The invention relates to pyridine derivatives of Formula (I)wherein A, R1, R2, R3, and R4 are as described in the description, their preparation and their use as pharmaceutically active compounds. Said compounds particularly act as immunomodulating agents.本發明係關於式(I)之吡啶衍生物其中A、R1、R2、R3及R4係如說明書中所闡述,並關於其製備及其作為醫藥活性化合物之用途。該等化合物尤其作為免疫調節劑。