Divergent total synthesis of the revised structures of marine anti-cancer meroterpenoids (+)-dysiherbols A-E.

We report here a concise and divergent enantioselective total synthesis of the revised structures of marine anti-cancer sesquiterpene hydroquinone meroterpenoids (+)-dysiherbols A-E (6-10) using dimethyl predysiherbol 14 as a key common intermediate. Two different improved syntheses of dimethyl predysiherbol 14 were elaborated, one starting from Wieland-Miescher ketone derivative 21, which is regio- and diastereoselectively α-benzylated prior to establishing the 6/6/5/6-fused tetracyclic core structure through intramolecular Heck reaction. The second approach exploits an enantioselective 1,4-addition and a Au-catalyzed double cyclization to build-up the core ring system. (+)-Dysiherbol A (6) was prepared from dimethyl predysiherbol 14via direct cyclization, while (+)-dysiherbol E (10) was synthesized through allylic oxidation and subsequent cyclization of 14. Epoxidation of 14 afforded allylic alcohol 45 or unexpectedly rearranged homoallylic alcohol 44. By inverting the configuration of the hydroxy groups, exploiting a reversible 1,2-methyl shift and selectively trapping one of the intermediate carbenium ions through oxy-cyclization, we succeeded to complete the total synthesis of (+)-dysiherbols B-D (7-9). The total synthesis of (+)-dysiherbols A-E (6-10) was accomplished in a divergent manner starting from dimethyl predysiherbol 14, which led to the revision of their originally proposed structures.

Total Synthesis of Anti-Cancer Meroterpenoids Dysideanone†B and Dysiherbol†A and Structural Reassignment of Dysiherbol†A.

The first total synthesis of marine anti-cancer meroterpenoids dysideanone B and dysiherbol A have been accomplished in a divergent way. The synthetic route features: 1) a site and stereoselective α-position alkylation of a Wieland-Miescher ketone derivative with a bulky benzyl bromide to join the terpene and aromatic moieties together and set the stage for subsequent cyclization reactions; 2) an intramolecular radical cyclization to construct the 6/6/6/6-tetracycle of dysideanone B and an intramolecular Heck reaction to forge the 6/6/5/6-fused core structure of dysiherbol A. A late-stage introduction of the ethoxy group in dysideanone B reveals that this group might come from the solvent ethanol. The structure of dysiherbol A has been revised based on our chemical total synthesis.

Syntheses and anti-pancreatic cancer activities of rakicidin A analogues.

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignant tumor and resistant to most therapies. Pancreatic cancer stem cells (PCSCs) had critical role in regulating PDAC progression, metastasis, and drug resistance. Therefore, targeting PCSCs is considered to be a promising strategy for treatment of PDAC. However, there is no effective drug that can selectively ablate PCSCs. A series of twenty rakicidin A analogues were synthesized via a combinatorial strategy and evaluated for their anti-PDAC activities, and the structure-activity relationship was also discussed. Compound 32g was prepared in 14 linear steps with 5.05% overall yield, which is much more efficient than our previously reported total synthesis of rakicidin A (19 linear steps with 0.19% yield). In a highly metastatic pancreatic cancer cell line ASPC-1, compound 32g showed about 4 times higher potency (IC50 = 0.022 µM) than rakicidin A (IC50 = 0.082 µM) at hypoxia condition, and 12 folds of hypoxia selectivity (IC50 = 0.27 µM at nomoxia condition). In contrast, the activity of adriamycin in the same hypoxic condition decreased. The percentage of PCSCs (with CD24+CD44+ESA+ biomarker), activity of ALDH, and the number of tumorspheres in PANC-1 cells were greatly reduced after treatment of 32g. More importantly, the tumor-initiating frequency was reduced by 19 folds after the treatment of 32g, which is better than that of rakicidin A (reduction of 4.7 folds).

Cyclic Depsipeptide BE-43547A2 : Synthesis and Activity against Pancreatic Cancer Stem Cells.

Asymmetric total synthesis of the cyclic depsipeptide BE-43547A2 was achieved in 15 linear steps on a 350 mg scale in one batch. The synthesis features the highly diastereoselective construction of an α-hydroxy-ß-ketoamide through α-hydroxylation with a d.r. of up to 86:1. BE-43547A2 significantly reduces the percentage of pancreatic cancer stem cells (PCSCs) in Panc-1 cell cultures, and dramatically reduces the tumorsphere-forming capability of Panc-1 cells. An in vivo tumor-initiation assay, a gold standard for cancer stem cell assays, confirmed that BE-43547A2 can abolish the tumorigenesis of Panc-1 cells. The anti-PCSC activity of BE-43547A2 could make this depsipeptide scaffold a promising starting point for discovering new PCSC-targeting drugs.

Sulforaphane Analogues with Heterocyclic Moieties: Syntheses and Inhibitory Activities against Cancer Cell Lines.

Recent studies have shown that sulforaphane (SFN) selectively inhibits the growth of ALDH⁺ breast cancer stem-like cells.Herein, a series of SFN analogues were synthesized and evaluated against breast cancer cell lines MCF-7 and SUM-159, and the leukemia stem cell-like cell line KG-1a. These SFN analogues were characterized by the replacement of the methyl group with heterocyclic moieties, and the replacement of the sulfoxide group with sulfide or sulfone. A growth inhibitory assay indicated that the tetrazole analogs 3d, 8d and 9d were significantly more potent than SFN against the three cancer cell lines. Compound 14c, the water soluble derivative of tetrazole sulfide 3d, demonstrated higher potency against KG-1a cell line than 3d. SFN, 3d and 14c significantly induced the activation of caspase-3, and reduced the ALDH⁺ subpopulation in the SUM159 cell line, while the marketed drug doxrubicin(DOX) increased the ALDH⁺ subpopulation.

Ardisiphenol D, a resorcinol derivative identified from Ardisia brevicaulis, exerts antitumor effect through inducing apoptosis in human non-small-cell lung cancer A549 cells.

CONTEXT: The in vitro and in vivo antitumor activities of ardisiphenol D, a natural product isolated from the roots of Ardisa brevicaulis Diels (Myrsinaceae), have been studied. OBJECTIVE: Previously, we have isolated and identified some chemical constituents from this plant. Furthermore, these compounds showed significant inhibition of the proliferation of human pancreatic PANC-1, human lung A549, human gastrointestinal carcinoma SGC 7901, human breast MCF-7, and human prostate PC-3 cancer cells. In the present paper, a major resorcinol derivative called ardisiphenol D was further studied for its antitumor mechanism. MATERIALS AND METHODS: MTT assay was used to detect the proliferation of A549 cancer cells. Apoptosis induced by ardisiphenol D was observed by Hoechst 33258 fluorescence staining. Caspase-3 enzyme activity was measured by a commercial caspase-3 enzyme activity detection kit. Protein expression of bax, bcl-2, and caspase-3 was tested by Western blots. In vivo antitumor activity of ardisiphenol D was evaluated by determination of A549 tumor growth in nude mice. RESULTS: Ardisiphenol D significantly inhibited the proliferation of A549 cells with an IC50 of 0.997 µM with a 48 h treatment. Hoechst 33258 fluorescence staining results indicated the apoptosis of A549 cells induced by 3.125 µM of ardisiphenol D. About 0.39 and 0.78 µM of ardisiphenol D also potently increased the caspase-3 enzyme activity in 24 h. Furthermore, 0.39-3.125 µM of ardisiphenol D induced the activation of caspase-3 protein and the up-regulation of the ratio of bax/bcl-2 protein expression in A549 cells. After i.p. injection, ardisiphenol D (5 mg/kg) also strongly suppressed the A549 tumor growth in nude mice. DISCUSSION AND CONCLUSION: Ardisiphenol D induced apoptosis of A549 cells via activation of caspase-3 and up-regulation of the ratio of bax/bcl-2 protein expression. Ardisiphenol D also strongly suppressed the A549 tumor growth in nude mice and exerted antitumor activity in vivo.