Scheme 8.

Linear assembly of fully protected hexasaccharide 51. Reagents and conditions: (a) DDQ, CH₂Cl₂/MeOH (9:1), rt, 70%; (b) 43, NIS, TfOH, CH₂Cl₂, −20 °C (no reaction) or 6, TMSOTf, Et₂O/CH₂Cl₂ (4:1), −20 °C (65%); (c) DDQ, CH₂Cl₂/MeOH (9:1), rt, 55%; (d) 7, TMSOTf, Et₂O/CH₂Cl₂ (4:1), −20 °C, 62%; (e) NaOMe (0.5 M in MeOH), THF/MeOH (1:1), rt, 90%; (f) i. TEMPO, BAIB, CH₂Cl₂/H₂O (4:1), rt; ii. MeI, K₂CO₃, DMF, rt, 35% over two steps; (g) 8, TMSOTf, CH₂Cl₂, −20 °C, 77%; (h) i. NaOMe (0.5 M in MeOH), THF/MeOH (1:1); ii. trimethyl orthoacetate, p-TsOH, toluene; iii. 80% AcOH, rt, 27% over three steps; (i) 9, NIS, TMSOTf, dioxane/toluene (3:1), −10 °C to 0 °C, 54%.