Orally bioavailable Syk inhibitors with activity in a rat PK/PD model.

Design and optimization of benzo- and pyrido-thiazoles/isothiazoles are reported leading to the discovery of the potent, orally bioavailable Syk inhibitor 5, which was found to be active in a rat PK/PD model. Compound 5 showed acceptable overall kinase selectivity. However, in addition to Syk it also inhibited Aurora kinase in enzymatic and cellular settings leading to findings in the micronucleus assay. As a consequence, compound 5 was not further pursued.