Compounds are provided according to Formula (A):and pharmaceutically acceptable salts thereof, and pharmaceutical compositions thereof; wherein R1,R2, R3, R4, R5, R6, and RGare 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R1、R2、R3、R4、R5、R6及RG如本文所定義。預期本發明之化合物適用於預防及治療各種病狀。