Isolation, characterisation, and anti-inflammatory activities of constituents from <i>Viburnum macrocephalum</i> f. <i>macrocephalum</i> leaves

From Viburnum macrocephalum f. macrocephalum leaves (VMML), three new iridoids, viburetins A–C (1–3), together with four previously reported constituents, were isolated following a phytochemical investigation. Structural elucidation of the new isolates was achieved via detailed spectroscopic analyses (1D/2D NMR, HRESIMS) coupled with ECD experiments. The suppression of nitric oxide (NO) generation in RAW264.7 murine macrophages stimulated by LPS was assessed to determine anti-inflammatory effects of these isolates. Notably, compound 2 exhibited potent suppressive effects on NO generation (IC50 = 5.39 μM). Furthermore, molecular docking studies showed that compound 2 could effectively bind to the catalytic cavities of iNOS/COX-2 via hydrogen bonds and hydrophobic interactions. These results suggested that VMML containing these constituents possessed promising anti-inflammatory activity.