Abstract
Biotransformation of 8-hydroxydaidzein by recombinant Escherichia coli expressing O-methyltransferase (OMT) SpOMT2884 from Streptomyces peucetius was investigated. Two metabolites were isolated and identified as 7,4′-dihydroxy-8-methoxy-isoflavone (1) and 8,4′-dihydroxy-7-methoxy-isoflavone (2), based on mass, 1H-nuclear magnetic resonance (NMR) and 13C-NMR spectrophotometric analysis. The maximum production yields of compound (1) and (2) in a 5-L fermenter were 9.3 mg/L and 6.0 mg/L, respectively. The two methoxy-isoflavones showed dose-dependent inhibitory effects on melanogenesis in cultured B16 melanoma cells under non-toxic conditions. Among the effects, compound (1) decreased melanogenesis to 63.5% of the control at 25 μM. This is the first report on the 8-O-methylation activity of OMT toward isoflavones. In addition, the present study also first identified compound (1) with potent melanogenesis inhibitory activity.
Highlights
Isoflavones exist in some plants, such as soybeans [1]
More studies have focused on ortho-hydroxyisoflavones due to their pharmaceutical activities, including anti-cellular proliferation [3], aldose reductase inhibition [4], tyrosinase inhibition [5], anti-mutagenesis [6], anti-melanogenesis [7], and enhancement of cancer chemotherapeutic activity [8]
We found that the methyl derivatives of daidzein and genistein possess potent melanogenesis inhibitory activity [13]
Summary
Isoflavones exist in some plants, such as soybeans [1]. Two major isoflavones found in soybeans are daidzein and genistein, which have been demonstrated to prevent hormone-dependent diseases [2]. The HMBC spectrum revealed a methoxyl proton signal at δ 3.85(s) correlated to carbon resonance at δ 135.0 (C-8) Based on these spectral data and with the comparison of 1H-NMR and 13C-NMR data in the literature [17], compound (1) was characterized as 7,41-dihydroxy-8-methoxy-isoflavone. The present study holds promise in a mass production method for the two isoflavones by use of recombinant E. coli if yields can be increased through further process improvements. This opens up pharmaceutical research and applications of the two methoxy-isoflavones in the future. FigurmFeieg5lua.rneoEg5fe.fneEecfstfiessct(osbf)ocofofcmBo1mp6opcuoenullnds.dsTs(h1(e1))c(e(oollppseewnnebrbeaarirsns)c)uaabnnaddte(d2()2f)o(fri(lfi1lelddleadyb,abrasan)rdso)tnhoetnnhettrhceeaeltlecdseulwlrvistiuvhardlvri(uvag)aslafn(oadr) and melananoogtehneres2isd(aby)s.oFfoBll1o6wcinegllsc.ulTtihveatcioenll,sthweerceellinvciuabbialitteydafnodr c1eldl amy,elaanndin tchoenntetnrteawteedre wmiethasudrreudgs for anothweirth tdhaeyps.roFtoolcloolws idnegsccruibletdivaintioMna, ttehreiaclselalnvdiaMb5ieltihtyodasn. dThceellamveeralagnein(nco=n3t)enist swheorwenm, weaisthurtehde with the psrtoatnodcaorlds ddeevsicartiiboendreinprMeseanteterdiablsyaenrdrorMbeatrhso. dTsh.e Tdhateaawveerreagceom(npa=re3d) wisitshhothwonse, wofitthhethcoensttraonl dard deviautsioinng rtheeprSetusednetnetd's tb-tyeset,rarondr bp a
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