JAK1 selective kinase inhibitor

A compound of Formula (I):

• or a pharmaceutically acceptable salt thereof,
• wherein,
• Ring A is a 6-membered monocyclic heteroaryl or saturated or unsaturated 8-10 membered bicyclic ring having 0-5 ring heteroatoms selected from oxygen, sulfur and nitrogen, wherein one or more ring forming —CH2— group of the heteroaryl, or the bicyclic ring may be replaced by a —C(O)— group;
• R1 is hydrogen, halogen, hydroxyl, amino, cyano, or C1-3 alkyl;
• R2 is hydrogen, C1-12 alkyl or C1-12 alkoxyl optionally mono- or multi-substituted by halogen, hydroxyl, amino, cyano, or C1-12 alkoxyl;
• each R3 and R4 is independently absent, or halogen, hydroxyl, C1-6 alkyl, carboxyl, C1-6 alkoxyl, C1-6 alkoxycarbonyl, —NRaRb, —C(O)NRaRb, sulfinyl, C1-6 alkylsulfinyl, sulfonyl, C1-6 alkylsulfonyl, sulfonoxyl, sulfoximinyl, C1-6 alkylsulfoximinyl, sulfonimidoyl, S—(C1-6 alkyl) sulfonimidoyl, N—(C1-6 alkyl) sulfonimidoyl, N, S—(C1-6 alkyl)2 sulfonimidoyl, phosphinoyl, C1-6 alkylphosphinoyl, (C1-6 alkyl)2 phosphinoyl, C1-6 alkylphosphonyl, 3-10 membered saturated or unsaturated carbocyclyl, 3-10 membered saturated or unsaturated heterocyclyl, which can be optionally mono- or independently multi-substituted by halogen, hydroxyl, C1-6 alkyl, C1-6 alkoxyl, C1-6 carboxyl, C1-6 alkoxycarbonyl, —NRaRb, —C(O)NRaRb, sulfonyl, C1-6 alkylsulfonyl, carbamoyl, N—(C1-6 alkyl) carbamoyl, or N,N—(C1-6 alkyl)2carbamoyl, phosphinoyl, C1-6 alkylphosphinoyl, (C1-6 alkyl)2 phosphinoyl, wherein one or more ring forming —CH2— group of the carbocyclyl or heterocyclyl may be replaced by a —C(O)— group;
• wherein, each Ra and Rb is independently selected from hydrogen, C1-6 alkyl, C1-6 alkylcarbonyl, which can be optionally mono- or independently multi-substituted by halogen, hydroxyl, or C1-6 alkoxy.