Studies on nitrophenylfuran derivatives part Xii. synthesis, characterization, antibacterial and antiviral activities of some nitrophenylfurfurylidene-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines.

Article abstract of DOI:10.1016/S0014-827X(01)01124-7

Synthesis of four 1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-2-propen-1-ones starting from substituted acetophenones and p-nitrophenylfurfuraldehyde is described. These propenones were then converted into corresponding dibromo derivatives which on dehydrobromin

Full text of DOI:10.1016/S0014-827X(01)01124-7

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Il Farmaco 56 (2001) 919–927
Studies on nitrophenylfuran derivatives
Part XII. Synthesis, characterization, antibacterial and antiviral
activities of some nitrophenylfurfurylidene-1,2,4-
triazolo[3,4-b]-1,3,4-thiadiazinesꢀ
B. Shivarama Holla *, P.M. Akberali, M.K. Shivananda
Department of Post Graduate Studies and Research in Chemistry, Mangalore Uni6ersity, Mangalagangotri 574 199, India
Received 15 May 2000; accepted 10 May 2001
Abstract
Synthesis of four 1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-2-propen-1-ones starting from substituted acetophenones and p-nitro-
phenylfurfuraldehyde is described. These propenones were then converted into corresponding dibromo derivatives which on
dehydrobromination afforded a-bromopropenones rather than acetylenic ketones. Condensation of these dibromopropanones
with 4-amino-5-mercapto-1,2,4-triazoles yielded a new class of nitrophenylfurfurylidene-1,2,4-triazolothiadiazines. The structures
of nitrophenylfurfurylidene-1,2,4-triazolothiadiazines were established on the basis of analytical, IR, NMR and mass spectral
studies. The formation of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines rather than 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines in the above
condensation was unambiguously confirmed by X-ray crystallographic analysis of one of them. A possible mechanism is proposed
to account for the formation of nitrophenylfurfurylidene-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines. Some of the newly synthesized
triazolothiadiazines were screened for their antibacterial and antiviral properties. © 2001 Elsevier Science S.A. All rights reserved.
Keywords: Nitrofurans; Nitrophenylfurans; Triazolothiadiazines; Antibacterial activity
1. Introduction
tendency to develop resistance towards bacterial strains
[3].
As a part of structural modification of nitrofurans,
with a view to reduce the toxicity of nitrofuran deriva-
tives, a nitrophenylfuran moiety is introduced in place
of nitrofuran in the compounds to be synthesized.
Several nitrophenylfuran derivatives have been synthe-
sized and screened for their antibacterial [4], tuberculo-
static [5] and fungistatic [6] properties in recent years. A
few arylfuran derivatives including the well known drug
Dantrolene possess muscle relaxant and CNS depres-
sant activities [7–15].
Triazoles fused with six-membered ring systems are
found to possess diverse applications in the field of
medicine, agriculture and industry. The commonly
known systems are triazoles fused with pyridines, pyri-
dazines, pyrimidines, pyrazines and triazines. The liter-
ature survey reveals that there are not many examples
of triazoles fused with thiadiazines. Moreover, a large
number of triazolothiadiazines has been shown to ex-
hibit antidepressant [16], central nervous depressant
Antibacterial nitrofurans are a class of synthetic
compounds characterized by the presence of a 5-nitro-
2-furanyl group. The antimicrobial activity of nitro-
furans was reported by Stillman et al. [1] and Dann et
al. [2] independently. These initial reports, thereafter
stimulated research on the synthesis of a large number
of compounds belonging to this class and led to the
exploration of nitrofurans as potential chemotherapeu-
tic agents. A number of nitrofurans have attained com-
mercial utility as antibacterial agents in human and
veterinary medicine because of their broad spectrum
antibacterial activity, relatively mild toxicity and low
ꢀ Presented at the 16th Conference of Indian Council of Chemists
held at Mangalore University, Mangalagangotri during December
29–31, 1998
* Corresponding author.
E-mail address: hollabs@yahoo.com (B.S. Holla).
0014-827X/01/$ - see front matter © 2001 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(01)01124-7

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B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
[17], bactericidal [18], fungicidal [18], and diuretic activ-
ities [19] and as photographic couplers [20].
An alternate regioisomeric structure for the conden-
sation product in the above reaction is 6-aryl-8-(5-aryl-
Further, nitrofuran containing triazolothiadiazines
have been prepared [21] and many such derivatives are
found to possess antibacterial activities. Interestingly,
one such derivative was found to possess anticancer
activity too. So, in order to study the structure–activity
relationship, it was contemplated to synthesize tri-
azolothiadiazines carrying arylfuran substituents.
Prompted by the varied biological properties of aryl-
furan derivatives and as a part of our general search for
chemotherapeutically active N-bridged heterocycles
[22–26], a project aimed at the synthesis of 1-aryl-3-[5-
2-furyl)-1.2,4-triazolo[3,4-b]-1,3,4-thiadiazepine
(9).
Hence, it was considered worthwhile to investigate the
reaction mechanism of the formation of the compound.
In one such approach, it was decided to isolate the
intermediate formed during the reaction. Thus, dehy-
drobromination
of
2,3-dibromo-1-aryl-3-(5-aryl-2-
furyl)-2 propanones (4) employing triethylamine in dry
benzene was investigated. One such reaction afforded
chemoselectively
a-bromo-1-aryl-3-(5-aryl-2-furyl)-2-
propenone (5) and not the acetylenic ketone (6), thus
suggesting the loss of only one molecule of HBr during
dehydrobromination. This a-bromo-1-aryl-3-(5-aryl-2-
furyl)-2-propenone (5) was then condensed with 3-sub-
stituted-4-amino-5-mercapto-1,2,4-triazoles (7) in the
presence of ethanolic potassium hydroxide to give re-
gioselectively the 3-substituted-6-aryl-7-(5-aryl-2-fur-
furylidene)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines (8).
The IR spectrum of the condensation product (8a)
showed an absorption band at 2926 cm−1, characteris-
tic of the exocyclic vinyl CꢀH stretching frequency The
absorption around 1599 cm−1 was assigned to the CꢁN
and CꢁC groupings. The asymmetric and symmetric
stretching frequencies of the nitro group were found at
1509 and 1329 cm−1, respectively. IR spectral data of a
few other condensation products were also in confor-
mity with the assigned structure (8) (Tables 1, 2 and 4).
(p-nitrophenyl)-2-furyl]-2-propen-1-ones
and
their
derivatives was undertaken. It was also contemplated to
employ them in the synthesis of chemotherapeutically
important N-bridged heterocycles. The results of such
studies are described in this paper.
2. Chemistry
For the present work, four 1-aryl-3-[5-(p-nitro-
phenyl)-2-furyl]-2-propen-1-ones (3) were prepared by
condensing 5-(p-nitrophenyl)-2-furfuraldehyde with
acetophenone, p-chloroacetophenone, p-methyl ace-
tophenone and p-methoxyacetophenone in the presence
of aqueous sodium hydroxide. These propenones (3)
were then brominated with bromine in glacial acetic
acid to afford 2,3-dibromo-1-aryl-3-[5-(p-nitrophenyl)-
2-furyl]-propan-1-ones (4). Dibromopropanones were
then dehydrobrominated in the presence of triethy-
lamine and were then condensed in situ with 3-substi-
tuted-4-amino-5-mercapto-1,2,4-triazoles (7) in ethanol
medium. The condensation products are now identified
as 6-aryl-7-[5-(p-nitrophenyl)-2-furfurylidene]-1,2,4-tria-
zolo[3,4-b]-1,3,4-thiadiazines (8) based on the analytical
and spectral data. The structure of one of the condensa-
tion products (8b) is unambiguously proved by X-ray
diffraction studies [27].
1
The examination of the H NMR spectra of some of
the condensation products further confirmed the forma-
1
tion of triazolothiadiazines (8). The 270 MHz H NMR
spectrum of triazolothiadiazine (8b) showed a triplet at
l 1.3 (J=7.5 Hz) and a quartet at l 2.8 (J=7.5 Hz)
confirmed the presence of ethyl group in (8b). A sharp
singlet at l 6.9 seen in this 1H NMR spectrum is
assigned to the exocyclic vinyl proton. Two dou-
blets(J=3.8 Hz) appearing at l 7.2 and 7.5 are charac-
teristic of the b-protons of the furan ring. The aromatic
protons of the p-nitrophenyl ring resonated as two
doublets at l 8.1 and 8.4; while the signals of the
Table 1
Characterization data of 1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-2-propen-1-ones (3)
Comp.
R
M.p. (°C)
Yield (%)
Molecular formula
Anal. (%), Found (calc.)
C
H
N
3a
3b
3c
3d
H
Cl
CH3
OCH3
170 a
212
168
93
92
95
89
C19H13NO4
C19H12ClNO4
C20H15NO4
C20H15NO5
71.75 (71.47)
64.81 (64.49)
72.34 (72.07)
68.93 (68.76)
4.39 (4.07)
3.65 (3.39)
4.81 (4.50)
4.17 (4.29)
4.64 (4.38)
4.28 (3.96)
4.38 (4.20)
4.15 (4.01)
180
UV (DMF): 3c, umax 270 (m=950) and 400 nm (m=4000). IR (w, cm−1): 3a, 1649 (CꢁO str.), 1585 (CꢁC str.), 1572 (NO2 asym.), 1338 (NO2 sym.);
3c, 1668 (CꢁO), 1599 (CꢁC); 3d, 1656 (CꢁO), 1558 and 1331 (NO2 asym. and sym.). 1H NMR (90 MHz): 3c, l 2.3 (s, 3H, tolyl-CH3), 6.8 (d, 1H,
furan 3H, J=3.3 Hz), 7.1 (d, 1H, furan 4H, J=3.3 Hz), 7.2–7.3 (d, 1H, ethylenic, J=15 Hz), 7.4–7.9 (m, 5H, ethylenic and aromatic protons),
7.9–8.0 (d, 2H, p-nitrophenyl, J=8 Hz), 8.1–8.2 (d, 1H, p-nitrophenyl, J=8 Hz). Mass, m/z (% abundance): 3a, 319 (M+, 100), 273 (MꢀNO2,
10), 242 (MꢀPh, 18), 197 (Mꢀnitrophenyl, 20) and 105 (PhꢀCO+, 28); 3d, m/z 349 (M+, 100).
a Although an earlier report [30] gave the m.p. of this compound as 192 °C, we did not observe an m.p. higher than 170 °C.

B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
921
Table 2
Characterization data of 2,3-dibromo-1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-propan-1-ones (4)
Comp.
R
M.p. (°C)
Yield (%)
Mol. formula
Colour and crystal form
Anal. (%), Found (calc.)
C
H
N
4a
4b
4c
4d
H
Cl
265
238
211–213
83
84
97
87
C
19H13Br2NO4
yellow microneedles
48.12 (47.59)
44.93 (44.40)
3.34 (2.71)
3.12 (2.33)
3.05 (3.11)
2.95 (2.88)
3.28 (2.92)
2.98 (2.72)
2.85 (2.75)
2.76 (2.87)
C19H12Br2ClNO4 yellow microneedles
C20H15Br2NO4
C20H15Br2NO5
CH3
OCH3 120–121
brown shining microneedles 48.87 (48.41)
yellow needles 47.33 (47.16)
Mass: 4c, m/z, 491,1493/495 (M+, 2.5%/1.3%/1%), 303 (Mꢀp-nitrophenylfuryl cation, 1.3%), 411 (M+ꢀHBr, 34.2%), 332 (411-Br, 59.4%), 119
(p-methyl benzoyl cation, 100%); 4d, m/z 507/509/511 (M+, 25.2%/13.8%/3.4%), 427 (MꢀHBr, 18.5%), 348 (427-Br, 76.3%), 361/363 (MꢀNO2,
2.5%/6.1%), 319 (Mꢀp-nitrophenylfuryl cation, 2.6%).
Table 3
Characterization data of a-bromo-1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-2-propen-1-ones (5)
Comp.
R
M.p. (°C)
Yield (%)
Mol. formula
Anal. (%), Found (calc.)
C
H
N
5a
5b
5c
H
CH3
OCH3
172
120–122
168–170
74
63
44
C
19H12BrNO4
57.84 (57.28)
58.31 (58.39)
56.24 (56.20)
3.66 (3.01)
3.43 (3.40)
3.29 (3.27)
3.87 (3.51)
3.41 (3.40)
3.25 (3.27)
C20H14BrNO4
C20H14BrNO5
IR (cm−1): 5a, 1650 (CꢁC str.), 1602 (CꢁC str.). 1H NMR (400 MHz, DMSO-d6): 5b, l 2.08 (s, 3H, p-tolyl-CH3), 7.27 (s, 1H, olefinic), 7.57–7.58
(d, 1H, furan 3H, J=3.4 Hz), 7.65–766 (d, 1H, furan 4H, J=3.91 Hz), 7.45–7.47 (d, 2H, p-tolyl, J=7.81 Hz), 8.03–8.05 (d, 2H, p-tolyl, J=7.81
Hz), 8.1–8.12 (d, 2H, p-nitrophenyl, J=8.79 Hz), 8.32–8.34 (d, 2H, p-nitrophenyl, J=8. 79 Hz). Mass: 5a, m/z, 397/399 (M+/M+2, 13%/17%),
313 (MꢀBr, 40%), 105 (PhꢀCꢁO, 100%), 77 (Ph, 43%); 5b, m/z 411/413 (M+/M+2, 5, 4%/4.4%), 332 (MꢀBr, 100%), 119 (p-methylbenzoyl cation,
65%), 91 (p-methylphenyl cation, 57%).
remaining aromatic protons appeared as a multiplet cen-
tered at l 7. 6. The NMR spectral data of other tria-
zolothiadiazines are given in Table 4. Due to poor
solubility of the condensation products in the solvents
commonly used in NMR spectral measurements, the
spectra of all the products could not be measured.
furylidene]-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine (8e).
The samples of 8e obtained under two different experi-
mental conditions were found to be identical.
The structures of a-bromopropenones (5a,c) were
confirmed by recording their mass spectra. The molecular
ion of (5c) appeared at m/z 411/413 corresponding to the
molecular formula C20H14BrNO4 consistent with the
structure assigned to it. The M+2 peak was also ob-
served at m/z 413 typical of bromine containing com-
pounds. The peak at m/z 332 was attributed to an ion
obtained by the loss of a bromine radical from the molec-
ular ion (M-79). Similarly, the mass spectrum of a-bro-
mopropenone (5a) showed a molecular ion at m/z 397
corresponding to the molecular formula C19H12-
BrNO4 consistent with the structure assigned to it. The
M+2 peak was observed at m/z 399 typical of bromine
containing compounds. This gave a peak at m/z 318 by
losing a bromine radical from the molecular ion (M-79).
The characterization data of these a-bromopropenones
are given in Table 3. The structures of a-bromo-
propenones were also confirmed by recording their IR
spectra. The strong absorption band appeared at 1650
cm−1 in the IR spectrum of 5 suggested the presence of
a CꢁO group. The absorption at 1602 cm−1 could be as-
signed to the CꢁC bond. The absence of an absorption
band around 2200 cm−1 ruled out the possibility
of acetylenic ketone formation during dehydro-
bromination.
The mass spectrum of the compound 8b showed the ex-
pected molecular ion peak at m/z 443, consistent with the
molecular formula C23H17N5O3S. The base peak was ob-
served at m/z 29 corresponding to C2H+5 ion. The peaks
at m/z 413 and 397 are indicative of the loss of NO and
NO2 radicals from the molecular ion; which is typical of
nitrophenyl derivatives. The mass spectrum of com-
pound 8g showed a very weak molecular ion peak at m/z
477, corresponding to the molecular formula, C23H16-
ClN5O3S. However, a peak at m/z 431 was observed
which can be assigned to a fragment ion (M-46) obtained
by the loss of an NO2 radical from the molecular ion.
To explore the mechanistic pathways of such conden-
sation reactions, the probable intermediate a-bromo-1-
phenyl-3-[5-(p-nitrophenyl)-2-furyl]-2-propen-l-ones (5,
RꢁH, Cl, CH3 and OCH3) were prepared starting from
dibromopropanones (4), employing triethylamine in ben-
zene medium. This a-bromopropenone (5a) was then
condensed with 3-substituted-4-amino-5-mercapto-1,2,4-
triazole (7, R1-p-chlorophenyl) and the conden-
sation product after usual work up was identified as 3-
p-chlorophenyl-6-phenyl-7-[5-(p-nitrophenyl)-2-fur-

922
B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
The formation of triazolothiadiazines (8) and not
molecular ion peak at m/z 525 corresponding to the
molecular formula C27H16ClN5O3S consistent with the
assigned structure. The UV and IR spectra of this
compound were also found to be identical with the
compound obtained from the one-pot synthesis of 8e
employing chalcone dibromide (4) and the correspond-
ing triazole (7).
The structures of the compounds (8) were unambigu-
ously proved by recording the X-ray crystal structure
[27] of the typical compound, 3-ethyl-6-phenyl-7-[5-(p-
nitrophenyl)-2-furfurylidene]-1,2,4-triazolo[3,4-b]-1,3,4-
thiadiazine (8b).
triazolothiadiazepines (9) was also proved by an alter-
nate chemical synthesis of 3-p-chlorophenyl-6-phenyl-
1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine (11) by con-
densing 4-amino-5-(p-chlorophenyl)-3-mercapto-1,2,4-
triazole (7) with phenacyl bromide (Schemes 1 and 2).
Condensation of triazolo[3,4-b]-1,3,4-thiadiazine (11)
with 5-(p-nitrophenyl)-2-furfuraldehyde in the presence
of piperidine afforded (8e). The IR spectra of samples
of 8e obtained by both methods were found to be
superimposable, thus confirming the assigned structure
8 for the condensation product. The structure of 8e was
confirmed by elemental analysis and mass spectral data.
The mass spectrum of the compound 8e showed a
A possible mechanism to account for the formation
of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines rather than
Scheme 1.

B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
923
tra were recorded on a Perkin–Elmer model 529 in
1
nujol mull. H NMR spectra of a few selected com-
pounds were recorded on a 270 MHz Bruker WH-200
pulsed FT NMR spectrometer using DMSO-d6 as sol-
vent and tetramethylsilane as an internal standard. All
chemical shift values are expressed in l scale. Mass
spectra of some of the selected compounds were
recorded on a JEOL JMS-D 300 mass spectrometer
operating at 70 eV.
3.1. General procedure for the synthesis of
1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-2-propen-1-ones (3)
To a solution of appropriate acetophenone in etha-
nol, an aqueous solution of sodium hydroxide (5%, 10
ml) was added. The resulting solution was heated to
80 °C and p-nitrophenylfurfuraldehyde (2.1 g, 10
mmol) was added with constant stirring. The reaction
mixture was kept stirring at this temperature for 3–4 h,
cooled to room temperature (r.t.) and was allowed to
stand overnight. The solid product separated was col-
lected by filtration, dried and recrystallized from a
mixture of dimethylformamide and ethanol to yield the
required propenones.
3.2. General procedure for the synthesis of
2,3-dibromo-1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-
propan-1-ones (4)
Scheme 2.
To a solution of 1-aryl-3-[5-(p-nitrophenyl)-2-furyl]-
2-propen-1-one (3, 10 mmol) in glacial acetic acid, a
solution of bromine in glacial acetic acid (10%, 18 ml)
was added with constant stirring. The colour of the
solution turned orange–red. The stirring was continued
at r.t. for 24 h. The separated solid was collected by
filtration, washed with ethanol, dried and recrystallized
from glacial acetic acid to afford the dibromo-
propanones (4).
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazepines (9) in the
present investigation can be rationalized by a mecha-
nism involving the initial formation of a Schiff base
(12) and its subsequent cyclization and dehydrobromi-
nation via path (a) as shown in Scheme 3. In the initial
stages of the investigation, it was believed that the
condensation products were triazolothiadiazepines (9).
However, X-ray crystallographic analysis of 8b clearly
confirmed that the condensation products are actually
triazolothiadiazines (8) and not triazolothiadiazepines
(9). In the present investigation, the formation of tria-
zolothiadiazines (8) rather than triazolothiadiazepines
(9) could also be attributed to the greater degree of
inductive and mesomeric effect of p-nitrophenylfuran
substituent as compared to the aroyl substituent of the
a-bromopropenones (5).
3.3. General procedure for the synthesis of
h-bromo-1-aryl-3-[(5-p-nitrophenyl)-2-furyl]-
2-propen-1-ones (5)
A solution of triethylamine (40 mmol) in dry benzene
(30 ml) was added to a solution of 2,3-dibromo-1-
phenyl-3-(5-aryl-2-furyl)-propan-1-one (5 g, 10 mmol)
in dry benzene (100 ml) with stirring. The reaction
mixture was stirred at r.t. for 24 h. After removal of the
separated triethylamine hydrobromide, the filtrate was
concentrated under reduced pressure to give a-bromo-
1-aryl-3-[(5-p-nitrophenyl)-2-furyl]-2 propen-1-one (5)
which was recrystallized from ethanol or a mixture of
dimethyl formamide and ethanol. The characterization
data of these compounds are given in Table 3.
3. Experimental
Melting points (m.p.s) of the newly synthesized com-
pounds were determined by capillary method and are
uncorrected. The UV spectra were recorded in DMF on
a Beckman model-24 spectrophotometer. The IR spec-

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B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
3.4. Synthesis of 3-substituted-6-aryl-7-
[5-(p-nitrophenyl)-2-furfurylidene]-1,2,4-
triazolo[3,4-b]-1,3,4-thiadiazines (8)
afforded the title compounds. The characterization data
of 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazines (8) prepared
according to this general method are given in Table 4.
A
suspension of 2,3-dibromo-1-aryl-3-[5-(p-nitro-
3.5. Synthesis of 3-substituted-6-aryl-7-
[5-(p-nitrophenyl)-2-furfurylidene]-1,2,4-
triazolo[3,4-b]-1,3,4-thiadiazines (8)
phenyl)-2 furyl]-propan-1-one (4, 20 mmol) in ethanol
was treated with triethylamine(1 ml) for 2–3 h. Suitably
substituted 4-amino-5-mercapto-1,2,4-triazole(7, 20
mmol) was then added to the reaction mixture and the
contents were refluxed for 6–8 h. On cooling the reac-
tion mixture, yellow to orange–red solid product sepa-
rated out. It was collected by filtration, washed with
water and dried. The product on recrystallization from
dimethyl formamide or aqueous dimethyl formamide
A mixture of aminomercaptotriazoles (7, 10 mmol),
a-bromo-1-phenyl-3-[5-(p-nitrophenyl)-2-furyl]-2-pro-
pen-1-ones (5, 10 mmol) and ethanolic potassium
hydroxide (5%, 10 ml) were refluxed in ethanol medium
for 6 h and cooled. The solid product thus separated
was filtered, washed, dried and recrystallized from a
Scheme 3.

B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
925
Table 4
Characterization data of 3-substituted-6-aryl-[5-(p-nitrophenyl)-2-furfurylidene]-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine (5)
Comp.
R1
R
M.p. (°C)
Yield (%)
Mol. formula
Anal. (%), Found (calc.)
C
H
N
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
8m
8n
8o
8p
8q
8r
Me
Et
Pr
Ph
p-ClC6H4
Me
Et
Pr
Ph
p-ClC6H4
Me
Et
Pr
Ph
Me
Et
Pr
H
H
H
H
H
Cl
Cl
Cl
268
265
270
260
335
278
234
194
78
80
75
76
81
84
76
75
85
87
84
88
87
81
74
78
77
95
C
22H17N5O3S
61.47 (61.25)
62.21 (62.02)
62.96 (62.75)
65.87 (65.72)
61.78 (61.48)
56.99 (56.77)
57.81 (57.62)
58.61 (58.41)
61.89 (61.48)
57.85 (57.75)
62.33 (62.30)
63.04 (62.88)
63.71 (63.55)
66.49 (66.53)
60.09 (60.13)
60.83 (60.88)
61.57 (61.60)
64.53 (64.49)
3.84 (3.94)
4.18 (4.26)
4.42 (4.58)
3.96 (3.85)
3.33 (3.41)
3.49 (3.44)
3.76 (3.75)
3.99 (4.05)
3.41 (3.41)
2.96 (3.03)
3.81 (3.83)
4.12 (4.15)
4.42 (4.45)
3.74 (3.76)
3.72 (3.70)
4.03 (4.01)
4.33 (4.31)
3.62 (3.64)
16.31 (16.24)
15.64 (15.73)
15.32 (15.25)
14.35 (14.19)
13.35 (13.28)
15.11 (15.05)
14.69 (14.61)
14.23 (14.19)
13.35 (13.28)
12.66 (12.47)
15.78 (15.80)
15.29 (15.28)
14.89 (14.83)
13.83 (13.86)
15.28 (15.25)
14.75 (14.79)
14.36 (14.37)
13.46 (13.43)
C23H19N5O3S
C24H21N5O3S
C27H19N5O3S
C27H18ClN5O3S
C22H16ClN5O3S
C
23H18ClN5O3S
C24H20ClN5O3S
27H18ClN5O3S
Cl
Cl
326
331
C
C27H17Cl2N5O3S
C23H17N5O3S
C
C25H21N5O3S
C28H19N5O3S
C23H17N5O4S
Me
Me
Me
Me
OMe
OMe
OMe
OMe
122–124
132–134
135–137
134–136
195–197
155–157
163–164
140–141
24H19N5O3S
C
24H19N5O4S
C25H21N5O4S
C28H19N5O4S
Ph
UV (umax): 8c, 270 nm (m=1736), 330 nm (m=2102) and 400 nm; 8b, 2926 (exocyclic vinyl CH),1599 (CꢁN and CꢁC), 1509 and CH str.),1602
(CꢁN and CꢁC), 1506 and 1335 (NO2 asym. and sym. str.). 1H NMR (270 MHz): 8b, l 1.3 (t, 3H, J=7.5 Hz), 2.8 (q, 2H, CH2, J=7.5 Hz), 6.9
(s, 1H, exocyclic vinyl proton), 7.2 (d, 1H, furan 3H, J=3.8 Hz), 7.5 (d, 1H, furan 4H, J=3.8 Hz), 8.1 (d, 2H, p-nitrophenyl, J=8 Hz), 8.4 (d,
2H, p-nitrophenyl, J=8 Hz), 7.6–8 (m, 5H, aromatic protons). 1H NMR (90 MHz): 8e, l 7.4 (s, 1H, exocyclic vinyl CH), 7.2–8.4 (m, 11H, furyl
and aromatic protons).
1H NMR (90 MHz): 8g, l 1.3 (t, 3H, CH3), 2.8 (q, 2H, CH2), 6.9 (s, 1H, exocyclic vinyl proton), 7.3–8.6 (m, 10H, furyl and aromatic protons).
1H NMR (400 MHz, DMSO-d6): 8l, l 0.93–0.94 (t, 3H, CH3, J=6.83 Hz), 1.17–1.19 (q, 2H, CH2, J=7.32 Hz), 2.09 (s, 3H, p-tolyl-CH3), 7.18
(s, 1H, exocyclic vinyl CH), 7.39–7.41 (d, 2H, p-tolyl, J=7.81 Hz), 7.8–7.82 (d, 2H, p-tolyl, J=8.3 Hz), 8.16–8.18 (d, 2H, p-nitrophenyl, J=8.31
Hz), 8.29–8.32 (d, 2H, p-nitrophenyl, J=8.3 Hz), 7.67–7.69 (d, 1H, furan 3H, J=3.3 Hz), 7.72–7.73 (d, 1H, furan 4H, J=3.3 Hz).
1H NMR (400 MHz, DMSO-d6): 8m, l 0.92–0.94 (t, 3H, CH3, J=7.33 Hz), 1.19–1.21 (t, 2H, CH2, J=7.33 Hz), 1.75 (m, 2H, CH2), 6.96 (s, 1H,
exocyclic vinyl CH), 2.09 (s, 3H, p-tolyl-CH3), 7.26–7.27 (d, 1H, furan 3H, J=3.42 Hz), 7.5–7.51 (d, 1H, furan 4H, J=3.42 Hz), 7.39–7.41 (d,
2H, p-tolyl, J=7.81 Hz), 8.07–8.09 (d, 2H, p-tolyl, 7.82 Hz), 8.17–8.19 (d, 2H, p-nitrophenyl, J=8.79 Hz), 8.3–8.32 (d, 2H, p-nitrophenyl,
J=8.79 Hz).
1H NMR (400 MHz, DMSO-d6): 8p, l 1.02–1.07 (t, 3H, CH3, J=6.84 Hz), 3.5–3.55 (q, 2H, CH2, J=3.9 Hz), 3.91 (s, 3H, OCH3), 6.83–6.84 (d,
1H, furan 3H, J=3.41 Hz), 6.98–6.99 (d, 1H, furan 4H, J=3.4 Hz), 7.01–7.03 (d, 2H, aromatic, J=8.6 Hz), 7.88–7.91 (d, 2H, aromatic, J=8
Hz), 7.26 (s, 1H, exocyclic vinyl CH), 8.06–8.09 (d, 2H, p-nitrophenyl, J=8.79 Hz), 8.27–8.31 (d, 2H, p-nitrophenyl, J=8.79 Hz).
Mass: 8o, m/z 459 (M+, 19.8%), 428 (MꢀOCH3, 2.5%), 133 (p-methoxy-benzonitrile, 3.6%), 214 (p-nitrophenyl furonitrile, 10.5%); 8r, m/z 521
(M+, 0.9%), 77 (phenyl cation, 42.4%); 8b, 443 (M+, 50%), 29 (Et+, 100%), 413 (MꢀNO2, 15%), 397 (MꢀNO2, 12%), 256 (Mꢀp-nitrophenyl-furan,
10.1%); 8g, m/z 477 (M+, 2%), 137 (p-chlorophenylnitrile, 100%); 8j, m/z 559/561/563 (M+/M+2/M+4, 50%/49%/30%), 137 (p-chlorophenylni-
trile, 50%); 8d, m/z 491 (M+, 34%).
mixture of dimethylformamide and ethanol to yield
triazolothiadiazines (8).
3.6.2. Step 2: Synthesis of 3-(p-chlorophenyl)-6-phenyl-
7-[5-(p-nitrophenyl)-2-furfurylidene]-1,2,4-
triazolo[3,4-b]-1,3,4-thiadiazine (8e)
3.6. Authentication of 3-(p-chlorophenyl)-6-phenyl-7-
[5-(p-nitrophenyl)-2-furfurylidene]-1,2,4-
triazolo[3,4-b]-1,3,4-thiadiazines (8e)
The compound 11 (0.33 g, 10 mmol) was treated with
p-nitrophenylfurfural (0.2 g, 10 mmol) in the presence
of piperidine (0.1 ml) in ethanol and refluxed for 6 h.
The solid separated out was filtered, dried and
recrystallized from a mixture of dimethylformamide
and ethanol to yield the title compound 8e.
It was found to be identical with the sample of 8e
prepared by direct condensation of 3-(p-chlorophenyl)-
4-amino-5-mercapto-1,2,4-triazole (0.22 g, 1 mmol)
with a-bromo-1-phenyl-3-[5-(4-nitrophenyl)-2-furyl]-2-
propen-1-one (0.4 g, 1 mmol) in ethanol, m.p. 335 °C
(mixed m.p. 335 °C). The IR spectra of the 12 samples
3.6.1. Step 1: Synthesis of 3-(p-chlorophenyl)-6-
phenyl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine (11)
To a solution of 3-(p-chlorophenyl)-5-mercapto-
1,2,4-triazole (0.23 g, 10 mmol) in ethanol, phenacyl
bromide(0.2 g, 10 mmol) was added and refluxed for 3
h to yield the title compound 11, m.p. 256 °C, yield,
80%. Anal. Calc.: C, 58.81; H, 3.37; N, 17.15; Found:
C, 59.12; H, 3.65; N, 17.45%

926
B.S. Holla et al. / Il Farmaco 56 (2001) 919–927
obtained were superimposable. Similarly, UV spectra
were also found to be identical.
showed good activity against P. aeruginosa. However,
the antibacterial activities of the remaining compounds
were comparable to that of Furacin. Hence, it is worth
pursuing these compounds for other biological
activities.
4. Biological activity studies
4.2. Anti6iral acti6ity
4.1.1. Antibacterial acti6ity
Some of the newly synthesized compounds were
screened for their antibacterial activity against Es-
cherichia coli, Staphylococcus aureus, Pseudomonas
aeruginosa, and Bacillus subtilis, according to the serial
dilution method [28]. Their minimal inhibitory concen-
trations (MIC values) were determined. Solutions of the
test compounds were prepared in dimethylformamide.
Furacin was used as a standard drug for comparison
and the solvent control was kept. Results of the screen-
ing studies are given in Table 5.
Some of the selected newly synthesized compounds in
the present investigation were screened in vitro for their
antiviral properties against human immunodeficiency
virus (HIV), the causative agent of acquired immune
deficiency syndrome (AIDS). The screening of the test
compounds were carried out at eight different molar
concentrations [29]. Solutions of the test compounds
were injected into culture media containing CEM-IW
cells infected with HIV and the percentage of protected
cells was measured. The concentrations of the test
compounds at which maximum protection of cells oc-
curred and the percentage of protected cells are given in
Table 6.
4.1.2. Results and discussion
Among the compounds tested, compound 8f carrying
p-nitrophenyl and a methyl group showed excellent
antibacterial activities against all the bacteria tested.
Compounds 8d,e,i also showed good activity against all
these four bacteria. Compound 8b possessed a greater
degree of antibacterial activity against E. coli, S. aureus
and P. aeruginosa compared to Furacin. Compound 8p
4.2.1. Results and discussion
The antiviral activity of the test compounds, how-
ever, gradually decreased at higher concentrations due
to their toxicity; hence were inactive as drugs for AIDS.
Table 5
Acknowledgements
Antibacterial activity data of 6-aryl-7-[5-(p-nitrophenyl)-2-furfuryli-
dene]-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines (8)
The authors are grateful to Head, RSIC, C.D.R.I.
Lucknow for analytical and mass spectral data, SIF,
IISc., Bangalore and Head, RSIC, Panjab University,
Chandigarh for NMR spectra. The authors are also
thankful to Dr. V.L. Narayanan, NIH, Bethesda, USA
for providing antiviral activity data. Two of the authors
(P.M.A. and M.K.S.) are grateful to UGC and CSIR,
New Delhi, respectively, for the award of research
fellowships.
Comp.
Minimum inhibitory concentration (mg/ml)
E. coli
S. aureus
P.
B. subtilis
aeruginosa
8b
8d
8e
8f
4.4
4.5
10.4
9.0
11.7
9.1
14.1
9.3
4.0
9.0
9.0
9.8
3.3
7.7
7.6
7.8
8i
3.9
8.8
9.2
9.8
8o
8p
8q
8r
12.5
6.0
12.5
12.5
6.0
12.5
12.5
12.5
12.5
12.5
12.5
6.0
12.5
12.5
12.5
12.5
12.5
12.5
12.5
12.5
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