Two new p-hydroxybenzoic acid glycosides, namely p-hydroxybenzoic acid-4-O-α-d-manopyranosyl-(1 → 3)-α-l-rhamnopyranoside (compound 1) and 4-O-α-l-rhamnopyran-osyl-(1 → 6)-α-d-manopyranosyl-(1 → 3)-α-l-rhamnopyranoside (compound 2), and seven known compounds, compound 3, 6, 7 (acid components), compound 8, 9 (flavonoids), compound 4 (a coumarin) and compound 5 (an alkaloid), were isolated from the 70% ethanol aqueous extract of the aerial parts of Melilotus officinalis (Linn.) Pall. The structures of all compounds were elucidated by use of extensive spectroscopic methods Infrared Spectroscopy (IR), High resolution electrospray ionization mass spectrometry (HR-ESI-MS), and ¹H and 13C-NMR). Sugar residues obtained after acid hydrolysis were identified by high-performance liquid chromatography (HPLC). The antioxidant activity of all the compounds was evaluated by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⁺) and 1,1-diphenyl-2-picrylhydrazyl (DPPH). The anti-inflammatory effects of the compounds were also evaluated in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. All compounds were shown to inhibit LPS-induced nitric oxide (NO) and prostaglandin E 2 (PGE 2) production by suppressing the expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively, in LPS-stimulated RAW 264.7 cells. The inhibitory effect of all the compounds on MCF-7 cells was determined by Cell Counting Kit-8 (CCK-8) method. The results showed that compounds 1, 2, 7, 8, 9 exhibited better antioxidant activity compared to the other compounds. compounds 1-9 had different inhibitory effects on the release of NO, TNF-α and IL-6 in LPS-stimulated RAW264.7 cells by LPS, of which compound 7 was the most effective against inflammatory factors. compounds 1 and 2 have better antitumor activity compared to other compounds. Further research to elucidate the chemical composition and pharmacological effects of Melilotus officinalis (Linn.) Pall is of major importance towards the development and foundation of clinical application of the species.
Keywords: ">d-manopyranosyl-(1 → 3)-α-; ">l-rhamnopyranoside; ">l-rhamnopyranosyl-(1 → 6)-α-; 4-O-α-; Melilotus officinalis (Linn.) Pall; anti-inflammatory; anti-tumor; antioxidant; p-hydroxybenzoic acid-4-O-α-.