The present invention relates to compounds of formula (I),,wherein R1to R3and L are as described herein, and their 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至R3及L如本文所描述;及其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;以及使用該等化合物之方法。