A solution of the product of Example 280B (446 mg, 1.3 mmol) and aqueous saturated lithium hydroxide (3 mL) in methanol (5 mL) was heated at 60° C. for 15 hours. The reaction mixture was then neutralized with hydrogen chloride (4 N in dioxane, 5 mL). The reaction mixture was concentrated in vacuo to dryness. To the residue was added sequentially L-methionine methyl ester hydrochloride (311 mg, 1.56 mmol), 3-hydroxy 1,2,3-benzotriazin-4(3H)-one (318 mg, 1.95 mmol), 1-(3-dimethylaminopropyl)-3-ethylcarbodimide (374 mg, 1.95 mmol), THF (10 mL) and pyridine (1 mL). After 15 hours, the reaction mixture was diluted with ethyl acetate, washed with water and brine, dried over anhydrous magnesium sulfate, filtered and concentrated in vacuo. The residue was then purified by column chromatography (ethyl acetate) to give the title compound.
