Pyrazolo[3,4-d]pyrimidine derivatives as irreversible Bruton's tyrosine kinase inhibitors

4,6-Disubstituted pyrazolo[3,4-d]pyrimidine derivatives were explored as irreversible Bruton's tyrosine kinase (BTK) inhibitors. The structure-activity relationship was established with over 20 derivatives synthesized to determine initial hit compounds, based on activities against BTK enzyme and TMD8 cells. It turns out that introducing 1-acrylamido-4-aminopiperdine (1b) at the C4 position of pyrazolopyrimidine as in 5e, and 3-acrylamido-aniline (1j) as 4-position substituent, such as in 9d, 10d, and 10e, delivered potent in vitro enzyme activities as well as TMD8 cell-based cytotoxicities. Considering kinase selectivity profiles, 5e was selected for in vivo efficacy studies with a murine xenograft model using TMD8 cells, where 5e exhibited moderate tumor growth inhibition activities. Further optimization of 5e and 9d may lead to clinically useful compounds to overcome B-cell-mediated hematologic cancers.