The salicylihalamides A and B, isolated from an Australian collection of a sponge from the genus Haliclona, are extremely promising novel cytotoxic agents. They are structurally novel 12-membered salicylate macrolides, carrying an unusual unsaturated enamide side chain at C15. Salicylihalamide A showed potent cytotoxicity at nanomolar concentrations and significant differential cytotoxicity (greater than l0/3). The melanoma cell lines showed the highest subpanel sensitivity (average G150 7+ -2 nM). A most exciting finding is the fact that the salicylihalamides apparently act by an unknown, new mechanism of action, as predicted by COMPARE pattern analysis of the mean graph profiles from the NCI's 60-cancer cell line assay. The discovery of the potent and highly selective salicylihalamides, possessing most likely a novel mechanism of action is, thus, a very promising starting point for the potential development of a new class of anticancer agents. In this proposal, we are detailing approaches toward the total synthesis of the salicylihalamides and their analogues. It is the goal of this project to carry out structure-activity studies and to elucidate the salicyliha1amide pharmacophore. Studies will also be directed at finding analogues that have greater chemical stability than the parent compounds. Another goal of this study is the preparation of salicylihalamide affinity labels, to be used to study, in detail, the interactions between the salicylihalamides and their biological target. The testing of the analogues and the affinity labeling studies will be carried out in collaboration with investigators at the National Cancer Institute.
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