6544
S. Dutta et al. / Bioorg. Med. Chem. 18 (2010) 6538–6546
Pd–C (5 mg) for 4 h at room temperature. The reaction mixture
4. Experimental
was filtered and concentrated in vacuum to afford a pale brown so-
lid which was further purified by precipitation in methanol ether
system to obtain compound 4 (0.013 g, 74.5%), 203–208 °C; dH
(MeOH-d4): 6.67 (1H, s, Ar-H), 6.58 (2H, s, Ar-H), 6.44 (1H, t,
J = 4.0 Hz, Ar-H), 6.13 (1H, s, Ar-H), 6.03 (1H, dd, J = 2.0, 2.4 Hz,
Ar-H), 5.81 (1H, s, Ar-H), 5.75 (1H, d, J = 2.0 Hz, Ar-H), 4.29 (1H,
d, J = 9.2, H-4), 4.12 (1H, d, J = 8.4 Hz, H-2), 3.75 (1H, ABq, J = 8.4,
H-3), 3.12 (br s, OH). dC (MeOH-d4): 157.7, 156.6, 156.1, 155.2,
144.9, 144.5, 129.6, 127.8, 121.0, 119.6, 114.9, 114.4, 107.6,
107.5, 103.8, 103.0, 96.9, 95.5, 81.8, 76.9, 40.2; mass: (ESI+) m/z
399 (MH+), 421 (MNa+), HRMS: calcd for C21H18O8 + H+ 399.1080
found 399.1084.
Ribonuclease A (RNase A), yeast tRNA, 30-CMP, 20, 30-cCMP, (+)-
catechin and (ꢀ)-epicatechin (EC) are from Sigma–Aldrich. All
other chemicals are from SRL India. UV measurements were made
using a Perkin–Elmer UV–vis spectrophotometer (Model Lambda
25). Concentrations of RNase A and 20, 30-cCMP (20, 30-cyclic cyti-
dine monophosphate) were determined spectrophotometrically
using the following data: for RNase A
e
278.5 = 9800 Mꢀ1 cmꢀ1 and
for 20, 30-cCMP 268 = 8500 Mꢀ1 cmꢀ1
e
.
4.1. Synthesis of the polyphenols (1–4)
Compound 9a: To a solution of 4-acetoxy tetrabenzyl epicate-
chin (8a) (0.075 g, 0.1 mmol) in a mixture of CH2Cl2 and THF
(2 ml each) phloroglucinol (0.063 g, 0.5 mmol) was added followed
by LiBr (0.043 g, 0.5 mmol). The mixture was refluxed for 24 h and
partitioned between ethyl acetate and water. The organic layer was
evaporated to dryness. The crude residue thus obtained was puri-
fied by flash column chromatography using 5% methanol in dichlo-
romethane as eluent to afford compound 9a (0.06 g, 79.1%); dH
(CDCl3): 7.38–6.91 (25H, m, Ar-H), 6.37 (1H, s, Ar-H), 6.28 (1H, s,
Ar-H), 5.12–5.02 (8H, m, 4 ꢂ OCH2Ph), 4.92 (1H, d, J = 3.6 Hz, H-
4), 4.62 (1H, s, H-2), 4.06 (1H, s, H-3), 1.26 (br s, OH); mass:
(ESI+) m/z 775 (MH+); HRMS: calcd for C49H42O9 + H+ 775.2907
found 775.2912.
Compound 9b: To a solution of 4-acetoxy tetrabenzyl catechin
(8b) (0.080 g, 0.11 mmol) in a mixture of CH2Cl2 and THF (2 ml
each) phloroglucinol (0.071 g, 0.55 mmol) was added followed by
LiBr (0.047 g, 0.55 mmol). The mixture was refluxed for 24 h and
partitioned between ethyl acetate and water. The organic layer
was evaporated to dryness. The crude residue thus obtained was
purified by flash column chromatography using 5% methanol in
dichloromethane as eluent to afford compound 9b (0.060 g,
76.2%). dH (CDCl3): 7.44–7.22 (20H, m, Ar-H), 7.05 (1H, s, Ar-H),
6.96–6.89 (4H, m, Ar-H), 6.27 (2H, s, Ar-H), 5.19–4.77 (8H, m,
4 ꢂ OCH2Ph), 4.55 (1H, d, J = 9.6 Hz, H-4), 4.47 (1H, d, J = 8.8 Hz,
H-2), 4.01 (1H, m, H-3), 3.30 (br s, OH) ; mass: (ESI+) m/z 775
(MH+); HRMS: calcd for C49H42O9 + H+ 775.2907 found 775.2914.
Compound 10a: To a solution of 8a (0.071 g, 0.098 mmol) in a
mixture of CH2Cl2 and THF (2 ml each) resorcinol (0.054 g,
0.49 mmol) was added followed by LiBr (0.042 g, 0.49 mmol). The
mixture was refluxed for 24 h and partitioned between ethyl ace-
tate and water. The organic layer was evaporated to dryness. The
crude oily residue thus obtained was purified by flash column
chromatography using 5% methanol in dichloromethane as eluent
to afford compound 10a (0.047 g, 62%). dH (CDCl3): 7.45–6.80 (24H,
m, Ar-H), 6.62 (1H, d, J = 7.6 Hz, Ar-H), 6.36–6.20 (3H, s, Ar-H),
5.17–4.83 (8H, m, 4 ꢂ OCH2Ph), 4.80 (1H, d, J = 3.6 Hz, H-4), 4.60
(1H, s, H-2), 4.06 (1H, s, H-3), 2.14 (br s, OH); mass: (ESI+) m/z
759 (MH+); HRMS: calcd for C49H42O8 + H+ 759.2958 found
759.2964.
The polyphenols (1, 2) were synthesized starting with (ꢀ)-epi-
catechin. For compound 3 and 4 (+)-catechin was used as starting
material. The benzyl ether was chosen as the protecting group be-
cause its deprotection can be done under neutral condition. Acid or
base sensitive protecting groups have been avoided because of pos-
sible racemization at C-2. Based upon the literature procedure of
LiBr-mediated coupling of 4-acetoxy tetrabenzyl catechin or epi-
catechin, the partially protected compounds were prepared which
were deprotected with H2 in presence of Pearlman’s catalyst12 or
30% Pd–charcoal to afford the target compounds.
Compound 1: The solution of 9a (0.04 g, 0.051 mmol) in a mix-
ture of THF/MeOH/H2O (20:1:1) (22 ml) were hydrogenated at
2 bar pressure over 20% Pd(OH)2/C (5 mg) for 4 h at room temper-
ature. The reaction mixture was filtered and concentrated in vac-
uum to afford a pale brown solid which was further purified by
precipitation in methanol ether system (0.016 g, 86%), mp 225–
16
230 °C; dH (MeOH-d4): 6.91 (1H, s, Ar-H), 6.72 (2H, s, Ar-H),
6.04 (1H, s, Ar-H), 5.96 (1H, s, Ar-H), 5.83 (2H, s, Ar-H), 5.00 (1H,
s, H-4), 4.48 (1H, s, H-2), 3.99 (1H, s, H-3), 3.31 (br s, OH); dC
(MeOH-d4): 157.0, 156.5, 155.9, 155.8, 144.8, 144.6, 130.9, 128.3,
127.1, 119.5, 114.6, 114.4, 113.6, 106.2, 105.3, 95.9, 94.8, 94.0,
82.8, 71.9, 37.0; mass: (ESI+) m/z 415.1119 (MH+), 437.1005
(MNa+) HRMS: calcd for C21H18O9 + H+ 415.1029 found 415.1033.
Compound 2: The compound 10a (0.04 g, 0.052 mmol) in etha-
nol solution (20 ml) was hydrogenated at 2 bar pressure over 30%
Pd–C (5 mg) for 4 h at room temperature. The reaction mixture
was filtered and concentrated in vacuum to afford a pale brown so-
lid which was further purified by precipitation in methanol ether
system (0.014 g, 79.6%), mp 205–210 °C; dH (MeOH-d4): 6.85 (1H,
s, Ar-H), 6.70 (1H, d, J = 8.4 Hz, Ar-H), 6.62 (1H, d, J = 8.4 Hz, Ar-
H), 6.50 (1H, d, J = 8.0 Hz, Ar-H), 6.32 (1H, s, Ar-H), 6.18 (1H, dd,
J = 8.4 Hz, Ar-H), 6.04 (1H, s, Ar-H), 5.96 (1H, s, Ar-H), 4.44 (1H, s,
H-4), 4.08 (2H, s, H-2, H-3), 3.3 (br s, OH); dC (MeOH-d4): 156.5,
156.4, 156.1, 155.1, 144.3, 144.0, 130.92, 130.0, 120.8, 118.0,
114.6, 113.8, 106.5, 105.9, 102.1, 100.4, 95.6, 94.3, 73.8, 70.0,
38.3; mass: (ESI+) m/z 399.1168 (MH+), 421.1000 (MNa+) HRMS:
calcd for C21H18O8 + H+ 399.1080 found 399.1085.
Compound 3: The solution of 9b (0.04 g, 0.051 mmol) in a mix-
ture of THF/MeOH/H2O (20:1:1) (22 ml) was hydrogenated at 2 bar
pressure over 20% Pd(OH)2/C (5 mg) for 4 h at room temperature.
The reaction mixture was filtered and concentrated in vacuum to
afford a pale brown solid which was further purified by precipita-
tion in methanol ether system. (0.015 g, 80%), mp 209–214 °C; dH
(MeOH-d4): 6.94 (1H, s, Ar-H), 6.84–6.74 (2H, m, Ar-H), 5.98–
5.83 (4H, m, Ar-H), 4.6 (1H, br s, H-4), 4.44 (2H, br s, H-2, H-3),
3.30 (br s, OH); dC (MeOH-d4): 157.2, 155.9, 155.8, 155.4, 144.7,
144.0, 131.2, 128.3, 127.1, 119.3, 114.6, 114.4, 113.3, 106.2,
105.3, 95.8, 94.8, 94.0, 82.6, 71.6, 37.5; mass: (ESI+) m/z 415
(MH+), 437 (MNa+), HRMS: calcd for C21H18O9 + H+ 415.1029 found
415.1037.
Compound 10b: To a solution of 8b (0.071 g, 0.098 mmol) in a
mixture of CH2Cl2 and THF (2 ml each) resorcinol (0.054 g,
0.49 mmol) was added followed by LiBr (0.042 g, 0.49 mmol). The
mixture was refluxed for 24 h and partitioned between ethyl ace-
tate and water. The organic layer was evaporated to dryness. The
crude residue thus obtained was purified by flash column chroma-
tography using 5% methanol in dichloromethane as eluent to afford
compound 10b (0.047 g, 62%). dH (CDCl3): 7.40–6.73 (25H, m, Ar-
H), 6.48 (1H, d, J = 8.4 Hz, Ar-H), 6.33 (1H, d, J = 2.0 Hz, Ar-H),
6.25 (1H, d, J = 2.0 Hz, Ar-H), 5.12–4.96 (8H, m, 4 ꢂ OCH2Ph), 4.54
(1H, d, J = 9.2 Hz, H-4), 4.38 (1H, d, J = 7.6 Hz, H-2), 3.9–3.83 (1H,
m, H-3), 3.30 (br s, OH); mass: (ESI+) m/z 759 (MH+); HRMS: calcd
for C49H42O8 + H+ 759.2958 found 759.2962.
Compound 4: The compound 10b (0.03 g, 0.039 mmol) in etha-
nol solution (20 ml) was hydrogenated at 2 bar pressure over 30%