The invention provides compounds having the general formula I wherein n, R1, R2a, R2b, R3a and R3b are as herein defined., composition comprising the compounds and methods of using the compounds.本發明提供具有通式I之化合物、包含該等化合物之組合物及使用該等化合物之方法,其中n、R1、R2a、R2b、R3a及R3b係如本文中所定義。