Reassignment of the guanine-binding mode of reduced mitomycin C

Mitomycin C (1) is a clinically used antitumor antibiotic that binds covalently to deoxyribonucleic acid under reductive or acidic catalysis. We have determined the structures of the adducts resulting from attack of reductively activated 1 on the dinucleoside phosphate d(GpC) to be N2-(2'' beta, 7''-diaminomitosen-1''alpha-yl)-2'-deoxyguanosine (2) and its 1'' beta-isomer (3). This represents a revision of the previously reported structures for these adducts in that the mitomycin residue is linked to the N2- rather than O6-position of 2'-deoxyguanosine. This revision is the result of applying to the mitomycin case a newly developed general method that leads to unambiguous assignment of the linkage position in complex alkylated guanosines. The method as described here takes advantage of the resolution enhancement gained by calculation of the second derivatives of absorbance Fourier transform infrared spectra. In addition, we present 1H NMR data that corroborate the assigned structures of 2 and 3 and that should serve as a useful reference for future investigations into the binding of mitomycin C to DNA. The convenient synthesis of adducts 2 and 3 from deoxyguanosine and mitomycin C reported here should facilitate such investigations as well. Furthermore, we demonstrate a useful acetylation procedure for adducts and metabolites of mitomycin C that furnishes spectroscopically superior chemical derivatives (e.g., triacetates 4 and 5, derived from acetylation of adducts 2 and 3).