J6,6′ 10.9 Hz, H-6′b), 4.25 (1H, at, J 9.3 Hz, H-3b), 4.31 (1H, d, J1,2
8.1 Hz, H-1a), 4.32–5.08 (14H, m, PhCH2), 5.51 (1H, d, J1,2 3.3 Hz,
H-1b), 6.99–7.38 (40H, m, ArH); C (100.6 MHz, CDCl3) 68.1,
68.9 (2 × t, 2 × C-6), 70.5, 75.1, 77.6, 77.9, 79.6, 81.8, 81.9, 84.8
(8 × d, 2 × C-2, 2 × C-3, 2 × C-4, 2 × C-5), 73.3, 73.4, 75.0, 75.7
(4 × d, 7 × PhCH2), 95.4 (d, C-1b), 103.6 (d, C-1a), 116.9, 122.3,
127.5, 127.6, 127.7, 127.8, 127.9, 128.0, 128.3, 128.4, 128.5, 129.4
(12 × d, ArCH), 138.0, 138.1, 138.2, 138.3, 138.4, 138.5, 138.9,
Methyl-2,3,4,6-tetra-O-benzyl--D-glucopyranoside
(17).
Selenoglycoside 1 (100 mg, 0.15 mmol), anhydrous methanol
(0.01 ml, 0.40 mmol) and tetrabutylammonium perchlorate
(850 mg), in acetonitrile (25 ml), gave the -methyl glucoside 17
(57 mg, 65%) as a white crystalline solid, m.p. 66–67 °C (methanol)
(lit.,26 68–69 °C); []2D4 +10 (c, 1.0 in CHCl3) {lit.,26 []2D0 +11 (c, 5.3
in dioxan)}; H (400 MHz, CDCl3) 3.47–3.54 (2H, m, H-2, H-5),
3.63 (3H, s, Me), 3.74 (1H, dd, J5,6 4.8 Hz, J6,6′ 10.8 Hz, H-6), 3.81
(1H, dd, J5,6′ 1.9 Hz, H-6′), 4.36 (1H, d, J1,2 7.9 Hz, H-1), 4.58,
4.87 (2H, ABq, JAB 10.6 Hz, PhCH2), 4.60, 4.67 (2H, ABq, JAB
12.3 Hz, PhCH2), 4.76, 4.99 (2H, ABq, JAB 10.9 Hz, PhCH2), 4.84,
4.97 (2H, ABq, JAB 11.0 Hz, PhCH2), 7.19–7.41 (20H, m, ArH). A
small amount of the corresponding -glycoside was also isolated:
a colourless oil (11 mg, 13%); []2D4 +19 (c, 0.5 in CHCl3) {lit.,27
[]2D0 +36 (c, 1.2 in CHCl3)}; H (400 MHz, CDCl3) 3.39 (3H, s,
Me), 3.57 (1H, dd, J1,2 3.5 Hz, J2,3 9.6 Hz, H-2), 3.62–3.68 (2H, m,
H-4, H-6), 3.71–3.77 (2H, m, H-5, H-6′), 3.99 (1H, at, J 9.2 Hz,
H-3), 4.48, 4.84 (2H, ABq, JAB 10.7 Hz, PhCH2), 4.49, 4.62 (2H,
ABq, JAB 12.4 Hz, PhCH2), 4.64 (1H, d, H-1), 4.68, 4.81 (2H, ABq,
JAB 12.1 Hz, PhCH2), 4.83, 4.99 (2H, ABq, JAB 10.9 Hz, PhCH2),
7.12–7.38 (20H, m, ArH).
+
156.7 (8 × s, ArC); m/z (ES+) 1066.4 (M + NH4 , 100%), 1067.5
(75), 1068.5 (21), 1069.5 (6). (Found: C, 76.68; H, 6.52. C67H68O11
requires C, 76.69; H, 6.53%).
Attempted glycosylation of 6 with diacetone galactose
at +1.7 V in the absence of PhSeSePh
Thioglycoside 6 (100 mg, 0.15 mmol), diacetone galactose (100 mg,
0.38 mmol) and tetrabutylammonium perchlorate (855 mg, 2.5 mol)
were dissolved in acetonitrile (25 ml) and transferred to a flame
dried cell containing a reticulated carbon working electrode, a
nickel mesh counter electrode and a silver wire pseudo reference
electrode. 4 Å molecular sieves were added and the reaction mixture
stirred under nitrogen for 30 min. A potential of +1.7 V was applied
for 2.5 h at which point t.l.c. (petrol:ethyl acetate, 3:1) indicated
the formation of a minor product (Rf 0.3). The reaction mixture was
filtered and concentrated in vacuo. The residue was taken up in
ethyl acetate (50 ml), washed with water (50 ml) and the aqueous
layer re-extracted with ethyl acetate. The combined organic phases
were washed with brine (50 ml), dried (MgSO4) and concentrated
in vacuo. The crude product was then purified by flash column
chromatography (petrol:ethyl acetate, 4:1) to afford unreacted
thioglycoside 6 (93 mg, 93%) and disaccharide 18 (6 mg, 5%).
2,3,4,6-Tetra-O-benzyl--D-glucopyranosyl-(1→6)-1,2:3,4-
di-O-isopropylidene--galactopyranoside (18). Selenoglycoside
1 (98 mg, 0.14 mmol), diacetone galactose (75 mg, 0.29 mmol) and
tetrabutylammonium perchlorate (855 mg), in acetonitrile (25 ml),
gave disaccharide 18 (104 mg, 90%) as a colourless oil: []2D2 −24
(c, 1.0 in CHCl3) {lit.,28 []2D2 −22 (c, 1.4 in CHCl3)}; H (400 MHz,
CDCl3) 1.33, 1.34 (2 × 3H, 2 × s, 2 × CH3), 1.48, 1.52 (2 × 3H,
2 × s, 2 × CH3), 2.11–4.06 (6H, m, H-2a, H-3a, H-4a, H-5a, H-6a,
H-6′a), 4.11 (1H, ddd, J4,5 7.5 Hz, J5,6 3.4 Hz, J5,6′ 1.8 Hz, H-5b),
4.19 (1H, dd, J6,6′ 10.7 Hz, H-6b), 4.27 (1H, dd, J6,6′ 8.0 Hz, H-6b),
4.34 (1H, J1,2 5.1 Hz, J2,3 2.4 Hz, H-2b), 4.48 (1H, d, J1,2 7.7 Hz
H-1a), 4.52 (1H, d, J 9.8 Hz, PhCHH), 4,55, 4.82 (2H, ABq, JAB
11.8 Hz, PhCH2). 4.60–4.66 (3H, m, H-3b, H-4b, PhCH2), 4.74, 5.08
(2H, ABq, JAB 11.0 Hz, PhCH2), 4.80, 4.98 (2H, ABq, JAB 10.9 Hz,
PhCH2), 5.59 (1H, d, J1,2 4.9 Hz H-1b).
Attempted glycosylation of 6 with diacetone galactose
at +1.7 V in the presence of PhSeSePh
Thioglycoside 6 (105 mg, 0.16 mmol), diacetone galactose (83
mg, 0.32 mmol), diphenyl diselenide (24 mg, 0.077 mmol) and
tetrabutylammonium perchlorate (873 mg, 2.6 mol) were dissolved
in acetonitrile (25 ml) and transferred to a flame dried cell
containing a reticulated carbon working electrode, a nickel mesh
counter electrode and a silver wire pseudo reference electrode.
4 Å molecular sieves were added and the reaction mixture stirred
under nitrogen for 30 min. A potential of +1.7 V was applied for
2.5 h at which point t.l.c. (petrol:ethyl acetate, 3:1) indicated the
formation of a product (Rf 0.3). The reaction mixture was filtered
and concentrated in vacuo. The residue was taken up in dichloro-
methane (50 ml), washed with water (50 ml) and the aqueous layer
re-extracted with dichloromethane. The combined organic phases
were washed with brine (50 ml), dried (MgSO4) and concentrated
in vacuo. The crude product was then purified by flash column
chromatography (petrol:ethyl acetate, 7:1) to afford thioglycoside
6 (50 mg, 48%) and disaccharide 18 (63 mg, 50%).
2,3,4,6-Tetra-O-benzyl--D-glucopyranosyl-(1→6)-tolyl-
2,3,4-tri-O-benzyl-1-thio--glucopyranoside (19). Selenoglyco-
side 1 (100 mg, 0.15 mmol), thioglycoside 2 (167 mg, 0.30 mmol)
and tetrabutylammonium perchlorate (872 mg), in acetonitrile
(25 ml), gave disaccharide 19 (60 mg, 35%) as a white crystalline
solid, m.p. 129–131 °C (petrol/ethyl acetate); []2D2 +5.0 (c, 0.5 in
CHCl3); max (KBr disk)/cm−1 3028, 2907; H (500 MHz, CDCl3)
2.30 (3H, s, Me), 3.46–3.56 (4H, m, H-2a, H-4a, H-2b, H-5b),
3.63–3.70 (3H, m, H-5a, H-3b, H-4b), 3.73–3.81 (3H, m, H-6a, H-6′a,
H-6′b,), 4.24 (1H, dd, J5,6′ 1.8 Hz, J6,6′ 11.2 Hz, H-6′a), 4.47 (1H, d,
J1,2 7.6 Hz, H-1b), 4.57–4.67 (4H, m, 2 × PhCH2), 4.70 (1H, d, J1′,2′
9.8 Hz, H-1a), 4.75–5.02 (10H, m, 5 × PhCH2), 7.06–7.52 (39H,
m, ArH); C (100.6 MHz, CDCl3) 21.1 (q, Me), 68.6, 68.7 (2 × t,
2 × C-6), 72.5, 73.4, 74.9, 75.1, 75.5, 75.9 (6 × t, 7 × PhCH2), 78.7,
78.9, 80.2, 80.8, 80.9, 82.2, 84.7, 86.7 (8 × d, 2 × C-2, 2 × C-3,
2 × C-4, 2 × C-5), 87.6 (d, C-1), 103.8 (d, C-1′), 127.5, 127.6, 127.7,
127.8, 127.9, 128.0, 128.1, 128.2, 128.3, 128.4, 128.5, 129.7, 132.8
(13 × d, 39 × ArCH), 129.7, 137.9, 138.2, 138.9 (3 × s, 9 × ArC);
2,3,4,6-Tetra-O-benzyl--D-glucopyranosyl-(1→6)-2,3,4-
tri-O-benzyl--D-glucopyranosyl-(1→6)-1,2:3,4-di-O-iso-
propylidene--galactopyranoside (22). Disaccharide 20
(120 mg, 0.11 mmol), diacetone galactose (64 mg, 0.25 mmol)
and tetrabutylammonium perchlorate (955 mg, 2.79 mol) were
dissolved in acetonitrile (25 ml) and transferred to a flame dried
cell containing a reticulated carbon working electrode, a nickel
mesh counter electrode and a silver wire pseudo reference electrode.
4 Å molecular sieves were added and the reaction mixture stirred
under nitrogen for 30 min. A potential of 2.0 V was applied for
2.5 h at which point t.l.c. (petrol:ethyl acetate, 3:1) indicated
the formation of a major product (Rf 0.1). The reaction mixture
was filtered and concentrated in vacuo. The residue was taken up
in dichloromethane (50 ml), washed with water (50 ml) and the
aqueous layer re-extracted with dichloromethane. The combined
organic phases were washed with brine (50 ml), dried (MgSO4) and
concentrated in vacuo. Flash column chromatography (petrol:ethyl
acetate, 1:4) afforded trisaccharide 22 (107 mg, 79%) as a white
crystalline solid, m.p. 137–139 °C (ethyl acetate/petrol); []2D2 −4.6
+
m/z (ES+) 1096.6 (M + NH4 , 24%), 1101.5 (M + Na+, 100).
[Isotope Distribution Calc. (M + Na+) 1101.46 (100%), 1102.46
(78), 1103.46 (26), 1104.47 (13). Found 1101.51 (100%), 1102.46
(70), 1103.48 (33), 1104.49 (9).]
2,3,4,6-Tetra-O-benzyl--D-glucopyranosyl-(1→6)-phenyl-
2,3,4-tri-O-benzyl--glucopyranoside (21). Selenoglycoside 1
(100 mg, 0.15 mmol), phenyl glycoside 3 (150 mg, 0.28 mmol)
and tetrabutylammonium perchlorate (855 mg), in acetonitrile
(25 ml), gave disaccharide 21 (122 mg, 79%) as a white crystalline
solid, m.p. 105–106 °C (petrol/ethyl acetate); []2D4 +19 (c, 0.5 in
CHCl3); max (KBr disk)/cm−1 3030, 2898; H (400 MHz, CDCl3)
3.41–3.44 (1H, m, H-5a), 3.51 (1H, at, J 8.5 Hz, H-2a), 3.57 (1H,
at, J 9.1 Hz, H-4a), 3.62–3.77 (6H, m, H-3a, H-6a, H-6′a, H-2b,
H-4b, H-6b), 3.96–3.98 (1H, m, H-5b), 4.15 (1H, dd, J5,6′ 1.5 Hz,
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 1 9 5 – 2 2 0 2
2 2 0 1