The invention relates to pyridine derivatives of Formula (I)whereinA, R1, R2, R3,andR4are as described in the description, their preparation and their use as pharmaceutically active compounds. Said compounds particularly act as immunomodulating agents.本發明係關於如下化學式(I)之吡啶衍生物:其中A、R1、R2、R3及R4係如說明書中所述,其製法及其作為醫藥活性化合物之用途。該等化合物尤其具有作為免疫調節劑之作用。