The product of Example 4 (18 mg) was combined with pyridine (2 mL), acetic anhydride (0.2 mL), and DMAP (5 mg). The reaction was heated to 85° C. for 1 hr at which point LC/MS indicated significant imide formation. The reaction was concentrated and redissolved in 1,4-dioxane before adding aqueous 1 M NaOH (1 mL). After 15 hours at room temperature the reaction was diluted with EtOAc and washed with brine before drying (Na2SO4). The concentrated residue was purified by preparative TLC (silica gel) eluted with EtOAc affording the title compound. HPLC/MS: 471.9 (M+1), 473.9 (M+3); Rt=3.79 inn.
