Swermilactones A and B: racemic xanthone–secoiridoid heterodimers from Swertia mileensis

Abstract

Two pairs of racemic xanthone–secoiridoid heterodimers, (±)-swermilactones A (1) and B (2), were isolated from the whole plants of Swertia mileensis. Their structures, featuring an unusual C–C bond linkage between the xanthone and secoiridoid moieties, were elucidated by extensive spectroscopic analysis and ECD calculations. Compounds (+)-1, (−)-1, (+)-2, and (−)-2 moderately inhibited the secretion of cytokines TNF-α and IL-6 in LPS-induced RAW 264.7 macrophages with IC₅₀ values ranging from 12.01 to 39.06 μM.