The synthesis and the microbiological evaluation of a novel series of substituted tricyclic ~ lactam derivatives (trinems, former named tribactams) is reported. Suitable basic groups were introduced within the key C-4 side chain with the aim of improving the antibacterial activity of this class of new antibiotics to Pseudomonas spp.. Among the different compounds prepared, basic derivatives 2 and 3 showed improved activity with respect to GV104326 1 against these highly resistant strains.