The invention provides novel compounds having the general formula (I)wherein R1, R2, Y and W are as described herein, compositions including the compounds and methods of using the compounds.本發明提供具有通式(I)之新穎化合物其中R1、R2、Y及W係如本文所述;包括該等化合物之組合物,及使用該等化合物之方法。