The invention provides novel compounds having the general formula: wherein R1, R2, R3, R4, R5 and R6 are as described herein, compositions including the compounds and methods of using the compounds.本發明提供新穎化合物,其具有通式:其中R1、R2、R3、R4、R5及R6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。