Synthesis of the cis-fused hexahydroxanthene system via cationic cascade cyclization

Synthesis and structure activity relationships of schweinfurthin indoles

As part of a program to explore the biological activity of analogues of the natural schweinfurthins, a set of compounds has been prepared where an indole system can be viewed as a substitution for the resorcinol substructure of the schweinfurthin's D-ring. Twelve of these schweinfurthin indoles have been prepared and evaluated in the 60 cell line screen of the National Cancer Institute. While a range of activity has been observed, it is now clear that schweinfurthin indoles can demonstrate the intriguing pattern of activity associated with the natural stilbenes. In the best cases, these indole analogues display both potency and differential activity across the various cell lines comparable to the best resorcinol analogues.

Synthesis of a dicyano abietane, a key intermediate for the anti-inflammatory agent TBE-31

The synthesis of dicyano abietane 11, a potential precursor to the biologically active tricyclic bis-cyano enone 6 (TBE-31), was accomplished in eight steps from epoxide 13. The synthesis features a Lewis acid promoted stereoselective cyclization of epoxide 13 to generate the tricyclic ring system 12 in one step.

Electrophilic aromatic prenylation via cascade cyclization

To gain access to prenylated hexahydroxanthenes, tandem cascade cyclization-electrophilic aromatic substitution reactions have been studied on substrates bearing allylic and propargylic substituents. Both BF₃·OEt₂ and TMSOTf can be used to initiate this reaction sequence, resulting in different ratios of the C-2 and C-6 substitution products. Even though allylic transposition is observed in some cases, the results of a crossover experiment are consistent with an intramolecular reaction sequence. Taken together, these studies now allow preparation of either the C-2 or C-6 prenylated hexahydroxanthene products.

Relevance of the C-5 position to schweinfurthin induced cytotoxicity

The schweinfurthins are an intriguing group of anti-proliferative agents that display low nanomolar activities against several cell types, including the human-derived glioblastoma cell line SF-295, but have little impact on other cell lines even at micromolar concentrations. This activity has inspired the synthesis of seven of the natural schweinfurthins, all with the correct absolute stereochemistry, and a variety of analogues designed to probe different facets of the pharmacophore. Reported herein is the synthesis of several new schweinfurthin analogues varied at the C-5 position along with data on their biological activity in the NCI 60 cell-line assay.

First total synthesis of (+)-Vedelianin, a potent antiproliferative agent

The total synthesis of (+)-vedelianin has been accomplished in 18 steps from vanillin. Preparation of a key intermediate in nonracemic form through a Shi epoxidation has allowed determination of the absolute stereochemistry of the natural product as the (2S, 3R, 4aR, 9aR)-isomer.

Exploration of cascade cyclizations terminated by tandem aromatic substitution: total synthesis of (+)-schweinfurthin A

The termination of epoxide-initiated cascade cyclizations with a range of "protected" phenols is described. When the protecting group can be lost as a stabilized electrophile, the cascade process continues beyond ring closure to afford products which have undergone a tandem electrophilic aromatic substitution. A number of groups have proven viable in this process and the regiochemistry of their substitution reactions has been studied. Application of this methodology in the first total synthesis of (+)-schweinfurthin A, a potent antiproliferative agent, has been achieved.

Fluorescent schweinfurthin B and F analogs with anti-proliferative activity

The natural tetracyclic schweinfurthins are potent and selective inhibitors of cell growth in the National Cancer Institute's 60 cell-line screen. At this time, the mechanism or cellular target that underlies this activity has not yet been identified, and efforts to illuminate the schweinfurthins' mode of action would benefit from development of potent fluorescent analogs that could be readily visualized within cells. This report describes the synthesis of fluorescent analogs of schweinfurthins B and F, and demonstrates that these compounds retain the potent and differentially toxic activities against select human cancer cells that are characteristic of the natural schweinfurthins. In addition, the synthesis of control compounds that maintain parallel fluorescent properties, but lack the potent activity of the natural schweinfurthin is described. Use of fluorescence microscopy shows differences between the localization of the active and relatively inactive schweinfurthin analogs. The active compounds localize in peripheral puncta which may identify the site(s) of activity.