A new alkaloid, Orychophragine D (1), together with three known alkaloids, were isolated from the seeds of Orychophragmus violaceus. Orychophragine D represented the first example of 2-piperazinone fused 5-azacytosine skeleton. Their structures and absolute configurations were determined by spectroscopic analyses and X-ray crystallography. Compared to Ex-RAD, compound 1 exhibited a significant radioprotective activity on cell survival of irradiated HUVEC. In vivo experiments showed that 1 not only remarkably enhanced the survival of irradiated mice in 30 days, but also significantly promoted the recovery of the blood system of irradiated mice. These results suggested that 1 was valuable for further research as promising radioprotectors. CI - Copyright (c) 2023. Published by Elsevier B.V.