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R.K. Singh et al. / European Journal of Medicinal Chemistry 45 (2010) 1078–1086
overnight at room temperature. The reaction mixture was poured
on to chilled water (5 ml) and worked up as in the case of
compound 3. The title compound was obtained as a yellow powder,
which was recrystallized from a mixture of ethanol and water.
Yield: 44%; m.p. ¼100 ꢁC, Rf ¼ 0.69 (EtOAc: Hexane, 3.0:7.0). UV
0.34 mmol) was dissolved in ethanol (7 ml) and NaOEt was added
dropwise at room temperature over 20 min and the reaction
mixture was stirred for another 30 min. The sodium salt was
concentrated under vacuum, washed thoroughly with ethanol,
dissolved in pyridine (5 ml) and further mixed with 2-chloroethanol
(0.067 ml, 1 mmol). The reaction mixture was stirred at room
temperature for 6 h. After completion of the reaction, the mixture
was poured on to crushed ice and extracted thoroughly with EtOAc,
dried over anhydrous Na2SO4 and concentrated to get the inter-
mediate compound 7 (183 mg, 0.29 mmol). The compound 7, dis-
solved in dry pyridine (5 ml), was added dropwise to the activated
folate ester 5 (286 mg, 0.51 mmol) and stirred the reaction mixture
for 15 min. TEA (0.5 ml), DCC (257 mg, 1.25 mmol) and DMAP
(61 mg) were further added. The reaction mixture was stirred for
5 h and the reaction was monitored on TLC.
(EtOH) lmax 260, 245, nm. 1H NMR (DMSO-d6 and D2O)
d 0.97 (t, 6H,
CH3 of palmitic acid); 1.29 (m, 44H, –CH2 of palmitic acid); 1.36 (m,
4H, –CH2 of palmitic acid); 1.58 (m, 4H, –CH2 of palmitic acid); 2.25
(t, 4H, –CH2 of palmitic acid); 3.73 (s, 6H OCH3, Ar of Cur); 4.59 (s,
2H, C4 of Cur); 6.68 (d, 2H, C2 and C6 of Cur); 6.76–6.93 (m, 6H, Ar
of Cur); 7.56 (d, 2H, C1 and C7 of Cur); 13C NMR (CDCl3):
d 196.5,
169.0, 154.8, 140.5, 137.9, 132.7, 126.6, 122.3, 118.9, 112.2, 56.0, 36.0,
33.2, 32.5, 32.0, 30.3, 30.0, 29.7, 25.4, 23, 14.0, MS m/z 844 (Mþ).
Anal. Calcd for C53H80O8: C, 75.20; H, 9.46 found: C, 75.32; H, 9.54.
5.1.4. p-Nitro phenyl ester of folic acid (5)
The precipitate of DCU started to appear after 30 min. After the
completion of the reaction, DCU was filtered off and the filtrate was
evaporated to dryness. After deprotection of both phenolic
hydroxyl functions on curcumin with NH3–pyridine (9:1v/v) at
55 ꢁC, ammonia was removed using water pump, the solvent
evaporated and the residue dissolved in EtOAc (20 ml). The product
was purified by silica gel column chromatography using ethyl
acetate (1–2%) in hexane as eluant. The title compound was
recrystallized from ethanol/water as light brown solid. Yield: 45%;
m.p. ¼ 210 ꢁC, Rf ¼ 0.57 (EtOAc:Hexane, 3.5:6.5), UV(EtOAc) lmax
To a stirred solution of folic acid (2 g, 5 mmol) in anhydrous
ethyl acetate (10 ml), added dropwise p-nitrophenol (0.834 g,
6 mmol) dissolved in ethyl acetate (10 ml). After 15 min, pyridine
and triethylamine (1 ml each) were added to make it more basic,
stirred for 15 min and further added DCC (2.579 g, 12.5 mmol). The
reaction mixture was stirred for 2.5 h and monitored on TLC. The
completion of the reaction was assessed by total consumption of
the starting material.
5.1.5. 1,7-Bis-[(4,4 -di-O-bis-(
g
,
g)-folyl)3-methoxy phenyl]-1,6-
245, 275, 300 nm. 1H NMR (DMSO-d6 and D2O);
d 1.75 (m, 2H, C2,
heptadiene-3,5-dione (6)
Curcumin (94 mg, 0.25 mmol) dissolved in dry pyridine (5 ml)
was added dropwise to activated folate ester (323 mg,
ethyl), 2.21 (m, 2H, C21, FA); 2.25 (m, 2H, C22, FA); 3.21 (t, 1H, C4,
Cur); 3.73 (s, 6H OCH3, Ar, Cur); 4.08 (t, 2H, C1, ethyl), 4.32 (s, 2H, C9
H, FA); 4.46 (m, 1H, C19, FA); 6.54 (d, 2H, C12 and C16 Ar, FA); 6.56
(d, 2H, C2 and C6, Cur); 6.57–6.69 (m, 6H, Ar-Cur); 7.54 (d, 2H, C1
and C7, Cur); 7.73 (d, 2H, C13 and C15, Ar, FA); 8.8 (s, 1H, C7, pyr-
5
0.57 mmol), stirred for 15 min and TEA (0.5 ml), DCC (292 mg,
1.42 mmol) and DMAP (61 mg) were further added. The reaction
mixture was stirred for 5 h and monitored on TLC. The precipitate of
DCU started to appear after 30 min. At the end of the reaction, DCU
was filtered off, the filtrate evaporated and the residue dissolved in
EtOAc (20 ml). This organic fraction was washed consecutively with
5% NaHCO3 solution (20 ml) (to neutralize the residual acid and to
separate excess amount of PNP), NaCl (20 ml), H2O (20 ml), dried
over anhydrous Na2SO4, filtered and reduced under vacuum. The
title compound was purified by silica gel column chromatography
using ethyl acetate (1.5–2%) in hexane as eluant and recrystallized
from ethanol/water. Yield: 48%; m.p. ¼ 238 ꢁC, Rf ¼ 0.6 (EtOA-
c:Hexane, 3.5:6.5), UV(EtOAc) lmax 280, 300 nm. 1H NMR (DMSO-d6
azine, FA); 13C NMR (CDCl3):
d 21.8, 26.3, 27.9, 56.7, 60.7, 63.5, 112.4,
113.2, 116.6, 119.9, 118.9, 121.9, 122.3, 126.6, 128.1, 128.5, 128.9, 138.1,
140.5, 142.1, 146.9, 148.4, 149.1, 150.8, 161.2, 167.9, 177.0, 172.0, 197.6,
MS m/z 835 (Mþ). Anal. Calcd for C42H41N7O12: C, 60.35; H, 4.91; N,
11.73 found: C, 60.38; H, 4.94; N, 11.77.
5.1.7. 1-(4-Hydroxy-3-methoxyphenyl)-7-(4-O-ethyl-O-folyl-3-
methoxyphenyl)-1,6-heptadiene-3,5-dione (10)
To curcumin (184 mg, 0.5 mmol) dissolved in aq NaOH (5%,
10 ml), added 2-chloroethanol (0.05 ml, 0.75 mmol) and stirred the
reaction mixture for 7 h. The reaction mixture was extracted with
EtOAc. The organic extract was concentrated under vacuum,
washed with 5% NaHCO3, dried over anhydrous Na2SO4, evaporated
and crystallized with ethanol and water to get the intermediate
compound 9. Yield (100 mg, 0.24 mmol, 48%).
Compound 9 (100 mg, 0.24 mmol), dissolved in dry pyridine
(6 ml), was added dropwise to the activated ester 5 (157 mg,
0.28 mmol), stirred the reaction mixture for 20 min and TEA
(0.5 ml), DCC (123 mg, 0.6 mmol) and DMAP (32 mg) were further
added.
The reaction mixture was stirred for 5 h and the reaction was
monitored on TLC. DCU was filtered off and the product was
obtained following the usual work up procedure and purification
by silica gel column chromatography using ethyl acetate (2%) in
hexane as eluant as a red solid which was recrystallized from EtOAc
and hexane. Yield: 26%; m.p. ¼168–170 ꢁC, Rf ¼ 0.53 (EtOAc:
Hexane 6.5:3.5). UV (EtOH) lmax 270, 290, nm. 1H NMR (DMSO-d6
and D2O); d 2.09 (m, 4H, C21, FA); 2.23 (m, 4H, C22, FA); 3.73 (s, 6H
OCH3, Ar, Cur); 4.32 (s, 4H, C9 H, FA); 4.46 (m, 2H, C19, FA); 4.58 (s,
2H, C4, Cur); 6.61 (d, 4H, C12 and C16, Ar, FA); 6.79 (d, 2H, C2 and C6,
Cur); 6.89–6.91 (m, 6H, Ar-Cur); 7.54 (d, 2H, C1 and C7, Cur); 7.73 (d,
4H, C13 and C15, Ar, FA); 8.8 (s, 2H, C7, pyrazine, FA); 13C NMR
(CDCl3):
d 26.3, 27.5, 51.9, 56.0, 56.7, 57.4, 112.2, 112.4, 118.9, 121.9,
122.3, 126.6, 128.1, 132.7, 137.9, 138.1, 140.5, 146.9, 148.4, 150.8,
154.8, 161.2, 163, 169.0, 170,196.5, MS m/z 1214 (Mþ). Anal. Calcd for
C59H54N14 O16: C, 58.31; H, 4.44; N, 16.14 found: C, 58.35; H, 4.48; N,
16.10.
5.1.6. 1,7-Bis-[(4-hydroxy-3-methoxyphenyl)]-1,6-heptadiene-C4-
ethyl-O-folyl-3,5-dione (8)
To curcumin (184 mg, 0.5 mmol) dissolved in dry pyridine
(10 ml), added KOH (67.2 mg, 1.2 mmol), cooled the solution and
further added benzoyl chloride (1.4 ml, 1.2 mmol) dropwise with
constant stirring which continued at ambient temperature for
another 2 h. The completion of the reaction was assessed on TLC.
The volume of the reaction mixture was reduced to half and poured
on to crushed ice and the product was extracted with EtOAc. The
organic phase was dried over anhydrous Na2SO4, concentrated and
the product was purified by silica gel column chromatography using
2% EtOAc/Hexane. This di-O-benzoyl curcumin (200 mg,
and D2O); d 2.23 (m, 2H, C21, FA); 2.25 (m, 2H, C22, FA); 3.23 (t, 1H,
C4, Cur); 3.75 (s, 6H OCH3, Ar, Cur); 4.22 (m, 2H, C2, ethyl), 4.34 (s,
2H, C9, FA); 4.50 (m, 2H, C1, ethyl), 4.45 (m,1H, C19, FA); 6.60 (d, 2H,
C12 and C16, Ar, FA); 6.68 (d, 2H, C2 and C6, Cur); 6.70–6.75 (m, 6H,
Ar-Cur); 7.55 (d, 2H, C1 and C7, H Cur); 7.72 (d, 2H, C13 and C15, Ar,
FA); 8.6 (s, 1H, C7 H, pyrazine, FA); 13C NMR (CDCl3): 26.3, 27.9, 51.9,
56.3, 56.7, 57.4, 67, 72.2, 112.4, 113.2, 115.1, 116.6, 119.1, 119.9, 126.6,