Inulabritanthymols A and B, thymols from Inula britannica and their anti-inflammatory effects

Inula britannica is a traditional Chinese medicine that possesses various pharmacological effects, including expectorant, cough suppressant, and antibacterial effects. Phytochemical investigation of I. britannica resulted in the isolation of a pair of novel thymols, (8 S,9 S)-inulabritanthymol A (1a) and (8 R,9 R)-inulabritanthymol A (1b), and a new thymol inulabritanthymol B (2) as well as five known thymols (3−7). Their structures were characterized using 1D and 2D NMR, HRMS, and electronic circular dichroism (ECD) spectra, and quantum chemical calculations. Compounds 5–7 showed inhibitory potentials toward NO production, and their IC₅₀ values were 6.39, 5.80, and 8.53 μM, respectively. Molecular docking indicated the interaction of compound 6 with iNOS. These findings demonstrated that thymols served as potential candidates for developing anti-inflammatory drugs.