The present invention provides compounds of the formula below or pharmaceutical salts thereof, wherein R1, R2 and R3 are as described herein; methods of treating osteoarthritis using the compounds; and a process for preparing the compounds.本發明提供下式化合物,或其醫藥鹽,其中R1、R2及R3如本文所述;使用該等化合物治療骨關節炎之方法;及製備該等化合物之方法。