A Pd-catalysed amination method is used to convert seco-CBI, a synthetic analogue of the alkylating subunit of the duocarmycin natural products, from the phenol to amino form. This allows efficient enantioselective access to the more potent S enantiomer of aminoCBI and its incorporation into analogues of DNA minor groove cross-linking agents. Evaluation in a panel of nine human tumour cell lines shows that the bifunctional agents containing aminoCBI are generally less cytotoxic than their phenolCBI analogues and more susceptible to P-glycoprotein-mediated resistance. However, all bifunctional agents are potent cytotoxins, some in the sub-pM IC50 range, with in vitro properties that compare favourably with established microtubule-targeted ADC payloads.
Keywords: AminoCBI; Antibody–drug conjugate; DNA cross-linking agent; Duocarmycin; Pyrrolobenzodiazepine.
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