R406 (free base) is primarily used in research settings as a potent inhibitor of Syk kinase, an enzyme involved in immune cell signaling pathways. It is widely applied in studies related to inflammation, autoimmune diseases, and allergic responses due to its ability to modulate immune cell activation. Researchers utilize R406 to investigate signaling mechanisms in B cells, mast cells, and macrophages, where Syk plays a critical role. Its inhibitory action helps in understanding the progression of diseases such as rheumatoid arthritis, asthma, and certain hematological malignancies. Additionally, R406 serves as a tool compound in the development and validation of more selective Syk inhibitors for potential therapeutic use.