This invention relates to purine derivatives, to processes for their preparation, to compositions containing them and to their use.The present invention provides compounds of formula (I) ##STR00001## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.9, R.sub.9a and Y are defined in the description. More particularly, the present invention relates to the use of purine derivatives in the treatment of a variety of viral infections and immune or inflammatory disorders, including those in which the modulation, in particular agonism, of Toll-Like Receptors (TLRs) is implicated. Accordingly, the compounds of the invention are useful in the treatment of infectious disease such as Hepatitis (e.g. HCV, HBV), genetically related viral infections, inflammatory diseases such as asthma and arthritis, and cancer.