New prenylated coumarins from the stems of Toddalia asiatica

Eight new prenylated coumarins (1a/1b, 2a/2b, and 3–6) including two pairs of enantiomers (1a/1b and 2a/2b), a new phenolic acid derivative, methyl (E)-3,4-bis(4-hydroxyphenyl)-4-oxobut-2-enoate (7), and 33 known compounds (8–40) were isolated from the stems of Toddalia asiatica. Their structures were established from spectroscopic data and by chemical methods. The absolute configurations of two pairs of enantiomers (1a/1b and 2a/2b) were determined by X-ray diffraction analysis together with ECD and specific optical rotation calculations. The inhibitory effects of selected compounds against phosphodiesterase-4 (PDE4) were evaluated, and compounds 12, 19, 21–23, 26, 34, and 35 exhibited PDE4 inhibition activities with IC50 values less than 10 μM.