Synthesis And In Vitro Antitumor Activities Of Natural Flavones, Flavans, Homoisoflavanone And Their Related Compounds

Cancer is a leading cause of death worldwide.It has accounted for 7.9 million deaths （around 13%of all death） in 2007 and deaths from cancer are projected to continue rising,with an estimated 12 million deaths in 2030.Natural anticancer agents from plant kingdom play important roles in cancer cure.Vascular disrupting agents（VDAs）,a kind of compounds based on a natural product combretastatin A-4（CA-4）,have been reported to show potential anticancer activity.They could cause cytoskeletal and morphological changes in endothelial cells via binding to colchicines-binding site in tubulin,which increase vascular permeability and disrupt tumor blood flow,leading to extensive ischemie necrosis in areas that are often resistant to conventional anti-cancer treatments.During the past years,hundreads of VDAs had been designed and synthesized based on the skeleton of CA-4.However,these analogues were well districted to CA-4,which was not beneficial to SAR study of VDAs.In our research program directed toward novel VDAs in traditional Chinese medicines,we identified flavonoids to be ideal targets due to their definite antieancer activity,unclear mechanism and similar structure to CA-4.Therefore,67 compounds distributed into 7 kinds of flavonoids（flavone,flavan,9-oxo-homoisoflavone,homoisoflavone,homoisoflavonone, homoisoflavan 4-ol,homoisoflavan）were designed based on five natural products, 7,8,3’,4’,5’-pentamethoxyflavone,5’-hydroxy-7,8,3’,4’-tertramethoxyflavone,（S）-7,8,3’,4’,5’-pentamethoxyflavane,（S）-5’-hydroxy-7,8,3’,4’-tertramethoxyflavane and（S）-4’-methoxy-7,8-methylenedioxyhomoisoflavanone according to the structures of CA-4 and its analogues.The synthesis of flavones were furnished from commercially available benzene-1,2,3-triol and（un）substituted benzoic acid via acetylation,selective di-methylation,esterification and Baker-Venkataraman rearrangement,etc.The two natural flavones 7,8,3’,4’,5’-pentamethoxy-flavone, 5’-hydroxy-7,8,3’,4’-tertramethoxyflavone had thus been obtained in 31.9%and 24.0% overall yield.Other nine flavones were prepared by the same method.During the synthesis,a straightforward synthetic procedure of flavans via Pd-C catalysed hydogenation/hydrogenolysis of corresponding flavones was developed.The two natural flavan racemates 7,8,3’,4’,5’-pentamethoxy-flavan and 5’-hydroxy-7,8,3’,4’-tertramethoxyflavan were obtained from corresponding flavones in 81.9%,82.6%yield,respectively. The eight 9-oxo-homoisoflavones were synthesized from benzene-1,2,3-triol and （un）substituted benzoic acid via acetylation,selective di-methylation,esterification, Baker-Venkataraman rearrangement and“one carbon extention”reaction,etc.The synthesis of homoisoflavones commenced with the commercially available benzene-1,2,3-triol.After acetylation and alkylation of benzene-1,2,3-triol,acetophenone intermediates were obtained,which reacted with benzaldehydes giving chalcones.Hydrogenation of chalcones and then treatment with DMF-DMA furnished the synthesis of 13 homoisoflavones.Homoisoflavanones were prepared via Raney Ni catalyzed hydogenation of corresponding homoisoflavones.The synthesis of the natural homoisoflavanone racemates 3-（4’-methoxy-benzyl） -7,8-methylenedioxy-homoisoflavanone was achieved in 4.0%.Eight Homoisoflavanones were also prepared.The approach for the conversion of homoisoflavones into homoisoflavan 4-ols directly through Pd/C catalyzed hydogenation under ultrasound was developed for the first time.14 homoisoflavan 4-ols were prepared by this method.It was also the first time that homoisoflavans had been synthesized via Pd/C catalyzed hydogenation/hydrogenolysis of homoisoflavones directly under ultrasound.10 homoisoflavans were prepared by this method.During the synthesis of dihydrochalcone intermediates,it’s found that Zn/HOAc could reduce the double bond conjugated with carbonyl groups in chalcones under ultrasound selectively and rapidly.The target compounds were characterized by the applications of MS,¹H-NMR and ¹³C-NMR.40 target compounds and 4 synthetic intermediates were evaluated by MTT assay for their in vitro antitumor activities against human SGC-7901,BEL-7402,HeLa,etc.7,8,3’,4’,5’-pentamethoxyflavane （ZLB-01）,7,8,3’,4’,5’- pentamethoxy-9-oxo-homoisoflavone（ZLC-01）, 3’-hydroxy-4’,7,8-trimethoxyhomoisoflavone（ZLD-05）,3’,4’,5’-trimethoxy-7,8-methylene dioxyhomoisoflavanone（ZLE-07）and 3’-hydroxy-4’-methoxy-7,8-methylenedioxy homoisoflavanone（ZLE-09）,7,8,3’,4’,5’-pentamethoxyhomoisoflavan（ZLG-01）, 3’-hydroxy-4’,7,8-trimethoxyhomoisoflavan（ZLG-05）and 3’-hydroxy-4’-methoxy-7,8-methylenedioxyhomoisoflavan （ZLG-10） possessed good in vitro antitumor activity.The homoisoflavan compounds were proved to be more potential among the seven kinds of flavonoids.In addition,it’s found that replacement of ring B in the target compounds with 3,4,5-trimethoxyphenyl（the fragment A of CA-4） or 3-hydroxy-4-methoxyphenyl（the fragment B of CA-4）,especially the latter one,led to the increase of antitumor activity.The IC₅₀ values of ZLG-10（3’-hydroxy-4’-methoxy-7,8-methylenedioxy-homoisoflavan）,ranged from 19 nM to 97 nM.The mechanism research of ZLB-01 and ZLG-10 proved that their anti-proliferative effects were associated with cell cycle arrest in G2/M phase,which was highly similar to the effect of CA-4.