As INDO/S (Intermediate Neglect of Differential Overlap/Spectrum) Study of Photochemical Reactivity of 2,4,6,8(1H, 3H, 7H, 9H)-Pyrimido[5,4-g]pteridinetetrone 5-Oxide

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The specific photochemical reactivity of 2,4,6,8(1H, 3H, 7H, 9H)-pyrimido[5,4-g]pteridinetetrone 5-oxide (1), an effective photochemical oxygen-atom transfer agent, was discussed based on the results of molecular orbital (INDO/S-CI (intermediate neglect of differential overlap/spectrum-conflguration interaction)) calculations of the excited states, in comparison with several simple aromatic N-oxides, pyridine 1-oxide (2), pyrazine 1-oxide (3), acridine 10-oxide (4), and phenazine 5-oxide (5). The lowerst π-π^* excited singlet (S^<x-x^*>_1) state of 1 was most characterized by the high proportion of the ψ_<a_2>→ψ^*<b_2> transition for the CI (conflguration interaction) state and by the marked decrease of the N-O bond order, distinct from those of 2-5. The low reactivity in photorearrangement of 1 was interpreted to result from the decrease of the N-O bond order in the S^<x-x^*>_1 state. Also, the high photochemical oxygen-atom transfer reactivity of 1 was well correlated to the special features of the lowest unoccupied molecular orbital in the ground state.
社団法人日本薬学会の論文
1991-12-25