Three new Diels-Alder adducts, macrourins E - G (1: -3: ), one new 2-arylbenzofuran, macrourin H (4: ), and eight known Diels-Alder adducts (5: -12: ) were isolated from . Their structures were elucidated through extensive analysis of spectroscopic data. TheH NMR and ECD trends in the determination of the configurations of these Diels-Alder adducts were summarized. The tyrosinase inhibitory activities of all compounds isolated were evaluated, and the new compounds (1: -4: ) as well as the eight known compounds (5: -12: ) were found to be potent with IC values ranging from 0.39 to 4.54 µM. Among them, 1 showed the best tyrosinase inhibitory activity with an IC value of 0.39 µM, approximately 50 times stronger than the positive control, kojic acid.
A novel benzofuranone unprecedentedly with a prenyl group at C-3, nigranol A (1), a new flavonol, nigranol B (2), and three known compounds, sanggenon M (3), nigrasin C (4), and nigrasin A (5) were isolated from the twigs of Morus nigra Linn.. Their structures were elucidated based on the analysis of multiple spectroscopic data. All of the compounds, along with eight previously isolated ones (6-13) were investigated for their α-glucosidase inhibitory activities. The result showed that compounds 1-13 except 4 exhibited prominent inhibitory activities against α-glucosidase. Among them, compounds 2 and 7 were the best α-glucosidase inhibitory candidates with IC 50 values at 1.63 and 1.43 μM, respectively. Furthermore, the structure-activity relationships of the sanggenon-type flavanones were summarized.
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