A novel series of pyrazolo[1,5-a]quinazolin-5(4H)-one derivatives proved to be a potent class of PARP-1 inhibitors. An extensive SAR around the 3-position of pyrazole in the scaffold led to the discovery of amides derivatives as low nanomolar PARP-1 inhibitors. ... Synthesis and SAR studies of a novel series of substituted pyrazolo[1,5-a]quinazolin-5(4H)-one derivatives as potent class of PARP-1 inhibitors are reported. ... Structure of PARP-1 inhibitors. Structure of ...