A solution of the compound from Example 5 (100 mg, 0.2 mmol) in dry DMF (15 mL) was treated with cesium carbonate (141 mg, 0.4 mmol) and 18-crown-6 (100 mg, 0.41 mmol) followed by 1-iodooctane (144 mg, 0.6 mmol). The resulting mixture was heated at 70° C. under argon for 20 h. The reaction was cooled, concentrated and the residue partitioned between water and ethyl acetate. The organic layer was washed with 10% Na2CO3 (aqueous), brine, dried over MgSO4 and evaporated. Purification by flash chromatography (4% MeOH in CH2Cl2) gave the ester as a yellow oil. The oil in ether was treated with HCl and filtered to give the above titled compound (50 mg, 46%). LC-MS m/e 549.4 [M+H]+.
