Characterization of 5-hydroxy-8-oxo-7,8-dihydroguanosine in the photosensitized oxidation of 8-oxo-7,8-dihydroguanosine and its rearrangement to spiroiminodihydantoin

The photosensitized oxidation of 2',3',5'-tris-(O-tert-butyldimethylsilyl)-8-oxo-7,8-dihydroguanosine (8-oxoG) with singlet oxygen was studied by low-temperature NMR. A stable intermediate was characterized at -60 degrees C by (13)C, 2D NMR HMBC spectra, and chemical shifts calculated by hybrid Hartree-Fock density functional theory which agreed with the structure 5-hydroperoxy-8-oxo-7,8-dihydroguanosine. Reduction of this intermediate at low temperature afforded the corresponding alcohol, the long-postulated 5-hydroxy-8-oxo-7,8-dihydroguanosine, the last intermediate in the formation of spiroiminodihydantoin. Upon warming to room temperature, this alcohol rearranges to form the spiroiminodihydantoin in good yield within 2 h.     

The pH-dependent role of superoxide in riboflavin-catalyzed photooxidation of 8-oxo-7,8-dihydroguanosine

[reaction: see text]. The riboflavin-catalyzed photooxidation of 2',3',5'-tri-O-acetyl-8-oxo-7,8-dihydroguanosine generates a radical intermediate that is competitively trapped by H(2)O, O2(-)(*), or O(2). The products of H(2)O trapping have been previously described as the spiroiminodihydantoin (pH >or= 7) and iminoallantoin/guanidinohydantoin (pH < 7) nucleosides. Trapping by O2(-)(*) leads to the oxaluric acid (pH or= 8.6) pathways (R' ', R' ' = H or 2,3,5-tri-O-Ac-ribofuranosyl). The pH-dependent role of superoxide was probed using Mn-SOD and compared to guanosine and 8-methoxyguanosine photooxidation.     

Characterization of spiroiminodihydantoin as a product of one-electron oxidation of 8-Oxo-7,8-dihydroguanosine

[reaction: see text] Further oxidation of the common DNA lesion 8-oxo-7,8-dihydroguanosine by one-electron oxidants such as IrCl6(2-), Fe(CN)6(3-), or SO4-* leads to two major products, depending upon reaction conditions. In nucleosides at pH 7, 22 degrees C, the principal product is shown herein to be a spiroiminodihydantoin nucleoside, as a diastereomeric mixture, that can be characterized by NMR, ESI-MS/MS, and independent synthesis.     

Synthese und Strukturaufklärung von 7-Alkylamino-7-phenyl-8-thioxo-1,2,3,4,5,6-hexathiocanen

Zusammenfassung Durch die gemeinsame Einwirkung von elementarem Schwefel und primären Aminen (Methyl-, Äthyl-, n-Propyl-, Isopropyl-und n-Butylamin) auf Acetophenon bei Raumtemp. entstehen die bisher unbekannten 7-Alkylamino-7-phenyl-8-thioxo-1,2,3, 4,5,6-hexathiocane. Die Struktur dieser neuen Verbindungsklasse wird durch Abbaureaktionen undNMR-Untersuchungen bewiesen.Dieselben Verbindungen erhält man in besseren Ausbeuten bei der Reaktion der entsprechenden Acetophenonimine mit Schwefel in Gegenwart freien Amins. Einige bisher unbekannte Acetophenonimine wurden synthetisiert.7-Alkylamino-7-phenyl-8-thioxo-1.2.3.4.5.6-hexathiocanes —so far unknown compounds — are formed by the reaction of excess elementary sulfur and primary amines (methyl-, ethyl-, n-propyl-, i-propyl- and n-butylamine) with acetophenone at room temperature. The structure of this new class of compounds is proved by degradation reactions andNMR-spectrum.The same compounds can be produced in better yields by the reaction of the corresponding acetophenone imines with sulfur in the presence of free amines. Some formerly unknown acetophenone-imines were synthesized.Mit 1 Abbildung52. Mitt.:F. Asinger, A. Saus, H. Offermanns undH. D. Hahn, Ann. Chem., im Druck.Teil der Dissertation vonH. W. Becker, Techn. Hochschule Aachen, 1965.     

5- and 7-substituted 2-methyl-8-quinolinols

The synthesis and characterization of the 5- and 7-monosubstituted 2-methyl-8-quinolinols where the substituents are fluorine, chlorine, bromine, iodine, nitro, amino, and sulfonic acid groups were carried out. The bischelates with copper(II) of those ligands containing hydrogen, fluorine, chlorine, bromine, iodine, and nitro are also reported.