A solution of compound 50.3 (50 mg, 0.1 mmol) in dichloromethane (2 mL) was treated with 1-hydroxybenzotriazole (15 mg, 0.11 mmol) and EDC (21 mg, 0.11 mmol) sequentially. The resulting mixture was stirred for 1 h. before dimethylamine (9 mg, 0.2 mmol) was added dropwise. The reaction was quenched 30 min. later with water (5 mL). The reaction mixture was extracted with dichloromethane (2 mL×3). The organic extracts were combined, dried over MgSO4 and concentrated under reduced pressure to yield amide 50.4 (48 mg). The product was used in the next step without further purification. MS ESI (pos.) m/e: 527 (M+).
