title: Isomerisation and conformation studies of (+)- and (-)6-hydroxy-5, 6-dihydrouridine.
abstract: (1) "Uridine hydrates" i.e. (+)- and (-)6-hydroxy-5, 6-dihydrouridine were formed under gamma irradiation in a deaerated aqueous solution of uridine. (2) The structures of two diastereoisomers were determined by spectroscopic measurements (infrared, ultraviolet and NMR) and verified by stereospecific synthesis; uridine hydrates were prepared by mild reduction of trans(+)- and (-)iodohydrins with acetic acid and zinc power. (3) The carbon 6 epimerisation of uridine hydrates 6R or 6S was performed in triated water (pH 5.5, 30 degrees C) and at the same time tritium incorporation on carbon 5 was noted. The mechanism of these reactions could be explained by the opening of the N1-C6 bond of the pyrimidine ring, followed by ketoenolisation reaction of carbons 4 and 5. (4) The 250 MHz NMR analysis has allowed us to determine the nucleoside conformations. Nucleosides had mainly the S(C2' endo) conformation. A slight preference of gauche-gauche (gg) rotamer of the exocyclic hydroxymethyl group was noted and the aglycone was in the anti conformation.
mesh_terms: D007553:Isotope Labeling; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D011830:Radiation Effects; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014316:Tritium; D014529:Uridine / Q000031:analogs & derivatives* / Q000528:radiation effects
chemical_list: D014316:Tritium; D014529:Uridine