Synthesis and antibacterial activity of substituted flavones, 4-thioflavones and 4-iminoflavones

Article abstract of DOI:10.1016/j.bmc.2006.03.031

Synthesis of flavones, 4-thioflavones and 4-iminoflavones was carried out with the substitution of variable halogens, methyl, methoxy and nitro groups in the A, B and AB rings of the respective compounds and we also report here their antibacterial activity. Most of the synthesized compounds were found to be active against Escherichia coli, Bacillus subtilis, Shigella flexnari, Salmonella aureus, Salmonella typhi and Pseudomonas aeruginosa. Activity of 4-thioflavones and 4-iminoflavones was found to be higher than that of their corresponding flavone analogues. Investigated compounds having substituents like F, OMe and NO₂ at 4′-position in ring-B exhibited enhanced activity and the presence of electronegative groups in the studied compounds showed a direct relationship to the antibacterial activity.

Full text of DOI:10.1016/j.bmc.2006.03.031

Bioorganic & Medicinal Chemistry 14 (2006) 4704–4711
Synthesis and antibacterial activity of substituted flavones,
4-thioflavones and 4-iminoflavones
Ehsan Ullah Mughal,a Muhammad Ayaz,b Zakir Hussain,c,* Aurangzeb Hasan,a
Amina Sadiq,a Muhammad Riaz,b Abdul Malik,b Samreen Hussainb and
M. Iqbal Choudharyb
aDepartment of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
bInternational Centre for Chemical Sciences, H.E.J. Research Institute of Chemistry, Karachi 75270, Pakistan
cMax-Planck-Institut fu¨r Bioanorganische Chemie, Postfach 101365, 45470 Mu¨lheim an der Ruhr, Germany
Received 16 November 2005; revised 9 March 2006; accepted 17 March 2006
Available online 5 April 2006
Abstract—Synthesis of flavones, 4-thioflavones and 4-iminoflavones was carried out with the substitution of variable halogens,
methyl, methoxy and nitro groups in the A, B and AB rings of the respective compounds and we also report here their antibacterial
activity. Most of the synthesized compounds were found to be active against Escherichia coli, Bacillus subtilis, Shigella flexnari, Sal-
monella aureus, Salmonella typhi and Pseudomonas aeruginosa. Activity of 4-thioflavones and 4-iminoflavones was found to be high-
er than that of their corresponding flavone analogues. Investigated compounds having substituents like F, OMe and NO2 at
40-position in ring-B exhibited enhanced activity and the presence of electronegative groups in the studied compounds showed a
direct relationship to the antibacterial activity.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
It is well known that halogenated compounds are also
strongly biologically active10 but to our knowledge no
natural flavonoids have been reported with halogens as
substituents. Additionally, we were also interested to
check the effect of sulfur and nitrogen atoms at 4-posi-
tion of flavones on their biological activity. Therefore,
in order to search for new compounds that can be used
for the treatment of bacterial infections, this paper de-
scribes the synthesis of variably substituted flavones, 4-
thioflavones and 4-iminoflavones and in vitro evaluation
of the new and known flavones, 4-thioflavones and
4-iminoflavones against a number of bacteria.
Flavonoids are a group of natural products present in a
wide variety of plants. They are found in seeds, citrus
fruits, olive oil, tea and red wine and are commonly con-
sumed with the human diet.1,2 Flavonoids exhibit a
broad range of biological activities, including antiviral,
antiinflammatory, antioxidant, antiallergic, hepatopro-
tective, antithrombotic and antitumoral actions.3–5 Fur-
thermore, these compounds are used in bacteriology,
pharmacology and medicine due to their bactericidal
activities.6 Moreover, amino group substituted flavone
derivatives exhibit strong antitumour activity in breast
cancer cells.7
2. Chemistry
Although, a little work has been carried out on sulfur
containing flavones; thioflavones have been reported to
show considerable antimicrobial activities, while flavone
imines show antimicrobial and antimalarial activities.8,9
In view of the importance of bioactive flavones, 4-thiof-
lavones and 4-iminoflavones in recent years as described
above, it was thought to replace the oxygen atom of the
keto group of flavone with a sulfur atom and with a
substituted amino group to check their effect as well as
the effect of various substituents on the biological activ-
ities of flavones.
Keywords: Synthesis; Flavones; 4-Thioflavones; 4-Iminoflavones;
Antibacterial.
Flavones (6 series) were synthesized using the Baker–
Venkataraman rearrangement11,12 as shown in Scheme 1.
*
Corresponding author. Tel.: +49 208 306 3595; fax: +49 208 306
3951; e-mail: zakir@mpi-muelheim.mpg.de
0968-0896/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.03.031

E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
4705
R2
O
R3
R4
R2
OH
O
Cl
OH
R3
R4
OH
O
(CH3CO)2O
Pyridine
AlCl3 (anhydrous)
Fries (~) /
4
O
R5
Pyridine / OH-
R1
R1
O
O
R5
R1
R1
1
2
3
5
4
2
R2
3´
R3
2´
1´
4´
5´
1
O
8
2
9
7
6
R4
6´
R5
4
3
10
R1
5
O
6 (A, A1-A12
)
Scheme 1. Synthesis of A, B-ring substituted flavones.
Acetylation of substituted/unsubstituted phenols (1) was
carried out in the presence of acetic anhydride to yield
intermediates 2 which on refluxing in the presence of
anhydrous aluminium chloride underwent Fries rear-
rangement to afford 3 in good yields (ꢀ80%). Substitut-
ed/unsubstituted 2-hydroxyacetophenones (3) were
further allowed to react with substituted/unsubstituted
benzoyl chlorides (4) in the presence of anhydrous pyri-
dine, and subsequent heating the mixture in the presence
of KOH yielded substituted/unsubstituted-2-hydrox-
ydibenzoyl methane (5). Intermediates 5 were further cyc-
lized in the presence of glacial acetic acid and concd
H2SO4 at 100 °C to afford the desired flavone series 6
(A, A1–A12) again in good yield (ꢀ80%). The substitution
pattern in all of the synthesized compounds (6 series) is
given in Table 1 (Scheme 2).
tion pattern in all of the synthesized 4-iminoflavones (8
series) is given in Table 3.
All of the compounds from different series (6–8) were
fully characterized through spectroscopic and other ana-
lytical techniques, details of which are given separately
in Section 6.
3. Biological activity
Synthesized compounds were tested for their antibacte-
rial activity by adopting agar well diffusion15 method.
The following bacterial cultures were used.
(i) Escherichia coli (ii) Bacillus subtilis (iii) Shigella flex-
nari (iv) Staphylococcus aureus (v) Salmonella typhi and
(vi) Pseudomonas aeruginosa
4-Thioflavones, that is, series 7 (B, B1–B12) were synthe-
sized from the previously synthesized flavones, that is,
series 6 (A, A1–A12) by refluxing them with toluene
(dry) in the presence of Lawesson’s reagent.13 The sub-
stitution pattern in all of the synthesized 4-thioflavones
(7 series) is given in Table 2.
Imipenem was used as standard drug and 24 h-old cul-
ture containing approximately 104–106 colony forming
unit (CFU) was spread on the surface of Muller Hinton
Agar (MHA) plates. Wells were created in the medium
with the help of a sterile metallic borer at appropriate
distances. Test samples of 100 lL (1 mg of test com-
pounds) were poured into each well and the plates were
incubated at 37 °C for 24 h. The results, in terms of inhi-
bition zones, were noted and compared with standard
drug. As a negative control, DMSO was used. The
results of these experiments are summarized in Table 4.
A parallel series of compounds 4-iminoflavones, that is,
8 (C, C1–C12) was synthesized by refluxing the flavone
series 6 (A, A1–A12) with 2,4-dinitrophenylhydrazine14
in the presence of concd H2SO4 in EtOH. The substitu-
Table 1. Substituent values for flavones A, A1–A12
4. Results and discussion
Compound
R1
R2
R3
R4
R5
A
H
H
H
H
H
H
H
F
H
H
H
H
H
H
H
H
NO2
H
H
I
The in vitro bioactivities of the synthesized compounds
have shown encouraging results against various classes
of bacteria as mentioned above.
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
H
H
OCH3
H
H
CH3
NO2
OCH3
H
H
H
H
H
Antibacterial activity analysis of B-series flavones
showed moderate activity against E. coli and S. typhi
but exhibited very low activity against B. subtilis, S. flex-
neri, S. aureus and P. aruginosa. However, 4-thioflav-
ones and 4-iminoflavones of the same series exhibited
significant activity against E. coli, S. flexneri, P. aerugin-
osa and S. typhi, but did not show significant activity
against B. subtilis and S. aureus.
NO2
H
H
H
NO2
H
H
H
Cl
Br
F
H
H
H
H
H
H
I
H
H
H
I
H
H
H
F
OCH3
H
OCH3
H
H
H

4706
E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
R2
3´
R3
4´
2´
1
8
5
1´
R2
3´
9
O
2
7
5´
R4
6´
R3
R4
2´
1´
6
R5
4
4´
3
10
R1
1
8
EtOH / H+
9
O
2
Toluene (dry)/ Reflux
Lawesson's Reagent
7
5´
N
6 (A, A1-A12)
6´
NH
6
2,4-Dinitrophenylhydrazine
NO2
R5
4
3
1´´
R1
10
5
6´´
5´´
2´´
S
3´´
4´´
NO2
7 (B, B1-B12)
8 (C, C1-C12
)
Scheme 2. Synthesis of A, B-ring substituted 4-thioflavones (7) and 4-iminoflavones (8).
Table 2. Substituent values for 4-thioflavones B, B1–B12
bacterial activity of the analyzed flavones, 4-thioflav-
ones and 4-iminoflavones.
Compound
R1
R2
R3
R4
R5
B
H
H
H
H
H
H
H
F
H
H
H
H
H
H
H
H
NO2
H
H
I
From Table 4, it is clear that antibacterial activity of
flavones increases accordingly on replacing oxygen atom
with sulfur and nitrogen atoms at 4-position. Thioana-
logues of flavones have more antibacterial activity as
compared to flavones. Similarly, 4-iminoflavones are
much more active against bacteria than 4-thioflavones.
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
H
H
OCH3
H
H
CH3
NO2
OCH3
H
H
H
H
H
NO2
H
H
H
NO2
H
H
H
Cl
Br
F
H
H
H
Furthermore, when flavones, 4-thioflavones and 4-imin-
oflavones have methoxy group in the B-ring at position
30, the linear growth inhibition against E. coli and S. ty-
phi was 12 and 13 (A1), respectively, for flavones, while
15 and 12 (B1) for 4-thioflavones and 15 and 9 (C1) for
4-iminoflavones, whereas standard drug Imipenem
showed 30 and 25, respectively. However, when a meth-
oxy group was present at 40-position in ring-B, the activ-
ity increased accordingly in flavones, 4-thioflavones and
4-iminoflavones. The same pattern of activity is found
with the replacement of –OMe group in ring-B with
–NO2 group but the percentage of inhibition is de-
creased to some extent. Thus increase in activity is prob-
ably due to the resonance effect of –OMe group that is
more prominent at 40-position than 30-position, whereas
in case of a nitro group, it operates in opposite direction
giving the results otherwise.
H
H
H
I
H
H
H
I
H
H
H
F
OCH3
H
OCH3
H
H
H
Table 3. Substituent values for 4-iminoflavones C, C1–C12
Compound
R1
R2
R3
R4
R5
C
H
H
H
H
H
H
H
F
H
H
H
H
H
H
H
H
NO2
H
H
I
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
H
H
OCH3
H
H
CH3
NO2
OCH3
H
H
H
H
H
NO2
H
H
H
NO2
H
H
H
Cl
Br
F
H
H
H
H
H
H
I
Moreover, when a methoxy group was present at both
positions like 30 and 40, then both groups enhanced
the activity mutually against E. coli, P. aeruginosa and
S. typhi. Linear growth inhibition against these three
bacteria, in this case (A12), was 19, 16 and 16, respective-
ly, whereas in case of B12 inhibition was enhanced to 19,
16 and 17, respectively. The 4-imino analogue, that is,
C12 exhibited further enhanced inhibition, that is, 21,
20 and 19 against these bacterial species.
H
H
H
I
H
H
H
F
OCH3
H
OCH3
H
H
H
4.1. Structure–activity relationship
Considering the varied structure–activity relationships
of different series of compounds, it cannot be inferred
that the biological behaviour of a drug is determined
by the influence of a single parameter or variable. Fur-
thermore, in most cases, the presence or introduction
of various functional groups in a compound does not al-
low to accurately explain the kind and intensity of its
biological activity. However, and taking the necessary
precautions, the information in Table 4 may allow us
to make some general remarks on the structure and anti-
In the presence of electron-withdrawing groups like
–NO2 at 20-and 5-0 positions in ring-B, the linear growth
inhibition decreased to lower percentage. Flavones,
4-thioflavones and 4-iminoflavones having F atom at
position 40 in ring-B showed a very significant inhibition
against E. coli, B. subtilis, S. flexneri, S. typhi and
P. aeruginosa but were inactive against S. aureus. This
increase in activity is probably due to the presence of

E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
4707
Table 4. Antibacterial activities of series of compounds, relative to the standard drug Imipenem
Compound
Bacteria
E. coli
B.subtilis
S. flexneri
S. aureus
P.aeruginosa
S. typhi
A
9
—
—
—
—
—
—
—
—
—
—
10
—
—
16
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
17
19
21
—
10
—
33
—
10
10
—
—
19
—
—
12
—
—
15
16
16
18
—
13
14
—
—
—
—
12
11
—
16
11
—
14
—
16
14
—
16
15
16
15
—
—
27
—
—
—
—
—
—
—
—
—
—
—
—
—
—
14
—
—
—
—
10
—
—
10
—
—
—
—
—
—
—
—
—
—
—
—
—
10
—
16
33
—
—
21
—
15
11
—
—
10
—
10
12
16
15
—
—
—
15
—
—
—
—
14
11
—
15
16
—
—
15
14
15
13
16
17
20
16
16
20
24
10
12
15
13
12
9
B
11
—
12
15
15
—
10
—
12
16
15
15
15
16
10
15
16
10
12
14
10
—
15
11
—
18
14
20
16
14
12
—
22
25
25
19
19
21
30
C
A1
B1
C1
A2
B2
—
9
C2
A3
16
10
12
20
17
16
19
13
14
15
10
14
—
15
—
17
15
15
13
16
21
15
—
—
15
21
20
21
16
17
19
25
B3
C3
A4
B4
C4
A5
B5
C5
A6
B6
C6
A7
B7
C7
A8
B8
C8
A9
B9
C9
A10
B10
C10
A11
B11
C11
A12
B12
C12
Imipenem
Inhibition zones are given in millimeter.
fluorine at 40-position which is the most electronegative
atom. However, compounds with a methyl group as a
substituent on B-ring were found to be inactive against
each bacterial species.
The flavones like A7, A8, A9 and A10 and their respective
sulfur and nitrogen analogues (B7, B8, B9 and B10), (C7,
C8, C9 and C10) have similar structures except the nature
of halogen atom present at 5-position. A comparison of
the antibacterial activities of the series of compounds
(Table 4) shows that the flavone A9 having a bromine
atom at 6-position in ring-A shows linear growth inhibi-
tion of 14 and 16 against E. coli and S. typhi and its
respective thio- and imino- analogues exhibit 20, 21
and 16, 15, respectively, against the same bacterial spe-
cies. However, when the bromine atom in ring-B is re-
placed by chlorine (A8) and fluorine (A10), inhibition is
changed to 11 and 14, respectively, whereas standard
drug Imipenem shows 30 inhibition. The same results
are found in case of their respective thio-(B8, B10) and
imino-(C8, C10) analogues.
Above results show that electron-donating and electro-
negative groups are responsible for the antibacterial
activity of flavones, 4-thioflavones and 4-iminoflavones
provided these groups are at 40-position in ring-B rather
than any other position. Additionally, increase in inhibi-
tion of thio-analogues is probably due to the larger size
of the sulfur atom.
Antibacterial analysis of C-series compounds revealed
that all flavones show good or low activity against
E. coli and S. typhi but were inactive against B. subtilis,
S. flexneri, S. aureus and P. aeruginosa, whereas their
respective sulfur and nitrogen analogues exhibited sig-
nificant activity against E. coli, S. flexneri, P. aeruginosa
and S. typhi, however, they were found to be inactive
against B. subtilis and S. aureus.
Antibacterial analysis of unsubstituted flavones and
their derivatives showed significant activity against
E. coli, S. flexneri, P. aeruginosa and S. typhi but were
inactive against B. subtilis and S. aureus species.

4708
E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
Compound C showed linear growth inhibition of 21, 15
and 10 against P. aeruginosa, S. typhi and S. flexneri,
respectively, whereas standard drug Imipenem showed
24, 27 and 25, respectively. However, compounds A
and B exhibited very low activity against E. coli and S.
typhi and no activity against other bacterial species.
Therefore, it is concluded that a 2,4-dinitrophenyl
hydrazine moiety in compound C is responsible for its
enhanced antibacterial activity, while unsubstituted flav-
ones and 4-thioflavone remain inactive or less active.
are given in the cited literature, while those of the new
compounds (A8, A9) are given below.
6.1.1. 2-(20-Iodophenyl)-6-chloro-4H-1-benzopyran-4-one
(A8). Yield: 80%; mp 130–131 °C; MS (EI): m/z
(%) = 384 [M+2] (12), 382.5 [M+] (100), 255 [M+ꢁX]
(57), 354 [M+ꢁCO] (12), 318.5 [M+ꢁCO–X] (2); IR
ꢁ1
~
(film): m ¼ 1645 cm (s, C@O), 1587 (m, C@C), 725
1
(C–X); H NMR (DMSO-d6, 500 MHz): d (ppm) 6.59
(s, 1H, H3), 8.06 (d, J = 2.18 Hz, 1H, H5), 7.91 (dd,
J = 8.96/2.27 Hz, 1H, H7), 7.86 (d, J = 7.06 Hz, 1H,
H8), 8.03 (dd, J = 7.70/2.17 Hz, 1H, H30), 7.34 (m, 1H,
H40), 7.59 (m, 1H, H50), 7.78 (dd, J = 8.91/2.30 Hz,
1H, H60); Anal. Calcd for C15H8IClO2 (382.58): C,
47.09; H, 2.11. Found: C, 46.91; H, 2.31.
5. Conclusion
Synthesis of flavones, 4-thioflavones and 4-iminoflav-
ones was carried out with the substitution of various
halogens, methyl, methoxy and nitro groups in the A,
B and AB-rings of the respective compounds. The syn-
thesized flavones, 4-thioflavones and 4-iminoflavones
were checked for their antibacterial activity. It is con-
cluded from the results that substituents on the flavones’
skeleton are responsible for the enhancement of the anti-
bacterial activity. It can further be concluded that the
percentage inhibition increases as the electronegativity
of the halogen atom on A-ring increases. Similarly, sul-
fur and nitrogen atoms, in addition to substituents at
certain positions, enhance the antibacterial activity of
flavone derivatives. Activities exhibited by thioflavones
as well as iminoflavones could be due to the combined
effect of the heteroatom as well as substituents present
in the system.
6.1.2. 2-(20-Iodophenyl)-6-bromo-4H-1-benzopyran-4-one
(A9). Yield: 85; mp 133–134 °C; MS (EI): m/z (%) = 429
[M+2] (50), 427 [M+] (100), 300 [M+–X] (37), 399
[M+ꢁCO] (15), 363 [M+ꢁCO–X] (7); IR (film):
ꢁ1
~
m ¼ 1650 cm (s, C@O), 1591 (m, C@C), 740 (C–X);
1H NMR(DMSO-d6, 500 MHz): d (ppm) 6.63 (s, 1H,
H3), 8.14 (d, J = 2.31 Hz, 1H, H5), 7.99 (dd, J = 8.52/
1.19 Hz, 1H, H7), 7.73 (d, J = 7.16 Hz, 1H, H8), 8.09
(dd, J = 7.83/2.13 Hz, 1H, H30), 7.40 (m, 1H, H40),
7.60 (m, 1H, H50), 7.81 (dd, J = 8.38/2.37 Hz, 1H,
H60); Anal. Calcd for C15H8IBrO2 (427.04): C, 42.19;
H, 1.89. Found: C, 42.03; H, 1.95.
6.2. General procedure for the synthesis of 7 series
(B, B1–B12)
A mixture of a substituted/unsubstituted flavone of the
described 6 series (5.0 mmol each), Lawesson’s reagent
(3.0 mmol) and anhydrous toluene (30 mL) was refluxed
under dry conditions for 3 h. The solvent was evaporat-
ed under reduced pressure and the residue was crystal-
lized from ethanol to afford substituted/unsubstituted
4-thioflavone (B, B1–B12) in good to excellent yields.
Spectroscopic as well as other physical data of the
known compounds in 7 series (B, B1–B4, B6, B7, B11
and B12) are given in the literature13,18, while those of
the new compounds (B5, B8–B10) are given below.
6. Experimental
Chemicals used in the present study were purchased
from Merck and Fluka (Germany). Solvents used were
dried with specific drying reagent under nitrogen. Rf val-
ues were calculated by using precoated silica gel alumin-
ium packed plates Kiesel gel 60F254 Merck (Germany).
Melting points were determined in open capillaries using
Gallenkamp melting point apparatus and are uncorrect-
ed. FTIR spectra were recorded on Bio-Rad Merlin
1
Spectrophotometer using KBr discs. H NMR spectra
were recorded on Bruker (400 MHz) AM-250 in
DMSO-d6 solution using TMS as internal standard.
EIMS was recorded on VG-70-SE Mass Spectrometer.
Purity of each compound was monitored by TLC.
Chemical analyses were carried out on Carlo-Erba-
1108 instrument.
6.2.1. 2-(20,50-Dinitrophenyl)-4H-1-benzopyran-4-thione
(B5). Yield: 60%; mp 232–233 °C; MS (EI): m/z
(%) = 328 [M+] (100), 237 [M+ꢁX] (17), 284 [M+ꢁCS]
+
ꢁ1
~
(27), 193 [M ꢁCS–X] (20); IR (film): m ¼ 1175 cm
(s, C@S), 1603 (m, C@C), 1502 (C–NO2); 1H NMR
(DMSO-d6, 500 MHz): d (ppm) 6.98, (s, 1H, H3), 8.15
(d, 1H, J = 7.03 Hz, H5), 7.81, (dd, 1H, J = 7.75, 7.40,
1.5 Hz, H6), 7.79 (dd, 1H, J = 8.31, 2.01 Hz, H7), 7.52
(d, 1H, J = 8.01 Hz, H8), 8.75 (d, 1H, J = 8.00, H30),
8.73 (d, 1H, J = 7.59 Hz, H40), 8.81 (s, 1H, H60); Anal.
Calcd for C15H8O5N2S (328.30): C, 54.88; H, 2.46; N,
8.53. Found: C, 54.81; H, 2.42; N, 8.58.
The procedure for the synthesis of a representative
compound from each series (A–C) is given below,
while the syntheses of rest of the members of each series
are based on similar procedures with the variation in
substitution pattern in reactants for different targets.
6.1. Synthesis of 6 series (A, A1–A12)
6.2.2. 2-(20-Iodophenyl)-6-chloro-4H-1-benzopyran-4-thi-
one (B8). Yield: 78%; mp 158–160 °C; MS (EI): m/z
(%) = 400 [M+2] (66), 398 [M+] (100), 271 [M+ꢁX]
(92), 354 [M+ꢁCS] (18), 319 [M+ꢁCS–X] (40); IR (film):
All of the compounds in the 6 series were synthesized
according to the standard procedures16,17 as outlined
in Scheme 1. Spectroscopic as well as other physical data
of the known compounds in 6 series (A, A1–A7, A10–A12)
1
ꢁ1
~
m ¼ 1176 cm (s, C@S), 1607 (m, C@C), 805 (C–N); H
NMR (DMSO-d6, 500 MHz): d (ppm) 7.19 (s, 1H, H3),

E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
4709
8.37 (d, J = 2.23 Hz, 1H, H5), 7.97 (dd, J = 7.96/
2.36 Hz, 1H, H7), 7.76 (d, J = 7.48 Hz, 1H, H8), 8.08
(dd, J = 7.89/2.12 Hz, 1H, H30), 7.36 (m, 1H, H40),
7.61 (m, 1H, H50), 7.83 (dd, J = 8.90/2.33 Hz, 1H,
H60); Anal. Calcd for C15H8IClOS (398.65): C, 45.19;
H, 2.02. Found: C, 45.39; H, 2.12.
6.3.2. 2-(2,4-Dinitrophenyl)-1-(2-(40-methylphenyl)-4H-
chromen-4-ylidene)hydrazine (C2). Yield: 81%; mp 241–
242 °C; MS (EI): m/z (%) = 416 [M+] (100), 401
[M+ꢁX] (4), 399 [M+ꢁOH] (36), 340 [M+ꢁC6H4] (4),
+
ꢁ1
~
294 [M ꢁC6H4–NO2] (56); IR (film): m ¼ 3460 cm
(NH), 1614 (s, C@N), 1665 (m, C@C), 1333 (C–Me);
1H NMR (DMSO-d6, 500 MHz): d (ppm) 2.40 (s, 3H,
Me), 7.07 (s, 1H, H3), 7.66 (d, J = 7.05 Hz, 1H, H5),
7.44 (m, 1H, H6), 7.46 (m, 1H, H7), 7.60
(d, J = 7.43 Hz, 1H, H8), 8.06 (d, J = 9.63 Hz, 2H,
H20/60), 7.95 (d, J = 8.19 Hz, 1H, H30/50), 8.88
(d, J = 2.52 Hz, IH, H300), 8.37 (dd, J = 7.01/2.50 Hz,
IH, H500), 8.28 (d, J = 7.25 Hz, 1H, H600); Anal. Calcd
for C22H16O5N4 (416.39): C, 63.46; H, 3.87; N, 13.46.
Found: C, 63.41; H, 3.90; N, 13.44.
6.2.3. 2-(20-Iodophenyl)-6-bromo-4H-1-benzopyran-4-thi-
one (B9). Yield: 80%; mp 146–147 °C; MS (EI): m/z
(%) = 445 [M+2] (50), 443 [M+] (100), 316 [M+ꢁX]
(95), 399 [M+ꢁCS] (27), 319 [M+ꢁCS–X] (30); IR (film):
1
ꢁ1
~
m ¼ 1171 cm (s, C@S), 1598 (m, C@C), 770 (C–X); H
NMR (DMSO-d6, 500 MHz): d (ppm) 7.20 (s, 1H, H3),
8.40 (d, J = 2.50 Hz, 1H, H5), 7.98 (dd, J = 7.45/
2.15 Hz, 1H, H7), 7.78 (d, J = 7.50 Hz, 1H, H8), 8.09
(dd, J = 7.90/2.23 Hz, 1H, H30), 7.40 (m, 1H, H40),
7.69 (m, 1H, H50), 7.89 (dd, J = 8.51/2.43 Hz, 1H,
H60); Anal. Calcd for C15H8BrIOS (443.10): C, 40.66;
H, 1.82. Found: C, 40.69; H, 1.72.
6.3.3.
2-(2,4-Dinitrophenyl)-1-(2-(40-nitrophenyl)-4H-
chromen-4-ylidene)hydrazine (C3). Yield: 72%; mp 297–
298 °C; MS (EI): m/z (%) = 447 [M+] (100), 401
[M+ꢁX] (19), 430 [M+ꢁOH] (25), 371 [M+ꢁC6H4]
6.2.4. 2-(20-Iodophenyl)-6-fluoro-4H-1-benzopyran-4-thi-
one (B10). Yield: 78%; mp 162–163 °C; MS (EI): m/z
(%) = 382 [M+] (100), 255 [M+ꢁX] (36), 338 [M+ꢁCS]
(28), 325 [M+ꢁC6H4–NO2] (48); IR (film):
ꢁ1
~
m ¼ 3440 cm (NH), 1611 (s, C@N), 1590 (m, C@C),
1475 (C–NO2); 1H NMR (DMSO-d6, 500 MHz): d
(ppm) 7.02 (s, 1H, H3), 7.68 (d, J = 7.11 Hz, 1H, H5),
7.49 (m, 1H, H6), 7.52 (m, 1H, H7), 7.38
(d, J = 7.40 Hz, 1H, H8), 8.21 (d, J = 8.03 Hz, 2H,
H20/60), 8.30 (d, J = 7.81 Hz, 2H, H30/50), 8.89 (d,
J = 2.31 Hz, IH, H300), 8.51 (dd, J = 7.51/2.50 Hz, IH,
H500), 8.28 (d, J = 7.81 Hz, 1H, H600); Anal. Calcd for
C21H13O7N5 (447.36): C, 56.38; H, 2.93; N, 15.65.
Found: C, 56.33; H, 2.97; N, 15.60.
+
ꢁ1
~
(2), 319 [M ꢁCS–X] (28); IR (film): m ¼ 1182 cm
(s, C@S), 1603 (m, C@C), 780 (C–X); 1H NMR
(DMSO-d6, 500 MHz): d (ppm) 7.35 (s, 1H, H3), 8.11
(d, J = 2.66 Hz, 1H, H5), 8.09 (dd, J = 7.92/2.89 Hz,
1H, H7), 7.75 (d, J = 7.42 Hz, 1H, H8), 7.83 (dd,
J = 7.88/4.79 Hz, 1H, H30), 7.45 (m, 1H, H40), 7.59 (m,
1H, H50), 7.86 (dd, J = 7.88/4.78 Hz, 1H, H60); Anal.
Calcd for C15H8FIOS (382.19): C, 47.14; H, 2.11.
Found: C, 47.10; H, 2.17.
6.3.4. 2-(2,4-Dinitrophenyl)-1-(2-(40-methoxyphenyl)-4H-
chromen-4-ylidene)hydrazine (C4). Yield: 69%; mp 150–
152 °C; MS (EI): m/z (%) = 432 [M+] (100), 401
[M+ꢁX] (38), 415 [M+ꢁOH] (27), 356 [M+ꢁC6H4]
6.3. General procedure for the synthesis of 8 series
(C, C1–C12)
A fresh solution of 5.05 mmol of 2,4-dinitrophenylhydr-
azine in concd H2SO4 (2 mL), 95% alcohol (15 mL) and
5.05 mmol of substituted/unsubstituted flavones, that is,
6 series were refluxed and allowed to stand in a stop-
pered flask for 24 h in order to precipitate the product
completely. The solution was diluted with 1 M solution
of concd H2SO4 in water and the precipitate washed
with dilute acid and crystallized from dioxane. Spectro-
scopic as well as other physical data of the known com-
pound in 8 series (C) are given in the literature19, while
those of the new compounds (C1–C12) are given below.
(39), 310 [M+ꢁC6H4–NO2] (58); IR (film):
ꢁ1
~
m ¼ 3390 cm (NH), 1619 (s, C@N), 1600 (m, C@C),
1030 (C–OMe); 1H NMR (DMSO-d6, 500 MHz): d
(ppm) 3.65 (s, 3H, –OMe), 7.01 (s, 1H, H3), 7.60
(d, J = 7.05 Hz, 1H, H5), 7.52 (m, 1H, H6), 7.50
(m, 1H, H7), 7.70 (d, J = 7.43 Hz, 1H, H8), 8.16
(d, J = 7.66 Hz, 2H, H20/60), 8.22 (d, J = 7.01 Hz, 2H,
H30/50), 8.69 (d, J = 2.53 Hz, IH, H300), 8.52 (dd,
J = 7.50/2.03 Hz, IH, H500), 8.41 (d, J = 8.00 Hz, 1H,
H600); Anal. Calcd for C22H16O6N4 (432.39): C, 61.11;
H, 3.73; N, 12.96. Found: C, 61.17; H, 3.69; N, 12.98.
6.3.1. 2-(2,4-Dinitrophenyl)-1-(2-(30-methoxyphenyl)-4H-
chromen-4-ylidene)hydrazine (C1). Yield: 83%; mp 230–
231 °C; MS (EI): m/z (%) = 432 [M+] (100), 401
[M+ꢁX] (36), 415 [M+ꢁOH] (20), 356 [M+ꢁC6H4]
6.3.5.
2-(2,4-Dinitrophenyl)-1-(2-(20,50-dinitrophenyl)-
4H-chromen-4-ylidene)hydrazine (C5). Yield: 60%; mp
185–186 °C; MS (EI): m/z (%) = 492 [M+] (100), 400
[M+ꢁX] (19), 475 [M+ꢁOH] (21), 416 [M+ꢁC6H4]
(33), 310 [M+ꢁC6H4–NO2] (51); IR (film):
(48), 370 [M+ꢁC6H4–NO2] (66); IR (film):
ꢁ1
ꢁ1
~
~
m ¼ 3425 cm (NH), 1616 (s, C@N), 1601 (m, C@C),
m ¼ 3445 cm (NH), 1614 (s, C@N), 1595 (m, C@C),
1097 (C–OMe); 1H NMR (DMSO-d6, 500 MHz): d
(ppm) 3.87 (s, 3H, OMe), 7.12 (s, 1H, H3), 7.69
(m, 1H, H5), 7.51 (m, 1H, H6), 7.66 (m, 1H, H7), 7.42
(m, 1H, H8), 8.07 (d, J = 2.38 Hz, 1H, H20), 7.45
(m, 1H, H40), 7.21 (m, 1H, H50), 7.75 (m, 1H, H60),
8.89 (d, J = 2.52 Hz, IH, H300), 8.38 (dd, J = 7.50/
2.46 Hz, IH, H500), 8.29 (d, J = 7.83 Hz, 1H, H600); Anal.
Calcd for C22H16O6N4 (432.39): C, 61.11; H, 3.73; N,
12.96. Found: C, 61.01; H, 3.75; N, 12.99.
1495 (C–NO2); 1H NMR: (DMSO-d6, 500 MHz): d
(ppm) 7.18 (s, 1H, H3), 7.91 (d, J = 8.01Hz, 1H, H5),
7.47 (m, 1H, H6), 7.80 (m, 1H, H7), 7.40
(d, J = 7.79 Hz, 1H, H8), 8.03 (d, J = 7.98 Hz, 2H,
H30), 8.10 (s, 2H, H60), 8.90 (d, J = 2.33 Hz, IH, H300),
8.86 (dd, J = 8.30/2.50 Hz, IH, H500), 8.81 (d,
J = 7.65 Hz, 1H, H600); Anal. Calcd for C21H12O9N6
(492.36): C, 51.23; H, 2.46; N, 17.07. Found: C, 51.21;
H, 2.49; N, 17.03.

4710
E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
6.3.6.
2-(2,4-Dinitrophenyl)-1-(2-(30-nitrophenyl)-4H-
6.3.10. 2-(2,4-Dinitrophenyl)-1-(2-(20-iodophenyl)-6-fluo-
ro-4H-chromen-4-ylidene)hydrazine (C10). Yield: 83%;
mp 263–264 °C; MS (EI): m/z (%) = 546 [M+] (100),
419 [M+ꢁX] (4), 529 [M+ꢁOH] (3), 470 [M+ꢁC6H4]
chromen-4-ylidene)hydrazine (C6). Yield: 81%; mp 225–
227 °C; MS (EI): m/z (%) = 447 [M+] (100), 401
[M+ꢁX] (9), 430 [M+ꢁOH] (35), 371 [M+ꢁC6H4] (78),
+
325 [M ꢁC6H4–NO2] (68); IR (film): m ¼ 3480 cm
(5),
424
[M+ꢁC6H4–NO2]
(28);
IR
(film):
ꢁ1
~
ꢁ1
~
(NH), 1610 (s, C@N), 1593 (m, C@C), 1479 (C–NO2);
1H NMR (DMSO-d6, 500 MHz): d (ppm) 7.26 (s, 1H,
H3), 8.08 (d, J = 8.55 Hz, 1H, H5), 7.87 (m, 1H, H6),
7.92 (m, 1H, H7), 7.69 (d, Hz, 1H, H8), 8.46 (s, 1H,
20-H), 7.93 (m, 1H, H40) 7.45 (m, 1H, H50), 8.43 (d,
J = 8.25 Hz, 1H, H60), 8.89 (d, J = 1.47 Hz, IH, H300),
8.84 (dd, J = 7.95/1.47 Hz, IH, H500), 8.57 (d,
J = 7.85 Hz, 1H, H600); Anal. Calcd for C21H13O7N5
(447.36): C, 56.38; H, 2.93; N, 15.65. Found: C, 56.31;
H, 2.97; N, 15.67.
m ¼ 3292 cm (NH), 1614 (s, C@N), 1584 (m, C@C),
775 (C–X); 1H NMR(DMSO-d6, 500 MHz): d (ppm)
6.56 (s, 1H, H3), 8.84 (d, J = 2.40 Hz, 1H, H5), 7.71
(dd, J = 6.65/0.9 Hz, 1H, H7), 7.62 (d, J = 7.45 Hz,
1H, H8), 8.05 (dd, J = 8.01/2.80 Hz, 1H, H30), 6.69 (m,
1H, H40), 7.33 (m, 1H, H50), 7.55 (dd, J = 5.25/
4.85 Hz, 1H, H60), 8.17 (s, IH, H300), 8.35 (dd,
J = 8.55/2.45 Hz, IH, H500), 8.07 (d, J = 8.0 Hz, 1H,
H600), 11.22 (s, 1H, N–H); Anal. Calcd for
C21H12FIO5N4 (546.25): C, 46.17; H, 2.21; N, 10.26.
Found: C, 46.20; H, 2.18; N, 10.22.
6.3.7.
2-(2,4-Dinitrophenyl)-1-(2-phenyl-6-fluoro-4H-
chromen-4-ylidene)hydrazine (C7). Yield: 85%; mp 270–
271 °C; MS (EI): m/z (%) = 420 [M+] (100), 328
[M+ꢁX] (24), 403 [M+ꢁOH] (80), 344 [M+ꢁC6H4]
6.3.11. 2-(2,4-Dinitrophenyl)-1-(2-(40-fluorophenyl)-4H-
chromen-4-ylidene)hydrazine (C11). Yield: 85%; mp
180–182 °C; MS (EI): m/z (%) = 420 [M+] (100), 401
[M+ꢁX] (2), 403 [M+ꢁOH] (69), 344 [M+ꢁC6H4] (47),
(53), 298 [M+ꢁC6H4–NO2] (95); IR (film):
+
ꢁ1
ꢁ1
~
~
m ¼ 3495 cm (NH), 1611 (s, C@N), 1585 (m, C@C),
298 [M ꢁC6H4–NO2] (95); IR (film): m ¼ 3470 cm
1329 (C–NO2), 1115 (C–F); 1H NMR (DMSO-d6,
500 MHz): d (ppm) 7.10 (s, 1H, H3), 11.34 (s, 1H, N–
H), 8.87 (s, 1H, H300), 8.34 (d, J = 8.35 Hz, 1H, H500),
8.15 (d, J = 9.3 Hz, 1H, H600), 8.03 (m, 3H, H5/7/8),
7.53–7.67 (m, 5H, H20/30/40/50/60); Anal. Calcd for
C21H13O5FN4 (420.36): C, 60.00; H, 3.12; N, 13.33.
Found: C, 59.89; H, 3.17; N, 13.30.
(NH), 1622 (s, C@N), 1603 (m, C@C), 1139 (C–F); H
1
NMR (DMSO-d6, 500 MHz): d (ppm) 6.98 (s, 1H,
H3), 7.70 (d, J = 7.90 Hz, 1H, H5), 7.60 (m, 1H, H6),
7.67 (m, 1H, H7), 7.21 (d, J = 8.03 Hz, 1H, H8), 8.28
(d, J = 7.98 Hz, 2H, H20/60), 8.38 (d, J = 8.02 Hz, 2H,
H30/50), 8.75 (d, J = 1.98 Hz, IH, H300), 8.62 (dd,
J = 7.78/2.02 Hz, IH, H500), 8.50 (d, J = 7.49 Hz, 1H,
H600); Anal. Calcd for C21H13FO5N4 (420.36): C,
60.00; H, 3.12; N, 13.33. Found: C, 60.07; H, 3.10; N,
13.39.
6.3.8. 2-(2,4-Dinitrophenyl)-1-(2-(20-iodophenyl)-6-chlo-
ro-4H-chromen-4-ylidene)hydrazine (C8). Yield: 82%;
mp 250–251 °C; MS (EI): m/z (%) = 564 [M+2] (70),
562 [M+] (100), 435 [M+ꢁX] (7), 545 [M+ꢁOH] (6),
486 [M+ꢁC6H4] (31), 440 [M+ꢁC6H4–NO2] (22); IR
(film): ~m ¼ 3425 cmꢁ1 (NH), 1616 (s, C@N), 1601 (m,
6.3.12. 2-(2,4-Dinitrophenyl)-1-(2-(30,40-dimethoxyphe-
nyl)-4H-chromen-4-ylidene)hydrazine (C12). Yield: 82%;
mp 268–270 °C; MS (EI): m/z (%) = 462 [M+] (100),
400 [M+ꢁX] (7), 445 [M+ꢁOH] (52), 386 [M+ꢁC6H4]
1
C@C), 1097 (C–X); H NMR (DMSO-d6, 500 MHz): d
(ppm) 6.59 (s, 1H, H3), 8.84 (d, J = 1.75 Hz, 1H, H5),
7.78 (dd, J = 8.90/1.96 Hz, 1H, H7), 7.34 (d,
J = 7.75 Hz, 1H, H8), 7.91 (dd, J = 8.35/2.61 Hz, 1H,
H30), 6.72 (m, 1H, H40), 7.69 (m, 1H, H50), 7.58 (dd,
J = 7.09/4.12 Hz, 1H, H60), 8.28 (s, IH, H300), 8.06 (dd,
J = 8.20/2.45 Hz, IH, H500), 8.03 (d, J = 8.60 Hz, 1H,
H600), 11.24 (s, 1H, N–H); Anal. Calcd for C21H12I-
ClO5N4 (562.71): C, 44.82; H, 2.15; N, 9.96. Found:
C, 44.88; H, 2.11; N, 9.99.
(42), 340 [M+ꢁC6H4–NO2] (87); IR (film):
ꢁ1
~
m ¼ 3410 cm (NH), 1618 (s, C@N), 1608 (m, C@C),
1090 (C–OMe); 1H NMR (DMSO-d6, 500 MHz): d
(ppm) 3.90 (s, 6H, 2-OMe), 7.08 (s, 1H, H3), 7.92 (dd,
J = 7.50/1.49 Hz, 1H, H5), 7.51 (m, 1H, H6), 7.87 (dd,
J = 7.06/1.47 Hz, 1H, H7), 7.41 (dd, J = 8.0/2.14 Hz,
1H, H8), 8.32 (s, 1H, H20), 8.15 (d, J = 8.30 Hz, 1H,
H50), 8.01 (d, J = 8.03 Hz, 1H, H60), 8.88 (d,
J = 2.0 Hz, IH, H300), 8.84 (dd, J = 7.75/2.01 Hz, IH,
H500), 8.81 (d, J = 7.77 Hz, 1H, H600); Anal. Calcd for
C23H18O7N4 (462.42): C, 59.74; H, 3.92; N, 12.12.
Found: C, 59.78; H, 3.88; N, 12.19.
6.3.9. 2-(2,4-Dinitrophenyl)-1-(2-(20-iodophenyl)-6-bro-
mo-4H-chromen-4-ylidene)hydrazine (C9). Yield: 82%;
mp 152–153 °C; MS (EI): m/z (%) = 609 [M+2] (54),
607 [M+] (100), 480 [M+ꢁX] (10), 590 [M+ꢁOH] (26),
531 [M+ꢁC6H4] (36), 485 [M+ꢁC6H4–NO2] (70); IR
Acknowledgement
ꢁ1
1
~
(film): m ¼ 3310 cm (NH), 1612 (s, C@N), 1596 (m,
C@C), 757 (C–X); H NMR (DMSO-d6, 500 MHz): d
Author (Z.H.) is grateful to Prof. Dr. W. Gaertner at
the MPI for Bioinorganic Chemistry, Muelheim,
Germany, for his comments and corrections during the
preparation of the manuscript.
(ppm) 6.53 (s, 1H, H3), 8.83 (d, J = 2.50 Hz, 1H, H5),
7.76 (dd, J = 8.30/2.01 Hz, 1H, H7), 7.40 (d,
J = 7.50 Hz, 1H, H8), 7.98 (dd, J = 8.35/20.68 Hz, 1H,
H30), 6.74 (m, 1H, H40), 7.59 (m, 1H, H5 ), 7.50 (dd,
J = 7.35/3.98 Hz, 1H, H60), 8.24 (s, IH, H300), 8.21 (dd,
J = 8.01/2.47 Hz, IH, H500), 8.05 (d, J = 8.36 Hz, 1H,
H600), 11.24 (s, 1H, N–H); Anal. Calcd for
C21H12BrIO5N4 (607.16): C, 41.54; H, 1.99; N, 9.23.
Found: C, 41.58; H, 2.02; N, 9.20.
References and notes
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E. Ullah Mughal et al. / Bioorg. Med. Chem. 14 (2006) 4704–4711
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