Purity >98%. O6 -Alkylguanine-DNA alkyltransferase (AGT, also known as methylguanine DNA methyltransferase, or MGMT) is a DNA repair protein that directly removes alkyl groups located on the O6 -position of guanine from DNA, restoring DNA integrity in a single step. In the process, AGT is alkylated and irreversibly inactivated. O6 -Benzylguanine is a guanine analog with antineoplastic activity. It serves as a pseudosubstrate for AGT, transferring a benzyl moiety to the active site cysteine of the enzyme. This leads to irreversible inactivation, with 40% reduction in alkyltransferase activity of recombinant human AGT achieved at 0.06 μM. O6 -Benzylguanine is effective in vivo as well as in vitro . Inactivation of AGT increases the chemotherapeutic effectiveness of chloroethylating and methylating agents.