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Flavonoids:structural requirements for antiroliferative
& && && && && && &Activity on breast cancer cells
& & Abstract—several classes of flavonoids.(flavones.flavanones.2’hydroxychalcones and flavan—ols)having a variety of substituents in a ring were investigated for their antiroliferative&&activity&&against&&MCF-7human&&breast&&cancer&&cells. Structure –activity reia of&&these&&compounds&&were&&discussed .&&2’hydroxychalcones&&and&&methoxylated&&flavanones&&were&&found&&to&&be& &potent&&inhibitors&&cf7 cells&&growth&&whreas&&flavones and&&flavan—ols appeared to be&&weak nhibitory agents except 7.8-dihydroxyflavone. 2001 Elsevier science Ltd . All rights reserved .
& && && && && && && && && && && && &Introduction
Many clinically successful anticancer drugs are themselves either natural products or have been developed&&and&&natural&&occuring lead compounds .Great interest is currently being paid to flavonoids –one of&&the&&mator classes of natural products with widespread&&distribution in fruits, vegetables, spices, tea and soy-based foodstuff ---for their interesting pharmacological activites.The antiproliferative effects against breast cancer cells, anti-aromatase activity and binding affinities for the estrogen receptor of these compounds have drawn attention due to their role as potential anti-breast cancer agents.
& && &In our attempt to design flavonoid-related compounds having a balance between the above activities, we undertook a screening relatng to several classes of flavonoids and we recently described the aromatase inhibitory effects of some flavones.,flavanones and chalcones. The aim of the present&&study was to explore thoroughly the structural requirements on A-ring of&&chalcones,flavones and flavones for inhibition of MCF-7 breast cancer cells growth, both to identify an optimal candidate among currently available compouds,as well as to ascertain potential directions for synthetic lead-optimization studies.
Finally , a previous study about anticancer activity of ois-and trans-4’,7 –dihydroxyisoflavan---ols., two proposed metabolites of daidzein&&(4’.7 –dihydroxyisoflavone)prompted es to investigate for the first time the antiroliferative activity against MCF-7 cells of&&synthetic&&flavan-4-ols, which are of a rare occurrence in nature .&&
Christelle pouget. Fabienne lauthier. Alain simon Catherine fagnere. Jean-philippe basly christiane delage and albert-jose chulia
For this study ,we synthesized a ser of falconoid derivatives .increased by commercially acailable compounds (flavanones la and 1d-li.chalcones 2a and 2c and flacones 3a -3e).all of which bearing either hydrogen.hydroxyl and/or methoxy substituents on the A-ring (Table 1).
2’.4’-dihydroxychaicone 2b was synthesized as preciously described (yield 36%).Flavanones 1d-1h were treated by a methanolic KOH.solution to afford 2’-hydroxychalcones 2d-2h respectively (yield 50-60%)while flacanones 1b and 1c were obtained.also in moderate yields,by cyclization of the corresponding 2’-hydroxychalcones 2b and 2c in a methanolic H2SO4 solution.Insprction of the H-NMR spectra of both commercial and synthesized chalcones clearly indicated that they were configured trans(Jh& &=15-16Hz)
Reduction of the flavanones 1d-1f was performed with sodium borohydride to give the corresponding flacan-4-ols-4d-4f for which the assingnment of stereochemistry was readily made on the basis of the H NMRcouping constants of the heterocyclic ring potons,(11)NaBH4 reduction of&&7-methoxyfavanone 1d was stereoselective leading to the 2.4-cis-7-methoxyflavan-4-ol while reduction of the 4-keto group of the 5-methoxyflavanone leand of 5.7-dimethoxyflavanone if afforded a mixture of 2.4-trans-flavan-4-ols which were seprated by TLC.
Tabke 1. structure iof flavanone chalcone flavone and flavan-4-ols dervanves
& && &Proliferation assay
The groxth inhibitory activity of the compounds was determinded in the MCF-7 human breadt cancer cekk kine using the MTT assay as described by Mosman et.13
Results were represented as% of inhibition vompsred to control absorbance The IC50 concentrantion which results in a 50%decrease in cell mean values are mean valules of three esperiments The deviations were within+_50%
& && &&&Results and discussion
&&The antiproliferative effects of flavanones and favones on MCF-7 cells are reported in Fifure I WHILE RESULTS FROM TESTING 2’-hydroxychalcones are summarized in Tabe2.
SOME structure-activity relationships for cytotoxicity are apparent from these results.
First.the unmmarizde flavanone&&1a appeared to be a weak inhibitor of MCF-7 cells growth as well as flavanones with hydroxyl froups cells growth as well as flavanones with hydroxyl groups like compounds 1b 1c 1g and li, Icontrast.the substitution by a methoxy group at position 7 and or 5 stitution by a methoxy group at position 7 and or 5 increased the abtiproliferative activity the IC50of flavanones Id 1e and if were respectively.35.7 35.7 and 36.0UM) WHILE A 6-MEGHOXY GROUP （compound 1h）did not enhance the growth inhibintion.
Flavone 3a and 7-hydroxyhavone 3b were shown to have only a weak antiprolifeative activity as previously described for corresponding favanones .then.the presence of a 7-methoxy group on the A-ring of flavaone did not enhance the inhibitory effect ad sgown by the low antivity of the 7-methoxyflavone 3d whike the substitution by a methoxy group at position 5(flavone 3e) invreased the antiprolifeative activity&&Among the flavone tested. 7.8-dihydroxyflavone 3c was found to be the most potent(IC50=27.5um)whereas the corresponding flavanone 1c was inactice.
The inhibitory dffects of some of the flanvanones were campared to those of corresponding 2’-hydroxy-flavanones we noted that in all cases. 2’hydroxychalcones were more potent against & & & & MCF-7 cells growth than corresponding flavanones surprisingly. The most active was the 2’.4’-dihydroxychalcome2b corresponding to the 7-hydroxyflavanope 1b which is inactive against MCF-7 cells proliferation the 2’3’4’-trihydroxychalcone 2c was also active whereas the corresponding 7.8-dihydroxyflavanone 1c had no effedt on MCF-7 cells&&growth. Therefore.unlike flavanones. Hydroxyl substituentson A ring of chalcones are not cnncal for antiproliferative effect except hydroxylationat postion o sinc 2.0-dinydroxy---metnoxycnaicone2g is much less active 2’-hydroxy-4-methoxycnalcone 2d
The flavan—olssynthesized snowed no inhibition of MCF-7 cells. Proliferation (data not shown) while the corresponding flavanones had significant activity. So. The 4-kelo functionality appeared to be essential for antipoliferative activity against this human breast cancer cell line. This result provides&&further support to previous studies which udderlined the importance of this structural feature for interaction with different cellular mecnanisms involved in cancer growth thus constantinou et al 4 have reported that some flavonoids were DNA topoisomerase inhibitors and than that the C-4carbonyl group of topoisomerase actibity. Edwards et al 15 have also showb tgat cgakcomes were effective antimitotic agents by bingding to tubulin and they noticed that reduction of the carbonyl group of chalcones diminished this activity interestingly, the 4-keto group of the flabonoids is also essential for aromatase inhibitory effect since the flavan-4-ols were found to be weak aromatase inhinbitors(unpublished results).
In conclusion. On the basis of the above tindings. The 7-methoxyflavanone 1d and the 7.8-dihydrixyflavone 3c scaffokds were selected as skeleton for the development of flavonoid structurally-related compounds having a balance between different anti-breast cancer activities since these compounds were found to possess not only abtiproliferative activity against MCF-7 cells but also aromatase inhibitoryeffect in spite of their great antiproliferative activity. Chalcones cound not be selected in our synthetic lead-optimization study because they were shown to be only weak inhibitors of aromatase activity however. A further evaluation of chaicones will be undertaken concerning the structural requirements on Bring for inhibition of homone-dependent human breast cancer line growth.
Ackonowledgements
The authors are gratefull to the region limousine for its&&financial support an Y.Champavier for running the NMR spectra
References and notes
1.& & & & petern.J:dwyer.Nmrinon Res.5
2.& & & & DI Carlo.G:Mascolo.N:lzzo.A>A:Capasso E line sck
3.& & & & Dimmock.J.R.Elias.D.w: beazely,MA:KandepuN>Mcurr.Vhem
4.& & & & So.FV: GuthrieN Chameper,A>F carroll K.Kcancer len
5.& & & & Ibrahim A. R: Abui-hajj.Y.J.J Steroid Biochem.Mol.Biol.
6.& & & & jeong. H.j shin Y.G: Kim L.H pezzuto.J.M.arch.Pham
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