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

ABSTRACT: 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 (IC 50 = 45.67 μg/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.