Deoxyribose is an aldopentose (C5H10O4) found in the backbone of DNA. It exists in two stereoisomeric forms, D and L. The isomer used in DNA is the D-form. It is derived biologically from D-ribose by reduction of the C2 hydroxyl group via a radical mechanism. It is typically found in deoxynucleotides in the pentofuranose form. In DNA, it is linked via the 3′ and 5′ hydroxyl groups to connecting phosphate groups. When attached to a nitrogenous base, it becomes part of a deoxynucleoside.