The invention provides novel compounds having the general formula (I) wherein R1, R2, R3, R4, R5, R6, X, Y and Z 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、R3、R4、R5、R6、X、Y及Z係如本文中所闡述;提供包括該等化合物之組合物及使用該等化合物之方法。