4,5-Difluoro-3-(3,5-dimethylphenylsulphonyl)indole 2-carboxylic acid (3.52 g) and L-serinamide hydrochloride (2.77 g) were dissolved in anhydrous dimethylformamide (90 ml). Triethylamine (2.8 ml) was added and the mixture stirred for 5 minutes. Benzotriazol-1-yloxy-tris(dimethylamino)phosphosphonium hexafluorophosphate (BOP) (4.69 g) was added and the orange mixture was stirred overnight at room temperature. The reaction mixture was diluted with water (350 ml) and the white solid precipitate collected by filtration, washed with water and dried to afford the title product (3.86 g) as a white powder (97.9% pure by hplc).
