Abstract
The metabolism and hypnotic mechanism of N3-phenacyluridine were studied in mouse. Of the radioactivity, 65% was excreted in urine within 48 hours after i.p. administration of [3H]N3-phenacyluridine. The urinary metabolites N3-phenacyluracil and N3-α-hydroxy-β-phenethyluridine were excreted, isolated and analyzed by mass spectrometry. Racemates of N3-α-hydroxy-β-phenethyluridine were synthesized and both isomers were separated as N3-(S)-(+)- and N3-(R)-(-)-α-hydroxy-β-phenethyluridine by HPLC (CHIRALCEL-OJ column). The reduction process took place with high stereo-selectivity, which gave an alcohol product in the urine with same retention as one of the synthetic isomers separated by HPLC. N3-Phenacyluracil and uridine were identified as minor metabolites. N3-(S)-(+)-α-hydroxy-β-phenethyluridine, but not N3-(R)-(-)-α-hydroxy-β-phenethyluridine, possessed hypnotic activity in mice and potentiated pentobarbital-induced sleep with a similar potency to the parent compound, N3-phenacyluridine. An active metabolite, N3-(S)-(+)-α-hydroxy-β-phenethyluridine, inhibited [3H]N3-phenacyluridine binding to synaptic membrane of bovine thalamus showing 10.2 nM of Ki value, while N3-phenacyluridine, N3-(R)-(-)-α-hydroxy-β-phenethyluridine and racemate had 0.65, 397.4 and 1908 nM of Ki values, respectively. The present study indicates that N3-(S)-(+)-α-hydroxy-β-phenethyluridinea, major metabolite of N3-phenacyluridine, is an active metabolite and bound a novel uridine receptor involving the hypnotic activity.
