Full details of the concise and convergent synthesis (eight steps, 19% overall yield), its extension to the preparation of a series of key analogues, and the molecular target and pharmacophore of largazole are described. Central to the synthesis of largazole is a macrocyclization reaction for formation of the strained 16-membered depsipeptide core followed by an olefin cross-metathesis reaction for installation of the thioester. The biological evaluation of largazole and its key analogues, including an acetyl analogue, a thiol analogue, and a hydroxyl analogue, suggested that histone deacetylases (HDACs) are molecular targets of largazole and largazole is a class I HDAC inhibitor. In addition, structure-activity relationship (SAR) studies revealed that the thiol group is the pharmacophore of the natural product. Largazole's HDAC inhibitory activity correlates with its antiproliferative activity.

Histone deacetylases (HDACs) are validated targets for anticancer therapy as attested by the approval of suberoylanilide hydroxamic acid (SAHA) and romidepsin (FK228) for treating cutaneous T cell lymphoma. We recently described the bioassay-guided isolation, structure determination, synthesis, and target identification of largazole, a marine-derived antiproliferative natural product that is a prodrug that releases a potent HDAC inhibitor, largazole thiol. Here, we characterize the anticancer activity of largazole by using in vitro and in vivo cancer models. Screening against the National Cancer Institute's 60 cell lines revealed that largazole is particularly active against several colon cancer cell types. Consequently, we tested largazole, along with several synthetic analogs, for HDAC inhibition in human HCT116 colon cancer cells. Enzyme inhibition strongly correlated with the growth inhibitory effects, and differential activity of largazole analogs was rationalized by molecular docking to an HDAC1 homology model. Comparative genomewide transcript profiling revealed a close overlap of genes that are regulated by largazole, FK228, and SAHA. Several of these genes can be related to largazole's ability to induce cell cycle arrest and apoptosis. Stability studies suggested reasonable bioavailability of the active species, largazole thiol. We established that largazole inhibits HDACs in tumor tissue in vivo by using a human HCT116 xenograft mouse model. Largazole strongly stimulated histone hyperacetylation in the tumor, showed efficacy in inhibiting tumor growth, and induced apoptosis in the tumor. This effect probably is mediated by the modulation of levels of cell cycle regulators, antagonism of the AKT pathway through insulin receptor substrate 1 down-regulation, and reduction of epidermal growth factor receptor levels.

The development of an enantioselective allylic alcohol dichlorination catalyzed by dimeric cinchona alkaloid derivatives and employing aryl iododichlorides as chlorine sources is reported. Reaction optimization, exploration of the substrate scope, and a model for stereoinduction are presented.