3deoxyribonucleoside

3'-deoxyribonucleoside, also written as 3'-deoxynucleoside, is a nucleoside in which the sugar component is 3'-deoxyribose, meaning the hydroxyl group at the 3' carbon is absent. In a deoxyribonucleoside, a purine or pyrimidine base is attached to the C1' of this sugar through an N-glycosidic bond, while the 2' position is deoxygenated relative to ribose.

Because the 3' position lacks a hydroxyl group, 3'-deoxynucleosides cannot participate in the usual 3'-5' phosphodiester linkage required for chain elongation in DNA synthesis. When the corresponding 3'-deoxynucleoside is phosphorylated to the triphosphate form, it becomes a chain-terminating analog used by DNA polymerases. In this context they are often discussed in relation to 2',3'-dideoxynucleosides (ddN nucleosides), whose sugar lacks both 2' and 3' hydroxyls relative to ribose; for deoxyribonucleosides, the 2' position is already deoxygenated, so these analogs effectively terminate DNA synthesis after a single incorporation.

Natural occurrence of 3'-deoxynucleosides is limited; most examples are synthetic derivatives prepared for research and therapeutic purposes. Commonly referenced examples include 3'-deoxyadenosine, 3'-deoxyguanosine, 3'-deoxythymidine, and 3'-deoxycytidine, as well as their phosphate forms used in laboratory techniques.

Applications include their use as chain-terminating agents in sequencing methods and as tools in molecular biology to study DNA synthesis and polymerase behavior.