Serine protease inhibitors derived from imidazo[1,5a]pyridine

In the present invention there are disclosed serine protease inhibitors derived from imidazo[1,5a]pyridine and containing a unit of the general formula I, in which Ri1 represents a hydrogen atom, alkyl group containing 1 to 6 carbon atoms or -CO(1-6C)alkyl group, Ri2 represents a hydrogen atom or alkyl group containing 1 to 6 carbon atoms, Ri3 and Ri4 represent independently on each other a hydrogen atom, alkyl group containing 1 to 6 carbon atoms or together they form the group =CH-NRi5Ri6, in which Ri5 and Ri6 represent alkyl group containing 1 to 6 carbon atoms, whereby the unit of the formula I is bound to a group Y that is capable to interact with parts Sin ... Si2 of serine protease active center, or pharmaceutically acceptable salt thereof.