A solution of Intermediate 150b (50 mg, 0.16 mmol) in DCM (2 mL) was treated with pyridine (26 μL, 0.32 mmol) and phenyl chloroformate (32 μL, 0.25 mmol). The resulting mixture was stirred at RT for 2 h. Further pyridine (26 μL, 0.32 mmol) and phenyl chloroformate (32 μL, 0.25 mmol) were added and the mixture stirred at RT for 16 h. The mixture was diluted with water and the phases separated. The aqueous layer was extracted with DCM and the combined organic phase was washed with brine, dried (Na2SO4), and concentrated in vacuo. The residue was purified by FCC, using 0-20% MeOH in DCM, to give the title compound (30 mg, 43%). LCMS (Method 3): Rt 2.97 min, m/z 436 [MH+].
