Pyridine (17 μL, 0.20 mmol) and 6-methoxy-m-toluenesulfonyl chloride (34 mg, 0.15 mmol) were added to a solution of tert-butyl 4-[(5-amino-1-benzofuran-7-yl)methyl]-3-methylpiperazine-1-carboxylate (45 mg crude material, 0.10 mmol; obtained in Step 2) in dry DCM:THF (2:1; 3 mL). The reaction mixture was stirred at room temperature for 2 h and the solvent was evaporated under reduced pressure followed by purification by flashtube (15% MeOH in DCM). The residue was dissolved in TFA:water (9:1; 4.5 mL) and the mixture was stirred at room temperature for 1 h to accomplish removal of the N-t-BOC group. The reaction mixture was diluted with DCM (10 mL) and saturated aqueous Na2CO3 was added to reach pH 8-9 (˜15 mL). The phases were separated using “phase separator” filters and the organic phase was concentrated. The crude product was purified by preparative HPLC (System B; 10-40% MeCN). Pure fractions were combined and concentrated to give the product as the free base, which was dissolved in MeOH and 1 M HCl in ether (200 μL, 0.2 mmol) was added. The solvent was evaporated to give the title compound (19 mg, 38%) as an off-white solid. HPLC 99%, RT=1.46 min (System A; 10-97% MeCN over 3 min), 100%, RT=1.29 min (System B; 10-97% MeCN over 3 min). 1H NMR (400 MHz, methanol-d4) δ ppm 1.72 (d, J=6.53 Hz, 3H) 2.20 (s, 3H) 3.39-3.62 (m, 5H) 3.67-3.74 (m, 1H) 3.87-3.96 (m, 1H) 3.98 (s, 3H) 4.60 (d, J=13.55 Hz, 1H) 4.93 (d, J=13.80 Hz, 1H) 6.87 (d, J=2.26 Hz, 1H) 7.04 (d, J=8.53 Hz, 1H) 7.28-7.37 (m, 2H) 7.52 (d, J=2.26 Hz, 1H) 7.54 (d, J=2.01 Hz, 1H) 7.85 (d, J=2.01 Hz, 1H). MS (ESI+) for C22H27N3O4S m/z 430 (M+H)+.
