Synthesis of Oligonucleotides containing the cis-Interstrand Crosslink Produced by Mitomycins in their Reaction with DNA.

Mitomycin C (MC) an antitumor drug and decarbamoylmitomycin C (DMC), a derivative of MC lacking the carbamoyl moiety, are DNA alkylating agents which can form DNA interstrand crosslinks (ICLs) between deoxyguanosine residues located on opposing DNA strands. MC forms primarily deoxyguanosine adducts with a 1"-R stereochemistry at the guanine-mitosene bond (1"-α, trans) whereas DMC forms mainly adducts with a 1"-S stereochemistry (1"-β, cis). The crosslinking reaction is diastereospecific: trans-crosslinks are formed exclusively at CpG sequences, while cis-crosslinks are formed only at GpC sequences. Until now, oligonucleotides containing 1"-β-deoxyguanosine adducts or ICL at a specific site could not be synthesized, thus limiting the investigation of the role played by the stereochemical configuration at C1'' in the toxicity of these compounds. Here, a novel biomimetic synthesis to access these substrates is presented. Structural proof of the adducted oligonucleotides and ICL were provided by enzymatic digestion to nucleosides, high resolution mass spectral analysis, CD spectroscopy and UV melting temperature studies. Finally, a virtual model of the 25-mer 1"-β ICL synthesized was created to explore the conformational space and structural features of the crosslinked duplex.