Example 1 Synthesis of 8-chloroadenine
(1) To a solution of DMA/HCl (0.5 M, 45 mL) of adenosine (2.67 g, 10 mmol) was added m-chloroperoxybenzoic acid (MCPBA, 3.22 g, 16 mmol, 87%) at room temperature and the reaction was carried out for 2.5 hours. Subsequently, MCPBA (0.9 g, 5 mmol) was added additionally and stirring was continued for 1 hour. Upon completion of the reaction, toluene (50 mL) was added and evaporated to dryness at 60 °C under vacuum. The residue was dissolved in water (50 mL) and extracted with ether (3 x 50 mL). The aqueous phase was adjusted to pH 5 with 2N NaOH and diluted with EtOH (100 mL). The solution was placed in a refrigerator overnight. The precipitated yellowish solid was collected by filtration, washed with cold EtOH (2 x 25 mL) and dried to give a product of 1.44 g (85.2% yield). The product was characterized as follows: melting point 305-310 °C (decomposition); IR (KBr) showed 630 cm1 (C-Cl) and 3100-3300 cm1 (NH) absorption peaks; UV spectra at pH 1 with λmax=262 nm (ε=8700), pH 7 with λmax=268 nm (ε=7900), and pH 11 with λmax= 269 nm (ε=8300); 1H NMR (MeSO-d) chemical shift δ 7.48 (broad peak, 2H, NH), 8.10 (single peak, 1H, C-H), 13.60 (broad peak, 1H, N-H).
