Leptomonines A and B, two novel rare benzyltetrahydroisoquinoline N-oxides from the aerial parts of Leptopyrum fumarioides as potential COX-2 inhibitors: in vitro and in silico studies.

Leptomonines A and B, two novel rare benzyltetrahydroisoquinoline N-oxides, were isolated from the aerial parts of Leptopyrum fumarioides (L.) Reichenb. collected in Tuv province, Mongolia. Their chemical structures, absolute configurations, and conformations were established by 2D-NMR and CD spectral analyses. Leptomonine A (1) can suppress TNF-α production and COX-2 expression in LPS-stimulated RAW 267.4 cells. This compound at a concentration of 100 µM significantly reduced the TNF-α and COX-2 levels by 36.43% and 47.10%, respectively, compared with the negative control. Moreover, leptomonine B (2) remarkably lowers COX-2 levels at the highest concentration. The docking simulations were conducted with the COX-2 enzyme and revealed the binding ability of leptomonine A (1) and leptomonine B (2) with binding energies of - 9.03 and - 8.96 kcal/mol, respectively. The interactions of these alkaloids with the targets were mainly with the hydrophobic and hydrophilic sites, which are quite similar to rofecoxib. Phytochemical investigation revealed the diversity and novelty of the natural isoquinoline alkaloids in Leptopyrum fumarioides. Two new benzyltetrahydroisoquinoline N-oxides were identified as the bioactive constituents of Leptopyrum fumarioides by assessing its anti-inflammatory effects. The findings provide scientific justification to support the traditional application of Leptopyrum fumarioides for treating liver diseases associated with inflammation.