Fialuridine is a nucleoside analogue.
A nucleoside normally consists of a nitrogenous base
section bonded to a pentose sugar
Fialuridine is similar to uridine. One part of the molecule is uracil, and the other part is arabinose, which differs from ribose in the direction -OH groups in the ring are pointing.
However two atoms have been substituted with halogen atoms. There is an iodo group
at carbon 5 of the uracil, and a fluoro group
at carbon 2' of arabinose. These points - actually C3' in several other successful compounds - are targeted in other drugs used to treat HIV infection and cancer.
Fialuridine was intended as a potential therapy for hepatitis B virus infection.
It acts as a selective inhibitor of reverse transcriptase enzyme, which converts viral RNA into DNA, to be incorporated into human liver cells.
However it was found to also be incorporated into mitochondrial DNA and result in changes to mitochondrial enzymes in the liver, leading to lactic acidosis.