The invention provides novel compounds having the general formula: wherein R1, R2, R3, R4 and A are as described herein, compositions including the compounds and methods of using the compounds.本發明提供具有以下通式之新穎化合物:其中R1、R2、R3、R4及A係如本文中所述,包括該等化合物之組合物,及使用該等化合物之方法。