8026 Iqbal et al.
Asian J. Chem.
monoesters and incubated at 28 °C for 22 h. and the antifungal
activity was determined by measuring the diameter of the
inhibition zone in mm.
Antimicrobial activities in terms of zones of inhibitions of
monoesters 1-27 are provided in Table-1. Zones of inhibition
displayed by 25 are C. albicans (25.72 mm), A. niger (24.17
mm), E. coli (26.70 mm) and P. mirabilis (26.73 mm) while
for 26 the values are C. albicans (24.66 mm), A. niger (25.14
mm), E. coli (26.67 mm) and P. mirabilis (26.64 mm). These
values are close to values exhibited by standard drugs chlor-
amphenicol and ketoconazole (Table-1). As is evident from
values for zones of inhibition for 1-27, the halogenated com-
pounds 1-10, 25 and 26 exhibited maximum inhibition zones
against microbes. Compounds 11-14 and 27 displayed lower
inhibition zones (9-14 mm) as compared with 1-10, 25 and 26
(Table-1).
Antibacterial activity of monoesters:Agar well diffusion
method using chloramphenicol as standard was used to
establish antibacterial activity of the monoesters22. Briefly,
wells were dug in the pre-coated agar nutrients media plates
with the help a sterile borer. Surface of the agar nutrient was
covered with eight-hour bacterial inoculum containing 104-
106 colony forming units (CFU/mL). To each well a 1 mL of
DMSO solution of monoesters (2-10 mg in DMSO 1 mL) was
placed. Two wells were reserved for negative and positive
controls. To the well for negative control 1 mL pure DMSO
and to the well for positive control 2 µg of chloramphenicol/
mL DMSO of were introduced. The plates were incubated
immediately at 37 °C for 22 h. The activity was determined
by measuring the diameter of the inhibition zone (in mm).
Minimum inhibitory concentrations (MICs) of mono-
esters (1-27): Minimum inhibitory concentrations (MICs)
were determined by agar dilution method22. Briefly, 25 mL of
the sterilized Mueller-Hinton agar (Oxoid) was added to
sterilized test tube containing 1 mL of 2-10 µg/mL of mono-
esters at 25 °C. The mixture was then thoroughly mixed and
poured into sterilized petri plates. The microbial suspension
with density adjusted to 0.5 McFarland turbidity standard was
inoculated (0.05 µL) on to the series of agar plates using
micropipette. The plates were then incubated at 37 °C for 24 h
and MIC values were calculated.
Conclusion
The prepared compounds except 1-10, 25 and 26 were
found to be noticeably bioactive. The highest activity was
observed for tri-halogenated derivatives. It can be concluded
that the compounds may be used as candidates for antifungal
and antibacterial drugs. It is recommended that in vivo studies
of these compounds may be carried out and their mode of
action against these microbes be explored.
in vitro MICs values of monoesters (1-27) are pre-
sented in Table-2. Dichlorobenzyl derivatives displayed MICs
values lower than 3 µg/mL while fluorinated monoesters dis-
played somewhat higher values (Table-2). Monoesters 9-24
and 27 displayed MICs values between 9 and 11 µg/mL.
Compounds 25 and 26 showed as low MICs values as standard
drugs (Table-2). As is evident from MICs values in Table-2,
monoester 25 exhibited lowest MIC value of 1.67 µg/mL
against bacterium E. coli while 26 displayed against P. mirabilis
an MIC value of 1.68 µg/mL. Furthermore, 25 displayed lowest
MICs value of 1.71 and 26 1.73 µg/mL against fungal strains
A. niger and C. albicans, respectively.
RESULTS AND DISCUSSION
Scheme-I listed the structures of antimicrobial mono-
esters of succinic acid.All of the di- and tri-substituted benzyl
esters (1-27) were probed for antimicrobial activities using
Ketoconazole and Chloramphenicol as standards. C. albicans
and A. niger were employed for antifungal while, E. coli and
P. mirabilis for antibacterial activity. In vitro results of this
study are presented in Tables-1 and 2. The obtained results
showed that all the compounds exhibited considerable anti-
microbial activity against used microbes (Tables 1 and 2).
ACKNOWLEDGEMENTS
The authors acknowledge Mr. Adnan Amin and Prof. Dr.
Muhammad Ayaz Khan, Director Biotechnology and Bio-
chemistry Centre, Gomal University Dera Ismail Khan, Khyber
Pakhtunkhwa, Pakistan for antifungal and antibacterial studies.
O
O
R'
R''
OH
OH
O
O
O
O
R'
R
R
4.
7.
1.
2.
3.
6.
R=R'=2,6-Dichloro
R=R'=2,4-Difluoro
R=R'=2,4-Dichloro
R=R'=2,5-Dichloro
R=R'=3,5-Dichloro
R=R'=2,6-Dichloro
R=R'=2,3-Difluoro
5
.
8.
9.
10.
14.
18.
11.
15.
19.
R=R'=2,5-Difluoro
R=R'=2,5-Dimethyl
R=R'=2,6-Difluoro
R=R'=2,4-Dimethyl
R=R'=3,4-Dinitro
12.
16.
13.
17.
R=R'=3,4-Dimethyl
R=R'=2,6-Diethoxy;R''=H
R=R'=3,5-Dimethyl
R=R'=3,4-Diethoxy;R''=H
R=R'=3,5-Dinitro;R''=H
R=R'=R''=2,3,4-Trimethoxy
R=R'=3,5-Dihydroxy;R''=H
R=3,Methoxy; R'=4-nitro;R''=H
R=R'=R''=2,4,5-Tribromo
20.
24.
21.
25.
22.
26.
23.
27.
R=R'=R''=2,4,5-Trimethoxy
R=R'=R''=3,4,5Ttrimethoxy
R=R'=R''=2,4,6-Trichloro
R=4-Methoxy; R'=3-nitro;R''=H
R=R'=R''=2,4,6-Trimethyl
R=2-Methoxy; R'=5-nitro;R''=H
Scheme-I: Structures of antimicrobial monoesters