New 5-methyl-4-hydroxycoumarin polyketide derivatives from Gerbera delavayi with anti-inflammatory activity

Five new 5-methyl-4-hydroxycoumarin polyketide derivatives (MPDs), delavayicoumarins A-E (1–5), were isolated from the whole plants of Gerbera delavayi. Among them, compounds 1–3 are the common monoterpene polyketide coumarins (MPCs), while 4 is a modified MPC with both the lactone ring contracted to a five-membered furan ring and a carboxyl at C-3, and 5 is a pair of unusual phenylpropanoid polyketide coumarin enantiomers (5a and 5b), featuring a phenylpropanoid unit at C-3. The planar structures were elucidated by spectroscopic methods and biosynthetic arguments, and the absolute configurations of 1–3, 5a and 5b were confirmed by calculated electronic circular dichroism (ECD) experiment. Furthermore, compounds 1–3, (+)-5 and (−)-5 were tested for the nitric oxide (NO) inhibitory activity by using lipopolysaccharide (LPS)-induced RAW 264.7 cells in vitro. The results showed that compounds 1–3, (+)-5 and (−)-5 remarkably inhibited NO production at the concentration of 10.0 μM, exhibiting that they have significant anti-inflammatory activity.