Provided in the present invention are a
small molecule compound, which is the compound represented by formula (I), or a stereoisomer, a
geometric isomer, a
tautomer, a
hydrate, a solvate, and a pharmaceutically acceptable salt or a
prodrug thereof, where R1 to R4 are each independently selected from C or N, and wherein R is selected from a cycloalkyl, substituted cycloalkyl, heterocycloalkyl, substituted heterocycloalkyl,
aryl, substituted
aryl, heteroaryl or substituted heteroaryl. The
small molecule compound of the present disclosure can inhibit a JAK
kinase, and more particularly is used as a JAK1 / Tyk2
dual inhibitor and a Tyk2 specific inhibitor.