Synthesis and QSAR modeling 1-[3-methyl-2-(aryldiazenyl)-2H-aziren-2-yl] ethanones as potential antibacterial agents

Article abstract of DOI:10.1007/s00044-012-0242-4

The present communication deals with the synthesis of a series of 1-[3-methyl-2-(aryldiazenyl)-2H-aziren-2-yl]ethanones. The compounds were synthesized in excellent yields (70-80 %), and the structures were established on the basis of consistent IR, ¹H NMR, and elemental analysis data. The purity has been ascertained by chromatographic resolution using hexane-ethyl acetate (6:4 v/v) as binary eluent. All the compounds have been tested for their antimicrobial activity against a representative panel of bacteria i.e., Bacillus subtilis, Escherichia coli, Pseudomonas diminuta, and Staphylococcus aureus using Chloramphenicol as reference drug. All the synthesized compounds were found to exhibit profound antimicrobial activity.

Full text of DOI:10.1007/s00044-012-0242-4

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:2476–2485
DOI 10.1007/s00044-012-0242-4
ORIGINAL RESEARCH
Synthesis and QSAR modeling 1-[3-methyl-2-(aryldiazenyl)-
2H-aziren-2-yl]ethanones as potential antibacterial agents
•
Vinita Sahu Pratibha Sharma Ashok Kumar
•
Received: 23 February 2012 / Accepted: 14 September 2012 / Published online: 27 September 2012
ꢀ Springer Science+Business Media New York 2012
Abstract The present communication deals with the
synthesis of a series of 1-[3-methyl-2-(aryldiazenyl)-2H-
aziren-2-yl]ethanones. The compounds were synthesized in
excellent yields (70–80 %), and the structures were
reactions and structural characteristics. Azirines with
phosphorus substituents regulate many important biologi-
cal functions (Kafarski and Lejezak, 1991). 2H-Azirine
2-carboxylic acids and esters are of particular interest as
they form various amino acids (Haddach et al., 1993).
Moreover, azirinomycin (Miller et al., 1971), disydazirine
(Molinski and Ireland, 1988), and antazirine (Salomon
et al., 1995) are naturally occurring antibiotics; the first
mentioned was isolated from Streptomyces aureus, and the
latter two were isolated from the marine sponge, Dysidea
fragilis. They are highly reactive and yet are found in a
number of natural products. Azirinomycin isolated from
Streptomyces aureus, and its methyl ester was found to
exhibit a broad antibiotic activity, in vitro, against both
gram-positive and gram-negative bacteria (Stapley et al.,
1971). The reactivity and biological significance of 2H-
azirines is dictated by the ring substituents, and in this
regard, 2H-azirine 2-carboxylate acids are of particular
significance because they are found as naturally occurring
antibiotics. For example, dysidazirine is cytotoxic to L1210
cells and inhibits the growth of gram-negative bacteria and
yeast (Miller et al., 1971; Calvo-Losado et al., 1998).
Several related azacyclopropene analogs, including antaz-
irine, a bromine containing azirine, have recently been
isolated.
1
established on the basis of consistent IR, H NMR, and
elemental analysis data. The purity has been ascertained by
chromatographic resolution using hexane–ethyl acetate
(6:4 v/v) as binary eluent. All the compounds have been
tested for their antimicrobial activity against a representa-
tive panel of bacteria i.e., Bacillus subtilis, Escherichia
coli, Pseudomonas diminuta, and Staphylococcus aureus
using Chloramphenicol as reference drug. All the synthe-
sized compounds were found to exhibit profound antimi-
crobial activity.
Keywords QSAR, Antibacterial ꢀ Molar refractivity ꢀ
1-[3-methyl-2-(aryldiazenyl)-2H-aziren-2-yl]ethanones
Introduction
2H-Azirines are important for their versatile chemical and
biological behavior (Pearson et al., 1995; Palacios et al.,
1998, 2002; Skepper and Molinski, 2008; Skepper et al.,
2008; Keffer et al., 2009). These have attracted consider-
able interest from the synthetic, mechanistic, and theoret-
ical points of view, largely because of their manifold
Three new o-halogenated long-chains 2H-azirines were
¨
isolated from the sponge Dysidea fragilis. Their structures
revealed heterogeneity in both composition of the terminal
1,1-dihalo-vinyl group, and enantiomeric ratios at C-2 of
the azirine-2-carboxylate ester terminus. Azirine-2-car-
boxylate esters were shown to racemize spontaneously.
Very recently Molinski et al. (Skepper et al., 2008) has
reported the synthesis and antifungal activity of (-)-(Z)-
dysidazirine derivatives containing 2H-azirine moiety.
These derivatives exhibited significant antifungal activity
V. Sahu (&)
Alliance College of Engineering and Design, Alliance
University, Bangalore, Karnataka, India
e-mail: drvinitasahu@gmail.com
P. Sharma ꢀ A. Kumar
School of Chemical Sciences, Devi Ahilya University,
Takshashila Campus, Indore, MP, India
123

Med Chem Res (2013) 22:2476–2485
2477
toward a range of Candida and Cryptococcus species.
Similarly, Bewley et al. (Keffer et al., 2009) have also
evaluated the antimicrobial activity of long-chain 2H-azi-
rine-2-carboxylic acid derivatives against a series of bac-
terial strain.
bacteria was prepared from broth culture in log phase
growth. Bacterial plates were prepared in triplicate and
incubated at 37 ꢁC within 16–24 h for bacteria. Also,
Chloramphenicol was tested under similar conditions as a
control drug.
Motivated by the aforementioned information and
keeping in view the biological highlights of 2H-azirine
nucleus and in continuation of our previous work on var-
ious heterocyclic systems (Sharma et al., 2004, 2005,
2009), we have explored the antimicrobial activity of some
of the newly synthesized 2H-azirine derivatives and per-
formed QSAR studies to synthesize some new biologically
significant lead compounds.
Results and discussion
All the compounds screened 6a–6o, exhibited remarkable
in vitro activity against the tested bacterial strains com-
pared to reference drugs within a MIC range of 2–57 lg/
ml. A systematic perusal of the data depicted in Table 1,
reveals that, their antibacterial effect is highly significant
and pronounced for these compounds. Particularly, gram-
positive bacteria are seems to be more sensitive toward the
newly synthesized 1-[3-methyl-2-(aryldiazenyl)-2H-azi-
ren-2-yl]ethanone analogs. In general, antimicrobial
activity of the tested compounds followed the pattern
(Fig. 1):
Chemistry
The synthesis of 1-[3-Methyl-2-(aryldiazenyl)-2H-aziren-
2-yl]ethanones derivatives were accomplished by treating
various pertinent aniline derivatives with ethylacetoacetate
under diazotized conditions. The 3-[aryldiazenyl]pentane-
2,4-dione derivatives afford oxime derivatives 4a–4o in
good yields. These derivatives undergoes tosylation in the
presence of tosyl chloride, and in the presence of 10 %
KOH under phase transfer catalysis conditions internal
nucleophilic displacement occurs to afford three-mem-
B: subtilis [ S: aureus [ P: diminuta [ E: coli
Further, a close inspection of screening result (Table 1)
reveals that the substitution in the aromatic ring attached to
azo functionality of azirine nucleus exerted significant
influence on the investigated biological activity. Com-
pound with bromo substituent was found to be the most
potent among the series members. The in vitro antimicro-
bial profile of 1-[3-methyl-2-(aryldiazenyl)-2H-aziren-2-
yl]ethanone is shown to be increased when groups such as
–Br, –OCH3, –Cl, and –COOH, are present at the aromatic
ring of azirine analogs. Moreover, it is further evident that
meta substituent for –Br, –OCH3 and ortho substituent for
–Cl, –COOH analog exhibit high biological potential as
inferred from the data presented in Tables 1 and 2.
1
bered 2H-azirine derivatives. IR, H NMR, and elemental
analysis data corroborated toward the structure of the
synthesized aziridines. A mechanistic overview of the
synthetic pathway is depicted in Scheme 1.
Biological studies
Antimicrobial screening and QSAR studies
The Quantitative Structure Activity Relationship
(QSAR) evaluation of 1-[3-Methyl-2-(aryldiazenyl)-
2H-aziren-2-yl]ethanone (6a–6o)
Studies on in vitro antimicrobial activity of 1-[3-Methyl-2-
(aryldiazenyl)-2H-aziren-2-yl]ethanones (6a–6o)
The newly synthesized 1-[3-methyl-2-(aryldiazenyl)-2H-
aziren-2-yl]ethanone derivatives 6a–6o were evaluated for
their in vitro antibacterial activity against Escherichia coli
ATCC 13607, Pseudomonas diminuta MTCC 3361,
Staphylococcus aureus ATCC 2943, and Bacillus subtilis
ATCC 6633. Nutrient agar was employed for bacterial
growth. Minimal inhibitory concentrations (MIC) were
determined by means of standard two-fold serial dilution
method using agar media (Murray et al., 1995) and
reported in the Table 1. MIC represents the lowest con-
centration of the compound that inhibits the in vitro growth
of the microorganism. Nutrient agar media were prepared
for bacterial growth. Stock solution was prepared in DMF
and suspension containing approximately 107 CFU/ml of
QSAR referred to statistical analysis of potential relation-
ships between chemical structures and biological activity.
QSAR is essentially a computerized statistical method
which tries to explain the observed variance in the bio-
logical effect of certain classes of compounds as a function
of molecular changes caused by the substituents. These
physicochemical descriptors, which included parameters to
account for hydrophobicity, electronic properties, and ste-
ric effect, are determined empirically or, more recently, by
computational methods. Activities used in QSAR include
chemistry measurements and biological assays. To obtain a
significant correlation between structural features and
biological activities QSAR model were predicted based on
123

2478
Med Chem Res (2013) 22:2476–2485
Scheme 1 Synthetic pathway
for 1-[3-methyl-2-
(aryldiazenyl)-2H-aziren-2-
yl]ethanone derivatives (6a–6o)
O
CH 3
H
2C
HNO 2/HCl
0-5 °C
COCH
3
N 2+Cl -
NH2
Coupling
R
R
2a-o
1a-o
O
N
N
CH 3
R
R
COCH
3
3a-o
H
a
b
c
d
e
f
2-Cl
3-Cl
4-Cl
2-OCH3
NH 2OHHCl
O H
N
N
CH
3
3-OCH3
2-CH3
3-CH3
4-CH3
N
R
g
h
i
COCH
3
4a-o
TsCl
j
Tos
3-Br
4-Br
K
l
N
N
CH
3
3-CO OH
4-CO OH
3-NO2
N
m
n
o
R
COCH
Tos
3
5a-o
4-NO2
N
N
CH 3
N
C-
R
COCH
3
10%KOH /
Phase transfer catalyst
CH
3
N
N
R
CH 3CO
N
6a-o
semiempirical descriptors using MOPAC 6.0 software. All
the studies were performed using the linear free energy
relationship (LFER) model of Hansch and Fujita (1964).
Biological activity data were reported in MIC which rep-
resents the minimal concentration of compounds that
inhibits visible growth. The same are further transformed to
-log MIC (Table 1) on molar basis and used as dependent
variable to get the linear relationship in the QSAR model.
These were correlated with different molecular and phys-
icochemical descriptors (Table 2). The various molecular
descriptors are energy of highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO); log of octanol–water partition coefficient
(log P), molar refractivity (MR), connolly accessible area
(CAA), dipole dipole energy (DDENE), connolly molec-
ular area (CMA), Van der Waals volume (VDW), non-Van
der Waals volume (NDVW), etc. The physicochemical
parameters viz. molar refractivity (MR) and Hammett (r)
constant were taken from the list of Skagerberg et al.
(1989).
All the calculations to figure out molecular descriptors
were done at SCF level using PM3 (Stewart, 1989) Ham-
iltonian incorporated in MOPAC 6.0 (Stewart, 1990)
package. Geometries were optimized at minimum gradient
123

Med Chem Res (2013) 22:2476–2485
2479
Table 1 Antibacterial screening data for 1-[3-methyl-2-(aryldiaze-
nyl)-2H-aziren-2-yl]ethanones (6a–6k)
Table 2 Antibacterial screening data and values of selected
descriptors with correlation (r \ 0.45) for 1-[3-methyl-2-(aryldiaze-
nyl)-2H-aziren-2-yl]ethanones (6a–6k)
MIC in lg/ml
Compound
MRa
VDW
NVDW
DDENE
Compound Gram-positive bacteria
Gram-negative bacteria
6a
6b
6c
6d
6e
6f
6g
6h
6i
0.103
0.603
0.603
0.285
0.285
0.693
0.693
0.565
0.565
0.888
0.888
7.267
7.699
7.869
6.135
4.781
8.046
8.653
9.449
7.863
6.518
9.459
-1.841
-2.411
-1.711
-2.830
-3.746
-2.014
-4.705
-1.758
-2.716
-2.132
-1.762
1.986
2.722
1.912
2.615
3.535
2.058
13.865
1.468
2.699
2.248
2.854
B. subtilis
-log MIC
S. aureus
-log MIC
P. diminuta
-log MIC
E. coli
-log MIC
6a
6b
6c
6d
6e
6f
4.046
4.364
4.337
4.118
4.094
4.399
4.378
4.276
4.228
4.441
4.414
4.024
4.354
4.325
4.096
4.072
4.377
4.356
4.244
4.216
4.429
4.402
4.032
4.317
4.324
4.014
4.119
4.328
4.339
4.298
4.178
4.457
4.433
4.026
4.348
4.315
4.078
4.056
4.366
4.378
4.213
4.298
4.425
4.401
6g
6h
6i
6j
6k
a
MR is scaled by factor 0.1
6j
6k
refractivity and biological activity. The resulting mono and
bi-parametric models are displayed in Eqs. (1)–(8) with
statistical parameters of regression. No outliers have been
detected and these Eqs. (1)–(8) were derived using entire
training data set (n = 11).
0.08
0.06
(B. subtilis)
(S. aureus)
(P. diminuta)
(E. coli )
0.04
The overall quality of the models is indicated by coef-
ficient of determination (r2), standard error of estimate (s),
and Fisher-statistics (F).
0.02
0.00
6a 6b 6c 6d 6e
6f 6g 6h
6i
6j
6k
-0.02
-0.04
-0.06
-0.08
-0.10
-0.12
•
QSAR model for activity against B. subtilis
Mono-parametric Model
BA ¼ ½3:9763ðꢁ0:0722Þꢂ þ MR½0:5436ðꢁ0:1186Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:92; variance ¼ 0:0016;
std ¼ 0:040; F ¼ 111:65
Compounds
ð1Þ
Fig. 1 Plot between residuals vs. compounds for gram-positive and
gram-negative bacteria
•
QSAR model for activity against B. subtilis
Bi-parametric Model
level using Chem 3D (CambridgeSoft corp. 2001) soft-
ware. In order to perform correlation studies for various
descriptors, intercorrelated parameters were discarded
depending upon their individual correlation with biological
activities (Table 3). Using the stepwise selection and
elimination procedures, the resultant parameters were
subjected to MLR analysis with the help of Valstat (Val-
stat, 2004) software.
BA ¼ ½3:9395ðꢁ0:1740Þꢂ þ MR½0:5254ðꢁ0:1482Þꢂ
þ VDW½0:0061ðꢁ 0:0262Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:93; variance ¼ 0:0017;
std ¼ 0:0419; F ¼ 51:70
ð2Þ
ð3Þ
•
QSAR model for activity against S. aureus
The best fit between biological activity and these
explaining parameters were obtained through multiple
regression analysis (MRA) using least square method as
shown in Tables 4 and 5.
Mono-parametric Model
BA ¼ ½3:9513ðꢁ0:0728Þꢂ þ MR½0:5558ðꢁ0:1196Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:93; variance ¼ 0:0016;
std ¼ 0:0406; F ¼ 114:67
Out of a number of parametric evaluations, best corre-
lation (r2 [ 0.90) was found to exist between Molar
123

2480
Med Chem Res (2013) 22:2476–2485
•
QSAR model for activity against S. aureus
Bi-parametric Model
BA ¼ ½3:9256ðꢁ0:1773Þꢂ þ MR½0:5431ðꢁ0:1511Þꢂ
þ VDW½0:0043ðꢁ0:0266Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:93; variance ¼ 0:0018;
std ¼ 0:0427; F ¼ 51:96
ð4Þ
•
QSAR model for activity against P. diminuta
Mono-parametric Model
BA ¼ ½3:9325ðꢁ0:0855Þꢂ þ MR½0:5803ðꢁ0:1405Þꢂ
n ¼ 11; r ¼ 0:9537; r2 ¼ 0:91; variance ¼ 0:0022;
std ¼ 0:0477; F ¼ 90:60
ð5Þ
ð6Þ
ð7Þ
•
QSAR model for activity against P. diminuta
Bi-parametric Model
BA ¼ ½3:9602ðꢁ0:1423Þꢂ þ MR½0:5753ðꢁ0:1508Þꢂ
þ NVDW½0:0099ðꢁ0:0392Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:91; variance ¼ 0:0024;
std ¼ 0:0495; F ¼ 42:24
•
QSAR model for activity against E. coli
Mono-parametric Model
BA ¼ ½3:9450ðꢁ0:0787Þꢂ þ MR½0:5685ðꢁ0:1293Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:92; variance ¼ 0:0019;
std ¼ 0:0439; F ¼ 102:67
•
QSAR model for activity against E. coli
Bi-parametric Model
BA ¼ ½3:9374ðꢁ0:0848Þꢂ þ MR½0:5608ðꢁ0:1366Þꢂ
þ DDENE½0:0034ðꢁ0:0096Þꢂ
n ¼ 11; r ¼ 0:96; r2 ¼ 0:93; variance ¼ 0:0019;
std ¼ 0:0447; F ¼ 50:01
ð8Þ
The F-values obtained in Eqs. (1), (3), (5), (7) are found
statistically significant at 99 % level. Moreover, we have
also tried to test bi- and tri-parametric correlation statisti-
cally, but, we have not found any significant result as can
be illustrated in Eq. (2), (4), (6), (8) which represents a bi-
parametric model for activity.
The predictive powers of these equations were also
checked by leave one out (LOO) cross-validated r2cv values
123

Med Chem Res (2013) 22:2476–2485
2481
Table 4 Observed versus predicted activity of 1-[3-methyl-2-(aryldiazenyl)-2H-aziren-2-yl]ethanones derivative (T1–T4) for test set
Entry
Comp
B. subtilis
S. aureus
P. diminuta
E. coli
Obs
Pred
Res
0.042
Obs
Pred
Res
Obs
Pred
Res
Obs
Pred
Res
T1
T2
T3
T4
6l
4.446
4.376
4.245
4.221
4.404
4.404
4.271
4.271
4.178
4.358
4.421
4.492
4.389
4.389
4.253
4.253
-0.211
-0.031
0.168
4.138
4.243
4.336
4.287
4.389
4.389
4.247
4.247
-0.251
-0.146
0.089
4.223
4.341
4.257
4.253
4.392
4.392
4.253
4.253
-0.169
-0.051
0.004
0
6m
6n
6o
-0.028
-0.026
-0.05
0.239
0.04
Obs observed activity, Pred predicted activity, Res residual
Table 5 Cross-validation parameters
n
PRESS
SSY
PRESS/SSY
SPRESS
SDEP
r2cv
r2bsp
Chance
BS
SA
PD
EC
11
11
11
11
0.025
0.025
0.038
0.031
0.240
0.247
0.277
0.263
0.104
0.101
0.137
0.118
0.048
0.048
0.059
0.053
0.043
0.043
0.053
0.048
0.896
0.899
0.863
0.882
0.926
0.928
0.876
0.917
\0.01
\0.01
\0.01
\0.01
BS, B. subtilis; SA, S. aureus; PD, P. Diminuta; EC, E. coli
([0.86). The observed biological activities are also in
accordance with calculated and predictive activities as
depicted in Fig. 2.
(1)–(8) suggest that molar refractivity is a key factor to
express biological activities, which may be possible due to
steric interaction occurring in polar species. Further, it is
also suggested that the presence of –Br, –Cl, –COOH, and
–OCH3 groups on phenyl moiety further increases the
biological activity. The Connolly accessible surface of the
most potent derivative 6j is depicted in Fig. 3.
To further validate our results, four compounds T1–T4
assigned as test set molecules with –log MIC ranging
between 4.221 and 4.446 which were not included in the
training set. Predicted and actual biological activities of
test set molecules are summarized in Table 4. Predicted
biological activity values agree well with the experimental
ones, which suggest that our model is good for prediction
of the biological activity of related compounds. The his-
tograms of the residuals for the training set are shown in
Fig. 1.
Conclusively, molar refractivity and polarizability
parameters were the main governing physicochemical
factors for the displayed anti-bacterial activities of these
synthesized compounds. Such a QSAR evaluation would
open future perspectives to use these compounds as new
lead compounds in clinical trials.
PRESS (Predicted residual sum of squares) is a cross-
validation parameter, value less than SSY (Sum of the
squares of response value) of which points out that the
model predicts the better chance and can be considered
statistically important. Table 5 suggests that all the pro-
posed models have PRESS ꢃ SSY demonstrating them
statistically significant. Further, to be a reasonable QSAR
model, PRESS/SSY ratio should be smaller than 0.4, and
its value smaller than 0.11 indicates an excellent model.
The data pertaining to Table 5 indicate that for all the four
proposed models this ratio is %0.1 suggesting all of them
to be excellent models. Moreover, the value of cross-vali-
dated correlation coefficient (r2cv) and bootstrapping r2 are
further supporting the predictive power of these explaining
models (Eqs. (1)–(8)).
Experimental
All the chemicals used were of AR grade purity. IR spectra
were recorded on Perkin Elmer model 377 spectropho-
tometer in KBr pellets. IR frequencies were measured in
cm-1. 1H NMR spectra were recorded in CDCl3 solution in
5 mm tubes at 25 ꢁC on a Bruker DRX-300 instrument
(300 MHz FT NMR with low and high temperature facility
-90 ꢁC to ?80 ꢁC) with deuterium signal as the lock and
TMS as internal standard. Chemical shifts were measured
in ppm units. The melting points were determined on an
electric melting point apparatus (Biotech Bombay, India)
in open capillaries and are uncorrected. The purity of all
the synthesized compounds was ascertained by TLC
Since, molar refractivity accounts for the polarizability,
size and polarity of groups as displayed through Eqs.
123

2482
Med Chem Res (2013) 22:2476–2485
4.5
4.4
4.3
4.2
4.1
4.0
resolution on silica gel-G (E Merck). Elemental analyses
were performed on Elemental analyzer (Elemental Vario,
EL III Carlo Erba 1108) at Central Drug Research Institute,
Lucknow, India.
Y=0.285+0.933X
r2=0.90
SD=0.05
Stage I: synthesis of 3-[aryldiazenyl]pentane-2,4-dione
(3a–3o)
A pertinent aniline derivative 1a–1o (0.01 mol) was dis-
solved in 4.0 ml HCl and 4.0 ml distilled water and kept at
freezing temperature in the refrigerator. To this, an aqueous
solution of sodium nitrite (0.69 g, 0.01 mol) in 5 ml of
distilled water was added drop wise with continuous stir-
ring, keeping the temperature in the vicinity of 0–5 ꢁC.
Meanwhile, in another beaker acetyl acetone (0.01 mol),
sodium acetate (7.0 g), and ethyl alcohol (25 ml) were
taken and cooled in an ice bath. Now, the diazotized
solution was added to this solution drop wise with thorough
stirring under temperature-controlled conditions. The
reaction mixture was kept for overnight period, filtered
through suction, washed well with water, and dried in
vacuum. Fine crystals of 3-[aryldiazenyl]pentane-2,4-dione
3a–3o were obtained in good yields.
4.0
4.1
4.2
4.3
4.4
4.5
Observed activity
4.5
4.4
4.3
4.2
4.1
4.0
Y=0.285+0.933X
r2=0.963
SD=0.04
Stage II: synthesis of 3-[aryldiazenyl]pentane-2,4-dione
oxime (4a–4o)
In an Erlenmeyer flask, 0.01 mol of 3a–3o was dissolved in
minimum amount of alcohol. To this, an equivalent quan-
tity of hydroxylamine hydrochloride (0.695 g, 0.01 mol)
dissolved in minimum alcohol was added followed by the
addition of crystalline sodium acetate (0.082 g, 0.01 mol)
dissolved in minimum water. This mixture was refluxed for
4.0
4.1
4.2
4.3
4.4
4.5
Observed activity
Fig. 2 Plots of observed versus calculated and observed versus
predicted activity of compounds 6a–6k screened against S. aureus
Fig. 3 Plot of Connolly
accessible surface of the most
potent derivative 6j
123

Med Chem Res (2013) 22:2476–2485
2483
1-[3-Methyl-2-(3-chrlorophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6c]
overnight. After cooling and removing the excess of sol-
vent using rotary evaporator, this mixture was poured into
ice cold water with continuous stirring. Oxime 4a–4o
crystallizes which is filtered and washed with cold water
and recrystallized from ethyl alcohol.
IR (KBr) (cm-1) 3031 (C–H, sp2), 2954 (C–H, sp3), 1805
(–C=N str. of azirine ring), 1664 (–C=O str.), 1590 (–N=N
str.), 1507, 1440 (C…..C, ring str.), 1329 (C–H bending),
1272, 1162 (C–N aromatic, aliphatic str.), 678 (C–Cl str.),
951, 841, 732, 657 (sub. phenyl); 1H NMR (d ppm) 1.21(s,
3H, –CH3), 2.37 (s,3H, –COCH3), 6.44–6.59 (dd, 2H, Ar–
H), 7.53–7.66 (dd, 2H, Ar–H); mp (ꢁC) 58–60, yield 58 %.
Anal. Calcd for C11H10ClN3O: C, 56.06; H, 4.28; N, 15.04.
Found: C, 55.93; H, 4.19; N, 14.96.
Stage III: synthesis of 1-[3-methyl-2-(aryldiazenyl)-2H-
aziren-2-yl] ethanone (6a–6o)
To a solution of oxime, 4a–4o (0.01 mol) in a mixture of
diethyl ether (150 ml) and chloroform (50 ml) was added
drop wise aqueous KOH (11.2 g of KOH dissolved in
50 ml of water) at 0 ꢁC. After the addition of the base
solution, the mixture was stirred vigorously at this tem-
perature for 30 min, and then a catalytic amount of tetra
butyl ammonium bromide (TBAB, PTC) was added. A
solution of p-toluenesulfonyl chloride (TsCl) in Et2O
(50 ml) was added drop wise at 0 ꢁC. After this addition,
the final mixture was stirred at 0–5 ꢁC for 6 h until the
solid reactants disappeared. The reaction mixture was
transferred into a separatory funnel and extracted with
diethyl ether. The combined organic layer was washed with
water and dried over MgSO4. The residue on removal of
solvents was purified by isocratic columns (hexane–ethyl
acetate, 6:4 v/v) to give the desired products 6a–6o. An
overview of synthetic pathway is delineated in Scheme 1.
1-[3-Methyl-2-(4-chlorophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6d]
IR (KBr) (cm-1) 3029 (C–H, sp2), 2951 (C–H, sp3), 1811
(–C=N str. of azirine ring), 1666 (–C=O str.), 1557 (–N=N
str.), 1520, 1443 (C…..C, ring str.), 1326 (C–H bending),
1248, 1149 (C–N aromatic, aliphatic str.), 754 (C–Cl str.),
936, 816, 738, 627 (sub. phenyl); 1H NMR (d ppm) 1.31(s,
3H, –CH3), 2.36 (s,3H, –COCH3), 6.36–6.58 (dd, 2H, Ar–
H), 7.11–7.31 (dd, 2H, Ar–H); mp (ꢁC) 61–63, yield 59 %.
Anal. Calcd for C11H10ClN3O: C, 56.06; H, 4.28; N, 15.04.
Found: C, 55.91; H, 4.22; N, 15.01.
1-[3-Methyl-2-(2-methoxyphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6e]
1-[3-Methyl-2-(phenyldiazenyl)-2H-aziren-2-yl]ethanone
[6a]
IR (KBr) (cm-1) 3025 (C–H, sp2), 2979 (C–H, sp3), 1807
(–C=N str. of azirine ring), 1678 (–C=O str.), 1571 (–N=N
str.), 1514, 1448 (C…..C, ring str.), 1365 (C–H bending),
1062 (C–N str.), 1053 (C–O str.),889, 858, 669 (sub. phe-
IR (KBr) (cm-1) 3031 (C–H, sp2), 2986 (C–H, sp3), 1811
(–C=N str. of azirine ring), 1692 (–C=O str.), 1553 (–N=N
str.), 1511, 1441 (C…..C, ring str.), 1371 (C–H bending),
1
1
nyl); H NMR (d ppm) 1.14 (s, 3H, –CH3), 2.55 (s,3H,
1067 (C–N str.), 976, 883, 651 (sub. phenyl).; H NMR (d
–COCH3), 3.38 (s, 3H, –OCH3), 6.89–7.31 (m, 4H, Ar–H);
mp (ꢁC) 55–57, yield 69 %. Anal. Calcd for C12H13N3O2:
C, 62.33; H, 5.67; N, 18.17. Found: C, 62.25; H, 5.59; N,
18.11.
ppm) 1.31 (s, 3H, –CH3), 2.51 (s,3H, –COCH3), 7.47–7.89
(m, 5H, Ar–H); mp (ꢁC) 68–70, yield 66 %. Anal. Calcd
for C11H11N3O: C, 65.66; H, 5.51; N, 20.88. Found: C,
65.55; H, 5.48; N, 20.75.
1-[3-Methyl-2-(3-methoxyphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6f]
1-[3-Methyl-2-(2-chlorophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6b]
IR (KBr) (cm-1) 3030 (C–H, sp2), 2969 (C–H, sp3), 1807
(–C=N str. of azirine ring), 1681 (–C=O str.), 1575 (–N=N
str.), 1511, 1442 (C…..C, ring str.), 1370 (C–H bending),
1052 (C–N aromatic, aliphatic str.), 1050 (C–O str.), 886,
IR (KBr) (cm-1) 3034 (C–H, sp2), 2924 (C–H, sp3), 1815
(–C=N str. of azirine ring), 1682 (–C=O str.), 1599 (–N=N
str.), 1516, 1442 (C…..C, ring str.), 1337 (C–H bending),
1292, 1171 (C–N aromatic, aliphatic str.), 761 (C–Cl str.),
956, 853, 749, 686 (sub. phenyl); 1H NMR (d ppm) 1.25 (s,
3H, –CH3), 2.41 (s,3H, –COCH3), 6.51–6.78 (dd, 2H, Ar–
H), 7.72–7.81 (dd, 2H, Ar–H); mp (ꢁC) 51–53, yield 67 %.
Anal. Calcd for C11H10ClN3O: C, 56.06; H, 4.28; N, 15.04.
Found: C, 55.94; H, 4.21; N, 15.01.
1
851, 667 (sub. phenyl); H NMR (d ppm) 1.31 (s, 3H,
–CH3), 2.49 (s,3H, –COCH3), 3.45 (s, 3H, –OCH3),
6.91–7.41 (m, 4H, Ar–H); mp (ꢁC) 71–72, yield 66 %.
Anal. Calcd for C12H13N3O2: C, 62.33; H, 5.67; N, 18.17.
Found: C, 62.24; H, 5.57; N, 18.13.
123

2484
Med Chem Res (2013) 22:2476–2485
1-[3-Methyl-2-(2-methylphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6g]
1-[3-Methyl-2-(4-bromophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6k]
IR (KBr) (cm-1) 3029 (C–H, sp2), 2971 (C–H, sp3), 1805
(–C=N str. of azirine ring), 1698 (–C=O str.) 1572 (–N=N
str.), 1508, 1446 (C…..C, ring str.), 1367 (C–H bending),
1061 (C–N aromatic, aliphatic str.), 1048 (C–O str.), 881,
IR (KBr) (cm-1) 3029 (C–H, sp2), 2981 (C–H, sp3), 1805
(–C=N str. of azirine ring), 1687 (–C=O str.), 1563 (–N=N
str.), 1502, 1444 (C…..C, ring str.), 1362 (C–H bending),
1051 (C–N aromatic, aliphatic str.), 1046 (C–O str.), 892,
851, 659 (sub. phenyl), 551 (C–Br); 1H NMR (d ppm) 1.21
(s, 3H, –CH3), 2.43 (s,3H, –COCH3), 6.71–7.08 (m, 4H,
Ar–H); mp (ꢁC) 53–55, yield 64 %. Anal. Calcd for
C11H10BrN3O: C, 47.16; H, 3.60; N, 15.00. Found: C,
47.13; H, 3.51; N, 14.93.
1
848, 658 (sub. phenyl); H NMR (d ppm) 1.30 (s, 3H,
–CH3), 1.45 (s, 3H, –CH3–Ar), 2.51 (s,3H, –COCH3),
6.52–7.11 (m, 4H, Ar–H); mp (ꢁC) 55–56, yield 64 %.
Anal. Calcd for C12H13N3O: C, 66.96; H, 6.09; N, 19.52.
Found: C, 66.89; H, 6.01; N, 19.47.
1-[3-Methyl-2-(3-methylphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6h]
1-[3-Methyl-2-(3-carboxyphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6l]
IR (KBr) (cm-1) 3035 (C–H, sp2), 2979 (C–H, sp3), 1812
(–C=N str. of azirine ring), 1701 (–C=O str.) 1568 (–N=N
str.), 1501, 1448 (C…..C, ring str.), 1375 (C–H bending),
1069 (C–N aromatic, aliphatic str.), 1051 (C–O str.), 887,
IR (KBr) (cm-1) 3250 (–OH broad band), 3034 (C–H, sp2),
2953 (C–H, sp3), 1809 (–C=N str. of azirine ring), 1731,
1682 (–C=O str.), 1579 (–N=N str.), 1502, 1432 (C…..C,
ring str.), 1326 (C–H bending), 1261, 1141 (C–N aromatic,
1
1
852, 678 (sub. phenyl); H NMR (d ppm) 1.26 (s, 3H,
aliphatic str.), 948, 843, 715, 622 (sub. phenyl); H NMR
–CH3), 1.47 (s, 3H, –CH3–Ar), 2.37 (s,3H, –COCH3),
6.57–7.18 (m, 4H, Ar–H); mp (ꢁC) 59–61, yield 59 %.
Anal. Calcd for C12H13N3O: C, 66.96; H, 6.09; N, 19.52.
Found: C, 66.91; H, 5.98; N, 19.44.
(d ppm) 1.33 (s, 3H, –CH3), 2.38 (s,3H, –COCH3),
7.83–8.02 (m, 4H, Ar–H); mp (ꢁC) 65–66, yield 67 %.
Anal. Calcd for C12H11N3O3: C, 58.77; H, 4.52; N, 17.13.
Found: C, 58.69; H, 4.44; N, 17.08.
1-[3-Methyl-2-(4-methylphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6i]
1-[3-Methyl-2-(4-carboxyphenyldiazenyl)-2H-aziren-2-
yl]ethanone [6m]
IR (KBr) (cm-1) 3028 (C–H, sp2), 2973 (C–H, sp3), 1809
(–C=N str. of azirine ring), 1691 (–C=O str.) 1574 (–N=N
str.), 1501, 1447 (C…..C, ring str.), 1361 (C–H bending),
1069 (C–N aromatic, aliphatic str.), 1050 (C–O str.), 891,
IR (KBr) (cm-1) 3211 (OH broad band.), 3038 (C–H, sp2),
2911 (C–H, sp3), 1813 (–C=N str. of azirine ring), 1672
(–C=O str.) 1622 (–NH, scissoring), 1576 (–N=N str.),
1502, 1433 (C…..C, ring str.), 1321 (C–H bending), 1278,
1168 (C–N aromatic, aliphatic str.), 925, 844, 751, 639
1
847, 678 (sub. phenyl); H NMR (d ppm) 1.24 (s, 3H,
1
–CH3), 1.41 (s, 3H, –CH3–Ar), 2.34 (s,3H, –COCH3),
6.50–7.13 (m, 4H, Ar–H); mp (ꢁC) 70–72, yield 61 %.
Anal. Calcd for C12H13N3O: C, 66.96; H, 6.09; N, 19.52.
Found: C, 66.87; H, 6.02; N, 19.46.
(sub. phenyl); H NMR (d ppm) 1.37 (s, 3H, –CH3), 2.52
(s,3H, –COCH3), 7.78–8.12 (m, 4H, Ar–H),; mp (ꢁC)
73–74, yield 68 %. Anal. Calcd for C12H11N3O3: C, 58.77;
H, 4.52; N, 17.13. Found: C, 58.68; H, 4.49; N, 17.05.
1-[3-Methyl-2-(3-bromophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6j]
1-[3-Methyl-2-(3-nitrophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6n]
IR (KBr) (cm-1) 3025 (C–H, sp2), 2968 (C–H, sp3), 1808
(–C=N str. of azirine ring), 1691 (–C=O str.), 1569 (–N=N
str.), 1512, 1449 (C…..C, ring str.), 1361 (C–H bending),
1054 (C–N aromatic, aliphatic str.), 1035 (C–O str.), 881,
841, 651 (sub. phenyl), 557 (C–Br); 1H NMR (d ppm) 1.29
(s, 3H, –CH3), 2.47 (s,3H, –COCH3), 6.87–7.11 (m, 4H,
Ar–H); mp (ꢁC) 66–68, yield 61 %. Anal. Calcd for
C11H10BrN3O: C, 47.16; H, 3.60; N, 15.00. Found: C,
47.11; H, 3.53; N, 14.91.
IR (KBr) (cm-1) 3023 (C–H, sp2), 2982 (C–H, sp3), 1801
(–C=N str. of azirine ring), 1679 (–C=O str.), 1578 (–N=N
str.), 1549 (–NO2 str. asym), 1503, 1423 (C…..C, ring str.),
1368 (C–H bending), 1334 (–NO2 str. sym), 1053 (C–N
str.), 876, 863, 667 (sub. phenyl); 1H NMR (d ppm) 1.21 (s,
3H, –CH3), 2.47 (s,3H, –COCH3), 7.54–8.10 (m, 4H,
Ar–H); mp (ꢁC) 59–60, yield 63 %. Anal. Calcd for
C11H10N4O3: C, 53.61; H, 4.01; N, 22.69. Found: C, 53.66;
H, 4.09; N, 22.75.
123

Med Chem Res (2013) 22:2476–2485
2485
Murray PR, Baron EJ, Faller MA, Tenover FC, Yolke RH (1995)
Manual of clinical microbiology. ASM Press, 6th Ed.,
Washington
1-[3-Methyl-2-(4-nitrophenyldiazenyl)-2H-aziren-2-
yl]ethanone [6o]
Palacios F, Ochoa de Retana AM, de Marigorta EM, de los Santos JM
(1998) 2H-Azirines as synthetic tools in organic chemistry. Eur J
Org Chem 2401
Palacios F, Ochoa de Retana AM, de Marigorta EM, de los Santo JM
(2002) Preparation, properties and synthetic applications of 2H-
azirines a review. Org Prep Proceed Int 34:219
Pearson WH, Lian BW, Bergmeier SC (1995) In: Katritzky AR, Rees
CW, Scriven EFV (eds) Comprehensive heterocyclic chemistry
II, vol 1A. Elsevier, Oxford, p 1
Salomon CE, Williams DH, Faulkner DJ (1995) New azacyclopro-
pene derivatives from Dysidea fragilis collected in Pohnpei.
J Nat Prod 58:1463
IR (KBr) (cm-1) 3025 (C–H, sp2), 2965 (C–H, sp3), 1805
(–C=N str. of azirine ring), 1671 (–C=O str.), 1555 (–N=N
str.), 1536 (–NO2 str. asym), 1510, 1434 (C…..C, ring str.),
1357 (C–H bending), 1327 (–NO2 str. sym), 1043 (C–N
str.), 856, 824, 639 (sub. phenyl); 1H NMR (d ppm) 1.22 (s,
3H, –CH3), 2.34 (s,3H, –COCH3), 7.47–7.89 (m, 4H,
Ar–H); mp (ꢁC) 75–77, yield 67 %. Anal. Calcd for
C11H10N4O3: C, 53.66; H, 4.09; N, 22.75. Found: C, 53.62;
H, 3.89; N, 22.72.
Sharma P, Sharma S, Rane N (2004) Synthesis and in vitro
antimicrobial activities of 2-hydroxy-6-methyl-7-(arylamino)-
1,7-dihydropurin-8-ones. Bioorg Med Chem 12:3135
Sharma P, Kumar A, Sharma S, Rane N (2005) Studies on synthesis and
evaluation of quantitative structure–activity relationship of 5-[(30-
chloro-40,40-disubstituted-2-oxoazetidinyl)(N-nitro)amino]-6-hy-
droxy-3-alkyl/aryl[1,3]azaphospholo[1,5-a]pyridin-1-yl-phosphorus
dichlorides. Bioorg Med Chem Lett 15:937
Acknowledgments Vinita Sahu is thankful to the Council of Sci-
entific and Industrial Research (CSIR), India for providing a senior
research fellowship (SRF).
References
Sharma P, Kumar A, Upadhyay S, Sahu V, Singh J (2009) Synthesis
and QSAR modeling of 2-acetyl-2-ethoxycarbonyl-1-[4(40-ary-
lazo)-phenyl]-N,N-dimethylaminophenyl aziridines as potential
antibacterial agents. Eur J Med Chem 44:251
Skagerbeg B, Bonelli D, Clementi S, Cruciani G, Ebert C (1989)
Principal properties for aromatic substituents. A multivariate
approach for design in QSAR. Quant Struct Act Relat 8:32
Skepper CK, Molinski TF (2008) Long-chain 2H-azirines with
heterogeneous terminal halogenation from the marine sponge
Dysidea fragilis. J Org Chem 73:2592
Skepper CK, Dalisay DS, Molinski TF (2008) Synthesis and
antifungal activity of (-)-(Z)-dysidazirine. Org Lett 10:5269
Stapley EO, Hendlin D, Jackson M, Miller AJ, Azirinomycin I (1971)
Microbial production and biological characteristics. J Antibiot
24:42
CambridgeSoft corp. (2001) 100 Cambridge Park, MA 02140-2317,
USA
Calvo-Losado S, Quirante JJ, Suarez D, Sordo TL (1998) Rearrange-
ment of azirine intermediates to nitriles: theoretical study of
cleavage of 3,4-dihydro-1aH-azirine[2,3-c]pyrrol-2-one to cya-
noketene–formaldimine complex. J Comput Chem 19:912
Haddach M, Pastor R, Riess JG (1993) Synthese et reactivite de
nouveaux synthons perfluoroalkyles. Comportement atypique
des azirines et aziridines F-alkylees. Tetrahedron 49:4627
Hansch C, Fujita T (1964) p-r-p analysis. A method for the
correlation of biological activity and chemical structure. J Am
Chem Soc 86:1616
Kafarski P, Lejezak B (1991) Biological activity of aminophosphonic
acids. Phosphorus Sulfur Silicon Relat Elem 63:193
Keffer JL, Plaza A, Bewley CA (2009) Motualevic acids A–F,
antimicrobial acids from the Sponge Siliquariaspongia sp. Org
Lett 11:1087
Stewart JJP (1989) Optimization of parameters for semiempirical
methods I. Method. J Comput Chem 10:209
Stewart JJP (1990) Mopac 6.0 QCPE 455. Indiana University,
Bloomington, IN 47405
Valstat software developed at department of pharmacy, SGSITS, 23,
Park road, Indore, India (available on request, 2004)
Miller TW, Tristram EW, Wolf FJ (1971) Azirinomycin. II. Isolation
and chemical characterization as 3-methyl-2(2H) azirinecarb-
oxylic acid. J Antibiot 24:48
Molinski TF, Ireland CM (1988) Dysidazirine, a cytotoxic azacyclo-
propene from the marine sponge Dysidea fragilis. J Org Chem
53:2103
123