Monoamine oxidase (MAO) inhibitors have been used in treatment of depression, Parkinson's disease, and other related psychiatric disorders. In our continuous work for MAO inhibitors from fungi, a new series of metabolites having MAO inhibitory activity was isolated from Monascus anka IFO 30873. Among nine pigments isolated from the fungus,
MP
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4
A〜4D, -5, and -6 showed strong fluorescence and very similar UV and IR spectra, which indicated the presence of same chromophores in these compounds. The partial structures of
MP
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4
A shown in Fig. 1 were estimated on the basis of NMR spectroscopic studies (e.g. COSY, COLOC). The units were connected from the HMBC data of its diacetate derivative. Comparing the NMR data of
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B〜4D, -5, and -6 with those of
MP
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A, the structures were proposed (Fig 2).
MP
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C exhibits MAO inhibitory activity (IC_<50> 1.1×10^<-5>M). The lack of methyl groups at C-3, -5 and/or -7 positions seemed to have some influence to decrease the activity [
MP
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A (IC_<50> 1.5×10^<-5> M) and MP-5 (IC_<50> 5.1×10^<-4>M)]. MP-1〜3 were identified as monascin, ankaflavin and co-enzyme Q_<10>, respectively, and these showed no inhibitory activity.
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