Synthesis of R-(-)-imperanene from the natural lignan hydroxymatairesinol

Design of 92 New 9-Norlignan Derivatives and Their Effect on Cell Viabilities of Cancer and Insect Cells

Ninety-two new 9-norlignan derivatives containing more effective compounds against both cancer and insect cells than lead compounds were synthesized. Against HeLa cells, 7-(3,4-dimethoxyphenyl)-7'-(3'-hydroxy-4'-methoxyphenyl) derivative 63 (IC₅₀ = 0.9 ± 0.2 μM) was to be around 6-fold more potent than lead compound 5. Moreover, against HL-60 cells, 7-(4-trifluoromethylphenyl)-7'-(3'/4'-hydroxyphenyl) derivatives 78 and 79 (IC₅₀ = 2.2 ± 0.4 μM and 2.4 ± 0.6 μM) were 3-fold more potent than lead compound 5. Furthermore, against Sf9 cells from the common cutworm, the 7-(4-trifluoromethylphenyl) derivatives bearing electron-withdrawing groups 76-96 showed a wider range of activity (around 20-fold difference), giving valuable information on the structure-activity relationship. The 7-(4-trifluoromethylphenyl)-7'-(2'/3'-hydroxyphenyl) derivatives 77 and 78 (IC₅₀ = 4.7 ± 0.6 μM and 4.9 ± 0.9 μM) had around 2-fold higher activity against Sf9 cells than lead compound 5. The 7-(4-trifluoromethylphenyl)-7'-(3'-hydroxyphenyl) derivative 78 was also effective against mosquito NIAS-AcAl-2 cells with an IC₅₀ value of 5.4 ± 0.3.

9-Norlignans: Occurrence, Properties and Their Semisynthetic Preparation from Hydroxymatairesinol

Lignans, neolignans, norlignans and norneolignans constitute a large class of phenolic natural compounds. 9-Norlignans, here defined to contain a β⁻β' bond between the two phenylpropanoid units and to lack carbon number 9 from the parent lignan structure, are the most rarely occurring compounds within this class of natural compounds. We present here an overview of the structure, occurrence and biological activity of thirty-five 9-norlignans reported in the literature to date. In addition, we report the semisynthetic preparation of sixteen 9-norlignans using the natural lignan hydroxymatairesinol obtained from spruce knots, as starting material. 9-Norlignans are shown to exist in different species and to have various biological activities, and they may therefore serve as lead compounds for example for the development of anticancer agents. Hydroxymatairesinol is shown to be a readily available starting material for the preparation of norlignans of the imperanene, vitrofolal and noralashinol family.

Enantioselective syntheses of both enantiomers of 9'-dehydroxyimperanene and 7,8-dihydro-9'-dehydroxyimperanene and the comparison of biological activity between 9-norlignans and dihydroguaiaretic acids

To estimate the effect of methyl group of dihydroguaiaretic acid, which shows many kinds of biological activities, on biological activity, both enantiomers of 9'-dehydroxyimperanene (5, 6) and 7,8-dihydro-9'-dehydroxyimperanene (7, 8) lacking one of the methyl groups of dihydroguaiaretic acid were synthesized. (S)-7,8-Dihydro-9'-dehydroxyimperanene (7) showed 4-6-fold higher cytotoxic activity than all stereoisomers of dihydroguaiaretic acid (2-4). The IC50 values of (S)-7,8-dihydro-9'-dehydroxyimperanene (7) against HL-60 and HeLa cells were 6.1μM and 5.6μM, respectively. Though only one of three stereoisomers of dihydroguaiaretic acid showed antibacterial activity against a gram negative bacterium, both enantiomers of 5-8 showed antibacterial activity against a gram negative bacterium. This is a Letter on biological activity of 9-norlignan, in which one of methyl groups of lignan is absent.

The antitumor lignan Nortrachelogenin sensitizes prostate cancer cells to TRAIL-induced cell death by inhibition of the Akt pathway and growth factor signaling

Prostate cancer cells frequently develop resistance toward androgen-deprivation and chemotherapy. To identify new approaches to treat androgen-dependent prostate cancer, we have performed a structure-activity analysis of lignan polyphenols for cancer cell specific sensitization to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a death ligand that has ability to induce tumor-specific cell death. In this study, we report that the lignan nortrachelogenin (NTG) is the most efficient of the 27 tested lignan compounds in sensitizing prostate cancer cells to TRAIL-induced apoptosis. Importantly, pretreatment with NTG does not sensitize a non-malignant prostate cell line to TRAIL-induced cell death. The structural comparison of lignans reveals that the dibenzylbutyrolactone skeleton is required for the apoptosis-sensitizing activity, while substitutions at the aromatic rings do not seem to play a critical role in this lignan function. Our study also characterizes the cellular effects and molecular mechanisms involved in NTG anticancer activity. We previously reported that specific lignans inhibit the Akt survival-signaling pathway in concert with TRAIL sensitization. While NTG is also shown to be a effective inhibitor of Akt signaling, in this study we further demonstrate that NTG potently inhibits tyrosine kinase (RTK) activation in response to growth factors, such as insulin and insulin-like growth factor I (IGF-I). Our results identify NTG as a novel agent for prostate cancer therapy with ability to inhibit Akt membrane localization and activity as well as the activation of growth factor receptors (GFRs), thereby efficiently synergizing with TRAIL exposure.

The antimicrobial effects of wood-associated polyphenols on food pathogens and spoilage organisms

The antimicrobial effects of the wood-associated polyphenolic compounds pinosylvin, pinosylvin monomethyl ether, astringin, piceatannol, isorhapontin, isorhapontigenin, cycloXMe, dHIMP, ArX, and ArXOH were assessed against both Gram-negative (Salmonella) and Gram-positive bacteria (Listeria monocytogenes, Staphylococcus epidermidis, Staphylococcus aureus) and yeasts (Candida tropicalis, Saccharomyces cerevisiae). Particularly the stilbenes pinosylvin, its monomethyl ether and piceatannol demonstrated a clear antimicrobial activity, which in the case of pinosylvin was present also in food matrices like sauerkraut, gravlax and berry jam, but not in milk. The destabilization of the outer membrane of Gram-negative microorganisms, as well as interactions with the cell membrane, as indicated by the NPN uptake and LIVE/DEAD viability staining experiments, can be one of the specific mechanisms behind the antibacterial action. L. monocytogenes was particularly sensitive to pinosylvin, and this effect was also seen in L. monocytogenes internalized in intestinal Caco2 cells at non-cytotoxic pinosylvin concentrations. In general, the antimicrobial effects of pinosylvin were even more prominent than those of a related stilbene, resveratrol, well known for its various bioactivities. According to our results, pinosylvin could have potential as a natural disinfectant or biocide in some targeted applications.

Chiral recognition of imperanene enantiomers by various cyclodextrins: a capillary electrophoresis and NMR spectroscopy study

The enantiomers of imperanene, a novel polyphenolic compound of Imperata cylindrica (L.), were separated via cyclodextrin-modified capillary electrophoresis. The anionic form of the analyte at pH 9.0 was subject to complexation and enantioseparation CE studies with neutral and charged cyclodextrins. As chiral selectors 27 CDs were applied differing in cavity size, sidechain, degree of substitution (DS) and charge. Three hydroxypropylated and three sulfoalkylated CD preparations provided enantioseparation and the migration order was successfully interpreted in each case in terms of complex mobilities and stability constants. The best enantioresolution (R(S)  = 1.26) was achieved using sulfobutyl-ether-γ-CD (DS ∼4), but it could be enhanced by extensive investigations on dual selector systems. After optimization (CD concentrations and pH) R(S)  = 4.47 was achieved using a 12.5 mM sulfobutyl-ether-γ-CD and 10 mM 6-monodeoxy-6-mono-(3-hydroxy)-propylamino-β-cyclodextrin dual system. The average stoichiometry of the complex was determined with Job's method using NMR-titration and resulted in a 1:1 complex for both (2-hydroxy)propyl-β- and sulfobutyl-ether-γ-CD. Further NMR experiments suggest that the coniferyl moiety of imperanene is involved in the host-guest interaction.

Lignans as food constituents with estrogen and antiestrogen activity

Phytoestrogens are plant-derived food ingredients assumed to contribute to the prevention of hormone-dependent cancers, osteoporosis, cardiovascular disease, and menopausal symptoms. Lignans occur in numerous food plants and various structures; they are common constituents of human diet, and estrogen activity has been assessed for lignan metabolites formed in the mammalian intestine. We examined natural lignans and semisynthetic norlignans for estrogen and antiestrogen activity. A transformed yeast strain (Saccharomyces cerevisiae) expressing the estrogen receptor alpha and a reporter system was applied as test system. Some plant lignans showed estrogen activity while others and the semisynthetic norlignans were moderately active antiestrogens. Docking of lignans to protein models of estrogen receptor alpha in the active and inactive form sustained the results of the yeast estrogen assay and supported the concept of plant lignans as phytoestrogens.

Synthesis of Threo-(±)-9,9-Dibenzoylsecoisolariciresinol and its Isomer

The total synthesis of threo-(±)-9,9-dibenzoylsecoisolariciresinol and its isomer based on two Stobbe reactions as C–C bond-forming steps used a protected vanillin and diethyl; succinate to give the skeleton of lignan, followed by reduction to afford threo- and meso-(±)-secoisolariciresinol Both were treated with benzoyl chloride to obtain the natural product threo-(±)-9,9-dibenzoylsecoisolariciresinol and Its isomer meso-(±)-9,9-dibenzoylsecoisolariciresinol for the first time.

Chromatographic analysis of lignans

Methods and procedures for analysis of lignans in trees and other plants are reviewed. The importance of cautious sample handling and pretreatment procedures to avoid contamination, loss of sample, and unwanted chemical reactions is discussed. Sequential extraction with a non-polar solvent followed by extraction with acetone or ethanol is recommended to separate the lignans from the plant matrix. An additional step of acid, alkaline, or enzymatic hydrolysis may be necessary for some plant matrixes. Flash chromatography is a convenient method for preparative separation and isolation of pure lignans from raw extracts. TLC is very suitable for qualitative screening of extracts and for monitoring of lignan isolation and purification steps. Trimethylsilyl ethers of lignans can be separated and quantified by GC even in the case of complex mixtures of lignans and other polyphenols, and the lignans can be identified by GC-MS in a routine manner. HPLC on reversed-phase columns is especially suited for analysis of lignans and their metabolites in biological matrixes. The recent development of HPLC-electrospray ionisation (ESI)-iontrap MS (MS(n)) and corresponding techniques with high sensitivity and selectivity has proven valuable in lignan analysis. Lignan enantiomers can be separated on chiral HPLC columns.

Screening analyses of pinosylvin stilbenes, resin acids and lignans in Norwegian conifers

The content and distribution of stilbenes and resin acids in Scots pine (Pinus sylvestris) and spruce (Picea abies), sampled in central Norway, have been examined. The contents of pinosylvin stilbenes in pine heartwood/living knots were 0.2-2/2-8 %(w/w). No stilbenes could be detected in spruce (Picea abies). The resin acid contents of pine sapwood/heartwood and knots were 1-4 and 5-10 % (w/w), respectively. Minor amounts of resin acids (<0.2/<0.04 %w/w) were identified in spruce wood/knots. The lignan content in knots of Norwegian spruce was 6.5 % (w/w). Diastereomerically pure hydroxymatairesinol (HMR, 84 % of total lignans) was readily isolated from this source since only minor quantities (2.6 % of total lignans) of the allo-HMR diastereomer was detected. Insignificant amounts of lignans were present in the sapwood. Lignans could not be detected in the sapwood or knots of Norwegian sallow (Salix caprea), birch(Betula pendula) or juniper (Juniperus communis).

Enantioselective Synthesis of Imperanene via Enzymatic Asymmetrization of an Intermediary 1,3-Diol

[reaction: see text] Using a chemoenzymatic synthetic strategy, (S)-imperanene and its (R)-enantiomer has been synthesized from vanillin in nine steps. The key step in the synthesis involves the use of Pseudomonas cepacia lipase (PS-30) to induce asymmetrization of the intermediary prochiral 1,3-diol in >97% ee.

A new lariciresinol-type butyrolactone lignan derived from hydroxymatairesinol and its identification in spruce wood

When the natural lignan hydroxymatairesinol (1) was treated with an alkaline aqueous solution, it partially rearranged to isomeric forms of a lariciresinol-type butyrolactone lignan. The two major diastereomers formed (2 and 3) were isolated by column and medium-pressure chromatography, and their structures were elucidated by MS and NMR techniques. These previously unknown butyrolactone lignans were identified as naturally occurring in spruce knotwood by GC, GC-MS, and HPLC-ESI MS/MS analyses. The formation of isohydroxymatairesinol (2) and epi-isohydroxymatairesinol (3) from hydroxymatairesinol (1), and their detection in rat urine after administration of 1, is discussed.

Reactions of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media: formation and reactivity of a quinone methide intermediate

The chemical properties and synthetic modifications of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media were studied. Hydroxymatairesinol presumably reacts via a quinone methide and a carbonium ion mechanism under basic and acidic conditions, respectively. In these conditions the benzylic hydroxyl group was displaced by nucleophiles yielding new 7-substituted butyrolactone lignans. Reactions in alcoholic basic solutions yielded the 7-alkoxy ethers diastereoselectively. Several previously known lignans as well as new lignans and lignan derivatives were synthesised. The transformations were monitored and the products identified by HPLC-MS and NMR.

Synthesis of novel lysophosphatidylcholine analogues using serine as chiral template

Four novel lysophosphatidylcholine (lysoPC) analogues, (S)-N-stearoyl-O-phosphocholineserine methyl ester [(S)-1a], (R)-1-lyso-2-stearoylamino-2-deoxy-sn-glycero-3-phosphatidylcholine [(R)-2a], (R)-N-stearoyl-O-phosphocholineserine methyl ester [(R)-1b], and (S)-1-lyso-2-stearoylamino-2-deoxy-sn-glycero-3-phosphatidylcholine [(S)-2b], were synthesized starting from serine as a chiral template. These synthetic compounds exhibited greatly enhanced hyphal transition inhibitory activity in Candida as compared to the natural lysoPC.