Hydrolyzable Tannins
J. Agric. Food Chem., Vol. 55, No. 1, 2007 49
over 10% Pd/C with 1 atm of H
was repeated twice to complete the deprotection. The gray-green glassy
solid obtained was triturated with three portions of Et O and three
portions of hexanes and purified by flash chromatography (5).
,3-Di(3,4,5-tribenzyloxy)galloyl-O-methylglucose (4). By use of the
2
, in distilled THF. The hydrogenation
2
2
general procedure of esterification, the acid 3 (1.40 g, 0.32 mmol),
DMAP (0.26 g, 0.21 mmol), DMAP‚HCl (0.34 g, 0.21 mmol), methyl
glucoside 1 (0.30 g, 0.11 mmol), and DCC (0.66 g, 0.32 mmol) were
coupled to afford, after flash chromatography (PE/EtOAc, 5:1, 3:1, and
2
:1), 956 mg of a mixture of R- and â-anomer of 4, and two small
fractions of the single anomers, that were used for their identification
1
(
overall yield ) 80%). R-Anomer: H NMR (CDCl
3
, 400 MHz), δ
), 3.89-4.07 (m, 2H, H ),
), 5.00-5.14 (m, 12H, CH and
), 5.57 (s, 1H, H ), 6.03 (t, J )
), 7.18-7.50 (m, 39H, CHphenol). â-Anomer: H NMR
, 200 MHz), δ 3.53 (s, 3H, OCH ), 3.82-3.87 (m, 1H, H ),
.08-4.11 (m, 2H, H ), 4.43-4.49 (m, 1H, H ), 5.00-5.14 (m, 12H,
and 1H, H ), 5.37-5.48 (m, 1H, H ), 5.55 (s, 1H, H ), 5.75-578
m, 1H, H ), 7.18-7.50 (m, 39H, CHphenol).
,3-Di(3,4,5-tribenzyloxy)galloyl-O-benzylglucose (5). By use of the
3
4
1
1
(
4
.45 (s, 3H, OCH
.39 (dd, J ) 10.0 and 4.8 Hz, 1H, H
H, H ), 5.24 (d, J ) 4.0 Hz, 1H, H
0.0 Hz, 1H, H
3
), 3.82-3.87 (m, 1H, H
5
6
4
2
2
1
7
1
3
CDCl
3
3
5
6
4
CH
(
2
1
2
7
3
2
general procedure of esterification, 3,4,5-tribenzyloxygallic acid 3 (0.84
g, 1.91 mmol), DMAP (0.17 g, 0.954 mmol), DMAP‚HCl (0.15 g, 0.954
mmol), benzyl glucoside 2 (0.31 g, 0.868 mmol), and DCC (0.40 g,
1
.91 mmol) were coupled to afford, after flash chromatography (PEE/
EtOAc/CH Cl , 5:1:1), 627 mg of a mixture of the two anomers of 5
yield 60%): H NMR (CDCl
2
2
1
(
3
, 400 MHz), δ 3.69 (dt, J ) 9.6 and 4.8
Hz, 1H, H5â), 3.81-3.97 (m, 4H, H6R+â), 4.18 (dt, J ) 10.0 and 4.8
Hz, 1H, H5R), 4.32 (dd, J ) 10.0 and 4.8 Hz, 1H, H4R), 4.48 (dd, J )
1
(
4
4
H
H
0.8 and 4.8 Hz, 1H, H4â), 4.60 (d, J ) 12.4 Hz, 1H, CH
d, J ) 12.4 Hz, 1H, CH Bn ), 4.80 (d, J ) 12.4 Hz, 1H, CH
.82 (d, J ) 8.0 Hz, 1H, H1â), 4.92 (d, J ) 12.4 Hz, 1H, CH
.93-5.11 (m, 24H, CH
2 R
Bn ), 4.66
2
â
2
Bn
Bn
R
),
),
2
â
2
BnR+â), 5.15 (dd, J ) 10.0 and 4.0 Hz, 1H,
2R), 5.36 (d, J ) 4.0 Hz, 1H, H1R) 5.52 (dd, J ) 8.0 and 1.6 Hz, 1H,
), 5.56 (s, 1H, CHBn ), 5.57 (s, 1H, CHBn ), 5.92 (t, J ) 9.6 Hz,
Figure 1. Synthesis of compounds 7 and 6. Reagents and conditions:
(
a) DCC, DMAP, DMAP
‚
2 2
HCl, CH Cl , reflux, 19 h, 80% for 4 and 60%
2
â
R
for 5; and (b) Pd/C, H , THF, 24 h, 73% for 6 and 73% for 7.
2
1H, H3â), 6.08 (t, J ) 10.0 Hz, 1H, H3R), 7.04-7.39 (m, 88H, CHphenol).
,3-Digalloyl-O-methylglucose (6). The general hydrogenation pro-
2
‘
consisting of (A) H
CN and a flow rate of 0.8 mL/min. The elution profile was as follows:
min 100% A, then solvent B was increased first to 20% in 8 min,
then to 50% in 10 min, linear for 5 min, and subsequently increased to
00% in 5 min, with 10 min for equilibration. HPLC-MS analyses were
2
O (adjusted to pH 3.2 by HCOOH) and (B) CH
3
-
cedure applied to glucogalloyl derivative 4 (780 mg, 0.69 mmol)
afforded, after chromatography (PE/THF/MeOH, 6:3:1), 321 mg of 2,3-
digalloyl-O-methylglucose 6 (yield 73%): MS, m/z (%) 497 (100, [M
2
-
1
- H] ), 345 (62), 169 (59), 125 (25); H NMR (CD
â, δ 3.54 (s, 3H, OCH ), 3.65-3.71 (m, 1H, H ), 3.76-3.84 (m, 2H,
), 4.67 (d, J ) 8.0 Hz, 1H, H ), 4.91 (s, 8H, OH), 5.11 (dd, J ) 8.0
and 9.6 Hz, 1H, H ), 5.42 (dd, J ) 9.2 and 9.6 Hz, 1H, H ), 6.98 (s,
2H, Hphenol), 7.02 (s, 2H, Hphenol); R, δ 3.47 (s, 3H, OCH ), 3.62-3.71
(m, 2H, H ), 3.76-3.79 (m, 1H, H ), 4.28 (td, J ) 0.8 and 6.4 Hz, 1H,
), 4.90 (s, 8H, OH), 5.01-5.07 (m, 2H, H1+2), 5.65-5.72 (m, 1H,
3
OD, 400 MHz),
1
3
5
performed using a HP 1100L liquid chromatograph linked to a HP 1100
MSD mass spectrometer with an API/ESI interface (Agilent Technolo-
gies). The mass spectrometer operating conditions were as follows:
gas temperature, 350 °C; nitrogen flow rate, 10.5 L/min; nebulizer
pressure, 40 psi; quadrupole temperature, 40 °C; and capillary voltage,
H
6
1
2
3
3
6
5
H
H
4
13
3
500 V. The orthogonal position of the nebulizer with respect to the
3 3
), 7.00 (s, 2H, Hphenol), 7.06 (s, 2H, CHphenol); C NMR (CD OD,
capillary inlet enabled the use of the same conditions as for HPLC-
DAD analysis. The mass spectrometer was operated in negative mode;
and the fragmentor was set at 120 eV for the standard and the synthetic
products and at 120 and 200 eV for the raspberry extracts.
100 MHz), â, δ 57.3, 62.3, 69.8, 73.4, 77.0, 78.1, 103.2, 110.26, 110.32,
120.9, 121.1, 139.8, 139.9, 146.29, 146.34, 167.2, 167.9; R, δ 55.6,
67.9, 69.8, 73.6, 74.3, 98.6, 110.3, 110.4, 120.6, 121.4, 140.0, 140.1,
146.3, 146.4, 167.6, 168.2.
Organic Synthesis. Solvents were purchased and dried according
to usual laboratory techniques. Unless otherwise noted, all air- and
moisture-sensitive reactions were performed under a nitrogen atmo-
sphere. Analytical thin-layer chromatography (TLC) was conducted on
glass-backed silica gel Durasil-25-UV254 plates (Macherey-Nagel,
Germany) with detection by UV light and charring with vanillin or
2,3-Digalloyl-O-glucose (7). The general hydrogenation procedure
applied to glucogalloyl derivative 5 (230 mg, 0.19 mmol) afforded,
after chromatography (PE/THF/MeOH, 6:3:1), 67 mg of 2,3-digalloyl-
-
O-glucose 7 (yield 73%): MS, m/z (%) 483 (100, [M - H] ), 313
1
(10), 169 (95); H NMR (CD
H
3
OD, 400 MHz), δ 3.47-3.54 (m, 1H,
5â), 3.70-3.94 (m, 6H, H6R,5R,6â,4â), 3.96-4.02 (m, 1H, H4â), 4.89 (d,
Pancaldi [(NH
4
)
6
MoO
4
, Ce(SO
4
)
2
, H
2
SO
4
, H
2
O] reagents. Flash chro-
J ) 8.0 Hz, 1H, H1â), 4.97 (dd, J ) 10.4 and 3.6 Hz, 1H, H2R), 5.05
(dd, J ) 9.6 and 8.0 Hz, 1H, H2â), 5.37 (at, 1H, H3â), 5.42 (d, J ) 3.8
Hz, 1H, H1R), 5.73 (at, 1H, H3R), 6.97 (s, 1H, Hphenol-â), 7.00 (s, 1H,
matography was carried out on 60M silica gel (Macherey-Nagel).
Esterification General Procedure (Figures 1 and 2). A mixture of
the properly protected glucose (1.0 equiv) and gallic acid (1.1 equiv
per hydroxyl), DMAP (0.5 equiv per hydroxyl), and DMAP‚HCl (0.5
Hphenol-â), 7.00 (s, 1H, Hphenol-R), 7.04 (s, 1H, Hphenol-R).
2,3-Di[3-tert-butyldimethylsilyloxy-4,5-diphenylmethylenedioxyben-
equiv per hydroxyl) was refluxed in dry CH
2
Cl
2
for 1 h, then DCC
zoyl]benzyl-O-glucose (9). By use of the general procedure of esteri-
fication, 3-tert-butyldimethylsilyloxy-4,5-diphenylmethylenedioxyben-
zoic acid 8 (757 mg, 1.55 mmol), DMAP (920 mg, 0.75 mmol), DMAP‚
HCl (120 mg, 0.75 mmol), benzyl-O-glucoside (200 mg, 0.74 mmol),
and DCC (309 mg, 1.55 mmol) were coupled to afford, after flash
(1.1 equiv per hydroxyl) was added, and the mixture was reacted for
16-19 h at room temperature. The reaction was cooled at -18 °C for
30 min and filtered through a pad of Celite. The organic phase was
washed with 3% HCl, brine, and H
2 2 4
O, dried over Na SO , concentrated,
and purified by flash chromatography (5).
Hydrogenation/Deprotection General Procedure (Figures 1 and 2).
A mixture of the benzylated glucogalloyl derivative was hydrogenated
chromatography (PE/EtOAc/CH
9 as a mixture of anomers (yield ) 31%): H NMR (CDCl
3 3
δ 0.09-0.15 [m, 24H, Si(CH ], 0.94-0.99 [m, 36H, C(CH )
2 2
Cl , 10:1:1), 265 mg of the derivative
1
3
, 400 MHz),
], 3.63
)
3 2