What Are 2'-O-Me Phosphoramidites?
2'-O-methyl (2'-OMe) phosphoramidites are nucleotide monomers in which a methyl group (-CH₃) is attached to the 2'-hydroxyl of the ribose sugar. They represent one of the most classic and widely adopted first-generation sugar modifications in RNA chemistry. The 2'-O-methyl modification occurs naturally in various RNA species – including ribosomal RNA (rRNA), transfer RNA (tRNA), small nucleolar RNA (snRNA), and messenger RNA (mRNA) – and plays a critical role in cellular RNA function regulation, with dysregulation linked to various diseases. In artificial oligonucleotide synthesis, this methyl modification is systematically introduced to significantly enhance nuclease resistance and thermal stability.
The chemical essence of 2'-OMe modification lies in its conformational impact: the introduction of the methoxy group stabilizes the ribose ring in the C3'-endo (A-form helix) conformation, which is highly compatible with the geometry of natural RNA duplexes. Consequently, 2'-OMe-modified oligonucleotides exhibit higher binding affinity to complementary RNA targets. Simultaneously, the methoxy group alters hydrogen-bonding properties at the 2' position and suppresses its nucleophilicity, conferring enhanced resistance against nucleases. Notably, 2'-OMe-modified oligonucleotides do not activate RNase H, making them suitable for steric-blocking antisense mechanisms or as wing modifications in gapmer designs.
A standard 2'-O-Me phosphoramidite monomer comprises the following structural features:
Sugar Backbone – 2'-O-methylribose, where the natural 2'-hydroxyl of ribose is replaced by a methoxy group (-OCH₃). This methoxy group is chemically stable under all standard oligonucleotide synthesis conditions and is not affected by conventional alkaline deprotection.
Nucleobase & Protecting Groups:
Natural bases include A, G, C, U (RNA format) or T (DNA format), with modified bases such as 5-methyl-dC and pseudouridine also available upon request.
Exocyclic amines on the bases are acyl-protected, with common combinations including benzoyl (Bz) for A, isobutyryl (iBu) or dmf (fast-deprotecting) for G, and acetyl (Ac) for C.
For mild deprotection applications, Hongene offers UltraMild versions employing more labile protecting groups (e.g., phenoxyacetyl (Pac) for A and isopropyl-phenoxyacetyl (iPr-Pac) for G), compatible with base-sensitive fluorescent dye labeling.
5'-O-DMT and 3'-CE Phosphoramidite Groups – The 5'-DMT reversibly blocks the 5'-hydroxyl to ensure single-monomer addition per cycle. The 3'-cyanoethyl (CE) phosphoramidite group, upon activation (e.g., by tetrazole), couples to the free 5'-OH of the growing chain, and the resulting phosphite triester is oxidized to a stable phosphate diester with iodine/water.
In automated solid-phase synthesis, 2'-O-Me phosphoramidites follow the standard four-step cycle – deblocking, coupling (recommended 6 minutes), capping, and oxidation – with parameters similar to DNA synthesis. Because the 2'-OMe group remains intact under ammonia deprotection conditions and the resulting products are nuclease-resistant, deprotection, isolation and handling procedures are identical to those for oligodeoxynucleotides, requiring no special RNase-free precautions.
Hongene's Core Advantages for 2'-O-Me Phosphoramidites
Comprehensive Portfolio Covering Multiple Base Protections and Modification Variants
Hongene offers a complete series of 2'-O-Me phosphoramidite monomers covering the four main bases with various protecting group options, along with variants for mild deprotection (UltraMild), fast deprotection, and phosphorothioate backbones. Additional monomers (including 5-methyl-dC, pseudouridine, UltraMild fast-deprotection versions, and phosphorothioate variants) are available upon request or for custom development.
Ultra-High Purity & Rigorous Quality Control
All products are QC-tested by HPLC/UPLC with ≥98.0% purity as the standard. Each monomer is accompanied by a full Certificate of Analysis (CoA) covering HPLC purity, moisture content, mass spectrometry, and impurity profiles. An in-house impurity reference library enables precise tracking of degradation and process-related impurities.
GMP Compliance & Industry-Leading Large-Scale Manufacturing Capacity
Hongene operates world-leading manufacturing capacity for nucleic acid raw materials: 58 tons/year of phosphoramidites and 54,000 liters/year of NTPs, with an approximately 301,000 sq. ft. (~28,000 m²) GMP-compliant production facility. Additionally, 48 flexible production lines enable seamless scale-up of API production from gram to ton scale, meeting NMPA, FDA and EMA standards. The company has been audited by multiple global pharmaceutical companies and, as one of the world's largest suppliers of mRNA vaccine raw materials during the COVID-19 pandemic, has fully validated its reliable large-scale delivery capability.
Continuous Innovation & Diversified Service Capabilities
With nearly 30 years of deep expertise in nucleic acid chemistry, Hongene continues to expand the modification toolbox for 2'-O-Me and related monomers through proprietary core technologies such as its exNA™. The company offers one-stop procurement and custom synthesis services ranging from standard and fast-deprotecting to UltraMild and phosphorothioate variants, as well as functionalized labeling monomers (fluorescent dyes, quenchers, biotin, GalNAc, etc.).
Main Applications of 2'-O-Me Phosphoramidites
Antisense Oligonucleotides (ASOs)
2'-O-Me modification is one of the most frequently used chemistries in ASO design. In fully 2'-OMe-modified ASOs, the oligonucleotide inhibits gene expression by sterically blocking mRNA translation without activating RNase H. Additionally, 2'-OMe modifications are commonly used as wing regions in gapmer architectures, enhancing overall nuclease resistance and serum stability while preserving RNase H activation and target affinity in the central DNA gap. These strategies have been widely applied in research for neuromuscular diseases, cancer and viral infections.
Small Interfering RNA (siRNA)
2'-OMe modifications confer enhanced thermal stability, serum stability and favorable RISC loading properties to siRNA duplexes. 2'-OMe modification at the termini of the sense strand can modulate Dicer processing and RISC loading, while introducing a single 2'-OMe at the second nucleotide of the antisense strand has been shown to significantly reduce off-target silencing. Moreover, 2'-OMe modification reduces the immunostimulatory potential of siRNA, a key advantage in developing siRNA as an in vivo therapeutic molecule.
RNA Aptamers & Ribozymes
Introduction of 2'-OMe modifications significantly extends the serum half-life of aptamers and enhances their binding affinity to protein targets. 2'-OMe-modified aptamers are widely used for protein recognition, biosensor construction, cancer biomarker detection, and targeted drug delivery. Furthermore, 2'-OMe modifications can stabilize ribozyme structures, preserving their activity in complex biological environments.
Diagnostic Probes & Detection Tools
2'-O-Me modification is a key enabling technology for highly sensitive and robust molecular probes. Studies have shown that 2'-OMe molecular beacons exhibit superior duplex stability and faster hybridization kinetics with RNA targets compared to their DNA counterparts, while being fully resistant to endogenous nucleases. This significantly improves the signal-to-background ratio and accuracy in cellular imaging and gene expression quantification. 2'-OMe-modified probes are also widely utilized in qPCR, FISH, and Northern blot assays.
Epitranscriptomics & RNA Modification Research
2'-O-methylation is one of the most abundant and widely distributed post-transcriptional modifications in naturally occurring RNAs. Using 2'-OMe phosphoramidite monomers to synthesize RNA analogues bearing site-specific 2'-OMe modifications enables researchers to investigate the functional roles of these natural modifications in RNA stability, conformational folding, translational regulation and RNA-protein interactions.
CRISPR Genome Editing & Synthetic Biology
2'-O-Me modifications can be incorporated into CRISPR gRNAs to improve their cellular stability and editing efficiency, particularly in applications requiring prolonged nuclear residence. Additionally, 2'-OMe-modified oligonucleotides are used in the construction of genetic circuits, development of riboswitches, and design of artificial RNA nanostructures in cutting-edge synthetic biology research.
