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The methanolic extract from the flowers of Mesua ferrea Linn. (Calophyllaceae) showed significant hyaluronidase inhibitory activity. Following a bioassay-guided separation of the extract, two biflavonoids, viz., mesuaferrone-A (1) and mesuaferrone-B (2), were isolated, along with ten flavonoids (3–12), two xanthones (13 and 14), three triterpenes (15–17), a phenylpropanoid (18), and five aromatics (19–24). Among the isolates, 1 and 2 (IC50 = 51.1 µM and 54.7 µM, respectively) exhibited hyaluronidase inhibitory activity equivalent to that of the commercially available antiallergic agents disodium cromoglycate (64.8 μM) and ketotifen fumarate (76.5 μM). These biflavonoids (1 and 2) are 8-8″ linked dimers that are composed of naringenin (1a) or apigenin (3), with their corresponding monomers lacking inhibitory activity (IC50 > 300 μM). In addition, 1 and 2 (IC50 = 49.4 µM and 49.2 µM, respectively) inhibited the release of β-hexosaminidase, which is a marker of antigen-IgE-mediated degranulation, in rat basophilic leukemia (RBL-2H3) cells. These inhibitory activities were more potent than those of the antiallergic agents tranilast and ketotifen fumarate (IC50 = 282 μM and 158 μM, respectively), as well as one of the corresponding monomers (1a; IC50 > 100 μM). Nonetheless, these effects were weaker than those of the other monomer (3; IC50 = 6.1 μM).

Six biflavonoids, succedaneaflavanone (1), mesuaferrone B (2), rhusflavanone (3), rhusflavone (4), agathisflavone (5), and cupressuflavone (6), were isolated from the fruits of Rhus parviflora. The chemical structures of the compounds were determined based on NMR, fast atom bombardment mass spectrometry, and IR. Biflavonoid compounds were evaluated for cytotoxicity against human cancer cell lines, including human colon carcinoma (HCT-116), human breast carcinoma (MCF-7), and human cervical carcinoma (HeLa). Biflavonoids 2, 3, and 5 showed significant cytotoxicity with IC50 values of 17.25 μM (mesuaferrone B against HCT-116), 17.50 μM (rhusflavone against MCF-7), and 15.20 μM (agathisflavone against HeLa). Compound 5 showed inhibition of β-secretase activity at a 10 μM concentration. Compound 6 showed inhibition of cyclin-dependent kinases (CDK2 and CDK5) with IC50 values of 18.58 and 9.29 μM, respectively.