N-Bromosuccinimide (2.99 g) and azobisisobutyronitrile (275 mg) were added to a solution of N-(isobutoxycarbonyl)-N-(3-methoxy-5-methylpyrazin-2-yl)-2-(4-methylphenyl)pyridine-3-sulphonamide (7.9 g) in carbon tetrachloride (150 ml) and the mixture was heated under reflux for 4 hours. Insoluble material was removed by filtration and the fitrate was concentrated by evaporation. The residue was redissolved in ethyl acetate (200 ml) and the solution was washed with water (100 ml) and saturated sodium chloride solution (100 ml). The solution was dried (MgSO4) and the solvent was removed by evaporation. The residue was triturated with ethyl acetate/hexane (3:7 v/v, 80 ml) to give 2-(4-bromomethylphenyl)-N-(isobutoxycarbonyl)-N-(3-methoxy-5-methylpyrazin-2-yl)-pyridine-3-sulphonamide (6.5 g), m.p. 125-128° C.
