To a solution of Boc-Tyr(OBn) (1.88 g, 6.50 mmol) in EtOAc (30 mL) at 0° C. was added HOBT hydrate (1.19 g, 7.80 mmol) followed by DCC (1.61 g, 7.80 mmol). A solution of Ser(OBn)-CO2Me.TFA (2.1 g, 6.50 mmol) in EtOAc (20 mL) was added followed by Et3N (1.09 mL, 7.80 mmol). The mixture was allowed to warm to room temperature and stirred overnight. The mixture was filtered, diluted with EtOAc, and washed twice with saturated aqueous NaHCO3, brine, dried over MgSO4, and concentrated. Flash chromatography (40% EtOAc/hexane) gave 2.67 g (73%) of the title compound as a white solid, mp 81°-84° C.
