Indole alkaloids exhibiting hCE2 inhibitory activity from the roots of Paeonia lactiflora using a feature-based molecular network strategy.

By employing a molecular networking analysis strategy, we successfully guided the isolation of alkaloids from the ethyl acetate extract of Paeonia lactiflora roots. This approach led to the discovery of previously undescribed indole alkaloids, (+)/(-)-paeonialkaloid A [(+)/(-)-1], paeonialkaloids B and C (2 and 3), along with one known alkaloid (4). The structures were fully established through comprehensive spectroscopic methods, including 1D/2D NMR, HRESIMS, UV, IR, and theoretical calculations of electronic circular dichroism (ECD) spectra. Indole alkaloids have been rarely reported from the Paeonia genus. In this study, the discovery of (+)/(-)-1, 2 and 3 provides only the second report of such compounds. In addition, (+)-1, (-)-1, 2 and 3 are moderate inhibitors of human carboxylesterase 2 (hCE2), with IC₅₀ values of 13.65 ± 0.64, 13.92 ± 0.72, 14.45 ± 0.43, and 14.16 ± 1.05 μM, respectively, which was revealed through the molecular docking studies.