In addition to the above-described major nucleosides of wide occurrence, nucleic acids also contain nucleosides that are derivatives of minor pyrimidine or purine bases or 2'-O-methylribose. Such nucleosides are referred to as rare or minor by analogy with the constituent bases or sugar. At present, more than 40 such compounds are known.

Minor nucleosides vary widely in chemical composition, and no classification has as yet been developed for them. Whatever classification exists has to do with the type of the pyrimidine or purine base of which the minor nucleoside is a derivative. Accordingly, minor nucleosides differing from major ones by substitution of functional groups in the carbohydrate moiety or base are grouped with minor components related to the major nucleoside. The structure of minor nucleosides was usually identified using the above-described techniques as well as through controlled conversion into nucleosides of a known structure. The structure of minor nucleosides has been corroborated by synthesis. Tables 1-5 and 1-6 give the structural formulas, names and abbreviated symbols of minor nucleosides isolated from RNA and DNA.