Tyrosinase and 5a-Reductase Inhibitory Components from Artocarpus incisus Tree

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  • Artocarpus incisus樹木からのチロシナーゼおよび5a-リダクターゼ阻害成分
  • Tyrosinase and 5α-Reductase Inhibitory Components from Artocarpus incisus Tree
  • Tyrosinase and 5 アルファ Reductase Inhibitory Components from Artocarpus incisus Tree

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Abstract

The inhibitory components on tyrosinase and 5a-reductase from Papua New Guinean (PNG) and Thai woody plants were investigated. First, the inhibitory components of Artocarpus incisus heartwood which showed the strongest inhibitory activity in 23 PNG wood species, their structure-activity relationships and inhibitory mechanism were evaluated. Tyrosinase inhibitory activity-guided fractionation led to the isolation of seven active compounds including two new compounds, 3,2',4'-trihydroxy- 6", 6"-dimethyl-pyrano(3",2":4,5)-trans- stilbene (artocarbene) and 6-(3"-methyl-1"- butenyl)-5,7,2',4'-tetrahydroxyflavone(isoartocarpesin). The structure-activity relation- ships suggested that specific natural or synthesized compounds having4-substituted resorcinol skeleton had potent tyrosinase inhibitory ability. Kinetic studies have indicated that specific compounds having 4-substituted resorcinol skeleton exhibit competitive inhibition of the oxidation of DL-DOPA by mushroom tyrosinase. Second, 5a-reductase inhibitory components from PNG and Thai plants were investigated respectively, and their structure-activity relationships were discussed. The methanol extract of heartwood of A. incisus showed potent 5a-reductase inhibitory activity. Chlorophorin and artocarpin showed more potent inhibitory effects (IC_50=37μM and 85μM, respectively) than did a-linolenic acid, which is known as a naturally occurring potent inhibitor. The inhibitory effects of 17 samples prepared from Thai plants on 5a-reductase activity were examined. The acetone extract of A. incisus leaves showed potent 5a-reductase inhibitory activity. Fractionation guided by 5a-reductase inhibitory test led to the isolation of 2-geranyl-2', 3,4,4'-tetrahydroxydihydrochalcone(IC_50=38μM) and a novel geranylated chalcone, 3'-ger- anyl-2',3,4,4'-tetrahydroxychalcone(IC_50=104μM) from the acetone extract of A. incisus leaves. Structure-activity relationship suggested that the presence of an isoprene-derived sub- stituent (prenyl and geranyl) would enhance 5a-reductase inhibitory effects.

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