Abstract: The object of the invention is a method of synthesis and purification of a nucleoside and/or a nucleotide being a mono-, di- or triphosphate, wherein a Huisgen' s azide-alkyne cycloaddition reaction is being performed using a compound of structure (1) with a compound chosen from the group of structures (2) to (5). The object of the invention is also a modified nucleoside and/or nucleotide of structure (10), a DNA molecule and an oligonucleotide library comprising one or more modified nucleotides and the use of said oligonucleotide library for aptamers selection.