Molecules 2012, 17
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purification or characterisation. (B) Na (a small piece) was added to a solution of the mixture from (A)
(above) (0.44 mmol, max.) in MeOH (4 mL) and the combined mixture stirred (rt, 1 h). The mixture
was evaporated and neutralised by the addition of Dowex 50X8 resin (H+ form), filtered and the filtrate
evaporated. The residue was subjected to workup (EtOAc) and flash chromatography (EtOAc/hexanes
1:19:1) to yield a colourless oil (210 mg). This residue was co-evaporated (2 × 10 mL CH3CN) and
used in the next reaction without further purification or characterisation. (C) BzCl (306 L,
2.64 mmol) was added to a solution of the mixture from (A) (above) (29) (0.44 mmol, max.) and
pyridine (2 mL) in 1,2-DCE (4 mL) and the combined mixture stirred (rt, o/n). The mixture was cooled
(0 C) and MeOH (2 mL) was introduced with continued stirring (0 °C→rt, 2 min) before evaporation
and co-evaporation (toluene) of the solvent. The residue was subjected to workup (EtOAc) and flash
chromatography (EtOAc/hexanes 1:93:7) to yield two compounds. Firstly, the -linked disaccharide
1
(30) was obtained as a colourless oil (217 mg, 60%, 3 steps). H-NMR: 1.48 (d, 3 H, J5,6 = 6.6 Hz,
H6I), 3.31 (s, 3H, OCH3), 3.40 (dd, 1H, J1,2 = 3.7, J2,3 = 10.6 Hz, H2II), 3.64–3.65 (m, 1H, H2I), 3.73
(m, 1H, H3I), 3.88–3.95 (m, 1H, H5I), 4.05–4.07 (m, 1H, H4I), 4.35 (ddd, 1H, J4,5 = 10.2, J5,6a = 3.3,
J5,6b = 5.8 Hz, H5II), 4.37, 4.61 (ABq, JA,B = 11.6 Hz; CH2Ph), 4.50 (dd, 1H, J6a,6b = 12.0 Hz, H6bII),
5.58 (dd, 1H, H6aII), 4.67, 4.77 (ABq, JA,B = 12.7 Hz, CH2Ph), 4.82 (d, 1H, J1,2 = 1.6 Hz, H1I), 5.24
(dd, 1H, J3,4 = 9.5, J4,5 = 10.1 Hz, H4II), 5.99 (dd, 1H, J2,3 = 10.7, J3,4 = 9.3 Hz, H3II), 6.14–6.15 (d,
1H, J1,2 = 4.0 Hz, H1II), 7.20–7.54, 7.90–7.99 (2 m, 25H, 5 × Ph); 13C-NMR: 17.6, 55.2, 61.8, 63.7,
66.9, 68.3, 70.5, 70.6, 70.6, 74.5, 96.3, 99.9, 127.7, 128.2, 128.4, 128.5, 128.5, 128.6, 128.6, 129.0,
129.5, 129.8, 129.9, 130.0, 130.1, 133.3, 133.4, 133.6, 136.3, 138.8, 165.6, 165.7, 166.3.
Next, the -linked disaccharide (31) was obtained as a colourless oil (36 mg, 10%, 3 steps).
1H-NMR: 1.46 (d, 3H, J5,6 = 6.6 Hz, H6I), 3.33 (s, 3H, OMe), 3.53 (t, 1H, J1,2 = J 2,3 = 3.2 Hz, H2I),
3.70–3.75 (m, 1H, H2II), 3.85–3.93, 3.97–4.01 (2 m, 4H, H3I, H4I, H5I, H5II), 4.29 (dd, 1H, J5,6a = 5.3,
J6a,6b = 12.2 Hz, H6aII); 4.44 (dd, 1H, J5,6b = 3.3, H6bII), 4.54, 4.73 (ABq, JA,B = 11.9 Hz, CH2Ph), 4.65
(d, 1H, J1,2 = 8.0 Hz, H1II), 4.72, 4.76 (ABq, JA,B = 12.7 Hz, CH2Ph), 4.77 (d, 1H, J1,2 = 3.5 Hz, H1I),
5.44–5.51 (m, 2H, H3II, H4II), 7.20–7.51, 7.83–7.94 (2 m, 25H, 5 × Ph).
Methyl 3,4,6-tri-O-methyl-2-azido-2-deoxy-α-D-glucopyranosyl-(1→4)-2,3-di-O-benzyl-6-deoxy-α-L-
talopyranoside 32. Tribenzoate 30 (110 mg, 128 µmol) was subjected to the Zemplén and methylation
procedures (as described above for the preparation of 25) with MeI (82 mg, 582 µmol). Flash
chromatography (hexanesEtOAc/hexanes 1:4) gave the trimethyl derivative 32 (52 mg, 69%,
2 steps) as a colourless oil. 1H-NMR: δ 7.42–7.22 (m, 10H, 2 × Ph), 5.73 (d, 1H, J = 3.7, H1II), 4.84 (d,
1H, J = 2.0, H1I), 4.82, 4.77 (ABq, 2H, J = 12.6, CH2Ph), 4.58, 4.54 (ABq, 2H, J = 11.9, CH2Ph),
3.95–3.93 (m, 1H), 3.90 (dt, 1H, J = 2.0, 6.7, H5I), (s, 3H, OMe), 3.76–3.57 (m, 6H), 3.65, 3.55, 3.42,
3.31 (4 × s, 4 × 3H, OMe), 3.28–3.21 (m, 2H), 1.34 (d, 3H, J = 6.5, H6I).
4. Conclusions
In conclusion, the 6-deoxy--L-taloside acceptor 14 was readily prepared in seven steps from
methyl -L-rhamnopyranoside in good overall yield. Glycosylation of 14 with the thiogalactoside
donors 11 or 12 with NIS/TfOH as the promoter gave good yields of the -linked disaccharide 22.
Glycosylation with the thiomethyl donor 11 was preferred as it gave a cleaner reaction mixture from