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Medically Speaking: Sulfur mustard (or mustard gas) is a chemical weapon used in World War I. It was sprayed as an aerosol mixture with other chemicals and exhibited a characteristic odor similar to that of mustard plants, thus the name mustard gas. It reacts with a DNA strand twice to cause a cross-linked DNA that leads to cell death. The reaction is very rapid, as the sulfur atom mediates the internal SN2 reaction. After the war was over, scientists started exploring this compound to use that as an antitumor drug. But sulfur mustard was too toxic to use as a drug. Then they synthesized mechloroethamine (or nitrogen mustard), a nitrogen analog of sulfur mustard. That was also a very reactive compound. The discovery of nitrogen mustard launched the field of chemotherapy. Later scientists came up with chlorambucil, which is less reactive and a successful antitumor drug. Identify the nitrogen atoms in the DNA strand that act as nucleophiles of the given reaction. Label the other nitrogen atoms in the DNA strand as nucleophilic or non-nucleophilic nitrogens. What makes Chlorambucil a less reactive (less toxic) than nitrogen mustard? Give a simple mechanism of how Chlorambucil reacts with DNA. General reaction scheme of mustard gas Nuc :S: DNA Nuc :S: - intrernal SN2 Sx2 ci Nitrogen mustard mustard gas DNA DNA NH2 но, NH2 NH NH mustard gas O NH NH NH2 NH Chlorambucil antitumor agent DNA DNA Cross-linked DNA strand leads to cell death