The present Invention provides compounds of formula (i), and pharmaceutically acceptable salts thereof, in which X1, X2, X3, Y1, y2, R1 and R3 are as defined in the specification,Processes for their preparation, Pharmaceutical compositions that contain and their use in therapy. These compounds are inhibitors of PhD.La presente invencion proporciona compuestos de la formula (I) y sales farmaceuticamente aceptables de estos, en la que X1, X2, X3, Y1, Y2, R1 y R3 son tal como se define en la memoria descriptiva, procesos para su preparacion, composiciones farmaceuticas que los continene y su uso en terapia. Estos compuestos son inhibidores de PHD.