What is rC(Bz)?

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

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

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

• Bz (benzoyl): Refers to the benzoyl protecting group attached to the N4 position of cytosine.

About the (Bz) Protecting Group

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

To prevent this, the N4 position is protected with a benzoyl (Bz) group during solid-phase synthesis.

After completion of RNA chain assembly, standard deprotection conditions (commonly aqueous ammonia or AMA) remove the benzoyl group, restoring the native ribocytidine structure.

Thus, rC(Bz) ensures:

• Reliable base protection during synthesis

• High coupling efficiency and fidelity

• Clean deprotection to natural rC

The benzoyl group is widely used due to its stability under synthesis conditions and predictable removal profile.

Applications of rC(Bz)-CPG

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

siRNA

When the 3′-terminal nucleotide of either strand is cytidine, rC(Bz)-CPG ensures accurate incorporation of ribocytidine at the 3′ end, maintaining duplex precision and integrity.

CRISPR gRNA / sgRNA

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

It is also suitable for synthetic RNA fragments used in ligation workflows or transcription-based assembly.

mRNA Fragments

In chemically synthesized RNA fragments for mRNA applications, rC(Bz)-CPG ensures:

• Defined ribocytidine at the 3′ end

• Compatibility with 2′-modifications

• Stability during phosphorothioate chemistry

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

Benefits of Co-Polymer Coated rC(Bz)-CPG in GMP-Scale RNA 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.

Typical loading levels:

• 500 Å: 200-240 μmol/g

• 1000 Å: 100–150 μmol/g

• 2000 Å: 40–80 μmol/g

This makes it especially advantageous for long RNA synthesis (>100 nt) at GMP industrial scale.

High Crude RNA Purity

The co-polymer coating demonstrates excellent resistance to:

• Acidic detritylation conditions

• Basic deprotection

• Organic solvents used in coupling

Resulting in:

• >80% crude RNA purity

This reduces purification burden and improves overall manufacturing efficiency.

Stable Physical Structure

Unlike traditional 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 reproducible GMP 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

• CRISPR gRNA

• Long-chain mRNA fragments

In summary, co-polymer coated rC(Bz)-CPG combines classical benzoyl cytidine protection chemistry with next-generation high-loading CPG architecture, enabling high-yield, high-purity, GMP-compatible RNA oligonucleotide production.