Discovery of new BTK inhibitors with B cell suppression activity bearing a 4,6-substituted thieno[3,2-: D] pyrimidine scaffold

A series of 4,6-substituted thieno[3,2-d]pyrimidine derivatives as Bruton's tyrosine kinase (BTK) inhibitors are designed, synthesized and evaluated for their enzymatic inhibition and immunosuppressive activities. These derivatives exhibit varying inhibitory activities against BTK in vitro. Compound 8 is a novel potent BTK inhibitor which has an IC₅₀ value of 29.9 nM, exerts excellent immunosuppressive activity by inhibiting the proliferation of B cells (IC₅₀ = 284 nM), and shows low cytotoxicity (CC₅₀ = 53 632 nM) on murine splenocytes. In addition, compound 8 displays considerable selectivity between T cells (IC₅₀ > 10 μM) and B cells. Furthermore, enzymatic assays on more than twenty kinases confirm that compound 8 is more selective than the reference compound Olmutinib. In summary, the results suggest that compound 8 is a potential BTK inhibitor for further evaluation and modification of the C-4 and C-6 position of the thieno[3,2-d]pyrimidine scaffold, which could be considered a new strategy in the development of BTK inhibitors.