Busulfan is an alkylating agent that contains 2 labile methanesulfonate groups attached to opposite ends of a 4-carbon alkyl chain. Once busulfan is hydrolyzed, the methanesulfonate groups are released and carbonium ions are produced. These carbonium ions alkylate DNA, which results in the interference of DNA replication and RNA transcription, ultimately leading to the disruption of nucleic acid function. Specifically, its mechanism of action through alkylation produces guanine-adenine intrastrand crosslinks. This occurs through an SN2 reaction in which the relatively nucleophilic guanine N7 attacks the carbon adjacent to the mesylate leaving group. This kind of damage cannot be repaired by cellular machinery and thus the cell undergoes apoptosis.