The reactions of OH radicals with D-ribose in deoxygenated and oxygenated aqueous solution

Aqueous solution ofD-ribose (10^?2M) saturated with N₂O and N₂O/O₂ (4/1) were γ-irradiated (dose rate: 3.85 x 10¹⁸ eV.g^?1.h^?1) at room temperature. The following products were identified:D-ribonic acid (1). D-erythro-pentos-2-ulose (2). D-erythro-pentos-4-ulose (3),D-erythro-pentos-3-ulose (4), D-ribo-pentodialdose (5), 2-deoxy-D-erythro-pentonic acid (6), 2-deoxypentos-3-ulose (7)(7), 4-deoxylpentos-3-ulose (8), 3-deoxypentos-4-ulose (9), 3-deoxypentos-2-ulose (10), 5-deoxypentos-4-ulose (11), erythrose (12), erythro-tetrodialdose (13), erythronic acid (14), threose/erythrulose (15). threonic acid (16), 2-deoxytetrose (17), and glyceraldehyde (18). In deoxygenated solutions, 13, 14, and 16 were absent. In the presence of oxygen, the formation of 6–11 and 17 was suppressed. From quantitative measurements, G-values were calculated for both deoxygenated and oxygenated conditions. Five different, primary, ribosyl radicals are formed which, in deoxygenated solution, undergo disproportionation reactions (to give 1-5), and transformations such as elimination of water and carbon monoxide followed by disproportionation reactions (to give6-12.17). Material-balance considerations indicate the formation of dimers (not measured). In oxygenated solutions, oxygen rapidly adds to the primary ribosyl radicals, thus preventing the transformation reactions, and the main products are 1–5 and 13. Possible mechanistic routes are discussed. The attack of HO radicals on D-ribose involves C-1, ～20%; C-2 and C-4, ～35%: C-3, ～ 20%; and C-5, ～25%