example, nopinone-based thiosemicarbazone A displayed potent in vitro
antitumor activity against three human cancer cell lines (MDA-MB-231, SMMC-7721 and Hela)
with the IC50 values of 2.79 ± 0.38, 2.64 ± 0.17 and 3.64 ± 0.13 μM, respectively.8
Thiosemicarbazone B exhibited antimycobacterial activity against Mycobacterium tuberculosis
H37Ra with MIC value of 0.031 μg/mL and MBC (minimum bactericidal concentration) value of
0.063 μg/mL.9 Compounds C were found to be the most active ALR2 inhibitors with IC50 values of
0.52 ± 0.04 μM (with R = Br) and 0.19 ± 0.03 μM (with R = F), respectively, and these compounds
were more effective inhibitors as compared to the ALR2 (standard aldose reductase 2) inhibitor,
sorbinil, which has an IC50 value of 3.14 ± 0.02 μM.10
H
O
N
S
O
H
H2N
N
N
S
N
N
NH
H
S
O
O
B
CH3
N
H
H
H
O
N
N
N
R
OCH3
A
S
O
C
Figure 1. Various bioactive thiosemicarbazones.
The synthesis of substituted aromatic or heterocyclic aromatic aldehyde/ketone thiosemicarbazones
with sugar moieties were reported.1, 4, 11-13 The series of aldehyde 4-(β-D-
2

glucopyranosyl)thiosemicarbazones12-14 were prepared from per-O-acetylated β-D-glucopyranosyl
isothiocyanate and several of them showed micromolar inhibitions against typical Gram-positive
(Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis), Gram-negative bacteria
(Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella typhimurium) and
fungi (Aspergillus niger, Candida albicans, Aspergillus flavus). These such compounds also had
shown various biological properties, such as antibacterial,13 antifungal,13 antioxidant,11 anti-
dyslipidemic,11 and anticancer activities.15 Figure 2 displayed some examples of bioactive
thiosemicarbazones bearing sugar moiety. Compound D of D-glucose significantly decreased cancer
cell growth with IC50 value of 1.60 μM on breast cancer cell line MDA-MB-231 and IC50 value of
2.8 μM on prostate cancer cell line PC-3, which was lower than that of cells treated with the well-
known anticancer drug 5-fluorouracil with IC50 = 4.75 ± 1.41 and 2.88 ± 1.39 μM, respectively).15
Sugar-based thiosemicarbazone of peracetylated galactoside (E) was discovered to be a potent
rhodesain inhibitor with IC50 = 1.2 ± 1.0 μM.16 Thiosemicarbazone F with para-F group had
inhibitory efficiency for rabbit muscle glycogen phosphorylase b with IC50 = 5.7 μM.17 Compound
G containing simultaneously monosaccharide and isatin moieties exhibited in vitro antibacterial and
in vivo antioxidant activities. When R′ = Br, R = H the compound showed selective cytotoxic effects
against some cancer (LU-1, HepG2, MCF7, P338, SW480, KB) cell lines and normal fibroblast cell
line NIH/3T3. This compound had good inhibitory activity with MIC of 1.56 μM against B. subtilis,
S. aureus, and S. epidermidis.13
NH2
H3CO
O
HN
N
OH
O
OAc
O
AcO
AcO
S
N
S
H
HO
HO
N
N
N
N
OH
OAc
H
H
E
D
R'
OH
O
R'
OAc
H
H
H
H
H
HO
HO
N
N
O
AcO
AcO
N
N
N
N
R
OH
N
OAc
S
S
F
O
F
G
3

Figure 2. Some bioactive thiosemicarbazones bearing sugar moiety.
Coumarin (2H-chromen-2-one) was a compound of cinnamon. This heterocycle possessed
remarkably pharmacological activities, such as antibacterial,18 antioxidant,19 anti-inflammatory,20
anticancer21 activity, and widely distributed in nature in many plants.22, 23 Compound H and I (Fig.
3) were potential anti-tubercular agents with MIC of 0.09 μg/mL and 3.9 μmol/mL, respectively.24,
25 Hydroxycoumarin J was used as selective MAO-B inhibitor with IC50 = 2.79 ± 0.19 μM.26
S
Cl
NH
N
N
N
S
OMe
S
N
O
OH
Cl
Cl
N
O
Cl
O
O
O
O
O
H
I
J
HO
O
CH3
O
O
H3C
CH3
HO
O
HO
O
O
HO
O
K
L
M
Figure 3. Some biologically active agents containing coumarin ring.
Some natural and synthetic coumarin-containing derivatives were used as biologically active agents.
For example, hymecromone (4-methylumbelliferone or 4-methyl-7-hydroxycoumarin, K) was used
as choleretic and antispasmodic agent.27 Armillarisin A (3-acetyl-5-hydroxymethyl-7-
hydroxycoumarin, L), extracted from the fungus Armillariella tabescens (Scop. ex Fr.) Sing.),28 was
used as an antibiotic agent. Scopoletin (6-methoxy-7-hydroxycoumarin, M), isolated from several
plant species, exhibited antioxidant, hepatoprotective, anti-inflammatory and antifungal activity and
inhibited in vitro against α-glucosidase enzyme.29
Based on the above-mentioned reviews on biological properties of coumarin- and sugar-containing
compounds and continuing our previous studies on the synthesis and reactivity of N-(per-O-acetyl-
4

D-glycopyranosyl)thiosemicarbazides,13, 30-32 we reported herein the synthesis and evaluation of
biological activities of a series of substituted 3-acetylcoumarins N-(2,3,4,6-tetra-O-acetyl-β-D-
glycopyranosyl)thiosemicarbazones having D-glucose moiety. The connection of monosaccharide
moiety to coumarin ring through thiosemicarbazone linkage could induce novel activities. They
were then evaluated by their antibacterial and antifungal activities against some Gram-positive
bacteria (S aureus, B subtilis, S epidermidis), Gram-negative bacteria (P aeruginosa, K pneumonia,
S typhimurium, and E coli), and some fungi (A niger, C albicans, S cerevisiae, and A flavus).
Synthetic pathway for target thiosemicarbazones was displayed in Scheme 1. Substituted coumarins
(3a-j) were prepared according to modified literature procedures by reaction of corresponding
substituted salicylaldehydes (1a-h) with resorcinol (1i) or o-hydroxyacetophenone (1j), respectively
(see Schema 1S-4S in Supplementary data in the online version of this article). Novel substituted 3′-
acetylcoumarin N-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)thiosemicarbazones (5a-j ) were
obtained by condensation of corresponding substituted 3-acetylcoumarins (3a-j) with N-(2,3,4,6-
tetra-O-acetyl-β-D-glucopyranosyl)thiosemicarbazide (Scheme 1). Reactions were performed in
absolute methanol in the presence of glacial acetic acid as catalyst using microwave-assisted heating
method. We found that these thiosemicarbazides could be soluble in methanol at room temperature,
and substituted 3-acetylcoumarins were dissolved with difficulty in this solvent with the same
conditions, but they were dissoluble in this hot solvent. At the initial stage of reaction, the initial
materials began dissolving when heated under the microwave-assisted conditions. Subsequently, the
appearance of precipitate was used to identify the product formation.
5

3a-h
R = CHO, for
(i)
R1
R2
R
R4
Me
R = R1 = R3 = H
OH
R1
R2
R3
1a-j
+
R = OH, for
2
O
3i
(ii)
O
O
R3
3a-j
R = COCH3
CH3COCH2CO2Et
1
2
3
3j
R = R = R = H, for
2
1a-j: R1 R2 R3
R
(iii)
a
( )
H
H
H
CHO
CHO
CHO
CHO
CHO
b
( )
Cl
Br
Me
H
H
H
AcO
H
c
( )
H
H
H
H
H
O
OAc
OAc
H
N
(iv)
N
d
( )
AcO
H2N
e
( )
Me
H
S
4
f
( )
H
OMe CHO
CHO
NO2 CHO
g
( )
NO2
H
H
H
h
( )
H
i
( )
H
OH
H
H
H
H
AcO
j
COCH3 ( )
6
H
Ha
N
4
R4
4'
1 O
Hb
N
OAc
OAc
Me
R1
4'a
2
6'
AcO
N
S
R2
O
7'
O
1'
R3
5a-j
3a-j 5a-j:
R1 R2 R3
R4
H
H
H
H
H
,
a
( )
H
H
H
b
( )
Cl
Br
Me
H
H
H
c
( )
H
H
H
H
H
d
( )
e
( )
Me
H
f
( )
H
OMe H
g
( )
NO2
H
H
H
H
h
( )
H
NO2
H
H
i
( )
H
OH
H
Me
Me
j
( )
H
H
Scheme 1. Synthetic route for final substituted 3-acetylcoumarin tetra-O-acetyl-β-D-
glucopyranosyl)thiosemicarbazones 5a-j. Reaction conditions: (i) Piperidine as catalyst, Method A:
MW Irradiation; Method B: Ultrasound Irradiation; Method C: Solvent-free Ultrasound Irradiation.
(ii) a) 70% Sulfuric acid, 0 °C then 25 °C, 24 h; b) Glacial acetic acid, POCl3, under reflux, 90 min.
(iii) Ethyl acetoacetate, CH3COONa, under microwave-assisted conditions, 90 min. (iv) Glacial
acetic acid (cat), MeOH (solvent), 30−45 min under MW-assisted conditions at 400W.
6

The end of reaction was monitored by thin chromatography. Irradiation times were 30−45 min at
microwave power of 400 W. Glacial acetic acid as catalyst was used in order to activate the
carbonyl group of 3-acetylcoumarins and to facilitate nucleophilic attack of thiosemicarbazide, and
protonation of hydroxyl group in the dehydration stage. Strong inorganic acids, such as HCl, H2SO4,
HClO4, did not favor for this reaction because so the nucleophilic amino group of thiosemicarbazide
was protonated, which loose unshared electron pair. Weak organic acids, such as acetic acid, was
sufficient to activate the carbonyl group without protonation of amino-thiosemicarbazide group. The
formation of thiosemicarbazone products 5a-j could be preliminary confirmed by IR spectroscopy
and compared to the IR spectra of corresponding substituted 3-acetylcoumarins 3a-j and
thiosemicarbazide 4. On IR spectrum of thiosemicarbazones, characteristic absorption bands
appeared for both components, coumarin and per-acetylated D-glucose, and stretching band for
imine group >C=N−, whereas specific bands for amino group in thiosemicarbazide and for carbonyl
group in substituted 3-acetylcoumarin were not present. These evidences initially indicated that the
reaction had occurred, and we expected thiosemicarbazone was formed. IR spectra showed
characteristic absorptions in the range of 3354−3447 and 3328−3234 cm−1 belonged stretching
vibrations of N−H groups of thiosemicarbazone linkage group (−NHCSNHN=C<). Chemical shifts
that appeared at 11.15−9.28 (singlet) and 9.05−8.66 ppm (doublet) in 1H NMR spectra confirmed
the presence of N−H groups in molecular structure of thiosemicarbazone 5a-j. The former chemical
shift was assigned to proton Hb and the latter one specified to proton Ha; this proton had coupling
interaction to proton H-1 on pyranose ring with coupling constant J = 9.25−8.50 Hz. These values
of coupling constants agreed with trans-axial H–H disposition and β-anomeric configuration.
Resonance of carbon atom C-1 on pyranose ring was easily recognized at δ= 81.5 ppm, which was
the signal lying in the weakest field in resonance region of pyranose’s carbon. The cause of this
phenomenon was that the carbon atom C-1 was influenced by electronegative oxygen atom of
pyranose ring and of the adjacent nitrogen atom of thiosemicarbazone linkage. 13C NMR spectra of
compound 5a-j showed resonance signals at =181.6−180.0 ppm (carbon atom in C=S group),
7

=170.5−168.8 ppm (carbon atoms in C=O bond of acetyl groups). Carbon atoms in coumarin ring
had chemical shifts at =155.4−110.1 ppm, whereas resonance signals at δ=82.0−61.1 ppm
belonged carbon atoms on D-glucopyranose ring, and chemical shifts were at =21.5−21.1 ppm
belonged methyl carbons in acetyl groups. Carbon atom in lactone carbonyl group on coumarin ring
had chemical shift at δ=159.6−158.7 ppm.
All the synthesized thiosemicarbazones 5a-j were screened for their in vitro antibacterial activity
against three representative Gram-positive bacteria, which were B. subtilis (ATCC 11774), S.
aureus (ATCC 11632), S. epidermidis (ATCC 12228), and four representative Gram-negative
bacteria, which were E. coli (ATCC 25922), P. aeruginosa (ATCC 25923), K. pneumoniae (ATCC
4352), S. typhimurium (ATCC 14028). Some antibiotics were used as positive references for
antibacterial activity, including ciprofloxacin and vancomycin. Vancomycin and ciprofloxacin are
used to treat a number of bacterial infections, with the former used to treat serious, life-threatening
infections by Gram-positive bacteria that are unresponsive to other antibiotics. The latter treated
serious infections caused by Gram-negative bacteria, including P. aeruginosa. All the experiments
were performed three times. Evaluated results for compounds 5a-j were given in Table 1.
The results showed that almost all novel molecules exhibited antibacterial activity against the tested
bacteria at their different concentrations. In general, it has been observed that almost all tested
compounds showed mild to moderate activity against the tested bacteria in comparison with the
MIC values of the reference compounds. MIC values of these reference drugs are as follows:
Ciprofloxacin, 3.125 μM (for Gram-positive bacteria), 1.56 μM (for Gram-negative bacteria);
Vancomycin, 0.78−3.125 μM (for Gram-positive bacteria). Some thiosemicarbazones 5a-j had
higher ability to inhibit to both Gram-positive bacteria (B. subtilis, C. difficile, S. aureus, and S.
epidermidis) and Gram-negative bacteria (E. Coli, K. pneumoniae, P. aeruginosa, and S.
Typhimurium), with MIC values of 1.56‒3.125 μM. From obtained results of inhibitory activities in
Table 1 for tested bacteria, some comments were discussed as follows. Almost all
thiosemicarbazones 5a-j series had remarkable inhibitory activity against Gram-positive bacteria S.
8

aureus, S. epidermidis (especially, compounds 5h and 5i with MIC = 0.78 and 1.56 μM), Gram-
negative bacteria E. coli (especially, compound 5f with 8-methoxy group, MIC = 1.56 μM) and P.
aeruginosa (5g, MIC = 1.56 μM). Thiosemicarbazones 5a-j exhibited similar inhibitory activities
for both Gram-negative and Gram-positive bacteria. Almost all these compounds displayed
significant inhibitory activity against all tested bacteria (with MIC were equal 3.125 μM or smaller),
especially for S. aureus and S. epidermidis. In ranges of MIC = 0.78−3.125 μM, thiosemicarbazones
5a-j series displayed better inhibitory activity against Gram-negative bacteria than against Gram-
positive bacteria. In ranges of MIC = 0.78−3.125 μM. Compound 5i and 5h had strongest inhibitory
activity against bacterium S. aureus. Both compounds had MIC values of 0.78 μM.
Based on the obtain results of the inhibitory activities in Table 1 for the tested bacteria, some SAR
results were deduced as follows:
1. Thiosemicarbazone 5a from unsubstituted 3-acetylcoumarin (3a) had unnoticeable inhibitory
activity against all tested bacteria, with MIC values in the range from 50 μM to 400 μM,
except against bacterium S. epidermidis with MIC = 12.5 μM
2. Electron-donating groups on benzene ring of coumarin (such as methyl, hydroxy, and
methoxy): Compounds that had strong inhibitory activity with MIC values of 0.78−3.125 μM
against Gram-positive bacteria were 5e and 5i (for S. aureus), 5f and 5i (for S. epidermidis).
Compounds that exhibited notable inhibition against Gram-negative bacteria included 5f (for
E. coli and K. pneumoniae), 5i (for S. typhimurium). The remaining compounds had
unremarkably inhibitory activity for both tested bacterial types. Additionally, all of the tested
compounds 5d,e,f,i,j had unremarkably inhibitory activity against B. subtilis. The methyl
group on position 4 led to decrease inhibition for almost all tested bacteria. The presence of 7-
hydroxy group in compound 5i strengthened inhibition against several tested bacteria, such as
S. aureus, S. epidermidis, and S. typhimurium.
3. Electron-withdrawing groups on benzene ring of coumarin (including 6-chloro, 6-bromo, 6-
nitro, and 8-nitro): In general, thiosemicarbazones 5b,c,g,h had unremarkable inhibitory
9

activity against tested Gram-positive bacteria, except 5h (for S. aureus) and 5c (for S.
epidermidis). For Gram-negative bacteria, compounds 5c (bromo substituent) and 5g (nitro
substituent) had strong inhibition against E. coli, and P. aeruginosa with MICs of 1.56−3.125
μM. The presence of chloro substituent (compound 5b) increased activity against only for P.
aeruginosa.
We also evaluated the antifungal activities of the above thiosemicarbazones 5a-j against some fungi,
such as Aspergillus niger (ATCC 439), Aspergillus flavus (ATCC 204304), Candida albicans
(ATCC 7754), and Saccharomyces cerevisiae (SH 20). Miconazole and fluconazole were used as
references. Miconazole is mainly used externally for the treatment and prophylactic treatment of
Candida infection in the oral cavity and the digestive tract. Fluconazole is a first-generation triazole
antifungal medication. It has a spectrum of activity, which includes most Candida species but not C.
krusei or C. glabrata, Cryptococcus neoformans, some dimorphic fungi, and dermatophytes. MIC
values of miconazole were 1.56, 1.56, 3.125 and 3.125 μM for each fungus, respectively, and of
fluconazole were 1.56, 0.78, 0.78 and 0.78 μM for each fungus, respectively. All the experiments
were performed three times. The obtained results were given in Table 2. Some comments could
deduce as follows. In range of MIC values of 0.78−3.125 μM, almost all the tested
thiosemicarbazones 5a-j were remarkably active against fungus A. niger and C. albicans, and were
more resistant to A. niger, A. flavus, and S. cerevisiae than miconazole and fluconazole.
Remarkably, compounds 5h (against C. albicans) and 5i (against S. cerevisiae) were more active
(all MIC = 0.78 μM) than miconazole and comparably active with miconazole. Almost all
compounds 5a-j did not exhibit inhibitory activity against fungus S. cerevisiae, except compound 5i
(bearing 4-methyl and 7-hydroxy) that expressed the best inhibition with MIC = 0.78 μM that could
be comparable with reference drug fluconazole (MIC = 0.78 μM). This compound had higher
inhibition than miconazole (MIC = 3.125 μM) against S. cerevisiae.
10

Table 1. Antibacterial activity of thiosemicarbazones 5a-j
Compounds
Micro-organisms/ MIC (μM)
Gram-positive bacteria
Gram-negative bacteria
E. coli K. pneumoniae P. aeruginosa
B. subtilis
S. aureus
S. epidermidis
12.5 ± 0.65
>100
S. typhimurium
100 ± 12.35
50 ± 3.75
25 ± 1.12
25 ± 1.18
N.E.
5a
>100
N.E.
N.E.
N.E.
N.E.
50 ± 4.23
25 ± 1.45
100 ± 12.35
N.E.
50 ± 3.56
3.125 ± 0.48
3.125 ± 0.51
12.5 ± 0.95
25 ± 1.15
N.E.
5b
>100
5c
100 ± 12.35
12.5 ± 0.78
1.56 ± 0.14
50 ± 3.39
3.125 ± 0.32
50 ± 3.51
3.125 ± 0.37
50 ± 3.54
25 ± 1.15
1.56 ± 0.75
3.125 ± 0.41
25 ± 1.15
100 ± 12.35
N.E.
25 ± 1.45
100 ± 12.35
25 ± 1.14
1.56 ± 0.71
50 ± 3.46
12.5 ± 0.71
100 ± 12.35
50 ± 4.35
1.56 ± 0.15
−
5d
5e
100 ± 11.45
50 ± 3.43
>100
N.E.
5f
3.125 ± 0.36
12.5 ± 0.75
12.5 ± 0.72
1.56 ± 0.15
100 ± 12.35
3.125 ± 0.35
0.78 ± 0.06
N.E.
5g
12.5 ± 0.86
0.78 ± 0.08
0.78 ± 0.07
25 ± 1.21
1.56 ± 0.21
N.E.
100 ± 12.35
>100
5h
12.5 ± 0.79
100 ± 11.35
>100
5i
12.5 ± 0.69
N.E.
3.125 ± 0.32
N.E.
5j
Ciprofloxacin
Vancomycin
3.125 ± 0.34
1.56 ± 0.12
3.125 ± 0.36
3.125 ± 0.25
1.56 ± 0.23
−
1.56 ± 0.16
−
1.56 ± 0.15
−
Note: N.E. = not evaluated

Table 2. Antifungal activity of thiosemicarbazones 5a-j
Compounds
Fungi/ MIC (μM)
A. niger
A. flavus
25 ± 1.65
C. albicans
100 ± 15.09
1.56 ± 0.06
50 ± 3.34
S. cerevisiae
50 ± 3.54
50 ± 3.35
25 ± 1.34
25 ± 1.65
>100
5a
>100
5b
100 ± 12.12
N.E.
12.5 ± 1.10
6.25 ± 0.78
N.E.
5c
5d
1.56 ± 0.27
25 ± 1.64
3.125 ± 0.89
3.125 ± 0.96
25 ± 1.26
5e
>100
5f
6.25 ± 0.84
12.5 ± 0.89
3.125 ± 0.34
3.125 ± 0.23
12.5 ± 0.97
1.56 ± 0.09
1.56 ± 0.12
6.25 ± 0.82
100 ± 12.17
12.5 ± 1.04
1.56 ± 0.34
25 ± 1.54
1.56 ± 0.21
0.78 ± 0.02
50 ± 3.46
25 ± 1.54
12.5 ± 0.96
0.78 ± 0.09
12.5 ± 0.89
3.125 ± 0.22
0.78 ± 0.02
5g
25 ± 1.52
5h
0.78 ± 0.06
>100
5i
5j
12.5 ± 0.89
3.125 ± 0.24
0.78 ± 0.03
Miconazole
Fluconazole
Some SAR results were deduced as follows, based on obtained results of inhibitory activities
for all tested fungi:
1. Thiosemicarbazones from unsubstituted 3-acetylcoumarin (5a) had no activity against all
tested fungi.
2. The electron-donating groups on benzene ring of coumarin, such as methyl, hydroxy, and
methoxy: In general, these groups created strong to medium inhibitory activity against
tested fungi in thiosemicarbazones 5d,e,f,i,j with MIC = 0.78−12.5 μM when compared
with thiosemicarbazone of unsubstituted 3-acetylcoumarin. Compound 5i had
remarkable inhibitory activity against three fungi, A. niger, A. flavus and S. cerevisiae.
12

3. The electron-withdrawing groups on benzene ring of coumarin (such as 6-chloro, 6-
bromo, 6-nitro, and 8-nitro): These substituents also decreased the inhibitory activity
against A. niger and S. cerevisiae of thiosemicarbazones 5b,c,g,h, but greatly increased
the inhibitory activity against A. flavus (5g,h) and C. albicans (5b,h). Compound 5h
exhibited strong activity against A. niger and C. albicans.
In summary, microwave-assisted heating method was an efficient and convenient method for
synthesis of N-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)thiosemicarbazones of substituted
3-acetylcoumarins. All synthesized thiosemicarbazones except for 5a displayed significant
inhibition in vitro against bacteria bacteria (B. subtilis, S. aureus, S. epidermidis, E. coli, P.
aeruginosa, K. pneumoniae, S. typhimurium) and fungi (A. niger, C. albicans, S. cerevisiae,
and A. flavus).
Appendix A. Supplementary data
Supplementary data (experimental section, IR, 1H NMR, 13C NMR, mass spectral data and
elemental analysis for the synthesized compounds) can be found, in the online version, at
http://dx.doi.org/10.1016/j.bmcl...
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Highlights
 Ten new thiosemicarbazones of substituted 3-acetylcoumarins with D-glucose moiety were
synthesized in 45−68% yields.
 Several thiosemicarbazones were active against Gram-(+) and Gram-(−) bacteria with MICs
of 1.56−3.125 μM.
 Some thiosemicarbazones had activity against fungi with MICs of 1.56−3.125 μM.
17

 Compounds 5h and 5i exhibited excellent activity against S. aureus with MIC of 0.78 μM.
 Compounds exhibited excellent activity with MIC of 0.78 μM, including 5h (for C.
albicans), and 5i (for S. cerevisiae).
18