Synthesis of a Rhamnogalacturonan-II Fragment
(1 H, broad s, OH), 3.20 (3 H, s, OCH3), 3.47 (1 H, dd, J3,4
)
2.6 Hz, H-1 R-Gal), 5.29 (1 H, d, J1,2 8.1 Hz, H-1 â-Gal), 5.57
(1 H, dd, J2,3 10.4 Hz, J3,4 3.3 Hz, H-3 â-Gal), 5.82-5.86 (2 H,
m, H-2 and H-4 â-Gal). δC (100 MHz, CDCl3): 17.8 (C-6 Rha),
54.6 (OCH3), 62.4 (C-6 â-Gal), 68.1 (C- 4 â-Gal), 68.2 (C-5
Rha), 69.3 (C-6 R-Gal), 70.1 (C-2 â-Gal), 70.3 (C-5 R-Gal), 71.2,
71.3 (C-5 â-Gal, C-3 Rha), 71.8 (C-3 â-Gal), 72.8, 72.9, 73.4
(PhCH2), 75.0 (PhCH2), 75.6, 77.3, 78.1, 78.9 (C-2 Rha, C-2,
C-3 and C-4 R-Gal), 80.6 (C-4 Rha), 98.1 (C-1 R-Gal), 99.1 (C-1
Rha), 101.6 (C-1 â-Gal), 114.3-139.1 (Ar), 165.1, 165.5, 165.6,
166.0 (PhCO). ESI-MS found m/z 1296.5 [M + NH4]+, calcd
for C75H74O19‚NH4 1296.4.
J4,5 8.9 Hz, H-4 Rha), 3.58-3.62 (1 H, m, H-5 Rha), 3.72 (3 H,
s, CH3OC6H4CH2O), 4.03 (1 H, dd, J2,3 3.3 Hz, J3,4 8.9 Hz, H-3
Rha), 4.07 (1 H, broad s, H-2 Rha), 4.27 (1 H, d, J 10.8 Hz,
CH3OC6H4CH2O), 4.40 (1 H, dd, J5,6a 4.4 Hz, J5,6b 8.2 Hz, H-5
Gal), 4.41 (1 H, s, H-1 Gal), 4.50 (1 H, d, J 10.8 Hz,
CH3OC6H4CH2O), 4.54 (1 H, dd, J5,6a 4.4 Hz, J6a,6b 11.6 Hz,
H-6a Gal), 4.62 (1 H, dd, J5,6b 8.2 Hz, J6a,6b 11.6 Hz, H-6b Gal),
5.11 (1 H, d, J1,2 8.1 Hz, H-1 Gal), 5.62 (1 H, dd, J2,3 10.2 Hz,
J3,4 3.5 Hz, H-3 Gal), 5.96 (1 H, dd, J1,2 8.1, J2,3 10.2 Hz, H-2
Gal), 6.00 (1 H, d, J3,4 3.5 Hz, H-4 Gal), 6.63-8.12 (24 H, m,
Ar). δC (100 MHz, CDCl3): 18.1 (C-6 Rha), 54.8 (OCH3), 55.4
(CH3OC6H4CH2O), 62.7 (C-6 Gal), 67.3 (C-5 Rha), 68.4 (C-4
Gal), 69.8 (C-2 Gal), 70.3 (C-5 Gal), 72.1 (C-3 Gal), 72.2 (C-2
Rha), 74.9 (CH3OC6H4CH2O), 78.9 (C-3 Rha), 83.3 (C-4 Rha),
100.1 (C-1 Rha), 101.9 (C-1 Gal), 113.7-159.1 (Ar), 165.6,
165.7, 165.9, 166.3 (PhCO). ESI-MS found m/z 894.3338 [M +
NH4]+, calcd for C49H48O15‚NH4 894.3331.
Methyl 2-O-(2,3,4,6-Tetra-O-benzyl-r-D-galactopyrano-
syl)-3-O-(2,3,4,6-tetra-O-benzoyl-â-D-galactopyranosyl)-4-
O-(2,3,4-tri-O-benzyl-r-L-fucopyranosyl)-r-L-rhamnopy-
ranoside (16). A mixture of trisaccharide acceptor 14 (110
mg, 86 µmol), thiofucoside donor 1534,35 (70 mg, 130 µmol,) and
4 Å molecular sieves (0.35 g) in CH2Cl2-Et2O (1:5, 6 mL) was
stirred for 17 h at 20 °C, and NIS (90 mg, 400 µmol) was added.
The mixture was cooled to -30 °C, TfOH (10 µL, 0.04 mmol)
was added, and stirring was continued for 0.5 h at -30 °C.
The mixture was allowed to warm to room temperature,
diluted with CH2Cl2, washed with water, aqueous NaHCO3
solution, and brine, dried, and concentrated. Column chroma-
tography (toluene-EtOAc, 4:1) of the residue afforded pro-
tected tetrasaccharide 16 (0.13 g, 87%): Rf ) 0.54 (toluene-
EtOAc, 8:1); [R]D +42 (c 1.02, CHCl3). δH (400 MHz, CHCl3):
1.06 (3 H, d, J5,6 6.4 Hz, H-6 Fuc), 1.23 (3 H, br s, H-6 Rha),
3.09 (3 H, s, OCH3), 3.61-3.77 (4 H, m, H-3, H-4, H-5 Rha,
H-2 R-Gal), 3.84-3.94 (4 H, m, H-3, H-6a, H-6b R-Gal, H-5
Fuc), 4.00-4.10 (4 H, m, H-2 Rha, H-2, H-3, H-4 Fuc), 4.17-
4.21 (2 H, m, H-5, H-6a â-Gal), 4.27-4.46 (3 H, m, H-5 R-Gal,
H-6b â-Gal, PhCH2), 4.46-4.84 (12 H, m, H-1 Rha and 11 H
Methyl 4-O-(4-Methoxylbenzyl)-2-O-(2,3,4,6-tetra-O-
benzyl-r-D-galactopyranosyl)-3-O-(2,3,4,6-tetra-O-benzoyl-
â-D-galactopyranosyl)-r-L-rhamnopyranoside (13). A so-
lution of disaccharide 12 (0.36 g, 0.41 mmol) and methyl
2,3,4,6-tetra-O-benzyl-1-thio-â-D-galactopyranoside 624 (0.47 g,
0.82 mmol) in 15 mL of dry CH2Cl2-Et2O (2:3) was stirred
with molecular sieves 4 Å (0.5 g) for 2 h at room temperature.
After addition of NIS (0.18 g, 0.8 mmol) the mixture was cooled
to -55 °C and TMSOTf (0.015 mL, 0.07 mmol) was added. The
mixture was stirred for 1 h at -55 °C, treated with Et3N (0.27
mL), then allowed to warm to room temperature, and diluted
with CH2Cl2. The organic solution was washed with 10%
aqueous Na2S2O3 solution, water, aqueous NaHCO3 solution,
and brine, dried, and concentrated. Purification of the residue
by column chromatography (toluene-EtOAc, 9:1) gave 13 (0.49
g, 87%): Rf ) 0.29 (toluene-EtOAc, 8:1); [R]D +77 (c 0.8,
CHCl3). δH (400 MHz, CDCl3): 1.10 (3 H, d, J5,6 6.2 Hz, H-6
Rha), 3.12 (3 H, s, OCH3), 3.42 (1 H, dd, J3,4 ) J4,5 9.2 Hz, H-4
Rha), 3.57-3.60 (1 H, m, H-5 Rha), 3.73 (3 H, s, CH3OC6H4-
CH2), 3.91-4.04 (2 H, m, H-6a and H-6b R-Gal), 4.09 (2 H, s,
H-2 Rha and H- 4 R-Gal), 4.13 (1 H, dd, J2,3 3.3 Hz, J3,4 9.2
Hz, H-3 Rha), 4.19-4.71 (14 H, m, PhCH2, H-2, H-3, H-5 R-Gal,
H-5, H-6a and H-6b â-Gal, H-1 Rha), 4.80 (2 H, m, PhCH2),
5.04 (1 H, d, J 10.7 Hz, PhCH2), 5.25 (2 H, m, H-1 â-Gal, H-1
R-Gal), 5.57 (1 H, dd, J2,3 10.4 Hz, J3,4 3.2 Hz, H-3 â-Gal), 5.92
(1 H, d, J3,4 3.2 Hz H-4 â-Gal), 5.96 (1 H, dd, J1,2 7.9, J2,3 10.4
Hz, H-2 â-Gal), 6.71-8.10 (44 H, m, Ar). δC (100 MHz,
CDCl3): 17.8 (C-6 Rha), 54.8 (OCH3), 55.4 (CH3OC6H4CH2O),
62.4 (C-6 â-Gal), 67.8 (C-5 Rha), 68.4 (C-4 â-Gal), 69.3 (C-6
R-Gal), 70.2, 71.5 (C-5 R-Gal, C-5 â-Gal), 70.4 (C-2 â-Gal), 72.9
(C-3 â-Gal), 72.7, 73.2, 73.7 (PhCH2), 74.5 (CH3OC6H4CH2O),
75.5 (PhCH2), 76.1, 78.3 (C-2 and C-3 R-Gal), 77.6 (C-4 R-Gal),
78.3, 79.3 (C-2 and C-4 Rha), 79.7 (C-3 Rha), 98.1 (C-1 R-Gal),
98.7 (C-1 Rha), 102.5 (C-1 â-Gal), 113.6-158.9 (Ar), 164.9,
165.5, 165.6, 165.9 (C6H5CO). ESI-MS found m/z 1416.8 [M +
NH4]+, calcd for C83H82O20‚NH4 1416.6.
Methyl 2-O-(2,3,4,6-Tetra-O-benzyl-r-D-galactopyrano-
syl)-3-O-(2,3,4,6-tetra-O-benzoyl-â-D-galactopyranosyl)-r-
L-rhamnopyranoside (14). A solution of protected trisac-
charide 13 (0.26 g, 0.18 mmol) and (NH4)2Ce(NO3)6 (0.58 g,
1.06 mmol) in CH3CN-H2O (9:1, 3 mL) was stirred at room
temperature for 0.5 h, diluted with CH2Cl2, washed with water,
aqeous NaHCO3 solution and brine, dried, and concentrated.
The residue was purified by column chromatography (toluene-
EtOAc, 4:1) to afford 14 (0.24 g, 93%): Rf ) 0.11 (toluene-
EtOAc, 8:1); [R]D +74 (c 2.7, CHCl3). δH (400 MHz, CDCl3):
1.15 (3 H, d, J5,6 5.5 Hz, H-6 Rha), 3.14 (3 H, s, OCH3), 3.59-
3.65 (2 H, m, H-5 Rha and H-3 Rha), 3.75 (1 H, dd, J5,6a 7.7
Hz, J6a,6b 9.2 Hz, H-6a R-Gal), 3.84 (1 H, dd, J5,6b 5.8 Hz, J6a,6b
9.2 Hz, H-6b R-Gal), 3.90-3.93 (1 H, m, H-4 Rha), 4.19-4.22
(4 H, H-2 Rha, H-2, H-3 and H-4 R-Gal), 4.25-4.29 (3 H, m,
H-5 R-Gal, H-5 and H-6a â-Gal), 4.44-4.68 (6 H, m, H-6a
â-Gal, PhCH2), 4.72 (1 H, d, J1,2 1.3 Hz, H-1 Rha), 4.80 (2 H,
m, PhCH2), 5.02 (1 H, d, J 10.9 Hz, PhCH2), 5.21 (1 H, d, J1,2
PhCH2), 4.88 (1 H, d, J 10.6 Hz, PhCH2), 4.91 (1 H, d, J1,2
8
Hz, H-1 â-Gal), 5.00 (1 H, d, J 10.6 Hz, PhCH2), 5.17-5.26 (1
H, m, H-3 â-Gal), 5.22 (1 H, d, J1,2 3.1 Hz, H-1 Fuc), 5.33 (1 H,
d, J1,2 3.5 Hz, H-1 R-Gal), 5.55 (1 H, broad s, H-4 â-Gal), 5.75
(1 H, dd, J1,2 7.8 Hz, J2,3 10.4 Hz, H-2 â-Gal). δC (100 MHz,
CHCl3): 16.6 (C-6 Fuc), 18.8 (C-6 Rha), 54.5 (OCH3), 62.2 (C-6
â-Gal), 66.2 (C-5 Rha), 66.9 (C-5 Fuc), 68.6 (C-4 â-Gal), 68.9
(C-6 R-Gal), 70.1 (C-5 R-Gal), 70.5 (C-2 â-Gal), 71.1 (C-3 â-Gal),
71.9, 72.6, 72.9, 73.0, 73.7, 75.2, 75.6 (PhCH2), 75.9 (C-2 R-Gal,
C-5 â-Gal), 77.6 (C-3 Rha), 77.6, 78.3, 79.3, 79.6, 79.7 (2C) (C-
2, C-4 Rha, C-2, C-3, C-4 Fuc, C-4 R-Gal), 80.4 (C-3 R-Gal),
97.1 (C-1 R-Gal), 99.2 (C-1 Rha), 99.5 (C-1 Fuc), 100.6 (C-1
â-Gal), 127.1-139.6 (Ar), 165.1, 165.5, 165.6, 165.7 (C6H5CO).
ESI-MS found m/z 1712.8 [M + NH4]+, calcd for C102H102O23‚
NH4 1712.7
Methyl 3-O-(â-D-Galactopyranosyl)-r-L-rhamnopyra-
noside (17). Protected disaccharide 11 (23.2 mg, 68.1 µmol)
and (NH4)2Ce(NO3)6 (3.61 mmol) were stirred in a mixture of
CH3CN-H2O (9:1, 5 mL) for 0.5 h at room temperature. The
mixture was diluted with CH2Cl2, washed with water, aqueous
NaHCO3 solution, and brine, dried, and concentrated. Products
were purified by column chromatography (toluene-EtOAc).
The resulting saccharide was treated with 0.05 M NaOMe in
MeOH (10 mL) at 20 °C until complete conversion of starting
material into a single product (∼1 h). The solution was then
neutralized with Amberlite IRA-120 (H+) resin, the resin was
filtered off and washed with MeOH, and the methanolic
solution was concentrated to dryness. Purification of the
residue by column chromatography (toluene-EtOAc, 4:1 f 2:1
then CH2Cl2-MeOH, 9:1) afforded 17 (16.2 mg; 67%): Rf )
0.40 (CH2Cl2-MeOH, 2:1); [R]D -36 (c 1.01, MeOH). δH (400
MHz, D2O): 1.29 (3 H, d, J5,6 6.2 Hz, H-6 Rha), 3.38 (3 H, s,
OCH3), 3.55-3.75 (7 H, H-2, H-3, H-4 H-6a,b Gal and H-4,
H-5 Rha), 3.83 (1 H, dd, J2,3 3.3 Hz, J3,4 9.5 Hz, H-3 Rha), 3.89
(1 H, d, J5,6a 3.3 Hz, H-5 Gal), 4.16 (1 H, dd, J1,2 1.6 Hz, J2,3
3.3 Hz, H-2 Rha), 4.58 (1 H, d, J1,2 7.7 Hz, H-1 Gal), 4.68 (1 H,
d, J1,2 1.6 Hz, H-1 Rha). δC (100 MHz, D2O): 16.8 (C-6 Rha),
54.8 (OCH3), 61.1 (C-6 â-Gal), 68.4 (C-5 Rha), 68.7 (C-5 Gal),
70.0 (C-2 Rha), 71.2 (2 C), 72.6, 75.2 (C-4 Rha, C-2, C-3, and
C-4 Gal), 80.1 (C-3 Rha), 100.6 (C-1 Rha), 104.5 (C-1 â-Gal).
J. Org. Chem, Vol. 70, No. 3, 2005 965