Polyphenols from pericopsis elata and synthesis of selected stilbenes

[摘要] English: The bark of Pericopsis elata (Afrormosia elata) is used by the local population of the Democratic Republic of Congo for the treatment of cancer and for external applicationsbecause of its weather resistance. Previous phytochemical studies on Pericopsis elataresulted in the isolation of flavonoids, isoflavonoids, chalcones and stilbene monomers.Among these, stilbenes are known to have biological activities such as antioxidants,antifungal, and act as microbial inhibitors. They posses COX-1 and COX-2 inhibitoryeffects, affect lipid peroxidation, LDL oxidation, and function as phytoalexins amongother activities. Prompted by these claims, we conducted an in depth investigation of the heartwood of P.elata by extraction, isolation and structural elucidation of the metabolites. Theenrichment and fractionation of monomeric and dimeric constituents were accomplishedmainly by Craig countercurrent distribution techniques and Sephadex LH-20 gelchromatography. Pure compounds were obtained by derivatization and preparative thinlayer chromatography. Structural elucidation of the phenolics is based mainly on NMRspectroscopic methods (1H NMR, 13C NMR, COSY, NOESY, HMBC and HMQC), Massspectrometry and synthetic methods.The monomeric compounds isolated during this study comprise the flavanones(naringenin and eriodictyol), the isoflavones (genistein and biochanin A), adihydrochalcone [(R)-α,4,2',4'-tetraacetoxydihydrochalcone] and a single α-methyldeoxybenzoin (angolensin). Among the stilbene monomers encountered areresveratrol, isorhapontigenin and large amounts of piceatannol.Structures of the dimeric stilbnes isolated apparently originate from differentcombinations of piceatannol (3,4,3',5'-tetrahydroxystilbene) (the major constituent ~ 16% of the phenolic content of P. elata) and 3,4,3',4'-tetrahydroxystilbene. To the best of ourknowledge rel-2,3-trans-2-(3,4-dimethoxyphenyl)-3-(3,5-dimethoxyphenyl)-6-[2-(3,5-dimethoxyphenyl)-E-1-ethenyl]benzodioxane, rel-2,3-trans-2-(3,4-dimethoxyphenyl)-3-(3,4-dimethoxyphenyl)-4-[2-(3,4- dimethoxyphenyl) )-E-1-ethenyl]-6-methoxy-2,3-dihydrobenzofuran, rel-2,3-trans-2-(3,4-diacetoxyphenyl)-3-(3,5-diacetoxyphenyl)-4-[2-(3,4-diacetoxyphenyl) )-E-1-ethenyl]-6-acetoxy-2,3-dihydrobenzofuran, rel-2,3-trans-2-(3,4-dimethoxyphenyl)-3-(3,5-dimethoxyphenyl)-4-[2-(3,5-dimethoxyphenyl) )-Z-1-ethenyl]-6-methoxy-2,3-dihydrobenzofuran, rel-2,3-trans-4-Formyl-2-(3,4-dimethoxyphenyl)-3-(3,5-dimethoxyphenyl)- 6-methoxy-2,3-dihydrobenzofuran and rel-2,3-trans-2-(3,5-diacetoxyphenyl)-3-(3,5-diacetoxyphenyl)-6-[2-(3,5-diacetoxyphenyl) )-E-1-ethenyl]-4-acetoxy-2,3-dihydrobenzofuran are novel compounds.Structural confirmation of the six novel dimeric stilbenes in particular required definitionof structure via synthetic methods. A synthetic approach was thus developed. Thisprotocol comprises the synthesis of piceatannol via the Wittig reaction followed byoxidative coupling of two piceatannols to afford novel dimeric stilbenes. 1H NMR of themethoxy-derivative of synthetic compounds is identical to that of the derivative of twodimeric stilbenes isolated from P. elata.

[发布机构] University of the Free State