QSAR Study and Synthesis of some new 2,
5-disubstituted 1, 3, 4-oxadiazole derivatives as Anti-microbial and
Anti-inflammatory Agents
Nachiket S. Dighe1*, Pankaj Shinde1,
Harshali Anap1, Sanjay Bhawar2
and Deepak S. Musmade3
1Department of Pharmaceutical Chemistry, Pravara
Rural College of Pharmacy, Loni, MS, India-413736.
2Department of Pharmacology, Pravara Rural College of Pharmacy, Loni,
MS, India-413736.
3Department of
Pharmaceutical Chemistry, Sanjivani College of
Pharmaceutical Education and Research, Kopargaon, MS,
India
ABSTRACT:
The synthesis,
structure and biological activity of Oxadiazole
derivatives have long been the focus of research interests in the field of
Medicinal Chemistry. A number of Oxadiazole
derivatives have been reported to possess interesting biological activities
such as Antimicrobial, Anti-inflammatory and Antifungal activities etc. All
synthesized compound were characterized by IR, H¬1-NMR and elemental Analysis.
All the compounds were evaluated for Antibacterial and Anti-inflammatory at the
concentration of 200 µcg/mL
by using cup-plate agar diffusion method. The activity was carried out on
different micro-organisms (E.coli, S. aureus, A.niger, C. albicans) measured in terms of zone of inhibition and
compared the standard drug Ciprofloxacin and Amphotericin
B for antimicrobial activity. All the newly synthesized derivatives were
screened for Anti-inflammatory activity by an in-vitro method of Inhibition of
protein denaturation using Zaltoprofen
as a standard.
KEY WORDS:
Anti-inflammatory, Antimicrobial and Oxadiazole.
INTRODUCTION:
The diverse biological activities of oxadiazole derivatives made an impact to direct the
attention of medicinal chemist as a promising class of a heterocyclic compounds
with profound biological activities. Varied bioactivities exhibited by oxadiazole, efforts have been made from time to time to
generate libraries of these compounds and screened them for potential
biological activities. Also it is well documented that oxadiazole
nucleus is associated with a variety of pharmacological actions. It displays
pronounced anticonvulsant1, antifungal2 and
antimycobacterial3, anticancer4 activities. Extensive
biochemical and pharmacological studies have confirmed that oxadiazole
molecules are effective against various strains of microorganisms. Looking at
the importance of oxadiazole nucleus, it was thought
that it would be worthwhile to design and synthesize some new oxadiazole derivatives and screen them for potential
biological activities.
On the other hand, five-membered
1, 3, 4-oxadiazole heterocycles are also useful
intermediates for the development of molecules of pharmaceutical interest where
several promising antitumor compounds are found to contain the oxadiazole ring system. 1, 3, 4-Oxadiazole heterocycles are good bioisosteres
of amides and esters, which can contribute substantially in increasing
pharmacological activity by participating in hydrogen bonding interactions with
the receptors.
MARERIALS AND METHODS:
Melting
points were determined in open capillary method and are uncorrected. Purity of
the compound was checked on Silica gel TLC plates. IR spectra were recorded on Jasco FT/IR-4100 spectrophotometer using KBr disc method. 1HNMR spectra were recorded on Bruker Advance –II 400, DMSO as internal standard.
Combustion analyses were found to be within the limits of permissible errors.
ANTIBACTERIAL ACTIVITY:
The newly
synthesized compounds were screened for their antibacterial activity against Escherichia
coli (MTCC 443), Bacilus subtilis (ATCC12228) and Staphylococcus aureus
(ATCC25923) bacterial strains by disc diffusion method. In all the determinations tests were
performed in triplicate and the results were taken as a mean of three determinations.
Levofloxacin was used as a standard drug5.
Anti-inflammatory activity:
In-vitro anti-inflammatory activity
Inhibition of protein denaturation
The standard drug and synthesized compounds were dissolved
in minimum quantity of dimethyl formamide
(DMF) and diluted with phosphate buffer (0.2 M, pH 7.4). Final concentration of
DMF in all solution was less than 2.5%. Test solution (1mL) containing
different concentrations of drug was mixed with 1 mL
of 1mM albumin solution in phosphate buffer and incubated at 27° + 1° C in BOD
incubator for 15 min. Denaturation was induced by
keeping the reaction mixture at 60° + 1° C in water bath for 10 min. After
cooling, the turbidity was measured at 660 nm (UV-Visible Spectrophotometer).
Percentage of inhibition of denaturation was
calculated from control where no drug was added. Each experiment was done in
triplicate and average is taken. The Ibuprofen was use as standard drug. The
percentage inhibition of denaturation was calculated
by using following formula.
% of Inhibition = 100 X [1- Vt / Vc]
Where,
Vt = Mean
absorbance of test sample.
Vc = Mean
absorbance of control 6-9.
Step
I: Synthesis of 1,4-dihydropyridine
0.01 mole of an aromatic aldehyde is refluxed for 3-4 hrs in presence of ethyl acetoacetate (0.02 mole)
and ammonia along with ethyl alcohol. The reaction mixture was then poured on
to cold water to offer 1, 4-dihydropyridine derivatives.
Step-II
synthesis of a hydrazide
0.01 mole of 1,4-dihydropyridine was
refluxed in presence of hydrazine and ammonia for 2 hrs and then reaction
mixture was cooled and precipitated with
addition of drops of hydrochloric acid to offer corresponding hydrazides.
Step
III Synthesis of 1, 3, 4-oxadiazoles (A1-A9)
0.01 mole of hydrazide
was refluxed with aromatic acids along with addition of phosphorous oxychloride for 2hrs. and the
resultant reaction mixture was then cooled in an ice bath to offer final
compounds with the addition of Sodium bicarbonate solution.
QSAR
Methodology
All molecules were drawn in Chem draw ultra 8.0 module in Chemoffice
2004 software and imported into TSAR software. Charges were derived using
Charge 2-Derive charges option and optimized by using Cosmic-optimize 3 D
option in the structure menu of the project table. Substituents
were defined and descriptors were calculated for whole molecule as well as for
the Substituents. Several equations were generated
correlating both Log (% Inh)
with physicochemical parameters (descriptors) by multiple linear regression
analysis (MLR) method. Data was standardized by range and leave one out method
was used for cross validation. Models were excluded if correlation was
exceeding 0.9 for more rigorous analysis. Correlation matrix was generated to
find any Intercorrelation between the descriptors. Intercorrelation between the descriptors in the final
equation is less than 0.2.10
Scheme
SPECTRAL DATA
A1- IR (KBr) cm-1
3213.45 (-NH str.), 3010.23 (Ar-CH
str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H
NMR: (δ ppm): 6.8-7.2 (14 H
phenyl), 2.26 (3H –CH3), 9.68 (OH, Aromatic C-OH), 8.75 (1H NH).
A2- IR (KBr) cm-1
3210.45 (-OH str.), 3208.13 (-NH2 str.),
3010.23 (Ar-CH str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H NMR: (δ ppm): 6.8-7.2 (14 H phenyl), 2.26 (3H –CH3),
9.68 (OH, Aromatic C-OH), 8.75 (1H NH).
A3- IR (KBr) cm-1
3310.43 (-CH=CH str.), 3213.45 (-NH str.), 3010.23 (Ar-CH
str.), 1525.32 (-C=N str)
1245.36 (-C-N str). 1H NMR: (δ ppm): 6.8-7.2 (14 H phenyl), 2.26 (3H –CH3),
9.4 (OH, Aromatic C-OH), 8.75
(1H NH).
A4- IR (KBr) cm-1
3213.45 (-NH str.), 3010.23 (Ar-CH
str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H
NMR: (δ ppm): 6.8-7.2 (14 H phenyl), 2.26 (3H –CH3), 9.68 (OH, Aromatic C-OH), 8.75 (1H NH), 6.07 (2H –CH=CH).
A5- IR (KBr) cm-1
3010.23
(Ar-CH str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H NMR: (δ ppm): 6.8-7.2
(14 H phenyl), 2.26 (3H –CH3), 9.68 (OH, Aromatic
C-OH),
8.75 (1H NH), 6.0 (2H
–CH=CH).
A6- IR (KBr) cm-1
3213.45 (-NH str.), 3010.23
(Ar-CH str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H NMR: (δ ppm): 6.8-7.2 (14 H phenyl), 2.26 (3H –CH3),
9.68 (OH, Aromatic C-OH), 8.75 (1H NH), 6.02(2H –CH=CH).
A7- IR (KBr) cm-1
3213.45 (-NH str.), 3010.23 (Ar-CH
str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H NMR: (δ ppm): 6.8-7.2
(14 H phenyl), 2.26 (3H –CH3), 9.68 (OH, Aromatic C-OH), 8.75 (1H NH).
A8- IR (KBr) cm-1
3010.23
(Ar-CH str.), 1525.32 (-C=N str), 1245.36
(-C-N str). 1H NMR: (δ ppm): 6.8-7.2 (14 H phenyl), 2.26 (3H –CH3),
9.68 (OH, Aromatic C-OH), 8.75 (1H NH).
A9- IR (KBr) cm-1
3213.45 (-NH str.), 3010.23 (Ar-CH str.), 1525.32 (-C=N str), 1245.36 (-C-N str). 1H NMR: (δ ppm): 6.8-7.2 (14 H phenyl), 2.26
(3H –CH3), 9.4 (OH, Aromatic C-OH), 8.75 (1H NH),
6.25(2H –CH=CH).
Table no. 1: Analytical
and Physicochemical data of the synthesized compounds (A1-A9)
|
Compound Code |
Mol.
Formula |
Mol. Wt. |
M.P. ° C |
Yield % |
Elemental
analyses Calcd. (found) |
||
|
C |
H |
N |
|||||
|
A1 |
C29H23N5O4 |
505 |
367-375 |
68 |
68.90
(68.45) |
4.59
(4.30) |
13.85 (13.50) |
|
A2 |
C33H27N5O2 |
525 |
345-350 |
65 |
75.41 (75.10) |
5.18 (4.95) |
13.32 (13.03) |
|
A3 |
C29H23N5O4 |
505 |
285-290 |
67 |
68.90 (68.60) |
4.59 (4.30) |
13.85 (13.50) |
|
A4 |
C31H25N5O4 |
531 |
365-370 |
56 |
70.04 (69.80) |
4.74 (4.50) |
13.18 (12.90) |
|
A5 |
C35H29N5O2 |
551 |
295-300 |
58 |
76.20
(76.02) |
5.30
(5.05) |
12.70 (12.40) |
|
A6 |
C31H25N5O4 |
531 |
305-310 |
56 |
70.04 (69.80) |
4.74 (4.50) |
13.18 (13.01) |
|
A7 |
C29H22ClN5O4 |
539 |
225-230 |
72 |
64.51 (64.10) |
4.11(3.95) |
12.97 (12.60) |
|
A8 |
C33H26ClN5O2 |
560 |
325-355 |
58 |
70.77 (70.50) |
4.68 (4.30) |
12.50 (12.20) |
|
A9 |
C29H22ClN5O4 |
539 |
285-290 |
72 |
64.51(64.20) |
4.11(3.80) |
12.97 (12.60) |
Table no.2: Antibacterial activity of synthesized compounds (A1-A9)
|
Compound |
Zone of
inhibition at 200µcg/mL (in mm.) |
||||
|
|
E. coli |
B. Subtilis |
S. aureus |
A. niger |
C. albicans |
|
A1 |
24 |
25 |
26 |
15 |
22 |
|
A2 |
20 |
23 |
25 |
16 |
21 |
|
A3 |
20 |
24 |
25 |
19 |
22 |
|
A4 |
25 |
26 |
23 |
20 |
21 |
|
A5 |
24 |
23 |
26 |
21 |
22 |
|
A6 |
20 |
22 |
24 |
18 |
23 |
|
A7 |
21 |
23 |
22 |
20 |
21 |
|
A8 |
22 |
24 |
25 |
20 |
22 |
|
A9 |
23 |
22 |
20 |
18 |
22 |
|
Ciprofloxacin |
26 |
25 |
26 |
- |
- |
|
Amphotericin B |
- |
- |
- |
22 |
23 |
Table
no. 3: Anti-inflammatory activity
of Synthesized compounds (A1-A9)
|
Treatment |
Mean
increase in paw volume (ml)±SEM |
|||||||||
|
Time in
minute |
||||||||||
|
0 |
% inh. |
30 |
% inh. |
60 |
% inh. |
90 |
% inh. |
120 |
% inh. |
|
|
Carrageenan (Control) |
0.22±0.01 |
|
0.46±0.03 |
|
0.76±0.09 |
|
0.83±0.12 |
|
0.87±0.14 |
|
|
Zaltoprofen |
0.22±0.03 |
0 |
0.29±0.07 |
33.41 |
0.28±0.07 |
59.53 |
0.25±0.06 |
66.23 |
0.24±0.13 |
68.78 |
|
A1 |
0.22±0.01 |
0 |
0.32±0.03 |
27.16 |
0.33±0.01 |
53.12 |
0.31±0.01 |
59.17 |
0.28±0.01 |
64.29 |
|
A2 |
0.22±0.02 |
0 |
0.31±0.03 |
29.25 |
0.30±0.01 |
56.97 |
0.28±0.01 |
62.70 |
0.26±0.02 |
66.53 |
|
A3 |
0.21±0.01 |
2.16 |
0.32±0.01 |
27.16 |
0.36±0.01 |
49.28 |
0.36±0.02 |
53.29 |
0.30±0.02 |
62.04 |
|
A4 |
0.22±0.02 |
0 |
0.31±0.01 |
29.25 |
0.31±0.02 |
55.69 |
0.29±0.02 |
61.52 |
0.27±0.01 |
65.41 |
|
A5 |
0.21±0.01 |
2.16 |
0.30±0.01 |
31.33 |
0.33±0.01 |
54.41 |
0.30±0.01 |
60.35 |
0.28±0.02 |
64.29 |
|
A6 |
0.22±0.02 |
0 |
0.33±0.01 |
25.08 |
0.37±0.02 |
48 |
0.36±0.01 |
53.29 |
0.30±0.03 |
62.04 |
|
A7 |
0.22±0.02 |
2.16 |
0.31±0.01 |
29.25 |
0.33±0.02 |
53.12 |
0.32±0.02 |
58 |
0.28±0.01 |
64.29 |
|
A8 |
0.22±0.02 |
0 |
0.31±0.02 |
29.25 |
0.33±0.03 |
53.12 |
0.29±0.02 |
61.52 |
0.28±0.02 |
64.29 |
|
A9 |
0.21±0.03 |
2.16 |
0.31±0.02 |
29.25 |
0.32±0.01 |
54.41 |
0.30±0.02 |
60.35 |
0.28±0.02 |
64.29 |
Inh. =
Inhibition
Result and discussion:
QSAR
Intercorrelation between the descriptors in the final
equations is less than 0.2. Best Equations correlating Log (% Inh) with descriptors for series
(A1-A12) generated are presented in Table no. 01
Table
no. 4: Equations generated between Log (% Inh.) and
descriptors
|
Sr. No. |
Equation |
N |
S |
R |
r2 |
r2cv |
F |
|
series (A1-A9) |
Y = -0.187 *X3 - 0.237 * X1 - 1.458 * X2 – 13.476 |
09 |
0.345 |
0.789 |
0.712 |
0.478 |
13.87 |
Where
Y = Log (% Inh)
X1: ClogP -
X2 = VAMP HOMO
(Whole Molecule)
X3 = Dipole Moment
Z Component (Whole Molecule)
X4 = Inertia
Moment 2 Length (Whole Molecule)
Significance of the terms –
N= No. of
Molecules
s = standard error
--- less is better
r = correlation
coefficient – higher is better > 0.7,
r2cv =
cross validated r2 - higher is better > 0.5,
F Value = higher
is better
Observed and predicted data and graphs are
presented in Table no. 06
and Graph I for Series.
Table no. 5: Observed and predicted log (% Inh.) value data for (A1-A9)
|
Comp.
No. |
Residual
Value |
Residual
Variance |
||
|
A1 |
1.808143 |
1.721245 |
0.086898 |
0.001923 |
|
A2 |
1.823018 |
1.730762 |
0.092256 |
0.001926 |
|
A3 |
1.792672 |
1.705281 |
0.087391 |
0.001889 |
|
A4 |
1.815644 |
1.728124 |
0.08752 |
0.001862 |
|
A5 |
1.808143 |
1.725689 |
0.082454 |
0.001848 |
|
A6 |
1.792672 |
1.702387 |
0.090285 |
0.001868 |
|
A7 |
1.808143 |
1.728213 |
0.07993 |
0.00179 |
|
A8 |
1.808143 |
1.728945 |
0.079198 |
0.001828 |
|
A9 |
1.808143 |
1.728076 |
0.080067 |
0.00189 |
Fig. no. 1: a) Correlation graph and b) Histogram of
observed and predicted log (% Inh.) data for 09 compounds
DISCUSSION:
Statistical evaluation of the equations is
in accepted range. The correlation coefficient is high with less standard
error. The residual value and residual variance for each series also is less
indicating good predictive power of models. From equation it is observed that two electronic parameters
Dipole Moment Z Component (Whole Molecule) and VAMP HOMO (Whole Molecule) as
well as one steric parameter Inertia Moment 2 Length
(Whole Molecule) contribute (-0.187, –1.458 and –0.237 respectively) negatively
for the activity so electron withdrawing groups may enhance the activity (%1 Inh.).
Beside this the synthesized compounds were subjected to various anti-bacterial,
anti-fungal anti-tubercular and anti-inflammatory activities by using standard
methods.
Anti-bacterial activity:
The compounds A2, A3,
A5, A8, has
excellent Antibacterial activity
against S. aureus, the compound A1,
have shown Antibacterial activity
against B. subtilis, while A4 show Antibacterial activity against E.coli., when compared with standard
ciprofloxacin
Fig. no.1.0: Anti bacterial activity of synthesized
compounds (Scheme I)
Anti-inflammatory activity:
All the compounds were evaluated for Anti-inflammatory activity by Carrageenan Induced Rat hind Paw method. The synthesized
compounds showed better anti-inflammatory activity found comparable with
standard drug zaltoprofen.
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Received on 20.11.2014 Accepted on 19.12.2014
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