Novel 6,7,8-trihydrobenzo[6',7']cyclohepta[2',1'-e]pyrazolo[2,3-a]pyrimidine derivatives as Topo IIα inhibitors with potential cytotoxic activity

•Novel tetracyclic pyrazolo[1,5-a]pyrimidine derivatives were synthesized as topoisomerase IIα inhibitors with potential anticancer activity.•The structure and their mechanistic pathway were confirmed based on spectral data and DFT calculations.•Four derivatives exhibited potent Topo II inhibitory activity at one-digit IC50 values (2.35 – 7.18 µM).•The oxo-pyrazolopyrimidine derivative 15c; was the most cytotoxic possessing one-digit IC50 values.•Compound 15c was two times more potent than Doxorubicin against MCF7 breast cancer cells.•Compound 15c was found to be a good apoptotic inducer.