Metabolism of anti-herpes agent 5-(2-chloroethyl)-2'-deoxyuridine in mice and rats

Bioavailability and pharmacokinetic parameters for 5-ethyl-2'-deoxyuridine

Pharmacokinetic parameters for 5-ethyl-2'-deoxyuridine (EDU) were determined following intravenous (iv) and oral (po) dosing in male Balb-C mice and iv dosing in male Sprague-Dawley rats. The concentrations of EDU in blood after 100 mg/kg iv bolus injections into mice and rats were consistent with a two compartment kinetic model. Based on this kinetic model, EDU showed a very short distribution half-life of 1.4 +/- 0.7 min in mice and 1.3 +/- 0.1 min in rats. The elimination half-life of EDU in rats following iv bolus injection, was substantially (18.5 +/- 1.0 min) shorter than that in mice (24.1 +/- 2.9 min). The mean residence time (MRT) of EDU was also substantially longer in mice (25.8 +/- 4.9 min) compared to rats (11.0 +/- 2.9 min). However, clearance of EDU was similar in both rats and mice. Although the biotransformation of EDU was similar in mice and rats, cleavage of the EDU glycoside bond was less extensive in mice than in rats. EDU showed a 49% bioavailability in mice after a 100 mg/kg po dose. The concentration of EDU in blood after a po dose provided the best fit to a one compartment model. The maximum blood concentration of EDU (Cmax) was 2.4 +/- 0.2 micrograms/g of blood which attained 31.1 +/- 1.2 min (Tmax) after a 100 mg/kg po dose. The AUC of 5-ethyluracil (EU) after a po dose of EDU was significantly higher (P < 0.05) than after an iv dose of EDU. This observation indicates that EDU undergoes degradation by phosphorylases present in the gastrointestinal tract and/or by presystemic metabolism.

Synthesis, biotransformation, pharmacokinetics, and antiviral properties of 5-ethyl-5-halo-6-methoxy-5,6-dihydro-2'-deoxyuridine diastereomers

Diastereomers of 5-ethyl-5-halo-6-methoxy-5,6-dihydro-2'-deoxyuridine were synthesized by the regiospecific addition of XOMe (X = Br, Cl) to the 5,6-olefinic bond of 5-ethyl-2'-deoxyuridine (EDU). 5-(1-Hydroxyethyl)-2'-deoxyuridine (HEDU) was identified as a metabolite of the 5-bromo-5-ethyl-6-methoxy-5,6-dihydro-2'-deoxyuridine diastereomers (BMEDU). The concentration of EDU and 5-ethyluracil (EU) in blood was higher after i.v. administration of the bromo diastereomers (BMEDU) to rats, relative to the concentration of EDU and EU after injection of the chloro (CMEDU) diastereomers. The CMEDU diastereomers were found to be oxidized less extensively to HEDU, were more stable to glycosidic bond cleavage, and were converted more slowly to EDU, than the BMEDU compounds. These BMEDU and CMEDU diastereomers exhibited pharmacokinetics characterized by a biphasic decline in plasma concentration. All diastereomers exhibited a characteristic second maximum blood concentration (Cmax), which was attributed to reabsorption after biliary excretion. All of these 5-ethyl-5-halo-6-methoxy-5,6-dihydro compounds, with the exception of (5S,6S)-BMEDU, had higher AUC values (ranging from 0.32 to 1.20 microM.hr.mL-1) and lower plasma clearances (10-36 mL.min-1) relative to the AUC values (0.14 microM.hr.mL-1) and plasma clearance (85 mL.min-1) of EDU. These BMEDU and CMEDU diastereomers are more lipophilic (log P = -0.42 to 0.40 range) than EDU (log P = -1.09), which should enhance their ability to cross the blood-brain barrier. These 5,6-dihydro compounds showed higher levels (11-22%) of binding to bovine serum albumin than EDU (7%). The BMEDU compounds exhibited equipotent in vitro antiviral activity to EDU against HSV-1 and HSV-2, whereas the CMEDU analogs were inactive. The (5S,6R)-CMEDU diastereomer was equipotent to ganciclovir in the human cytomegalovirus assay.