Synthesis and antimicrobial studies of hydroxylated chalcone derivatives with variable chain length

Article abstract of DOI:10.1080/14786419.2010.502896

A series of (E)-1-(4-alkyloxyphenyl)-3-(hydroxyphenyl)-prop-2-en-1-one have been successfully synthesised via Claisen-Schmidt condensation. The synthesised chalcone derivatives consisted of hydroxyl groups at either ortho, meta or para position and differed in the length of the alkyl groups, C_nH _2n+1, where n=6, 10, 12 and 14. The structures of all compounds were defined by elemental analysis, IR, ¹H- and ¹³C-NMR. The antimicrobial studies were carried out against wild-type Escherichia coli American Type Culture Collection 8739 to evaluate the effect of the hydroxyl and the alkyl groups of the synthesised chalcones. All the synthesised compounds have shown significant antimicrobial activities. The optimum inhibition was dependent on the position of the hydroxyl group as well as the length of the alkyl chains.

Full text of DOI:10.1080/14786419.2010.502896

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Synthesis and antimicrobial studies of
hydroxylated chalcone derivatives with
variable chain length
Zainab Ngaini a , Siti M. Haris Fadzillah a & Hasnain Hussain b
a Department of Chemistry, Faculty of Resource Science
and Technology , Universiti Malaysia Sarawak , 94300 Kota
Samarahan , Sarawak , Malaysia
b Department of Molecular Biology, Faculty of Resource Science
and Technology , Universiti Malaysia Sarawak , 94300 Kota
Samarahan , Sarawak , Malaysia
Published online: 14 Jun 2011.
To cite this article: Zainab Ngaini , Siti M. Haris Fadzillah & Hasnain Hussain (2012)
Synthesis and antimicrobial studies of hydroxylated chalcone derivatives with variable chain
length, Natural Product Research: Formerly Natural Product Letters, 26:10, 892-902, DOI:
10.1080/14786419.2010.502896
To link to this article: http://dx.doi.org/10.1080/14786419.2010.502896
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Natural Product Research
Vol. 26, No. 10, May 2012, 892–902
Synthesis and antimicrobial studies of hydroxylated chalcone
derivatives with variable chain length
a
Zainab Ngaini , Siti M. Haris Fadzillah and Hasnain Hussain
a
b
*
aDepartment of Chemistry, Faculty of Resource Science and Technology, Universiti Malaysia
Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia; Department of Molecular Biology,
b
Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, 94300 Kota
Samarahan, Sarawak, Malaysia
(Received 1 February 2010; final version received 23 May 2010)
A series of (E)-1-(4-alkyloxyphenyl)-3-(hydroxyphenyl)-prop-2-en-1-one
have been successfully synthesised via Claisen–Schmidt condensation.
The synthesised chalcone derivatives consisted of hydroxyl groups at either
ortho, meta or para position and differed in the length of the alkyl groups,
CnH2nþ1, where n ¼ 6, 10, 12 and 14. The structures of all compounds were
1
defined by elemental analysis, IR, H- and 13C-NMR. The antimicrobial
studies were carried out against wild-type Escherichia coli American Type
Culture Collection 8739 to evaluate the effect of the hydroxyl and the alkyl
groups of the synthesised chalcones. All the synthesised compounds have
shown significant antimicrobial activities. The optimum inhibition was
dependent on the position of the hydroxyl group as well as the length of
the alkyl chains.
Keywords: chalcones; hydroxyl group; alkyl group; antimicrobial activities
1. Introduction
Chalcone is a natural pigment which is commonly found in plants. It is one of the
important intermediates in the biosynthesis of flavonoid. A large number of
chalcones have been studied in the recent decades mainly due to their numerous
biological properties such as anticancer, antioxidant (Aichaoui et al., 2009;
˜
Echeverria, Santibanez, Donoso-Tauda, Escobar, & Ramirez-Tagle, 2009) as well
as antimicrobial activities (Prasad, Rao, & Rambabu, 2008). Claisen–Schmidt
condensation is a common method for the synthesis of chalcone, which involves
cross aldol condensation of appropriate benzaldehyde and acetophenone in the
presence of a base as a catalyst.
Chalcone with the presence of hydroxyl groups has been claimed to have
antimicrobial activities (Devia, Pappano, & Debattista, 1998; Ngaini, Haris-
Fadzillah, Hussain, & Kamaruddin, 2009; Oyedapo, Makanju, Adewunmi,
Iwalewa, & Adenowo, 2004). Naturally occurring chalcones are mostly found in
hydroxylated form and many reports have documented their biologically active
*Corresponding author. Emails: nzainab@gmail.com; nzainab@frst.unimas.my
ISSN 1478–6419 print/ISSN 1478–6427 online
ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/14786419.2010.502896
http://www.tandfonline.com

Natural Product Research
893
properties such as cytotoxicity, antitumour, immunosuppresion and antioxidant
(Go, Wu, & Liu, 2005). The presence of alkyl chains either in the naturally occurring
chalcones (de Andrade Cunha et al., 2003; Stevens, Miranda, Frei, & Buhler, 2003)
or in the synthetic chalcones (Hsieh, Tsao, Wang, & Lin, 2000) has also been
reported for their significant biological activities.
The long alkyl chains have attracted significant attention as they could also give
biologically active properties (Abel et al., 2002; Cohen et al., 2004). This is due to the
lipophilic alkyl chains which have the ability to disrupt microorganism cell wall
(Birnie, Malamud, & Schnaare, 2000; Park et al., 2004). For instance, water-soluble
methacrylate polymers with alkyl chain of 12, 14 and 16 carbons for ammonium
groups have shown an increase in antibacterial activities against Staphylococcus
aureus (Dizman, Elasri, & Mathias, 2006). However, the presence of short chain
also has a significant influence on the antimicrobial activities (Birnie et al., 2000).
In view of the involvement of hydroxyl groups and long alkyl side chains, in this
article, we report the synthesis of novel chalcone derivatives (E)-1-(4-alkyloxyphe-
nyl)-3-(hydroxyphenyl)-prop-2-en-1-one (2a–d, 3a–d and 4a–d) possessing alkyl
chain of varying length (C6, C10, C12 and C14) except 4a–4b (Nam, Kang, & Chang,
2007). The antibacterial activities of these novel chalcone derivatives were performed
towards Escherichia coli ATCC 8739 to evaluate the effect of the hydroxyl group
arrangement as well as the optimum length of alkyl chain.
2. Results and discussion
2.1. Synthesis of chalcone derivatives
Preparation of 1a–d prior to the chalcone synthesis is depicted in Scheme 1.
Compounds 1a–d were synthesised by refluxing 4-hydroxyacetophenone with a series
of bromoalkanes (C6, C10, C12 and C14) in the presence of K2CO3 and TBAI in MEK
to give compounds in yields ranging from 78–94%. The infrared spectra of 1a–d
showed the presence of new bands attributed to aliphatic carbon chains at
1
2920–2850 cmꢀ1. The H-NMR of 1a–d indicated the presence of long alkyl chains
in the structure, as revealed by the resonance at 0.84–0.85 ppm and 3.96–3.98 ppm.
These assignments were complemented by the 13C-NMR spectra which showed
signals at 14.05–68.19 ppm indicating the presence of carbon chains.
All chalcone derivatives (2a–d, 3a–d and 4a–d) were synthesised via the base-
catalysed Claisen–Schmidt condensation. Compounds 1a–d were reacted with
appropriate benzaldehydes in refluxing methanol to the target compounds with
yields ranging from 22–61%. The relatively low yield was attributed to trace amount
O
R1
B
O
O
R1
O
R2
R3
R-Br, K2CO3,
TBAI, MEK
R2
R3
KOH,MeOH
Reflux
CH3
H
CH3
+
RO
Reflux
RO
HO
1a-d
2a-d, 3a-d, 4a-d
2:R1=OH;R2=R3=H
3:R1=R3=H;R2=OH
4:R1=R2=H;R3=OH
a:R=C6H13 b:R=C10H25
c:R=C12H27 d:R=C14H29
a:R=C6H13 b:R=C10H25
c:R=C12H27 d:R=C14H29
Scheme 1. Synthesis of chalcone derivatives.

894
Z. Ngaini et al.
of side products of Cannizzaro reaction or ketone auto condensation (Calvino,
Picallo, Lopez-Peinado, Martın-Aranda, & Duran-Valle, 2006; Climent, Corma,
´
´
´
Iborra, & Velty, 2004). The IR spectra showed the presence of vOH at 3100–
3400 cmꢀ1 and long carbon chain at 2924–2845 cmꢀ1. Strong bands attributable to
vC¼O appeared at 1636–1651 cmꢀ1. The chemical structures of all compounds were
1
confirmed by H- and 13C-NMR spectroscopic methods and showed the peaks that
1
corresponded to the structures. From the H-NMR spectra, the coupling constant,
Jab ¼ 15–16 Hz indicated that all chalcones obtained were in trans configuration.
2.2. Antibacterial activities
The results of the antibacterial study showed that 2a–d, 3a–d and 4a–d exhibited
bacteriostatic activities against E. coli. All synthesised chalcones demonstrated a
similar trend of bacteriostatic activities upon introduction at different concentrations
of 50, 80 and 100 ppm. The inhibition activities were greater with increasing
concentration indicating that the bacteriostatic activities were concentration depen-
dent as shown in Figure 1. Chalcone 2a with C6 alkyl chains showed almost complete
inhibition at 100 ppm compared to 2b–d. However, upon introduction of different
alkyl chains, chalcones 2a–d with C6, C10, C12 and C14 alkyl groups showed
decreasing bacteriostatic activities.
The effect of the synthesised chalcones at various concentrations was further
shown by their minimum inhibitory concentrations (MICs). The MIC of these
compounds were determined by extrapolating the concentration at the zero growth
rate of E. coli (m ¼ 0) (Pappano et al., 1985).
2a
2b
28
26
24
22
20
18
28
26
24
22
20
18
C(–)
C(+)
50
C(–)
C(+)
50
80
80
10 0
10 0
0
1
2
3
4
5
6
0
1
2
3
h
4
5
6
h
2c
2d
C(–)
28
26
24
22
20
18
28
26
24
22
20
18
C(–)
C(+)
50
C(+)
50
80
80
10 0
10 0
0
1
2
3
h
4
5
6
0
1
2
3
h
4
5
6
Figure 1. Inhibition activities of chalcones 2a–d towards E. coli shown as ln Nt for E. coli
growth vs. time.

Natural Product Research
895
Table 1. MIC of compounds 2a–d, 3a–d and 4a–d.
Compound
MIC (ppm)
Compound
MIC (ppm)
Compound
MIC (ppm)
2a
2b
2c
2d
109.8
126.0
132.1
152.3
3a
3b
3c
3d
104.0
129.8
131.5
156.5
4a
4b
4c
4d
111.9
138.9
143.3
163.8
All compounds produced the MIC values ranging from 104–164 ppm (Table 1).
These results indicated that the presence of hydroxyl groups in all the synthesised
compounds influenced the antimicrobial activities (Anto et al., 1995; Tsuchiya et al.,
1994; Won et al., 2005). The presence of hydroxyl group at ortho position further
attenuated the inhibition activities. However, the activities decreased when the
hydroxyl groups were at meta and para position. The importance of the hydroxyl
group at the ortho position in chalcone derivatives was frequently reported for
antimicrobial studies (Alvarez, Zarelli, Pappano, & Debattista, 2004; Mascaretti,
2003; Olivella, Zarelli, Pappano, & Debattista, 2001). In addition, the lipophilicity of
alkyl chains appears to be another important factor for bacteriostatic activities where
the inhibition activities decrease as the alkyl chain becomes longer. This trend could
be observed for all chalcones with C14 alkyl chains with the MIC values greater than
150 ppm.
However, the antibacterial activities increased upon the introduction of C6
aliphatic chain onto chalcone derivatives. Meta-hydroxyl group on the ring B
chalcone displayed the best activity as shown by 3a (104 ppm) followed by 2a
(109.8 ppm) and 4a (111.9 ppm) respectively. This implied that the length of alkyl
chain in the different compounds had a significant influence in giving the optimum
antimicrobial activities (Birnie et al., 2000).
We believed that the bacteriostatic actions of the synthesised chalcones could be
explained through the ability of compounds to cause perturbation of bacterial cell
wall. This integration caused disruption thus rupturing the normal barrier property
of the outer membrane (Kanazawa, Ikeda, & Endo, 1994; Scholar & Pratt, 2000).
Several studies also reported on the membrane perturbation caused by the long chain
molecules in promoting the antimicrobial activities (Birnie et al., 2000; Kanazawa
et al., 1994; Sheu & Freese, 1973).
3. Experimental
3.1. General
4-Hydroxybenzaldehyde, 4-hydroxyacetophenone and 1-bromoalkanes were
obtained from Merck and used without further purification. All other reagents
and solvents were used as received. Melting points were determined by the open tube
capillary method and are uncorrected. Infrared spectra were recorded on a Perkin
Elmer 1605 FTIR Spectrophotometer (FTIR, Fourier transform infrared spectros-
copy) using neat liquid film and potassium bromide (KBr) pellet. 1H- and 13C-NMR
spectra were recorded on JEOL ECA 500 at 500 MHz with the chemical shifts

896
Z. Ngaini et al.
(ꢀ, ppm) reported relative to deuterated chloroform (CDCl3) and dimethyl
sulphoxide (DMSO-d6) as the standards. Flash column chromatography was
performed at atmospheric pressure using Malinckrodt Silica Gel 60, (230–400
mesh) as a stationary phase.
3.2. Synthesis of alkyloxyphenyl-ethanone (1a–d)
3.2.1. General procedure
Bromoalkane (72 mmol), 4-hydroxyacetophenone (72 mmol), K2CO3 (72 mmol),
tetrabutylammonium iodide (TBAI; 6 mmol) in methyl ethyl ketone (MEK; 200 mL)
were heated at reflux for 10 h. The mixture was filtered and cooled at room
temperature. Water (30 mL) was added to the filtrate and the layers separated. The
aqueous layer was extracted with dichloromethane (2 ꢁ 30 mL). The combined layers
were washed with water (2 ꢁ 20 mL), dried (MgSO4), filtered and concentrated
in vacuo. The crude was recrystallised from ethanol to give 1a–d.
3.2.1.1. 4-Hexyloxyacetophenone (1a). Compound 1a was obtained as a viscous
brown oil. Yield (82.6%); the FTIR and NMR were consistent with those reported
in literature (Nam et al., 2007).
3.2.1.2. 4-Decyloxyacetophenone (1b). Compound 1b was obtained as colourless
solid. Yield (89%); m.p. 36–37ꢂC. The FTIR and NMR were consistent with those
reported in literature (Nam et al., 2007).
3.2.1.3. 4-Dodecyloxyacetophenone (1c). Compound 1c was obtained as a colour-
less solid. Yield (78%); m.p. 52–53ꢂC. (Found: C, 78.73 and H, 10.45%. C20H32O2
requires the following: C, 78.90 and H, 10.59%); ꢁmax (KBr cmꢀ1) 2918, 2849, 1676,
1602 and 1255. ꢀH: (500 MHz, CDCl3) 0.85 (3H, t, J ¼ 5.45, J ¼ 7.50, 1CH3), 1.24–
1.77 (20H, m, 10 CH2), 2.52 (3H, t, J ¼ 6.85, J ¼ 6.30, 1 ꢁ CH3), 3.98 (2H, t, J ¼ 6.30,
J ¼ 6.80), 6.87 (2H, d, J ¼ 9.20, Ar–H) and 7.88 (2H, d, J ¼ 9.20, Ar–H). ꢀC:
(125.77 MHz, CDCl3) 14.06, 22.63, 25.91, 26.24, 29.03, 29.29, 29.50, 29.53, 29.58,
29.60, 31.86, 68.19, 114.06, 130.01, 130.50, 163.06 and 196.71.
3.2.1.4. 4-Tetradecyloxyacetophenone (1d). Compound 1d was obtained as a
colourless solid. Yield (94%); m.p. 58–59ꢂC; (Found: C, 79.23; H, 10.51%.
C22H36O2 requires the following: C, 79.46; H, 10.91%); ꢁmax (KBr cmꢀ1) 2917,
2849, 1676, 1605 and 1255. ꢀH: (500 MHz, CDCl3) 0.84 (3H, t, J ¼ 6.30, J ¼ 7.45,
1 ꢁ CH3), 1.23–1.76 (24H, m, 12 ꢁ CH2), 2.50 (3H, s, 1 ꢁ CH3), 3.96 (2H, t, J ¼ 6.85,
J ¼ 6.30, 1 ꢁ CH2), 6.86 (2H, d, J ¼ 8.00, Ar–H) and 7.87 (2H, d, J ¼ 8.00, ArH).
ꢀC: (125.77 MHz, CDCl3) 14.02, 22.60, 25.88, 26.16, 29.01, 29.28, 29.47, 29.51, 29.57,
29.59, 31.83, 68.13, 113.72, 129.97, 130.44, 163.02 and 196.55.

Natural Product Research
897
3.3. Synthesis of (alkyloxy)phenyl-hydroxyphenyl]prop-2-en-1-one (2a–d, 3a–d
and 4a–d)
3.3.1. General procedure
A mixture of hydroxybenzaldehydes (12.5 mmol), 1a–d (12.5 mmol) in 35 mL of
methanol was added under stirring to a solution of KOH 2.52 g in methanol (10 mL).
The mixture was heated at reflux for 10 h. The reaction was cooled to room
temperature and acidified with cold diluted HCl (2 N). The resulting precipitate was
filtered, washed and dried. The crude product was recrystallised from hexane : eth-
anol (7 : 1) to give (2a–d, 3a–d and 4a–d).
3.3.1.1. (E)-1-(4-hexyloxyphenyl)-3-(2-hydroxyphenyl)-prop-2-en-1-one (2a).
2-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1a (12.5 mmol). Compound
2a was obtained as orange crystals. Yield (42.1%); m.p. 131.8–132.6ꢂC; (Found:
C, 78.34: H, 8.75. C21H24O3 requires the following: C, 78.91: H, 8.48%; ꢁmax (nujol
mull cmꢀ1) 3156, 2924, 2855, 1639, 1601, 1266, 996 and 754. ꢀH: (500 MHz, DMSO-d6)
0.84 (3H, t, J ¼ 6.85, J ¼ 7.45, 1 ꢁ CH3), 1.25–1.69 (8H, m, 4 ꢁ CH2), 4.02 (2H, t,
J ¼ 6.30, J ¼ 6.85, 1 ꢁ CH2), 6.83 (1H, t, J ¼ 7.45, J ¼ 7.40, Ar–H), 6.91 (1H, d,
J ¼ 8.55, Ar–H), 7.03 (2H, d, J ¼ 9.20, Ar–H), 7.22 (1H, t, J ¼ 6.90, J ¼ 6.85, Ar–H),
7.80 (1H, dd, J ¼ 8.00, Ar–H), 7.83 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H), 7.95 (1H, d,
J ¼ 16.00, 1 ꢁ olefinic H), and 8.04 (2H, d, J ¼ 9.20, Ar–H). ꢀC: (125.77 MHz, CDCl3)
14.07, 25.75, 29.27, 31.57, 68.24, 115.11, 117.51, 118.59, 118.82, 120.03, 130.54, 130.65,
136.03, 145.52, 161.68, 163.54 and 193.85.
3.3.1.2. (E)-1-(4-decyloxyphenyl)-3-(2-hydroxyphenyl)-prop-2-en-1-one (2b).
2-hydroxybenzaldehyde (12.5 mmol) was reacted with 1b (12.5 mmol). Compound
2b was obtained as yellow crystals. Yield (55.3%); m.p. 119.5–119.9ꢂC; (Found: C,
78.83: H, 8.58. C25H32O3 requires the following: C, 78.91: H, 8.48%); ꢁmax (nujol
mull cmꢀ1) 3158, 2924, 2851, 1642, 1601, 1264, 995, and 761. ꢀH: (500 MHz, DMSO-
d6) 0.84 (3H, t, J ¼ 6.30, J ¼ 6.90, 1 ꢁ CH3), 1.24–1.73 (16H, m, 8 ꢁ CH2), 4.05 (2H, t,
J ¼ 6.90, J ¼ 6.30, 1 ꢁ CH2), 6.87 (1H, t, J ¼ 7.45, J ¼ 7.40, Ar–H), 6.94 (1H, d,
J ¼ 8.00, Ar–H), 7.04 (2H, d, J ¼ 9.20, Ar–H), 7.25 (1H, t, J ¼ 6.85, J ¼ 6.85, Ar–H),
7.83–7.86 (2H, m, Ar–H, 1 ꢁ olefinic H), 8.00 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H) and
8.08 (2H, d, J ¼ 9.20, Ar–H). ꢀC: (125.77 MHz, DMSO-d6) 14.40, 22.56, 29.16, 29.21,
29.42, 29.47, 31.76, 68.32, 114.83, 116.66, 119.82, 121.28, 122.02, 129.04, 131.15,
132.20, 139.03, 157.57, 162.98 and 188.06.
3.3.1.3. (E)-1-(4-dodecyloxyphenyl)-3-(2-hydroxyphenyl)-prop-2-en-1-one (2c).
2-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1c (12.5 mmol). Compound
2c was obtained as yellow crystals. Yield (30%); m.p. 111.1–111.5ꢂC; (Found: C,
79.03: H, 8.70. C27H36O3 requires the following: C, 79.37: H, 8.88%); ꢁmax
(nujol mull cmꢀ1) 3359, 2919, 2851, 1651, 1607, 1267, 996 and 786. ꢀH: (500 MHz,
CDCl3) 0.86 (3H, t, J ¼ 6.85, J ¼ 6.90, 1 ꢁ CH3), 1.25–1.77 (20H, m, 10 ꢁ CH2), 4.01
(2H, t, J ¼ 6.30, J ¼ 6.90, 1 ꢁ CH2), 6.11 (1H, s, OH), 6.91 (1H, d, J ¼ 8.00, Ar–H),
6.95 (2H, d, J ¼ 8.60, Ar–H), 7.17–7.20 (2H, m, Ar–H), 7.24–7.26 (1H, m, Ar–H),
7.52 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H), 7.77 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H) and 8.01
(2H, d, J ¼ 9.20, Ar–H). ꢀC: (125.77 MHz, CDCl3) 14.59, 23.16, 26.44, 29.56, 29.83,

898
Z. Ngaini et al.
30.10, 32.38, 68.81, 114.44, 115.27, 116.34, 117.83, 118.68, 122.23, 130.96, 131.37,
131.55, 136.87, 144.81, 157.00, 163.83 and 189.76.
3.3.1.4. (E)-1-(4-tetradecyloxyphenyl)-3-(2-hydroxyphenyl)-prop-2-en-1-one (2d).
2-hydroxybenzaldehyde (12.5 mmol) was reacted with 1d (12.5 mmol). Compound
2d was obtained as an orange solid. Yield (61.1%); m.p. 107.9–109.6ꢂC; (Found: C,
78.80: H, 9.10. C29H40O3 requires the following: C, 79.77: H, 9.23%; ꢁmax
(nujol mull cmꢀ1) 3182, 2918, 2845, 1636, 1605, 1273, 994 and 765. ꢀH: (500 MHz,
CDCl3) 0.87 (3H, t, J ¼ 6.85, J 6.90, 1 ꢁ CH3), 1.25–1.82 (24H, m, 12 ꢁ CH2), 4.03
(2H, t, J ¼ 6.90, J ¼ 6.30, 1 ꢁ CH2), 6.77 (1H, s, OH), 6.91–6.97 (4H, m, Ar–H), 7.24–
7.27 (1H, m, Ar–H), 7.58 (1H, d, J ¼ 8.00, Ar–H), 7.70 (1H, d, J ¼ 16.00, 1 ꢁ olefinic
H), 8.05 (2H, d J ¼ 9.20, Ar–H) and 8.16 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H). ꢀC:
(125.77 MHz, CDCl3) 14.10, 22.68, 25.99, 29.13, 29.37, 29.59, 29.65, 31.92, 68.31,
114.30, 116.66, 120.79, 122.47, 122.54, 129.19, 130.99, 131.54, 139.96, 155.77, 163.14
and 190.08.
3.3.1.5. (E)-1-(4-hexyloxyphenyl)-3-(3-hydroxyphenyl)-prop-2-en-1-one (3a). 3-Hydro-
xybenzaldehyde (12.5 mmol) was reacted with 1a (12.5 mmol). Compound 3a was
obtained as tan crystals. Yield (22.2%); m.p. 118.6–118.9ꢂC; (Found: C, 78.78: H,
8.45. C21H24O3 requires the following: C, 78.91: H, 8.48%); ꢁmax (nujol mull cmꢀ1
)
3306, 2930, 2845, 1650, 1580, 1268, 972 and 783. ꢀH: (500 MHz, CDCl3) 0.90 (3H,
t, J ¼ 7.45, J ¼ 6.85, 1 ꢁ CH3), 1.34–1.80 (8H, m, 4 ꢁ CH2), 4.02 (2H, t, J ¼ 6.30,
J ¼ 6.85, 1 ꢁ CH2), 6.40 (1H, s, OH), 6.94 (1H, d, J ¼ 8.05, Ar–H), 6.96 (2H,
d, J ¼ 9.20, Ar–H), 7.19–7.21 (1H, m, Ar–H), 7.20 (1H, d, J ¼ 7.50, Ar–H), 7.27 (1H,
t, J ¼ 8.00, J ¼ 8.00, Ar–H), 7.53 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H), 7.75 (1H, d,
J ¼ 16.00, 1 ꢁ olefinic H) and 8.00 (2H, d, J ¼ 9.00, Ar–H). ꢀC: (125.77 MHz, CDCl3)
14.19, 22.76, 25.67, 29.07, 31.56, 68.37, 114.42, 115.31, 117.72, 120.62, 122.06,
130.14, 130.59, 130.99, 136.56, 144.18, 156.44, 163.35 and 189.21.
3.3.1.6. (E)-1-(4-decyloxyphenyl)-3-(3-hydroxyphenyl)-prop-2-en-1-one (3b).
3-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1b (12.5 mmol). Compound
3b was obtained as a tan solid. Yield (52%); m.p. 129.9–130.0ꢂC; (Found: C, 78.48:
H, 8.51. C25H32O3 requires the following: C, 78.91: H, 8.48%); ꢁmax
(nujol mull cmꢀ1) 3334, 2924, 2853, 1651, 1592, 1267, 977 and 787. ꢀH: (500 MHz,
CDCl3) 0.86 (3H, t, J ¼ 6.85, J ¼ 6.90, 1 ꢁ CH3), 1.26–1.79 (16H, m, 8 ꢁ CH2), 4.02
(2H, t, J ¼ 6.30, J ¼ 6.85, 1 ꢁ CH2), 5.70 (1H, s, OH), 6.90 (1H, d, J ¼ 8.00, Ar–H),
6.96 (2H, d, J ¼ 9.20, Ar–H), 7.15 (1H, s, Ar–H), 7.21 (1H, d, J ¼ 7.50, Ar–H), 7.27
(1H, t, J ¼ 8.00, J ¼ 8.00, Ar–H), 7.52 (1H, d, J ¼ 15.00, 1 ꢁ olefinic H), 7.72 (1H, d,
J ¼ 15.00, 1 ꢁ olefinic H) and 7.99 (2H, d, J ¼ 8.60, Ar–H). ꢀC: (125.77 MHz, CDCl3)
14.56, 23.14, 26.45, 29.57, 29.82, 30.01, 32.35, 68.23, 114.85, 115.64, 118.10, 121.13,
122.57, 130.57, 131.11, 131.39, 137.02, 144.47, 156.87, 163.87 and 189.32.
3.3.1.7. (E)-1-(4-dodecyloxyphenyl)-3-(3-hydroxyphenyl)-prop-2-en-1-one (3c).
3-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1c (12.5 mmol). Compound
3c was obtained as a tan solid. Yield (39.9%); m.p. 110.1–111.0ꢂC; (Found: C,
79.57: H, 8.93. C27H36O3 requires the following: C, 79.37: H, 8.88%); ꢁmax (nujol
mull cmꢀ1) 3338, 2923, 2853, 1651, 1606, 1267, 977 and 787. ꢀH: (500 MHz, CDCl3)

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899
0.87 (3H, t, J ¼ 6.90, J ¼ 6.85, 1 ꢁ CH3), 1.26–1.80 (20H, m, 10 ꢁ CH2), 4.03 (2H, t,
J ¼ 6.30, J ¼ 6.90, 1 ꢁ CH2), 5.89 (1H, s, OH), 6.91 (1H, d, J ¼ 8.00, Ar–H), 6.97
(2H, d, J ¼ 9.20, Ar–H), 7.12 (1H, s, Ar–H), 7.22 (1H, d, J ¼ 8.10, Ar–H), 7.28
(1H, t, J ¼ 8.05, J ¼ 8.00, Ar–H), 7.53 (1H, d, J ¼ 15.00, 1 ꢁ olefinic H), 7.74 (1H,
d, J ¼ 15.00, 1 ꢁ olefinic H) and 8.00 (2H, d, J ¼ 8.60, Ar–H). ꢀC: (125.77 MHz,
CDCl3) 13.74, 21.37, 28.40, 29.29, 29.52, 29.83, 113.61, 114.05, 120.74, 122.75,
130.81, 131.04, 131.19, 142.53, 144.09, 156.12, 163.26 and 189.15.
3.3.1.8. (E)-1-(4-tetradecyloxyphenyl)-3-(3-hydroxyphenyl)-prop-2-en-1-one (3d).
3-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1d (12.5 mmol). Compound
3d was obtained as a tan solid. Yield (32%); m.p. 111.3–111.9ꢂC; (Found: C, 78.61:
H, 8.87. C29H40O3 requires the following: C, 79.37: H, 8.88%); ꢁmax
(nujol mull cmꢀ1) 3340, 2924, 2853, 1651, 1592, 1264, 976 and 786. ꢀH: (500 MHz,
CDCl3) 0.86 (3H, t, J ¼ 6.25, J ¼ 6.90, 1 ꢁ CH3), 1.24–1.79 (24H, m, 12 ꢁ CH2), 4.01
(2H, t, J ¼ 6.85, J ¼ 6.30, 1 ꢁ CH2), 6.91 (1H, d, J ¼ 8.00, Ar–H), 6.95 (2H, d,
J ¼ 8.60, Ar–H), 7.16 (1H, s, Ar–H), 7.20 (1H, d, J ¼ 7.45, Ar–H), 7.26 (1H, t,
J ¼ 8.00, J ¼ 8.05, Ar–H), 7.52 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H), 7.73 (1H, d,
J ¼ 16.00, 1 ꢁ olefinic H) and 7.99 (2H, d, J ¼ 8.60, Ar–H). ꢀC: (125.77 MHz, CDCl3)
14.22, 22.78, 26.07, 29.20, 29.45, 29.75, 32.01, 68.43, 114.03, 114.87, 117.41, 122.05,
130.67, 130.92, 131.10, 136.66, 144.04, 156.41, 163.37 and 189.11.
3.3.1.9. (E)-1-(4-hexyloxyphenyl)-3-(4-hydroxyphenyl)-prop-2-en-1-one (4a).
4-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1a (12.5 mmol). Compound
4a was obtained as yellow crystals. Yield (22.2%); the FTIR and NMR were
consistent with those reported in literature (Nam et al., 2007).
3.3.1.10. (E)-1-(4-decyloxyphenyl)-3-(4-hydroxyphenyl)-prop-2-en-1-one (4b).
4-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1b (12.5 mmol). Compound
4b was obtained as yellow crystals. Yield (34%); the FTIR and NMR were consistent
with those reported in literature (Nam et al., 2007).
3.3.1.11. (E)-1-(4-dodecyloxyphenyl)-3-(4-hydroxyphenyl)-prop-2-en-1-one (4c).
4-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1c (12.5 mmol). Compound
4c was obtained as a yellow solid. Yield (44%); m.p. 110.6–111.2ꢂC; (Found:
C, 79.52; H, 8.90%. C27H36O3 requires the following: C, 79.37: H, 8.88%); ꢁmax
(nujol mull cmꢀ1) 3195, 2921, 2852, 1651, 1581, 1223, 990 and 825. ꢀH: (500 MHz,
CDCl3) 0.87 (3H, t, J ¼ 6.85, J ¼ 6.90, 1 ꢁ CH3), 1.25–1.79 (20H, m, 10 ꢁ CH2), 4.02
(2H, t, J ¼ 6.30, J ¼ 6.30, 1 ꢁ CH2), 6.91 (2H, d, J ¼ 8.60, Ar–H), 6.96 (2H, d,
J ¼ 9.20, Ar–H), 7.42 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H), 7.53 (2H, d, J ¼ 8.60, Ar–H),
7.74 (1H, d, J ¼ 16.00, 1 ꢁ olefinic H) and 8.01 (2H, d, J ¼ 8.60, Ar–H). ꢀC:
(125.77 MHz, CDCl3) 14.10, 22.67, 25.96, 29.08, 29.33, 29.55, 29.58, 29.61, 30.96,
31.89, 68.29, 114.30, 116.09, 119.03, 127.24, 130.45, 130.84, 144.66, 158.75, 163.12
and 189.62.

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Z. Ngaini et al.
3.3.1.12. (E)-1-(4-tetradecyloxyphenyl)-3-(4-hydroxyphenyl)-prop-2-en-1-one (4d).
4-Hydroxybenzaldehyde (12.5 mmol) was reacted with 1d (12.5 mmol). Compound
4d was obtained as a pale yellow solid. Yield (39%); m.p. 107.2–108.2ꢂC. (Found: C,
78.83; H, 9.04%. C29H40O3 requires the following: C, 79.77; H, 9.23%; ꢁmax
(nujol mull cmꢀ1) 3208, 2918, 2850, 1646, 1585, 1223, 990 and 825. ꢀH: (500 MHz,
DMSO-d6) 0.82 (3H, t, J ¼ 6.85, J ¼ 6.90, 1 ꢁ CH3), 1.24–1.71 (24H, m, 12 ꢁ CH2),
4.04 (2H, t, J ¼ 6.30, J ¼ 6.90, 1 ꢁ CH2), 6.81 (2H, d, J ¼ 8.60, Ar–H), 7.02 (2H, d,
J ¼ 9.20, Ar–H), 7.61 (1H, d, J ¼ 15.00, 1 ꢁ olefinic H), 7.69 (1H, d, J ¼ 15.00,
1 ꢁ olefinic H), 7.70 (2H, d, J ¼ 9.20, Ar–H), 8.09 (2H, d, J ¼ 8.60, Ar–H) and 10.04
(1H, s, OH); ꢀC: (125.77 MHz, DMSO-d6) 13.93, 22.09, 25.42, 28.54, 28.72, 28.97,
29.02, 29.05, 30.67, 31.29, 67.81, 114.28, 115.76, 118.36, 125.90, 130.60, 130.65,
130.81, 143.52, 159.92, 162.44 and 187.12.
3.3.2. Antibacterial screening
The antibacterial activities of the synthesised compounds were carried out towards
E. coli ATCC 8739 using turbidimetric kinetic method. The inoculums were allowed
to grow on media containing nutrient broth at 37ꢂC with permanent stirring at
200 rpm for 18 h. The culture medium of volume 10 mL, with increasing concentra-
tion of the compounds dissolved in propanol was inoculated with 0.2 mL of
inoculums and the mixture was shaken at 250 rpm at 37ꢂC. Inoculums with the
solvent were used as controls. Aliquots of each replicate were taken every 1 h interval
for 6 h and the transmittances (T) were registered in a UV–vis spectrophotometer
(Optima SP-300). The antibacterial activities were determined by a graph as ln Nt
which was related to the number CFU mLꢀ1 (CFU, colony forming units) for E. coli
versus time (Pappano et al., 1985).
4. Conclusion
A series of hydroxylated chalcone derivatives with different chain lengths have been
successfully synthesised. All the synthesised chalcones exhibited promising anti-
bacterial activities against E. coli. The presence of hydroxyl groups at the meta
position with C6 alkyl chains showed the highest antimicrobial activities. Besides
hydroxyl groups, the presence of alkyl chains also contributed to the antibacterial
activities where the inhibition activity was observed to be concentration dependent.
However, the inhibition activity decreased with increasing chain length.
Acknowledgements
The authors thank Universiti Malaysia Sarawak for financing this project through UNIMAS
grant DI/01/2007(01). The authors also thank Mr Kamarulzaman Kamarudin for providing
the E. coli ATCC 8739 used in this study.
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