An oven dried round bottom flask, equipped with a magnetic stirbar under argon, was charged with tert-butyl 2-(methyl(2-(7-(thiophene-2-carboximidamido)-2H-benzo[b][1,4]thiazin-4(3H)-yl)ethyl)amino)acetate (200 mg, 0.448 mmol) in CH2Cl2 (3 mL), and the solution was cooled to 0° C. (ice/water bath). To this solution was added anisole (0.098 mL, 0.896 mmol) followed by the dropwise addition of trifluoroacetic acid (2.92 mL, 26.9 mmol). The reaction was stirred at 0° C. for 20 minutes. The ice bath was then removed, and the mixture was stirred for 3 additional hours. At this time, the mixture was concentrated and treated with 4.0 M HCl in 1,4-dioxane (4 mL). The resulting suspension was diluted with Et2O (20 mL) and then stirred for 20 minutes. The mixture was filtered, and the solid was washed with Et2O (20 mL). The solid was dried under reduced pressure to give compound 17 as light yellow powder (200 mg, 96%). An HPLC analysis indicated that the sample contained ˜3.4% of the starting material. 1H-NMR (CD3OD) δ 7.99 (d, J=5.1 Hz, 1H), 7.97 (d, J=3.6 Hz, 1H), 7.31 (pseudo t, J=4.5 Hz, 1H), 7.11-6.99 (m, 2H), 6.95 (d, J=8.7 Hz, 1H), 4.16 (s, 2H), 3.81 (brt, J=6.9 Hz, 2H), 3.68 (brt, J=4.8 Hz, 2H), 3.52-3.39 (m, 2H), 3.10 (brt, J=4.8 Hz, 2H), 3.03 (s, 3H); ESI-MS (positive ion mode): 391 (MH+, free base, 100); ESI-MS (negative ion mode): 389 (M−1, free base, 100); ESI-HRMS calculated for C18H23N4O2S2 (MH+, free base): 391.1256, Observed: 391.1255; HPLC purity: 96.64% a/a.
