Absolute stereochemistry and anti-inflammatory activity of cycloisobrachycoumarin, brachycromone, cyclobrachycoumarin, and cyclobrachycoumarin 2’-epimer from Gerbera delavayi

Four isomeric 5-methyl-4-hydroxycoumarin-monoterpene hybrids (MMHs) comprising three known MMHs, cycloisobrachycoumarin (1), brachycromone (2), cyclobrachycoumarin (3), and a new epimer of 3, cyclobrachycoumarin 2’-epimer (4) were isolated from Gerbera delavayi. The absolute configuration of 1–4 was elucidated by utilizing ECD calculations and X-ray diffraction analysis. As a result, the absolute configurations of C-2’ and C-3’ in 1 and 2 were revised to be 2′S, 3′R and 2′R, 3′S respectively. Consequently, the diagnostic negative/positive cotton effect (CE) at around 210–220 nm for the stereochemistry of angular/linear furano-MMHs is discussed and formulated. Moreover, compounds 1–4 were tested for the nitric oxide (NO) inhibitory activity by using lipopolysaccharide (LPS)-induced RAW 264.7 cells in vitro. The results showed that 1–4 significantly inhibited NO production at the concentration of 10.0 μM, indicating that 1–4 possessed potent anti-inflammatory activity.