Previous efforts by our group have established pyrazolo [1, 5-a] pyrimidine as a viable core for the development of potent and selective CDK inhibitors. As part of an effort to utilize the pyrazolo [1, 5-a] pyrimidine core as a template for the design and synthesis of potent and selective kinase inhibitors, we focused on a key regulator in the cell cycle progression, CHK1. Continued SAR development of the pyrazolo [1, 5-a] pyrimidine core at the C5 and ...