There is provided a compound of formula (I) wherein Ra, R1, R2, Y and R3 have meanings given in the description and pharmaceutically-acceptable derivatives (including prodrugs) thereof, which compounds and derivatives are useful as, or are useful as prodrugs of, competitive inhibitors of trypsin-like proteases, such as thrombin, and thus, in particular, in the treatment of conditions where inhibition of thrombin is required (e.g. thrombosis) or as anticoagulants.