Synthetic and Chemical Biological Studies of the Diazofluorene Antitumor Antibiot

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DESCRIPTION (provided by applicant): This proposal describes the synthesis and study of the kinamycins and lomaiviticin A, bacterial metabolites with unprecedented structures and powerful biological activities. These isolates are nanomolar inhibitors of human cancers and microbial infections, which are among the public health issues that are central to the mission of the NIH. Lomaiviticin A is active against ovarian cell lines at single-digit picomolar concentrations, and is approximately 2-5 orders of magnitude more potent than any of the kinamycins. Overall, lomaiviticin may be regarded as a dimeric form of the kinamycins, although other structural dissimilarities exist, most notably four 2, 6-dideoxycarbohydrate residues that are found only in lomaiviticin. Common to all of these metabolites is a unique diazofluorene functional group, which has not been seen before in natural products. This functional group has been established as reactive under reducing conditions, but a clear understanding of the role of this reactivity in the observed biological activity of lomaiviticin A has not been developed. The objective of the proposed research is to complete the synthesis of lomaiviticin A and to elucidate the mechanism of action of this natural product. We hypothesize that the diazofluorene functional group is essential to biological activity, and that peripheral substituents can be used to modulate its reactivity. In order to probe this hypothesis, we will complete the synthesis of lomaiviticin A by developing a method for the dimerization of two "monomeric" precursors. A robust dimerization method will facilitate the preparation of simple dimeric diazofluorenes for chemical biological investigations. In parallel with these synthetic studies, we have initiated, and will continue, chemical biological investigations to elucidate the mechanism of action of lomaiviticin A. Evidence to date suggests lomaiviticin A targets DNA by a unique mode of interaction. Therefore we will focus our efforts on understanding the interaction of lomaiviticin and related analogs with DNA. Additionally, we will seek to understand the influence of substituent effects on the reactivity of the diazofluorene, with the goal of identifying easily-prepared, diazofluorene-based anticancer agents. To achieve this, we will conduct structure-function studies and probe the interaction of our synthetic constructs, and the natural product, with DNA. We expect that our research will enable efficient access to this entire family of natural products and related diazofluorenes, thereby overcoming the synthetic obstacles that have hindered the study of these natural products. These synthetic studies are complemented by our chemical biological investigations, which are aimed at developing a lucid understanding of the mechanism of action of lomaiviticin. These are important contributions that will provide the foundation for detailed evaluation of these natural products as new treatments for cancers and bacterial infections.