fig4

Figure 4. Most popular nucleotide analogs used in ASO and siRNA drugs. A: Natural DNA (R = H) and RNA (R = OH) units; B: linkage analogs. C: Ribose analogs; D: Base analogs. 5-methyl cytosine is the only one having been used in clinically approved drugs at the present time. Pseudouridine (Psi) is not used in RNA drugs but in mRNA vaccines, because it suppresses the innate immune response against double-stranded RNA stretch.