Solstar Pharma has developed an siRNA platform technology using proprietary modified nucleic acid chemistry. Our modified nucleotides enhance the stability and optimize the mRNA target activity of our siRNAs.


We are harnessing the power of siRNA to inhibit pathogen replication such as in coronavirus disease or block the production of cancer-causing proteins.

Gene-based nucleic acid therapeutic technologies, such as RNA interference (RNAi), for sequence-specific target mRNA degradation, include small interfering RNA (siRNA). These oligonucleotide therapeutics are applied to direct mRNA degradation. We focus on siRNA-based therapeutics by applying our modified nucleotide platform technology.

siRNA enters the cell as a double stranded RNA molecule

One siRNA strand is recruited by the RISC complex

RISC + siRNA binds to a complementary mRNA

mRNA is cleaved in a specific site

Cleaved mRNA is degraded in the cell

Target any gene

Our siRNAs are designed using sequence algorithms and optimized to target specific disease-causing genes.

SOLSTAR Modified Nucleotides

Solstar Pharma has developed novel nucleotides that contain modifications on the ribose sugar,
5′-C-aminopropyl-2′-O-methyl, which are applicable to siRNAs. These monomers significantly increase the stability of siRNAs by protecting them from nucleolytic degradation.

Structure of 5′-aminopropyl-nucleotides (5’ AA-Nt)


Drug candidate
Phase I
Phase II
Phase III
Ovarian Cancer Pancreatic Cancer Colon Cancer
Ovarian Cancer
Lung Cancer
Water-Soluble API
Helicobacter pylori


Property Suite

Nucleoside derivative and use therefor (4’-AminoAlchyl Nucleosides)

STATUS: JAPAN – Patent No. 7016170

Antiviral silencing RNA molecules, chemically modified antiviral silencing RNA molecules with enhanced cell penetrating abilities, pharmaceutical compositions comprising same and uses thereof for treatment of viral infections

STATUS: Published

Nucleoside derivative and use thereof (5’-AminoPropyl Nucleosides)

STATUS: JAPAN – Patent No. 7173467

Nucleoside derivative and use therefor (4’-AminoAlchoxyl Nucleosides)

STATUS: Published

Extended release gastroretentive formulation against helicobacter pylori

STATUS: Published

Water-soluble artesunate-based therapy for coronavirus infection

STATUS: Published

RNA interference agent, multiple chemically modified oligonucleotide, and use thereof

STATUS: Examination

Scientific References

siRNA Mechanism

Tsukimura, R., Kajino, R., Zhou, Y., Chandela, A., Ueno, Y.*: 4′-C-Aminoethoxy modification enhanced nuclease resistance of RNAs and improved thermal stability of RNA duplexes. Results in Chemistry 3: 100231, 2021.

Kajino, R. and Ueno, Y.*: (S)-5′-C-Aminopropyl-2′-O-methyl nucleosides enhance antisense activity in cultured cells and binding affinity to complementary single-stranded RNA. Bioorg. Med. Chem. 30: 115925, 2021.

Zhou, Y., Kajino, R., Ishii, S., Yamagishi, K. and Ueno, Y.*: Synthesis and evaluation of (S)-5′-C-aminopropyl and (S)-5′-C-aminopropyl-2′-arabinofluoro modified DNA oligomers for novel RNase H-dependent antisense oligonucleotides. RSC Advances 10: 41901-41914, 2020.

Tsuchihira, T., Kajino, R., Maeda, Y. and Ueno, Y.*: 4′-C-Aminomethyl-2′-deoxy-2′-fluoroarabinonucleoside increases the nuclease resistance of DNA without inhibiting the ability of a DNA/RNA duplex to activate RNase H. Bioorg. Med. Chem. 28: 115611, 2020.

Uematsu, A., Kajino, R., Maeda, Y. and Ueno, Y.*: Synthesis and characterization of 4′-C-guanidinomethyl-2′-O-methyl-modified RNA oligomers. Nucleotides & Nucleic Acids 39: 280-291, 2020.

Kajino, R., Maeda, Y., Yoshida, H., Yamagishi, K. and Ueno, Y.*: Synthesis and biophysical characterization of RNAs containing (R)- and (S)-5′-C-aminopropyl-2′-O-methyluridines. J. Org. Chem. 84: 3388-3404, 2019.

Kano, T., Katsuragi, Y., Maeda, Y. and Ueno, Y.*: Synthesis and properties of 4′-C-aminoalkyl-2′-fluoro-modified RNA oligomers. Bioorg. Med. Chem. 26: 4574-4582, 2018.

Koizumi, K., Maeda, Y., Kano, T., Yoshida, H., Sakamoto, T., Yamagishi, K. and Ueno, Y.*: Synthesis of 4′-C-aminoalkyl-2′-O-methyl modified RNA and their biological properties. Bioorg. Med. Chem. 26: 521-3534, 2018.