The roots of Melastoma malabathricum subsp. normale (D. Don) Karst. Mey have been used in traditional ethnic medicine systems in China to treat inflammation-triggered ailments, such as trauma, toothache, and fever. Therefore, the aim of this study is to screen for compounds with anti-inflammatory activity in the title plant. The extract of M. malabathricum subsp. normale roots was separated using various chromatographic methods, such as silica gel, ODS C18, MCI gel, and Sephadex LH-20 column chromatography, as well as semi-preparative HPLC. One new complex tannin, named whiskey tannin D (1), and an undescribed tetracyclic depsidone derivative, named guanxidone B (2), along with nine known polyphenols (2–10) and three known depsidone derivatives (12–14) were obtained from this plant. The structures of all compounds were elucidated by extensive NMR and CD experiments in conjunction with HR-ESI-MS data. All these compounds were isolated from this plant for the first time. Moreover, compounds 1–4, 8, and 10–14 were obtained for the first time from the genus Melastoma, and compounds 1, 2, and 11–14 have not been reported from the family Melastomataceae. This is the first report of complex tannin and depsidone derivatives from M. malabathricum subsp. normale, indicating their chemotaxonomic significance to this plant. Compounds 1–12 were investigated for their anti-inflammatory activities on the production of the nitric oxide (NO) in lipopolysaccharide (LPS)-stimulated RAW264.7 cells, and compounds 1, 11, and 12 showed anti-inflammatory activities with IC₅₀ values of 6.46 ± 0.23 µM, 8.02 ± 0.35 µM, and 9.82 ± 0.43 µM, respectively. The structure–activity relationship showed that the catechin at glucose C-1 in ellagitannin was the key to its anti-inflammatory activity, while CH₃O- at C-16 of aromatic ring A in depsidone derivatives had little effect on its anti-inflammatory activity. The study of structure–activity relationships is helpful to quickly discover new anti-inflammatory drugs. The successful isolation and structure identification of these compounds, especially complex tannin 1, not only provide materials for the screening of anti-inflammatory compounds, but also provide a basis for the study of chemical taxonomy of the genus Melastoma.

Polyphenols, widely distributed in the genus Melastoma plants, possess extensive cellular protective effects such as anti-inflammatory, anti-tyrosinase, and anti-obesity, which makes it a potential anti-inflammatory drug or enzyme inhibitor. Therefore, the aim of this study is to screen for the anti-inflammatory and enzyme inhibitory activities of compounds from title plant. Using silica gel, MCI, ODS C18, and Sephadex LH-20 column chromatography, as well as semipreparative HPLC, the extract of Melastoma normale roots was separated. Four new ellagitannins, Whiskey tannin C (1), 1-O-(4-methoxygalloyl)-6-O-galloyl-2,3-O-(S)-hexahydroxydiphenoyl-β-d-glucose (2), 1-O-galloyl-6-O-(3-methoxygalloyl)-2,3-O-(S)-hexahydroxydiphenoyl-β-d-glucose (3), and 1-O-galloyl-6-O-vanilloyl-2,3-O-(S)-hexahydroxydiphenoyl-β-d-glucose (4), along with eight known polyphenols were firstly obtained from this plant. The structures of all isolates were elucidated by HRMS, NMR, and CD analyses. Using lipopolysaccharide (LPS)-stimulated RAW2 64.7 cells, we investigated the anti-inflammatory activities of compounds 1–4, unfortunately, none of them exhibit inhibit nitric oxide (NO) production, their IC₅₀ values are all > 50 μM. Anti-tyrosinase activity assays was done by tyrosinase inhibition activity screening model. Compound 1 showed weak tyrosinase inhibitory activity with IC₅₀ values of 426.02 ± 11.31 μM. Compounds 2–4 displayed moderate tyrosinase inhibitory activities with IC₅₀ values in the range of 124.74 ± 3.12–241.41 ± 6.23 μM. The structure–activity relationships indicate that hydroxylation at C-3′, C-4′, and C-3 in the flavones were key to their anti-tyrosinase activities. The successful isolation and structure identification of ellagitannin provide materials for the screening of anti-inflammatory drugs and enzyme inhibitors, and also contribute to the development and utilization of M. normale.

In this study, emodin was used as the starting material to synthesize two novel ligands, L1 and L2, containing bipyridine or phenanthroline moieties. Seven metal complexes (1–7) were obtained through coordination with Co, Rh, Ru, and Pt ions. Their structures were confirmed via NMR, HRMS, UV–Vis, IR, HPLC and SC-XRD analyses. The MTT assay showed that L1 and complex 2 selectively inhibited HepG-2 cells, with IC₅₀ values of 8.77 μM and 6.10 μM, respectively. Both compounds exhibited stronger activity than cisplatin (9.05 μM) and low toxicity toward normal 293T cells. Mechanistic studies demonstrated that they induced G2/M phase arrest by regulating Cyclin B1 and P21 expression, which was accompanied by ROS and Ca²⁺ accumulation, mitochondrial membrane potential disruption, and activation of the Caspase-9/3 cascade. Complex 2 showed superior antitumor activity to L1, and this finding was further supported by molecular docking analysis. In sum, Rh(III) complex 2 was identified as a selective and mechanistically defined anti-hepatocellular carcinoma lead compound, providing a potential strategy for the development of natural product-based metal anticancer agents.