Compounds are provided according to Formula (I): and pharmaceutically acceptable salts thereof, and pharmaceutical compositions thereof; wherein R2, R3, R4, R5, and and R6are as defined herein. Compounds of the present invention are contemplated useful for the prevention and treatment of a variety of conditions.本發明提供根據式(I)之化合物:及其醫藥學上可接受之鹽以及其醫藥組合物;其中R2、R3、R4、R5及R6如本文中所定義。預期本發明之化合物適用於預防及治療各種病狀。