To a cold solution of Boc-Asp(O-cHex) (31.5 g, 100 mmol) and N-methylmorpholine (13.1 g, 120 mmol) in THF (500 mL), isobutylchloroformate (15.6 mL, 1.2 mmol) was added dropwise. The reaction mixture was stirred for a few minutes, then a solution of Man(4-MBzl) (22.0 g, 96 mmol) in THF (500 mL) was added. The reaction mixture was allowed to warm to room temperature and stirred for 18 h. Upon completion of the reaction (monitored by TLC), the amine sand the filtered off and the filtrate was concentrated to dryness. The residue was dissolved in ethyl acetate (500 mL) and washed successively with 5% aqueous citric acid (3×150 mL), water (1×400 mL), aqueous NaHCO3 (1×300 mL), water (1×400 mL) and saturated salt solution (1×30 mL). The organic solvent was dried (anhydrous K2CO3), filtered and concentrated to yield the title product (53 g).
