Used in solid-phase oligonucleotide synthesis, this 2'-CE phosphoramidite building block enables the incorporation of a 3'-deoxy-5-methyluridine modification specifically at the 3'-terminal position in RNA strands. The 3'-deoxy feature prevents further chain elongation after incorporation, functioning as a chain terminator while introducing the modified nucleoside. The 5-methyluridine residue enhances the thermal stability of duplexes and increases resistance to nucleolytic degradation, making it valuable in the development of antisense oligonucleotides, siRNA, and diagnostic probes. The DMT (dimethoxytrityl) group provides protection at the 5′-end, facilitating attachment to the solid support and real-time monitoring of coupling efficiency during synthesis. The 2′-CE (2-cyanoethyl) group is the protecting group on the phosphoramidite phosphorus, with the reactive group positioned at the 2'-O of the 3'-deoxy nucleoside, leading to a 2'-5' internucleotide linkage upon coupling. This modified nucleoside is particularly useful in therapeutic nucleic acid applications requiring improved binding affinity, in vivo stability, and precise 3'-end modifications.