An easy procedure for synthesis of 1,3,4-oxadiazines: A potential antimicrobial agents

Article abstract of DOI:10.14233/ajchem.2017.20540

An efficient and accessible procedure for the synthesis of 1,3,4-oxadiazines was developed. Reaction involves the cyclocondensation of phenylhydrazones catalyzed by a mild base triethylamine to produce 1,3,4-oxadiazines in good yields. The synthesized new

Full text of DOI:10.14233/ajchem.2017.20540

Asian Journal of Chemistry; Vol. 29, No. 8 (2017), 1687-1689
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20540
An Easy Procedure for Synthesis of 1,3,4-Oxadiazines: A Potential Antimicrobial Agents
*
PAVITHRA GURUNANJAPPA and AJAY KUMAR KARIYAPPA
Department of Chemistry, Yuvaraja's College, Mysuru-570 005, India
*
Corresponding author: E-mail: ajaykumar@ycm.uni-mysore.ac.in
Received: 25 January 2017; Accepted: 12 April 2017;
Published online: 12 June 2017;
AJC-18421
An efficient and accessible procedure for the synthesis of 1,3,4-oxadiazines was developed. Reaction involves the cyclocondensation of
phenylhydrazones catalyzed by a mild base triethylamine to produce 1,3,4-oxadiazines in good yields. The synthesized new compounds
were characterized by spectral studies and elemental analyses and were screened to explore in vitro antimicrobial activity against bacteria
and fungi species. The compounds displayed good to excellent potency against tested microorganisms, in particular, compound with
chloro substitution showed good antimicrobial potential.
Keywords: Antimicrobial, Hydrazone, Phosgene, Triethylamine.
INTRODUCTION
EXPERIMENTAL
Six membered heterocyclic compounds with three hetero
Melting points were determined by an open capillary tube
method and are uncorrected. Purity of the compounds was
checked on thin layer chromatography (TLC) plates pre-coated
with silica gel using solvent system ethyl acetate: n-hexane
atoms are less scarcity in nature, but they possess good appli-
cations in most of the fields such as medical [1], agriculture as
insecticides [2] and industries as adhesives [3]. Oxadiazines
contains oxygen and two nitrogen atoms and were considered
as interesting heterocycles for their varied biological activities.
A diversity of biological effects is associated with hetero atoms
at 1,2,4 or 1,3,4 positions, since they are oxa-analogues of
nucleosides-6-oxadihydro uracil, among these 1,3,4-oxadiazines
were the most important frameworks for a variety of bioactive
1
(1:4 v/v). The spots were visualized under UV light. The H
13
NMR and C spectra were recorded on a Spect 500 MHz and
125.6 MHz spectrometer respectively, using DMSO as solvent
and TMS as internal standard. The chemical shifts are expressed
in δ ppm. Mass spectra were obtained on Shimadzu LCMS-
2010A spectrometer (ESI). Elemental analyses were obtained
on a Thermo Finnigan Flash EA 1112 CHN analyzer. Purifi-
cation of compounds was done by column chromatography
on silica gel (70:230 mesh Merck).
molecules [4]. First representatives of 4H-1,3,4-oxadiazine-
5
th
,6-diones were synthesized in the first half of the 20 century
by reaction of oxalyl chloride with N-substituted benzohydra-
zides and acetohydrazides [5-7].
Synthesis of 2-chlorophenyl chloroformate (1): To a
cold and stirred solution of phosgene (2.955 g, 0.01 mol) in
dichloromethane (20 mL), a solution of 2-chlorophenol (1 g,
0.01 mol) in dichloromethane (10 mL) was added drop-wise.
Then a solution of sodium hydroxide (0.4 g, 0.01 mol) in water
(72 mL) was added. During addition, the temperature was
maintained at 0-5 °C. Then the temperature of the reaction
mixture was allowed to slowly rise to room temperature and
stirred for 2 h. After completion of reaction the mixture was
extracted in to ether, washed with cold water (3 × 50 mL),
dried over anhydrous sodium sulphate to obtain 2-chlorophenyl
chloroformate in 80 % yield.
Zen and Harada [8] reported that the synthesis of oxadiazine
by the reaction of di-ketones with aliphatic nitro compounds
in the presence of acetyl chloride through one-step synthesis.
Oxadiazine derivatives have been demonstrated to be important
scaffolds with promising therapeutic potential, which present
wide activities such as antimicrobial [9], antitumor [10],
anticonvulsant [11], COX-1 inhibitors [12], anti-HIV [13], etc.
In addition, these are useful intermediates in the synthesis of
prodrugs or β-lactam antibiotics, particularly the synthesis of
carbapenems and penems [14]. In view of broad spectrum of
applications associated with oxadiazines, we herein report the
synthesis of fused 1,3,4-oxadiazines and their antimicrobial
potentialities.
General procedure for synthesis of hydrazones (3a-f):
To a solution of 2-chlorophenyl chloroformate (0.01 mol) in

1
688 Gurunanjappa et al.
Asian J. Chem.
1
3
dichloromethane (15 mL), a solution of phenylhydrazine
hydrochlorides (2a-f) (0.01 mol) in dichloromethane (10 mL)
and pyridine (7-8 drops) were added. Then the mixture was
stirred at room temperature for 2-3 h. The progress of the reaction
was monitored by TLC.After completion, the reaction mixture
was poured in to ice cold water, solids separated were filtered,
washed successively with ice cold hydrochloric acid (5 %)
and water and dried to obtain the hydrazones (3a-f).
(s, 1H, NH), 7.326-8.213 (m, 8H,Ar-H); C NMR: 119.2 (2C),
120.3 (2C), 122.6 (1C), 123.8 (1C), 126.7 (1C), 129.5 (2C),
136.5 (1C), 140.1 (1C), 143.9 (1C), 157.1 (1C); MS m/z: 260
+
(M ), 262 (M+2);Anal. calcd. (%) for C13
H
N
9 2
2
O Cl: C, 59.90;
H, 3.48; N, 10.75; Found (%): C, 59.75; H, 3.69; N, 10.94.
1-(4-Fluorophenyl)-1,2-dihydrobenzo[e][1,3,4]oxadia-
1
zine-3-one (4d): Yield 75 %, m.p. 130-131 °C; H NMR: 6.119
13
(s, 1H, NH), 7.106-8.121 (m, 8H,Ar-H); C NMR: 117.4 (2C),
119.2 (2C), 120.2 (2C), 122.3 (1C), 125.1 (1C), 134.8 (1C),
140.6 (1C), 141.8 (1C), 148.3 (1C), 159.7 (1C); MS m/z: 244
General procedure for the synthesis of 1,3,4-oxadia-
zines (4a-f): To a stirred solution of hydrazones (3a-f, 0.01
mol) in dichloromethane (10 mL), a solution of triethylamine
+
(M ); Anal. calcd. (%) for C13
H N O
9 2 2
F: C, 63.93; H, 3.71; N,
(
2 mL) in dichloromethane (20 mL) was added. The mixture
11.47; Found (%): C, 63.75; H, 3.88; N, 11.63.
1,2-Dihydro-1-(4-methoxyphenyl)benzo[e][1,3,4]-
was refluxed for 4-5 h at 95-100 °C. The progress of the reaction
was monitored by TLC, after completion, the reaction mass
was diluted with 20 mL dichloromethane and washed with
water; the organic layer was dried over anhydrous sodium
sulphate. The solvent was evaporated in vacuo to obtain the
crude products and were purified column chromatography
using silica gel (60-120 mesh) and ethyl acetate:hexane (1:4
v/v) as eluent (Scheme-I).
1
oxadiazine-3-one (4e): Yield 76 %, m.p. 145-146 °C; H
3
NMR: 2.725 (s, 3H, OCH ), 6.115 (s, 1H, NH), 7.112-8.065
13
(m, 8H, Ar-H); C NMR: 55.6 (1C), 116.9 (2C), 119.8 (2C),
120.6 (2C), 121.8 (1C), 124.6 (1C), 135.9 (1C), 139.7 (1C),
+
141.6 (1C), 150.1 (1C), 159.8 (1C); MS m/z: 256 (M ); Anal.
12 2 3
calcd. (%) for C14H N O : C, 65.62; H, 4.72; N, 10.93; Found
(%): C, 65.88; H, 4.56; N, 10.71.
1,2-Dihydro-1-(2,4-dimethylphenyl)benzo[e][1,3,4]-
1
oxadiazine-3-one (4f): Yield 78 %, m.p. 158-159 °C; H NMR:
1
one (4a): Yield 82 %, m.p. 141-142 °C; H NMR: 6.263 (s,
,2-Dihydro-1-phenylylbenzo[e][1,3,4]oxadiazine-3-
1
1
H, NH), 7.218-8.152 (m, 9H, Ar-H); C NMR: 118.2 (2C),
3
1
1
1
3
1.983 (s, 6H, CH ), 6.128 (s, 1H, NH), 7.115-8.123 (m, 7H,
13
18.7 (1C), 119.3 (2C), 119.5 (1C), 121.8 (1C), 127.3 (2C),
35.5 (1C), 140.4 (1C), 145.9 (1C), 156.6 (1C); MS m/z: 226
Ar-H); C NMR: 15.6 (1C), 23.8 (1C), 118.6 (2C), 119.2 (1C),
121.8 (1C), 124.8 (1C), 126.2 (1C), 127.1 (1C), 127.9 (1C),
+
(
M ); Anal. calcd. (%) for C13
H
10
2 2
N O : C, 69.02; H, 4.46; N,
128.5 (1C), 135.9 (1C), 140.3 (1C), 141.8 (1C), 160.5 (1C);
+
MS m/z: 254 (M ); Anal. calcd. (%) for C15
1
2.38; Found (%): C, 69.23; H, 4.28; N, 12.57.
14 2 2
H N O : C, 70.85;
1
4b): Yield 80 %, m.p. 126-127 °C; H NMR: 1.274 (s, 3H,
,2-Dihydro-1-p-tolylbenzo[e][1,3,4]oxadiazine-3-one
1
H, 5.55; N, 11.02; Found (%): C, 71.02; H, 5.37; N, 11.24.
(
13
RESULTS AND DISCUSSION
3
CH ), 6.286 (s, 1H, NH), 7.243-8.189 (m, 8H,Ar-H); C NMR:
2
1
1
2.4 (1C), 118.8 (2C), 119.4 (2C), 119.8 (1C), 121.8 (1C),
27.8 (1C), 130.1 (2C), 135.8 (1C), 140.3 (1C), 144.5 (1C),
The schematic diagram for the synthesis of target 1,3,4-
oxadiazines is outlined in Fig. 1. The synthetic strategy involves
the preparation of hydrazones (3a-f) by the reaction of substi-
tuted phenylhydrazine hydrochloride (2a-f) with 2-chloro-
phenyl chloroformate (1). Then, the reaction of hydrazones
(3a-f) in the presence of triethylamine to leading to the forma-
tion of 1,3,4-oxadiazines (4a-f).
+
56.8 (1C); MS m/z: 240 (M );Anal. calcd. (%) for C14
12 2 2
H N O :
C, 69.99; H, 5.03; N, 11.66; Found (%): C, 69.85; H, 5.17; N,
1.81.
-(4-Chlorophenyl)-1,2-dihydrobenzo[e][1,3,4]oxadia-
1
1
1
zine-3-one (4c): Yield 75 %, m.p. 158-159 °C; H NMR: 6.112
O
O
O
O
OH
CH Cl /NaOH
2
2a-f
2
NH
COCl2
R
1
Cl
o
CH Cl /
2
Cl
HN
1
R
0
-5 C, 2 h
2
Cl
Cl
Pyridine
0oC, 2 h
1
3a-f
2
R
Et N/CH Cl
2
3
2
.
NHNH HCl
reflux, 4-5 h
2
1
2
2
.a) R=H, R =H, R =H;
1
R
O
O
2
b) R=H, R =CH , R =H;
3
1
c) R=Cl, R =H, R =Cl;
2
N
1
R
1
2
N
H
R
d) R=H, R =H, R =F;
1
2
R
2
e) R=H, R =H, R =OCH ;
3
2a-f
1
2
f) R=CH , R =H, R =CH .
3
3
1
R
4a-f
2
R
Fig. 1. Schematic diagram for the synthesis of 1,3,4-oxadiazines (4a-f)

Vol. 29, No. 8 (2017)
An Easy Procedure for Synthesis of 1,3,4-Oxadiazines 1689
TABLE-1
MIC’S OF THE TEST COMPOUNDS 4a-f AGAINST BACTERIAL AND FUNGAL SPECIES
Minimum inhibitory concentration (MIC’s) (µg/mL)*
Compound
S. aureus
E. coli
25
P. aeruginosa
A. niger
25
A. flavus
C. albicans
4
4
a
25
25
50
25
12.5
50
25
–
50
25
25
25
25
25
25
75
–
50
25
50
25
25
–
b
12.5
25
25
4
c
25
25
4
d
12.5
12.5
75
12.5
12.5
100
12.5
–
12.5
12.5
75
4
e
4
f
Ciprofloxacin
Nystatin
12.5
–
–
–
12.5
25
25
*The results are expressed as mean of three determinations (n = 3).
The synthesized new compounds were characterized by
spectral analysis and evaluated for their in vitro antimicrobial
and fluoro substituents demonstrated potent antimicrobial
activities. The compound, particularly 4e exhibited greater
activity in comparison to the standard drug. The SAR study of
the synthesized compounds remains the topic of interest.
1
activities. In H NMR spectra, compounds 4a-f showed the
signals in the region δ 6.236-6.314 ppm, which were assigned
to NH protons and signals in the region δ 7.438-8.528 ppm
13
ACKNOWLEDGEMENTS
corresponds to aromatic protons. In C NMR spectra, the C-
O and C-N carbons of 4a-f appeared in the region δ 136.62-
One of the authors, Pavithra G is grateful to the UGC for
awarding NON-NET Fellowship (Order No. DV9/192/NON-
NETFS/2013-14, Dated 11-11-2013). Dr. B.N. Mylarappa,
Rangos Research Center, University of Pittsburgh, PA 15201,
USA, for help in biological activity studies.
1
38.45 and δ 141.42-143.63 ppm. While, C=O carbons of
appeared in the region δ 178.64-180.92. Further, all compounds
signals due to aromatic, substituent protons and carbons in
the expected region. The synthesized new molecules showed
M+1 ion peak as a base peak in their mass spectra. Further,
the analytical data obtained for the compounds 4a-f were in
good agreement with theoretically calculated data. All these
spectral and analytical results confirmed the formation of the
products.
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3
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in the synthesized compounds enhanced the activity to the
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activity against all organisms tested. Nitro substitution present
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1
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The simple easy accessible procedure for the synthesis of
,3,4-oxadiazines and their in vitro antimicrobial activity results
1
revealed the significance of the study.All the newly synthesized
compounds exhibited moderate to good antimicrobial activity
against the tested microorganisms, compounds having chloro
1
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