Sodium cyanoborohydride (63 mg, 1.0 mmol) was added to a mixture of 1-(6-oxohexyl)-3,7-dimethylxanthine (150 mg, 0.5 mmol), undecylamine (0.43 mL, 2.5 mmol), 38% aqueous hydrochloric acid solution (0.2 mL, 2.5 mmol), methanol (5 mL), and tetrahydrofuran (5 mL). The resulting mixture was stirred for 48 hours. Saturated aqueous ammonium chloride solution (20 mL) was added to the stirred mixture, followed by an additional 20 minutes of stirring and addition of 30% aqueous ammonium hydroxide solution (30 mL). The mixture was extracted with 25% methanol-dichloromethane (3×35 mL) and the combined extracts dried over sodium sulfate. The solvents were evaporated under vacuum, resulting in 190 mg of 1-[5-(Undecylamino)hexyl]-3,7-dimethylxanthine (86% yield).
