The present disclosure relates to compounds that are Syk inhibitors and to their use in the treatment of various disease states, including cancer and inflammatory conditions. In particular embodiments, the structure of the compounds is given by Formula I: wherein R1, R2, R3, and R4 are as described herein. The present disclosure further provides pharmaceutical compositions that include a compound of Formula I, or pharmaceutically acceptable salts thereof, and methods of using these compounds and compositions to treat conditions mediated by Syk. In certain embodiments, also disclosed are methods for treating a cancer in a subject (e.g., a human) in need thereof, comprising administering to the subject a therapeutically effective amount of a compound of formula I, or a pharmaceutically acceptable salt thereof, in combination with a vinca-alkaloid, or a pharmaceutically acceptable salt thereof.