Syntheses and cytotoxic properties of the curcumin analogs 2,6-bis(benzylidene)-4-phenylcyclohexanones

Article abstract of DOI:10.1002/ardp.200800028

Fifteen curcumin analogs were synthesized and tested for in-vitro cytotoxicity towards B16 and L1210 murine cancer cell lines using an MTT assay. Significant activity was discovered for two analogs: 8 (B16 IC₅₀ = 1.6 μM; L1210 IC₅₀ =

Full text of DOI:10.1002/ardp.200800028

440
Arch. Pharm. Chem. Life Sci. 2008, 341, 440–445
Full Paper
Syntheses and Cytotoxic Properties of the Curcumin Analogs
2,6-Bis(benzylidene)-4-phenylcyclohexanones
Ryan Davis1, Umashankar Das2, Hilary Mackay1, Toni Brown1, Susan L. Mooberry3,
Jonathan R. Dimmock2, Moses Lee1, and Hari Pati2
1 Department of Chemistry, Hope College, Holland, MI, USA
2 College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
3 Department of Physiology and Medicine, Southwest Foundation for Biomedical Research, San Antonio, TX,
USA
Fifteen curcumin analogs were synthesized and tested for in-vitro cytotoxicity towards B16 and
L1210 murine cancer cell lines using an MTT assay. Significant activity was discovered for two
analogs: 8 (B16 IC50 = 1.6 lM; L1210 IC50 = 0.35 lM) and 9 (B16 IC50 = 0.51 lM; L1210 IC50 = 1.2 lM).
Several other analogs exhibited notable cytotoxicity. The data from quantitative structure-activ-
ity relationships suggest that large electron-withdrawing substituents placed in the meta-posi-
tion of the arylidene aryl rings enhance potencies. Compounds 8 and 9 were found using a cell-
based assay to have virtually no effects on microtubules at concentrations up to 40 lM. These
results suggest that tubulin inhibition is not the principal mechanism by which the curcumin
analogs act.
Keywords: B16 / Curcumin analogs / L1210 / Microtubules / Structure-activity relationships /
Received: January 26, 2008; accepted: March 27, 2008
DOI 10.1002/ardp.200800028
Introduction
Curcumin (Fig. 1), a bis-a,b-unsaturated b-diketone found
in the rhizomes of the herbaceous plant turmeric, has
been extensively studied due to its biological effects,
Figure 1. Structure of curcumin.
especially its anticancer properties. Curcumin has signif-
icant anti-proliferative effects towards various human
cancer cell lines derived from prostate, large intestine,
bone, and white blood cells [1–4]. In addition, curcumin
has been shown to have a degree of tumor specificity, tar-
geting malignant cells in preference to non-malignant
cells [5] and it is effective at low micromolar concentra-
tions [6].
The mechanisms by which curcumin acts to control
malignant cell growth are varied, and have been pro-
posed to be tissue-specific [6]. Cellular apoptosis is one of
the main mechanisms that has been studied [7, 8]. Curcu-
min is also known to slow angiogenesis by blocking AP-1
[9] and is known to down-regulate the oncogene MDM2
in prostate cancer [10]. It has also been reported that cur-
cumin can inhibit the polymerization of tubulin for spin-
dle- fiber formation during mitotic cell division [11]. This
is of particular interest to one of the author's laboratory,
which has extensively studied the effects of combretasta-
tin-A4 analogs, such as chalcones and diarylheterocycles,
as mitotic inhibitors. Presumably, cytotoxicity is medi-
ated, at least in part, by microtubule depolymerization
and inhibition of tubulin polymerization [12–17].
Correspondence: Prof. Moses Lee, Department of Chemistry, Hope Col-
lege, Holland, MI 49423, USA.
E-mail: lee@hope.edu
The current study reports the synthesis of fifteen cur-
cumin analogs 1–15 for evaluation as cytotoxins. These
analogs replaced the diketone moiety of curcumin with a
Fax: +1 616 395 7923
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Arch. Pharm. Chem. Life Sci. 2008, 341, 440–445
Cytotoxic Curcumin Analogs
441
Table 1. Cytotoxicity results of synthesized curcumin analogs in B16 and L1210 cell lines as determined by MTT assay.
4-phenylcyclohexanone moiety. Cyclohexanone analogs the conformation of the diaryl moieties and cytotoxicity,
that lack the 4-phenyl group have recently been reported as well as the Hammett constant r, was reported [20].
and they were discovered to have significant anti-angio-
In the present study, the hydroxyl and methoxy sub-
genic activity, measured by the inhibition of the growth stituents present on the aryl rings in curcumin were
of SVR endothelial cells in culture [18]. Substituted heter- retained and, in addition, other groups were introduced
ocyclic analogs of curcumin namely various 3,5-bis(ben- in order to examine the possible relationships between
zylidene)-4-piperidones have also been reported and they stereo-electronic and hydrophobic factors and cytotoxic-
were found to be active in inhibiting the growth of can- ity. The cytotoxicity studies on the compounds were per-
cer cells in culture [19, 20]. From molecular modeling formed with a 72 h continuous exposure MTT assay,
and X-ray crystallography studies, a relationship between using murine B16 (melanoma) and L1210 (leukemia) cell
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R. Davis et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 440–445
Scheme 1. Synthesis of the 2,6-bis(benzylidene)-4-phenylcyclohexanones or curcumin analogs 1–15.
Table 2. Physical constants of the substituents in analogs 1–15:
Hammett r and Taft r*, Hansch p, and molar refractivity MR.
lines. Two of the most potent compounds, 8 and 9, under-
went further evaluation for effects on cellular microtu-
bules.
Analogs
Substituents
r/r*
p
MR
1
2
4
4-OCH3
H
3,4-O-CH2-O
4-Cl
–0.28
0.00
–0.27
0.24
–0.02
0.00
–0.05
0.71
9.93
3.09
9.99
Results and discussion
5
8.09
6
7
8
9
12
13
14
4-F
3-OCH3
4-NO2
3,4,5-(OCH3)
3-Br
2-Cl
0.06
0.11
0.78
–0.06
0.39
0.14
2.98
9.93
9.42
23.61
10.94
8.09
Chemistry
–0.02
–0.28
–0.06
0.86
0.71
–0.69
The curcumin analogs depicted in Table 1 were synthe-
sized using an acid catalyzed aldol condensation of the
appropriate aryl aldehyde with 4-phenylcyclohexanone
(Scheme 1). The products were purified by recrystalliza-
tion from ethanol and were obtained in yields of 45–
80%. The structures were ascertained by IR, NMR, and
mass spectrometry. Compounds 1 and 10 have been
described previously but only their photophysical prop-
erties were studied [21].
0.37
–0.27
3-OCH-3,4-OH
11.75
Specifically, the following comparisons were made in
attempting to discern correlations between the nature of
the aryl substituents and cytotoxic potencies. First, the
mode of action of conjugated unsaturated ketones
includes alkylation of cellular thiols [22]. Hence, the elec-
tronic nature of the aryl substituents will affect the
charge densities on the olefinic carbon atoms, which, in
turn, will control the rate and extent of thiol alkylation.
Linear and semilogarithmic plots were made between
the Hammett s and Taft r* values (Table 2) of the aryl sub-
stituents and the IC50 values which were less than 100 lM
in the B16 assay. A trend towards a negative correlation
was noted in the linear plot (p = 0.083). The analyses were
repeated using the biological data in the L1210 screen,
which indicated a negative correlation in the semilogar-
ithmic plot (p = 0.060) and a linear plot (p = 0.117). Thus,
cytotoxic potencies rise as the electron-withdrawing
capacity of the aryl substituents increases. This observa-
tion is in accord with the view that a mode of action of
these compounds is likely by reaction with cellular thi-
ols.
Cytotoxic activity in murine cell lines
The cytotoxicity of curcumin analogs 1–9, 11–15 was
assessed in B16 (murine melanoma) and L1210 (murine
leukemia) cell lines using a 72 h continuous exposure
MTT assay as previously described [14]. The concentration
at which 50% cell growth was inhibited (IC50, lM) was
determined for each compound in triplicate experi-
ments. Data could not be obtained for compound 10
because it was insoluble in different solvents including
dimethylsulfoxide. The results from the cytotoxicity
studies are presented in Table 1.
The following general observations were made. First,
the IC50 values of a number of the compounds are in the
low micromolar range (1–10 lM) in 61% of the bioassays.
In addition, the IC50 figures of both 8 and 9 in one of the
bioassays are sub-micromolar and they are clearly lead
molecules. Second, with the exception of 1, the IC50 val-
ues of the compounds are similar in both screens.
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Arch. Pharm. Chem. Life Sci. 2008, 341, 440–445
Cytotoxic Curcumin Analogs
443
confirms that in developing the cluster of unsaturated
ketones, strongly electron-attracting groups should be
attached to the benzylidene aryl rings. The meta position
appears to be optimal for the methoxy group. Thus, the
potency of 7 which possesses a single meta-methoxy sub-
stituent is greater than 1 having a single para-methoxy
group. The addition of a 4-hydroxy moiety to 7 led to 14,
which has similar IC50 values as 7. The number of meta-
methoxy groups was increased in 9 which possesses high
potency. On the other hand, placing methoxy groups in
the ortho position as in 11 eliminates significant cyto-
toxic potency. The possibility that the meta position may
be the optimal location was enhanced by the fact that the
3-bromo analog 12 had the lowest IC50 values apart from
the lead compounds 8 and 9. One may note, however,
that the size of the group in the meta position is a consid-
eration since the placing of the bulky 3-phenoxy substitu-
ent into 6 leading to 15 led to a marked reduction in
potency. In summary, the available evidence in regard to
structure-activity relationships in this series of com-
pounds reveals that in general (i) the compounds are
potent cytotoxins, (ii) large electron-withdrawing groups
should be placed in the benzylidene aryl rings, and (iii)
the meta position is likely the preferred location in pro-
ducing analogs with low IC50 values.
Figure 2. Superimposed structures of 1, 7, and 9.
Second, the hydrophobic and steric properties of aryl
substituents can influence the magnitude of biological
responses [23]. Linear and semilogarithmic plots were
constructed between the IC50 values of 1, 2, 4–9, and 12–
14 in the B16 screen and both the Hansch p and molar
refractivity (MR) values (Table 2). The process was
repeated using the biological data for 2, 4–9, and 12–14
in the L1210 assay. No correlations were noted (p A 0.05),
although a trend towards a negative correlation was
observed in the semilogarithmic plot between the IC50
values in the B16 screen and the MR figures (p = 0.089).
This observation suggests that potency is enhanced by
increasing the size of the aryl substituents. A further
steric feature of these molecules, which could influence
cytotoxic potencies are the torsion angles h1 and h2
between the aryl rings and the adjacent olefinic linkages.
Consequently, models of 1, 2, 4–9, and 12–14 were built
and the h1 and h2 angles recorded. Linear and semilogar-
ithmic plots between the h1 and h2 values of these com-
pounds and the IC50 figures in the B16 screen were made.
The process was repeated using the data from the L1210
test except 1 was omitted (IC50 value of A 100 lM). No cor-
relations were observed (p A 0.05). Thus, these torsion
angles are unlikely to exert a major influence on cyto-
toxic potencies. Models revealed that the locations of the
methoxy group of 7 and the 3-methoxy substituent of 9
virtually overlapped (Fig. 2) which may explain the signif-
icant potencies of both compounds. In addition, since
the IC50 values of 1 are greater than 2, the 4-methoxy
group lowers cytotoxic potencies. Figure 2 reveals that
the 4-methoxy substituents of 1 and 9 are in similar loca-
tions, suggesting that this group in 9 has an adverse
effect on potency and that the 3,5-dimethoxy analog may
well exceed the potencies of 9.
Effects on cellular microtubules
Since curcumins have been reported to cause microtu-
bule depolymerization and inhibit tubulin polymeriza-
tion and angiogenesis, the effects of the two active com-
pounds 8 and 9 on cellular microtubules were investi-
gated [15, 24]. Results from these studies showed that
compounds 8 and 9 were virtually inactive at concentra-
tions up to 40 lM. These results suggest that the mecha-
nism of cytotoxicity is unrelated to the disruption of
microtubules.
Conclusion
The results from this study confirm that readily accessi-
ble curcumin analogs are potential cytotoxins for anti-
cancer-drug discovery. It is concluded that large electron-
withdrawing groups at the meta positions enhance cyto-
toxic potencies.
Third, the positions of the substituents on the benzyli-
dene aryl rings in relation to cytotoxic potencies were
addressed. A review of the IC50 values for compounds
which possess a single para substituent namely 1, 3, 5, 6,
8 indicates that those molecules with electron-withdraw-
ing groups (5, 6, 8) are more potent than the analogs with
electron-repelling substituents (1, 3). This observation
The authors thank Taiho Pharmaceutical Co. and Hope College
for support.
The authors have declared no conflict of interest.
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R. Davis et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 440–445
2,6-Bis[(4-fluorophenyl)methinyl]-4-
phenylcyclohexanone 6
Yellow solid. M.p. 1598C. H-NMR (CDCl3, 400 MHz): d (ppm) =
2.96 (m, 3H), 3.22 (m, 2H), 7.02–7.06 (m, 4H), 7.24–7.35 (m, 5H),
7.39 (m, 4H), 7.81 (s, 2H). IR (KBr pellets cm– 1) m = 3043, 2899,
2838, 1946, 1666, 1600, 1566, 1508, 1414, 1292, 1232, 1187,
1148, 1101, 989, 832, 754, 702. ESI(APCI)-MS: m/z = 387 [M + 1].
Experimental
1
Chemistry
All fifteen analogs were synthesized according to the following
general procedure. Aqueous hydrochloric acid (35%, 0.5 mL) was
added dropwise to
a solution of 4-phenylcyclohexanone
(500 mg) and the appropriate aryl aldehyde (2 equivalents) in
ethanol (20 mL) at room temperature. The reaction mixture was
stirred under reflux for 3–4 h monitoring by silica gel TLC
plates (hexane / ethyl acetate, 9 : 1). The precipitate formed
upon cooling to room temperature was filtered, washed with
chilled ethanol, and recrystallized from ethanol (with the excep-
tion of 15 which was purified over silica eluting with ethyl ace-
tate / hexane, 5 : 95). The isolated chemical yields were between
70–80%, except compound 8 was isolated in 45% yield.
2,6-Bis[(3-methoxyphenyl)methinyl]-4-
phenylcyclohexanone 7
Yellow solid. M.p. 978C. 1H-NMR (CDCl3, 400 MHz): d (ppm) = 2.96
(m, 3H), 3.27 (m, 2H), 3.78 (s, 6H), 6.83 (m, 2H), 6.94 (s, 2H),
7.00(m, 2H), 7.21–7.33 (m, 7H), 7.81 (s, 2H). IR (KBr pellets cm– 1
)
m = 3068, 3017, 2952, 2891, 2837, 2577, 1938, 1660, 1601, 1575,
1481, 1433, 1246, 1196, 1215, 1157, 1051, 947, 899, 785, 743,
695. ESI(APCI)-MS: m/z = 411 [M + 1].
2,6-Bis[(4-methoxyphenyl)methinyl]-4-
2,6-Bis[(4-nitrophenyl)methinyl]-4-phenylcyclohexanone
phenylcyclohexanone 1
1
Yellow solid. M.p. 1150C. H-NMR (CDCl3, 400 MHz): d (ppm) =
8
Yellow solid. M.p. 818C. 1H-NMR (CDCl3, 400 MHz): d (ppm) = 3.04
(m, 3H), 3.22 (m, 2H), 7.24–7.37 (m, 5H), 7.56 (d, 4H, J = 8.4 Hz),
7.87 (s, 2H), 8.22 (d, 4H, J = 8.8 Hz). IR (KBr pellets cm– 1) m = 3070,
2924, 2847, 2447, 1935, 1665, 1594, 1518, 1345, 1300, 1240,
1192, 1152, 1110, 995, 908, 855, 761. ESI(APCI)-MS: m/z = 439
[M – 1].
2.98 (m, 3H), 3.28 (m, 2H), 3.81 (s, 6H), 6.88 (d, 4H, J = 8.8 Hz),
7.25–7.37 (m, 5H), 7.42 (d, 4H, J = 8.8 Hz), 7.83 (s, 2H). IR (KBr pel-
lets cm– 1) m = 3029, 2954, 2904, 2836, 2042, 1663, 1599, 1509,
1460, 1254, 1175, 1030, 988, 833, 703. ESI(APCI)-MS: m/z = 411
[M + 1].
2,6-bis(phenylmethinyl)-4-phenylcyclohexanone 2
2,6-Bis[(3,4,5-trimethoxyphenyl)methinyl]-4-
1
Yellow solid. M.p. 1328C. H-NMR (CDCl3, 400 MHz): d (ppm) =
phenylcyclohexanone 9
2.99 (m, 3H), 3.29 (m, 2H), 7.26–7.45 (m, 15H), 7.87 (s, 2H). IR (KBr
pellets cm– 1) m = 3054, 3026, 2881, 1961, 1816, 1659, 1603, 1566,
1493, 1446, 1294, 1235, 1189, 1159, 986, 935, 762, 697.
ESI(APCI)-MS: m/z = 351 [M + 1].
Yellow solid. M.p. 1838C. 1H-NMR (CDCl3, 400 MHz): d (ppm) =
3.03 (m, 3H), 3.33 (m, 2H), 3.85 (s, 12H), 3.88 (s, 6H), 6.69 (s, 4H),
7.26-7.35 (m, 5H), 7.81 (s, 2H). IR (KBr pellets cm– 1) m = 2995,
2941, 2838, 2000, 1657, 1578, 1503, 1454, 1417, 1346, 1286,
1243, 1127, 1020, 936, 836, 733. ESI(APCI)-MS: m/z = 531 [M + 1].
2,6-Bis[(4-methylphenyl)methinyl]-4-
2,6-Bis[(4-dimethylaminophenyl)methinyl]-4-
phenylcyclohexanone 3
1
Yellow solid. M.p. 1890C. H-NMR (CDCl3, 400 MHz): d (ppm) =
phenylcyclohexanone 10
1
2.35 (s, 6H), 2.98 (m, 3H), 3.27 (m, 2H), 7.16 (d, 4H, J = 8.0 Hz),
7.23–7.36 (m, 9H), 7.84 (s, 2H). IR (KBr pellets cm– 1) m = 3026,
2919, 2732, 1917, 1661, 1599, 1563, 1510, 1316, 1291, 1239,
1179, 1149, 989, 818, 750, 700. ESI(APCI)-MS: m/z = 379 [M + 1].
Orange solid. M.p. 708C. H-NMR (CDCl3, 400 MHz): d (ppm) =
2.99 (m, 15H), 3.31 (m, 2H), 6.66 (d, 4H, J = 8.8Hz), 7.24–7.35 (m,
5H), 7.41 (d, 4H, J = 8.8 Hz), 7.83 (s, 2H); IR (KBr pellets cm– 1) m =
3027, 2892, 2812, 2530, 1883, 1651, 1586, 1522, 1444, 1367,
1300, 1230, 1168, 1066, 988, 945, 818. ESI(APCI)-MS: m/z = 437
[M + 1].
2,6-Bis[(3,4-methylenedioxyphenyl)methinyl]-4-
phenylcyclohexanone 4
2,6-Bis[(2,6-dimethoxyphenyl)methinyl]-4-
1
Yellow solid. M.p. 1968C. H-NMR (CDCl3, 400 MHz): d (ppm) =
phenylcyclohexanone 11
2.96 (m, 3H), 3.25 (m, 2H), 5.97 (s, 4H), 6.81 (d, 2H, J = 8.0 Hz),
6.94–6.99 (m, 4H), 7.25–7.37 (m, 5H), 7.77 (s, 2H). IR (KBr pellets
cm– 1) m = 3076, 3003, 2896, 2778, 1855, 1657, 1589, 1556, 1500,
1435, 1359, 1336, 1293, 1224, 1146, 1096, 1039, 989, 934, 867,
814, 759. ESI(APCI)-MS: m/z = 439 [M + 1].
Yellow solid. M.p. 2108C. 1H-NMR (CDCl3, 400 MHz): d (ppm) =
2.62 (m, 4H), 2.97 (m, 1H), 3.79 (s, 12H), 6.51 (d, 4H, J = 8.4 Hz),
7.13–7.25 (m, 7H), 7.73 (s, 2H). IR (KBr pellets cm– 1) m = 2997,
2937, 2837, 2531, 1910, 1671, 1615, 1582, 1469, 1433, 1294,
1254, 1138, 1107, 1033, 988 761. ESI(APCI)-MS: m/z = 471 [M + 1].
2,6-Bis[(4-chlorophenyl)methinyl]-4-
2,6-Bis[(3-bromophenyl)methinyl]-4-
phenylcyclohexanone 5
phenylcyclohexanone 12
1
1
Yellow solid. M.p. 1718C. H-NMR (CDCl3, 400 MHz): d (ppm) =
Yellow solid. M.p. 1718C. H-NMR (CDCl3, 400 MHz): d (ppm) =
2.97 (m, 3H), 3.22 (m, 2H), 7.25–7.28 (m, 4H), 7.33–7.38 (m, 9H),
7.80(s, 2H). IR (KBr pellets cm– 1) m = 3064, 3028, 2899, 2564, 1911,
1666, 1604, 1490, 1407, 1309, 1281, 1237, 1185, 1146, 1094,
1011, 989, 833, 762, 698. ESI(APCI)-MS: m/z = 419 [M + 1].
2.98 (m, 3H), 3.21 (m, 2H), 7.22–7.45 (m, 11H), 7.54 (s, 2H), 7.76 (s,
2H). IR (KBr pellets cm– 1) m = 3056, 3027, 2908, 1947, 1745, 1662,
1605, 1574, 1475, 1411, 1286, 1239, 1188, 1153, 1103, 994, 788,
763. ESI(APCI)-MS: m/z = 506 [M + 1].
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Arch. Pharm. Chem. Life Sci. 2008, 341, 440–445
Cytotoxic Curcumin Analogs
445
[3] M. L. Kuo, T. S. Huang, J. K. Lin, Biochim. Biophys. Acta. 1996,
1317, 95–100.
2,6-Bis[(2-chlorophenyl)methinyl]-4-
phenylcyclohexanone 13
1
[4] K. Ozaki, Y. Kawata, S. Amano, S. Hanazawa, Biochem. Phar-
macol. 2000, 59, 1577–1581.
Yellow solid. M.p. 1648C. H-NMR (CDCl3, 400 MHz): d (ppm) =
2.86–3.11 (m, 5H), 7.20–7.32 (m, 11H), 7.41–7.43 (m, 2H), 7.98
(s, 2H). IR (KBr pellets cm– 1) m = 3060, 3026, 2870, 1960, 1812,
1671, 1609, 1587, 1467, 1436, 1295, 1230, 1189, 1150, 1047, 989,
919, 867, 760, 701. ESI(APCI)-MS: m/z = 419 [M + 1].
[5] S. Plummer, D. Wakelin, M. Bouer, Br. J. Cancer 2000, 83
(Suppl. 1), 20.
[6] R. A. Sharma, A. J. Gescher, W. P. Steward, Eur. J. Cancer
2005, 41, 1955–1968.
2,6-Bis[(3-hydroxy-4-methoxyphenyl)methinyl]-4-
[7] B. B. Aggarwal, A. Kumar, A. C. Bharti, Anticancer Res. 2003,
23, 363–398.
phenylcyclohexanone 14
1
Yellow solid. M.p. 1618C. H-NMR (CDCl3, 400 MHz): d (ppm) =
[8] P. Tsvetkov, G. Asher, V. Reiss, Y. Shaul, et al., Proc. Natl.
Acad. Sci. U.S.A. 2005, 102, 5535–5540.
2.99 (m, 3H), 3.29 (m, 2H), 3.88 (s, 6H), 5.78 (s, 2H), 6.89 (d, 2H, J =
8.4 Hz), 6.96 (d, 2H, J = 1.6 Hz), 7.04 (m, 2H), 7.24–7.36 (m, 5H),
7.80 (s, 2H). IR (KBr pellets cm– 1) m = 3525, 3209, 2928, 1641,
1579, 1514, 1422, 1250, 1166, 1126, 1035, 1007, 936, 911, 856,
819. ESI(APCI)-MS: m/z = 443 [M + 1].
[9] T. S. Huang, S. C. Lee, J. K. Lin, Proc. Natl. Acad. Sci. U.S.A.
1991, 88, 5292–5296.
[10] M. Li, Z. Zhang, D. L. Hill, H. Wang, R. Zhang, Cancer Res.
2007, 67, 1988–1996.
2,6-Bis[(4-fluoro-3-phenoxyphenyl)methinyl]-4-
[11] K. K. Gupta, S. S. Bharne, K. Rathinasamy, N. R. Naik, D.
Panda, FEBS J. 2006, 273, 5320–5332.
phenylcyclohexanone 15
1
[12] H. N. Pati, H. L. Holt, R. LeBlanc, J. Dickson, et al., Med.
Chem. Res. 2005, 14, 19–25; H. N. Pati, M. Wicks, H. L. Holt,
R. LeBlanc, et al., Heterocyclic Commun. 2005, 11, 117–120.
Yellow semisolid. H-NMR (CDCl3, 400 MHz) d (ppm) = 2.77 (m,
3H), 3.10 (m, 2H), 6.95–7.35 (m, 21H), 7.69 (s, 2H). IR (KBr pellets)
m = 3030, 2928, 2854, 1943, 1741, 1670, 1586, 1508, 1418, 1271,
1211, 1149, 1117, 1003, 818, 752, 694. ESI(APCI)-MS: m/z = 571
[M + 1].
[13] H. L. Holt Jr., R. LeBlanc, J. Dickson, T. Brown, et al., Hetero-
cyclic Commun. 2005, 11, 465–470.
[14] R. LeBlanc, J. Dickson, T. Brown, M. Stewart, et al., Bioorg.
Med. Chem. 2005, 13, 6025–6034.
Statistical analyses
The Hammett s values were taken from the literature [25] and
the Taft r* figure has been reported previously [26]. The Hansch
p and molar refractivity (MR) figures were obtained from pub-
lished data [27]. The MR value of hydrogen is 1.03. Hence, in
order that the relative bulk of the substituents was compared
accurately, this figure was added to the MR value of the two
groups in disubstituted compounds and 2.06 (261.03) for the
monosubstituted analogs. The MR value for the unsubstituted
compound 2 is 3.09. The linear and semilogarithmic plots were
made using a commercial software package [28].
[15] J. Ruprich, A. Prout, J. Dickson, B. Younglove, et al., Lett.
Drug Des. Discov. 2007, 4, 144–148.
[16] M. Johnson, B. Younglove, L. Lee, R. LeBlanc, et al., Bioorg.
Med. Chem. Lett. 2007, 17, 5897–5901.
[17] L. Lee, R. Davis, J. Vanderham, P. Hills, et al., Eur. J. Med.
Chem. 2008, in press.
[18] T. P. Robinson, T. Ehlers, R. B. Hubbard, X. H. Bai, et al.,
Bioorg. Med. Chem. Lett. 2003, 13, 115–117.
[19] J. R. Dimmock, M. P. Padmanilayam, R. N. Puthucode, A. J.
Nazarali, et al., J. Med. Chem. 2001, 44, 586–593.
Molecular modeling
[20] J. R. Dimmock, A. Jha, G. A. Zello, J. W. Quail, et al., Eur. J.
Med. Chem. 2002, 37, 961–972.
Models of 1,2,4–9, and 12–14 were built using BioMedCache 6.1
for Windows [29]. The lowest energy conformations were
obtained from optimized geometry calculations in MOPAC
using AM1 parameters. The torsion angles for these compounds
are as follows 1: 46.7, –42.1; 2: 48.7, –44.6; 4: 49.0, –45.6; 5:
51.0, –44.5; 6: 48.7, –44.1; 7: 47.4, –48.0; 8: 49.5, –45.2; 9: 53.4,
–45.7; 12: 47.8, –46.5; 13: 92.9, –50.4 and 14: 48.3, –45.6. Energy
minimized structures of 1, 7 and 9 were superimposed (the five
carbon atoms, C=C-C-C=C) and are depicted in Fig. 2.
[21] A. Badaeva, T. V. Timoteera, A. Masunov, S. Tretiak, J. Phys.
Chem. A 2005, 109, 7276–7284.
[22] H. N. Pati, U. Das, R. K. Sharma, J. R. Dimmock, Mini Rev.
Med. Chem. 2007, 7, 131–139.
[23] G. Thomas Medicinal Chemistry An Introduction, John Wiley
and Sons, Ltd., Chichester, 2000, pp. 50–54, 57–59.
[24] Y. Kong, J. Grembecka, M. C. Edler, E. Hamel, et al., ACS
Chem. Biol. 2005, 12, 1007–1014.
Biology
[25] D. D. Perrin, B. Dempsey, E. P. Serjeant pKa Prediction for
Organic Acids and Bases, Chapman and Hall, London, 1981,
pp. 109–112, 120.
Curcumin analogs 1–15 were subjected to a continuous expo-
sure 72 h MTT assay as described previously [14]. L1210 and B16
cell lines were purchased from ATCC (Manassas, VA, USA) and
were maintained as previously reported [14]. The microtubule
disrupting effects were evaluated in A-10 cells by indirect immu-
nofluorescent techniques as previously described [24].
[26] R. W. Taft Jr. in Steric Effects in Organic Chemistry (Ed.: M.S.
Newman), John Wiley and Sons, Inc., New York, 1956, p.
591.
[27] C. Hansch, A. J. Leo Substituent Constants for Correlation
Analysis in Chemistry and Biology, John Wiley and Sons,
New York, 1979, pp. 49, 84.
References
[28] Statistical Package for Social Sciences, SPSS for Windows,
Standard Version, release 13.0 Chicago, SPSS Inc., 2004.
[1] A. P. Chen, J. Xu, Am. J. Physiol. 2005, 288, G447–G456.
[2] T. Dorai, N. Gehani, A. Katz, Prostate Cancer Prostatic Dis.
2000, 3, 84–93.
[29] BioMedCache 6.1 Windows, BioMedCache, Fujitsu Amer-
ica, Inc., 2003.
i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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