Assembly of a Guluronic Acid Alginate Trisaccharide
FULL PAPER
was taken up in Et2O and washed three times with H2O. The organic
layer was dried over MgSO4 and concentrated in vacuo. Column chroma-
tography yielded 7 as a colourless oil (3.19 g, 89%). [a]2D2 =+9.17 (c=
Bn), 137.7 (Cq Bn), 137.8 (Cq Bn), 169.1 ppm (COOMe); HRMS: m/z:
calcd for C34H34O6S+NH4+: 588.24144; found: 588.24210; IR (neat): n˜ =
731, 897, 814, 939, 1026, 1074, 1126, 1209, 1265, 1304, 1358, 1420, 1439,
1
1454, 1477, 1497, 1734, 1765, 2876 cmꢀ1
.
0.024, CH2Cl2); H NMR (400 MHz, CDCl3): d=3.51 (m, 1H, H-4), 3.57–
3.67 (m, 2H, H-6), 3.71 (t, 1H, J=3.2 Hz, H-3), 3.75 (dd, 1H, J=2.8,
10 Hz, H-2), 4.13 (t, 1H, J=6.4 Hz, H-5), 4.26 (d, 1H, J=12 Hz, CH2
Bn), 4.31 (d, 1H, J=12 Hz, CH2 Bn), 4.37 (d, 1H, J=10.8 Hz, CH2 Bn),
4.40 (d, 1H, J=8.8 Hz, CH2 Bn), 4.47–4.52 (m, 2H, CH2 Bn), 4.59 (d,
1H, J=11.6 Hz, CH2 Bn), 4.66 (d, 1H, J=12 Hz, CH2 Bn), 5.23 (d, 1H,
J=10 Hz, H-1), 7.08–7.10 (m, 2H, Ar-H), 7.12–7.35 (m, 21H, Ar-H),
7.51–7.60 ppm (m, 2H, Ar-H); 13C NMR (100 MHz, CDCl3): d=69.0 (C-
6), 72.4 (CH2 Bn), 72.8 (CH2 Bn), 73.1 (C-3), 73.2 (CH2 Bn), 73.4 (CH2
Bn), 74.4 (C-5), 74.8 (C-2), 74.9 (C-4), 84.3 (C-1), 126.8–128.6 (Ar-CH),
131.4 (Ar-CH), 138.2 ppm (Cq Bn); HRMS: m/z: calcd for C40H40O5S+
Na+: 655.24887; found: 655.24860; IR (neat): n˜ =741, 1001, 1028, 1076,
Methyl-2,3,4-tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzyl-a,b-l-gulopyrano-
side)-a-d-glucopyranoside (13): solution of donor (0.127 g,
A
7
0.2 mmol), diphenyl sulfoxide (0.045 g, 0.22 mmol), and tri-tert-butylpyri-
midine (0.124 g, 0.5 mmol) in CH2Cl2 (4 mL) was stirred over activated 3-
molecular sieves (MS) for 30 min. The reaction mixture was cooled to
ꢀ788C before triflic acid anhydride (37 mL, 0.22 mmol) was added. The
reaction mixture was stirred for 10 min at ꢀ788C followed by the addi-
tion of acceptor 10 (0.139 g, 0.3 mmol) in CH2Cl2 (3 mL). Stirring was
continued and the reaction mixture was allowed to warm to 08C and
Et3N (0.15 mL) was added. The reaction mixture was diluted with
CH2Cl2 and washed with NaHCO3 (aq). The aqueous layer was extracted
twice with CH2Cl2. The collected organic layers were dried over MgSO4
and concentrated in vacuo. Purification by size exclusion and column
chromatography yielded 13 as a colourless oil (71%, 0.140 g, a/b=13:1).
Determination of the a/b ratio by 1H NMR: d= 3.25 (s, 3H, OCH3 a),
1101, 1207, 1360, 1439, 1454, 1497, 2866, 3032, 3061 cmꢀ1
.
Phenyl-2,3,4-tri-O-benzyl-1-thio-b-l-gulopyranoside (8): Compound
6
(5.45 g, 20 mmol) was dissolved in pyridine (100 mL) and trityl chloride
(8.36 g, 30 mmol) was added, and the reaction mixture was stirred for
3 days. The reaction was quenched with MeOH and concentrated in
vacuo. The mixture was diluted with EtOAc, washed with 1m HCl (aq),
NaHCO3 (aq), and brine. The organic layer was dried over MgSO4 and
concentrated in vacuo. The residue was dissolved in DMF (100 mL) and
cooled to 08C. Respectively, BnBr (8.55 mL, 72 mmol) and NaH (2.88 g,
72 mmol, 60% dispersion in oil) were added. After stirring overnight, the
reaction mixture was quenched with MeOH and concentrated in vacuo.
The residue was taken up in Et2O and washed three times with H2O. The
organic layer was dried over MgSO4 and concentrated in vacuo. The resi-
due was dissolved in CH2Cl2 (50 mL) and MeOH (200 mL) and a catalyt-
ic amount of p-TsOH was added. The reaction mixture was stirred over-
night. The reaction mixture was neutralised with Et3N and concentrated
in vacuo. Column chromatography yielded 8 as a colourless oil (9.58 g,
1
3.33 ppm (s, 0.22H, OCH3 b). a isomer: H NMR (400 MHz, CDCl3): d=
3.25 (s, 3H, OCH3), 3.38 (dd, 1H, J=3.6, J=9.6 Hz, H-2), 3.53–3.62 (m,
2H, H-6’), 3.63–3.85 (m, 6H, H-3’, H-4, H-6, H-5, H-2’, H-4’), 3.96 (t,
1H, J=9.2 Hz, H-3), 4.01 (d, 1H, J=10 Hz, H-6’), 4.33–4.55 (m, 9H, H-
5’, CH2 Bn), 4.57 (d, 1H, J=3.6 Hz, H-1), 4.68 (d, 1H, J=12.4 Hz, CH2
Bn), 4.71 (d, 1H, J=12.4 Hz, CH2 Bn), 4.80 (d, 1H, J=10.8 Hz, CH2
Bn), 4.83 (d, 1H, J=12 Hz, CH2 Bn), 4.93 (d, 1H, J=10.8 Hz, CH2 Bn),
4.98 ppm (d, 1H, J=3.2 Hz, H-1’); 13C NMR (100 MHz, CDCl3): d=54.8
(OCH3), 65.5 (C-5), 67.2 (C-6’), 68.8 (C-6), 70.1 (C-4’), 71.1 (CH2 Bn),
72.7 (C-2’), 72.7 (CH2 Bn), 72.8 (CH2 Bn), 73.0 (CH2 Bn), 73.1 (CH2 Bn),
74.2 (C-5’), 74.8 (CH2 Bn), 75.5 (CH2 Bn), 75.6 (C-3’), 77.9 (C-4’), 80.2
(C-2), 82.0 (C-3), 97.7 (C-1’), 97.8 (C-1), 127.1–128.3 (Ar-CH), 138.1 (Cq
Bn), 138.3 (Cq Bn), 138.4 (Cq Ph), 138.5 (Cq Bn), 138.8 (Cq Bn), 139.1 (Cq
1
88%). [a]2D2 =+11.8 (c=0.024, CH2Cl2); H NMR (400 MHz, CDCl3): d=
+
Bn), 139.4 ppm (Cq Bn); HRMS: m/z: calcd for C62H66O11 +NH4
:
3.40 (m, 1H, H-3), 3.45–3.53 (m, 1H, H-6), 3.76 (m, 2H, H-2, H-4), 3.80–
3.85 (m, 1H, H-6), 3.94–3.97 (m, 1H, H-5), 4.22 (d, 1H, J=12 Hz, CH2
Bn), 4.29 (d, 1H, J=12 Hz, CH2 Bn), 4.40 (d, 1H, J=12 Hz, CH2 Bn),
4.49 (d, 1H, J=12 Hz, CH2 Bn), 4.61 (d, 1H, J=11.6 Hz, CH2 Bn), 4.71
(d, 1H, J=12 Hz, CH2 Bn), 5.23 (d, 1H, J=9.6 Hz, H-1), 7.07–7.10 (m,
2H, Ar-H), 7.23–7.36 (m, 16H, Ar-H), 7.55–7.57 ppm (m, 2H, Ar-H);
13C NMR (100 MHz, CDCl3): d=62.5 (C-6), 72.1 (CH2 Bn), 72.7 (C-2 or
C-4), 72.9 (CH2 Bn), 73.4 (CH2 Bn), 74.9 (C-2 or C-4), 75.2 (C-3), 75.8
(C-5), 84.0 (C-1), 127.0–128.8 (Ar-CH), 131.6 (Ar-CH), 134.0 (Cq Bn),
137.5 (Cq Bn), 137.8 (Cq Bn), 138.1 ppm (Cq Bn); HRMS: m/z: calcd for
C33H34O5S+H+: 543.21997; found: 543.22015; IR (neat): n˜ =739, 922,
1001, 1026, 1042, 1074, 1207, 1358, 1439, 1454, 1477, 1497, 2878, 3030,
1004.49434; found: 1004.49579; IR (neat): n˜ =733, 820, 908, 1026, 1047,
1069, 1194, 1207, 1310, 1327, 1360, 1454, 1497, 2870, 3030, 3063 cmꢀ1
.
Methyl-2,3,6-tri-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-a,b-l-gulopyrano-
side)-a-d-glucopyranoside (14): As described for the synthesis of 13 using
acceptor 11 (0.139 g, 0.3 mmol). Purification by size exclusion and
column chromatography yielded 14 as a colourless oil (91%, 0.179 g, a/
b=10:1). Determination of the a/b ratio by 1H NMR: d=5.11 (d, 1H,
J=4.0 Hz, H-1’ a), 5.38 ppm (d, 0.09H, J=8.0 Hz, H-1’ b). a isomer:
1H NMR (400 MHz, CDCl3): d=3.34 (s, 3H, CH3 OMe), 3.45 (m, 1H),
3.51 (dd, 1H, J=3.6 Hz, 8.8 Hz), 3.60 (m, 1H), 3.68 (t, 1H, J=3.2 Hz),
3.73 (m, 1H, H-2’), 3.76–3.89 (m, 4H), 4.09 (d, 1H, J=11.6 Hz, CH2 Bn),
4.15 (d, 1H, J=11.6 Hz, CH2 Bn), 4.26–4.40 (m, 7H), 4.51–4.56 (m, 3H,
H-1), 4.66 (d, 1H, J=8.8 Hz, CH2 Bn), 4.68 (d, 1H, J=8.8 Hz, CH2 Bn),
4.88 (d, 1H, J=11.2 Hz, CH2 Bn), 4.95 (d, 1H, J=11.2 Hz, CH2 Bn), 5.11
(d, 1H, J=4.0 Hz, H-1’), 7.08–7.30 ppm (m, 35H, Ar-CH); 13C NMR
(100 MHz, CDCl3): d=54.9 (CH3 OMe), 65.3, 68.1, 68.9, 70.1, 71.3, 72.6,
72.7, 72.8, 72.9, 73.0, 73.1, 73.3, 73.9, 74.5, 75.8, 80.3, 80.5, 97.6 (C-1’), 97.8
(C-1), 126.8–128.7 (Ar-CH), 137.9–139.5 ppm (Cq Bn); ESI-MS: m/z:
3063 cmꢀ1
.
Methyl (phenyl-2,3,4-tri-O-benzyl-1-thio-b-d-gulopyranosyluronate) (9):
Compound 8 (1.95 g, 3.6 mmol) was taken up in CH2Cl2 (24 mL) and
H2O (12 mL) and TEMPO (0.115 g, 0.74 mmol) and BAIB (2.89 g,
9.0 mmol) were added. The reaction mixture was stirred vigorously until
analysis by TLC showed complete conversion of the starting material.
Na2S2O3 (50 mL, aq) was added and the resulting mixture was stirred for
15 min. The layers were separated and the aqueous phase acidified with
1m HCl and extracted three times with CH2Cl2. The combined organic
layers were dried over MgSO4 and concentrated in vacuo. The residue
was taken up in DMF (20 mL) and K2CO3 (2.49 g, 18 mmol) and MeI
(0.56 mL, 9.0 mmol) was added. After 2 h, the reaction mixture was dilut-
ed with Et2O (50 mL) and washed three times with H2O. The organic
layer was dried over MgSO4 and concentrated in vacuo. Purification by
987.5 [M+H+]; IR (neat): n˜ =732, 909, 1027, 1454, 2866, 3030 cmꢀ1
.
para-Methoxyphenyl-2-O-benzyl-(2,3,4,6-tetra-O-benzyl-a-l-gulopyrano-
side)-4,6-benzylidene-b-d-galactopyranoside (15): As described for the
synthesis of 13 using acceptor 12 (0.139 g, 0.3 mmol). Purification by size
exclusion and column chromatography yielded 15 as a colourless oil
(73%, 0.144 g). Determination of the a/b ratio by 1H NMR: d=5.47 (s,
0.07H, CH benzylidene b), 5.55 ppm (s, 1H, CH benzylidene a). a
1
column chromatography yielded 9 as a white solid (1.48 g, 72%). [a]D22
=
anomer: H NMR (400 MHz, CDCl3): d=3.28 (s, 1H, H-6), 3.43 (dd, 1H,
+17.0 (c=1, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=3.72–3.75 (m,
4H, H-3, CH3 CO2Me), 3.83 (dd, 1H, J=3.2, J=10 Hz, H-2), 3.91 (dd,
1H, J=3.6, 1.6 Hz, H-4), 4.31 (d, 1H, J=12 Hz, CH2 Bn), 4.39 (d, 1H,
J=12 Hz, CH2 Bn), 4.41 (d, 1H, J=12 Hz, CH2 Bn), 4.56 (d, 1H, J=
12 Hz, CH2 Bn), 4.60 (s, 1H, H-5), 4.61 (d, 1H, J=12 Hz, CH2 Bn), 4.71
(d, 1H, J=12.4 Hz, CH2 Bn), 5.23 ppm (d, 1H, J=10 Hz, H-1);
13C NMR (100 MHz, CDCl3): d=52.1 (CH3 CO2Me), 72.5 (CH2 Bn), 72.7
(CH2 Bn), 72.7 (C-3), 72.2 (CH2 Bn), 73.9 (C-2), 74.7 (C-5), 76.2 (C-
4),84.4 (C-1), 127.2–128.6 (Ar-C), 132.4 (Ar-C), 133.7 (Cq Bn), 137.4 (Cq
J=10 Hz, H-6), 3.57–3.60 (m, 1H, H-4’), 3.62 (t, 1H, J=10 Hz, H-5’),
3.68 (dd, 1H, J=10, 3.6 Hz, H-3), 3.71 (s, 1H, H-6’), 3.86 (m, 1H, H-2’),
3.90 (m, 1H, H-3’), 4.03–4.10 (m, 2H, H-2, H-6), 4.30–4.49 (m, 6H, CH2
Bn), 4.58–4.63 (m, 2H, H-4, CH2 Bn), 4.71–4.72 (m, 1H, H-5), 4.76 (d,
1H, J=11.2 Hz, CH2 Bn), 4.87–4.90 (m, 2H, H-1, CH2 Bn), 5.23 (d, 1H,
J=3.6 Hz, H-1’), 5.55 (s, 1H, CH benzylidene), 6.74–6.76 (m, 2H, Ar-H),
6.99–7.01 (m, 2H, Ar-H), 7.12–7.31 (m, 35H, Ar-H), 7.38–7.40 (m, 3H,
Ar-H), 7.50–7.52 ppm (m, 2H, Ar-H); 13C NMR (100 MHz, CDCl3): d=
55.5 (OCH3 pMP (p-methoxyphenyl)), 66.6 (C-5), 68.5 (C-6), 70.9 (C-6’),
Chem. Eur. J. 2008, 14, 9400 – 9411
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9405