Polyphenolic Acids from Mint (the Aerial of Mentha haplocalyx Briq.) with DPPH Radical Scavenging Activity

Vegetables of mint ( the aerial part of Mentha haplocalyx) contain a significant amount of polyphenols with many health benefits. The crude aqueous acetone extract exhibited high antioxidant activity (IC50 = 45.67 mu g/mL) in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. The activity-guided separation of chlorophyll removal fraction on column chromatography afforded 8 polyphenolic acids, including a new compound, cis-salvianolic acid J ( 1), and 7 known compounds, salvianolic acid J ( 2), lithospermic acid ( 3), rosmarinic acid ( 4), lithospermic acid B ( 5), magnesium lithospermate B ( 6), sodium lithospermate B ( 7), and danshensu ( 8), respectively. Their structural elucidations of all the compounds were based on extensive spectroscopic methods, including HRESIMS and 2D NMR experiments (HSQC, HMBC, and ROESY) and by comparison with reference values. Compounds 2, 3, and 5 to 8 were isolated from Mentha genus for the 1st time. The DPPH radical scavenging activities of all the isolated compounds were evaluated.