J. Elhalabi, K.G. Rice / Carbohydrate Research 335 (2001) 159–165
163
acetone containing 1 mL of water. Silver car-
bonate (0.64 g) was then added, and the mix-
ture was stirred for 6 h at rt with the exclusion
of light. The progress of the reaction was
monitored by TLC using 2:1 (v/v) hexane–
EtOAc to reveal the formation of one major
product (Rf 0.33). The mixture was then
filtered at rt and washed with acetone (30
mL), and the solution was evaporated to dry-
ness. Final purification was accomplished us-
ing flash chromatography on silica gel (2:1 v/v
hexane–EtOAc) to give 430 mg of 7 (1.2
71.21, 70.49, 67.92, 54.43, 47.31, 29.94.
HRMS: Calcd, 540.2076; found, 540.2081.
1,2,3,6-Tetra-O-acetyl-4-S-acetyl-4-thio-h-
D
-galactopyranoside (5).—Methyl 4-S-acetyl-
2,3,6-tri-O-benzyl-4-thio-a- -galactopyrano-
D
side (4) (2.1 g, 4.0 mmol) was dissolved in 20
mL of Ac2O, along with 5.12 g of anhyd
FeCl3. The reaction was stirred at 80 °C for 2
days. After cooling, the reaction was
quenched with water (5 mL) and evaporated
to dryness using a vacuum pump at 35 °C.
The residue was redissolved in CH2Cl2, and
TLC analysis (4:1 v/v toluene–EtOAc) re-
vealed a single major product with Rf 0.45.
The organic phase was washed with water,
concentrated to dryness using a water aspira-
tor, and then purified using flash chromatog-
raphy on silica gel, eluting with 4:1 (v/v)
toluene–EtOAc to yield 1.1 g of 5 (2.7 mmol,
1
mmol, 47%). H NMR (CDCl3, 300 MHz): l
5.59 (dd, 1 H, H-3a, J3,4 4.3, J2,3 10.7), 5.48
(broad d, 1 H, H-1a, J1,2 3.3), 5.32 (s, 1.5 H,
ꢁOH), 5.25 (dd, 0.5 H, H-3b, J3,4 4.3, J2,3
10.0), 4.99 (dd, 1 H, H-2a, J2,3 10.7, J1,2 3.7),
4.88 (dd, 0.5 H, H-2b, J2,3 10.3, J1,2 9.9),
4.66–5.75 (m, 1.5 H, H-5a, H-1b), 4.38 (dd, 1
H, H-4a, J3,4 4.3, J4,5 1.8), 4.32 (dd, 0.5 H,
H-4b, J3,4 4.5, J4,5 1.5), 4.11–4.27 (m, 2.5 H,
H-6,6% (a,b), H-5b), 2.41 (s, 3 H, SAc), 2.11,
2.07, 1.99 (each s, each 3 H, each OAc). 13C
NMR (CDCl3, 125 MHz) (only a anomer
shown): l 194.03 (SAc), 170.79, 170.64, 170.31
(OAc), 91.18, 70.01, 67.20, 67.00, 64.22, 60.83,
47.33, 31.21 (SAc), 21.49, 21.22, 21.07.
HRMS: Calcd, 364.0828; found, 364.0824.
1
68%). H NMR (CDCl3, 300 MHz): l 6.31 (d,
1 H, H-1, J1,2 3.7), 5.51 (dd, 1 H, H-3, J3,4 4.3,
J2,3 10.8), 5.17 (dd, 1 H, H-2, J1,2 3.7, J2,3
10.8), 4.58 (pseudo t, 1 H, H-5, J4,5 1.8, J5,6
6.3, J5,6% 6.8), 4.40 (dd, 1 H, H-4, J3,4 4.3, J4,5
1.7), 4.08–4.20 (m, 2 H, H-6 and H-6%), 2.41
(s, 3 H, SAc), 2.17, 2.05, 2.02, 1.98 (each s,
13
each 3 H, each OAc). C NMR (125 MHz): l
193.81 (SAc), 170.88, 170.41, 170.17, 169.28
(each OAc), 90.08 (C-1), 69.78 (C-5), 68.15
(C-3), 67.96 (C-2), 63.69 (C-6), 46.64 (C-4),
31.21 (SAc), 21.29, 21.11, 20.91 (3OAc).
HRMS: Calcd, 406.0934; found, 406.0913.
2,3,6-Tri-O-acetyl-4-S-acetyl-4-thio-h-
D
-
galactopyranosyl-1-phosphate mono-tributy-
lammonium salt (9).—Tetrabenzylpyrophos-
phate (TBPP) was prepared by reacting 2
equiv of dibenzyl phosphate with 1 equiv of
DCC in toluene at rt with stirring for 5 h. The
dicyclohexylurea was removed by gravity
filtration, the filtrate was dried at rt using a
vacuum pump, and the TBPP solidified upon
freezing as a white powder.
2,3,6-Tri-O-acetyl-4-S-acetyl-4-thio-h,i-
galactopyranose (7).—1,2,3,6-Tetra-O-acetyl-
4-S-acetyl-4-thio-a- -galactopyranoside (5)
D
-
D
(930 mg, 2.3 mmol) was dissolved in CH2Cl2
(20 mL) and EtOAc (2 mL). TiBr4 (3.12 g, 8.5
mmol) was added, and the reaction mixture
was stirred at rt under nitrogen. The progress
of the reaction was monitored using TLC (2:1
v/v hexane–EtOAc), which demonstrated a
complete conversion in 6 h of the a-acetate
2,3,4-Tri-O-acetyl-4-S-acetyl-4-thio-a,b- -
D
galactopyranose (7) (210 mg, 0.58 mmol) was
dissolved in 4 mL of dry THF. Butyllithium
(390 mL, 0.63 mmol, from a 1.6 M solution in
hexane) was added to 7 at −78 °C. The mix-
ture was stirred for 5 min, at the end of which
time, 974 mg (1.74 mmol) of TBPP (dissolved
in 1 mL dry THF) was added dropwise over a
period of 5 min. The reaction was then al-
lowed to proceed at −60 °C for 30 min. After
being brought to rt, the reaction mixture was
diluted with Et2O (30 mL) and washed with
satd NaHCO3 (2×10 mL) and water (2×10
into the faster moving a- -galactopyranosyl
D
bromide (6). Sodium acetate (1.2 g) was
added, and the reaction mixture was stirred
for 15 min. The mixture was then filtered over
Celite, and the Celite pad was washed with
CH2Cl2 (20 mL). The organic phase was then
washed with 100 mL of cold water and evapo-
rated to dryness using a water aspirator. The
crude product was dissolved in 30 mL of