The 2,6-diaryl-3,7-dioxabicyclo[3,3,0]octanes (or furofurans) belong to the lignan family of natural products. Lignans represent very attractive synthetic targets owing to their large range of biological properties including anticancer, antiviral and immunosuppressant activities. There is considerable structural variation in this series in both the nature and the stereochemistry of the aryl substituents. Since activity is dependent on stereochemistry, synthetic routes, which can provide controlled but tuneable access to one particular class, are very attractive. In this respect, we have been interested in developing efficient ways to synthesise the furofuran skeleton. Based on previous work in our group, the first synthesis of a natural endo-endo furofuran, Epiasarinin, has been achieved via a five step strategy. It included a Darzens condensation followed by a thermal rearrangement of vinyl epoxide to cis dihydrofuran, a Lewis acid promoted cyclisation of a dihydrofuryl alcohol and a reduction of a glycosidic bond. Variations of this methodology afforded the selective the thermal rearrangement has been explored and improvement of this step via different activation methods considered. Another aim of this thesis was to extend this existing method to generate aza analogues. Two strategies have been explored. Generation of furopyrroles can be achieved via the thermal rearrangement of vinyl aziridines or via the acid catalysed cyclisation of dihydrofuryl amines. In conclusion, this short and selective synthetic route leads to a large range of natural or unnatural furofurans and the extension to their aza analogues was also explored.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 186-200).

by Mabel Siu-Man Yuen. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (p. 146-161). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

Natural Health Products (NHPs) are regulated and require safety and efficacy information for their approval into the Canadian market. Flaxseed lignans are NHPs with putative health benefits in a number of chronic diseases. In the flaxseed the principal lignan is secoisolariciresinol diglucoside (SDG). After oral consumption SDG is converted into its aglycone secoisolarisiresinol (SECO) and subsequently into mammalian lignans (enterodiol (ED) and enterolactone (EL)) in the presence of gastrointestinal microflora. In my Ph.D. research, I conducted a series of in vitro and in vivo PK studies to enable the design of prospective safety and efficacy studies of lignans. In vitro PK studies in the Caco-2 cell monolayer suggest that SDG has poor intestinal permeation and intestinal conjugation characteristics (glucuronidation and sulphation); however, SECO, ED and EL undergo passive permeation and extensive conjugation (SECO<ED<EL) by Caco-2 cells. Single oral and intravenous dose pharmacokinetics in male Wistar rats showed that these lignans exhibit high volumes of distribution, high systemic clearance values, and short half-lives. EL was fatal to the rats at the given intravenous and oral doses while SDG was not orally bioavailable and may not likely be the bioactive lignan form. I investigated the effect of acute SDG and chronic BeneFlax oral administration in blunting the postprandial hyperglycemia in healthy and streptozotocin induced male Wistar type II diabetic rats, respectively; however, my pilot study failed to show any change in postprandial blood glucose levels. Further, I conducted selective cytotoxicity evaluations in prostate and breast cancer cell lines. Only EL caused selective cytotoxicity of breast and prostate cancer cells with IC50 values that may be physiologically achievable. To elucidate the mechanism of action, I tested concentration and time dependent effects of EL on various enzymes and transcription factors of fatty acid metabolism at mRNA and protein levels in cancer (PC-3) and normal (RWPE-1) prostate cell lines. mRNA and protein expression analysis showed a concentration and time dependent inhibition of fatty acid synthase (FAS) and suggested that EL may inhibit FAS to show anti-proliferative effect on prostate cancer. The pharmacokinetic characteristics and pharmacodynamics properties of flaxseed lignans warrant their further investigation.

Previous work on the biosynthesis of mycophenolic acid is discussed. [1’-¹⁴C]-Orsellinic acid (22) and [1'-¹⁴C]-2,4-dihydroxy-5,6-dimethylbenzoic acid (23) were synthesized and administered to Penicillium brevi-compactum. The purpose of feeding these two acids was to determine the order or sequence of the reactions involved in the biosynthesis of mycophenolic acid. It was found that acid (22) was not incorporated into mycophenolic acid but that acid (23) was incorporated specifically to the extent of 11.5%. Degradation of the mycophenolic acid from the feeding of (23) showed that a completely specific incorporation had occurred and thus supported the role of this acid (23) as a precursor of mycophenolic acid. [1- ¹⁴C]-geraniol (24) was also fed in an attempt to determine the origin of the C₇ side chain of mycophenolic acid. (24) was incorporated but degradation of the mycophenolic acid showed that the geraniol was decomposed to acetate before incorporation, leaving the precursor status in doubt. Three attempts were made to synthesize mycophenolic acid using suspected biological intermediates with no success. This was presumably due to the difficulty encountered in trying to alkylate the aromatic skeleton of mycophenolic acid. A synthesis of lignans involving intramolecular phenolic oxidative coupling was attempted with little success, due to the inability to obtain the ester required to couple to give the lignan skeleton. / Science, Faculty of / Chemistry, Department of / Graduate

The vinylepoxide-diliydrofuran rearrangement offers a route to substituted 2,3- dihydrofurans with a high degree of diastereoselectivity. The rearrangement proceeds via an ylide-type intermediate arising from the thermolysis of a carbon-carbon epoxide bond. This thesis discusses work aimed at developing the rearrangement, introducing asymmetric control, and application of the dihydrofuran products in target molecule synthesis. Synthesis of the vinylepoxide rearrangement precursors is described, and development of the rearrangement to achieve a moderate scale rearrangement process is discussed. Alternative rearrangement technologies are also explored. Asymmetric induction into the rearrangement was approached by the use of chiral auxiliaries and in particular C2 symmetric amines. A novel synthesis of (S,S)-2,5-diphenylpyrrolidine and (S,S)-2,6-diphenylpiperidine is reported. High degrees of enantiomeric purity were achieved through the application of an effective oxazaborolidine catalyst in the reduction of dibenzoylethane and dibenzoylpropane. Use of this chiral reduction catalyst on further diketones is described. Application of the dihydrofuran products in the synthesis of several 2,6-disubstituted- 3,7-dioxabicyclo[3.3.0]octanes. These compounds, commonly termed furofuran lignans exhibit a wide range of biological properties. The dihydrofuran products were combined with a range of dimethylacetals, in a one pot synthesis, with high degrees of stereocontrol, by a Noyori type transacetalisation. Further derivatisation of these bicyclic compounds was accomplished and is discussed.Finally, with the vinylepoxide - dihydrofuran rearrangement established a preliminary exploration of the related vinylaziridine - 2-pyrroline rearrangement is reported.

Thesis (Ph. D.)--Washington State University, December 2008. / Title from PDF title page (viewed on July 10, 2009). "School of Molecular Biosciences." Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 223-236).

Thesis (Ph.D.)--Kent State University, 2007. / Title from PDF t.p. (viewed July 8, 2009). Advisor: Angelo L. DeLucia. Keywords: human papilloma virus, mammalian lignans, p53, E6 oncogene. Includes bibliographical references (p. 133-149).

Podophyllotoxin is an aryltetralin lignan and anticancer agent produced by the <i>Podophyllum</i> and some other species and is extracted from Podophyllin in up to 30 percent yield. Little definitive information is available on the biosynthetic pathways to podophyllotoxin. Administering various specifically labelled precursors into intact plants and tissue cultures can give a much improved insight into the lignan biogenesis. The first part of the work has been to the synthesis of two diastereotopically labelled with ²H at C-4. Desoxypodophyllotoxin is the penultimate intermediate of the podophyllotoxin pathway and specifically labelled compounds can be used for the C-4 hydroxylation studies. Doubly ²H labelled desoxypodophyllotoxin at C-4 was also prepared which can be used for a control experiment. This work also led to the unambiguous assignment of the proton nmr of desoxypodophyllotoxin. A second part of the work has been the synthesis of p-coumarlc acid, a known lignan precursor, doubly labeled with ²H or ²H and ¹³C at the C-3â position. This labeling was selected because the availability of a C-3-labeled monomeric precursor would thus make possible the isolation and study of dimeric compounds labeled at this key positions. These compounds were synthesized, and their identity and stereochemistry were determined by spectroscopic and analytical techniques. The isotopic incorporation of these compounds was 95% d, or d₂ (or greater), as determined by mass spectral analysis. / Master of Science