A solution of 2-chloro-N-(2,2-diphenylethyl)-9-(tetrahydro-2H-pyran-2-yl)-9H-purin-6-amine (Preparation 2) (49.7 g, 0.11 mol) in dry N,N-dimethylformamide (200 ml) was treated with sodium thiomethoxide (10 g, 0.14 mol) and the resulting mixture heated under an atmosphere of nitrogen at 100° C. for 90 minutes. The mixture was stirred at room temperature for 72 hours and then reheated at 100° C. for a further 2 hours. The reaction mixture was cooled and diluted with water (1000 ml). A suspension was formed which was extracted with diethyl ether (×2). The combined organic layers were washed sequentially with water and brine, dried over anhydrous magnesium sulphate, filtered and the solvent removed under reduced pressure. The residue was azeotroped with diethyl ether followed by pentane to afford the title compound as a foam (48.9 g).
