Remdesivir is an analog of adenosine, one of the four building blocks of RNA. Just look at the main structure and you'll agree they look similar. It turns out the mechanism of action of this drug is that it's supposed to be confused with adenosine, so that the viral RNA replication process uses remdesivir instead of adenosine, which later breaks the RNA†.
Our body, or really, all biological processes can synthesize incredibly complicated molecules that can take human chemists a huge amount of effort to synthesize. It really is amazing how awesome our body is.
†: My description here is a dumbed down description. For a more precise description see section 2 of Arguments in favour of remdesivir for treating SARS-CoV-2 infections, Wen-Chien Ko et al, https://www.sciencedirect.com/science/article/pii/S092485792...
Our body, or really, all biological processes can synthesize incredibly complicated molecules that can take human chemists a huge amount of effort to synthesize. It really is amazing how awesome our body is.
†: My description here is a dumbed down description. For a more precise description see section 2 of Arguments in favour of remdesivir for treating SARS-CoV-2 infections, Wen-Chien Ko et al, https://www.sciencedirect.com/science/article/pii/S092485792...