Fusaric acid and derivatives as novel antimicrobial agents

Article abstract of DOI:10.1007/s00044-020-02596-3

The synthesis and screening of several fusaric acid (FA) and analogues against five common clinical pathogens (gram-positive and gram-negative) and in vitro hemolytic activity assay in human red blood cells, for the first time, were reported. The biological results reveal that FA and its analogues exhibited moderate antimicrobial activities. Compounds 2–5 and 7 showed growth inhibitory activity in gram-positive bacteria. Compounds 6 and 9 showed growth inhibitory activity in both gram-positive and gram-negative bacteria. None of the compounds induce hemolysis, which is potent for future drug development on this template. In addition, the structure–activity relationship and docking studies are discussed.

Full text of DOI:10.1007/s00044-020-02596-3

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research
https://doi.org/10.1007/s00044-020-02596-3
ORIGINAL RESEARCH
Fusaric acid and derivatives as novel antimicrobial agents
1
,2 ●
Thang Nguyen Quoc Huy Luong Xuan1,2
3 ●
Tung Truong Thanh
Received: 28 April 2020 / Accepted: 23 June 2020
Springer Science+Business Media, LLC, part of Springer Nature 2020
©
Abstract
The synthesis and screening of several fusaric acid (FA) and analogues against five common clinical pathogens (gram-
positive and gram-negative) and in vitro hemolytic activity assay in human red blood cells, for the first time, were reported.
The biological results reveal that FA and its analogues exhibited moderate antimicrobial activities. Compounds 2–5 and 7
showed growth inhibitory activity in gram-positive bacteria. Compounds 6 and 9 showed growth inhibitory activity in both
gram-positive and gram-negative bacteria. None of the compounds induce hemolysis, which is potent for future drug
development on this template. In addition, the structure–activity relationship and docking studies are discussed.
●
●
Keywords Fusaric acid Antimicrobial Docking
Introduction
Etherton 1984; Fakhouri et al. 2003; Wang et al. 2013; Li
et al. 2013; Asano and Hidaka 1977). For example, FA is
known as a key role in wilt disease in plants (Bacon et al.
1996), inhibiting plant proton pump (Fakhouri et al. 2003),
damaging roots, and leaves of banana (Li et al. 2013). In
mammals, the relaxation effect of FA in an isolated aorta of
the rabbit was observed (Asano and Hidaka 1977). Yin
et al. (2015) reported that FA/copper chelate can cause
malformation in zebrafish. Metal complexes of FA also
found to have antimycobacterial activity in a report by Pan
et al. (2011). Besides several reports, the mechanism of
action of FA is not fully understood (Fig. 1).
Recently, we have discovered that FA and analogues are
potent quorum sensing (QS) inhibitors of gram-negative
bacteria (Tung et al. 2017). Compounds showed moderate
QS inhibitory activity from 6.20 to 100.00 μg/mL con-
centration ranges without interrupting the growth of the
bacteria. Interestingly, some compounds, especially acid
derivatives (including FA) (Fig. 2) exhibited the growth
inhibitory effect of Escherichia coli under our reported
condition (luxI-gfp, E. coli) (Tung et al. 2017).
Infectious diseases affecting to an estimated a quarter of the
global population, and along with an increase in anti-
microbial drug resistance, are the top leading causes of
death annually (Brown et al. 2012). Finding new anti-
bacterial and antifungal compounds is hence urgently nee-
ded for the development of effective drugs to treat these
diseases (Rafique et al. 2017; Ashraf et al. 2017).
Fusaric acid (FA) is a well-known mycotoxin produced
by Fusarium species (Yabuta et al. 1934). This compound
can be isolated in a decent amount from 20 to 1080 μg per
gram of Fusarium strain (Bacon et al. 1996). As one of the
main chemical components of Fusarium sp., many research
groups have focused on revealing the biological role of FA
in the internal activities as well as external effects toward
other microorganism (López-Díaz et al. 2018). In fact,
recent studies have shown that FA exhibit moderate toxicity
toward bacteria, plants, and animals (D’Alton and
*
Tung Truong Thanh
tung.truongthanh@phenikaa-uni.edu.vn
1
2
3
Faculty of Pharmacy, PHENIKAA University, Hanoi 12116,
Vietnam
PHENIKAA Institute for Advanced Study (PIAS), PHENIKAA
University, Hanoi 12116, Vietnam
Nuclear Medicine Unit, Vinmec International Hospital,
Hanoi 10000, Vietnam
Fig. 1 Structure of fusaric acid

Medicinal Chemistry Research
In vitro antibacterial and antifungal assay
Minimum inhibitory concentrations (MIC) were determined
as previously described (Broth microdilution) (Mygind
et al. 2005). The MIC value was measured as the lowest
concentration where no visible growth was observed as
compared to the control (no compound added).
Fig. 2 Growth inhibitory activity of fusaric acid (FA) in E. coli as
previously reported (Tung et al. 2017)
In vitro hemolytic activity
The lysis of human red blood cells (hRBCs) was measured
as previously described (Jahnsen et al. 2014; Schmitt et al.
2007). The freshly drawn hRBCs were, first, washed with
PBS buffer (twice, Sigma Aldrich, DK: 0.01 M Phosphate,
2.7 mM KCl, 0.137 M NaCl, pH 7.4) then centrifuged for
Intriguing from this finding, we report here the synthesis
and screening of some potent FA analogues toward five
clinical pathogens (for both gram-negative and gram-posi-
tive) in an effort of fighting antibiotic resistance.
8
min (×2) at 3000 rpm (116 g) and 4000 rpm (206 g). FA
and analogues were diluted in PBS buffer. Samples were
then added to sterile polypropylene V-bottom 96-well plate
Materials and methods
Chemistry
(Whatman, UK), to give a total volume of 75 μL. 75 μL of
0.5% v/v hRBC suspension in PBS buffer was added to
reach a final volume of 150 μL in each well. The plate was
incubated at 37 °C for 1 h. Then, the cells were pelleted by
centrifugation at 4000 rpm for 10 min. The 75 μL of
supernatants was transferred to clear, flat-bottomed plastic
96-well plates. The concentration of hemoglobin was
determined by recording the OD at 414 nm (VERSAmax
microplate reader, Molecular Devices, USA). Hundred
percent hemolysis was defined as the OD of cells incubated
with melittin (400 μg/mL), and 0% hemolysis was defined
as the OD of cells incubated with PBS buffer.
General information
Reagents were purchased from a commercially available ven-
dor (Aldrich) and were used without further purification. NMR-
spectra were recorded using a 400/600 MHz Bruker Avance
13
(
cryogenically cooled 5 mm dual-probe optimized for C and
H is equipped). NMR solvents: DMSO-d , CDCl , MeOH-d ,
1
6
3
4
samples ran at 300 K. 1H-NMR, COSY, HMBC, HSQC are
13
recorded at 400 or 600 MHz. CNMR were recorded at 151 or
01 MHz. Chemical shifts (δ) are reported in ppm relative to
1
1
the residual solvent peak ( HNMR) or the solvent peak
1
3
(
CNMR) as the internal standard. J values are reported in
Results and discussion
Hertz. Solvents for reaction were of analytical grade (water
content <25 ppm). TLC was performed using silica gel 60 F254
plates (pre-coated) and visualized under UV light. Column
chromatography was performed using silica 60 (Merck).
Melting points were recorded on a MP70 Mettler Toledo. All
tested compounds possess at least 95% purity. Purities were
checked on a Waters 2795 system equipped with a Waters 996
PDA detector and a Waters Symmetry C18 Column (2.1 ×
Synthesis and characterization
General procedure for the synthesis of library compounds
Synthesis of fusaric and analogues was prepared as pre-
viously described (depicted in Schemes 1, 2) (Tung et al.
2017). In brief, compounds 1–7 were prepared from methyl
5-bromopicolinate as starting material via Suzuki coupling
reaction and saponification (Scheme 1). Compounds 8–10
were prepared from the alkylation of methyl 5-
hydroxypicolinate followed by saponification (Scheme 2).
50 mm, 3.5 l m), flow rate 0.2 ml/min. HRMS data were
recorded on an electrospray (ESI) mass spectrometer.
Biology
Bacterial and fungal strains
Characterization of 1–7
Standard laboratory test strains: Staphylococcus aureus
ATCC29213, Enterococcus faecalis ATCC29212, E. coli
ATCC25922, Pseudomonas aeruginosa ATCC27853 (pur-
chased from ATCC, Manassas, VA, USA), and Candida
albicans were chosen for antimicrobial activity experiments.
5-Bromopicolinic acid (1) Yellow solid; MP 176.9–177 °C;
1
>98% purity; HNMR (600 MHz, DMSO-d ) δ 13.41 (br,
6
1H), 8.84 (d, J = 2.3 Hz, 1H), 8.25 (d, J = 2.4 Hz, 1H), 7.98
1
3
(d, J = 8.3 Hz); CNMR (151 MHz, DMSO-d ) δ 166.0,
6

Medicinal Chemistry Research
Scheme 1 Synthetic route for the preparation 1–7. a NaOH(aq) (5
equiv.), rt, 12 h, then HCl (1 M); b bis(pinacolato)diboron, potassium
acetate, 10 mol % Pd(dppf)Cl2 complex with chloroform, MW,
30 min; c R-Br, Pd(dppf)Cl2 complex with chloroform 10%, Cs2CO3,
1,4-Dioxane/water (1/0.5), MW, 90 min
Scheme 2 Synthetic route for the preparation 8–10. a R-Br, DMF, rt, 18 h; then b NaOH(aq) (5 equiv.), rt, 12 h, then HCl (1 M)
1
50.8, 147.6, 140.5, 126.8, 124.6; HRMS (ESI) m/z [M+Na]
(t, J = 7.4, 1H), 7.76 (d, J = 7.3 Hz, 1H), 6.91 (d, J = 8.2 Hz,
+
+
13
calcd for C H BrNO Na 223.9323, found 223.9323.
1H), 3.99 (s, 3H); CNMR (151 MHz, DMSO-d ) δ 166.4,
6
4
2
6
1
64.0, 150.8, 148.8, 148.0, 148.8, 136.7, 135.3, 125.1, 114.8,
Methyl 5-(6-methoxyquinolin-4-yl)picolinate (2) White solid;
111.5, 53.6; HRMS (ESI) m/z [M+H]+ calcd for
1
+
MP 121.8–122.6 °C; >98% purity; HNMR (600 MHz,
C H N O 231.0770, found 231.0768.
1
2
11
2
3
CDCl3) δ 8.94 (d, J = 2.1 Hz, 1H), 8.86 (d, J = 4.3 Hz, 1H),
8
=
.34 (d, J = 7.9 Hz, 1H), 8.11 (d, J = 9.2 Hz, 1H), 8.03 (dd, J
8.0, 2.2 Hz, 1H), 7.43 (dd, J = 9.1, 2.7 Hz, 1H), 7.31 (d, J =
5-(6-Methoxyquinolin-4-yl)picolinic acid (5) White solid;
MP 246–247 °C; >98% purity; HNMR (600 MHz, DMSO-
1
4
3
1
1
.3 Hz, 1H), 7.01 (d, J = 2.7 Hz, 1H), 4.09 (s, 3H), 3.79 (s,
H); 13 C NMR (151 MHz, CDCl3) δ 165.4, 158.6, 149.9,
47.7, 147.4, 144.9, 142.0, 137.8, 137.6, 131.8, 127.1, 125.1,
d6) δ 13.36 (s, 1H), 8.93 (q, J = 1.1, 0.7 Hz, 1H), 8.86 (d,
J = 4.4 Hz, 1H), 8.25 (m, 2H, H3), 8.08 (d, J = 9.2 Hz, 1H),
7.54 (d, J = 4.4 Hz, 1H), 7.51 (dd, J = 9.2, 2.8 Hz, 1H),
+
13
22.5, 121.9, 102.4, 55.6, 53.2; HRMS (ESI) m/z [M+H]
7.10 (d, J = 2.7 Hz, 1H), 3.85 (s, 3H); CNMR (151 MHz,
+
calcd for C H N O 295.1083, found 295.1083.
DMSO-d ) δ 166.3, 159.6, 149.8, 149.4, 147.9, 144.1,
17
15
2
3
6
1
38.9, 138.5, 135.6, 128.1, 126.7, 125.5, 125.2, 123.4,
+
Ethyl 5-butylpicolinate (3) Yellow oil; >98% purity;
104.1, 56.3; HRMS (ESI) m/z [M+H] calcd for
C H N O 281.0926, found 281.0927.
1
+
HNMR (600 MHz, CDCl ) δ 8.57 (d, J = 2.2 Hz, 1H), 8.05
3
16 13
2
3
(
d, J = 7.8 Hz, 1H), 7.63 (dd, J = 2.2, 7.8 Hz, 1H), 4.47 (q,
J = 7.1 Hz, 2H), 2.69 (t, J = 7.6 Hz, 2H), 1.62 (m, 2H), 1.44
Fusaric acid (6) Slightly yellow solid; MP 97.0–98.0 °C;
1
(
t, J = 7.1, 3H), 1.37 (qt, J = 7.3, 7.6 Hz, 2H), 0.94 (t, J =
>99% purity; HNMR (600 MHz, DMSO-d ): δ 8.46 (d, J =
6
1
3
7
1
1
2
.3 Hz, 3H); CNMR (151 MHz, CDCl ) d 165.4, 150.1,
2.2 Hz, 1H), 8.16 (d, J = 8.1 Hz,1H), 7.76 (dd, J = 8.1,
2.2 Hz,1H), 2.74 (t, J = 7.7 Hz, 2H), 1.66 (m, 2H), 1.4 (tq, J =
3
45.9, 141.9, 136.5, 124.8, 61.7, 32.9, 32.7, 22.2, 14.4,
3.8; HRMS (ESI) m/z [M+H]+ calcd for C H NO
+
7.7, 7.3 Hz, 2H), 0.96 (t, J = 7.3 Hz, 3H); CNMR (151 MHz,
13
12
18
2
08.1338, found 208.1340.
DMSO-d ) δ 164.2, 148.2, 143.8, 143.5, 138.1, 123.4, 32.9,
6
+
3
2.8, 22.2, 13.8; HRMS (ESI) m/z [M+H] calcd for
C H NO 180.1025, found 180.1025.
10 14 2
+
6
-Methoxy-[2,3′-bipyridine]-6′-carboxylic acid (4) Off-white
1
solid; MP 210–215 °C; >98% purity; HNMR (600 MHz,
DMSO-d ) δ 13.23 (s, 1H, OH), 9.39 (d, J = 1.6, 1H), 8.61
5-(p-Tolyl)picolinic acid (7) Off-white solid; MP
192.7–195.0 °C; >97% purity; HNMR (600 MHz,
6
1
(
dd, J = 8.2, 2.2 Hz, 1H), 8.15 (dd, J = 8.2, 0.6 Hz, 1H), 7.88

Medicinal Chemistry Research
1
3
DMSO-d ) δ 13.15 (b. s, 1H), 9.0 (d, J = 1.6 Hz, 1H),
CNMR (151 MHz, DMSO-d ) δ 166.2, 157.7, 140.7,
6
6
8
.23 (dd, J = 8.1, 2.1 Hz, 1H), 8.09 (dd, J = 8.1, 0.7 Hz,
H), 7.72 (m, 2H), 7.35 (d, J = 8.1 Hz, 2H), 2.38 (s, 3H);
138.3, 126.7, 121.1, 70.2, 22.3, 10.7; HRMS (ESI)
m/z [M+H]+ calcd for C H NO
+
182.0817, found
1
9
12
3
1
3
CNMR (151 MHz, DMSO-d ) δ 165.9, 147.2, 146.8,
182.0817.
6
1
2
2
38.5, 138.2, 134.7, 133.0, 129.8(2 C), 127.0(2 C), 124.8,
+
+
0.7; HRMS (ESI) m/z [M+H] calcd for C H NO
5-(Cyclopropylmethoxy)picolinic acid (9) Off-white solid;
MP 138–139.5 °C; >98% purity; HNMR (600 MHz,
1
3
12
2
1
14.0868, found 214.0872.
DMSO-d ) δ 12.81 (s, 1H), 8.36 (d, J = 2.7 Hz, 1H), 8.01
6
Characterization of 8–10
(d, J = 8.8 Hz, 1H), 7.48 (dd, J = 8.8, 2.9 Hz, 1H), 3.99 (d,
J = 7.1 Hz, 2H), 1.23–1.29 (m, 1H), 0.59–0.62 (m, 2H),
1
3
5
-Propoxypicolinic acid (8) Off-white solid; MP
0.35–0.38 (m, 2H); CNMR δ (151 MHz, DMSO-d6)
166.2, 157.7, 140.7, 138.4, 126.6, 121.2, 73.4, 10.3, 3.6
(2 C); HRMS (ESI) m/z [M+H]+ calcd for C H NO
1
1
29.0–129.2 °C; >98% purity; HNMR (600 MHz, DMSO-
+
d6) δ 12.82 (s, 1H), 8.35 (s, 1H), 8.01 (dd, J = 8.6, 0.8 Hz,
10
12
3
1
2
H), 7.48 (dt, J = 8.7, 2.6 Hz, 1H), 4.03 (td, J = 6.5, 1.7 Hz,
H), 1.73–1.78 (m, 2H), 0.98 (td, J = 7.4, 1.7, 3H);
194.0817, found 194.0816.
Table 1 Minimal inhibitory
concentration (in μg/mL) against
several pathogens
MIC (μg/mL)a
Cpds
Structure
S. aureus
ATCC29213
E. faecalis
ATCC29212
E. coli
ATCC25922
P. aeruginosa C. albicans
ATCC27853
1
>150
>150
>150
>150
>150
2
3
4
5
6
7
8
9
>150
>150
>150
68
121
112
100
64
>150
>150
>150
>150
128
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
>150
98
100
>150
107
>150
>150
125
116
1
0
>150
Ampicillinb
Fluconazoleb
8
2.5
5.5
–
c
–
–
–
–
–
0.5
aExperiments were performed in triplicate
bPositive control
cNot determined

Medicinal Chemistry Research
Table 2 Hemolytic activitya
5
-(2-Oxo-2-(phenylamino)ethoxy)picolinic acid (10) Light
1
yellow solid; MP 225–226 °C; >98% purity; HNMR
600 MHz, DMSO-d ) δ 12.9 (s, 1H), 10.18 (s, 1H), 8.45 (d,
Compounds Structure
ClogP Hemolytic
activityb
5% blood
agar
c
(
6
J = 2.9 Hz, 1H), 8.04 (d, J = 8.7 Hz, 1H), 7.62 (m, 2H),
1
2
1.45
(−)
>106
7
1
1
1
.53 (dd, J = 8.7, 2.9 Hz, 1H), 7.31–7.35 (m, 2H), 7.09 (m,
1
3
H), 4.91 (s, 2H); CNMR (151 MHz, DMSO-d ) δ 166.1,
6
66.1, 157.0, 141.5, 138.7, 138.6, 129.2, 126.6, 124.3,
+
>106
1.91
(−)
21.6, 120.2(2 C), 67.6; HRMS (ESI) m/z [M+H] calcd
+
for C H N O 273.0875, found 273.0873.
1
4
13
2
4
Biological screening
>106
3
4
5
2.83
1.51
2.28
(−)
(−)
(−)
FA and analogues were screened against four common
clinical bacteria (S. aureus, E. faecalis, E. coli, P. aeru-
ginosa) and fungi (C. albicans) (Table 1). Except for 5
>106
>106
(
MIC of 68 μg/mL) none of the compounds affected the
growth of S. aureus. The library compounds do not inhibit
the growth of P. aeruginosa and C. albicans under the
concentration tested. However, except for 1 and 10, other
compounds showed moderate growth inhibitory activity
toward E. faecalis and E. coli.
In E. faecalis, the MIC values range from 64 to 121 μg/
mL with 5 being the most potent inhibitor. Interestingly, the
acid derivatives (5, 6) are slightly better in activity com-
pared to its corresponding esters (2, 3). This observation is
in accordance with our previous study where ester deriva-
tives showed a QS effect without interrupting the growth
6
7
8
9
2.67
2.98
1.57
1.48
1.12
(−)
(−)
(−)
(−)
(−)
>106
>106
>106
>106
>106
(
Tung et al. 2017).
In E. Coli, compounds 6, 8, 9 exhibited a weak inhibitory
activity with MIC values of 128, 125, and 116 μg/mL,
respectively.
1
0
From a different perspective, compounds 2–5 and 7 are
selective for gram-positive bacteria (E. faecalis). In contrast,
aExperiments were performed in triplicate
b(−) negative, (+) positive
6
and 9 are selective for both gram-positive and gram-
cNumber of hemoglobin in 5% blood agar
negative (E. faecalis and E. coli, respectively). Noteworthy,
compounds 2, 4, 5, and 7 having an aromatic side chain
attach to pyridine core, while 6 and 9 are an acyclic satu-
rated hydrocarbon group. This structure–activity relation-
ship could possibly be related to the polarity of the
compounds and the physical properties of the peptidoglycan
layer of the bacteria. In this series, 8 is the only substance
that shows (weak) selective inhibition of gram-negative
bacteria.
Compound-induced hemolysis can cause serious health
problems when used in humans (Sharma et al. 1978).
Therefore, it is important that the compounds do not cause
any hemolysis effects. To best of our knowledge, none of
the literature reports the hemolytic activities to demonstrate
the drug’s ability of FA. In this work, the in vitro hemolytic
activity assay of the synthesized compounds has been per-
formed (Table 2).
compounds are generally safe to humans. Moreover, FA
could be a good template for future drug design and
development. In order to demonstrate the drug-likeness of
this scaffold, the prediction of ADME properties of the
compounds was showed in Table 3.
The calculation of the key pharmacokinetic properties of
the library compounds showed that none of them violated
Lipinski “rule of five” (Table 3). In brief, the
octanol–water partition coefficient values of the com-
pounds were within acceptable range (<5). Number of
acceptors, donors, and ROT bonds are perfectly suitable
for future drug development on this scaffold compared to
ampicillin (Tables 2, 3). Noteworthy, topological polar
surface area of all compounds is <90, which demonstrated
the excellent permeating cell membranes ability compared
to that of ampicillin (Pajouhesh and Lenz 2005; Hitchcock
and Pennington 2006).
None of the compounds caused damage to the hRBCs at
the concentration tested. The result indicated that the

Medicinal Chemistry Research
Table 3 Drug-likeness of the library compounds
Compounds Structure
MW
TPSAa Number
of atoms
Number of
acceptors
Number
of donors
Number of ROT Number of
bondsb
violations
c
1
202.01 50.19 10
3
1
1
0
2
3
4
5
6
7
8
9
294.31 61.32 22
207.27 39.20 15
230.22 72.32 17
280.28 72.32 21
175.19 53.09 13
213.24 50.19 16
181.19 59.42 13
193.20 59.42 14
5
3
5
5
3
3
4
4
0
0
1
1
2
1
1
1
4
6
3
3
1
2
4
4
0
0
0
0
0
0
0
0
1
0
272.26 88.52 20
349.41 112.73 24
6
7
2
4
5
4
0
0
Ampicillin
aTopological polar surface area
bNumber of rotatable bonds
cAccording to the Lipinski’s rule of five
Docking studies
active site of S. aureus tyrosyl-tRNA synthetase with the same
stable energy of −8.9 kcal/mol. Noteworthy, Pi-Anion inter-
action of ASP-195 with Quinoline moiety was seen (Fig. 3).
Thus, the docking results indicated that compound 5 is equal
affinities to that of ampicillin toward S. aureus tyrosyl-tRNA
synthetase. Overall results indicated that even though com-
pounds exhibited moderate antimicrobial activities, they are
good candidates for further drug development.
Compound 5 is the only one that showed good growth
inhibitory activities toward gram-positive bacteria tested (S.
aureus and E. faecalis). In addition, an earlier report indi-
cated that S. aureus tyrosyl-tRNA synthetase is a good
template for studying the possible mechanism of actions
(
Xiao et al. 2011). Therefore, in order to gain some possible
mechanism of actions, docking studies have been performed
for hit compound 5 and ampicillin to the crystal structure of
S. aureus tyrosyl-tRNA synthetase (Protein Data Bank ID:
Overall, the structure–activity relationship observed in
this study was summarized in Fig. 4.
1
JIJ) (Fig. 3) (Qiu et al. 2001).
After removed from the crystal structure of S. aureus tyr-
osyl-tRNA synthetase, SB-239629 was re-docked as a control
Conclusion
docking experiment using AutoDock Vina (Trott and Olson
In this work, 10 FA and analogues were synthesized and
screened toward five common clinical pathogens. The
library compounds possess the most sensitive toward E.
2010). Then compound 5 and ampicillin were docked. Inter-
estingly, compound 5 and ampicillin located perfectly to the

Medicinal Chemistry Research
Fig. 3 Prediction of the binding mode of compound 5 and ampicillin toward S. aureus tyrosyl-tRNA synthetase
faecalis as seen in compounds 2–7 and 9. In E. Coli, three
compounds 6, 8, 9 present a weak growth inhibition with
MIC of over 120 μg/mL. Compound 5 shows good growth
inhibition with MIC of 68 μg/mL in S. aureus. In the
concentration tested, no antimicrobial activities were
found in P. aeruginosa and C. albicans. Structure–activity
relationship indicated that compounds having an acyclic
saturated hydrocarbon moiety are effective for both gram-
positive and gram-negative bacteria. Replacing the alkane
side chain by an aromatic ring, compounds seem to be

Medicinal Chemistry Research
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4
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Acknowledgements This research is funded by The PHENIKAA
University Foundation for Science and Technology Development. The
authors would like to thank Prof. Niels Frimodt-Møller, Department of
Clinical Microbiology, Rigshospitalet, Københavns Universitet, Den-
mark for hemolytic activity assay. We would like to thank Prof. John
Nielsen, Department of Drug Design and Pharmacology, Københavns
Universitet, Denmark for essential support at an early stage of the
fusaric acid project.
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