Arabinosylcytosine (Ara-C) is a synthetic nucleoside analog, specifically a cytarabine derivative where the sugar moiety is arabinose instead of ribose. Its chemical name is 2'-deoxy-1-β-D-arabinofuranosylcytosine, and it is a key intermediate in the synthesis of the important anticancer drug Cytarabine (Ara-C). The structural modification at the 2'-position of the sugar ring (arabino configuration) is crucial for its biological activity. The primary and most significant application of this compound and its derivatives is in oncology. Cytarabine, synthesized from this intermediate, is a cornerstone chemotherapeutic agent used primarily in the treatment of acute myeloid leukemia (AML) and other hematologic malignancies. It functions as an antimetabolite by being incorporated into DNA during the S phase of cell division, where it inhibits DNA polymerase, ultimately leading to DNA chain termination and apoptosis of rapidly dividing cancer cells. As a specialized nucleoside building block, it is not a general-purpose synthetic reagent but a high-value pharmaceutical intermediate. Its production and handling require controlled conditions due to its biological activity and application in the manufacture of a critical API. Research continues into its derivatives and prodrugs to improve efficacy and reduce side effects.