Nucleic acids and functional proteins are key components of multicellular organisms. Drug-discovery associated with nucleic acids has become popular in recent years because of their successfully applications as novel medicines of mRNA and oligonucleotide therapeutics compared with traditional small molecule medicines. Nucleic acids or oligonucleotide molecules have to be uptake and be survived in cellular environments in order to be therapeutic agents. The stability of nucleic acids and oligonucleotides are usually dependent on their nucleotide sequences, the basic nucleoside units (A, G, C, U, and T) of nucleic acids are eventually necessary to be chemically modified. We offered chemical modifications either on sugar or base moiety to achieve such a reality of drug-like molecule. Chemical modified nucleosides are widely also used as substrates or inhibitors targeting for either DNA or RNA polymerases. There are more a lot of chemical modified nucleosides and nucleotides in our data base. Please search for them with a CAS number, ACS chemical name or catalog number if you have one.