Pharmaceutical piperazine compounds

A diketopiperazine of formula (A): wherein one or both of R1 and R2, which may be the same or different, is: X, substituted phenyl, CH=C(W)V or cyclohexyl; and where appropriate, the other of R1 and R2 is an optionally substituted phenyl group X is a naphthyl group or an optionally substituted five- or six-membered saturated or unsaturated heterocyclic group W is hydrogen or a phenyl group; V is an optionally substituted phenyl group, and the pharmaceutically acceptable salts and esters thereof have activity as inhibitors of plasminogen activator inhibitor.