J. Ravindran et al. / Biochemical Pharmacology 79 (2010) 1658–1666
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Because of these anti-inflammatory and anti-cancer activities,
there has been lot of interests in the origin of these activities from
within the curcumin molecule. Indeed, the interest has persisted
ever since curcumin was first synthesized by Lampe in 1918. The
entire molecule can be divided into halves that are mirror images
obtain 3,4-dihydroxybenzaldehyde (53.0 g, yield: 83%, HPLC
purity: 98.5%).
To a solution of acetylacetone (9.6 mL, 0.094 mol, 5 equiv.) in
ethyl acetate was added tributyl borate (25 mL, 0.09 mol, 5 equiv.)
and stirred for 30 min at 70 8C. To the reaction mixture, was added
3,4-dihydroxybenzaldehyde (2.6 g, 0.01 mol, 1 equiv.) and stirred
for 30 min at 70 8C. After 30 min, the temperature was raised to
85 8C and n-butyl amine (1.8 mL, 0.01 mol, 1 equiv.) in ethyl
acetate was added drop-wise and the stirring was continued for 1 h
at 100 8C and boric anhydride (0.9 g, 0.013 mol, 0.7 equiv.). The
mixture was cooled to 50 8C and hydrolyzed by adding 1N HCl and
stirred for 30 min at 30 8C. The organic layer was separated and the
aqueous layer was extracted with ethyl acetate. The combined
layers were washed with water until neutral and dried over
sodium sulphate. After removal of the solvent in vacuum the crude
product was purified by column chromatography using chloroform
as eluent followed by recrystallization with ethyl acetate and
hexane to obtain hispolon monomethyl ether (1 g, yield: 24%, HPLC
purity: 99%).
of each other. Besides a
b-diketone, it consists of two phenyl, two
methoxy, and two hydroxyl groups. Besides natural analogues
(e.g., demethoxycurcumin and bisdemethoxycurcumin), numer-
ous analogues have been synthesized in an attempt to find ‘‘super
curcumin’’ [13]. In the current report, we describe certain
analogues of curcumin that are more potent than curcumin as
anti-inflammatory and anti-proliferative agents against various
tumor cells including cancers of the colorectum, prostate, and
breast, and against human myeloid leukemia and multiple
myeloma cells.
2. Materials and methods
2.1. Materials
Synthetic curcumin and bisdemethylcurcumin were synthe-
sized as described [18]. A series of hispolon analogs were
synthesized through the condensation of appropriately pro-
tected hydroxybenzaldehydes with acetylacetone, as described
below.
2.1.3. Synthesis of hispolon (alternative method)
To an ice cold solution of hispolon methylether (11 g, 0.04 mol,
1 equiv.) in ethylacetate was added aluminum chloride (15 g,
0.11 mol, 2.3 equiv.) followed by the drop-wise addition of
pyridine (35 mL, 0.43 mol, 9.26 equiv.) for 15 min and the reaction
mixture was heated under reflux for 7 h at 65 8C. After completion
of the reaction, the reaction mixture was cooled to 10 8C and added
cold HCl (20%) to decompose aluminum chloride complex and
extracted with ethyl acetate. The combined ethyl acetate layer was
washed with water, brine and dried over anhydrous sodium
sulphate. The solvent was evaporated and the crude product
obtained was purified by column chromatography using chloro-
form as eluent followed by recrystallization from a mixture of ethyl
acetate and hexane to obtain hispolon (5.3, yield: 51%, HPLC purity:
2.1.1. Synthesis of hispolon methyl ether (HME)
To a solution of acetylacetone (335 mL, 3.28 mol, 5 equiv.) in
ethyl acetate was added boric anhydride (32 g, 0.459 mol,
0.7 equiv.) and stirred for 30 min at 70 8C. To the above solution
was added vanillin (100 g, 0.657 mol, 1 equiv.) and tributyl borate
(177 mL, 0.657 mol, 1 equiv.) and stirred for 30 min at 70 8C. After
30 min the temperature was raised to 85 8C and n-butyl amine
(64.9 mL, 0.657 mol, 1 equiv.) in ethyl acetate was added drop-
wise and the stirring was continued for 1 h at 100 8C. The reaction
mixture was cooled to 50 8C and hydrolyzed by adding 1N HCl
(200 mL) and stirred for 30 min at 30 8C. The organic layer was
separated and the aqueous layer was extracted with ethyl acetate.
The combined organic layer was washed with water until neutral
and dried over sodium sulphate. After removal of the solvent in
vacuum the crude product obtained was purified by column
chromatography using chloroform as eluent followed by recrys-
tallization from ethyl acetate and hexane to obtain hispolon
monomethyl ether (26% yield, HPLC purity: 99%). M.p. 140–
99%). M.p. 150.0–151.9 8C, 1H NMR (d6-acetone, 300 MHz):
d 15.75
(1H, brs), 8.47 (1H, brs), 8.14 (1H, brs), 7.46 (1H, d, J = 15.9 Hz), 7.13
(1H, d, J = 2.0 Hz), 7.02 (1H, d, J = 8.2, 2.0 Hz), 6.84 (1H, d,
J = 8.2 Hz), 6.46 (1H, d, J = 15.9 Hz), 5.76 (1H, s), 2.09 (3H, s);
Mass: m/z 221 (M+H)+; 243 (M+Na)+; 219 (M–H)ꢀ.
2.1.4. Synthesis of methoxy hispolon methyl ether (MHME)
To a solution of acetylacetone (69.9 mL, 0.68 mol, 5 equiv.) in
ethyl acetate was added boric anhydride (6.68 g, 0.09 mol,
0.7 equiv.) and stirred for 30 min at 70 8C. To the above solution
was added syringaldehyde (25 g, 0.13 mol, 1 equiv.) and tributyl
borate (37 mL, 0.13 mol, 1 equiv.) and stirred for 30 min at 70 8C.
After 30 min the temperature was raised to 85 8C and n-butyl
amine (13.5 mL, 0.13 mol, 1 equiv.) in ethyl acetate was added
drop-wise and the stirring was continued for 1 h at 100 8C. The
mixture was cooled to 50 8C and hydrolyzed by adding 1N HCl and
stirred for 30 min at 50 8C. The organic layer was separated and the
aqueous layer was extracted with ethyl acetate. The combined
layers were washed with water until neutral and dried over
sodium sulphate. After removal of the solvent in vacuum the crude
product was purified by column chromatography using chloroform
as eluent followed by recrystallization with ethyl acetate and
hexane to obtain methoxy hispolon methyl ether (11 g, yield: 30%,
HPLC purity: 99%). M.p. 118–120 8C, 1H NMR (d6-acetone,
144.5 8C, 1H NMR (d6-acetone, 300 MHz):
d 15.74 (1H, brs), 8.12
(1H, brs), 7.52 (1H, d, J = 15.8 Hz), 7.29 (1H, d, J = 2.0 Hz), 7.11 (1H,
d, J = 8.2 Hz), 6.85 (1H, d, J = 8.2 Hz), 6.57 (1H, d, J = 15.8 Hz), 5.75
(1H, s), 3.89 (3H, s), 2.09 (3H, s); Mass: m/z 235 (M+H)+; 257
(M+Na)+; 273 (M+K)+.
2.1.2. Synthesis of hispolon
Vanillin (70 g, 0.46 mol, 1 equiv.) and ethylene dichloride
(1400 mL, 20 vol.) were taken in
a 5 L RB flask at room
temperature and cooled slowly to 0–5 8C and added aluminum
chloride (153.3 g, 1.15 mol, 2.5 equiv.) lot wise followed by
pyridine (349 mL, 4.324 mol, 9.4 equiv.) drop-wise for 15 min.
The temperature of the reaction was raised to reflux and
maintained for 2 h under reflux. After completion of the reaction
(progress of the reaction was monitored by TLC), the contents of
the flask were cooled to 0–5 8C and added aq. HCl (20%) drop-
wise maintaining the temperature below 20 8C. The organic
layer was separated and the aqueous layer was extracted with
ethyl acetate (four times) and the combined organic layer was
washed with water (thrice), dried over anhydrous sodium
sulphate. The solvent was removed and the crude product
obtained was recrystllized from ethyl acetate and hexane to
300 MHz):
d 15.45 (1H, brs), 7.51 (1H, d, J = 15.8 Hz), 6.76 (2H,
s), 6.32 (1H, d, J = 15.8 Hz), 5.75 (1H, s), 5.64 (1H, s), 3.93 (6H, s),
2.16 (3H, s); Mass: m/z 265 (M+H)+; 287 (M+Na)+.
2.1.5. Synthesis of methoxy hispolon (MH) and hydroxy hispolon (HH)
N,N-Dimethylaniline (34.5 mL, 0.27 mol, 12 equiv.) was taken
in a flask at room temperature and slowly the temperature was
raised to 40 8C and aluminium chloride (36.3 g, 0.27 mol, 5 equiv.)