To a solution of
ProOt-Bu (5 g, 29.2 mmol) and FmocThr(t-BuO)OH
(12.8 g, 32.2 mmol) in DCM (150 mL) at 0 C were
added EDAC (8.6 g, 45 mmol) and HOBT (5.8 g, 43
mmol). The mixture was warmed to 25 C overnight.
The solvent was evaporated and the residue was com-
bined with ethyl acetate and 10% citric acid. The
organic layer was washed with satd Na2CO3, and dried
with Na2SO4. The solvent was evaporated to give crude
solids which were used directly for the next step.