STRUCTURAL CHARACTERIZATION OF THE 1 1 ADDUCT FORMED BETWEEN THE ANTITUMOR ANTIBIOTIC HEDAMYCIN AND THE OLIGONUCLEOTIDE DUPLEX D(CACGTG)(2)BY 2D NMR-SPECTROSCOPY/

2D NMR spectroscopic methods-have been used to determine the structure of the adduct formed between the antitumor antibiotic hedamycin and t he oligodeoxyribonucleotide duplex d(CACGTG)(2), Evidence for both int ercalation and alkylation in the adduct was observed, and a model for the binding interaction was constructed based on intermolecular NOEs a nd distance-restrained molecular dynamics, In our computationally refi ned model, the anthrapyrantrione chromophore of hedamycin is intercala ted between the 5'-CG-3' bases with the two aminosugar groups placed i n the minor groove and the six carbon bisepoxide side chain located in the major groove. The anglosamine sugar attached at C8 is oriented in the 3' direction relative to the intercalation site, while the N,N-di methylvancosamine attached at C10 is oriented to the 5' side, with eac h aminosugar wedged between a guanine exocyclic amino group and one of the groove walls, The terminal epoxide carbon C18 is covalently bound to the N7 atom of the central guanine, as evidenced by lability of th e C8 hydrogen of this purine upon reaction with hedamycin, Our binding model places the C10-attached N,N-dimethylvancosamine of hedamycin in van der Waals contact with the alkylated strand, A strong NOE contact verifies the close proximity of the terminal methyl group (C19) of th e bisepoxide side chain to the methyl group of the thymine on the 3' s ide of the alkylated guanine. This, in conjunction with other data, su ggests hydrophobic interactions between the bisepoxide chain and the f loor of the major groove may contribute to sequence recognition, Furth ermore, it is proposed that the 5'-CGT sequence selectivity of hedamyc in arises, in part, from complementarity in shape between the chromoph ore substituents and the major and minor groove at the binding site.