Amino acid derivatives

There is provided amino acid derivatives of formula I, ##STR1##

wherein p, q, R¹, R², R³, R⁴, Y, n and B have meanings given in the description which are useful as competitive inhibitors of trypsin-like proteases, such as thrombin, and in particular in the treatment of conditions where inhibition of thrombin is required (e.g. thrombosis) or as anticoagulants.