Certain imidazopyrazines having the structure of formula (I): or pharmaceutically acceptable salts thereof, wherein R1, R2, R3, R4 and R5 are as defined herein, and pharmaceutical compositions thereof are provided herein. Methods of treating patients suffering from certain diseases and disorders responsive to the inhibition of Syk activity, which comprises administering to such patients an amount of at least one chemical entity effective to reduce signs or symptoms of the disease or disorder are provided. Also provided are methods for determining the presence or absence of Syk kinase in a sample.