N-cyanopyrrolidines with activity as usp30 inhibitors

A compound of formula (I), which is selected from formula (I)(i) and formula (I) (ii):

• or a tautomer thereof, or a pharmaceutically acceptable salt of said compound or tautomer,
• wherein:
• R1 is selected from (C1-C4)alkyl, (C1-C4) fluoroalkyl and CH2OCH3;
• R2 is selected from (C1-C4)alkyl, CF3 and cyclopropyl;
• and
• R3, R4 and R5 are each independently selected from hydrogen and halogen.