The present invention provides activity as an inhibitor of deubiquitinating enzymes, particularly ubiquitin C-terminal hydrolase 30 or ubiquitin-specific peptidase 30 (USP30), which has utility in the therapeutic field including cancer and conditions associated with mitochondrial dysfunction. It relates to substituted cyanopyrrolidines of the formula (I) having (Formula (I))本発明は、癌及びミトコンドリア機能不全を伴う状態を含む治療分野において有用性を有する、脱ユビキチン化酵素、特にユビキチンC末端加水分解酵素30又はユビキチン特異的ペプチダーゼ30(USP30)の阻害剤としての活性を有する式(I)の置換シアノピロリジン類に関する。(式(I))