Torcitabine (b-L-2u-deoxycytidine) (L-dC) is the b-L-enantiomer of the natural nucleoside D-cytidine. The drug is currently under development by Idenix as an antiviral agent for the treatment of chronic hepatitis B virus infection. Torcitabine has poor oral bioavailability, but its 3u,5u-divaline ester (val-L-dC) and the 3u-monovaline ester, valtorcitabine dihydrochloride, have excellent oral bioavailability and consequently the torcitabine prodrug, valtorcitabine, has replaced torcitabine in clinical development.
