Sodium hydride (0.35 g of a 60% suspension in oil, 8.7 mmol) was added to a suspension of 8-amino-1,3-di(cyclopropylmethyl)xanthine (2 g, 7.3 mmol ) in dimethoxyethane (40 ml) and the resulting mixture stirred at ambient temperature for 2 hr. Isopropylsulphonyl chloride (1.24 g, 8.7 mmol) was added and the mixture was heated at reflux for 18 hours. The reaction mixture was allowed to cool and then water (1 ml) was added dropwise. The mixture was added to ethyl acetate (200 ml), washed with water (50 ml) and dried (MgSO4). The solvent was removed at reduced pressure to afford the crude residue which was chromatographed on silica (acetone/hexane 1:3) to afford 8-amino-1,3-di(cylcopropylmethyl )-7-(isopropylsulphonyl)xanthine (1.25 g, 45%) as a yellow foam. Recrystallisation from ethyl acetate/hexane afforded a white flocculent solid, m.p. 119°-120° C.
