The present invention relates to compounds of formula (I), wherein R1, R2 and R3 are as described herein, and their prodrugs or pharmaceutically acceptable salt, enantiomer or diastereomer thereof, and compositions including the compounds and methods of using the compounds.本發明係關於式(I)化合物,其中R1、R2及R3如本文所描述;及其前藥或醫藥學上可接受之鹽、其對映異構體或非對映異構體;及包括該等化合物之組合物;及使用該等化合物之方法。