Novel Anti-inflammatory Lignans Identified in Piper nigrum L. Leaves via Bioactivity-Guided Isolation

Piper nigrum L. is widely cultivated in Hainan, China, and its abundant leaves represent an underutilized resource. This study aims to investigate its phytochemical constituents and anti-inflammatory potential. Through anti-inflammatory activity-guided phytochemical isolation, thirty-one compounds were isolated from P. nigrum leaves, including three novel lignans (1–3) and twenty-eight known compounds (4–31). Notably, 24 components are identified in P. nigrum for the first time. All isolated compounds were assessed for anti-inflammatory activity in LPS-induced BV-2 cells, of which 4 showed potent inhibitory activity of NO production (IC50 = 2.7 μM) and dose-dependently reduced the levels of TNF-α, IL-6, and IL-1β. In addition, a validated UPLC-TQ-ESI-MS/MS method was developed to quantify eight representative compounds (4, 6, 9, 14, 16, 17, 29, and 30). These findings enrich the phytochemical profile of P. nigrum and identify promising anti-inflammatory candidates, exploring the potential for developing natural anti-inflammatory agents and herbal supplements from agricultural waste.