- Photosensitized Oxidation of Oxopurines by Rose Bengal
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Photosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7-trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive 1O2 quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, ET[30], AN, DN, π*, ∈), the initial formation of an exciplex between 1O2 and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3-methyl-5-(methylamine)-1,5-dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.
- Murgida, Daniel H.,Aramendia, Pedro F.,Erra Balsells, Rosa
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p. 467 - 473
(2007/10/03)
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- Purines. XIV [1]. Synthesis and properties of 8-nitroxanthine and its N- methyl derivatives
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Xanthine (1) and its N-methyl derivatives 2-16 have been nitrated to the corresponding 8-nitro derivatives 17-32 under different reaction conditions. Nitration in glacial acetic acid with nitric acid works well with the N-7 unsubstituted and some of the 9-methylxanthines, respectively, whereas the 7- methylxanthine derivatives react best with nitronium tetrafluoroborate in sulfolane or glacial acetic acid. The 8-nitro group can be displaced nucleophilically to form 8-chloro-, 33, 34, 8-ethoxy-, 35, 36, and uric acid derivatives 37-40, respectively. The newly synthesized 8-nitroxanthines have been characterized by elemental analyses, pK-determinations and uv and 1H- nmr spectra.
- Mosselhi,Pfleiderer
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p. 1221 - 1228
(2007/10/02)
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