Scheme 4. Further transformations and scale up reaction. Reaction conditions: (i) (Boc)₂O (4.0 equiv.), Et₃N (4.0 equiv.), CH₂Cl₂, rt; (ii) Fmoc-Osu (4.0 equiv.), CH₃CN, rt; (iii) 4-toluene sulfonyl chloride (2.0 equiv.), Na₂CO₃ (2.0 equiv.), THF/H₂O, rt; and (iv) sulfamide (3.0 equiv.), Na₂CO₃ (2.0 equiv.), 1,4-dioxane, 100 °C.