In continuing efforts of improving benzoxazepine derivatives as an anti-breast cancer agent, a new chemical entity, benzoxazine, was designed from scaffold morphing. Structure-activity relationship studies revealed that H, -OMe, -CF<sub>3</sub>, and -F were well tolerated on R<sub>1</sub> and R<sub>2</sub> positions of ring <b>A</b>, and R<sup>2</sup> as -CH<sub>2</sub>CH<sub>2</sub>N(CH<sub>2</sub>)<sub>4</sub> (<i>N</i>-ethyl pyrrolidine) and -CH<sub>2</sub>CH<sub>2</sub>N(CH<sub>2</sub>)<sub>5</sub> (<i>N</i>-ethyl piperidine) chains on ring D increased activities (<b>Series B</b>, Figure 3). <b>13d</b> selected as a lead compound (IC<sub>50</sub>: 0.20 to 0.65 μM) induces apoptosis, cell cycle arrest, and loss of mitochondrial membrane potential in breast cancer cells. Compound <b>13d</b> was formulated into <b>13d-f</b> using cyclodextrin to improve its solubility for a pharmacokinetic, <i>in vivo</i> efficacy study. Both <b>13d</b> and <b>13d-f</b> regressed tumor growth at concentrations of 5 and 20 mg/kg better than tamoxifen without any mortality in a rat syngenic mammary tumor model. Collectively, our data suggest that tyrosine-derived novel benzoxazine <b>13d</b> could be a potential lead for the treatment of breast cancer and hence deserve further in-depth studies.