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Cholesterol & Sterol-Modified Oligonucleotides

Custom cholesterol, plant-sterol, and bile-acid modification for DNA, RNA, ASO, siRNA, aptamers, probes, and specialty oligonucleotides using commercial direct-incorporation reagents, published sterol phosphoramidite chemistry, 3′ modified supports, custom building blocks, and post-synthetic conjugation

Cholesterol Cholesteryl-TEG 3′ Cholesterol CPG Plant Sterols Bile-Acid Derivatives 5′ • 3′ • Internal

Rigid Sterol Scaffolds Create a Distinct Hydrophobic Oligonucleotide Architecture

Sterol-modified oligonucleotides differ from flexible fatty-acid conjugates because the sterol framework contains a rigid fused-ring scaffold with a defined three-dimensional shape. Cholesterol and related sterols can alter lipophilicity, membrane association, serum and lipoprotein interactions, cellular uptake, biodistribution, self-assembly, and purification behavior.

The platform is broader than cholesterol alone. Bio-Synthesis can evaluate cholesterol, cholic acid, brassicasterol, campesterol, β-sitosterol, and stigmasterol, and additional sterol or bile-acid derivatives through direct-incorporation chemistry where established or through custom post-synthetic conjugation.

Classification note: cholic acid is a bile acid rather than a sterol in the strict chemical sense. It is included here because it shares the steroidal framework and is relevant to sterol-like oligonucleotide conjugation strategies.
Representative oligonucleotide conjugates with cholesterol, cholic acid, brassicasterol, campesterol, sitosterol and stigmasterol.
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Representative cholesterol, sterol and bile-acid oligonucleotide architectures

Commercial Direct Chemistry

Cholesterol-containing modifiers, Cholesteryl-TEG reagents, and 3′ cholesterol-support formats have established solid-phase synthesis routes.

Published Direct Chemistry

Cholic-acid phosphoramidite chemistry has literature precedent, although it is not equivalent to a routine commercial cholesterol modifier.

Custom Sterol Conjugation

Plant sterols and specialty steroidal lipids can be evaluated through post-synthetic coupling and custom building-block development.

Position & Linker Control

5′, 3′, selected internal, short-linker, TEG, PEG, and multivalent architectures can be designed around the final application.

Compare Sterol Chemistry by Incorporation Route and Position

The library distinguishes commercial direct incorporation, published direct-incorporation precedent, custom building-block chemistry, and post-synthetic conjugation. Commercial availability and project feasibility should be confirmed for the exact sterol, linker, position, scale, and oligonucleotide chemistry.

Direct incorporation

Established cholesterol modifier phosphoramidite and cholesterol-bearing solid-support formats can provide defined terminal architectures.

Post-conjugation

Reactive oligonucleotide handles allow custom cholesterol attachment, alternative spacers, internal positions, or multi-modification constructs.

Applications

siRNA and ASO delivery research, membrane anchoring, lipoprotein-interaction research, imaging, and specialty lipid-oligo assemblies.

Design watch

Linker length, strand, position, hydrophobicity, purification, and biological context should be optimized together.

Multiple Routes to Cholesterol-Modified Oligonucleotides

Cholesterol Phosphoramidite

Direct solid-phase incorporation provides a defined cholesterol-containing modifier architecture during oligonucleotide synthesis.

Cholesterol AmiditeAutomated SynthesisDefined Product

Cholesteryl-TEG

A cholesterol anchor separated from the oligonucleotide by a flexible triethylene glycol spacer.

CholesterolTEGOligo

3′ Cholesterol CPG

A cholesterol-functionalized support defines the 3′ cholesterol architecture from the beginning of solid-phase synthesis.

Cholesterol SupportChain Growth3′ Chol-Oligo

Post-Synthetic Conjugation

Reactive oligonucleotide handles provide flexibility for 5′, 3′, internal, custom-linker, and multi-modification cholesterol designs.

Reactive Oligo + Cholesterol DerivativeConjugate

Choose the Route from the Desired Final Architecture

5′ Terminal

A cholesterol-containing or Cholesteryl-TEG phosphoramidite may be used when compatible with the desired linkage; post-synthetic conjugation provides additional flexibility for custom spacers and alternative sterols.

3′ Terminal

A cholesterol-functionalized CPG/support can provide a defined 3′ cholesterol architecture; alternative sterols generally require post-synthetic conjugation or project-specific support development.

Internal

Internal handles, branching units, or custom modifier chemistry can place sterols away from the termini.

Multiple Sterols

Branched or orthogonal-handle architectures can support dual- or multivalent sterol presentation where purification and solubility permit.

Important: “cholesterol-modified” does not define one unique structure. Direct cholesterol, Cholesteryl-TEG, 3′ cholesterol support, and post-conjugated cholesterol may differ in linkage, spacer, position, and biological behavior.

The Spacer Can Be as Important as the Sterol

Direct / Short

Compact architecture with minimal separation between sterol and oligonucleotide.

Sterol—Oligo

C3 / C6

Short flexible spacer that can reduce local steric crowding while keeping the sterol close to the oligonucleotide.

Sterol—C3/C6—Oligo

TEG

Flexible hydrophilic spacing used widely in cholesterol-oligonucleotide architectures.

Sterol—TEG—Oligo

PEG / Custom

Longer spacing for surface presentation, complex assemblies, or application-specific sterol separation.

Sterol—PEG—Oligo

Where Cholesterol and Sterol-Modified Oligonucleotides Are Used

RNAi

Cholesterol-siRNA Delivery Research

Evaluate strand, terminus, linker, backbone chemistry, and sterol identity together rather than treating cholesterol as a stand-alone delivery solution.

  • Passenger- or guide-strand designs
  • 5′ or 3′ cholesterol
  • Cholesterol versus Chol-TEG
Antisense

Cholesterol-ASO & Gapmer Studies

Hydrophobic sterol conjugation can be combined with phosphorothioate and affinity-enhancing sugar chemistries for uptake and distribution research.

  • Terminal sterol placement
  • Backbone compatibility
  • Protein-interaction studies
Membrane

Membrane Anchoring

Cholesterol and related sterols can act as hydrophobic anchors for cell-surface display, membrane association, liposomes, and lipid-rich model systems.

Lipoprotein

Serum & Lipoprotein Interaction

Sterol identity and linker architecture can alter how the conjugate interacts with serum components and lipid-transport pathways.

Imaging

Imaging & Localization

Cholesterol can be combined with fluorophores or reporters for membrane-localization and trafficking studies when sterol and dye placement are designed together.

Assembly

Nanoparticle & Surface Presentation

Cholesterol-, TEG-, or PEG-spaced oligonucleotides can be explored in lipid-rich assemblies and multicomponent delivery systems.

Sterol Conjugation Across DNA and RNA Formats

ssDNA

Terminal or selected internal sterol conjugation for specialty DNA, probes, and surface-association studies.

ssRNA

Sterol-modified RNA with position and deprotection strategy matched to the intended architecture.

ASO / Gapmer

Cholesterol and custom sterols coordinated with PS, 2′-modified, or constrained-sugar designs.

siRNA / Duplex RNA

Strand, terminus, linker, valency, and chemical stabilization should be optimized together.

Aptamer

Sterol anchors for membrane display, liposome association, and specialty delivery research.

Imaging Oligos

Dual sterol + fluorophore architectures for localization and membrane-interaction studies.

Branched Oligos

Branched scaffolds can present multiple sterols or combine a sterol with a second functional ligand.

Custom Constructs

Customer-supplied sterols, bile acids, and custom steroidal building blocks can be reviewed for feasibility.

Build a Sterol-Oligonucleotide SAR Panel

Sterol Identity

Compare rigid-ring and side-chain differences.

Cholesterol → Campesterol → Sitosterol → Stigmasterol

Sterol vs Bile Acid

Compare neutral sterols with more polar steroidal bile-acid scaffolds.

Cholesterol ↔ Cholic Acid

Linker

Separate sterol identity from spacer effects.

Direct → C6 → TEG → PEG

Position & Valency

Compare how the same sterol behaves when presented differently.

5′ → 3′ → Internal • 1× → 2× → Multi

Common Sterol-Oligonucleotide Design Challenges

Select a common problem below to review the likely causes and practical design strategies. The goal is to help researchers choose the right sterol, position, linker, and valency before a project is manufactured.

Poor aqueous solubility or incomplete dissolution

Cholesterol and other sterols can substantially increase oligonucleotide hydrophobicity, especially when the linker is short or more than one sterol is present.

Observed problem
    Likely causes
      Design response
        Design principle: sterol identity, linker, position, valency, sequence, oligonucleotide chemistry, and formulation all influence the final construct. A more hydrophobic or more highly sterolated design is not automatically the better-performing design.

        Plan QC Around the Sterol Architecture

        Identity

        Expected molecular mass and sterol-conjugate assignment by an appropriate mass method.

        Purity

        RP-HPLC/UPLC or fit-for-purpose chromatography adapted to high hydrophobicity.

        Conjugation

        Assessment of full sterol conversion and separation from unconjugated oligo or excess sterol reagent.

        Duplex

        Annealing and duplex assessment for siRNA or other duplex RNA formats when required.

        Concentration

        OD and project-specific documentation, with additional testing where appropriate.

        Cholesterol & Sterol-Oligonucleotide FAQ

        FAQ

        Can cholesterol be introduced directly during oligonucleotide synthesis?
         Yes. Cholesterol-containing phosphoramidite modifiers and cholesterol-functionalized 3′ supports are established routes. Cholesteryl-TEG is another direct-incorporation architecture with a flexible spacer between the sterol and oligonucleotide.
        Is Cholesteryl-TEG the same as a directly attached cholesterol?
         No. Cholesteryl-TEG contains a triethylene glycol spacer, which changes the distance and local environment between cholesterol and the oligonucleotide.
        Can cholic acid be incorporated by phosphoramidite chemistry?
         Published cholic-acid phosphoramidite chemistry exists, but that should be distinguished from routine commercial availability. Post-synthetic conjugation remains an important route for custom cholic-acid architectures.
        Does cholesterol automatically improve siRNA delivery?
         No. Cholesterol can change hydrophobicity, membrane and serum interactions, and tissue exposure, but productive RNAi activity depends on the complete construct, including strand, position, linker, nucleotide chemistry, sequence, and formulation.
        Can multiple sterols be attached to one oligonucleotide?
         Dual- and multivalent sterol architectures can be evaluated using branched scaffolds or orthogonal conjugation handles, subject to purification, solubility, and analytical feasibility.
        Can brassicasterol, campesterol, β-sitosterol, and stigmasterol be attached to oligonucleotides?
         Yes, these sterols can be evaluated through custom post-synthetic conjugation or project-specific building-block development. Routine commercial phosphoramidite availability should not be assumed.

        Design a Cholesterol or Sterol-Modified Oligonucleotide

        Share your sequence, oligonucleotide modality, sterol or bile-acid identity, desired position, linker, valency, scale, purification grade, and analytical requirements. If the route is not defined, Bio-Synthesis can review direct phosphoramidite, modified support, custom building-block, or post-synthetic conjugation options.

        What to Specify

        Sterol: Cholesterol, Cholic Acid, Brassicasterol, Campesterol, β-Sitosterol, Stigmasterol, other
        Position: 5′, 3′, internal
        Linker: direct, C6, TEG, PEG, custom
        Valency: 1×, 2×, multivalent

        Route Selection

        Commercial direct incorporation, published direct chemistry, 3′ support, custom building-block development, or post-synthetic conjugation.

        Controlled Support from Sterol Incorporation Through Release

        QMS

        ISO-Supported Sterol-Oligonucleotide Manufacturing

        Custom cholesterol, sterol, and bile-acid modified oligonucleotides are supported by documented synthesis or conjugation, purification, analytical QC, traceability, and project-specific handling from feasibility through repeat manufacturing.

        ISO 9001:2015 Quality management system supporting documented synthesis, conjugation, purification, and release workflows.
        ISO 13485:2016 Medical-device quality framework supporting controlled documentation and traceable manufacturing processes.
        ISO 14001 Environmental management system supporting responsible laboratory and manufacturing operations.
        Analytical QC HPLC/UPLC or fit-for-purpose chromatography, MS where compatible, OD, COA, and project-specific release testing.

        Selected Literature on Sterol & Lipid-Oligonucleotide Conjugation

        1. Wolfrum C, et al. Mechanisms and optimization of in vivo delivery of lipophilic siRNAs. Nature Biotechnology. 2007;25:1149-1157. PubMed →
        2. Osborn MF, et al. Hydrophobicity drives the systemic distribution of lipid-conjugated siRNAs via lipid transport pathways. Nucleic Acids Research. 2019;47:1070-1081. PubMed →
        3. Biscans A, et al. Diverse lipid conjugates for functional extra-hepatic siRNA delivery in vivo. Nucleic Acids Research. 2019;47:1082-1096. PubMed →
        4. Manoharan M, et al. Synthesis and properties of bile acid phosphoramidites 5′-tethered to antisense oligodeoxynucleotides against HCV. Representative literature supporting direct bile-acid phosphoramidite incorporation into oligonucleotides. PubMed →

        Scientific note: sterol identity, linker, position, valency, oligonucleotide chemistry, and route of administration can all change conjugate behavior. Literature examples should be treated as design guidance rather than a universal ranking of sterols.

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