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.