To a stirred solution of 3-{4-[(4,6-dimethyl-3-nitro-2-pyridinyl)amino]phenyl}propanoic acid (step 1, 10 g, 31.7 mmol) in dioxane (200 mL) was added diphenylphosphoryl azide (DPPA) (7.54 ml, 35 mmol) and triethylamine (4.87 mL, 35 mmol). The reaction mixture was heated at 120° C. for 2 h. To the reaction mixture was added phenol (6.6 g, 70 mmol) and the reaction mixture was refluxed. After 3 h, to the reaction mixture was added an additional amount of phenol (3.3 g, 35 mmol). The resulting mixture was heated under reflux temperature overnight. The volatile component was removed and the residue was partitioned between aqueous 10% aqueous citric acid (200 mL) and ethyl acetate (300 mL). The organic phase was separated and the aqueous phase was extracted with ethyl acetate (300 mL). The combined organic extracts were washed with water (300 mL) and brine (300 mL), then dried (Na2SO4), and concentrated. The crude product was purified by flash column chromatography on silica gel eluting with hexane/EtOAc (2:1) to afford 10.3 g (77%) of the title compound as orange solids.
