3-(Aziridin-1-yl)propyl Hydrogen Aziridin-1-ylphosphonate-d4, a deuterium labelledCyclophosphamide Impurity 1 (C984600),is a derivative ofCyclophosphamide Monohydrate (C988580), a known human carcinogen that is widely used in cancer chemotherapy because it can cross-link DNA causing strand breakage and mutation.