The crude azlactone (40.2 mg, 0.0972 mmol) was then dissolved in MeOH (2 mL) and treated dropwise with 1 N NaOH (970 L, 0.97 mmol, 10 equiv). The resulting mixture was stirred at rt for 24 h, then washed with sat aq NaHCO3 (2 × 5 mL) and acidified by the addition of 1 N HCl to pH ~2. The mixture was extracted with EtOAc (3 × 5 mL), and the combined organic layers were dried (Na2SO4) and concentrated in vacuo. The crude C-terminal dehydroamino acid was dissolved in anhydrous THF-DMF