STRUCTURE OF THE PHOTOHYDRATION PRODUCTS OF CYTIDINE AND URIDINE

Abstract

reaction vessels and were arranged at a distance of 5 cm from the burner. The entire photochemical apparatus was immersed in a bath which was kept at 10?. The reaction solution was freed from oxygen and thoroughly mixed during the irradiation with a constant stream of nitrogen. Ultraviolet absorption spectra were measured on a Cary model 15 spectrometer; nuclear magnetic resonance spectra on a Varian A60A spectrometer in D20 with sodium3-(trimethylsilyl)-l-propane-sulfonate (in D20) as an external standard; infrared spectra (KBr) on a Perkin-Elmer Infracord. Solvent systems used for thin-layer chromatography were: n-butanol-water, 86:14 (system A); and n-propanol-conc. ammonia, 8:1 (system B). The mobility of the compounds is given relative to D-ribose (Rr). (1) Reduction of the major photoproduct of cytidine (I) to N1-(a,3-D-ribopyranosyl)-N3('y-hydroxypropyl)urea (III): A solution of cytidine (400 mg, 1.6 mmole) in 400 ml of water was irradiated under the conditions described above until the absorption at 270 mg had virtually disappeared. Sodium borohydride (4 gm, 108 mmoles) was then added and the reaction allowed to proceed for 18 hr. The reaction mixture was treated with Dowex 50W-X8(H+) to destroy excess sodium borohydride and the pH was adjusted to 5. The acidified solution and the resin were placed on a column (Dowex 50W-X8(H+), 2 X 15 cm) to ensure complete removal of sodium and unreacted cytidine. The products were eluted with about 500 ml of water. Unreacted cytidine (220 mg) was recovered by elution with 300 ml of 2 N ammonia. The aqueous eluate was evaporated to dryness in vacuo. Boric acid was removed as methylborate by repeated evaporation with methanol. The