58 g BocAsnOH (0.25 moles) and 29 g HOSu are dissolved in 250 ml DMF and cooled to -20°. 52 g DCC dissolved in 250 ml DMF is added. After 4 hours stirring at room temperature 85 g GlyOBzl, pTos and 35 ml TEA is added. After stirring overnight the DCU i filtered off, DMF removed in vacuo on a Rotavap, and the resulting oil dissolved in EtAc. After extraction with sat. NaCl, sat. NaHCO3, and 10% citric acid, the solvent is dried with Na2SO4 and evaporated. The resulting crystalline ma is dried in a desiccator. Yield: 64 g (67%).
