The present disclosure relates to quinazoline derivatives and a process for their preparation. In particular, the present disclosure provides quinazoline-based ATR kinase inhibitors having reduced toxicity and better selectivity towards ATR Kinase for cancer therapy. The quinazoline derivatives of the present disclosure have enhanced tolerability in patients with minimized treatment interruptions. The present disclosure also provides a process for the preparation of quinazoline derivatives, which is simple, economical and easy to scale up.