What is rC(Ac)?

rC(Ac) is a commonly used abbreviation in nucleic acid chemical synthesis.
Its full name is N4-Acetyl-cytidine.

• r (ribo): Indicates ribose, meaning this is an RNA component rather than DNA (which is typically denoted as dC).

• C (Cytidine): Refers to cytidine, with cytosine as the nucleobase.

• Ac (acetyl): Refers to the acetyl protecting group attached to the N4 position of cytosine.

About the (Ac) Protecting Group

During RNA oligonucleotide synthesis, the exocyclic amino group (–NH₂) at the N4 position of cytosine is chemically reactive and may participate in unwanted side reactions during coupling and oxidation/sulfurization steps.

To prevent this, the N4 position is protected with an acetyl (Ac) group during solid-phase synthesis.

After completion of the full RNA chain assembly, standard deprotection (typically aqueous ammonia or AMA conditions) removes the acetyl group, restoring the native ribocytidine structure.

Thus, rC(Ac) ensures:

• Controlled base protection during synthesis

• High coupling fidelity

• Clean deprotection to natural rC

Applications of rC(Ac)-CPG

rC(Ac)-CPG is selected whenever the 3′-terminal base of the RNA sequence is cytidine.

siRNA

In siRNA synthesis, when the 3′-terminal nucleotide of either the sense or antisense strand is cytidine (C), rC(Ac)-CPG is chosen as the solid support.

It guarantees that the final duplex contains a precisely defined ribocytidine at the 3′ end.

CRISPR gRNA / sgRNA

For chemically synthesized guide RNAs, if the 3′ terminus begins with cytidine, rC(Ac)-CPG serves as the appropriate starting support.

It is also used for chemically synthesized RNA fragments prior to enzymatic ligation or in vitro transcription workflows.

mRNA

Cytidine residues are frequently incorporated within coding regions and structural elements of mRNA.

When chemical synthesis of RNA fragments is required, rC(Ac)-CPG ensures that:

• The 3′ end contains a defined ribocytidine

• The sequence is compatible with downstream 2′-modifications

• Phosphorothioate chemistry remains stable during processing

Overall, rC(Ac)-CPG provides a classical and highly reliable cytidine protection strategy for complex RNA synthesis.

Benefits of Co-Polymer Coated rC(Ac)-CPG in GMP-Scale Industrial RNA Oligonucleotide Production

Ultra-High Loading Capacity

Poresyn Solutions’ co-polymer coated CPG solid support delivers 3–6× higher loading than conventional functionalized CPG solid supports, significantly increasing RNA oligonucleotide output per batch.

For example:

• 500 Å:200 ~240 μmol/g

• 1000 Å: 100-150 μmol/g

• 2000 Å: 40-80 μmol/g

Our RNA modified CPG co-polymer solid support is particularly advantageous for long RNA synthesis (>100 nt) at GMP scale.

High Crude RNA Purity

The co-polymer coating demonstrates excellent resistance to:

• Acidic detritylation conditions

• Basic deprotection

• Organic solvents used in coupling

This results in: 80% crude purity

Reducing purification burden and improving overall process efficiency.

Stable Physical Structure

Unlike polystyrene-based resins that swell in organic solvents, the rigid CPG core:

• Maintains dimensional stability

• Ensures consistent flow characteristics

• Prevents bed compression during large-scale synthesis

This is critical for industrial RNA API manufacturing.

No Silica Shedding Risk

The co-polymer coating tightly stabilizes the CPG surface, minimizing:

• Silica particle shedding

• Column clogging

• Backpressure increase

This ensures reliable synthesis of long and complex RNA oligonucleotides, including:

• siRNA

• gRNA

• Long-chain mRNA fragments