The present invention relates to novel compounds and methods for the manufacture of inhibitors of deubiquitylating enzymes (DUBs). In particular, the invention relates to the inhibition of ubiquitin C-terminal hydrolase 30 or ubiquitin specific peptidase 30 (USP30). The novel compounds have formula (I): (Formula (I)) or are pharmaceutically acceptable salts thereof, wherein: R1a, R1b, R1c, R1d, R1e and R1f each independently represent hydrogen, optionally substituted C1-C6 alkyl or optionally substituted C3-C4 cycloalkyl, or R1b and R1c together form an optionally substituted C3-C6 cycloalkyl ring, or R1d and R1e together form an optionally substituted C3-C6 cycloalkyl ring; R2 represents hydrogen or optionally substituted C1-C6 alkyl; A represents an optionally further substituted 5 to 10 membered monocyclic or bicyclic heteroaryl, heterocyclyl or aryl ring; L represents a covalent bond or linker; B represents an optionally substituted 3 to 10 membered monocyclic or bicyclic heterocyclyl, heteroaryl, cycloalkyl or aryl ring; and when -A-L-B is at position x attachment to A is via a carbon ring atom of A, and either: A cannot be triazolopyridazinyl, triazolopyridinyl, imidazotriazinyl, imidazopyrazinyl or pyrrolopyrimidinyl; or B cannot be substituted with phenoxyl; or B cannot be cyclopentyl when L is an oxygen atom.