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ENA — Ethylene-Bridged Nucleic Acid for Advanced Oligonucleotide Design

Explore 2′-O,4′-C-ethylene-bridged nucleic acid chemistry for high-affinity RNA recognition, nuclease-resistant oligonucleotides and antisense research.

2′-O,4′-C Ethylene Bridge RNA Hybridization ASO / Gapmer Research Nuclease Resistance Specialty Phosphoramidites
Discuss ENA Feasibility Explore ENA Design
Overview Benefits Design Guide ENA Placement Applications Manufacturing Related Services Reding FAQ Contact
Scientific Overview

What Is Ethylene-Bridged Nucleic Acid (ENA)?

Ethylene-bridged nucleic acid (ENA) is a sugar-modified nucleic acid in which the 2′-oxygen and 4′-carbon are connected by an ethylene bridge. This 2′-O,4′-C linkage restricts sugar conformation and favors an RNA-compatible, north-type geometry.

This more rigid sugar structure can help an oligonucleotide bind complementary RNA more tightly and resist breakdown by nucleases. Both effects have been reported in ENA studies, although the degree of improvement depends on the sequence and test conditions.

ENA is closely related to locked nucleic acid (LNA), but it is not the same modification. ENA uses an ethylene bridge; conventional LNA uses a shorter methylene bridge. This difference matters when comparing RNA affinity, stability, and synthesis requirements.

For antisense research, ENA can be explored in the modified wings of a gapmer or in oligonucleotides designed to block RNA interactions. If the goal is RNase H-mediated RNA cleavage, the gapmer still needs a suitable central DNA region, and its activity must be confirmed experimentally.

Molecular Architecture
Chemical structure of 2′-O,4′-C-ethylene-bridged nucleic acid (ENA)

2′-O,4′-C-ethylene-bridged nucleic acid (ENA) structure.

Structure note: ENA modifies the sugar framework rather than the nucleobase. Confirm nucleobase identity, stereochemistry, and phosphoramidite protection for synthesis.

Why Consider ENA?

Why Researchers Explore ENA Chemistry

ENA offers several properties worth exploring when designing RNA-targeting oligonucleotides. The benefits below come from published studies, but the results can vary with sequence and experimental conditions.

Tm

RNA-Binding Affinity

By holding the sugar in a favorable conformation, ENA can strengthen binding to complementary RNA in some sequences.

Stab

Nuclease Resistance

Studies have shown that ENA modifications can help oligonucleotides withstand nuclease exposure under certain conditions.

ASO

Antisense Design

ENA can be tested in gapmer wings or in oligonucleotides that bind RNA without relying on RNase H cleavage.

R&D

Chemistry Comparison

The best way to assess ENA is to compare it with LNA, cEt, or 2′-MOE in the same sequence and application.

Evidence boundary: Published fold-change and Tm measurements are study-specific; they should not be treated as universal performance guarantees.

Practical Design Guidance

Choosing ENA for Your Oligonucleotide

Start with what the oligonucleotide needs to do. Once the target and mechanism are clear, you can decide where ENA might help and whether the required chemistry is practical to synthesize.

Modified Wings with a DNA Gap

For a gapmer intended to recruit RNase H, ENA is generally considered for the outer wings rather than as a replacement for the central DNA gap. Even small changes near the wing–gap boundary can affect activity, so it is useful to compare several placements.

Important: ENA substitution alone does not guarantee RNase H recruitment or target knockdown.

Chemistry Sugar modification Research use Consideration
ENA 2′-O,4′-C ethylene bridge Affinity and nuclease-stability optimization Reagent availability; sequence-specific results
LNA 2′-O,4′-C methylene bridge High-affinity ASO wings and probes Strong binding is not a safety guarantee
cEt Constrained ethyl bridge ASO wing optimization Access, IP and design-specific performance
2′-MOE Unbridged 2′-O-methoxyethyl Established ASO comparator Different binding and stability profile

Check the Monomer Before Quoting

Before quoting a project, we would first confirm which ENA amidites are available and whether their protecting groups and deprotection conditions fit the proposed sequence. We would also review purification, mass confirmation, and the amount of purified material required.

ENA Incorporation Strategy

How ENA Can Be Positioned in a Gapmer

A typical gapmer has modified nucleotides at both ends and a DNA region in the middle. Researchers can test ENA at selected wing positions while keeping the DNA gap needed for the intended RNase H mechanism.

Conceptual ENA–DNA–ENA arrangement Illustrative regions, not a validated sequence or recommended nucleotide count
5′ → 3′ ASO
Modified wing (possible ENA) DNA gap
5′ Wing

Screen ENA positions

DNA Gap

RNase H-compatible design

3′ Wing

Screen ENA positions

01 Define the mechanism

Determine whether RNA cleavage or steric blocking is the intended outcome.

02 Screen wing placement

Compare ENA positions against a same-sequence unmodified or established-chemistry control.

03 Retain the DNA gap

For RNase H gapmers, preserve an appropriate central DNA region.

04 Measure outcomes

Evaluate Tm, stability, RNA cleavage, target activity, purity and MS identity.

Design note: The schematic is educational only. Dot counts are not a recommended gapmer length. ENA wing placement and activity require sequence-specific validation.

Research Applications

Potential Applications for ENA-Modified Oligonucleotides

ENA is worth considering when stronger RNA binding or greater nuclease resistance could benefit a project. Its value should be tested against other available modifications.

ASO

Antisense Research

Study how ENA affects binding to a selected RNA target in an antisense sequence.

Explore ASO Services →
Gap

Gapmer ASOs

Compare ENA-modified wings while preserving the central DNA gap.

Explore Gapmer Synthesis →
SSO

Steric-Blocking Oligos

Explore ENA in oligonucleotides intended to block RNA interactions rather than cleave RNA.

Explore Splice Switching →
Dev

Candidate Optimization

Compare ENA with other sugar modifications to identify a useful balance of binding, stability, and activity.

Explore Development Support →
Synthesis & Analytics

From an ENA Design to a Purified Oligonucleotide

Before starting synthesis, we review the ENA modifications, available phosphoramidites, and purification requirements. This helps establish a realistic synthesis plan and final-yield target.

01

Review Sequence

Identify ENA positions, backbone and target application.

02

Confirm Reagents

Check ENA amidite availability, base identity and lead time.

03

Plan Synthesis

Review coupling and deprotection compatibility.

04

Purify & Confirm

Use fit-for-purpose HPLC and mass analysis.

05

Release & Evaluate

Agree on yield, purity and any functional testing.

Bio-Synthesis: Our team can evaluate ENA-containing custom oligonucleotide projects. Availability, price and timeline depend on monomer sourcing, technical feasibility and applicable permissions.

ENA Chemistry FAQ

FAQ

What is ENA?
ENA is 2′-O,4′-C-ethylene-bridged nucleic acid, a conformationally constrained sugar-modified nucleotide.
How is ENA different from LNA?
ENA contains a 2′-O,4′-C ethylene bridge; conventional LNA has a shorter methylene bridge. Their affinity and stability depend on experimental context.
Can ENA be used in gapmer ASOs?
ENA may be evaluated in modified wings surrounding an RNase H-compatible DNA gap; RNase H activity must be tested.
Does ENA improve nuclease resistance?
Published studies reported increased resistance under particular assay conditions, but results depend on sequence and formulation.
Does ENA itself recruit RNase H?
An ENA-modified duplex should not automatically be assumed to recruit RNase H; gapmer designs retain a suitable DNA gap.
Can Bio-Synthesis manufacture ENA oligonucleotides?
Bio-Synthesis can review sequences, monomer availability, permitted use, synthesis and QC requirements before confirming feasibility.
More FAQsAll FAQs
Scientific Collaboration

Discuss Your Next ENA or Advanced ASO Project

Tell us about your sequence, target application, and desired final amount. We can review the ENA positions, reagent availability, synthesis approach, and analytical requirements.

CUSTOM OLIGONUCLEOTIDE DEVELOPMENT

Turn an ENA design into a practical synthesis plan.

Whether you are comparing ENA with LNA or cEt, developing a gapmer, or exploring a steric-blocking oligonucleotide, our team can discuss the chemistry and the next steps for feasibility.
Request a Quote → Discuss with a Scientist ↗

Contact Bio-Synthesis

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Phone: 800-227-0627 (US/CAN)
Phone: +001-972-420-8505 (INT)
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01

Design Consultation

Sequence, ENA positions, RNA target, RNase H compatibility and comparator chemistry.

Gapmer ASO Splice switching
02

Feasibility & QC Review

ENA monomer sourcing, synthesis conditions, purification and analytical identity.

HPLC LC-MS Custom scale

ENA-modified oligonucleotide projects are subject to reagent availability, technical feasibility and applicable intellectual-property requirements. Synthesis availability is confirmed only after review.

Technology & Supply

ENA Technology, Reagent Availability, and Supply

ENA chemistry was reported in early work by Morita, Koizumi, and colleagues. Their studies described ENA nucleosides and oligonucleotides and helped establish a foundation for later antisense research.

For a custom ENA project, the next question is practical: can the required monomers be sourced, and are there any restrictions on their intended use? Published methods do not by themselves establish unrestricted commercial rights.

Bio-Synthesis can review your sequence and requirements, but ENA monomer availability and manufacturing feasibility must be confirmed before we provide a firm quotation.

Scientific Publications

Selected Peer-Reviewed ENA References

The publications below provide background on ENA synthesis, RNA binding, and nuclease resistance. They describe specific experiments rather than guaranteed performance for every sequence.

Literature comparisons do not establish universal superiority over LNA, cEt or 2′-MOE, or guarantee clinical efficacy.

Why Choose Bio-Synthesis

Trusted by biotech leaders worldwide for over 45 years of delivering high-quality, fast, and scalable synthetic biology solutions.

Greetings, Researchers,

Please be advised that any information, guidelines, write-ups, and oral/video/graphic content on our website are intended solely as general guidelines.

It is the researcher's sole responsibility to conduct thorough research on the design of products intended for their experiments before submitting
their designs to Biosynthesis for production feasibility review.

Thank you for your understanding.

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