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XNA Backbone Analogs for Synthetic Genetic Polymers

Alternative nucleic acid scaffolds for enhanced nuclease resistance, synthetic genetics, molecular evolution, aptamer discovery, therapeutic research, and next-generation molecular engineering.

GNA TNA HNA CeNA FANA tcDNA aTNA SNA
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Overview Platform Fit Design Objective XNA Explorer Comparison Applications Combinations Related Platforms FAQ Contact
Beyond DNA and RNA

Alternative Backbones for New Genetic Polymers

Xeno nucleic acids, or XNAs, are synthetic genetic polymers in which the natural ribose or deoxyribose scaffold is replaced with an alternative chemical framework while sequence-specific base pairing is retained. Changing the backbone can alter duplex geometry, chemical stability, nuclease resistance, recognition behavior and compatibility with engineered polymerases.

Bio-Synthesis supports a growing portfolio of XNA backbone analogs including GNA, TNA, HNA, CeNA, FANA, tcDNA, acyclic threoninol nucleic acid (aTNA), and SNA. These chemistries are used in synthetic biology, molecular evolution, XNA aptamer development, diagnostics, therapeutic research, nanotechnology and fundamental studies of alternative genetic systems.

Scientific comparison of GNA, TNA, HNA, CeNA, FANA, tcDNA, acyclic threoninol nucleic acid and serinol nucleic acid structures

Representative XNA backbone analogs showing how alternative scaffolds can preserve base-pairing information while changing structural and biochemical properties.

Alternative Scaffolds

Replace the natural sugar or sugar-phosphate geometry with a new backbone architecture.

Enhanced Stability

Many XNAs resist degradation by enzymes evolved for natural DNA and RNA.

Synthetic Genetics

Selected XNAs can store information and participate in engineered replication or evolution systems.

Functional Molecules

XNA libraries can support aptamer, XNAzyme, probe and molecular-recognition research.

Terminology note: This page uses TNA for α-L-threofuranosyl nucleic acid and aTNA for acyclic L-threoninol nucleic acid. They are distinct scaffolds and should not be treated as synonyms.

Advanced Chemistry Architecture

How XNA Backbone Analogs Fit into the Platform

XNAs occupy a different design space from constrained sugars, flexible analogs, phosphorus-backbone modifications and artificial base pairs.

Constrained Nucleic Acids

Restrict sugar conformation to increase affinity and stability.

Flexible Nucleic Acids

Increase local flexibility to tune duplex stability and specificity.

Backbone Chemistries

Modify charge, stereochemistry or phosphorus-containing linkages.

XNA Backbone Analogs

Replace the natural sugar or backbone scaffold with a new genetic polymer.

Artificial Base Pairs

Alter or expand the nucleobase alphabet while retaining a nucleic acid scaffold.

Application-First Selection

What Are You Trying to Achieve?

Select your research objective below to view recommended XNA chemistries, design priorities and key tradeoffs.

↘ Choose a project goal below to update the recommendation panel.
Recommended Starting Point

HNA, FANA, tcDNA or TNA

Alternative backbones can provide strong resistance to nucleases and altered chemical stability. The best chemistry depends on whether the construct must also hybridize with DNA or RNA, support a biological mechanism, or function in an engineered polymerase system.

HNA FANA tcDNA TNA

Stability

High–Very High

Hybridization

Scaffold-Dependent

Mechanism

Project-Specific

Testing

Required

Design Priorities

  • Define target nucleic acid.
  • Specify biological matrix.
  • Plan analytical characterization.

Main Caution

Nuclease resistance does not guarantee compatible hybridization or cellular delivery.

Recommended Starting Point

TNA, HNA, FANA or CeNA

XNAs used in directed evolution require an information-transfer system capable of copying between DNA and XNA. TNA, HNA, FANA and CeNA have comparatively strong histories in engineered polymerase and X-SELEX research.

TNA HNA FANA CeNA

Use

X-SELEX

Requirement

Polymerase

Output

Aptamer / XNAzyme

Complexity

High

Design Priorities

  • Select compatible triphosphates.
  • Define transcription and reverse transcription.
  • Validate library fidelity.

Main Caution

Chemical synthesis of an XNA oligo is not the same as establishing an evolvable XNA system.

Recommended Starting Point

FANA, TNA, HNA or SNA

XNA aptamers can combine sequence-defined recognition with improved biological stability and folding behavior distinct from DNA or RNA. The choice depends on selection technology, target, library architecture and desired downstream use.

FANA TNA HNA SNA

Recognition

Sequence-Defined

Stability

High

Selection

X-SELEX

Conjugation

Possible

Design Priorities

  • Define selection platform.
  • Review folding and target binding.
  • Plan labels or delivery ligands.

Main Caution

DNA or RNA aptamer sequences cannot be assumed to retain function after full XNA conversion.

Recommended Starting Point

TNA, HNA, CeNA or FANA

Polymerase engineering projects should begin with the intended direction of information transfer: DNA-to-XNA synthesis, XNA-templated DNA synthesis, or full XNA replication. Substrate synthesis, enzyme fidelity and processive copying must be evaluated separately.

TNA HNA CeNA FANA

Focus

Information Transfer

Substrate

XNA Triphosphates

Readout

Yield / Fidelity

Program

Enzyme Engineering

Design Priorities

  • Define primer and template.
  • Specify linkage direction.
  • Measure fidelity and processivity.

Main Caution

Polymerase compatibility varies widely among enzymes and XNA substrates.

Recommended Starting Point

FANA or tcDNA

FANA has been investigated in antisense, aptamer and catalytic systems, while tcDNA is strongly associated with steric-blocking and splice-modulation research. GNA and TNA insertions are also being explored for RNAi and oligonucleotide optimization.

FANA tcDNA GNA TNA

Mechanism

ASO / Steric Block

Stability

High

Delivery

Critical

Status

Research

Design Priorities

  • Define mechanism before chemistry.
  • Coordinate backbone and delivery.
  • Plan impurity and QC strategy.

Main Caution

Therapeutic performance depends on distribution, delivery and safety—not stability alone.

Recommended Starting Point

GNA, aTNA or SNA

Acyclic and compact XNAs can provide orthogonal recognition, alternative helical geometry and new options for programmable molecular assemblies, fluorescence systems and responsive nanostructures.

GNA aTNA SNA

Use

Nanotechnology

Geometry

Alternative

Function

Recognition / Assembly

Status

Emerging

Design Priorities

  • Define partner strand.
  • Model helical compatibility.
  • Validate assembly experimentally.

Main Caution

Orthogonal XNA:XNA pairing may not translate to strong XNA:DNA or XNA:RNA binding.

Interactive XNA Platform

Explore Eight XNA Backbone Analogs

Choose an XNA chemistry below to compare its scaffold, hybridization behavior, applications and design guidance.

↘ Select any XNA tab below to open its chemistry profile.
GNA

Glycol Nucleic Acid

GNA uses a compact acyclic glycol backbone. It can form highly ordered self-paired duplexes, but cross-pairing with natural nucleic acids depends strongly on stereochemistry and sequence context.

Scaffold

Acyclic Glycol

Stability

High

Best Known For

Simplicity

View GNA Guide →

Applications

  • Synthetic genetics
  • Prebiotic chemistry
  • siRNA insert research
  • Orthogonal recognition

Advantages

  • Structurally simple scaffold
  • Strong self-pairing possible
  • High nuclease resistance

Use Caution

  • Chirality is critical
  • DNA/RNA cross-pairing may be limited
  • Sequence effects are strong

Typical Design

  • Defined GNA blocks
  • Single GNA insertions
  • Comparative stereoisomer studies
TNA

α-L-Threofuranosyl Nucleic Acid

TNA uses a four-carbon threose sugar and a backbone repeat unit shorter than DNA or RNA. It can self-pair and cross-pair with natural nucleic acids and is a major platform for synthetic genetics and engineered polymerase research.

Scaffold

4-Carbon Sugar

Stability

Very High

Best Known For

Synthetic Genetics

View TNA Guide →

Applications

  • X-SELEX and aptamers
  • XNAzymes
  • Polymerase engineering
  • Prebiotic chemistry

Advantages

  • Information storage
  • High nuclease resistance
  • DNA/RNA cross-pairing

Use Caution

  • Linkage direction differs
  • Specialized monomers and enzymes
  • Not interchangeable with aTNA

Typical Design

  • Full TNA polymers
  • TNA aptamer libraries
  • Defined TNA substitutions
HNA

Hexitol Nucleic Acid

HNA replaces the natural five-membered sugar with a six-membered 1,5-anhydrohexitol scaffold. It forms stable duplexes and has been used in synthetic genetics, aptamer selection and XNA enzyme research.

Scaffold

6-Membered Hexitol

Stability

Very High

Best Known For

Stable Duplexes

View HNA Guide →

Applications

  • XNA aptamers
  • Molecular evolution
  • Stable hybridization
  • XNAzymes

Advantages

  • Strong duplex stability
  • High nuclease resistance
  • Engineered polymerase systems

Use Caution

  • Different helical geometry
  • Specialized monomer synthesis
  • Polymerase system required for evolution

Typical Design

  • Full HNA libraries
  • HNA:RNA recognition
  • Functional XNA selections
CeNA

Cyclohexene Nucleic Acid

CeNA uses a cyclohexenyl scaffold that preorganizes the backbone and supports stable pairing with complementary nucleic acids. It has been investigated in antisense, synthetic biology and engineered polymerase systems.

Scaffold

Cyclohexene

Stability

High

Best Known For

Preorganization

View CeNA Guide →

Applications

  • Synthetic genetics
  • Antisense research
  • Polymerase studies
  • Stable probes

Advantages

  • Stable hybridization
  • Nuclease resistance
  • Alternative helical geometry

Use Caution

  • Specialty monomer availability
  • Position-dependent behavior
  • Project-specific analytics

Typical Design

  • CeNA-modified oligos
  • Full CeNA polymers
  • Comparative XNA panels
FANA

2′-Deoxy-2′-Fluoro-Arabino Nucleic Acid

FANA is a fluorinated arabino nucleic acid with strong nuclease resistance, useful RNA recognition and broad relevance to antisense, aptamer, XNAzyme and synthetic biology research.

Scaffold

2′-Fluoro Arabino

Stability

Very High

Best Known For

Functional XNA

View FANA Guide →

Applications

  • Antisense research
  • FANA aptamers
  • FANAzymes
  • Synthetic biology

Advantages

  • Strong biostability
  • Functional folding
  • RNase H-compatible ASO designs

Use Caution

  • Mechanism depends on architecture
  • Delivery remains important
  • Specialized synthesis and analytics

Typical Design

  • FANA ASO segments
  • Full FANA aptamers
  • Catalytic XNA libraries
tcDNA

Tricyclo-DNA

tcDNA is a highly conformationally restricted DNA analog with strong RNA affinity and high nuclease resistance. It is especially associated with steric-blocking and splice-modulation research.

Scaffold

Tricyclic

Affinity

Very High

Best Known For

Splice Modulation

View tcDNA Guide →

Applications

  • Splice-switching oligos
  • Steric-blocking ASOs
  • Neuromuscular research
  • Therapeutic development

Advantages

  • Very high RNA affinity
  • Strong nuclease resistance
  • Distinct tissue-distribution research

Use Caution

  • Highly specialized synthesis
  • Delivery and safety require review
  • Not primarily an X-SELEX scaffold

Typical Design

  • Fully modified steric blockers
  • Splice-switching architectures
  • Therapeutic screening constructs
aTNA

Acyclic L-Threoninol Nucleic Acid

aTNA uses an acyclic L-threoninol scaffold and can form stable heteroduplexes with RNA or DNA. It is being explored in orthogonal recognition, template-directed ligation, nanotechnology and functionalized XNA systems.

Scaffold

Acyclic Threoninol

Pairing

RNA / DNA

Best Known For

Orthogonal Design

View aTNA Guide →

Applications

  • Template-directed ligation
  • Molecular nanotechnology
  • Functionalized probes
  • Orthogonal recognition

Advantages

  • Stable heteroduplex formation
  • Acyclic functional scaffold
  • Alternative helical structure

Use Caution

  • Distinct from α-L-TNA
  • Specialty monomers required
  • Emerging manufacturing history

Typical Design

  • aTNA blocks
  • Functionalized aTNA probes
  • Template-ligation systems
SNA

Serinol Nucleic Acid

SNA uses a non-carbohydrate serinol backbone and can hybridize with natural nucleic acids. Its acyclic scaffold is useful for functionalization, fluorescence, photoswitching and molecular nanotechnology.

Scaffold

Serinol

Stability

Very High

Best Known For

Functionalization

View SNA Guide →

Applications

  • Fluorescent probes
  • Photoswitching systems
  • Nanotechnology
  • Orthogonal hybridization

Advantages

  • Non-carbohydrate scaffold
  • High nuclease resistance
  • Flexible functionalization

Use Caution

  • Emerging specialty platform
  • Helical geometry differs
  • Project-specific analytics required

Typical Design

  • SNA probes
  • Base-functionalized SNA
  • Responsive molecular systems
XNA Comparison

Compare GNA, TNA, HNA, CeNA, FANA, tcDNA, aTNA and SNA

The table provides relative design guidance. Hybridization, enzyme compatibility and biological performance depend on sequence, stereochemistry, linkage pattern and application.

Property GNA TNA HNA CeNA FANA tcDNA aTNA SNA
Full Name Glycol nucleic acid α-L-Threofuranosyl nucleic acid Hexitol nucleic acid Cyclohexene nucleic acid 2′-Deoxy-2′-fluoro-arabino nucleic acid Tricyclo-DNA Acyclic L-threoninol nucleic acid Serinol nucleic acid
Backbone Scaffold Acyclic glycol Four-carbon threose Six-membered hexitol Cyclohexenyl Fluorinated arabino sugar Rigid tricyclic sugar Acyclic threoninol Acyclic serinol
Natural-Strand Pairing Stereochemistry-dependent Pairs with DNA and RNA Strong RNA/DNA recognition Stable natural-strand pairing Strong RNA recognition Very strong RNA affinity Pairs with RNA and DNA Pairs with RNA and DNA
Nuclease Resistance High Very high Very high High Very high Very high High Very high
Engineered Polymerase History Research / limited Strong Strong Established research Strong Limited Chemical ligation research Emerging
Aptamer / XNAzyme Potential Emerging High High Research Very high Not primary Emerging Functional probe focus
Therapeutic Research siRNA insert research siRNA and ASO research Emerging Antisense research ASO and aptamer research Splice modulation Emerging Emerging
Best-Fit Application Structural simplicity and orthogonal pairing Synthetic genetics and evolution Stable functional XNAs Preorganized XNA research Functional and therapeutic XNA Steric blocking and splice switching Nanotechnology and ligation Functionalized probes and nanotechnology

Important: XNAs are not interchangeable. A scaffold that forms a strong XNA:XNA duplex may not form an equally stable duplex with DNA or RNA, and polymerase compatibility must be evaluated independently.

Application Guide

Common Applications for XNA Backbone Analogs

XNA Aptamers

Directed evolution can generate stable XNA ligands with binding functions beyond conventional DNA and RNA.
Common choices: FANA, TNA, HNA

↗

RNAi & Therapeutic Research

FANA, GNA and TNA modifications can tune stability, silencing, specificity and off-target behavior.
Common choices: FANA, GNA, TNA

↗

Splice Modulation

Highly stable steric-blocking scaffolds can support splice-switching and transcript-modulation research.
Common choice: tcDNA

↗

XNAzymes & Catalysis

Selected XNAs can fold into catalytic structures capable of RNA cleavage or ligation.
Common choices: FANA, TNA, HNA

↗

Synthetic Genetics

Engineered polymerases can transfer genetic information between DNA and selected XNA systems.
Common choices: TNA, HNA, CeNA, FANA

↗

Molecular Nanotechnology

Acyclic and orthogonal XNAs support responsive probes, assemblies and alternative recognition systems.
Common choices: GNA, aTNA, SNA

↗

Functionalization & Conjugation

Combine XNA Scaffolds with Labels, Handles and Delivery Technologies

Depending on scaffold compatibility, XNAs can be functionalized for detection, immobilization, molecular selection, delivery and advanced structure-function studies.

XNA + Fluorophore

Supports hybridization probes, folding studies, imaging and fluorescence-based assays.

XNA + Biotin or Affinity Tag

Enables capture, selection, pull-down and surface-binding applications.

XNA + Click Handle

Provides modular access to dyes, ligands, peptides, polymers and nanoparticles.

XNA + Peptide or Lipid

Supports exploratory delivery, cell uptake and targeted-conjugate research.

FAQ

Are all XNAs compatible with DNA and RNA?
No. Hybridization with natural nucleic acids depends on scaffold geometry, stereochemistry and sequence. Some XNAs pair strongly with DNA or RNA, while others primarily form stable self-paired duplexes.
What does XNA mean?
 XNA means xeno nucleic acid. It refers to synthetic nucleic acid systems containing chemical components that differ from natural DNA or RNA.
Are TNA and aTNA the same?
No. TNA on this page is α-L-threofuranosyl nucleic acid. aTNA is acyclic L-threoninol nucleic acid, a structurally different noncyclic scaffold.
Which XNAs are used for X-SELEX?
TNA, HNA and FANA are among the best-established XNA systems for engineered polymerase, selection and functional-molecule research.
Which XNA is most suitable for therapeutic research?
FANA and tcDNA have comparatively strong therapeutic research histories. The best choice depends on whether the goal is RNase H activity, steric blocking, splice modulation, delivery or another mechanism.
Can XNAs be labeled or conjugated?
Yes, depending on scaffold compatibility. Fluorophores, affinity tags, click handles, peptides, lipids and other groups may be introduced through suitable terminal or internal functionality.
More FAQ'sAll FAQ's
Contact & Quote Request

Need help selecting an XNA backbone analog?

Send the sequence, requested XNA scaffold, modification pattern, target strand, intended application, scale, purification target, conjugation needs and analytical requirements. Bio-Synthesis can review monomer availability, synthesis feasibility, purification and project-specific QC.
Request a Quote Speak to a Scientist

Need help before quoting?

Email: info@biosyn.com
Phone: 800-227-0627 (US/CAN)
Phone: +001-972-420-8505 (INT)

What to Send

  • Sequence and XNA type
  • Full or partial modification
  • Target and application
  • Scale, purification and QC
  • Label or conjugation needs

What We Review

Monomer availability, linkage direction, hybridization context, synthesis route, purification, analytical characterization and scale-up feasibility.

Quality Systems

Quality Systems & Manufacturing Support

XNA projects require controlled chemistry development, purification, analytical review and documentation tailored to each alternative scaffold.

QMS

ISO-Supported Advanced Oligonucleotide Manufacturing

Bio-Synthesis supports XNA feasibility studies and custom synthesis programs with controlled production, project-specific purification, analytical QC, documentation and packaging.

ISO 9001:2015 Quality management system
ISO 13485:2016 Medical-device quality framework
ISO 14001 Environmental management system
Analytical QC HPLC/UPLC, MS where compatible, OD and COA
Recommended Reading

Selected XNA Literature

  1. Pinheiro VB, et al. Synthetic genetic polymers capable of heredity and evolution.
  2. Chaput JC and colleagues. Engineered polymerases, structural biology and directed evolution of TNA systems.
  3. Taylor AI, Holliger P and colleagues. XNA aptamers and XNAzymes from alternative genetic polymers.
  4. FANA synthetic biology studies. FANA aptamers, FANAzymes and engineered information-transfer systems.
  5. Asanuma H and colleagues. Structural and functional studies of acyclic threoninol nucleic acid and serinol nucleic acid.
  6. tcDNA therapeutic research. Tricyclo-DNA steric-blocking and splice-modulation studies.

Why Choose Bio-Synthesis

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