Synthesis, physicochemical properties and antimicrobial evaluation of new (E)-chalcones

Article abstract of DOI:10.1016/j.ejmech.2007.05.006

In a wide search program towards new and efficient antimicrobial agents, a series of 40 substituted chalcones have been synthesized and tested for their in vitro antibacterial and antifungal activities. The structures of these compounds have been investigated by nuclear magnetic resonance spectroscopy and mass spectrometry. Among the (E)-4-aminoalkylthiochalcones and (E)-4-aminoalkoxychalcones tested, compounds 7, 10, 11, 30 and 31 have exhibited good antibacterial property against Staphylococcus aureus, Enterococcus faecalis and Bacillus subtilis.

Full text of DOI:10.1016/j.ejmech.2007.05.006

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 43 (2008) 707e713
http://www.elsevier.com/locate/ejmech
Original article
Synthesis, physicochemical properties and antimicrobial
evaluation of new (E )-chalcones
b
a
Z. Nowakowska a, , B. Ke˛dzia , G. Schroeder
*
a
´
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
b
´
Institute of Medicinal Plants, Libelta 27, 61-707 Poznan, Poland
Received 28 February 2007; received in revised form 18 May 2007; accepted 24 May 2007
Available online 2 June 2007
Abstract
In a wide search program towards new and efficient antimicrobial agents, a series of 40 substituted chalcones have been synthesized and
tested for their in vitro antibacterial and antifungal activities. The structures of these compounds have been investigated by nuclear magnetic
resonance spectroscopy and mass spectrometry. Among the (E )-4-aminoalkylthiochalcones and (E )-4-aminoalkoxychalcones tested, compounds
7, 10, 11, 30 and 31 have exhibited good antibacterial property against Staphylococcus aureus, Enterococcus faecalis and Bacillus subtilis.
Ó 2007 Elsevier Masson SAS. All rights reserved.
Keywords: Chalcone; Antibacterial activity; Antifungal activity
1. Introduction
no reports on the mercaptochalcones natural occurrence in
plants, although a few sulfur-containing chalcone derivatives
have been synthesized and tested as antibacterial agents and
potential leukotriene receptor antagonists [14,15]. Thus, it is
of interest to further elucidate the contribution of basic amino
function to the biological activity of chalcones.
Chalcones represent an important group of natural com-
pounds with a variety of biological activities including anti-
bacterial and antifungal ones. They have found numerous
applications as pesticides, photoprotectors in plastics, solar
creams, food additives as well as anti-inflammatory and anti-
cancer agents [1e5]. The oxygenated chalcone, licochalcone
A, has been previously described as a moderately potent anti-
bacterial compound with activity against Gram-positive bacte-
ria. Rapid development of resistance to clinically important
Gram-positive bacteria is a serious public health threat. Staph-
ylococcus aureus can produce a number of diseases affecting
humans and animals. Therefore, the search for novel bacteri-
cidal compounds is the object of continuous investigation
[6e12]. Additionally, chalcones with basic amino functions
have been reported to have enhanced selectivity and potency
in biological properties [8,13]. To this date there have been
2. Chemistry
The aim of this investigation is to procure (E )-4-bromoal-
kylthiochalcones 1e4, (E )-4-piperidino-N-alkylthiochalcones
5e8, (E )-4-(40-methylpiperidino)-N-alkylthiochalcones 9e12,
(E )-4-morpholino-N-alkylthiochalcones 13e16 and (E )-4-
piperazino-N-alkylthiochalcones 17e20 from (E )-4-mer-
captochalcone I, as well as (E )-4-bromoalkoxychalcones
21e24, (E )-4-piperidino-N-alkoxychalcones 25e28, (E )-4-
(40-methylpiperidino)-N-alkoxychalcones 29e32, (E )-4-mor-
pholino-N-alkoxychalcones 33e36, and (E )-4-piperazino-N-
alkoxychalcones 37e40 from (E )-4-hydroxychalcone II in
the hope of obtaining new derivatives, which might show bi-
ological activity as antimicrobial and antifungal agents. The
synthesis reaction is shown in Scheme 1 and the numbering
* Corresponding author. Tel.: þ48 61 829 1002; fax: þ48 61 865 8008.
E-mail address: zdzisian@amu.edu.pl (Z. Nowakowska).
0223-5234/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2007.05.006

708
Z. Nowakowska et al. / European Journal of Medicinal Chemistry 43 (2008) 707e713
Scheme 1. Scheme of synthesis of compounds 1e40.
of the compounds is presented in Table 1. (E )-4-Mer-
captochalcone I was alkylated with dibromoalkanes (1,4-
dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane and
1,10-dibromodecane) at room temperature in N,N-dimethyl-
formamide in the presence of triethylamine as a base. The re-
actions were usually carried out for 3e4 h. Under these
conditions, a chemoselective alkylation affording the corre-
sponding (E )-4-bromoalkylthiochalcones, as convenient
intermediates for the synthesis of the planned bridged chal-
cone derivatives, was possible. Yields of the products 1e4
were of the order of 76e88%. However, in the reaction of
(E )-4-mercaptochalcone with dibromoalkanes with 4, 5 or 6
carbon atoms in the alkyl chain, an additional product was
also detected and isolated in 12%, 8% and 5% yield. This minor
compound was identified as bis-(4-chalconylthio)alkane.
(E )-4-Hydroxychalcone II was alkylated with dibromoal-
kanes in a boiling anhydrous acetone solution containing
anhydrous potassium carbonate. Under these conditions, a che-
moselective alkylation affording the corresponding (E )-4-bro-
moalkoxychalcones 21e24 was possible. The reactions were
usually carried out for 5e6 h. During these reactions bis-(4-
chalconyloxy)alkane with 4, 5 or 6 carbon atoms in the alkyl
chain, was also obtained in the yield of 10%, 8% and 6%,
respectively.
Table 1
Labeling of compounds 1e40
Compd.
n
X
Compd.
n
X
Compd.
n
X
1
4
5
6
e
15
16
17
18
19
20
21
22
6
O
O
29
30
4
5
6
CHeCH3
CHeCH3
CHeCH3
2
e
10
4
3
e
e
NeH 31
NeH 32
NeH 33
4
10
4
5
10 CHeCH3
5
CH2
CH2
CH2
6
4
5
O
6
5
10 NeH 34
O
7
6
4
5
e
e
35
36
37
38
39
40
6
O
8
10 CH2
10
4
O
9
4
5
6
CHeCH3 23
CHeCH3 24
CHeCH3 25
6
e
NeH
NeH
NeH
10
11
12
13
14
10
4
e
5
CH2
CH2
CH2
6
10 CHeCH3 26
5
10 NeH
4
5
O
O
27
28
6
10 CH2

Table 2
Chemical and physical data of compounds 1e20
Compd.
M.p. (ꢀC)
IR (KBr) [cmꢁ1
]
13C, 1H NMR (d), ppm
Elemental analyses, obs. (calc.)
C-a, H-a
C-b, H-b
C-1
C-2,6, H-2,6
C-3,5, H-3,5
C-4
C-20,60, H-20,60
C (%)
H (%)
N (%)
1
96e97a
91e93a
1660, 1589, 1492, 1446, 1221, 992
1655, 1592, 1490, 1447, 1227, 989
1657, 1587, 1496, 1448, 1216, 986
1660, 1587, 1487, 1446, 1230, 985
1659, 1591, 1491, 1448, 1224, 988
1659, 1587, 1489, 1447, 1229, 988
1655, 1592, 1495, 1446, 1220, 980
1658, 1586, 1492, 1448, 1228, 989
1660, 1590, 1487, 1446, 1224, 986
1659, 1589, 1492, 1444, 1221, 992
1655, 1593, 1495, 1447, 1219, 980
1658, 1589, 1492, 1446, 1224, 988
1659, 1585, 1489, 1442, 1229, 1118, 990
1660, 1589, 1492, 1446, 1221, 1122, 992
1652, 1593, 1495, 1449, 1220, 1111, 980
1660, 1589, 1492, 1446, 1221, 1120, 992
3290, 1655, 1595, 1490, 1440, 1227, 988
3310, 1659, 1589, 1492, 1446, 1221, 986
3298, 1658, 1587, 1489, 1448, 1226, 989
3245, 1655, 1589, 1494, 1442, 1220, 985
121.17, 7.50
121.15, 7.50
121.11, 7.50
121.09, 7.49
121.09, 7.49
121.06, 7.50
121.04, 7.50
121.06, 7.49
121.49, 7.50
120.99, 7.50
121.02, 7.50
120.97, 7.50
120.99, 7.49
121.11, 7.49
121.07, 7.50
120.99, 7.49
121.13, 7.49
121.09, 7.50
121.07, 7.49
120.99, 7.49
144.12, 7.77
144.16, 7.77
144.21, 7.78
144.26, 7.77
144.29, 7.77
144.30, 7.78
144.20, 7.77
144.29, 7.77
144.01, 7.77
144.10, 7.78
144.19, 7.77
144.23, 7.77
144.10, 7.78
144.10, 7.77
144.13, 7.78
144.14, 7.77
144.23, 7.77
144.25, 7.78
144.31, 7.78
144.30, 7.78
131.89
131.88
131.78
131.70
131.60
131.63
131.70
131.67
131.99
131.86
131.80
131.55
131.68
131.64
131.60
131.58
131.89
131.80
131.85
131.87
128.78, 7.55
128.84, 7.55
128.81, 7.55
128.80, 7.55
128.70, 7.55
128.75, 7.55
128.78, 7.56
128.79, 7.55
128.83, 7.56
128.80, 7.55
128.82, 7.56
128.75, 7.55
128.68, 7.55
128.69, 7.55
128.72, 7.55
128.70, 7.55
128.72, 7.55
128.74, 7.55
128.75, 7.56
128.82, 7.55
127.71, 7.29
127.70, 7.30
127.66, 7.29
127.54, 7.29
127.68, 7.29
127.58, 7.29
127.62, 7.30
127.50, 7.29
127.69, 7.30
127.70, 7.29
127.63, 7.29
127.43, 7.30
127.56, 7.29
127.50, 7.29
127.64, 7.29
127.41, 7.30
127.48, 7.29
127.52, 7.30
127.56, 7.30
127.68, 7.29
140.72
140.78
140.89
141.29
140.86
141.05
141.16
141.34
140.81
140.93
140.99
141.25
141.20
141.27
140.82
141.18
141.23
141.20
141.30
141.32
128.43, 8.02
128.42, 8.02
128.39, 8.01
128.43, 8.02
128.30, 8.02
128.36, 8.02
128.37, 8.02
128.43, 8.01
128.33, 8.02
128.39, 8.02
128.34, 8.02
128.35, 8.02
128.38, 8.01
128.28, 8.02
128.30, 8.02
128.33, 8.02
128.27, 8.02
128.28, 8.01
128.31, 8.02
128.38, 8.02
60.71 (60.80)
61.63 (61.70)
62.45 (62.53)
65.30 (65.35)
75.87 (75.95)
76.21 (76.29)
76.56 (76.61)
77.61 (77.70)
76.20 (76.29)
76.57 (76.61)
76.85 (76.91)
77.82 (77.94)
72.35 (72.40)
72.80 (72.87)
73.24 (73.31)
74.71 (74.79)
72.48 (72.59)
73.01 (73.06)
73.40 (73.49)
74.92 (74.95)
5.17 (5.10)
5.49 (5.44)
5.80 (5.75)
6.86 (6.80)
7.75 (7.70)
7.99 (7.94)
8.23 (8.16)
8.94 (8.91)
7.99 (7.94)
8.20 (8.16)
8.39 (8.37)
9.16 (9.07)
7.21 (7.13)
7.50 (7.39)
7.74 (7.63)
8.53 (8.44)
7.55 (7.42)
7.73 (7.66)
7.92 (7.89)
8.69 (8.68)
e
2
e
3
82e83a
e
4
71e73a
e
5
98e100b
110e112b
118e119b
59e61b
3.62 (3.69)
3.51 (3.56)
3.43 (3.44)
2.99 (3.02)
3.49 (3.56)
3.40 (3.44)
3.27 (3.32)
2.88 (2.93)
3.65 (3.67)
3.56 (3.54)
3.40 (3.42)
3.06 (3.01)
7.30 (7.36)
7.05 (7.10)
6.84 (6.86)
6.04 (6.03)
6
7
8
9
102e103b
108e110b
79e80b
10
11
12
13
14
15
16
17
18
19
20
125e127b
99e102b
93e94b
76e78b
68e69b
104e105b
92e95b
107e108b
121e123b
a
Crystallization solvent: ethanol.
Crystallization solvent: chloroformeethanol.
b

Table 3
Chemical and physical data of compounds 21e40
Compd.
M.p. (ꢀC)
IR (KBr) [cmꢁ1
]
13C, 1H NMR (d), ppm
Elemental analyses, obs. (calc.)
C-a, H-a
C-b, H-b
C-1
C-2,6, H-2,6
C-3,5, H-3,5
C-4
C-20,60, H-20,60
C (%)
H (%)
N (%)
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
a
97e98a
100e101a
78e79a
1660, 1592, 1568, 1510, 1292, 1213, 1176, 993
1655, 1589, 1566, 1511, 1291, 1212, 1176, 986
1653, 1589, 1569, 1508, 1293, 1216, 1172, 985
1650, 1585, 1560, 1505, 1291, 1212, 1170, 985
1663, 1591, 1570, 1512, 1293, 1218, 1174, 985
1659, 1589, 1568, 1511, 1291, 1216, 1173, 993
1657, 1586, 1566, 1512, 1297, 1215, 1174, 997
1660, 1588, 1567, 1511, 1297, 1214, 1174, 994
1658, 1590, 1568, 1516, 1295, 1219, 1175, 989
1655, 1586, 1567, 1511, 1295, 1214, 1176, 998
1658, 1589, 1569, 1513, 1295, 1216, 1176, 989
1652, 1588, 1570, 1511, 1291, 1217, 1174, 995
1649, 1590, 1569, 1513, 1295, 1215, 1178, 1113, 996
1657, 1591, 1577, 1512, 1298, 1212, 1174, 1113, 987
1652, 1591, 1567, 1513, 1295, 1216, 1179, 1111, 989
1652, 1598, 1571, 1512, 1291, 1216, 1175, 1115, 986
3260, 1650, 1590, 1565, 1511, 1296, 1212, 1174, 989
3275, 1652, 1588, 1571, 1511, 1294, 1216, 1175, 990
3330, 1647, 1588, 1565, 1512, 1295, 1216, 1174, 988
3280, 1649, 1590, 1564, 1512, 1295, 1213, 1175, 990
119.75, 7.42
119.65, 7.42
119.62, 7.41
119.59, 7.42
119.48, 7.42
119.53, 7.41
119.49, 7.41
119.44, 7.41
119.79, 7.43
119.65, 7.42
119.69, 7.41
119.49, 7.42
119.62, 7.42
119.58, 7.42
119.49, 7.42
119.60, 7.42
119.96, 7.41
119.68, 7.42
119.53, 7.41
119.70, 7.42
144.65, 7.78
144.69, 7.79
144.64, 7.79
144.60, 7.78
144.40, 7.79
144.48, 7.78
144.58, 7.78
144.63, 7.78
144.34, 7.78
144.48, 7.78
144.54, 7.78
144.67, 7.79
144.71, 7.79
144.59, 7.79
144.68, 7.79
144.62, 7.79
144.59, 7.78
144.65, 7.78
144.64, 7.79
144.70, 7.79
127.62
127.48
127.55
127.50
127.40
127.36
127.30
127.18
127.67
127.60
127.48
127.24
127.43
127.40
127.33
127.50
127.40
127.32
127.29
127.35
130.23, 7.59
130.19, 7.60
130.18, 7.59
130.20, 7.59
130.09, 7.61
130.15, 7.59
130.10, 7.59
130.09, 7.59
130.10, 7.60
130.16, 7.59
130.11, 7.59
130.10, 7.59
130.21, 7.59
130.20, 7.60
130.16, 7.60
130.18, 7.60
130.09, 7.60
130.14, 7.59
130.10, 7.59
130.14, 7.59
114.84, 6.92
114.80, 6.93
114.79, 6.92
114.81, 6.92
114.80, 6.91
114.78, 6.91
114.79, 6.92
114.80, 6.92
114.73, 6.92
114.78, 6.92
114.80, 6.92
114.82, 6.91
114.84, 6.92
114.86, 6.92
114.81, 6.93
114.82, 6.93
114.84, 6.92
114.80, 6.93
114.81, 6.92
114.79, 6.92
160.93
161.01
160.90
160.88
161.01
160.97
160.88
161.11
160.43
160.59
160.68
161.15
161.11
160.98
160.88
160.90
161.06
160.07
161.09
160.91
128.39, 8.01
128.36, 8.02
128.30, 8.01
128.32, 8.02
128.29, 8.02
128.28, 8.01
128.24, 8.01
128.25, 8.01
128.23, 8.02
128.27, 8.02
128.28, 8.02
128.28, 8.01
128.37, 8.02
128.35, 8.02
128.30, 8.02
128.35, 8.02
128.30, 8.02
128.29, 8.02
128.28, 8.01
128.30, 8.01
63.49 (63.52)
64.34 (64.35)
65.10 (65.12)
67.70 (67.72)
79.19 (79.30)
79.46 (79.54)
79.69 (79.76)
80.35 (80.49)
79.45 (79.54)
79.68, (79.76)
79.95 (79.96)
80.63 (80.65)
75.57 (75.59)
75.86 (75.96)
76.29 (76.30)
77.40 (77.47)
75.68 (75.79)
76.10 (76.16)
76.48 (76.49)
77.60 (77.64)
5.37 (5.33)
5.69 (5.67)
6.01 (5.99)
7.07 (7.05)
8.11 (8.04)
8.30 (8.28)
8.55 (8.50
8.30 (9.23)
8.33 (8.28)
8.61 (8.50)
8.72 (8.70)
9.45 (9.39)
7.48 (7.45)
7.78 (7.70)
7.96 (7.94)
8.79 (8.74)
7.79 (7.74)
8.11 (7.99)
8.25 (8.22)
9.11 (8.99)
e
e
e
68e79a
e
102e105b
113e115b
118e119b
134e135b
92e93b
3.82 (3.85)
3.65 (3.71)
3.61 (3.58)
3.14 (3.13)
3.64 (3.71)
3.67 (3.58)
3.45 (3.45)
3.02 (3.03)
3.80 (3.83)
3.69 (3.69)
3.58 (3.56)
3.11 (3.12)
7.60 (7.69)
7.42 (7.40)
7.15 (7.14)
6.20 (6.24)
103e104b
92e94b
83e84b
83e85b
78e81b
98e100b
90e92b
115e116b
123e125b
128e129b
138e140b
Crystallization solvent: ethanol.
b
Crystallization solvent: chloroformeethanol.

Z. Nowakowska et al. / European Journal of Medicinal Chemistry 43 (2008) 707e713
711
Table 4
Antimicrobial activity of the active compounds
being a measure of hydrophobicity/lipophilicity was calcu-
lated using ChemDraw Ultra 5.0 software integrated with
CambridgeSoft Software Development Kit (CambridgeSoft
Corporation) [17]. The results obtained are given in Table 5.
The calculated values of log P for derivatives of (E)-4-mercap-
tochalcone were about 0.56 higher than for the corresponding
compounds with an oxygen atom in the moiety. The lipophilic
aptitude of a compound increased with increasing log P. The
activity observed for compounds 1e20 was slightly higher
than that of the oxygen analogues 21e40. The piperidino and
4-methylpiperidino substituted derivatives of chalcone which
had higher values of log P than the corresponding morpholino
and piperazino substituted compounds were more active.
Regarding the correlation of the antimicrobial activity of
substituted chalcones with the planarity of their molecules,
the presence of a group in the ortho-position of the B-ring could
introduce steric hindrance. The para-position appears to be of
marginal steric effect. The molar refractivity (MR e which rep-
resents size and polarizability of a fragment or molecule) de-
scribing steric effects was calculated using ChemDraw Ultra
5.0 software (Table 5). Compounds holding electron withdraw-
ing groups in the para-position improved the antimicrobial
properties compared with the non-ring B-substituted chalcone.
Compd. Minimum inhibitory concentration (MIC, mM)
S. aureus E. faecalis B. subtilis E. coli C. albicans M. gypseum
1
267
e
e
e
e
e
e
e
254
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
15
e
e
e
e
127
<246
e
e
2
e
193
264
254
5
26
254
25
216
25
18
24
e
264
254
25
e
26
6
254
25
e
7
<246
216
191
184
<237
189
<244
e
8
9
254
25
24
e
254
25
18
e
e
10
11
14
15
17
19
22
25
26
27
28
29
30
31
33
34
35
A
184
<237
e
e
e
e
263
e
e
e
263
245
e
263
245
e
e
e
e
e
e
268
e
275
265
256
21
133
19
25
e
275
265
256
209
265
26
25
e
275
265
256
209
265
128
19
e
e
e
e
<256
e
e
e
265
256
123
274
264
254
e
e
e
e
e
e
e
e
e
e
e
e
15
e
15
e
15
e
e
4.1. Antibacterial activity
B
0.5
11
MIC e the minimum inhibitory concentration is the lowest value of concen-
tration of the investigated compound which breakes the evolution of the micro-
organism; A e Chloramphenicol; B e Amphotericin B.
The antibacterial data indicated that among (E )-4-bromo-
alkylthiochalcones 1e4 and (E )-4-bromoalkoxychalcones
21e24, only compound 1 showed appreciable antibacterial ac-
tivity (MIC 267 mM) against S. aureus. Substitution of a piper-
idine group for a bromo group in 1e4 and 21e24 led to
compounds 5e8 and 25e28, respectively. These compounds
exerted appreciable antibacterial activity against all the
Gram-positive strains tested. Of these, 5 and 7 were found
to be the most potent against S. aureus and B. subtilis, showing
MICs of 26 and 25 mM, respectively. Compound 7 was also ef-
fective against E. faecalis with MIC of 25 mM. Additionally,
compound 6 was found to be more active than the other deriv-
atives with the MIC value of 254 mM against Gram-negative
bacteria E. coli. (E )-4-(Piperidino-N-alkylthio)chalcones 5
and 7 showed higher antibacterial activity than (E )-4-(piper-
idino-N-alkoxy)chalcones 25 and 27, respectively.
reference antibacterial drug) and Amphotericin B (the refer-
ence antifungal drug) were used for comparison.
It is believed that the strong lipophilic character of the mol-
ecule plays an essential role in its producing the antibacterial
effect. The permeability of the cell to the test compounds is
one of the factors determining their antibacterial activity. In
this context the presence of a hydrophobic moiety would be
important for such activity. Basic amino functions (piperidine,
4-methylpiperidine, morpholine or piperazine) which are pro-
tonated at physiological pH, enhance the aqueous solubility of
a generally hydrophobic chalcone template.
The lipophilicity of compounds, expressed as log P of the
substituents in the B-ring, appears to be the main predictor
for the activity. The octanol/water partition coefficient C log P
Replacement of the bromo group by a 4-methylpiperidine
group brought an appreciable change in the activity. The
Table 5
Calculated C log P and MR values
Compd.
C log P
MR
Compd.
C log P
MR
Compd.
C log P
MR
95.2
Compd.
C log P
MR
1
2
5.41
5.83
6.25
7.92
5.32
5.73
6.15
7.82
5.65
6.06
101.6
106.2
110.8
129.2
119.4
124.1
128.6
147.1
124.0
128.6
11
12
13
14
15
16
17
18
19
20
6.48
8.15
4.18
4.60
5.02
6.69
3.96
4.38
4.80
6.47
133.2
151.6
116.4
121.0
125.6
144.0
118.1
122.7
127.2
145.7
21
22
23
24
25
26
27
28
29
30
4.85
5.26
5.68
7.35
4.75
5.17
5.58
7.25
5.08
5.50
31
32
33
34
35
36
37
38
39
40
5.91
7.58
3.62
4.04
4.45
6.12
3.40
3.81
4.23
5.90
126.7
145.2
109.9
114.5
119.2
137.6
111.6
116.2
120.8
139.2
99.8
104.4
122.8
113.0
117.6
122.2
140.6
117.6
122.2
3
4
5
6
7
8
9
10

712
Z. Nowakowska et al. / European Journal of Medicinal Chemistry 43 (2008) 707e713
MIC values of 9e11 and 29e31 indicated that the 4-methyl-
piperidinoalkylthio and 4-methylpiperidinoalkoxy derivatives
of (E )-chalcone were active compounds against all the
Gram-positive strains of the bacteria tested (MIC ¼ 18e
265 mM). Compounds with six carbon atoms in the alkyl chain
(11 and 31) were the most potent against B. subtilis with MIC
of 18 and 19 mM, respectively. The compounds with five car-
bon atoms in the alkyl chain, (10 and 30), were the most potent
against S. aureus with MIC of 18 and 19 mM, respectively.
Compounds 9, 11, and 31 were found to be active at MIC
values of 24e25 mM against S. aureus. Compounds 10, 11,
30 and 31 showed a significant antibacterial activity against
E. faecalis with MIC values of 24e26 mM.
distance between the cyclic amino group (morpholine, piper-
idine, 4-methylpiperidine or piperazine) and the B-ring of
the chalcone moiety was found to be of importance for the
activity. An amino substituent spaced to the B-ring by four,
five or six methylene groups increased the activity, whereas
an amino substituent spaced by 10 methylene groups totally
eliminated the activity. The most potent class of compounds
has a piperidine and six carbon atoms in the alkyl chain (com-
pound 7) or 4-methylpiperidine and five (10, 30) or six (11, 31)
carbon atoms in the alkyl side. The high activity of chalcones
having the piperidine and 4-methylpiperidine groups (hydro-
philic substituents) may reflect the fact that these compounds
are more basic than the compounds with piperazine or mor-
pholine group, and consequently have a higher degree of pro-
tonation in the assay.
Substitution of a morpholine group for a bromo group did
not change the activity of 13e16 and 33e36 towards Gram-
positive cocci and Gram-negative rods.
In the series of compounds with a piperazine group (17e20
and 37e40), only the derivatives with a sulfur atom and four or
six methylene groups in the alkyl chain (17 and 19) were found
to be active against Gram-positive strains of the bacteria tested.
All the compounds tested in this study displayed insignifi-
cant effect against the Gram-negative rods E. coli, K. pneumo-
niae and P. aeruginosa.
6. Experimental section
6.1. Chemistry
6.1.1. General
The purity of all described compounds was checked by
m.p., TLC and elemental analysis. Melting points (uncor-
rected) were determined on MEL-TEMPII apparatus. Rf values
refer to TLC silica gel F254 TLC plates (Merck) developed
with CHCl3:MeOH (100:1) or CHCl3:MeOH (10:1) and ob-
served under UV light (l ¼ 254 and 366 nm). The IR spectra
were recorded as KBr pellets using a Bruker IFS 113v FT-
IR spectrometer. The 1H NMR (300 MHz) and 13C NMR
(75 MHz) spectra were recorded on a Varian Mercury Spec-
trometer operating at 300.07 MHz (proton) or 75.46 MHz
(carbon). The data were obtained from CDCl3 solutions.
Chemical shifts are given in the d scale (ppm) using tetrame-
thylsilane as an internal standard and coupling constants are
expressed in Hz. 1H NMR spectra were recorded with spectral
width 9 kHz, acquisition time 2.0 s, pulse width 6 ms and
double precision acquisition time. 13C NMR spectra were
recorded with spectral width 18.76 kHz, acquisition time
1.0 s, recycle delay 1.0 s and pulse width 15 ms. Heteronuclear
2D 13CNMRe1H NMR chemical shift correlation experiments
were carried out using HETCOR spectra. The spectra were ac-
quired with 2K data points, 256 increments and spectral width
19.63 kHz for 13C NMR and 4.97 kHz for 1H NMR. Elemental
analyses were performed with a Vector Euro EA 3000 Ana-
lyzer. Analyses were within ꢂ0.4% of the theoretical values.
Piperidine, 4-methylpiperidine, piperazine and morpholine
were purchased from Aldrich.
4.2. Antifungal activity
The in vitro antifungal activity of the substituted derivatives
of (E )-4-mercaptochalcone 1e20 and (E )-4-hydroxychalcone
21e40 and of Amphotericin B as a reference drug on three fungi
species is characterized in Table 4. Some of the compounds
tested were endowed with a medium activity against M. gyp-
seum. Of these, (E )-4-(40-methylpiperidino)-N-hexylochalcone
31 was found to be most potent, showing MIC of 123 mM,
whereas the MIC values for 2, 9, 10 and 14 were in the range
of 184e193 mM or for 5e8, 11, 15, 22, 27, 29, 30, and 33e
35 they were in the range of 216e265 mM. Compounds with
five or six carbon atoms in a piperidinoalkylthio or 4-methylpi-
peridinoalkylthio group (6, 7 and 10, 11) were also found to be
potent against C. albicans with a medium activity. All the other
compounds tested (3, 4, 12, 16) exhibited no chemotherapeuti-
cal activity in vitro against the microorganisms tested.
5. Conclusion
In conclusion, several substituted (E )-chalcones were
synthesized starting with (E )-4-mercaptochalcone or (E )-4-
hydroxychalcone through the pathway involving bromoalkyla-
tion and amination. The microbiological study was undertaken
to evaluate the effects of the substituted chalcones on the
antibacterial and antifungal activities. As regards the
structureeactivity relationship of the derivatives of (E )-4-mer-
captochalcone and (E )-4-hydroxychalcone the introduction of
4-alkylthio-N-piperidine, 4-alkylthio-N-40-methylpiperidine or
4-alkoxy-N-40-methylpiperidine group as a substituent in the
para position of the (E )-4-mercaptochalcone or (E )-4-hydrox-
ychalcone moiety, noticeably enhanced the antimicrobial
activity displayed by the unsubstituted chalcones. The
6.1.2. General synthesis of (E )-4-bromoalkylthiochalcones
1e4
To a stirred solution of a proper dibromoalkane (2 mmol) in
N,N-dimethylformamide (5 ml) at room temperature, a solution
of (E )-4-mercaptochalcone (0.240 g, 1 mmol) and triethyl-
amine (0.32 ml, 2 mmol) in 10 ml of DMF was added in
a drop-wise fashion. After stirring for 3.5e4 h, the obtained
crude solid was filtered off (bis-(4-chalconylthio)alkanes
were obtained). The reaction mixture was poured into ice-cold

Z. Nowakowska et al. / European Journal of Medicinal Chemistry 43 (2008) 707e713
713
water (50 ml) on continuous stirring, the crude product was
precipitated. Purification of a (E )-4-bromoalkylthiochalcones
1e4 was accomplished by column chromatography (column
e length 30 cm, diameter 2.0 cm) over silica gel (18 g e 63e
100 mesh, Merck), eluting with chloroform. The fractions of
20 ml were collected and monitored by analytical TLC. The
products desired were obtained from fractions 4e7. The prod-
uct-containing fractions were collected and concentrated under
reduced pressure to yield a yellow solid. Crystallization from
ethanol gives yellow crystalline products.
obtained from fractions 6e12. The isolated crude product
was recrystallized from chloroformeethanol.
6.2. Microbiology
The microorganisms used were supplied by the National In-
stitute of Hygiene in Warsaw (S. aureus 209P FDA, E. coli PZH
026 B6, C. albicans PCM 1409 PZH), American type Culture
Collection (Streptococcus faecalis ATCC 8040, B. subtilis
´
ATCC 1633), Department of Microbiology, Poznan University
of Medical Sciences (K. pneumoniae 231, P. aeruginosa SP1),
´
Department of Medical Mycology, Poznan University of Med-
6.1.3. General synthesis of (E )-4-aminoalkylthiochalcones
5e20
ical Sciences (A. fumigatus C1, M. gypseum K1).
Compounds were dissolved using DMSO (Serva); concen-
tration was 1000 mg mlꢁ1. The MIC values of the compounds
were determined, with reference to standard microorganisms,
by introducing 1 ml of the corresponding solutions at various
concentrations into a series of tubes (each 12 ꢃ 100 mm), then
0.1 ml of a standardized 1:1000 diluted suspension of a micro-
organism was added. The MIC values were determined after
18 h of incubation at 37 ꢀC. As a test medium for bacteria
the fluid medium Penassay Broth (Difco) was used. In each as-
say both the bacterial culture sterility and standard bacterial
growth were controlled. Sabouraud dextrose broth (Difco)
was used as a test medium for fungi; MIC values were deter-
mined after 3e7 days of incubation at 25 ꢀC. In all assays both
fungi culture sterility and standard fungi growth were checked.
To a stirred solution of (E )-4-bromoalkylthiochalcone
(1 mmol) in N,N-dimethylformamide (10 ml) at room tempera-
ture, triethylamine (0.28 ml, 2 mmol) and piperidine (4-methyl-
piperidine, morpholineorpiperazine, 1 mmol)were added. After
stirring for 3 days, the reaction mixture was added drop-wise to
cold water. The crystalline precipitate was isolated by filtration
and the precipitated solid was purified by column chromatogra-
phy (column e length 30 cm, diameter 2.0 cm) on silica gel
(15 g e 63e100 mesh, Merck). The column was eluted succes-
sively with the following solvents: chloroform [70 ml], chloro-
formemethanol mixtures [50:1 e 150 ml]. The fractions of
20 ml were collected and monitored by analytical TLC. The
products desired were obtained from fractions 5e10. The
isolated crude product was recrystallized from chloroforme
ethanol.
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