photodimerization of heteroaryl chalcones: comparative antimicrobial activities of chalcones and...
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ORIGINAL RESEARCH
Photodimerization of heteroaryl chalcones: comparativeantimicrobial activities of chalcones and their photoproducts
Rekha Nagwanshi • Meena Bakhru •
Shubha Jain
Received: 15 December 2010 / Accepted: 10 May 2011 / Published online: 29 May 2011
� Springer Science+Business Media, LLC 2011
Abstract The heterocyclic analogues of chalcones were
synthesized by Claisen Schmidt reaction of (a) benzaldehyde
with 2-acetylfurane, 2-acetylpyrrole and 2-acetylthiophene
and (b) acetophenone with furfural, thiophene-2-carbalde-
hyde and pyrrole-2-carbaldehyde. The photolysis of class
(a) and (b) chalcones under UV lamp gave different products.
The stereoselective photodimerization of 1-(furane-2-yl)-
3-phenylprop-2-en-1-one (1), 3-phenyl-1-(1H-pyrrole-2-yl)-
prop-2-en-1-one (2) gave b-truxinic type dimers,
(3,4-diphenylcyclobutane-1,2-diyl)bis (furane-2-yl metha-
none) (7), (3,4-diphenylcyclobutane-1,2-diyl)bis ((1H-pyrrol-
2-yl) methanone) (8) by syn head-to-head coupling whereas
3-phenyl-1-(thiophen-2-yl)-prop-2-en-1-one (3) gave d-tru-
xinic type dimers, (3,4-diphenylcyclobutane-1,2-diyl)bis
(thiophen-2-yl methanone) (9) by anti head-to-head coupling.
The photolytic products of 3-(furane-2-yl)-1-phenylprop-2-
en-1-one (4), 1-phenyl-3-(thiophen-2-yl)-prop-2-en-1-one (5)
and 1-phenyl-3-(1H-pyrrole-2-yl)- prop-2-en-1-one (6) were
identified as corresponding 1,6-di(furane-2-yl)-3,4-diphenyl-
hexa-1,5-diene-3,4-diol (10), 3,4-diphenyl-1,6-di(thiophen-
2-yl)hexa-1,5-diene-3,4-diol (11) and 3,4-diphenyl-1,6-di
(1H-pyrrol-2-yl)hexa-1,5-diene-3,4-diol (12) pinacol dimers.
The antibacterial and antifungal activity of the precursor
chalcones and the dimeric products showed antimicrobial
activities of different extents with respect to individual com-
pounds. In general, photolysis of heteroaryl chalcones causes
the depletion of antimicrobial activity.
Keywords Chalcones � Photodimerization �Pinacol dimer � Cyclobutane dimer � Antimicrobial activity
Introduction
Chalcones (1,3-diaryl-2-propen-1-ones), the largest class of
plants secondary metabolites, are natural or synthetic
compounds belonging to the flavonoid family. Chalcones
and their heterocyclic analogues exert various biological
activities. Their antibacterial properties were intensively
studied in the late 1940s. Chalcones and their analogues are
used as anti-inflammatory (Viana et al., 2003), analgesic
(Viana et al., 2003), antiulcerative (Lin et al., 1999),
antiviral (Cheenpracha et al., 2006), antifungal (Opletalova
and Sedivy, 1999), antimalarial (Domı́nguez et al., 2005),
bactericidal (Rajendra et al., 2005), insecticidal (Nowa-
kowska et al., 2001), anti-fertility (Jacob and Kaul, 1973),
sedative (Reddy et al., 2008) and anti-cancer agent (Shar-
ma et al., 2010; Srinivasan et al., 2009) etc. Chemically
they consist of open-chain flavonoids in which the two
aromatic rings are joined by a 3-carbon a,b-unsaturated
carbonyl system. In terms of structure, the compounds can
be divided into three groups: 3-(aryl, heteryl)-1-phenyl-1-
propen-3-one derivatives (1st group), 1-(aryl, heteryl)-
3-phenyl-1-propen-3-one derivatives (2nd group) and
disubstituted chalcone derivatives (3rd group) (Rtishchev
et al., 2001). The 1st group chalcones are prepared by the
condensation of heteroaryl aldehyde with acetophenone,
Electronic supplementary material The online version of thisarticle (doi:10.1007/s00044-011-9667-4) contains supplementarymaterial, which is available to authorized users.
R. Nagwanshi (&)
Department of Chemistry, Government College Barnagar,
Ujjain, Madhya Pradesh, India 456010
e-mail: [email protected]
M. Bakhru � S. Jain
School of Studies in Chemistry & Biochemistry, Vikram
University, Ujjain, Madhya Pradesh, India 456010
123
Med Chem Res (2012) 21:1587–1596
DOI 10.1007/s00044-011-9667-4
MEDICINALCHEMISTRYRESEARCH
whereas 2nd group chalcones are prepared by the reaction
of heteroaryl ketone with benzaldehyde (Alexander et al.,
1950). The photolysis of 1st and 2nd group chalcones give
different products. There are few reports on the photolytic
product, i.e. d-truxinic type dimer of 2nd group chalcones
(Yayli et al., 2005). There is no report on the pinacol
dimeric product of 1st group chalcone to the best of our
knowledge.
Intramolecular photocycloaddition of chalcones, het-
eroaryl chalcones and their derivatives to give cyclobutane
ring is the photochemical dimerization of a,b-unsaturated
carbonyl compounds and particular of 1,3-diaryl-2-propen-
1-one (chalcones) (D’Auria et al., 2000; 2001; Toda et al.,
1998; Cesarin-Sobrinho and Netto-Ferreira, 2002; Turo-
wska-Tryk et al., 2003; Ishikawa et al., 1994). It has been
proven to be a fast and simple method to minimize a
cyclophane ring to a tricyclic system. These reactions can
be carried out in solid state (Cesarin-Sobrinho and Netto-
Ferreira, 2002), molten state (Toda et al., 1998) and solu-
tion by UV–Visible irradiation (D’Auria et al., 2001), with
variable results in terms of product composition and yield.
Although, photodimerization of chalcones have been
studied especially in solid state (Turowska-Tryk et al.,
2003), few studies found for the photodimerizations of
chalcones in solution. Therefore, the need is still high for
unstudied photodimerizations of heteroaryl chalcones,
stereoselectively in solution.
The cycloaddition of trans-chalcones may give four
possible stereoisomers, namely syn, anti, head-to-head and
head-to-tail. The formation of different stereoisomers in the
dimerization of chalcones and related compounds may be
dependent on the physical state of the substrate (solution,
solid and molten state). In these cases, a regiospecific ring
closure is certainly favoured by structures of the precur-
sors. In the literature, various cyclobutane containing
chalcones have been reported to be synthesized and iso-
lated from various plants (Seidel et al., 2000; Katerere
et al., 2004; D’Auria and Racioppi, 1998). Analogues to
these dimers of chalcones, two new dimers of heteroaryl
chalcones were synthesized steroselectively in this study.
In this investigation, all the heteroaryl chalcones have
been prepared by reported method (Alexander et al., 1950)
according to the route in Scheme 1. These heteroaryl
chalcones, when exposed to UV light (125 W low-pressure
Hg lamp), are converted to the respective (a) cyclobutanes
and (b) pinacol dimers as major products, with the yields
(chromatographated products, PTLC) of 62% (1) and 52%
(2). The minor products of these reactions were less than
5% which were not characterized.
In the literature, antiviral and antimicrobial activities of
chalcones were studied but, antimicrobial activity of the
heteroaryl chalcones was not reported. Thus, the antibac-
terial and antifungal activity of all the chalcones and their
dimerization products were tested by using disc diffusion
assay.
Experimental
The precursors required for synthesis viz. furfural, thio-
phene-2-carbaldehyde, pyrrole-2-carbaldehyde, 2-acetyl-
furan, 2-acetylthiophene, 2-acetylpyrrole were purchased
from Lanchaster.
All the chalcones were synthesized using the general
synthetic protocol. In general, to a cold solution of het-
eroaryl ketone and benzaldehyde or heteroaryl aldehyde
and acetophenone in dry ethanol, a strong solution of KOH
(3.5 gm in 5 ml of water) was added with constant stirring
at 0–5�C. The solution was neutralized with 5% HCl. The
precipitated product was filtered, washed with water and
recrystallized from ethanol.
1. 1-(2-furyl)-3-phenyl-2-propen-1-one. Light yellow
flakes, m. p. 89�C. (lit. m. p. 88.2–89.5�C, Shibata
et al., 1991). 1H NMR (CDCl3, 300 MHz) d (ppm): 7.92–
7.86 (d, J = 18 Hz), 7.68–7.64 (m, 3H); 7.49–7.39 (m,
4H), 7.35–7.34 (d, J = 3 Hz), 6.61–6.59 (m, 1H). 13C
NMR (CDCl3, 60 MHz) d (ppm): 178.3, 153.7, 146.7,
144.3, 134.9, 130.9, 129.1, 128.7, 121.3, 117.6, 112.7.
2. 1-(1H-pyrrol-2-yl)-3-phenyl-2-propen-1-one. Dark
yellow amorphous solid, m. p. 141�C. (lit. m. p.
140–142�C, Matoba and Yamazakit, 1982). 1H NMR
(CDCl3, 300 MHz) d (ppm): 10.30 (b s, 1H), 7.90–
7.84 (d, J = 18 Hz); 7.68–7.64 (m, 2H), 7.48–7.37 (m,
4H), 7.18–7.11 (m, 1H), 6.39-6.36 (m, 1H). 13C NMR
(CDCl3, 60 MHz) d (ppm): 179.3, 142.5, 135.3, 133.3,
130.4, 129.1, 128.5, 125.9, 122.2, 116.7, 111.2.
3. 1-(2-thienyl)-3-phenyl-2-propen-1-one. Pale yellow amor-
phous solid, m. p. 83�C. (lit. m. p. 83.6–84�C, Robert
and Nord, 1951). 1H NMR (CDCl3, 300 MHz) d(ppm): 7.30 (d, J = 3 Hz), 7.80 (d, J = 16 Hz), 7.72
(dd, 2H), 7.20 (m, 1H), 7. 90 (dd, 1H), 7.54 (m, 2H).
7.39 (m, 2H), 7.33 (m, 1H). 13C NMR (CDCl3,
60 MHz) d (ppm): 181.7, 127.9, 143.9, 145.5, 131.4,
123.1, 133.4, 135.2, 126.4, 128.7, 128.0, 126.4.
4. 3-(2-furyl)-1-phenyl-2-propen-1-one. Yellow flakes.
m. p. 41�C. (lit. m. p. 47�C, Alexander et al., 1950).1H NMR (CDCl3, 300 MHz) d (ppm): 8.06–8.01 (m,
2H), 7.65–7.44 (m, 6H); 6.74–6.73 (d, J = 3 Hz),
6.54–6.52 (m, 1H). 13C NMR (CDCl3, 60 MHz) d(ppm): 190.0, 151.7, 145.1, 138.4, 132.9, 130.8, 128.7,
128.6, 119.4, 116.4, 112.8.
5. 3-(2-thienyl)-1-phenyl-2-propen-1-one. Dark yellow crys-
talline solid. m. p. 59�C. (lit. m. p. 59–60�C, Robert
and Nord, 1951) 1H NMR (CDCl3, 300 MHz) d (ppm):
8.08 (d, 2H), 8.02 (d, J = 15.9 Hz); 7.70 (dd, 1H),
1588 Med Chem Res (2012) 21:1587–1596
123
7.25 (m, 1H), 8.10 (dd, 1H), 7.79 (m, 2H), 7.38 (m,
2H), 7.75 (m, 1H). 13C NMR (CDCl3, 60 MHz) d(ppm): 188.0, 127.0, 133.1, 137.6, 130.5, 128.2, 127.2,
129.9, 129.2, 134.6, 137.0.
6. 3-(1H-pyrrol-2-yl)-1-phenyl-2-propen-1-one. Dark yel-
low amorphous solid, m. p. 138–139�C. (lit. m. p. 138–
139�C, Lubrzynska, 1916) 1H NMR (CDCl3, 300
MHz) d (ppm): 9.19 (b s, 1H), 8.0–7.97 (m, 2H); 7.81–
7.75 (d, 1H), 7.60–7.45 (m, 3H), 7. 20–7.16 (d,
J = 12 Hz), 7.01(s, 1H), 6.73 (s, 1H), 6.36–6.33 (m,
1H). 13C NMR (CDCl3, 60 MHz) d (ppm): 190.9,
135.2, 132.6, 128.8, 128.6, 123.5, 116.0, 115.6, 111.7.
Photolysis of 1-6 in solution
Solutions of compounds 1–6 (1.6 mM) in 200 ml of etha-
nol, kept in a Pyrex flask, were exposed to UV light (125
low-pressure mercury lamp) inside a SAIC make immer-
sion well photoreactor. The progress of the reactions was
followed by silica gel TLC (n-hexane–benzene, 1:1). The
reactions completed in 28, 33, 25, 22, 30 and 25 h
respectively for compounds 1–6. The solutions were
evaporated, and residues were purified by column chro-
matography to give products: 7 (1.04 g, 52% yield, 6–9
fractions, n-hexane–benzene); 8 (0.98 g, 49% yield, 9–12
fraction, benzene–ethyl acetate); 9 (1.18 g, 59% yield, 2–4
fractions, n-hexane); 10 (1.2 g, 60% yield, 5-6 fractions,
n-hexane–benzene); 11 (1.12 g, 56%, 2-3 fractions,
n-hexane); 12 (1.15 g, 57.5%, 9-10 fractions, benzene–
methanol). The assignments of the NMR peaks for the
products 7, 8 and 9 were given to the protons on the basis
of the position given in structure I.
A'
B
B'
A
1
23
4
1'
2' 3'
4'
OX
O X
X = O (4), S(5), NH(6)
1"
2"3"
4"
5"6"
1. (3,4-diphenylcyclobutane-1,2-diyl)bis (furane-2-yl meth-
anone), Yellowish amorphous solid, m. p. 103�C. FT-
IR (cm-1): 3028 (arom. CH str.), 2931, 2836 (aliph.
CH str.), 1645 (C=O str.), 1561, 1464 (arom. C=C str.),
1390 (aliph. CH bend.), 1272 (O–C str.), 768, 746 (aryl
CH bend.); 1H NMR (CDCl3, 300 MHz) d (ppm): 4.50
[m, H-1,2], 4.14 [m, H-3,4], 6.90 [d, H-20], 6.98–7.08
[dd, H-30], 7.20 [d, H-40], 7.14–7.18 [m, phenyl]; 13C
CH3
O
X+ H
O
X
O
hv, EtOH
OO
X X
NaOH95 % EtOH
X = O (1), NH (2), S (3)
Route (a)
X = O (7), NH (8), S (9)
H
O
X+ H3C
O
NaOH95 % EtOH
X = O (4), S (5), NH (6)
X
O
hv, EtOH
X
X
OH
OH
Route (b)
X = O (10), S (11), NH (12)
Scheme 1 Synthesis of
chalcones and their
photoproduct
Med Chem Res (2012) 21:1587–1596 1589
123
NMR (CDCl3, 60 MHz) d (ppm): 48.45 [C-1,2], 47.70
[C-3,4], 186.82 [CO], 152 [C-10], 118 [C-20], 112 [C-
30], 147 [C-40], 142, 129, 128.3, 127.9 [phenyl]; FAB
Mass (m/z): 396 (M?), 368, 329, 301, 289, 217, 198
(monomer peak), 197, 121, 115, 105, 95.
Elemental analysis: calculated for C26H20O4: C 78.78%,
H 5.05%. Found 78.75, H 5.12.
2. (3,4-diphenylcyclobutane-1, 2-diyl)bis ((1H-pyrrol-2-
yl) methanone), Light yellowish amorphous solid, m.
p. 141�C. FT-IR (cm-1): 3298 (NH str.), 3010 (arom.
and heteroarom. CH str.), 2924, 2838 (aliph. CH str.),
1640 (C=O str.), 1548 (NH bend.), 1500, 1410 (arom.
and heteroarom. C=C ring str.), 1350 (aliph. CH
bend.), 1290 (C–N str.), 1110, 1050 (C–O str.), 950,
850, 753, 700 cm-1 (out of plane arom. CH bend.); 1H
NMR (CDCl3, 300 MHz) d (ppm): 4.77 [m, H-1,2],
4.48 [m, H-3,4], 6.35 [d, H-20], 7.05 [dd, H-30], 7.65 [d,
H-40], 7.26–7.40 [m, phenyl], 9.6 [s, NH]; 13C NMR
(CDCl3, 60 MHz) d (ppm): 47.74 [C-1,2], 46.90 [C-
3,4], 191.82 [CO], 132 [C-10], 117 [C-20], 111 [C-30],125 [C-40], 140, 127, 128.3 [phenyl]; FAB Mass: m/z
395 [M ? 1], 394 [M?], 328, 304, 300, 272, 215, 197
(monomer peak), 169, 131, 94.
Elemental analysis: calculated for C26H22O2N2: C
79.18%, H 5.68%, N 7.10%; Found 79.20, H 5.62, N 7.15.
3. (3,4-diphenylcyclobutane-1, 2-diyl)bis (thiophen-2-yl
methanone), Grayish white, crystalline solid, m. p.
105�C. FT-IR (cm-1): 3103, 3085 (arom. CH str.),
2964, 2925 (aliph. CH str.), 1642 (C=O str.), 1549,
1518, 1452, 1411 (arom. C=C str.), 1355, 1302 (aliph.
CH bend.), 1156, 1060 (C–CO–C str. and bend.), 991,
967, 639, 753, 727 (out of plane arom. CH bend.), 610
(C–S str.); 1H NMR (CDCl3, 300 MHz) d (ppm): 4.56
[m, H-1,2], 3.95 [m, H-3,4], 7.44 [d, H-20], 6.90 [dd,
H-30], 7.75 [d, H-40], 7.3–7.42 [m, phenyl]; 13C NMR
(CDCl3, 60 MHz) d (ppm): 48.54 [C-1,2], 47.57 [C-
3,4], 191.82 [CO], 143 [C-10], 133 [C-20], 128.7 [C-30],134 [C-40], 142, 129, 128.3, 127 [phenyl]; FAB Mass:
m/z 429 [M ? 1], 428 [M?], 351, 317, 305, 249, 227,
214 (monomer peak), 180, 111, 103. Elemental
analysis: Calculated for C26H20O2S2: C 72.89%, H
4.67%, S 14.95. Found 72.82, H 4.70, S 14.98.
4. 1,6-di (furan-2-yl)-3,4-diphenylhexa-1,5-diene-3,4-
diol, Light yellow solid, m. p. 80�C. FT-IR (cm-1):
3479 (OH str.), 3086, 3098 (arom. and heteroarom. CH
str.), 1605 (olefinic C=C str.), 1575, 1519, 1498, 1447
(arom. and heteroarom. C=C ring str.), 1415, 1310 (in
plane O–H bend.), 1285, 1242, 1082 (asym. and sym.
C–O str.), 973, 858, 849, 763, 734 (out of plane arom.
C–H bend.), 686 (ring C=C str.), 662 (out of plane
arom. C–H bend.) cm-1; 1H NMR (CDCl3, 300 MHz)
d (ppm): 7.0 [d, H-2,3], 6.6 [d, H-5], 6.9 [dd, H-6], 7.4
[d, H-7], 7.9 [s, C–OH], 7.1–7.25 [m, phenyl]; 13C
NMR (CDCl3, 60 MHz) d (ppm): 132 [C-2], 122 [C-
3], 144 [C-4], 112 [C-5], 116 [C-6], 146 [C-7], 135,
130, 129.7, 129.3 [phenyl], 95.82 (C–OH), FAB Mass:
m/z 398 [M?], 364, 329, 244, 199 (monomer peak),
198, 182, 115, 105.
Elemental analysis: calculated for C26H22O4: C 78.39%,
H 5.52%; Found C 78.37%, H 5.57.
5. 3,4-diphenyl-1,6-di (thiophen-2-yl) hexa-1,5-diene-
3,4-diol, Crystalline creamy white solid, m. p. 119–
120�C, gives positive test for sulphur. FT-IR (cm-1):
3250–3300 (OH str.), 3007 (arom. and heteroarom. C–
H str.), 1670 (olefinic C=C str.), 1545, 1498, 1452
(arom. and heteroarom. C=C ring str.), 1400 (OH
bending), 1150, 1045 (asym. and sym. C–O str.), 930,
810, 750 (out of plane C–H bend.), 698 (ring C=C
bend.), 650 (out of plane O–H bend.), 610 (C–S str.);1H NMR (CDCl3, 300 MHz) d (ppm): 7.2 [d, H-5,6],
6.94 [dd, H-6], 7.6 [d, H-7], 7.1 [s, C–OH], 7.26–7.35
[s, phenyl], 6.82 [d, H-3], 7.0 [d, H-2]; 13C NMR
(CDCl3, 60 MHz) d (ppm): 132 [C-2], 121 [C-3], 142
[C-4], 124.6 [C-5], 125 [C-6], 129 [C-7], 135, 127,
128.3, 130 [phenyl], 92.82 (C–OH); FAB Mass: m/z
430 [M?], 429, 396, 353, 345, 259, 237, 215 (mono-
mer peak), 119, 105, 95.
Elemental analysis: calculated for C26H22O2S2: C
72.55%, H 5.11%, S 14.88%; Found C 72.607%, H 5.17%,
S 14.85%.
6. 3,4-diphenyl-1,6-di (1H-pyrrol-2-yl) hexa-1,5-diene-
3,4-diol, Light brown solid, m. p. 121�C. FT-IR
(cm-1): 3430 (OH str.), 3295 (N–H str.), 3085, 3028
(arom. and heteroarom. C–H str.), 1621 (N–H bend and
olefinic C=C str.), 1543, 1495, 1453 1427 (arom. and
heteroarom. C=C ring str.), 1405 (O–H bend.), 1288 (C–
N str.), 1109, 1043 (asym. and sym. C–O str.), 885, 842,
750 (out of plane arom. C–H bend.), 698 (ring C=C
bend.); 1H NMR (CDCl3, 300 MHz) d (ppm): 6.6 [s, H-
2], 6.2 [s, H-3], 7.2 [d, H-5], 7.7 [dd, H-6], 7.9 [d, H-7],
6.9 [s, C–OH], 7.4–7.5 [m, phenyl], 10.4 [s, NH]; 13C
NMR (CDCl3, 60 MHz) d (ppm): 131 [C-2], 123 [C-3],
134 [C-4], 114 [C-5], 110 [C-6], 115 [C-7], 138, 127-
128.3 [phenyl], 94(C–OH); FAB Mass: m/z 396 [M?],
362, 288, 212, 198 (monomer peak), 181, 105, 91.
Elemental analysis: calculated for C26H24N2O2: C
78.78%, H 6.06%, N 7.07%; Found C 78.65%, H 6.10%, N
6.98%.
1590 Med Chem Res (2012) 21:1587–1596
123
The antimicrobial activity measurements
All test micro-organisms were obtained from Department
of Microbiology, Vikram University Ujjain and were as
follows: Citrobactor sruendi, Klebsiella pneumoniae,
Proteus vulgaris, Bacillus megaterium, Escherichia coli,
Pseudomonas aeruginosa, Micrococcus luteus, Serratia
marcescens, Aspergillus oryzae, Aspergillus niger, Fusar-
ium moniliformae and Candida albicans.
All the synthesized compounds were dissolved in rec-
tified ethanol for dilution to prepare stock solutions of 10–
60 lg/ml for antimicrobial assay. The antimicrobial
activities of the substrates were tested by disc diffusion
(Midolo et al., 1995; Drew et al., 1972) and poisoned food
technique (Shakil et al., 2010). Quantitatively in high
media muller hinton agar and potato dextrose agar and the
minimum inhibitory concentration (MIC) values (lg/ml)
were determined. The MIC was defined as the lowest
concentration that showed no growth of microorganisms.
Ampicillin and fluconazole were used as standard antimi-
crobial and antifungal drugs, respectively. Rectified etha-
nol was used as solvent control.
Results and discussion
Photolysis of compounds 1–3
Scheme 1 illustrates the synthetic approach chosen for
the preparation of dimeric products of 1-(furan-2-yl)-3-
phenylprop-2-en-1-one (1), 1-(1H-pyrrol-2-yl)-3-phenyl
prop-2-en-1-one (2) and 1-(thiophen-2-yl)-3-phenyl-prop-
2-en-1-one (3). The most noticeable feature of the structural
characterization of 1, 2 and 3 chalcones is the assignment of
the proton resonances of a,b-unsaturated moiety, which was
made by a careful analysis of their 1H and 2D COSY NMR.
On the basis of the vicinal coupling constants (3JHa-Hb 16.4/
15.8/15.8 Hz, respectively), the trans configuration of these
two protons is suggested. Two symmetrical multiplets
(AA0BB0) at dH 4.50 (dC 48.45)/dH 4.14 (dC 47.70) for
product 7, and at dH 4.77 (dC 47.74)/dH 4.48 (dC 46.90)
for product 8 and at dH 4.56 (dC 48.54)/dH 3.95 (dC 47.57)
for product 9 were observed for the cyclobutyl protons in 1H
NMR spectra. Simulation of these NMR patterns has
allowed the calculation of the coupling constants of the
cyclobutyl protons (JAA0 = 6.6/6.1, JAB = 4.1/4.2, JAB0 =
1.5/1.9, JBB0 = 6.6/6.1, respectively) for products 7 and 8
and (JAA0 = 9.2/9.0, JAB = 5.2, JAB0 = not detected,
JBB0 = 8.6, respectively) for product 9 (Rajendra et al.,
2005; Reddy et al., 2008; Robert and Nord, 1951; Rtishchev
et al., 2001; Seidel et al., 2000; Shakil et al., 2010; Sharma
et al., 2010; Shibata et al., 1991).
The values of these coupling constants and 1H and 13C
NMR patterns of the cyclobutyl moieties of products 7 and
8 suggest that the formation of cyclobutane ring occurs by
syn head-to-head junction to give b-truxinic structure
(D’Auria et al., 2001, 2002), different from the earlier
studies (D’Auria et al., 2000, 2001, 2002). The close
similarity of the 1H and 13C NMR patterns of the cyclo-
butyl moieties of product 9 with d-truxinic structure
strongly suggests that the formation of cyclobutane ring
occurs by anti head-to-head junction in product 9 (D’Auria
et al., 2001; Toda et al., 1998; Turowska-Tryk et al., 2003).
The positive FAB mass spectra gave M? at m/z 390
(100) for 7, at m/z 394 (100) for 8 and at m/z 428 (100) for
9 which were consistent with the molecular formula to be
C26H20O4 for 7, C26H22N2O2 for 8 and C26H20O2S2 for 9
requiring dimeric structure (Scheme 3). FAB mass showed
a typical chalcone fragmentation with a fragment ions for 7
at m/z 198 (chalcone monomer, C13H10O2), for 8 at m/z 197
(chalcone monomer, C13H11NO) and for 9 at m/z 214
(chalcone monomer, C13H10OS). The other important
fragments were obtained as shown in Scheme 2.
The products 7–9 were characterized on the basis of
spectral data evaluations (1H, 13C, 1H—1H COSY NMR,
FT-IR, UV–Vis and FAB Mass), whose results were in
agreement with the proposed structures. Based upon the
above observation, the complete chemical shift assign-
ments for 7, 8 and 9 were deduced. Products 7, 8 and 9
were thus shown to be (1b, 2a)-di-(2-oxenoyl)-(3b,4a)-di-
(4-phenyl)cyclobutane (7) and (1a,2a)-di-(2-azaenoyl)-
(3b,4b)-di-(4-phenyl)cyclobutane (8) and (1a,2a)-di-(2-
thienoyl)-(3b,4b)-di-(4-phenyl)cyclobutane (9).
Photolysis of compounds 4–6
On the basis of spectral and elemental analyses, it has been
found that the chalcones undergo H-abstraction reaction
followed by dimerization on irradiation (Scheme 1b) giving
the pinacols 10, 11 and 12 with good yields. The formation of
pinacols was established from the 1H NMR spectra which
show singlet for OH proton in the region 6.9–7.9. The
structures of the products were confirmed by 1H NMR, 13C
NMR and IR spectral data. The FAB mass gave M? ion at
398 and [M ? H] at 399 m/z for compound 4, at 430 and
431 m/z for compound 5 and at 396 and 399 m/z for com-
pound 6 which were consistent with their molecular weights.
The chalcone monomer fragment ions were observed at m/z
199, 215 and 198 for 10, 11 and 12, respectively. The other
important fragments were obtained as shown in Scheme 3.
Antimicrobial activity
The antimicrobial activity of all the compounds (1–12) was
determined (Tables 1, 2, 3, 4). The activities of the
Med Chem Res (2012) 21:1587–1596 1591
123
synthesized compounds were investigated by disc diffusion
and potato dextrose assays. The compounds 1–12 showed
antimicrobial activity against Gram-positive bacteria,
Gram-negative bacteria, fungi and yeast. The compounds
showed better antimicrobial activity against Gram-positive
bacteria compared to Gram-negative bacteria. Compounds
1–6 exhibited broad spectrum antimicrobial activity. Fig-
ure 1 shows the antibacterial activities of both the class of
chalcones, e.g. 1-(2-thienyl)-3-phenyl-2-propen-1-one and
3-(2-furyl)-1-phenyl-2-propen-1-one and antifungal activi-
ties of 1-(2-thienyl)-3-phenyl-2-propen-1-one and 3-(2-
furyl)-1-phenyl-2-propen-1-one. It is evident from figure
that antibacterial and antifungal activities increase with
increasing the concentration of chalcones in the range 10–
60 lg/disc. These six compounds were active against all
test organisms except for E. coli, P. aeruginosa, S. typhi
and S. marcescens (Supporting information). The MIC
values for test micro-organisms were between 10 and
40 lg/ml. Compounds 4 and 5 were specifically effective
against B. megaterium, P. vulgaris with the MIC values of
20 lg/ml respectively. The comparison of percentage
antimicrobial activities relative to that of Streptomycin and
Fluconazole revealed that the monomeric starting com-
pounds were more active than the dimers. Compounds 1
and 2 were found to be highly effective antimicrobial
agents. A little increase was observed in the antimicrobial
activity of the monomer against K. pneumoniae and
S. typhi. The anti bacterial and antifungal activities of the
heteroaryl chalcones both make them potential agents for
the cure of bacterial and fungal infections.
The antimicrobial strains reveal that the heteroaryl
substitutions on the parent chalcones (II) showed differ-
ential activities (Fig. 1 and Supporting informations).
Amongst the heterocyclic analogues of chalcones having
furane, thiophene and pyrrole as A ring (Class (a) chal-
cones) were found to be more active against most of the
bacterial and fungal strains than the chalcones having these
heterocyclic rings their B ring (class (b) chalcones). The
presence of heteroaryl ring at the place of phenyl ring of
benzoyl group makes it more basic which increases its
OO
X X
X
O
X OO
X = O (7), m/z 396X = NH (8), m/z 394X = S (9), m/z 428
X = O (1), m/z 198X = NH (2), m/z 197X = S (3), m/z 214
X = O, m/z 95X = S, m/z 111X = NH, m/z 94
m/z 131
m/z 103m/z 180
Scheme 2 Fragmentation of
cyclobutane-type dimers
X
X
OH
OHX = O (10), m/z 398X = S (11), m/z 430X = NH (12), m/z 396
X
OH
X = O, m/z 199X = S, m/z 215X = NH, m/z 198
XX = O, m/z 93X = S, m/z 96X = NH, m/z 92
m/z 212
HO OH
X
XX = O, m/z 364X = S, m/z 396X = NH, m/z 362
Om/z 105
Scheme 3 Fragmentation of
pinacol dimers
1592 Med Chem Res (2012) 21:1587–1596
123
penetrating power on bacterial cell wall, and the com-
pounds becomes more active. In these cases, heteroaryl
part is associated with the lipophilic region of the bacterial
cell wall which makes them more active. Class a chalcone
having O atom in a ring was observed to be more active
than the ring containing S and N atoms. Later two
Table 1 Comparative antibacterial activity of class (a) chalcones with dimeric products
S. no. Bacteria Diameter of zone of inhibition in mm (lg)
Comp. 1 Comp. 2 Comp. 3 Comp. 7 Comp. 8 Comp. 9
1. Citrobactor sruendi 13 (10) 6 (20) 7 (20) 5 5 5
2. Klebsiella pneumoniae 7 (10) 8 (20) 10 (10) 5 5 5
3. Proteus vulgaris 8 (10) 5 (10) 11(20) 7 5 5
4. Bacillus megaterium 11 (10) 13 (10) 10 (10) 5 5 9
5. Escherichia coli 5 (10) 7 (30) 5 (10) 5 5 5
6. Pseudomonas aeruginosa 5 (10) 7 (40) 5 (10) 5 6 5
7. Salmonella typhi 5 (10) 7 (50) 12(10) 5 5 6
8. Micrococcus luteus 11 (10) 7 (10) 9 (10) 7 5 7
9. Serratia marcescens 5 (10) 9 (10) 9 (20) 5 5 5
Table 2 Comparative antibacterial activity of class (b) chalcones with pinacol products
S. no. Bacteria Diameter of zone of inhibition in mm (lg)
Comp. 4 Comp. 5 Comp. 6 Comp. 10 Comp. 11 Comp. 12
1. Citrobactor sruendi 7 (10) 6 (20) 9 (20) 9 5 5
2. Klebsiella pneumoniae 6 (10) 8 (20) 9 (20) 5 7 5
3. Proteus vulgaris 9 (10) 6 (20) 5 (10) 9 5 5
4. Bacillus megaterium 9 (10) 5 (10) 12 (10) 7 5 5
5. Escherichia coli 5 (10) 5 (10) 6 (10) 5 5 5
6. Pseudomonas aeruginosa 5 (10) 5 (10) 9 (40) 5 5 5
7. Salmonella typhi 5 (10) 10 (10) 5 (10) 5 7 5
8. Micrococcus luteus 9 (10) 7 (10) 7 (10) 6 8 5
9. Serratia marcescens 7 (10) 7 (10) 7 (10) 5 5 5
Table 3 Comparative antifungal activity of class (a) chalcones with dimeric products
S. no. Fungi Diameter of zone of inhibition in mm (lg)
Comp. 1 Comp. 2 Comp. 3 Comp. 7 Comp. 8 Comp. 9
1. Aspergillus oryzae 8 (10) 9 (30) 9 (10) 5 5 5
2. Aspergillus niger 11 (10) 11 (20) 7 (20) 5 5 5
3. Fusarium moniliformae 7 (20) 8 (30) 9 (10) 6 5 5
4. Candida albicans 7 (20) 7 (10) 9 (40) 5 5 5
Table 4 Comparative antifungal activity of class (b) chalcones with pinacol products
S. no. Fungi Diameter of zone of inhibition in mm (lg)
Comp. 4 Comp. 5 Comp. 6 Comp. 10 Comp. 11 Comp. 12
1. Aspergillus oryzae 8 (30) 9 (30) 9 (10) 5 5 9
2. Aspergillus niger 8(10) 7 (30) 7 (50) 9 5 5
3. Fusarium moniliformae 7 (20) 7 (10) 8 (40) 7 5 5
4. Candida albicans 9 (10) 7 (30) 6 (40) 5 5 5
Med Chem Res (2012) 21:1587–1596 1593
123
exhibited almost similar activity. Similarly, class b chal-
cone having O atom in A ring showed somewhat greater
activity than the chalcones containing S and N atoms. This
can be explained on the basis of the fact that oxygen is
most basic amongst O, N and S.
The comparative antibacterial and antifungal activities
of the chalcones and their photoproducts are summarized in
Tables 1, 2, 3 and 4. The comparison of antibacterial
activities of chlacones relative to that of standard Strep-
tomycin and Fluconazole revealed that the monomeric
starting compounds (chalcones) were more active than the
dimer (photolyzed product). This may be because the
dimerization reduces the conjugation, a factor responsible
for bacterial activity and thus causes decrease in biological
activities. Thus in case of Class a chalcones antibacterial
activity is decreased in their photoproducts against most of
the strains of bacteria and fungi.
It is reported that the enone function (conjugated keto
group) in the molecule confers antibiotic activity
10 20 30 40 50 60
4
6
8
10
12
14
16
18
20
22In
hibi
tion
Zone
(in
mm
)
Concentration, µg/disc
Citrobactor sruendiKlebsiella pneumoniaeProteus vulgarisBacillus megateriumEscherichia coliPseudomonas aeruginosaSalmonella typhiMicrococcus luteusSerratia marcescens
10 20 30 40 50 60
4
6
8
10
12
14
16
18
20
22
24
26
28
Inhi
bitio
n Zo
ne (I
n m
m)
Concentration, µg/disc
Concentration, µg/disc Concentration, µg/disc
Citrobactor sruendiKlebsiella pneumoniaeProteus vulgarisBacillus megateriumEscherichia coliPseudomonas aeruginosaSalmonella typhiMicrococcus luteusSerratia marcescens
(i) (ii)
10 20 30 40 50 60
5
6
7
8
9
10
11
12
13
14
15
Inhi
bitio
n Zo
ne (I
n m
m)
Aspergillus oryzaeAspergillus nigerFusarium moniliformaeCandida albicans
10 20 30 40 50 60
4
6
8
10
12
14
16
18
Inhi
bitio
n Zo
ne (I
n m
m)
Aspergillus oryzaeAspergillus nigerFusarium moniliformaeCandida albicans
(iii) (iv)
Fig. 1 Antibacterial activity of (a) 1-(2-thienyl)-3-phenyl-2-propen-1-one and (b) 3-(2-furyl)-1-phenyl-2-propen-1-one, (c) antifungal activity of
1-(2-thienyl)-3-phenyl-2-propen-1-one and (d) 3-(2-furyl)-1-phenyl-2-propen-1-one
O
A B
(II)
1594 Med Chem Res (2012) 21:1587–1596
123
(bacteriostatic, bactericidal) upon it. Class (b) chalcones
form pinacol type products on photolysis. In such products
enone group is reduced which may affect the binding
capacity of compounds on receptor-site bacterial cell wall.
Hence, the photolyzed products possess somewhat less
activity than the starting compounds.
The mechanism of antifungal effects of chalcones and
their analogues have not been investigated in greater detail.
Due to the presence of reactive ketovinyl moiety in the
molecule, the compounds of this type are able to react with
the thiol groups of enzymes. It has been reported that the
anticandida activity of chalcone was lost by cyclization to
corresponding flavones or by reduction to dihydrochal-
cones (Opletalova et al., 2000). These results indicate that
the structure of chalcone (1,3-diphenyl-2-propen-1-one) is
fundamental for the growth inhibitory properties to can-
dida. Overall heterocyclic chalcones are more reactive
than their photolyzed products. As the dimerization or
H-abstraction reactions decrease the delocalization of
p-electrons and depress the lipophilicity of the compounds.
The decreased lipophilicity leads to cause permeable bar-
rier of the cell, and thus the compounds cannot much affect
the normal cell process.
Acknowledgments We are thankful to the Head, School of Studies
in Chemistry, Vikram University Ujjain for providing facilities.
Constructive suggestions from Dr. Manmohan L. Satnami, School of
Studies in Chemistry, Pt. Ravishankar Shukla University, Raipur is
acknowledged with appreciation. We are thanks to the Head, Institute
of Environment Management and Plant Science, Vikram University,
Ujjain for providing microorganisms.
References
Alexander K, Hafner LS, Smith GH, Schniepp LE (1950) The partial
hydrogenation of difurfuralacetone and related compounds.
J Am Chem Soc 72:5506–5507
Cesarin-Sobrinho D, Netto-Ferreira J (2002) Fotoquimica de chalco-
nas fluoradas no estado solido. Quim Nova 1:62–68
Cheenpracha S, Karalai C, Ponglimanont C, Shubhadhirasakul S,
Tewtrakal S (2006) Anti-HIV-1 protease activity of compounds
from Boesenbergia pandurata. Bioorg Med Chem 14:1710–1714
D’Auria M (2001) Photochemical dimerization in solution of
heterocyclic substituted alkenes bearing an electron withdrawing
group. Heterocycles 54:475
D’Auria M, Racioppi R (1998) Photochemical dimerization of esters
of urocanic acid. J Photochem Photobiol A Chem 112:145–148
D’Auria M, Emanucle G, Mauriello R, Racioppi R (2000) Photo-
chemical dimerization of 2-vinylfuran and 2-vinylthiophene
derivatives bearing electron-withdrawing groups. J Photochem
Photobiol A Chem 134:147–154
D’Auria M, Emanueke L, Esposito V, Racioppi R (2002) The
photochemical dimerization of 3-heteroaryl-acrylates. Arkivoc
11:65–78
Domı́nguez JN, Leon C, Rodrigues J, Domı́nguez JG, Rosenthal PJ
(2005) Synthesis and antimalarial activity of sulfonamide
chalcone derivatives. Farmaco 60:307–311
Drew WL, Barry AL, O’Toole R, Sherris JC (1972) Reliability of the
Kirby–Bauer disc diffusion method for detecting methicillin-
resistant strains of Staphylococcus aureus. Appl Microbiol
24:240–247
Ishikawa T, Koseki N, Furukawa T, Sakurada E, Koseki C, Saito Y,
Ogata K, Harayama T, Ishii H (1994) Photochemistry of
2-(3,4,5-trimethoxyphenyl)-4-(3,4-methylenedioxy)-4-oxo-2-but-
enonitrile (b-cyanochalcone) and its related compounds. Tetra-
hedron 50(31):9287–9302
Jacob D, Kaul DK (1973) Oestrogenic and antifertility effects of
chalcone derivatives. Acta Endocrinol 74:371–378
Katerere RD, Gray IA, Kennedy RA, Nash JR, Waigh DR (2004)
Cyclobutanes from Combretum albopunctatum. Phytochemistry
65:433–438
Lin Z, Ming C, Jens B, Thor G, Theander S, Brogger C, Arsalan K
(1999) The antileishmanial activity of novel oxygenated chal-
cones and their mechanism of action. J Antimicrob Chemother
43:793–803
Lubrzynska C (1916) Chalcone and its analogs as agents for the
inhibition of angiogenesis and related disease states. J Chem Soc
1118–1120
Matoba K, Yamazakit T (1982) Michael addition of [1H] Pyrrole.
Chem Pharm Bull 30(7):2586–2589
Midolo PD, Turnidge J, Lambert JR, Bell JM (1995) Validation of a
modified Kirby–Bauer disk diffusion method for Metronidazole
susceptibility testing of helicobacter pylori. Diagn Microbiol
Infect Dis 21(3):135–140
Nowakowska Z, Wyrzykiewicz E, Kezia B (2001) Synthesis and
antimicrobial properties of N-substituted derivatives of (E)-4-
azachacones. Farmaco 56:325–329
Opletalova V, Sedivy D (1999) Chalcones and their heterocyclic
analogs as potential antifungal chemotherapeutic agents. Ceska
Slov Farm 48:252–255
Opletalova V, Ricicarova P, Sedivy D, Meltrova, D, Krivakova J
(2000) Chalcones and their heterocyclic analogues as potential
medicaments. Folia Pharm Univ Carol 25: 21–33 and references
therein
Rajendra K, Saini A, Choudhary S, Yogesh C, Joshi P (2005) Solvent
free synthesis of chalcones and their antibacterial activities. E J
Chem 02:224–227
Reddy MVB, Su CR, Chiou WF, Liu YN, Chen RYH, Bastow KF,
Lee KH, Wu TS (2008) Design, synthesis, and biological
evaluation of Mannich bases of heterocyclic chalcone analogs as
cytotoxic agents. Bioorg Med Chem 16:7358–7370
Robert EM, Nord FF (1951) Studies on the chemistry of heterocyc-
lics. XVII. Thiophene polyene acids, aldehydes, and ketones.
J Org Chem 16(11):1720–1730
Rtishchev NI, Nosova GI, Solovskaya NA, Lukyashina VA, Galak-
tionova EF, Kudryavtsev VV (2001) Spectral properties and
photochemical activity of chalcone derivatives. Russ J Gen
Chem 71:1272–1281
Seidel V, Bailleul F, Waterman GP (2000) (Rel)-1b, 2a-di-(2,4-dihydroxy-
6-methoxybenzoyl)-3b, 4a-di-(4-methoxyphenyl)-cyclobutane and
other flavonoids from the arial parts of Goniothalamus dardneri and
Goniothalamus thwaitesii. Phytochemistry 55:439–446
Shakil NA, Singh MK, Kumar J, Sathiyendiran M, Kumar G, Singh
MK, Pandey RP, Pandey A, Parmarv VS (2010) Microwave
synthesis and antifungal evaluations of some chalcones and their
derived diaryl-cyclohexenones. J Environ Sci Health B 45: 524–
530 and references therein
Sharma A, Chakravarti B, Gupt MP, Siddiqui JA, Konwar R, Tripathi
RP (2010) Synthesis and anti breast cancer activity of biphenyl
based chalcones. Bioorg Med Chem 18:4711–4720
Shibata K, Katsuyama I, Matsui M, Muramatsu H (1991) Synthesis of
3-cyano-2-methylpyridines substituted with heteroaromatics.
J Heterocycl Chem 28:161–165
Med Chem Res (2012) 21:1587–1596 1595
123
Srinivasan B, Johnson TE, Lad R, Xing C (2009) Structure-activity
relationship studies of chalcone leading to 3-hydroxy-4,30,40,50-tetramethoxychalcone and its analogues as potent nuclear factor
kappaB inhibitors and their anticancer activities. J Med Chem
52:7228–7235
Toda F, Tanaka K, Kato M (1998) Stereoselective photodimerisation
of chalcones in the molten state. J Chem Soc Perkin Trans
1:1315–1318
Turowska-Tryk I, Grzesniak K, Trzop E, Zych TJ (2003) Monitoring
structural transformations in crystals. Part 4. Monitoring structural
changes in crystals of pyridine analogues of chalcones during
[2 ? 2]-photodimerization and possibilities of the reaction in
hydroxyl derivatives. J Solid State Chem 174:459–465
Viana GSB, Bandeira MAM, Matos FJA (2003) Analgesic and anti-
inflammatory effects of chalcones isolated from Myracrodruon
urundeuva Allemao. Phytomedicine 10:189–195
Yayli N, Ucuncu O, Aydin E, Gok Y, Yasar A, Baltact C, Yildirim N,
Kucuk M (2005) Stereoselective photochemistry of heteroaryl
chalcones in solution and the antioxidant activities. J Photochem
Photobiol A Chem 169:229–234
1596 Med Chem Res (2012) 21:1587–1596
123