Studies on the synthesis of fluorinated Schiff bases; biological activity of resulting (E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4-amine and 4-amino-2-ethoxy-3,5,6-trifluoropyridine

Article abstract of DOI:10.13005/ojc/320408

The present work is aimed mainly to synthesize new fluorinated compounds and their biological significance against tested bacteria and fungus. Thus, the 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4 was synthesized by the reaction of 4-amino 2,3,5,6-tetraflu

Full text of DOI:10.13005/ojc/320408

ISSN: 0970-020 X
CODEN: OJCHEG
2016, Vol. 32, No. (4):
Pg. 1799-1813
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Studies on the Synthesis of Fluorinated Schiff Bases;
Biological Activity of Resulting (E)-N-benzylidene-2,3,5,6-
tetrafluoropyridin-4-amine and 4-amino-2-ethoxy-3,5,6-
trifluoropyridine
IMANE RAACHE, LAKHDAR SEKHRI* and AHMED TABCHOUCHE
Lab. Dynamic Interactions and Reactivity of Systems, Process Engineering Department,
Faculty of Applied Sciences, University Kasdi Merbah, Ouargla 30000, Algeria.
*Corresponding author E-mail : sekhril@yahoo.fr
http://dx.doi.org/10.13005/ojc/320408
(Received: June 28, 2016; Accepted: July 30, 2016)
ABSTRACT
The present work is aimed mainly to synthesize new fluorinated compounds and their
biological significance against tested bacteria and fungus. Thus, the 4-amino-2-ethoxy-3,5,6-
trifluoropyridine 4 was synthesized by the reaction of 4-amino 2,3,5,6-tetrafluoropyridine 1 with
benzaldehyde 2 in EtOH to obtain the pure product as white crystals in 33% yield.The purity of this
compound was estimated by TLC technique and microanalysis while its structure was supported
1
by the usual spectroscopic methods such as UV, infrared, H. NMR, and gas chromatography
coupled by a mass spectrometry (GC/MS). 4-amino 2,3,5,6-tetrafluoropyridine 1 coupled readily to
benzaldehyde 2 when we have usedTHF as solvent resulting a new Schiff base (E)-N-benzylidene-
2,3,5,6-tetrafluoropyridin-4-amine 3 in 48 % yield.Exploration of the anti-bacterial activity against both
gram-positive and gram-negative bacteria showed that these compounds 3 and 4 compounds at a
concentration of 250 µg/ml exhibited a slight activity towards Enterococcus feacium; Streptocoque
B and Staphylococus aureus exhibited a mild/moderate activity for the case of Escherichia coli and
Salmonella typhimurium when compared to Ampicillin. From the results obtained by the antifungal
activity, it is found that this fluorinated Schiff base 3 and fluorinated ethoxypyridine 4 are more active
against Candida albicans at a concentration of 250 µg/ml when compared to Nystatine.
Keywords: Synthesis, Anti-bacterial activities, Antifungal activity, Fluorinated Schiff bases.
INTRODUCTION
applications in different fields of chemistry, such as
supramolecular studies;design of new materials and
as important starting materials in the syntheses of
new molecules with biological functions.1-4
Fluorinated compounds have gained
an increasing interest due to their successful

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Due to its small steric size, fluorine has In general, Schiff bases have a wide
been used as a replacement for hydrogen in many range of potential applications in various biological
biologically active molecules, including amino acids.4 fields,12 also fluorinated Schiff bases derivatives
And the introduction of fluorine into an organic have been widely studied because they have
13, 14
molecule via electrophilic or nucleophilic reactions antifungal, antibacterial,1,
DNA cleavage15
and most commonly, from fluorinated building blocks, and anticancer16 activities which give it attracted
have become a key in the search and discovery remarkable attention.
of new drugs or increasing the activity of those
that already exist; fluorine can cause significant
Thus, in this opportunity we report here the
changes in an organic molecule, mainly by its synthesis and characterization of new fluorinated
electron-withdrawing inductive effect, which in turn compounds from 4-amino-2,3,5,6-tetrafluoropyridine
causes differences in interactions with biological 1 with benzaldehyde 2. The structural analysis
receptors or enzymes, as well as on the metabolic alongside with their preliminary studies of their
fate of the drug.5, 6 It is curious that notwithstanding biological activity on gram-positive and gram-
the abundance of this element, natural fluorinated negative bacteria and on Candida Albicans fungus
compounds are very rare. In fact, most of the of these compounds is also informed.
known fluorinated organic compounds have been
synthesized in the laboratory.7
EXPERIMENTAL
On the other hand, Schiff bases, named Material
after Hugo Schiff,8 are formed when any primary
2,3,4,5,6-Pntafluoropyridine, KOH, and
amine reacts with an aldehyde or a ketone under benzaldehyde are used without further purification
specific conditions. Structurally, a Schiff base (also as well as solvents dichloromethane, ethanol were
known as imine or azomethine) is an interesting purchased from Aldrich.
compound with a functional group that contains a
carbon–nitrogen double bond with the nitrogen atom
The microbiological material consists of
connected to an aryl or alkyl group (R2R3C=N-R1). five bacterial pathogens strains: Escherichia coli
The chain on the nitrogen makes the Schiff bases a ATCC 8739 G (-),Salmonella typhimurium ATCC
stable imine.9, 10
14028 G (-) Staphylococus aureus ATCC 6538
G (+),Enterococcus feacium ATCC 19434 G (+),
Schiff bases appear to be important Streptocoque B G (+) and a fungus specie is Candida
intermediates in a number of enzymatic reaction Albicans ATCC 10231; were obtained from INRAP
involving interaction of the amino group of an (National Institute of Research and physico-chemical
enzyme, usually that of a lysine residue, with a analysis) of Tunisia.
carbonyl group of the substrate.11
F
NH2
N
N
F
F
F
F
F
+
CHO
ETOH
N
F
KOH, rt
F
NH2
N
F
F
F
O
Scheme 1: Synthesis of the fluorinated Schiff base 3 and fluorinated ethoxy ethoxy
aminopyridine 4

RAACHE et al., Orient. J. Chem., Vol. 32(4), 1799-1813 (2016)
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Instrumentation
The FT-IR spectra were performed in the
Perkin Elmer Hitachi R20A spectrometer operating
1
at 60°C MHz for H NMR spectra and 54.6 MHz
range from 4000 to 400 cm-1on a SHIMADZU 2000
with KBr pellets. Melting points were determined in
a Gallenhamp capillary melting points apparatus
and were reported without correction. The 1H NMR
spectra of 4-amino-2-ethoxy-3,5,6-trifluoropyridine
4 and (E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-
4-amine 3 were recorded on a BRUKER Ultrashield
Plus 500 spectrometer with frequency of 500 MHz.
using DMSO-d6 as solvent and internal standard
at room temperature number of scan is (16-1K).
Nuclear magnetic resonance (NMR) spectra of
4-amino-2,3,5,6-tetrafluoropyridine 1 were normally
recorded at 35°C using a Perkin Elmer R10 or R12 or
for 19F NMR spectra. Tetramethylsilane (TMS) was
1
used as a reference for H NMR spectra and for
19F NMR spectra, chemical shifts were measured
relative to trifluoroacetic acid (TFA) as an external
interchange reference unless otherwise stated.
Positive chemical shifts are in ppm downfield of
appropriate reference.
Mass spectra was performed at the INRAP
(National Institute of Research and physico-chemical
analysis) of Tunisia, The gas chromatograph used
is an Agilent 6890, coupled to a mass spectrometer
type Agilent 5975B with a quadrupole ionization
Table 1: Analytical data for compounds 1, 3 and 4
Comp. Molecular
Formula
Melting
Point °C
Yield
(%)
Physical
state
1
34
C5H2N2F4
C7H4N2F4C7H4N2OF3
85-87
80
long white needles
48,5248,52
80-8380-83
white microcrystalline powder
Fig. 1: GC-MS Chromatogram of (E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4-amine 3

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voltage of 70 eV. The column used is a TR-FAME; Procedure
with a length of 60 m and an internal diameter equal Preparation of 4-amino-2,3,5,6-
to 250 µm. The wire thickness being 0.25 ìm.
tetrafluoropyridine 1
4-amino-2,3,5,6-tetrafluoropyridine 1 was
synthesized from 2,3,4,5,6-Pentafluoropyridine
The operating conditions are:
•
•
•
The temperature of the injector (split mode): (25 g, 148 mmol) was dissolved in THF (175 ml)
240°C. in a round-bottomed flask equipped with a reflux
The temperature programming: from 40°C to condenser to give a clear solution. On addition of
260°C at a rate of 2°C/ minutes. aqueous ammonia (0.88, 125 ml) a cloudy solution
The vector gas used is helium with a flow rate was produced and an exothermic reaction ensued.
of 0.8 ml / minutes.
The mixture was then refluxed for 18 hours. The
clear solution produced was poured into water (500
Fig. 2: Mass spectra of (E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4-amine 3
NH2
NH2
NH2
EtOH
F
F
N-
F
F
N-
+ HF + EtO-
OEt
N
OEt
-OEt
Scheme-2
Scheme 2: Mechanism of nucleophilic substitution in amino-compound 1 by Nu (KOEt)

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ml) and the whole mixture was extracted with ether stirred at room temperature for 72h.The reaction was
(3x75ml).The extract was dried (MgSO4), evaporated followed by TLC (petroleum ether /acetone, 95:5%).
using rotary evaporator and the residue freed from After evaporation under vacuum a cream powder was
the last traces of solvent in vacuo, to give a pale obtained corresponding to new compound 3 (0.66 g,
cream solid. Recrystallization of the crude material 48.52%), mp. 80–83°C; IR (KBr, cm-1): 3000–2850 n
from light petroleum gave long white needles of C-H Aromatic, 1660–1614 íC=N, 1100 µPy-F; MS:
4-amino-2,3,5,6-tetrafluoropyridine 1 (20 g, 0.12 mol, m/z 254 ([M]+,30.7%), 91(C7H7]+, 100%).
80%), mp. 85–87°C; IR (KBr, cm-1): 3500-3300 í(NH
str.) 1450-1190 íPy-F; 1H (CDCl3): d 5.05 (2H, br s,
In the FT-IR spectra of the imino-compound
-NH2; 19F (CDCl3): d 15.1 (2F, m, F-2 and F-6), -85.1 3, a stretching vibration bands due to the presence
(2F, F-3 and F-5); MS: m/z 166 ([M]+,100%).
of the C-H aromatic were observed in the range of
3000–2850 cm-1. However, more important resulted
Preparation of 4-amino-2-ethoxy-3,5,6- the observation of strong stretching vibration bands
trifluoropyridine 4 due to the presence of the imino functional group
0.93 g (5 mmol) of 4-amino-2,3,5,6- (C=N) in the range of 1660–1614 cm-1. The strong
tetrafluoropyridine 1 was added to potassium bands around 1100 cm-1 are attributed to the C-F
hydroxide 0.28 g (5 mmol) in 15 ml of ethanol stretching vibrations.
contained in 50 mL three-necked round bottom
flask equipped with a reflux condenser maintained Antimicrobial studies
under nitrogen. The mixture was stirred and heated
The evaluation of the antibacterial and
to reflux for 1h. Then 0,53g (5 mmol) benzaldehyde Antifungal effects was tested by the agar diffusion
was then added and the mixture was stirred at test according to R. Alizadeh et al15
room temperature for 72 hours. The reaction was
followed by TLC (petroleum ether /acetone, 95:5%). Antibacterial activity
After filtration, the filtrate was vaporated using rotary
evaporator and the residue freed from the last traces benzylidene-2,3,5,6-tetrafluoropyridin-4-amine
of solvent in vacuo, to afford a pale white solid and 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4
The synthesized Schiff base (E)-N-
3
which was then recrystallized from ethanol to yield were screened for their in vitro antibacterial activity
a white microcrystalline powder corresponding to against Gram–negative and Gram-positive bacterial
2-ethoxy-3,5,6-trifluoropyridin-4-amine (0.66g, mmol, strains.
48.52%), mp. 80–83°C; The product was identified
by comparison its spectra with those of an authentic
A suspension of the tested microorganisms
sample: IR (KBr,cm-1): 3500-3300 í(NH str.) 1450- was spread on the appropriate solid media plates and
1190 íPy-F, 1250 í(C-O asym str.) and 1040 í(C-O incubated overnight at 37°C. After 1 day, 4-5 loops
sym str.); 1H NMR (500 MHz, DMSO d6): d 1.4 (3H, of pure colonies were transferred to saline solution
t, CH3), 4.2 (2H, q, CH2) and 6.7 (2H, br s, -NH2; MS: in a test tube for each bacterial strain and adjusted
m/z 192 ([M]+, 66.6%), 177 ([M-Me]+, 29.33%),164 to the 0.5 Mc Farland turbidity standards (~108
([MH-Et]+,100%).
cells/mL). Sterile cotton dipped into the bacterial
suspension and the agar plates were streaked three
Preparation of (E)-N-benzylidene-2,3,5,6- times, each time turning the plate at a 60° angle
tetrafluoropyridin-4-amine 3 and finally rubbing the swab through the edge of the
The previous procedure was used except plate. Sterile paper discs (Glass Microfibre filters,
THF was used instead of Ethanol. 0.83g of (5 mmol) Whatman; 6mm in diameter) were placed onto
of 4-amino-2,3,5,6-tetrafluoropyridine 1 was added inoculated plates and impregnated with different
to potassium hydroxide 0.28g (5 mmol) in 15 ml of concentrations of the Schiff base. Ampicillin (10 µg/
ethanol contained in 50 mL three-necked round disc) and solvent (DMSO) were used as positive and
bottom flask equipped with a reflux condenser negative control for all strains.
maintained under nitrogen. The mixture was stirred
and heated to reflux for 1h. Then 0.53 g (5 mmol)
Inoculated plates with discs were placed in
benzaldehyde was then added and the mixture was a 37°C incubator. After 24 hours of incubation, the

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results were recorded by measuring the zones of strong bands around 1100 cm-1 are attributed to the
growth inhibition surrounding the disc.Clear inhibition C-F stretching vibrations.
zones around the discs indicated the presence of
antimicrobial activity. The test was run in duplicate.
Gas chromatography–mass spectrometry GC-
MS analysis
Antifungal activity
Analytical GC-MS (70 eV) (Gas
All cultures were routinely maintained on Chromatography-Mass Spectrometry) of the Schiff
Sabouraud Dextrose Agar (SDA) and incubated at base revealed the presence of one component only
28°C.The inoculums of non–sporing fungi, Candida as shown in (Fig.1).
albicans were performed by growing the culture in
Sabouraud Dextrose broth at 37°C for overnight. Mass spectroscopy
Volume of 0.1 ml of diluted fungal culture suspension
The mass spectrum was characteristic of a
was spread with the help of spreader on SDA plates schiff base with a molecular ion at m/z 254 (66.6%);
uniformly. Sterile 6 mm discs were impregnated the major breakdown pattern is tbenzyl (C6H5CH2 ion
with the test complexes. Wells of 6 mm size were at m/z192 (100%) (Fig. 2).
cut and loaded with different concentrations of the
Schiff base. Antibiotic disc, Nystatin (100 µg/disc) 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4
was used as positive control C. albicans plates were
However, when we used EtOH as solvent,
incubated at 37 °C for 18"48 h and antifungal activity only 4 was produced and no schiff base 3 obtained.
was determined by measuring the diameters of the This coud be interpreted that the presence of EtO-/
inhibition zone (mm).
EtOH in the mixture favorized the nucleophilic
substitution in order to yield 4 instead the nucleophilic
addition to the carbonyl group of aldehyde in order
to give the schiff base 3.
RESULTS AND DISCUSSION
Synthesis part
The strategy we have adopted for
In 2005 we reported that the reaction
the synthesis of fluorinated Schiff base, (E)-N- of 2,3,5,6-tetrafluoro-4-(2,4,6-trimethylphenylazo)
benzylidene-2,3,5,6-tetrafluoropyridin-4-amine pyridine with an equimolar of sodium methoxide
3 and fluorinated ethoxy aminopyridine 4 was to in methanol gave 2,3,5-trifluoro-6-methoxy-4-
condense 4-amino-2,3,5,6-tetrafluoropyridine 1 with (2,4,6-trimethylphenylazo) pyridine.17 This reaction
benzaldehyde 2 by using EtOH as solvent and again is analogous to a reaction we carried out in this
by usingTHF as shown in (Scheme 1). The analytical project which involved treating 4-amino 2,3,5,6-
and physical data are listed in Table 1.
tetrafluoropyridine 1 with equimolar of EtO-/EtOH.
Moreover, the formation of product 4 provides further
(E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4- evidence that nucleophilic substitution in amino-
amine 3
compound 1 by Nu (KOEt) is directed strongly to the
As we might expect, the fluorinated base ortho positions.
schiff 3 was successefully obtained when we used
THF, and its structure was confirmed by the following
spectroscopic data.
Aswemightexpected,theamino-compound
1 requires no more than its own inbuilt capicity for
electron withdrawal and is itself attacked by powerful
nucleophiles, e.g., by –OEt (sodium OEt ethoxide)
FT-IR spectrometry analysis
In the FT-IR spectra of the imino-compound in methanol. The F- leaving group is helped off by
3, a stretching vibration bands due to the presence EtOH, HF being evolved and –OEt regenerated
of the C-H aromatic were observed in the range of (Scheme-2).
3000–2850 cm-1. However, more important results
were the observation of strong stretching vibration
The structure of compound 4 was confirmed
bands due to the presence of the imino functional by the following spectroscopic data:
group (C=N) in the range of 1660–1614 cm-1. The

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Fig. 3: GC-MS Chromatogram of amino-2-ethoxy-3,5,6-trifluoropyridine 4
Fig. 4: Mass spectra of amino-2-ethoxy-3,5,6- trifluoropyridine 4

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Fig.5 : 1H NMR spectrum of 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4
Fig. 6: GC-MS of 4-amino-2,3,5,6-tetrafluoropyridine 1

RAACHE et al., Orient. J. Chem., Vol. 32(4), 1799-1813 (2016)
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FT-IR spectrometry analysis
The IR spectrum showed that the amino
Gas chromatography–mass spectrometry
analysis
group was still present (3500-3300 í(NH str.), 1450-
1190 íPy-F, 1250 í(C-O asym str.) and 1040 í(C-O
sym str.)
Analytical GC-MS (70 eV) (Gas
Chromatography-Mass Spectrometry) of 4-amino-
2-ethoxy-3,5,6-trifluoropyridine 4 revealed the
presence of one component only as shown in
(Fig. 3).
Fig.7: Mass spectra of 4-amino-2,3,5,6-tetrafluoropyridine 1
Fig. 8:The influence of difference concentrations of 4-amino-2-ethoxy-
3,5,6-trifluoropyridine 4 vs the inhibition diameter on the five bacterial pathogens strains

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4.2 (2H, q, CH2) and 6.7 (2H, br s, -NH2) as shown
Mass spectroscopy
The mass spectrum showed a molecular in (Fig.5).
ion at m/z 192 and base peak at m/z 164 as shown
in (Fig. 4).
Starting material 4-amino-
2,3,5,6-tetrafluoropyridine 1
The purity of starting material 1 was
1H NMR spectrometry analysis
1H NMR spectrum comprises three confirmed by spectroscopic data:
absorptions of intensity 3: 2 : 2 at 1.4 (3H, t, CH3),
Analytical GC-MS (70 eV) (Gas
Table 2: Antibacterial activity of 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4
diameters of the inhibition (mm)
Concentration (µg/ml)
Ampicilline
10µg
100
150
200
250
300
Escherichia coli
ATCC 8739 G(-)
12 1.4
14,5 0.7
31,5 0.7
37.75 0.3
26,5 0.7
8,75 0.3 10,25 0.3
11 0.7
12,75 1.0
13,5 0.7
13 0.0
14 1.4
14,5 0.0
14.25 0.3
Salmonella typhimurium
ATCC 14028 G(-)
Staphylococus aureus
ATCC 6538 G(+)
Enterococcus feacium
ATCC 19434 G(+)
Streptocoque B
9 0.0
9.5 0.7
8,5 0.0
10,75 0.3 11,5 0.7
10,5 0.0 11,25 0.3
10,5 0.7
13,5 0.7 14,75 0.3 16,5 0.7
9,25 0.3 10,25 1.7 11,75 2.4 14,5 0.7
16,5 0.7
(Streptococcus agalactiae) G(+)
Table 3: Antifungal activity of 4-amino-2-ethoxy-3,5,6-
trifluoropyridine 4 diameters of the inhibition (mm)
Concentration
(µg/ml)
Nystatine
100µg
100
150
200
250
300
Candida albicans
ATCC 10231
33,5 0.7
9 0.7
10,75 0.3 12,25 1.0 14,25 0.3 14,75 0.3
Fig. 9:The influence of difference concentrations of 4-amino-2-
ethoxy-3,5,6-trifluoropyridine 4 vs the inhibition diameter on Candida albicans

RAACHE et al., Orient. J. Chem., Vol. 32(4), 1799-1813 (2016)
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1
Chromatography-Mass Spectrometry revealed the
presence of one component only as shown in (Fig.
6 ).; the FT-IR showed that a free amine group is
present and this was confirmed by the down-field
shift in the N-H stretching and bending bands around
3500–3300 cm-1.The strong bands around 1100 cm-1
are attributed to the C-F stretching vibrations. H
NMR showed the chemical shift d 6.7 and this due to
the presence of –NH2, Whereas the chemical shifts
d 15.1 and -85.1 of 19F NMR are attributed
respectively to the (F-2 and F-6), (F-3 and F-5);mass
spectrum complied with a normal fragmentation
Table 4: Antibacterial activity of (E)-N-benzylidene-2,3,5,6-
tetrafluoropyridin-4-amine 3 diameters of the inhibition (mm)
Concentration (µg/ml)
100
150
200
250
Ampicilline
Escherichia coli ATCC 8739 G(-)
Salmonella typhimurium ATCC 14028 G(-)
Staphylococus aureus ATCC 6538 G(+)
Enterococcus feacium ATCC 19434 G(+)
Streptocoque B G(+)(Streptococcus
agalactiae)
7 0.0
7 0.3
-
-
9 0.7
8.75 0.3
8.75 0.3
9 0.0
10.25 0.3 11 0.0
12.5 0.7
9.5 0.0
9.5 0.7
10.5 0.0 15,5 0.7
10 0.7
39,5 0.7
37 0.7
10.25 0.3 11.5 0.7
9 0.7
12.75 0.3 16.25 1.0 19.5 0.7 35,5 0.7
Table 5: Antifungal activity of (E)-N-benzylidene-2,3,5,
6-tetrafluoropyridin-4-amine 3 diameters of the inhibition (mm)
Concentration (µg/ml)
100
150
200
250
Nystatin
Candida albicans ATCC 10231
-
9 0.0
10.75 0.3
11.25 0.3
35,75
Fig. 10: showing zone of inhibition against all bacterial and fungus pathogens strains

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Fig.11:The influence of difference concentrations of 3 vs the
inhibition diameter on five bacterial pathogens strains
Fig.12:The influence of difference concentrations of 3 vs
the inhibition diameter on Candida albicans ATCC 10231
mechanism for this compound:m/z:166 ([M]+,100%) Streptocoque B and Salmonella typhimurium at
as shown in (Fig. 7).
concentration 200; 250 and 300 µg/ml, a mild/
moderate activity for the case of Staphylococus
aureus; Streptocoque B and Enterococcus feacium
at concentration 100;150;200 µg/ml when compared
to Ampicilline.
Antibacterial activity part
4-amino-2-ethoxy-3,5,6-trifluoropyridine 4
Antibacterial activity
The antibacterial activity of the 2-ethoxy-
3,5,6-trifluoropyridin-4-amine 4 was evaluated by the Antifungal activity
agar diffusion method at concentrations of 100; 150;
The antifungal activity of the imino
200;250 µg/ml using Dimethyl Sulfoxide (DMSO) as fluorinated compound was evaluated by the agar
solvent and ampicillin as standard drug. Inhibition diffusion method at concentrations of 100; 150; 200;
areas were measured in mm at the end of 24 h of 250;300 µg/ml using Dimethyl Sulfoxide (DMSO) as
incubation at 35°C.The results are reported in Table solvent and ampicillin as standard drug.The results
2 and figure 8.
are reported in Table 3 and figure 9 and 10.
From the screening results, it is clearly
From the screening results it is clearly
observed that the fluorinated compound 4 showed observed that compound 4 showed a slight activity
a significant activity towards Escherichia coli; towards Candida albicans at concentration 200;250

RAACHE et al., Orient. J. Chem., Vol. 32(4), 1799-1813 (2016)
1811
and 300 µg/ml, a mild/moderate activity for the case
of concentration 100; 150 µg/ml when compared to
Nystatine.
case of Staphylococus aureus; Streptocoque B and
Enterococcus feacium at concentration 100;150 and
200 µg/ml when compared to Ampicilline .
(E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4-
amine 3
Antifungal activity
The antifungal activity of the imino
fluorinated compound was evaluated by the agar
diffusion method at concentrations of 100; 150; 200
and 250 µg/ml using dimethyl sulfoxide (DMSO) as
solvent and ampicillin as standard drug.The results
are reported in Table 5 and (fig.12).
Antibacterial activity
The antibacterial activity of the (E)-N-
benzylidene-2,3,5,6-tetrafluoropyridin-4-amine
3 was evaluated by the agar diffusion method at
concentrations of 100; 150; 200; 250 µg/ml using
Dimethyl Sulfoxide (DMSO) as solvent and ampicillin
as standard drug. Inhibition areas were measured
in mm at the end of 24 h of incubation at 35°C. The
results are reported in Table 4 and fig. 11.
From the screening results it is clearly
observed that compound showed a mild/moderate
activity towards Candida albicans at concentration
200 and 250µg/ml when compared to Nystatine.
From the screening results it is clearly
observedthatcompoundshowednoinhibitoryactivity
for the Staphylococus aureus and Enterococcus
feacium at concentration 100 µg/ml and exhibited a
slight activity towards Escherichia coli; Streptocoque
B and Salmonella typhimurium at concentration
200 and 250 µg/ml, a mild/moderate activity for the
The antibacterial and antifungal activity
may be due to the effect of compounds 3 and 4
on the permeability of the cell membrane and the
function of the bacterial cell. This can be attributed
to the presence carbon-fluorine bond that have
inhibitory efficacy on the positive and negative gram
bacteria. On the other hand, Schiff bases appear to
Fig. 12: showing zone of inhibition against all bacterial and fungus pathogens strains

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be important intermediates in a number of enzymatic a mild/moderate activity for the case of Escherichia
reaction involving interaction of the amino group of coli and Salmonella typhimurium when compared to
an enzyme, usually that of a lysine residue, with a Ampicillin.From the results obtained by the antifungal
carbonyl group of the substrate.11 Schiff bases have activity, it is found that this fluorinated Schiff base
also a wide range of potential applications in various 3 and fluorinated ethoxypyridine 4 are more active
biological fields,12 also fluorinated Schiff bases against Candida albicans at a concentration of 250
derivatives have been widely studied because they µg/ml when compared to Nystatine.
have antifungal, antibacterial,1,13,14 DNA cleavage15
and anticancer16 activities which give it attracted
remarkable attention.
The results obtained in the present study
suggest that the synthesized Schiff base (E)-N-
benzylidene-2,3,5,6-tetrafluoropyridin-4-amine
Generally, the two fluorinated compounds 3 and 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4
(E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4-amine can be used in treating deseases caused by the
3 4-amino-2-ethoxy-3,5,6-trifluoropyridine 4 are more tested organisms. Further fluorinated Schiff base
or less effective towards the tested bacteria.
investigations may be carried out to synthesize and
identify the sites responsible for the antimicrobial
activity.
CONCLUSION
The reaction of 4-amino tetrafluoropyridine 1 with
benzaldehyde 2 in EtOH/ or THF gave 4-amino-2-
ethoxy-3,5,6-trifluoropyridine 4 and a Schiff base
ACKNOWLEDGMENT
The authors wish to express their sincere
(E)-N-benzylidene-2,3,5,6-tetrafluoropyridin-4-amine thanks to Algerian Ministry of Higher Education and
3 in 33 and 48 % yields respectively.
Scientific Research (MHESR) for their support and
providing the necessary facilities to carry out this
Exploration of the anti-bacterial activity research. They are thankful to the staff of INRAP
against both gram-positive and gram-negative (National Institute of Research and physico-chemical
bacteria showed that these compounds 3 and 4 analysis) of Tunisia. Sincere thanks are due to the
compounds at a concentration of 250 µg/ml exhibited staff of the analytical and spectroscopic services
a slight activity towards Enterococcus feacium; of the Department of chemistry, University of
Streptocoque B and Staphylococus aureus exhibited Manchester for their assistance and providing the
necessary facilities.
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