Amberlite IRA 458 ‘chloride’ resin (40 g, wet) was converted to the besylate equivalent by passing a solution of benzene sulphonic acid (400 mL, 10% aqueous solution) through the resin in a glass column at a slow rate of 5-10 mL/minute. Following this, the resin was washed with water until the filtrate had a pH of ˜5/6. The resin was stored “damp” prior to use. A solution of Example 40 (1 g, 1.57 mmol) in a round-bottom flask (250 mL) was treated with 30% MeCN/water (60 mL) and then mixed with the besylate resin (40 g, wet). The resulting mixture was gently agitated by slowly rotating the flask on a Buchi evaporator for 50 minutes at atmospheric pressure. The contents were placed in a resin tube, then filtered and washed with 30% MeCN/water and the filtrate was freeze dried to give the title compound as a white electrostatic solid (1.01 g).
