Phosphoramidites

What are Phosphoramidites?
Phosphoramidites are specialized chemical compounds that serve as the essential building blocks in automated solid-phase oligonucleotide synthesis. These molecules consist of a nucleoside (adenosine, guanosine, cytidine, thymidine, or uridine, often with protective groups and sugar modifications) attached to a reactive phosphoramidite group, typically with a dialkylamine moiety (e.g., diisopropylamine) that acts as the leaving group during coupling reactions.

Synthesis and Key Characteristics
Our phosphoramidites are manufactured through a meticulous multi-step process:

• Nucleoside Preparation: Starting nucleosides are carefully protected at exocyclic amines (with groups like acetyl, benzoyl, or isobutyryl) and at the 5'-hydroxyl position (typically with DMTr or MMTr groups) to prevent undesired reactions during synthesis.
• Phosphitylation: The protected nucleoside reacts with a phosphitylating reagent (e.g., 2-cyanoethyl N,N-diisopropylchlorophosphoramidite) under controlled anhydrous conditions to form the phosphoramidite.
• Purification and Stabilization: The crude product undergoes rigorous purification through chromatography and/or crystallization. Stabilizers may be added to enhance shelf life.
• Quality Control: Each batch undergoes comprehensive analysis including HPLC for purity assessment, ³¹P NMR to confirm phosphoramidite structure and purity, and moisture analysis to ensure stability.

Application in Oligonucleotide Synthesis
Phosphoramidites are designed for use in automated synthesizers following a four-step cycle:

• Detritylation: Acidic removal of the 5'-protecting group (DMTr)
• Coupling: Activation with weak acid (e.g., tetrazole) enables nucleophilic attack by the free 5'-OH of the growing chain, forming a phosphite triester linkage
• Capping: Acetylation of unreacted chains prevents deletion sequences
• Oxidation: Conversion of the phosphite triester to a more stable phosphate triester