The invention provides a compound of formula (I):or tautomer or a solvate or a pharmaceutically acceptable salt thereof, wherein the various substituents are as defined in the claims.Also provided are pharmaceutical compositions containing the compounds of formula (I), processes for making the compounds and the medical uses of the compounds.本發明提供一種式(I)化合物:或其互變異構體或溶劑合物或醫藥學上可接受之鹽,其中各種取代基如申請專利範圍中所定義。亦提供含有所述式(I)化合物之醫藥組合物、製造所述化合物之方法及所述化合物之醫療用途。