  We study the non-perturbative dynamics of an unoriented Z_5-quiver theory of
GUT kind with gauge group U(5) and chiral matter. At strong coupling the
non-perturbative dynamics is described in terms of set of baryon/meson
variables satisfying a quantum deformed constraint. We compute the effective
superpotential of the theory and show that it admits a line of supersymmetric
vacua and a phase where supersymmetry is dynamically broken via gaugino
condensation.
