Fostamatinib disodium hexahydrate (R788 disodium hexahydrate), a prodrug of the active metabolite R406, is a potent Syk inhibitor with IC50 of 41 nM.
References:
[1]. Braselmann, S., et al. R406, an orally available spleen tyrosine kinase inhibitor blocks fc receptor signaling and reduces immune complex-mediated inflammation. J Pharmacol Exp Ther, 2006. 319(3): p. 998-1008.
[2]. Chen, L., et al., SYK-dependent tonic B-cell receptor signaling is a rational treatment target in diffuse large B-cell lymphoma. Blood, 2008. 111(4): p. 2230-7.
[3]. Suljagic, M., et al., The Syk inhibitor fostamatinib disodium (R788) inhibits tumor growth in the Emu- TCL1 transgenic mouse model of CLL by blocking antigen-dependent B-cell receptor signaling. Blood, 2010. 116(23): p. 4894-905.