Bioassay-guided screening and isolation of α-glucosidase and tyrosinase inhibitors from leaves of Morus alba
2012
Yang, Zhenzhong | Wang, Yingchao | Wang, Yi | Zhang, Yufeng
In this study, bioassay-guided fractionation of extracts from the leaves of Morus alba L. led to the isolation of 15 bioactive constituents with α-glucosidase and tyrosinase inhibitory activities, among which prenylated stilbenes were proved to be a new group of α-glucosidase inhibitors apart from iminosugars derived from Morus alba. Their structures were identified on the basis of extensive spectroscopic analysis and chemical evidence, as well as comparing with data from the literature. Among them, compounds (2R)/(2S)-Euchrenone a₇ (6a/6b), Chalcomoracin (7), Moracin C (8), Moracin D (9) and Moracin N (10) exhibited a significant degree of α-glucosidase inhibitory activity with IC₅₀ of 6.28, 2.59, 4.04, 2.54 and 2.76μM, respectively, while (2R)/(2S)-Euchrenone a₇ (6a/6b), Moracin N (10), Quercetin (13), Norartocarpetin (14), the interconvertible epimeric mixture of (2R)/(2S)-7-methoxyl-8-ethyl-2′,4′-dihydroxylflavane-2″-O-β-d-glucopyranoside (1a/1b) and the interconvertible enantiomers of (2R)/(2S)-7-methoxyl-8-hydroxyethyl-2′,4′-dihydroxylflavane (5a/5b) displayed a potent tyrosinase inhibitory effect with IC₅₀ of 0.260, 0.924, 0.523, 0.0824, 0.616 and 0.528μM, respectively. Especially, (2R)-7-methoxyl-8-ethyl-2′,4′-dihydroxylflavane-2″-O-β-d-glucopyranoside (1a), (2S)-7-methoxyl-8-ethyl-2′,4′-dihydroxylflavane-2″-O-β-d-glucopyranoside (1b), (2S)-8-hydroxyethyl-7,4′-dimethoxylflavane-2′-O-β-d-glucopyranoside (2), (2R)-7-methoxyl-8-hydroxyethyl-2′,4′-dihydroxylflavane (5a) and (2S)-7-methoxyl-8-hydroxyethyl-2′,4′-dihydroxylflavane (5b) were identified as new compounds.
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