Ara-Nucleotides feature an opposite stereochemistry at the 2' carbon atom compared to ribo-nucleotides. They are incorporated into DNA by polymerases however, the DNA strand is only poorly elongated from the 3' ara-nucleotide residue and thus provides an opportunity for exonucleases to remove the ara-nucleotide.
Cytarabine (Cytosine arabinoside, ara-C) is a commonly used chemotherapy agent used mainly in the treatment of leukemia and non-Hodgkin lymphoma. It been shown to be misincorporated into DNA double helix, which has significant conformational consequences that affect the function of DNA.
Vidarabine (Adenosine arabinoside, ara-A) is an anti-viral drug which is active against herpes simplex and varicella zoster viruses.
Fludarabine (F-ara-A) is an antineoplastic agent which causes inhibition of DNA synthesis by inhibiting ribonucleotide reductase and DNA polymerase.
 Young et al. (1995) Applied Therapeutics. The Clinical Use of Drugs. 6th ed. Vancouver, WA., Applied Therapeutics, Inc., p. 90.