Abstract
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.
Highlights
Tyrosinase is the key enzyme of melanin synthesis, and its overexpression can lead to pigmentation diseases such as freckles, chloasma and melanoma [2]
Finding out the effective and lower side effects anti-inflammatory drugs and tyrosinase inhibitor is of great importance
The known compounds 5–12 were identified as mongolicain A (5) [12], 1-hydroxy-3,4,5-trimethoxy phenyl-1-O-[60 -O-(4”-carboxy-1”,3”,5”-trihydroxy)phenyl]-β-D-glucopyranoside (6) [13], kaempferol (7) [14], kaempferol-3-rhamnoside (8) [15], gentisic acid-5-O-β-D-(6’-O-galloyl)glucopyranside (9) [16], quercetin (10) [17], quercetin-3-O-α-L-rhamnoside (11) [18], and myricetin-3-O-α-L-rhamnopyranoside (12) [19], respectively
Summary
Inflammation, as a common clinical pathological process, is closely related to many diseases such as arthritis, psychosis, cardiovascular and cerebrovascular diseases, and cancer [1]. Tyrosinase is the key enzyme of melanin synthesis, and its overexpression can lead to pigmentation diseases such as freckles, chloasma and melanoma [2]. Anti-inflammatory drugs such as glucocorticoids, insulin, and tyrosinase inhibitors such as kojic acid have been proven to have significant side effects [3,4]. Finding out the effective and lower side effects anti-inflammatory drugs and tyrosinase inhibitor is of great importance. Polyphenols, the characteristic component of Melastoma plants, have broad cytoprotective effects, such as anti-oxidation, anti-inflammatory, anti-tyrosinase [5], and anti-obesity [6,7], which make it a potential anti-inflammatory drug or enzyme inhibitor.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
