Phenolic constituents from Isodon lophanthoides var. graciliflorus and their antioxidant and antibacterial activities

Isodon lophathoides var. graciliflorus (Lamiaceae) has been used as an herb for making health beneficial beverages and an ingredient for making soup in China. This study revealed thirteen phenolic compounds isolated from the aerial parts of the herb for the first time. They were rosmarinic acid (1), methyl rosmarinate (2), clinopodic acid A (3), salvianolic acid A (4), nepetoidin B (5), caffeic acid (6), vinyl caffeate (7), danshensu (8), latifolicinin C (9), hydroxytyrosol (10), procatechuic aldehyde (11), 3,4-dihydroxybenzoic acid (12) and syringic acid (13). Their structures were determined by spectroscopic method including nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) and comparison of the data with the values reported in references. Ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of these compounds were evaluated, and compounds 1-8 and 13 were more potent or comparable to l-ascorbic acid. In addition, compounds 5 and 13 showed antibacterial activity against Staphyloccocus aureus and Shigella dysenteriae with IC50 values ranging from 44.15 to 79.13 μM, and compound 5 was also active towards Bacillus cereus.