The highly electrophilic compound, which reacts with nucleophile group to form a strong covalent bond, is referred as alkylating agent. Many nucleophile group are present on bases of deoxyribonucleic acid (DNA), which react with electrophilic group. N-7 of guanine is the common site, which contains nucleophile group.
N-7 of guanine contain two lone pair of electrons. The alkyl group of alkylating agent binds with a lone pair of electrons of N-7 guanine and form strong covalent bond. It prevents the further base pairing of guanine with cytosine. This results in break in single strand of DNA. Further same changes can occur on the complementary strand of DNA.
The alkylating halides with two alkylating group react with base to cross link the strands. It disrupts the base sequence so that the replication and transcription of the DNA strand is prevented. If the two nucleophile groups are present on the same strand of DNA, then two alkyl group attaches and form limpet in the DNA strand. This alkylated portion becomes resistant to the enzymes of replication and translation, resulting in cell death.