The DNA phosphate backbone is not involved in catalysis of the duocarmycin and CC-1065 DNA alkylation reaction.

The rates of DNA alkylation were established for the reaction of (+)-duocarmycin SA (1) with the native duplex d(G(1)TCAATTAGTC(11))*d(G(12)ACTAATTGAC(22)), an 11 bp deoxyoligonucleotide that contains a single high-affinity alkylation site that has been structurally characterized at exquisite resolution, and modified duplexes in which the four backbone phosphates proximal to the C4 carbonyl of bound 1 were replaced with methylphosphonates. All were found to react at comparable rates establishing that these backbone phosphates do not participate in catalysis of the DNA alkylation reaction.