Synthesis And Biological Activity Study Of Norlignans Arylolefin Dimerizati On Compounds

Lignans are a class of natural products with potent antiviral, antitumor,antioxidant and antiinflammatory properties, and they are widely distributed in theplant kingdom and found in roots, rhizomes, stems, leaves, seeds and fruits. It has beenreported many compounds with phenylpropane units, the basic molecular backbone oflignans, exhibit the similar biological activity as that of lignans. Therefore,methodology for the synthesis of these compounds has been received widespreadinterest.In this study, we have developed novel methodologies for dimerization of styrenesto1,3-diaryl-1-butenes, the basic molecular backbone of norlignans, and investigatedtheir biological assay.1,3-diaryl-1-butenes are generally prepared by dimerization ofstyrene derivatives via transition-metal catalysts or Br nsted acid catalysts. ButBr nsted acid catalytic dimerization of styrenes affords the mixtures of E, Z-isomersand subsequent byproducts in moderate yield such as indan derivatives or higheroligomers through carbocation process. Although many potent and selectivetransition-metal catalysts have been developed, the limited availability of these metalsas well as their high price and significant toxicity restricts their large-scaleapplications of this reaction. Therefore, we hope to develop novel and multiple catalystsystems for such type of dimerization.First, we have developed dimerization of styrenes (-asarone based compunds)proceeded by a novel catalyst system of Mn(II)/Co(II)/O2combined with alkylphenylphosphinate, PhP(O)HOR. We next have investigated the optimizedexperimental conditions and a series of stereoselective E-dimer of styrenes basedcompounds have been synthesized. Second, in connection with our previousinvestigation of dimerization of styrenes catalyzed by PhP(O)HOR/Mn(II)/Co(II)/O2,an interesting acid-catalyzed/PhP(O)HOR-promoted dimerization of styrenes hasbeen discovered which involves giving the exclusive E-isomers of head-to-taildimers in excellent yield. The procedure has offered simplicity in operation withregard to facile catalyst system and solvent-free condition. The structure of dimers hasbeen characterized by1H NMR,13C NMR and HPLC-MS. The biological activity ofproducts has been measured by MTT assay using human hepaioma Bel-7402cells,human breast adenocarcinoma MCF-7cells, human lung carcinoma A549cells andhuman cervical carcinoma HeLa cells. The experimental results are as follows: 1. The dimerization of styrenes catalyzed by Mn(II)/Co(II)/PhP(O)HOR/O2Due to the discovered experiment, we have aimed to test the effects of individualcatalytic factor on the reaction. This result has demonstrated that the dimerizationrequires a synergistic relationship between styrenes, alkyl phenylphosphinate andMn(II)/Co(II)/O2redox system. The optimized condition is: the molar ratio of styrenesto PhP(O)HOR=1:3, the molar amount of Mn(II)/Co(II) is5%that of substrate, at90°C for24h under oxygen condition.We have further investigated the influence of styrene-based compounds withdifferent substituents on the scope and limitations of dimerization. It is shown thatsubstrate with electron-donating groups preferred the reaction. And it is found that thepresent dimerization of styrenes would proceed via a radical mechanism involving anaddition–elimination sequence.Taken together, we have found that dimerization of styrenes proceeded by a novelcatalyst system of Mn(II)/Co(II)/O2combined with alkyl phenylphosphinate,PhP(O)HOR, in which PhP(O)HOR acts as a co-catalyst rather than a substrate forhydrophosphorylation of styrenes. Mechanistic studies suggestes the reaction mostlikely proceeded via addition–elimination.2. The dimerization of styrenes catalyzed by H+/PhP(O)HORIt was suggested that a simple synthesis for PhP(O)HOR with hydrochloric acidresidues by the addition of phenyldichlorophosphine to alcohol. Drawing inspirationsfrom dimerization via Br nsted acid catalysts, we have conducted the dimerization ofstyrenes using unpurified PhP(O)HOBu as catalyst and the E-isomer of dimer isexclusively obtained in good yield (95%).Due to the discovered experiment, we have systematically examined individualcatalytic factors. It is shown lack of acid catalysis or acid catalysis in the absence ofPhP(O)HOBu resulted in no or slow reaction, demonstrating acid catalysis makessignificant contribution to this kind of reaction, and PhP(O)HOBu further promotesthe formation of styrene dimer. Meanwhile, in the presence of PhP(O)HOBu, thebyproduct can be completely suppressed under independent acid condition andstereoselective E-dimers have been obtained. The studied dimerization efficientlyoccurs the molar ratio of ratio of styrenes to unpurified PhP(O)HOR=1:3,solvent-free condition and room temperature.We have further investigated the influence of styrene-based compounds withdifferent substituents on the scope and limitations of dimerization. It is shown thatsubstrate with electron-donating groups preferred the reaction. Mechanism study indicates the combined H+/PhP(O)HOR catalyst system plays pivotal dual roles, theformation of carbonium ion intermediate catalyzed by acid and PhP(O)HOR-promotedtertiary hydrogen elimination.In conclusion, we have developed a novel and efficient acid-catalyzed/PhP(O)HOR-promoted styrene dimerization, in which a series of stereoselective E-dimer of substituted styrenes can be synthesized with good yield under mild andsolvent-free condition. Based on the synthesis of PhP(O)HOR with hydrochloricacid residues, H+/PhP(O)HOR is a readily available catalyst system requiringno further purification facilitating to simply reaction procedure.3. Biological activity assay of products and investigation of their anticancermechanismCytotoxicity has been studied by using an MTT assay to identify Bel-7402cells,MCF-7cells, A549cells and HeLa cells still active in respiration. It is shown thatproducts exhibit cytotoxicity to cells; especially,3b treated with Bel-7402cells showslower cytotoxicity (IC50:18.9g/mL) than free paclitaxel (28.0g/mL). In addition,we have analyzed the relationship between structure and activity based on the result ofIC50. It was indicated that a basic backbone with anticancer activity is3f.We have preliminarily investigated anticancer mechanism of products usingBel-7402cells by Hoechst-PI dual staining and flow cytometry method. Fromfluorescent image, it is observed the decreased amount of apoptotic cells, nuclearshrinkage, chromatic condensation, and apoptotic body formation when cells treatedwith3a,3b,3c and3f. In contrast, cell morphology treated with other threecompounds changed little, which is consistent with the result of IC50. From cellmorphology initial analysis, apoptosis mechanism of synthesized products may inducecell death. From result of cell cycle as measured by flow cytometry assay, thesynthesized products exhibit the same cytotoxic activity as paclitaxel, which can causecell cycle arrest in the G2/M phase and finally cell death through apoptosismechanism.In summary, we have analyzed biological activity and anticancer mechanism bycytotoxicity, cell morphology and cell cycle. It is indicated that products exhibitcytotoxicity to cancer cells, especially Bel-7402cells. The synthesized products causecell death by apoptosis mechanism. It is worth noting that3b can be a promisinganticancer agent for application of cancer chemotherapeutic drugs.