Discovery and structure–activity relationship of N-phenyl-1H-pyrazolo[3,4-b]quinolin-4-amines as a new series of potent apoptosis inducers

Abstract We report the discovery and SAR study of a series of N -phenyl-1 H -pyrazolo[3,4- b ]quinolin-4-amines as potent inducers of apoptosis. N -(3-Acetylphenyl)-2,3-dihydro-1 H -cyclopenta[ b ]quinolin-9-amine ( 2 ) was discovered through our cell- and caspase-based HTS assays as an inducer of apoptosis. Compound 2 is active against cancer cells derived from several human solid tumors, with EC 50 values ranging from 400 to 700 nM. SAR study of hit 2 led to the discovery of N -phenyl-1 H -pyrazolo[3,4- b ]quinolin-4-amines as a novel series of potent apoptosis inducers, with 1,3-dimethyl- N -(4-propionylphenyl)-1 H -pyrazolo[3,4- b ]quinolin-amine ( 6b ) having EC 50 values ranging from 30 to 70 nM in cancer cells. These compounds also demonstrated potent activity in the cell growth inhibition assay, with GI 50 values of 16–42 nM for compound 6b .