If the nitrogenous base forming the nucleoside is purine, it is called purine nucleoside. Carbon 1 of pentose sugar is linked to nitrogen 9 of base by glycosidic bond to form purine nucleoside. It is of two types. Adenosine nucleoside and guanosine nucleoside. Pentose sugars combine with adenine to form adenosine nucleosides and pentose sugars combine with guanine to form guanosine nucleosides.