General method: suitable phenolic compounds 8a-13a (1 mmol) were mixed with 60% nitric acid (4.8 mmol). The resulting suspension was stirred at room temperature, where compounds 8a and 9a were stirred for 10 min, compounds 10a, 12a, and 13a were stirred for 30 min, and compound 11a was stirred overnight until a deep red solution was formed.HPLC analysis confirmed complete consumption of the starting material and detected three major products corresponding to the nitro derivatives generated by hydroxyl-neighboring and para-nitrosylation of meso-substituted phenols 8a, 10a, and 12a; while para-substituted phenols 9a, 10a, and 12a, and the nitro derivatives generated by hydroxyl neighboring and para nitro derivatives generated by nitration; while only one product was generated from para-substituted phenols 9a, 11a and 13a. The crude products, nitrophenol 8b or 9b, were diluted with water (20 mL) and upsampled onto a Dowex 50W-X2 (200-400 mesh) column (1.5 cm × 6 cm, H+ type, pre-equilibrated with water). The column was first washed with water (100 mL), and then the product was eluted with 2 M hydrochloric acid (20 mL/grade fraction). The grades containing 3-nitrotyramine were combined and evaporated to dryness to give a yellow powder. For the nitration products (10b, 12b, and 13b) of phenols 10a, 12a, and 13a, the reaction mixture was diluted with water (20 mL) and extracted with ethyl acetate (2 × 100 mL). The organic phases were combined, washed with water (2 x 50 mL), dried over anhydrous sodium sulfate and concentrated under reduced pressure. The nitration reaction of compound 11a directly gave orange powder 11b, which was filtered, washed with water and dried under reduced pressure to give dark powder 11b.
