A mixture of N-Boc-L-valine (528 mg; 2.1 mmol) and N,N′-dicyclohexyl carbodiimide (250 mg; 1.21 mg) in dichloromethane (20 ml) was stirred over night at room temperature, dicyclohexylurea filtered off and extracted with a small volume of dichloromethane, and the filtrate evaporated in vacuo to a small volume. (R)-9-[2-Hydroxymethyl-4-(stearoyloxy)butyl]guanine (340 mg; 0.654 mmol), 4-dimethylaminopyridine (25 mg; 0.205 mmol), and dry N,N-dimethylformamide (15 ml) were added and the mixture was stirred for 4 h at 50° C. under N2. The solvent was evaporated in vacuo to a small volume. Column chromatography on silica gel, then on aluminum oxide (ethyl acetate:methanol: water 15:2:1 as eluent) gave 185 mg (39%) pure title compound as a white solid.
